Digestion

1Why it matters

Every cell in the body needs fuel and raw materials, and food carries both. But food arrives as large molecules, such as starches, proteins and fats, that cannot cross into the blood. The digestive system breaks food down into pieces small enough to absorbabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close, takes them into the body, and gets rid of what is left.

You meet this system in a large share of general surgery.

• Surgeons remove and rejoin these organs. A gallbladder or an appendixappendixuh-PEN-diksA small, finger-shaped pouch attached to the first part of the large intestine, in the lower right abdomen.Full entry Close comes out, and a diseased stretch of stomach or bowel is removed and the ends joined.
• The bowel is full of bacteria. The colon holds the most of them. Once the bowel is opened, its contents can infect the wound, so the team handles the field differently.
• The liver and pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close reach far beyond digestion. The liver makes clotting factorsclotting factorKLOT-ing FAK-terAny of the proteins in blood plasma that work together in a chain to form a blood clot.Full entry Close and breaks down drugs, and the pancreas makes insulininsulinIN-suh-linA hormone made by the pancreas that lets the body's cells take in glucose, also made as a medicine.Full entry Close, so disease in either one can change how a patient bleeds and clots, handles anestheticanesthetican-us-THET-ikA drug that causes loss of feeling, with or without loss of consciousness.an- withoutesthesi/o feeling, sensation-ic relating toFull entry Close drugs and controls blood sugar.
• Scopes look inside. Flexible endoscopesendoscopeEN-duh-skohpA thin tube with a light and a camera that is passed into the body to look inside an organ or cavity.endo- within-scope instrument for viewingFull entry Close pass through the mouth or the anus to look at the lining and to find, mark and sometimes treat disease there, such as polypspolypPOL-ipA growth that sticks out from the lining of a hollow organ, such as the colon, nose or uterus.Full entry Close that can be removed before they turn into cancer.

This chapter follows a meal from the mouth to the anus, then turns to the liver, gallbladder and pancreas, the nutrients food supplies, the words for digestion and elimination, and what all of it means at the field. Other chapters hold the rest: the abdominal wall, quadrants and regions in chapters 2 and 3; the nerves that drive the gut in chapter 4; the arteries and veins of the gut, the portal vein among them, in chapter 5; the pharynxpharynxFAIR-inksThe throat: the passage behind the nose and mouth that carries air to the voice box and food to the esophagus.pharyng/o throatFull entry Close and larynxlarynxLAIR-inksThe voice box: the part of the airway in the neck, above the windpipe, that holds the vocal cords.laryng/o larynxFull entry Close as an airway in chapter 6; the kidneys in chapter 8; insulin, glucagonglucagonGLOO-kuh-gonA hormone made by the pancreas that raises blood sugar; also given as a drug for severe low blood sugar.Full entry Close and the endocrineendocrineEN-doh-krinRelating to the glands that release hormones straight into the blood, or to those hormones.endo- withincrin/o to secreteFull entry Close pancreas in chapter 9; the gut's germs and infection in chapter 10; tumors and wound healingwound healingwoond HEE-lingThe body's process of repairing damaged skin and tissue.Full entry Close in chapter 11; drugs for the stomach and bowel in chapter 12; bowel technique in chapters 29 and 32; the parotid operation in chapter 36; surgery of the teeth and jaws in chapter 37; and herniasherniaHER-nee-uhA bulge of an organ or tissue through a weak spot in the muscle or tissue wall that normally holds it in.Full entry Close and the general surgery operations, with their setups, in chapter 32.

2How digestion works

A tube and its helpers

The digestive system has two groups of organs.

• The alimentary canal, also called the gastrointestinal (GI) tract or the gut, is one long tube. It runs from the mouth through the pharynxpharynxFAIR-inksThe throat: the passage behind the nose and mouth that carries air to the voice box and food to the esophagus.pharyng/o throatFull entry Close and esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close to the stomach, then through the small intestine and the large intestine, and ends at the anus.
• The accessory organs help from outside the tube: the teeth, tongue and salivary glandssalivary glandSAL-ih-vair-ee GLANDA gland that makes saliva and releases it into the mouth.Full entry Close in the mouth, and the liver, gallbladder and pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close, which send their juices into the small intestine through ducts.

In a living person the tube is about 6 to 7.6 meters long. After death, once its muscle loses its tone, it measures longer, about 10.7 meters.

The mouth and the anus both open to the outside, so food inside the tube is, strictly speaking, still outside the body. Nutrients enter the body only when the lining absorbsabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close them.

Six processes

Digestion is the breaking down of food into molecules small enough to be absorbed. Six processes carry a meal through the system.

1. Ingestion: taking food into the mouth.
2. Propulsion: moving food along the tube. It starts with swallowing, which you control, and goes on as peristalsisperistalsispair-ih-STAWL-sisWaves of muscle squeezing that push food and waste along the digestive tract.peri- around-stalsis squeezing, contractionFull entry Close, which you do not: waves in which the smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close of the wall tightens and relaxes in turn, pushing the contents forward. Peristalsis is strong enough to carry a drink to your stomach even if you are upside down.
3. Mechanical digestion: breaking food into smaller pieces without changing what it is made of. Chewing (mastication), the churning of the stomach and the squeezing of the small intestine all do it. Smaller pieces give the digestive juices more surface to work on.
4. Chemical digestion: enzymesenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close in the digestive juices split large molecules into their building blocks, for example proteins into amino acidsamino aciduh-MEE-noh AS-idOne of the small building blocks that join together in chains to make proteins.Full entry Close. It starts in the mouth and is finished in the small intestine.
5. Absorption: the building blocks, with water, vitamins and minerals, pass through the lining into the blood or the lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close. Almost all of it happens in the small intestine.
6. Defecationdefecationdef-ih-KAY-shunPassing stool out of the body through the anus.Full entry Close: what cannot be digested or absorbed leaves the body as feces.

Some references count the steps a little differently and list secretionsecretionsih-KREE-shunA substance a gland or cell makes and releases, such as mucus, saliva, sweat or a hormone.Full entry Close of the digestive juices, or mixing, as steps of their own.

What runs it

The gut has its own nervous system, the entericentericen-TAIR-ikRelating to the intestines.enter/o intestine-ic relating toFull entry Close nervous system, built into its wall from the esophagus to the anus. One network of nerves, in the muscle layer, controls how the wall moves; another, in the submucosa, controls what it secretes.

The autonomic nervous systemautonomic nervous systemaw-tuh-NOM-ik NUR-vus SIS-tumThe part of the nervous system that controls body functions without conscious thought, such as heart rate, breathing and digestion.auto- selfnom/o law, control-ic relating toFull entry Close adjusts it from outside. Parasympatheticparasympatheticpair-uh-sim-puh-THET-ikRelating to the part of the autonomic nervous system that calms the body and supports "rest and digest" functions.para- besidesympathetic the other autonomic divisionFull entry Close signals, carried by the vagus nervesvagus nerveVAY-gus nervThe 10th cranial nerve, which runs from the brain stem to the chest and belly and slows the heart and helps digestion.Full entry Close and the pelvic splanchnic nerves, speed up secretion and movement. Sympathetic signals, the fight-or-flight response, slow them down. Chapter 4 teaches these two divisions.

Hormones also run digestion. Cells in the lining of the stomach and small intestine release them into the blood when food arrives, and they switch the other organs' secretions on or off. The main ones appear with their organs below.

3The abdominal cavity and the peritoneum

Two layers and the space between

Most digestive organs sit in the abdominal cavity, held in place by the peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close, the largest serousserousSEER-usThin, watery and clear to pale yellow, like the fluid part of blood.Full entry Close membrane in the body. Like the pleurapleuralPLOOR-ulHaving to do with the pleura, the thin two-layer membrane that covers the lungs and lines the chest wall.pleur/o pleura-al relating toFull entry Close around the lungs, it has two layers with a thin film of fluid between them.

• The parietalparietalpuh-RY-uh-tulRelating to the wall of a body cavity; also names a lobe of the brain and two bones of the skull.pariet/o wall-al relating toFull entry Close peritoneum lines the inside of the abdominal wall.
• The visceralvisceralVIS-er-ulHaving to do with the internal organs, especially those in the chest and belly.viscer/o internal organs-al relating toFull entry Close peritoneum wraps the organs. On the stomach and intestines it forms their outer layer, the serosa.

