Hormones: the endocrine system

1Why it matters

Your body has two systems that carry messages. The nervous system sends fast electrical signals along nerves, and its effects are over quickly. The endocrine system sends chemical messengers, called hormones, through the blood. Hormones take longer to work, but their effects usually last longer.

Hormones run growth, 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, the balance of water and salts, the body's answer to stress, and reproduction. Each one acts on particular cells, and each one is kept within a narrow range, because too much or too little causes disease.

You meet this system at the surgical field in four ways.

• Surgeons operate on the glands. They remove all or part of the thyroid, the parathyroid glandsparathyroid glandpair-uh-THY-royd glandOne of four small glands behind the thyroid that control the amount of calcium in the blood.para- besidethyr/o thyroid gland-oid likeFull entry Close, the adrenal glandsadrenal glanduh-DREE-nul GLANDOne of two small glands that sit on top of the kidneys and make hormones such as cortisol, aldosterone and epinephrine.ad- toward, nearren/o kidney-al relating toFull entry Close, the pituitary and the thymusthymusTHY-musA small gland in the upper chest, behind the breastbone, where T cells (a kind of white blood cell) mature.Full entry Close. These glands sit close to nerves and vessels that must be protected, such as the nerve that moves the vocal cords.
• Every operation is a stress, and the body answers it with hormones. CortisolcortisolKOR-tih-solA steroid hormone made by the adrenal glands that helps control blood sugar, blood pressure, stress and inflammation.Full entry Close and epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close pour out, the heart speeds up and the blood sugar rises, even in a patient without diabetes.
• Many patients live with a gland disorder. Diabetes, thyroid disease and long-term steroidsteroidSTAIR-oydA fat-based chemical built from cholesterol; the group includes hormones such as cortisol and estrogen, and many drugs.ster/o solid-oid likeFull entry Close use change how a patient heals, how well they fight infection and how they handle the stress of surgery.
• Some hormones are drugs on the field. The hormones most often given in surgery are epinephrine, oxytocinoxytocinok-sih-TOH-sinA hormone that makes the uterus contract and releases breast milk; also given by IV to start or strengthen labor and control bleeding after birth.Full entry Close and the steroids called glucocorticoidscorticosteroidkor-tih-koh-STER-oydA drug that acts like the hormones of the adrenal glands, used mainly to calm inflammation and the immune system.cortic/o cortex (the outer layer of the adrenal gland)-oid likeFull entry Close.

This chapter explains how hormones work and how the body keeps them in balance, then goes gland by gland, and ends with what surgery and gland disease mean for the patient on the table. Other chapters teach what it leaves out: the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close as part of the brain in chapter 4; the thymus as lymphoid tissue in chapter 5; 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 as a digestive organ, with its enzymesenzymeEN-zimeA protein that speeds up a chemical reaction in the body without being used up.Full entry Close, in chapter 7; the ovaries and testes and the kidneys' own hormones in chapter 8; immunityimmunityih-MYOO-nih-teeThe body's ability to resist or fight off a particular infection or disease.immun/o protection-ity stateFull entry Close in chapter 10; diabetes as it affects wound healingwound healingwoond HEE-lingThe body's process of repairing damaged skin and tissue.Full entry Close and infection in chapter 11; 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, steroids and other hormone drugs in chapter 12; blood sugar, temperature and malignant hyperthermiamalignant hyperthermiamuh-LIG-nunt hy-per-THER-mee-uhA rare inherited reaction to certain general anesthesia drugs in which the muscles' metabolism speeds up out of control.mal- badhyper- above normaltherm heat-ia conditionFull entry Close under anesthesiaanesthesiaan-us-THEE-zhuhLoss of feeling or sensation, often brought on by drugs so that surgery or a procedure can be done without pain.an- withoutesthesi/o feeling, sensation-ia conditionFull entry Close in chapter 13; the thyroid and parathyroid operations and the Whipple procedure in chapter 32; adrenaladrenaluh-DREE-nulHaving to do with the adrenal glands, the two small glands that sit on top of the kidneys.ad- nearren/o kidney-al relating toFull entry Close surgery in chapter 34; the thymectomy in chapter 41; and pituitary surgery in chapter 42.