The peritonealperitonealper-ih-toh-NEE-ulHaving to do with the peritoneum, the thin lining of the belly cavity and the organs inside it.Full entry Close cavity is the thin space between the two layers. In health it holds only a few milliliters of watery fluid, which lets the organs slide against each other and the wall without rubbing.

Peritonitisperitonitispair-ih-tuh-NY-tisInflammation of the peritoneum, the thin membrane that lines the inside of the belly and covers the organs there.peritone/o peritoneum-itis inflammationFull entry Close is inflammation of the peritoneum. It follows anything that lets gut contents, blood or germs into the peritoneal cavity: an ulcerulcerUL-serAn open sore where the skin or the lining of an organ has broken down.Full entry Close that eats through the stomach wall, a burst appendixappendixuh-PEN-diksA small, finger-shaped pouch attached to the first part of the large intestine, in the lower right abdomen.Full entry Close, a hole in the bowel, or a bleeding liver or spleenspleenspleenAn organ in the upper left abdomen that filters the blood and helps fight infection.splen/o spleenFull entry Close. It is life-threatening and often needs emergency surgery.

The retroperitoneal space

Some organs lie behind the peritoneum, against the back wall, in the retroperitoneal space, or retroperitoneum. The peritoneum covers only their front.

• Digestive organs there: most of the duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close, the pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close, the ascending and descending colon, and the rectum.
• Others: the kidneys and the uretersureterYOOR-uh-terOne of the two tubes that carry urine from the kidneys down to the bladder.Full entry Close, which chapter 8 teaches.

The surgeon reaches these organs either through the peritoneum from the front or from the flank.

The folds that hold the organs

The visceral peritoneum folds into double sheets that tie the organs to the back wall and to each other. Blood vessels, lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close vessels and nerves run between the two layers of each sheet to reach the organs.

These folds matter at the field. Before part of the stomach is removed, its omentum is separated from it, and when a segment of jejunum or ileum comes out, its mesentery, with the vessels inside, is clamped and divided too.

4The wall of the digestive tube

Along its whole length, the wall of the tube follows one plan of four layers, changed a little in each organ to suit its job. From the inside out:

1. Mucosamucosamyoo-KOH-suhThe moist lining of body passages that open to the outside, such as the mouth, nose, gut and bladder.Full entry Close: the lining, a mucous membrane that touches the food. It has three parts: the epitheliumepitheliumep-ih-THEE-lee-umThe tissue that covers the body's surfaces and lines its organs, vessels and cavities.Full entry Close on the surface; a thin connective tissueconnective tissuekuh-NEK-tiv TISH-ooBody tissue that supports, binds together and protects other tissues and organs.Full entry Close under it, the lamina propria, with blood and lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close vessels and clusters of lymphocyteslymphocyteLIM-foh-syteA type of white blood cell that targets specific germs and abnormal cells, including T cells, B cells and natural killer cells.Full entry Close that guard against swallowed germs; and a thin sheet of smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close, the muscularis mucosae, that ripples the lining into folds. Goblet cells in the epithelium make mucus, and other cells release hormones. The epithelium is stratified squamous where it takes the most wear (the mouth, pharynxpharynxFAIR-inksThe throat: the passage behind the nose and mouth that carries air to the voice box and food to the esophagus.pharyng/o throatFull entry Close, esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close and anal canal) and a single layer of tall columnar cells in the stomach and intestines. Its cells live only a few days to about a week before new ones replace them.
2. Submucosa: dense connective tissue that binds the mucosa to the muscle layer. It carries blood and lymph vessels, some glands, and the nerve network that controls secretionsecretionsih-KREE-shunA substance a gland or cell makes and releases, such as mucus, saliva, sweat or a hormone.Full entry Close.
3. Muscularis, also called the muscularis externa: smooth muscle in two layers, an inner circular layer and an outer longitudinal layer, with the nerve network that controls movement between them. Their contractions mix the food and move it along.
4. Serosa: the outer covering, a layer of visceralvisceralVIS-er-ulHaving to do with the internal organs, especially those in the chest and belly.viscer/o internal organs-al relating toFull entry Close peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close over loose connective tissue. It is found only where the tube lies inside the abdominal cavity, and it continues into the mesentery.

The pattern changes where the job changes.

• The stomach adds a third muscle layer, an oblique one, so it can churn food hard.
• In the large intestine, the outer longitudinal muscle gathers into three narrow bands, the teniae coli.
• At both ends of the tube (the mouth, the pharynx, the top of the esophagus and the external anal sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close) the muscle is skeletal, so you control swallowing and defecationdefecationdef-ih-KAY-shunPassing stool out of the body through the anus.Full entry Close.
• The mouth, pharynx and esophagus have no serosa. A tough sheathsheathSHEETHA covering that wraps around a structure; in procedures, a short hollow tube left in a blood vessel to pass catheters through.Full entry Close of collagencollagenKOL-uh-jenThe main structural protein of the body, which gives strength to skin, bones, tendons, ligaments and scar tissue.coll/a glue-gen producingFull entry Close fibers, the adventitia, holds them in place instead.

5The mouth

Palate, uvula, tongue and teeth

The mouth, or oral cavity, is framed by the cheeks, the tongue and the palate. The lips close its front, and at the back it opens into the throat through an opening called the fauces.

The roof of the mouth is the palate.

• The hard palatehard palateHARD PAL-itThe bony front part of the roof of the mouth.Full entry Close, in front, is a shelf of bone. It separates the mouth from the nose and gives the tongue something firm to press food against.
• The soft palatesoft palateSOFT PAL-itThe soft, muscular back part of the roof of the mouth, with no bone in it.Full entry Close, behind it, is mostly skeletal muscleskeletal muscleSKEL-uh-tul MUS-ulMuscle attached to bones that a person moves by choice, such as the muscles of the arms and legs.Full entry Close.
• The uvula is the small fleshy piece that hangs from the middle of the soft palate's back edge. When you swallow, the soft palate and the uvula rise and keep food and drink out of the nose.

The tongue is skeletal muscle covered with mucous membrane, tied to the floor of the mouth by a fold called the lingual frenulum. Its muscles move food into place for chewing, gather it into a bolusbolusBOH-lusA single amount of a drug or fluid given all at once or over a short time.Full entry Close and push it back to be swallowed. Its surface carries papillae, some of them holding taste buds, and its glands release lingual lipaselipaseLY-payssAn enzyme, made mainly by the pancreas, that breaks down fats; its blood level is a common lab test.lip/o fat-ase enzymeFull entry Close, an enzymeenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close for fats that starts working only once it reaches the acid of the stomach.

The teeth tear and grind food. A child has 20 deciduous (baby) teeth, and an adult has 32 permanent teeth: 8 incisors for biting, 4 cuspids (canines) for tearing, 8 premolars for mashing and 12 molars for crushing. Each tooth has a crown above the gum and a root set in the jaw, and enamel, the hardest substance in the body, covers the crown. Under the enamel lies dentin, a bone-like tissue, which in the root is covered by cementum, a layer of modified bone. At the tooth's center the pulp cavity holds nerves and blood vessels, and the part of it running through the root is the root canal. The gums (gingivae) surround each tooth's neck, and a periodontal ligament holds it in its socket.

The salivary glands and their ducts

Saliva comes from many small glands in the lining of the mouth and from three pairs of large glands outside it, which empty into the mouth through ducts.

The glands make about 1 to 1.5 liters of saliva a day. It is more than 99 percent water, and it does several jobs.

• It moistens food and binds it into the soft, easily swallowed ball called the bolus.
• It starts chemical digestion: salivary amylase begins breaking down starch, and keeps working in the stomach until the acid stops it.
• It protects the mouth: lysozyme and antibodiesantibodyAN-tih-bod-eeA Y-shaped protein made by the immune system that sticks to one specific germ or foreign substance and marks it for destruction.anti- againstbody Full entry Close (IgAIgAeye-jee-AY (said as letters)Immunoglobulin A: a kind of antibody found mostly in the body's linings and in saliva, tears and breast milk.Full entry Close) fight germs, and buffers keep its pH close to neutral.
• It dissolves food so you can taste it, and it rinses the teeth.

The sight, smell, taste or even the thought of food increases the flow. Parasympatheticparasympatheticpair-uh-sim-puh-THET-ikRelating to the part of the autonomic nervous system that calms the body and supports "rest and digest" functions.para- besidesympathetic the other autonomic divisionFull entry Close nerves drive it, and in stress the sympathetic nerves cut it back, which is why fear dries the mouth.

The facial nervefacial nerveFAY-shul NERVThe seventh cranial nerve, which moves the muscles of the face and carries taste from the front of the tongue.Full entry Close runs through the parotid gland and divides it into a superficial lobe and a deep lobe. Most parotid tumors are benign, and in a parotidectomy the surgeon identifies the facial nerve, sometimes with a nerve stimulator, so it can be kept safe; chapter 36 teaches the operation.

6The pharynx and swallowing

The pharynx

The pharynxpharynxFAIR-inksThe throat: the passage behind the nose and mouth that carries air to the voice box and food to the esophagus.pharyng/o throatFull entry Close, the throat, is a short tube of skeletal muscleskeletal muscleSKEL-uh-tul MUS-ulMuscle attached to bones that a person moves by choice, such as the muscles of the arms and legs.Full entry Close lined with mucous membrane. It runs from the back of the nose and mouth down to the esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close behind and the larynxlarynxLAIR-inksThe voice box: the part of the airway in the neck, above the windpipe, that holds the vocal cords.laryng/o larynxFull entry Close in front, so it carries both air and food. Chapter 6 teaches its three parts and the airway; here it is the passage for food.

Three groups of constrictor muscles wrap the pharynx. When they squeeze, they push the bolusbolusBOH-lusA single amount of a drug or fluid given all at once or over a short time.Full entry Close down into the esophagus.

Swallowing

Swallowing, or deglutition, moves food from the mouth to the stomach. Solid food takes about 4 to 8 seconds, liquids about 1 second, in three phases.

1. Voluntary (oral) phase: once chewing is done, the tongue presses up and back against the palate and pushes the bolus into the oropharynxoropharynxor-oh-FAIR-inksThe middle part of the throat, behind the mouth, from the soft palate down to the top of the voice box.or/o mouthpharyng/o throatFull entry Close. You choose when this happens.
2. Pharyngeal phase, automatic: receptorsreceptorrih-SEP-terA structure on or in a cell that a specific chemical, such as a hormone or drug, attaches to in order to act.Full entry Close in the throat signal the swallowing center in the medullamedullamuh-DUL-uhThe inner part of an organ; most often the medulla oblongata, the lowest part of the brainstem.Full entry Close. The soft palatesoft palateSOFT PAL-itThe soft, muscular back part of the roof of the mouth, with no bone in it.Full entry Close and uvula rise to close off the nose, the larynx rises and the epiglottisepiglottisep-ih-GLOT-isA leaf-shaped flap of cartilage at the back of the throat that covers the windpipe during swallowing.epi- upon, overglott/o the opening of the larynxFull entry Close folds down over its opening, and breathing stops for a moment. The constrictors squeeze the bolus down, and the upper esophageal sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close relaxes to let it in.
3. Esophageal phase, automatic: peristalsisperistalsispair-ih-STAWL-sisWaves of muscle squeezing that push food and waste along the digestive tract.peri- around-stalsis squeezing, contractionFull entry Close carries the bolus down the esophagus, and the lower esophageal sphincter relaxes to let it into the stomach.

When food "goes down the wrong way" into the tracheatracheaTRAY-kee-uhThe windpipe: the tube that carries air from the throat to the lungs.Full entry Close, a cough usually forces it back up. Under general anesthesiageneral anesthesiaJEN-er-ul an-es-THEE-zhuhDrug-induced loss of consciousness and feeling over the whole body, so a person feels nothing and is not aware during surgery.an- withoutesthesi/o feeling, sensation-ia conditionFull entry Close the protective reflexesreflexREE-fleksAn automatic body response to something that stimulates it, which happens without thought, such as the knee jerk.Full entry Close, swallowing and gagging among them, are lost, which is why the anesthesia provideranesthesia provideran-us-THEE-zhuh pruh-VY-derThe licensed professional who gives anesthesia and watches over the client's breathing and vital functions during a procedure.Full entry Close guards the airway; chapter 13 teaches how.

7The esophagus

Where it runs

The esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close is a muscular tube about 25 cm (10 inches) long that carries food from the pharynxpharynxFAIR-inksThe throat: the passage behind the nose and mouth that carries air to the voice box and food to the esophagus.pharyng/o throatFull entry Close to the stomach. It lies behind the tracheatracheaTRAY-kee-uhThe windpipe: the tube that carries air from the throat to the lungs.Full entry Close and in front of the spine, runs down through the chest in the mediastinum, and passes through an opening in the diaphragmdiaphragmDY-uh-framThe dome-shaped sheet of muscle under the lungs that is the main muscle of breathing; also the flat side of a stethoscope.Full entry Close, the esophageal hiatus, to join the stomach at its cardia. When it is empty, it lies flat.

Its layers

Its wall has the usual layers, with differences in the lining, the muscle and the outer coat.

• Mucosamucosamyoo-KOH-suhThe moist lining of body passages that open to the outside, such as the mouth, nose, gut and bladder.Full entry Close: stratified squamous epitheliumepitheliumep-ih-THEE-lee-umThe tissue that covers the body's surfaces and lines its organs, vessels and cavities.Full entry Close, which stands up to rough food, with glands that make mucus to ease the bolusbolusBOH-lusA single amount of a drug or fluid given all at once or over a short time.Full entry Close down.
• Submucosa: connective tissueconnective tissuekuh-NEK-tiv TISH-ooBody tissue that supports, binds together and protects other tissues and organs.Full entry Close carrying vessels and glands.
• Muscularis: skeletal muscleskeletal muscleSKEL-uh-tul MUS-ulMuscle attached to bones that a person moves by choice, such as the muscles of the arms and legs.Full entry Close in the upper third, a mix of skeletal and smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close in the middle third, and smooth muscle in the lower third.
• Adventitia in place of a serosa, because most of the esophagus lies in the chest, outside the peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close.

Two sphincters

A sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close is a ring of muscle around a tube: it closes the tube when it contracts and opens it when it relaxes.

• The upper esophageal sphincter, made of skeletal muscle, lets the bolus in from the pharynx.
• The lower esophageal sphincter (LES), made of smooth muscle where the esophagus meets the stomach, is also called the gastroesophageal or cardiac sphincter. It relaxes to let food into the stomach, then closes to keep stomach acid out of the esophagus. The diaphragm around it helps hold it shut.

When the LES does not close fully, acid washes back up into the esophagus. This backward flow is reflux. It causes heartburn, and when it keeps happening it is gastroesophageal reflux diseasegastroesophageal reflux diseasegas-troh-ih-sof-uh-JEE-ul REE-fluks dih-ZEEZA long-term condition in which stomach contents, including acid, flow back up into the esophagus.gastr/o stomachesophag/o esophagus-al relating toFull entry Close (GERD), which over time can inflame the esophagus, scar and narrow it, and raise the risk of cancer. In a hiatal herniaherniaHER-nee-uhA bulge of an organ or tissue through a weak spot in the muscle or tissue wall that normally holds it in.Full entry Close, a weak hiatus lets the lowest part of the esophagus and the top of the stomach push up into the chest.

When medicine does not control severe reflux, a fundoplication can: the surgeon folds the top of the stomach, the fundusfundusFUN-dusThe rounded top or base of a hollow organ, most often the top of the uterus.Full entry Close, around the lower esophagus so it acts as a new sphincter. A Nissen fundoplication wraps it all the way around. Chapter 32 teaches the operation.

Laparoscopic Nissen Fundoplication31 instruments · 2 photos

An esophagogastroduodenoscopyEGDee-jee-DEE (said as letters)Esophagogastroduodenoscopy: a test using a flexible scope through the mouth to look at the esophagus, stomach and start of the small intestine.esophag/o esophagusgastr/o stomachduoden/o duodenum-scopy looking, viewingFull entry Close (EGD) passes a flexible scope through the mouth to look at the lining of the esophagus, the stomach and the first parts of the duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close.