2How hormones work

Endocrine and exocrine glands

A gland is one cell or a group of cells that makes and releases a chemical substance. Glands come in two kinds.

• Endocrine glandsendocrine glandEN-doh-krin GLANDA gland that releases hormones straight into the blood instead of through a tube or duct.endo- within-crine to secreteFull entry Close have no ducts. They release their hormones into the fluid around their cells, and the blood carries the hormones through the body.
• Exocrine glands release their products through ducts, onto a surface or into a cavity. Sweat glands and the oil (sebaceous) glands of the skin are exocrine glands.

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 both. Most of it is exocrine and sends digestive juice down a duct into the small intestine, but small clusters of cells scattered through it, the islets, release hormones into the blood.

The main endocrine glands are the pituitary, pineal, thyroid, parathyroidparathyroid glandpair-uh-THY-royd glandOne of four small glands behind the thyroid that control the amount of calcium in the blood.para- besidethyr/o thyroid gland-oid likeFull entry Close and adrenal glandsadrenal glanduh-DREE-nul GLANDOne of two small glands that sit on top of the kidneys and make hormones such as cortisol, aldosterone and epinephrine.ad- toward, nearren/o kidney-al relating toFull entry Close, the islets of the pancreas, the thymusthymusTHY-musA small gland in the upper chest, behind the breastbone, where T cells (a kind of white blood cell) mature.Full entry Close, and the ovaries and testes. Many other organs also have cells that make hormones, including the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close, the heart, the kidneys, the stomach and small intestine, the liver, the skin and fat tissue.

Target cells and receptors

A hormone travels everywhere the blood goes, but it acts only on its target cells: the cells that carry a receptorreceptorrih-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 for it. A receptor is a protein shaped to fit one hormone, the way a lock fits one key. When the hormone binds, the cell changes what it is doing, for example by making a new protein, changing how it uses nutrients, or making a hormone or other product of its own.

Hormones fall into two chemical groups, and the group decides how a hormone works.

• SteroidsteroidSTAIR-oydA fat-based chemical built from cholesterol; the group includes hormones such as cortisol and estrogen, and many drugs.ster/o solid-oid likeFull entry Close hormones are made from cholesterol. CortisolcortisolKOR-tih-solA steroid hormone made by the adrenal glands that helps control blood sugar, blood pressure, stress and inflammation.Full entry Close, aldosteronealdosteroneal-DOS-tuh-rohnA hormone from the adrenal glands that makes the kidneys keep sodium and water and get rid of potassium.aldo- from aldehyde (a chemical group)-sterone steroid hormoneFull entry Close, estrogenestrogenES-truh-jenA female sex hormone, made mainly by the ovaries, and the group of drugs that act like it.Full entry Close, progesteroneprogesteroneproh-JES-tuh-rohnA female sex hormone that prepares the lining of the uterus for pregnancy and helps keep a pregnancy going, also given as a drug.Full entry Close and testosteronetestosteronetes-TOS-tuh-rohnThe main male sex hormone, made mostly in the testes and in small amounts by the ovaries and adrenal glands.test/o testis-sterone steroid hormoneFull entry Close are steroids. They dissolve in fat, not water, so they ride in the blood on carrier proteins. They pass straight through the cell membrane to a receptor inside the cell and switch genes on. Riding on their carriers, they last much longer in the blood than most other hormones.
• Nonsteroid hormones are built from amino acidsamino aciduh-MEE-noh AS-idOne of the small building blocks that join together in chains to make proteins.Full entry Close. The smallest are amines, made from a single amino acid, such as epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close, norepinephrinenorepinephrinenor-ep-ih-NEF-rinA hormone and nerve messenger that narrows blood vessels and raises blood pressure, also given as an IV drug.Full entry Close and the thyroid hormonesthyroid hormoneTHY-royd HOR-mohnA hormone made by the thyroid gland that controls how fast the body uses energy.Full entry Close. Peptides, such as antidiuretic hormoneantidiuretic hormonean-tee-dy-yoo-RET-ik HOR-mohnA hormone from the pituitary gland that tells the kidneys to hold on to water, making the urine more concentrated.anti- againstdiuretic making urineFull entry Close and oxytocinoxytocinok-sih-TOH-sinA hormone that makes the uterus contract and releases breast milk; also given by IV to start or strengthen labor and control bleeding after birth.Full entry Close, are short chains of amino acids, and proteins, such as growth hormonegrowth hormoneGROHTH HOR-mohnA hormone from the pituitary gland that drives growth in children and helps control body build and metabolism in adults.Full entry Close, 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 and 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, are longer chains. Most of them cannot cross the cell membrane, so they bind a receptor on the cell's surface, which sets off a chain of signals inside. The thyroid hormones are the exception: they enter the cell.