8The stomach

The stomach is a widening of the tube, a bag in the upper left abdomen just under the diaphragmdiaphragmDY-uh-framThe dome-shaped sheet of muscle under the lungs that is the main muscle of breathing; also the flat side of a stethoscope.Full entry Close, between the esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close and the duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close. Empty, it is about the size of a fist; it can stretch to hold about 4 liters and then shrink back.

Regions and curvatures

The stomach has four regions.

• Cardia: the area around the opening from the esophagus.
• FundusfundusFUN-dusThe rounded top or base of a hollow organ, most often the top of the uterus.Full entry Close: the dome that rises above and to the left of the cardia, under the diaphragm. It holds food for a while, and the gas made during digestion.
• Body: the large middle part.
• Pylorus: the funnel at the end that leads to the duodenum. Its wide part, the pyloric antrum, joins the body; its narrow part, the pyloric canal, ends at the pyloric sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close, a ring of smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close that controls how fast the stomach empties.

References divide it a little differently. Some name three parts (the fundus, the body and the antrum), and others name the antrum and the pyloric canal as separate regions. The Core Curriculum's list names the antrum and the pylorus separately.

The stomach's short, concave inner border, which faces the liver, is the lesser curvature. Its long, convex outer border is the greater curvature. The lesser omentum ties the lesser curvature to the liver, and the greater omentum hangs from the greater curvature.

The wall and its glands

When the stomach is empty, its mucosamucosamyoo-KOH-suhThe moist lining of body passages that open to the outside, such as the mouth, nose, gut and bladder.Full entry Close and submucosa lie in folds called rugae, which flatten out as it fills.

Its muscularis has three layers instead of two: an inner oblique layer, a middle circular layer and an outer longitudinal layer. The extra layer lets it churn food hard.

The mucosa is dotted with tiny pits that lead down into the gastric glands, which make gastric juice. Their main cells:

What the stomach does

The stomach is first a holding tank. You can eat a meal far faster than the small intestine can digest it, so the stomach keeps it and lets it out a little at a time.

• Mechanical digestion: about every 20 seconds, mixing waves churn the food with gastric juice until it becomes chymechymeKYMEThe thick, soupy mix of partly digested food and digestive juices that passes from the stomach into the small intestine.Full entry Close, a thick, soupy liquid.
• Chemical digestion: HCl and pepsin start breaking down proteins. SalivarysalivarySAL-ih-vair-eeRelating to saliva, the watery fluid in the mouth, or to the glands that make it.Full entry Close amylaseamylaseAM-uh-laysAn enzyme made mainly by the pancreas and salivary glands that breaks down starch; its blood level is a lab test.Full entry Close goes on working on starch for a while in the fundus until the acid stops it, and the lipases begin on fats.
• Absorption: very little, because the stomach wall lets few substances through. It does absorb some water and certain salts (ions), alcohol, some simple sugars, and some drugs such as aspirin. Nearly everything else waits for the small intestine.
• Intrinsic factor: the one stomach job the body cannot do without. Vitamin B12, which the body needs to make mature red blood cells and to keep the nerves working, cannot be absorbed without it, so a patient whose whole stomach is removed needs B12 injections.

The pylorus lets only liquid and very small pieces through, a few milliliters at a time, and pushes the rest back for more mixing. A meal leaves the stomach in about 2 to 4 hours: carbohydrates fastest, then proteins, and fatty meals slowest.

Why does the stomach not digest itself? Its mucosal barrier has three parts: a thick coat of mucus with bicarbonatebicarbonateby-KAR-buh-naytA base in the blood that balances acid; the kidneys control it, and its level is measured on blood gas and chemistry tests.Full entry Close in it to neutralize acid, tight seals between the lining cells, and fast repair, so the surface lining is completely replaced every 3 to 6 days.

When the barrier breaks down, gastric juice eats into the lining. A shallow break is an erosion. A deeper one is an ulcerulcerUL-serAn open sore where the skin or the lining of an organ has broken down.Full entry Close, a crater-like sore in a membrane; one in a part of the tract bathed in stomach acid is a peptic ulcer. Most come from Helicobacter pylori infection or from heavy use of NSAIDsnonsteroidal anti-inflammatory drugnon-STAIR-oy-dul an-tee-in-FLAM-uh-tor-ee DRUGA drug that relieves pain, fever and inflammation and is not a steroid, such as ibuprofen or naproxen.non- notanti- againstinflamm/o inflammationFull entry Close such as aspirin. An ulcer that eats through the wall, a perforatedperforationper-fuh-RAY-shunA hole that goes all the way through the wall of an organ or tissue.per- throughforat bored (a hole)-ion processFull entry Close ulcer, spills stomach contents into the abdomen and causes peritonitisperitonitispair-ih-tuh-NY-tisInflammation of the peritoneum, the thin membrane that lines the inside of the belly and covers the organs there.peritone/o peritoneum-itis inflammationFull entry Close; it must be repaired surgically.

Weight-loss operations work on the stomach. A sleeve gastrectomy cuts the stomach's size by 70 to 90 percent. A Roux-en-Y gastric bypass makes a small pouch at the top of the stomach and joins it to the jejunumjejunumjeh-JOO-numThe second of the three sections of the small intestine; it follows the duodenum and leads into the ileum.jejun/o jejunum (from the Latin for empty)Full entry Close, so food bypasses most of the stomach. Chapter 32 teaches both.

Laparoscopic Sleeve Gastrectomy24 instruments Laparoscopic Gastric Bypass Roux-EN-Y35 instruments · 5 photos

9The small intestine

The small intestine runs from the pyloric sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close to the ileocecal valve. It is the longest part of the tube, about 3 meters in a living person and about twice that after death, when its muscle tone is gone. Its name comes from its width, about 2.5 cm (1 inch) across, against about 7.6 cm (3 inches) for the large intestine. Most chemical digestion and nearly all absorptionabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close happen here.

Three parts

• Duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close: the first and shortest part, about 20 to 25 cm (8 to 10 inches). Its first 2 cm, the duodenal bulb or cap, is mobile and lies inside the peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close; the rest is retroperitoneal, fixed to the back wall.
• Jejunumjejunumjeh-JOO-numThe second of the three sections of the small intestine; it follows the duodenum and leads into the ileum.jejun/o jejunum (from the Latin for empty)Full entry Close: the middle part, about 0.9 m (3 feet) in life. It begins at a bend, the duodenojejunal flexure, held up by the ligament of Treitz in the left upper quadrant; surgeons use this ligament as the landmark for the start of the jejunum. Most carbohydrates and proteins are absorbed here.
• IleumileumIL-ee-umThe last and longest part of the small intestine, which joins the large intestine.Full entry Close: the last and longest part, about 1.8 m (6 feet) in life, which ends in the right lower quadrant at the ileocecal valve (or sphincter), where it opens into the cecum. It is a little narrower than the jejunum, with fewer circular folds. Its lining holds clusters of lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close tissue called Peyer's patches, and its last stretch, the terminal ileum, absorbs vitamin B12vitamin B12VY-tuh-min bee TWELVA vitamin from animal foods that the body needs to make red blood cells and keep nerves healthy; also called cobalamin.Full entry Close and takes back bilebilebileA yellow-green fluid made by the liver and stored in the gallbladder that helps digest fats.chol/e bileFull entry Close salts to be reused.

The duodenum curves in a C around the head of the pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close in four portions.

1. The first (superior) portion, which includes the bulb, where most duodenal ulcersulcerUL-serAn open sore where the skin or the lining of an organ has broken down.Full entry Close form.
2. The second (descending) portion, where bile and pancreatic juice enter through the ampulla of Vater.
3. The third (horizontal) portion, which crosses in front of the spine.
4. The fourth (ascending) portion, which rises to the jejunum.

Some references give longer figures for the jejunum and ileum: a jejunum of about 2.5 to 2.7 m and an ileum of about 3.5 to 4 m.

There is no sharp line where the jejunum ends and the ileum begins. The mesentery ties both to the back wall, and their blood comes from the superior mesenteric artery through it.

Built for absorption

The lining of the small intestine has a huge surface, about 200 square meters, because three features multiply its area more than 600 times.

• Circular folds (plicae circulares): deep ridges of the mucosamucosamyoo-KOH-suhThe moist lining of body passages that open to the outside, such as the mouth, nose, gut and bladder.Full entry Close and submucosa. They make the chymechymeKYMEThe thick, soupy mix of partly digested food and digestive juices that passes from the stomach into the small intestine.Full entry Close spiral slowly through, which gives time for absorption.
• VillivillusVIL-usOne of the tiny, finger-like folds that line the small intestine and take in nutrients.Full entry Close: tiny fingerlike projections, 0.5 to 1 mm long, that give the lining a velvety surface. Each villus holds a network of blood capillariescapillaryKAP-ih-lair-eeOne of the tiniest blood vessels, joining the smallest arteries to the smallest veins.Full entry Close and a lymph capillary called a lacteal. Sugars and amino acidsamino aciduh-MEE-noh AS-idOne of the small building blocks that join together in chains to make proteins.Full entry Close enter the blood capillaries; fats enter the lacteals and reach the blood through the lymph.
• Microvilli: microscopic projections on each lining cell that together form the brush border. EnzymesenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close fixed to them finish the digestion of carbohydrates and proteins.

Glands between the villi make about 1 to 2 liters of intestinal juice a day. Glands in the submucosa of the duodenum add an alkaline mucus that protects it from the acid chyme arriving from the stomach.

What the small intestine does

• Mixes and moves: in segmentation, rings of the wall squeeze and relax to mix chyme with the digestive juices and press it against the lining. Slow waves of peristalsisperistalsispair-ih-STAWL-sisWaves of muscle squeezing that push food and waste along the digestive tract.peri- around-stalsis squeezing, contractionFull entry Close then move it along. Chyme takes about 3 to 5 hours to pass through.
• Digests: bile from the liver and gallbladder and juice from the pancreas pour into the duodenum and, with the brush border enzymes, finish breaking down carbohydrates, proteins and fats. Fats arrive mostly undigested, so most fat digestion happens here.
• Absorbs: nutrients, electrolytes, vitamins and water. About 9 liters of fluid enter it each day, most of it the body's own secretionssecretionsih-KREE-shunA substance a gland or cell makes and releases, such as mucus, saliva, sweat or a hormone.Full entry Close and the rest from food and drink, and it absorbs about 90 percent of the water. The fat-soluble vitamins (A, D, E and K) go in with the fats, so fat absorption carries them. Iron and calcium are absorbed in the duodenum.
• Makes hormones: cells in its lining release hormones into the blood when chyme arrives.

The ileocecal valve stays mostly closed. When the ileum becomes more active after a meal, it relaxes and lets residue into the cecum, then closes again so nothing flows back.

When a stretch of small intestine is diseased or damaged, a small bowel resectionresectionrih-SEK-shunSurgery to remove part of an organ or tissue.re- back, againsect to cut-ion processFull entry Close removes it: the mesentery and the vessels inside it are clamped and divided, the segment comes out, and the healthy ends are joined; chapter 32 teaches the operation.

Small Bowel Resection36 instruments · 2 photos

10The large intestine

The large intestine runs from the ileocecal valve to the anus. It is about 1.5 m (5 feet) long and about 7.6 cm (3 inches) across, and it frames the small intestine on three sides.

Its parts

• Cecum: a blind pouch, about 6 cm long, that hangs below the ileocecal valve and receives what comes from the ileumileumIL-ee-umThe last and longest part of the small intestine, which joins the large intestine.Full entry Close.
• Appendixappendixuh-PEN-diksA small, finger-shaped pouch attached to the first part of the large intestine, in the lower right abdomen.Full entry Close (vermiform appendix): a narrow, winding tube, about 7 to 10 cm long and closed at its tip, attached to the cecum below the ileocecal junction by its own small mesentery, the mesoappendix. It holds lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close tissue but has no clear digestive job.
• Ascending colon: rises up the right side to the underside of the liver, where it turns sharply left at the hepatichepatichih-PAT-ikRelating to the liver.hepat/o liver-ic relating toFull entry Close flexure, also called the right colic flexure.
• Transversetransversetrans-VERSLying across something, at a right angle to its length.Full entry Close colon: crosses the abdomen below the stomach to just below the spleenspleenspleenAn organ in the upper left abdomen that filters the blood and helps fight infection.splen/o spleenFull entry Close, where it turns down at the splenic flexure, also called the left colic flexure.
• Descending colon: runs down the left side.
• SigmoidsigmoidSIG-moydShaped like the letter S; most often short for the sigmoid colon, the S-shaped last part of the colon before the rectum.Full entry Close colon: the S-shaped part in the pelvis, which curves toward the midlinemidlineMID-lineAn imaginary line down the center of the body; also, a type of IV catheter placed in a vein of the upper arm.Full entry Close and leads into the rectum.

The ascending colon, the descending colon and the rectum lie in the retroperitoneum, fixed to the back wall. The transverse colon and the sigmoid colon hang on their own mesentery, the mesocolon, so they move more freely.

Landmarks you can see

Three features set the colon apart from the small intestine at surgery.

• Teniae coli: three long bands of smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close, the outer muscle layer gathered into strips.
• Haustra: the pouches the teniae bunch the colon into, which give it its puckered look.
• Epiploic appendices, or appendages: small fat-filled tags of peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close along the teniae, with no known job.

Where the teniae spread out and disappear, at the level of the sacralsacralSAY-krulHaving to do with the sacrum, the triangle-shaped bone at the base of the spine between the hip bones.Full entry Close promontory, the rectum begins.

What it does

The large intestine has no villivillusVIL-usOne of the tiny, finger-like folds that line the small intestine and take in nutrients.Full entry Close and makes no digestive enzymesenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close. Its glands make mucus, which eases the passage of feces and protects the wall. Its jobs:

• Absorbsabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close water and electrolytes: it takes most of the water left in the residue and turns liquid into semisolid feces. Each day about 500 mL of residue reaches the cecum, and only about 150 mL of it is passed as feces.
• Houses bacteria: trillions of bacteria of more than 700 kinds live in the colon, and most do no harm while they stay inside it. They ferment leftover carbohydrates, making gas, or flatusflatusFLAY-tusGas passed from the intestines through the anus.Full entry Close, up to 1500 mL a day. They make vitamin K and several B vitamins, such as biotin, which the colon absorbs. They also break down bilirubinbilirubinbil-ih-ROO-binA yellow pigment made when old red blood cells break down, which the liver clears into bile.Full entry Close from the bilebilebileA yellow-green fluid made by the liver and stored in the gallbladder that helps digest fats.chol/e bileFull entry Close into stercobilin, the pigment that colors stool brown.
• Finishes digestion: since the colon makes no enzymes, the last digestion of food residue is the bacteria's work.
• Compacts and stores: the residue stays 12 to 24 hours while water is drawn out, then moves on toward the rectum.

It moves in three ways: slow haustral contractions push the residue from one pouch to the next; peristalsisperistalsispair-ih-STAWL-sisWaves of muscle squeezing that push food and waste along the digestive tract.peri- around-stalsis squeezing, contractionFull entry Close, slower here than higher up; and strong mass movements, usually three or four times a day during or just after a meal, which sweep the contents toward the rectum. Food entering the stomach sets them off, the gastrocolic reflexreflexREE-fleksAn automatic body response to something that stimulates it, which happens without thought, such as the knee jerk.Full entry Close.

Feces are water, undigested residue such as plant fiber, bacteria, worn-out lining cells and salts.

Appendicitisappendicitisuh-pen-dih-SY-tisInflammation of the appendix, the small pouch that hangs from the start of the large intestine.append/o appendix-itis inflammationFull entry Close starts when the appendix's narrow lumenlumenLOO-menThe open space inside a tube, such as a blood vessel, the intestine or a catheter.Full entry Close is blocked. It swells, becomes infected, and can burst within a day, spilling germs into the abdomen. The pain usually begins around the navel and settles in the right lower quadrant.

Laparoscopic Appendectomy29 instruments · 3 photos

A right hemicolectomy removes the end of the ileum, the cecum, the ascending colon and part of the transverse colon, for disease of the cecum, ascending colon or hepatic flexure. Diverticulitisdiverticulitisdy-ver-tik-yuh-LY-tisInflammation or infection of one or more small pouches that bulge out from the wall of the colon.diverticul/o a small pouch-itis inflammationFull entry Close, cancer or other disease lower down can need a sigmoid colectomycolectomykoh-LEK-tuh-meeSurgery to remove all or part of the colon.col/o colon-ectomy surgical removalFull entry Close.