The difference shows in how long a hormone lasts. Half of a dose of cortisol is gone from the blood in about 60 to 90 minutes, but half of a dose of epinephrine is gone in about a minute.

Hormones also work on each other. Some pairs are antagonistsantagonistan-TAG-uh-nistA drug that attaches to a receptor and blocks it, so the body's own chemicals or other drugs cannot act there.ant- againstagon struggle-ist one whoFull entry Close, with opposite effects: insulin lowers the blood sugar and glucagon raises it. Others are synergists, which together give a stronger effect than either alone.

Negative feedback keeps levels in range

Chapter 2 introduced negative feedbackfeedbackFEED-bakInformation about a result that is sent back to change what happens next, in the body or between people.Full entry Close, the body's main way of keeping a value steady. Most hormones are controlled this way: once the blood holds enough of a hormone, its release slows, so the level stays in a narrow range.

Three kinds of trigger start a gland releasing its hormone.

• A change in the blood: a rise in blood sugar makes the pancreas release insulin, and blood that is too concentrated makes the pituitary release antidiuretic hormone.
• Another hormone: the hypothalamus releases hormones that control the pituitary, and the pituitary releases hormones that control other glands.
• A nerve signal: in danger, sympathetic nerves make the adrenal glands release epinephrine and norepinephrine within seconds.

Positive feedback, which pushes a change further, is rare. During labor, oxytocin makes the uterus contract, the baby's head stretches the cervix, and the stretch brings out more oxytocin, until the baby is born.

The hypothalamus and the pituitary: the command center

The hypothalamus, part of the brain (chapter 4), and the pituitary glandpituitary glandpih-TOO-ih-tair-ee glandA gland the size of a pea, hanging below the brain, whose hormones control many other glands.Full entry Close hanging below it work together as the command center of the endocrine system. Many signals that reach the nervous system pass through them and are turned into hormones.

The hypothalamus controls the pituitary in two ways.

• The anterior pituitary answers to releasing hormones and inhibiting hormones made by the hypothalamus. They travel down the pituitary stalk in a short chain of vessels, the hypophyseal portal system, which carries them straight to the anterior pituitary before they reach the rest of the body.
• The posterior pituitary is wired to the hypothalamus. Nerve cellsneuronNOOR-onA nerve cell: a cell that carries electrical and chemical signals through the nervous system.neur/o nerveFull entry Close in the hypothalamus make two hormones, send them down their axonsaxonAK-sonThe long, thin part of a nerve cell that carries electrical signals away from the cell body.Full entry Close in the stalk, and store them in the posterior pituitary until they are released.

Many glands sit at the bottom of a chain of three. The hypothalamus releases a hormone that tells the anterior pituitary to release a second hormone, which tells a target gland to release a third. As the third hormone rises in the blood, it slows the hypothalamus and the pituitary, and the chain winds down. The thyroid is the classic example, and the adrenal cortexadrenal cortexuh-DREE-nul KOR-teksThe outer layer of each adrenal gland, which makes the steroid hormones cortisol and aldosterone.ad- nearren kidney-al relating tocortex outer layer (Latin, bark)Full entry Close works the same way.