A colonoscopycolonoscopykoh-luh-NOS-kuh-peeAn exam of the inside of the large intestine with a long, flexible tube that has a camera on its end.col/o colon-scopy looking with an instrumentFull entry Close looks at the whole large intestine from the rectum to the cecum. Most colon cancers grow from polypspolypPOL-ipA growth that sticks out from the lining of a hollow organ, such as the colon, nose or uterus.Full entry Close, benign growths of the lining, and polyps found during a colonoscopy can be removed before they turn into cancer.

Colonoscopy4 instruments · 4 photos

11The rectum and anal canal

The rectum

The rectum follows the sigmoidsigmoidSIG-moydShaped like the letter S; most often short for the sigmoid colon, the S-shaped last part of the colon before the rectum.Full entry Close colon down in front of the sacrumsacrumSAY-krumThe large, triangle-shaped bone at the base of the spine, between the two hip bones.sacr/o sacrumFull entry Close and coccyxcoccyxKOK-siksThe small, triangle-shaped bone at the very bottom of the spine; the tailbone.Full entry Close. It is not straight: three bends to the side make three folds inside, the rectalrectalREK-tulRelating to the rectum, the last part of the large intestine; also, given or measured through the rectum.rect/o rectum, straight-al relating toFull entry Close valves, which help keep gas apart from feces. Its lower end, the rectal ampulla, widens to hold feces until they are passed. It is about 10 to 12.5 cm (4 to 5 inches) long; some anatomy references give about 20 cm.

The anal canal

The anal canal, about 3.8 to 5 cm (1.5 to 2 inches) long, is the last part of the tube. It lies in the perineumperineumpair-ih-NEE-umThe area of skin and muscle between the genitals and the anus.perine/o perineumFull entry Close, below the pelvic cavity, and opens to the outside at the anus. Its two sphincterssphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close stay closed except during defecationdefecationdef-ih-KAY-shunPassing stool out of the body through the anus.Full entry Close.

• The internal anal sphincter is smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close and works without your control.
• The external anal sphincter is skeletal muscleskeletal muscleSKEL-uh-tul MUS-ulMuscle attached to bones that a person moves by choice, such as the muscles of the arms and legs.Full entry Close under your voluntary control.

Inside the canal, the pectinate (dentate) line marks where the lining of the gut meets skin. Above it the lining feels little pain; below it, pain is sharp.

The canal also holds cushions of blood vessels. When their supporting tissue weakens, or when they swell, they become hemorrhoidshemorrhoidHEM-uh-roydA swollen vein in or around the anus or lower rectum.Full entry Close: external ones are covered with skin, and internal ones lie under the lining.

Hemorrhoidectomy27 instruments · 3 photos

A low anterior resectionresectionrih-SEK-shunSurgery to remove part of an organ or tissue.re- back, againsect to cut-ion processFull entry Close removes the lower sigmoid colon and the upper rectum, often for cancer, and keeps the anal sphincter so the patient can still control the bowel.

Storing and passing stool

When a mass movement pushes feces into the rectum, the stretch of its wall sets off the defecation reflexreflexREE-fleksAn automatic body response to something that stimulates it, which happens without thought, such as the knee jerk.Full entry Close: the sigmoid colon and rectum contract and the internal sphincter relaxes. The brain then chooses whether to open the external sphincter and pass the stool or to hold it for later. Bearing down, by closing the glottis and tightening the diaphragmdiaphragmDY-uh-framThe dome-shaped sheet of muscle under the lungs that is the main muscle of breathing; also the flat side of a stethoscope.Full entry Close and the abdominal muscles (the Valsalva maneuverValsalva maneuverval-SAL-vuh muh-NOO-verBreathing out forcefully against a closed airway, as when bearing down or straining.Full entry Close), helps push.

Timing changes the stool.

• If defecation keeps being put off, more water is drawn out and the stool hardens. Constipation is passing stool less often than normal, with hard, dry stool that is difficult to pass.
• If residue moves through too fast, too little water is absorbedabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close. Diarrhea is the passing of loose, unformed stool.
• Fecal incontinenceincontinencein-KON-tih-nensLoss of control over the bladder or bowel, so urine or stool leaks out without the person meaning it to.in- notcontin/o to hold back-ence state ofFull entry Close is the loss of bowel control, so that stool, gas or mucus leaks out without the person meaning it to.

Normal habits vary widely, from two or three bowel movements a day to three or four a week.

12The liver

Where it sits and how it is built

The liver is the largest gland in the body, about 3 pounds in an adult. It fills most of the right upper quadrant and reaches into the left upper quadrant, just under the diaphragmdiaphragmDY-uh-framThe dome-shaped sheet of muscle under the lungs that is the main muscle of breathing; also the flat side of a stethoscope.Full entry Close, where the lower ribs shield it.

• A tough fibrousfibrousFY-brusMade of or containing tough threads (fibers), especially of connective tissue.fibr/o fiber-ous full of, relating toFull entry Close capsule, the Glisson capsule, wraps it, and the visceralvisceralVIS-er-ulHaving to do with the internal organs, especially those in the chest and belly.viscer/o internal organs-al relating toFull entry Close peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close covers almost all of that.
• It has a large right lobe and a smaller left lobe, divided in front by the falciform ligament. Two small lobes, the quadrate and the caudate, sit on its underside; references differ on whether to count them with the right lobe or the left.
• Surgeons also divide it into eight segments, each with its own branch of the portal vein, hepatichepatichih-PAT-ikRelating to the liver.hepat/o liver-ic relating toFull entry Close artery and bile ductbile ductbyle duktOne of the tubes that carry bile from the liver and gallbladder to the small intestine.Full entry Close, so a segment can be removed on its own.
• The ligamentum teres, or round ligament, runs in the free lower edge of the falciform ligament from the navel to the liver. It is what remains of the umbilical vein, which brought blood from the placentaplacentapluh-SEN-tuhThe organ that grows in the uterus during pregnancy and passes oxygen and food from the parent's blood to the fetus.Full entry Close before birth.

Blood reaches the liver two ways, at the porta hepatis on its underside. The hepatic artery brings blood rich in oxygen. The hepatic portal vein brings blood from the stomach, intestines, spleenspleenspleenAn organ in the upper left abdomen that filters the blood and helps fight infection.splen/o spleenFull entry Close and pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close, full of absorbedabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close nutrients, and also of any drugs and toxinstoxinTOK-sinA poison made by a living thing, such as a bacterium, plant or animal.Full entry Close that were swallowed. Blood leaves through the hepatic veins into the inferior vena cavainferior vena cavain-FEER-ee-er VEE-nuh KAY-vuhThe large vein that carries blood from the lower body back to the right atrium of the heart.inferior lowervena veincava hollowFull entry Close. Because all the blood from the gut passes through the liver first, the liver is the most common place for cancers of the gut to spread. Chapter 5 traces these vessels.

Inside, the liver is built of tiny lobules. In each one, plates of liver cells, the hepatocytes, line wide blood channels called sinusoids, where they take up and process what the blood brings. Kupffer cells in the sinusoids are macrophagesmacrophageMAK-roh-fayjA large white blood cell in the tissues that swallows and digests germs, dead cells and debris.macro- large-phage eaterFull entry Close that eat bacteria, worn-out blood cells and debris. BilebilebileA yellow-green fluid made by the liver and stored in the gallbladder that helps digest fats.chol/e bileFull entry Close made by the hepatocytes drains the opposite way, through tiny canals to the bile ducts.

What the liver does

The liver carries out hundreds of jobs. These are the ones you are expected to know.

Hemoglobin itself is made by developing red blood cells in the red bone marrowbone marrowbone MAIR-ohThe soft, spongy tissue inside bones that makes blood cells.Full entry Close. The liver's part is to store the iron those cells need and to clear away the bilirubinbilirubinbil-ih-ROO-binA yellow pigment made when old red blood cells break down, which the liver clears into bile.Full entry Close left over when old hemoglobin is broken down.

A diseased liver shows at the field. It may make too few clotting factors, so the patient bleeds more easily, and it may break down anestheticanesthetican-us-THET-ikA drug that causes loss of feeling, with or without loss of consciousness.an- withoutesthesi/o feeling, sensation-ic relating toFull entry Close drugs differently.