3The pituitary gland

Where it sits

The pituitary glandpituitary glandpih-TOO-ih-tair-ee glandA gland the size of a pea, hanging below the brain, whose hormones control many other glands.Full entry Close, or hypophysis, is about the size of a pea. It hangs from the underside of the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close on a stalk called the infundibulum, and it sits in a small hollow on top of the sphenoid bone in the floor of the skull, the sella turcica.

Its neighbors explain how a pituitary tumor shows itself and how surgeons reach it.

• The optic chiasm, where the two optic nervesoptic nerveOP-tik nervThe nerve that carries visual signals from the back of the eye to the brain; the second cranial nerve.Full entry Close cross, lies just above it. A tumor that presses up on the chiasm changes the field of vision, classically taking away the outer half of what each eye sees.
• The cavernous sinusessinusSY-nusA hollow space in the body, most often one of the air-filled spaces in the skull bones around the nose.Full entry Close lie on each side, holding cranial nervescranial nerveKRAY-nee-ul NERVOne of the 12 pairs of nerves that come straight from the brain and brainstem rather than the spinal cord.Full entry Close III to VI and the internal carotidcarotidkuh-ROT-idHaving to do with the carotid arteries, the two large arteries on each side of the neck that carry blood to the head and brain.Full entry Close arteries.
• The sphenoid sinus lies in front of and below it, so surgeons can reach the gland through the nose and the sinus (chapter 6).

The pituitary is often called the master gland, because its hormones control the thyroid, the adrenal cortexadrenal cortexuh-DREE-nul KOR-teksThe outer layer of each adrenal gland, which makes the steroid hormones cortisol and aldosterone.ad- nearren kidney-al relating tocortex outer layer (Latin, bark)Full entry Close and the ovaries and testes.

It has two lobes, which grow from different tissue before birth and work differently.

• The anterior lobe, or adenohypophysis, is glandular tissue. It makes its own hormones.
• The posterior lobe, or neurohypophysis, is nerve tissue. It makes no hormones; it stores and releases two hormones made in the hypothalamus.

Anterior lobe hormones

The anterior lobe makes six hormones that you need to know.

TSH, ACTH, FSH and LH are called tropic hormones ("turning" hormones), because they turn other glands on and off. Some references spell the word "trophic," and the Core Curriculum lists them that way. FSH and LH together are the gonadotropins, the hormones that run the ovaries and testes; chapter 8 shows where the surge of LH falls in the menstrual cycle.

The hypothalamus has a releasing hormone for each one: TRH brings out TSH, CRHCRHsee-ar-aych (said as letters)Corticotropin-releasing hormone: a hormone from the hypothalamus that signals the pituitary gland to release ACTH.Full entry Close brings out ACTH, GnRH brings out FSH and LH, and GHRH brings out growth hormone. Growth hormone also has an inhibiting hormone, GHIH, also called somatostatin.

The anterior lobe also releases beta endorphinendorphinen-DOR-finA natural chemical made in the brain that eases pain and creates a sense of well-being.Full entry Close, one of the brain's own painkilling chemicals, and cells between the two lobes release melanocytemelanocytemuh-LAN-uh-syteA cell in the bottom layer of the skin's outer layer that makes melanin, the pigment that gives skin and hair their color.melan/o black-cyte cellFull entry Close-stimulating hormone, which can darken the skin.

When growth hormone is out of balance, the signs depend on age. Too much in a child, before the bones stop growing, causes gigantism. Too much in an adult, once growth has stopped, causes acromegalyacromegalyak-roh-MEG-uh-leeA rare hormone disorder in adults in which the body makes too much growth hormone.acr/o extremities (hands and feet)-megaly enlargementFull entry Close: the bones of the face, hands and feet grow larger. Too little in a child stunts growth (pituitary dwarfism, or growth hormone deficiency).