Bile, bilirubin and jaundice

Bile is a yellow-green to yellow-brown, slightly alkaline fluid: water, bile salts, bile pigments, cholesterol, lecithin and other fats, and electrolytes. The bile salts are what help digestion. Working like dish soap, they split large globules of fat into tiny droplets, a process called emulsification, which gives the fat-digesting enzymes far more surface to work on. They then carry the products of fat digestion to the lining to be absorbed. Most bile salts are absorbed again in the ileumileumIL-ee-umThe last and longest part of the small intestine, which joins the large intestine.Full entry Close and sent back to the liver to be used again.

Bilirubin is the main pigment in bile. When old red blood cells are broken down, in the spleen and also in the liver and the bone marrow, the heme from their hemoglobin becomes bilirubin. The liver puts the bilirubin into bile, and it leaves the body in the feces. It gives bile its color, and bacteria in the colon change it into the brown pigment of stool.

JaundicejaundiceJAWN-disYellow color of the skin, the whites of the eyes and other tissues from too much bilirubin in the blood.Full entry Close is a yellow color of the skin, the whites of the eyes (the sclerascleraSKLAIR-uhThe tough white outer layer of the eyeball.Full entry Close) and the mucous membranes, caused by bilirubin building up in the blood. There are three kinds of cause: too much bilirubin, from red blood cells breaking down; a liver too sick to process it, as in hepatitishepatitishep-uh-TY-tisInflammation of the liver, most often caused by a virus.hepat/o liver-itis inflammationFull entry Close or cirrhosiscirrhosissih-ROH-sisLong-term scarring of the liver, in which scar tissue replaces healthy tissue and keeps the liver from working normally.cirrh/o orange-yellow-osis abnormal conditionFull entry Close; or a blocked bile duct, from a gallstone or a tumor, that stops bile from leaving. When bile cannot reach the intestine, the stool turns pale, because no pigment reaches it, and fat is poorly absorbed, because no bile salts reach it.

13The gallbladder and the biliary tree

The gallbladder

The gallbladder is a pear-shaped muscular sac, about 8 to 10 cm long, that sits in a shallow hollow on the underside of the right lobe of the liver. It holds about 40 to 70 mL of bilebilebileA yellow-green fluid made by the liver and stored in the gallbladder that helps digest fats.chol/e bileFull entry Close.

• It has three parts: the wide fundusfundusFUN-dusThe rounded top or base of a hollow organ, most often the top of the uterus.Full entry Close, which juts out past the lower edge of the liver; the body; and the narrow neck, which bends into the cystic duct.
• The cystic duct, only 1 to 2 cm long, joins the gallbladder to the common hepatichepatichih-PAT-ikRelating to the liver.hepat/o liver-ic relating toFull entry Close duct. Bile travels both ways through it: in for storage and out when it is needed.
• The cystic artery, its blood supply, usually branches from the right hepatic artery, though it can come off other arteries nearby.
• Its wall has no submucosa. The lining draws water and salts out of the bile, concentrating it as much as tenfold, and the smooth musclesmooth musclesmooth MUS-ulMuscle that works without conscious control and lines hollow organs such as the stomach, intestines, bladder, airways and blood vessels.Full entry Close of the wall squeezes it out. The visceralvisceralVIS-er-ulHaving to do with the internal organs, especially those in the chest and belly.viscer/o internal organs-al relating toFull entry Close peritoneumperitoneumpair-ih-toh-NEE-umThe thin membrane that lines the belly cavity and covers most of the organs inside it.peri- aroundton stretched-eum a structureFull entry Close holds it against the liver.

The Calot triangle is bordered by the cystic duct, the common hepatic duct and the cystic artery. A closely related area, the hepatocystic triangle, has the underside of the liver as its upper border. These small spaces matter in every gallbladder operation, because the common bile ductcommon bile ductKOM-un BILE DUKTThe tube that carries bile from the liver and gallbladder into the small intestine.Full entry Close runs right beside them; chapter 32 explains what the surgeon must see before clipping anything.

The biliary tree

Bile takes this path from the liver to the duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close.

1. Tiny canals between the liver cells collect it and drain into bile ductsbile ductbyle duktOne of the tubes that carry bile from the liver and gallbladder to the small intestine.Full entry Close.
2. The bile ducts join into the right and left hepatic ducts.
3. These two join to form the common hepatic duct.
4. The cystic duct from the gallbladder joins the common hepatic duct, and from that point on it is the common bile duct.
5. The common bile duct runs down behind the first portion of the duodenum and through the head of the pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close. In the wall of the second portion of the duodenum it meets the main pancreatic duct, and they open together at the ampulla of Vater, also called the hepatopancreatic ampulla, on a small mound, the major duodenal papilla.
6. The sphinctersphincterSFINGK-terA ring of muscle that tightens to close an opening or passage in the body and relaxes to open it.Full entry Close of Oddi, also called the hepatopancreatic sphincter, is a ring of smooth muscle at the ampulla. It opens to let bile and pancreatic juice pass into the duodenum and closes to hold them back.

Storing and releasing bile

Between meals the sphincter of Oddi stays closed, so bile from the liver backs up through the cystic duct into the gallbladder, which stores and concentrates it. When fatty chymechymeKYMEThe thick, soupy mix of partly digested food and digestive juices that passes from the stomach into the small intestine.Full entry Close reaches the duodenum, the lining there releases cholecystokinin (CCK): the gallbladder contracts, the sphincter relaxes, and bile flows down the common bile duct into the duodenum.

The biliary tree carries waste as well as digestive juice. Bilirubinbilirubinbil-ih-ROO-binA yellow pigment made when old red blood cells break down, which the liver clears into bile.Full entry Close and other waste the liver puts into bile travel down the ducts and leave the body in the feces.

Gallstones (cholelithiasischolelithiasiskoh-lee-lih-THY-uh-sisStones in the gallbladder.chol/e bilelith/o stone-iasis conditionFull entry Close) form when bile holds too much cholesterol or too few bile salts. A stone stuck in the cystic duct inflames the gallbladder (cholecystitischolecystitiskoh-luh-sis-TY-tisInflammation of the gallbladder.chol/e bilecyst/o sac, bladder-itis inflammationFull entry Close). A stone in the common bile duct blocks bile and causes jaundicejaundiceJAWN-disYellow color of the skin, the whites of the eyes and other tissues from too much bilirubin in the blood.Full entry Close, and one that moves down to the ampulla can cause pancreatitispancreatitispan-kree-uh-TY-tisInflammation of the pancreas, which may come on suddenly (acute) or last for years (chronic).pancreat/o pancreas-itis inflammationFull entry Close.

Laparoscopic Cholecystectomy23 instruments · 6 photos

14The pancreas

Where it lies and how it is built

The pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close is a long, soft gland that lies across the back of the upper abdomen, behind the stomach, in the retroperitoneum.

• Head: the wide part, tucked into the C-shaped curve of the duodenumduodenumdoo-uh-DEE-numThe first, short part of the small intestine, just after the stomach.Full entry Close.
• Neck: the short part beside the pylorus that joins the head to the body.
• Body: lies across the spine, over the superior mesenteric artery and vein.
• Tail: tapers to the left and reaches the hilum of the spleenspleenspleenAn organ in the upper left abdomen that filters the blood and helps fight infection.splen/o spleenFull entry Close.

The main pancreatic duct, the duct of Wirsung, runs the length of the gland and joins the common bile ductcommon bile ductKOM-un BILE DUKTThe tube that carries bile from the liver and gallbladder into the small intestine.Full entry Close at the ampulla of Vater. Many people also have a second, smaller duct, the accessory duct or duct of Santorini, which opens into the duodenum on its own, about an inch above the ampulla.

The pancreas is two glands in one.

• Its exocrine part, most of the gland, is made of grape-like clusters of cells (acini) that make pancreatic juice and send it down the ducts to the duodenum.
• Its endocrineendocrineEN-doh-krinRelating to the glands that release hormones straight into the blood, or to those hormones.endo- withincrin/o to secreteFull entry Close part is the islets of Langerhans, small clusters of cells scattered through it that release hormones straight into the blood.

Pancreatic juice

The pancreas makes more than a liter of pancreatic juice a day. It is clear and mostly water, with salts, sodium bicarbonatesodium bicarbonateSOH-dee-um by-KAR-buh-nateAn alkaline drug, given by mouth or IV, that neutralizes acid in the stomach or the blood.Full entry Close and digestive enzymesenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close.

• Sodium bicarbonate makes the juice slightly alkaline. It neutralizes the acid chymechymeKYMEThe thick, soupy mix of partly digested food and digestive juices that passes from the stomach into the small intestine.Full entry Close arriving from the stomach, stops pepsinpepsinPEP-sinAn enzyme in the stomach that begins breaking down proteins.peps digestion-in substanceFull entry Close working, and gives the enzymes of the small intestine the pH they need.
• Enzymes break down all three kinds of food, as the table shows.

The enzymes that digest protein leave the pancreas in an inactive form, such as trypsinogen. In the duodenum an enzyme on the lining switches trypsinogen into trypsin, and trypsin then switches on the others. If these enzymes become active inside the pancreas, they digest the gland itself: that is pancreatitispancreatitispan-kree-uh-TY-tisInflammation of the pancreas, which may come on suddenly (acute) or last for years (chronic).pancreat/o pancreas-itis inflammationFull entry Close. Heavy alcohol use and gallstones are its common causes.

Hormones from the duodenum control the flow: secretin brings out the bicarbonatebicarbonateby-KAR-buh-naytA base in the blood that balances acid; the kidneys control it, and its level is measured on blood gas and chemistry tests.Full entry Close, and CCK brings out the enzymes.

The islets

Each islet holds several kinds of cells.

• Alpha cells, about 20 percent of the islet, make glucagonglucagonGLOO-kuh-gonA hormone made by the pancreas that raises blood sugar; also given as a drug for severe low blood sugar.Full entry Close, which raises a low blood sugarhypoglycemiahy-poh-gly-SEE-mee-uhA blood glucose level below normal, under 70 mg/dL.hypo- belowglyc/o sugar, glucose-emia in the bloodFull entry Close.
• Beta cellsbeta cellBAY-tuh SELA cell in the pancreas that makes and releases insulin.Full entry Close, about 75 percent, make insulininsulinIN-suh-linA hormone made by the pancreas that lets the body's cells take in glucose, also made as a medicine.Full entry Close, which lowers a high blood sugarhyperglycemiahy-per-gly-SEE-mee-uhA blood glucose level above normal, over 100 mg/dL when fasting.hyper- aboveglyc/o sugar-emia in the bloodFull entry Close.
• Delta cells, about 4 percent, make somatostatin, which slows the secretionssecretionsih-KREE-shunA substance a gland or cell makes and releases, such as mucus, saliva, sweat or a hormone.Full entry Close of the stomach and the pancreas and the absorptionabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close of nutrients.

Chapter 9 teaches these hormones and diabetes.

A pancreaticoduodenectomy, or Whipple procedure, is done to cure pancreatic cancer. It removes the head of the pancreas together with the duodenum that wraps around it, part of the jejunumjejunumjeh-JOO-numThe second of the three sections of the small intestine; it follows the duodenum and leads into the ileum.jejun/o jejunum (from the Latin for empty)Full entry Close, the lower stomach, the end of the common bile duct and the gallbladder. Chapter 32 teaches it.

Pancreaticoduodenectomy (Whipple)40 instruments · 2 photos

15Nutrients and metabolism

The six kinds of nutrients

Nutrients are the substances in food and drink that the body needs to survive. There are six kinds. Carbohydrates, fats and proteins supply energy and, with water, are needed in large amounts; vitamins and minerals are needed in very small amounts.

Fiber is the part of plant foods the body has no enzymes to digest. It supplies no nutrients, but it helps move food through the tube and softens the stool.

Metabolism

Metabolismmetabolismmuh-TAB-uh-liz-umAll the chemical processes in the body's cells that make energy, build tissue and break substances down.Full entry Close is the sum of all the chemical reactions in the body. It has two halves, running side by side all the time.

• Catabolism breaks large molecules into smaller ones and releases energy. About 40 percent of that energy is captured in ATPATPay-tee-PEE (said as letters)Adenosine triphosphate: the molecule that stores and delivers energy for nearly every process in a cell.Full entry Close, the cell's energy currency, and the rest is given off as heat. Breaking down food for fuel is catabolism.
• Anabolism uses that energy to build large molecules from small ones, such as proteins from amino acids or glycogen from glucose, and to build new tissue and repair damaged tissue.

When the body takes in more energy than it uses, it stores the extra as fat; when it takes in less, it draws on its stores.

16Words for digestion and elimination

The Core Curriculum lists these terms, and the cert exam uses them. Most appear above; here they are together.

17Where surgery meets the gut

The layers and the anastomosis

When the surgeon joins two pieces of gut, an anastomosisanastomosisuh-nas-tuh-MOH-sisA connection between two tube-shaped structures, such as two ends of bowel or two blood vessels, made by surgery or found naturally.Full entry Close, the stitches or staples must hold the right layers.

• The submucosa is the strongest layer of the bowel wall, thanks to its collagencollagenKOL-uh-jenThe main structural protein of the body, which gives strength to skin, bones, tendons, ligaments and scar tissue.coll/a glue-gen producingFull entry Close, and every anastomosis must include it.
• In a two-layer hand-sewn joint, the inner stitches catch the mucosamucosamyoo-KOH-suhThe moist lining of body passages that open to the outside, such as the mouth, nose, gut and bladder.Full entry Close, the submucosa and the muscle, and the outer stitches join the serosa of the two ends.
• The esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close has no serosa and gets its blood in segments, so a join there is less forgiving than one in the bowel.

Chapter 25 teaches the suturessutureSOO-cherA stitch, or the thread used to stitch, that holds the edges of a wound or incision together.Full entry Close and staplers, and chapter 32 the steps of each operation.

Germs inside the lumen

The bowel's bacteria do no harm inside it, but in the wound they can cause infection. Once the bowel is opened, the risk of a surgical site infection remains even after a bowel prep and antibiotics, so the team uses isolation technique, also called bowel technique: instruments and items that touch the open bowel are kept apart from the rest of the field. Chapters 29 and 32 teach the steps, chapter 10 the germs, and chapter 11 the wound classes.

The mesentery comes with the specimen

Blood, nerves and lymphlymphLIMFThe clear fluid that flows through the lymphatic vessels and carries white blood cells.Full entry Close reach the intestine through its mesentery, so when a segment comes out, its mesentery and the vessels inside it are clamped and divided with it. The lymph from the bowel drains through nodes beside the mesentery, the same path cancer cells can follow, which is why a cancer operation also removes the lymph nodeslymph nodelimf nohdA small, bean-shaped organ of the immune system that filters lymph fluid and holds white blood cells.Full entry Close in that part of the mesentery.

After surgery

Surgery slows the bowel down. After abdominal or pelvic surgery, peristalsisperistalsispair-ih-STAWL-sisWaves of muscle squeezing that push food and waste along the digestive tract.peri- around-stalsis squeezing, contractionFull entry Close may be slowed for at least a day, and after bowel surgery for several days. Fluids and early walking help it return; the nurse listens for bowel soundsbowel soundBOW-ul sowndA gurgling or clicking sound made by gas and fluid moving through the intestines, heard with a stethoscope.Full entry Close and checks the abdomen for swelling, and constipation is common.

Disease of the liver, the bile ductsbile ductbyle duktOne of the tubes that carry bile from the liver and gallbladder to the small intestine.Full entry Close or the pancreaspancreasPAN-kree-usA long, flat gland behind the stomach that makes digestive enzymes and the hormones insulin and glucagon.pan- allcreas fleshFull entry Close reaches the field too. A patient with a blocked bile duct or liver diseaseliver diseaseLIV-er dih-ZEEZAny condition that damages the liver or keeps it from working normally.hepat/o liverFull entry Close may clot poorly, because the liver makes the clotting factorsclotting factorKLOT-ing FAK-terAny of the proteins in blood plasma that work together in a chain to form a blood clot.Full entry Close and needs bilebilebileA yellow-green fluid made by the liver and stored in the gallbladder that helps digest fats.chol/e bileFull entry Close to absorbabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close vitamin K, and may handle anestheticanesthetican-us-THET-ikA drug that causes loss of feeling, with or without loss of consciousness.an- withoutesthesi/o feeling, sensation-ic relating toFull entry Close drugs differently.

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