Posterior lobe hormones

The posterior lobe is really an extension of the brain. Nerve cellsneuronNOOR-onA nerve cell: a cell that carries electrical and chemical signals through the nervous system.neur/o nerveFull entry Close in the hypothalamus make antidiuretic hormoneantidiuretic hormonean-tee-dy-yoo-RET-ik HOR-mohnA hormone from the pituitary gland that tells the kidneys to hold on to water, making the urine more concentrated.anti- againstdiuretic making urineFull entry Close and oxytocinoxytocinok-sih-TOH-sinA hormone that makes the uterus contract and releases breast milk; also given by IV to start or strengthen labor and control bleeding after birth.Full entry Close, pass them down their axonsaxonAK-sonThe long, thin part of a nerve cell that carries electrical signals away from the cell body.Full entry Close, store them in their endings in the posterior lobe, and release them into the blood when the cells fire. That is the "production of neural transmitter" in the Core Curriculum's list: hormones made and released by nerve cells.

Antidiuretic hormone (ADH), also called vasopressinvasopressinvay-zoh-PRES-inA man-made form of antidiuretic hormone, given by IV mainly to raise blood pressure in shock.Full entry Close, saves water.

• Sensors in the hypothalamus watch how concentrated the blood is. When it is too concentrated, as in dehydration or after a salty meal, the posterior lobe releases ADH.
• ADH makes the tubulestubuleTOO-byoolA very small tube in the body, most often one of the tiny tubes in the kidney that turn filtered fluid into urine.Full entry Close of the kidneys take back more water, so less urine is made and the blood is diluted back to normal. Then the release slows, by negative feedbackfeedbackFEED-bakInformation about a result that is sent back to change what happens next, in the body or between people.Full entry Close.
• At high levels, ADH also narrows blood vessels and raises the blood pressure, which is where the name vasopressin comes from.
• Alcohol blocks its release, which is why drinking alcohol makes you pass more urine.

Oxytocin acts on the uterus and the breasts. It makes the uterus contract during childbirth, through the positive feedback loop above, and it makes the milk ducts squeeze milk out when a baby nurses (the let-down reflexletdownLET-downThe reflex that pushes milk out of the breast's milk glands toward the nipple during breastfeeding.Full entry Close). It also seems to play a part in bonding.

Too little ADH causes diabetes insipidusdiabetes insipidusdy-uh-BEE-teez in-SIP-ih-dusA disorder of antidiuretic hormone: the body makes too little of it, or the kidneys do not respond to it.Full entry Close: the kidneys cannot hold on to water, so the patient passes large amounts of dilute urine, is always thirsty, and can become dehydrated. It is treated with a drug form of vasopressin.

At the field, oxytocin is also a drug. After a cesarean birthcesarean birthsih-ZAIR-ee-un berthBirth of a baby through surgical cuts in the belly and the uterus.Full entry Close, 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 gives it into the vein to help the uterus contract and slow the bleeding, and the surgeon may ask for it to be injected straight into the uterine muscle. The scrub draws it up from a vial held by the circulator and labels the syringe before passing it. Chapter 12 teaches drugs on the field.

4The pineal gland

The pineal glandpineal glandPIN-ee-ul GLANDA small gland deep in the brain that makes melatonin, the hormone that helps control sleep.Full entry Close is a tiny gland deep in the brain, below and behind the thalamusthalamusTHAL-uh-musA pair of egg-shaped masses deep in the brain that relay sensory signals to the cerebral cortex.thalam/o thalamus (from the Greek for inner chamber)Full entry Close. It lies behind the pituitary.

Its cells make the hormone melatoninmelatoninmel-uh-TOH-ninA hormone made by the pineal gland in the brain, mostly at night, that helps control the sleep-wake cycle.Full entry Close, built from serotoninserotoninser-uh-TOH-ninA chemical messenger in the brain, gut and blood that helps control mood, sleep, appetite and other functions.Full entry Close. Light controls how much they make.

• In daylight, light striking the retinasretinaRET-ih-nuhThe thin layer of light-sensing tissue at the back of the inside of the eye.Full entry Close sends signals through the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close to the pineal gland, which then makes less melatonin, and you stay awake.
• As darkness falls, the pineal gland makes more melatonin, and you grow drowsy.

So melatonin helps set the body's daily sleep and wake cycle, its circadian rhythm, which also shapes appetite and body temperature. Jet lag comes from crossing time zones faster than melatonin can reset, and some travelers take melatonin pills to sleep. Children have higher levels than adults, which may help hold back puberty.

A tumor in the region of the pineal gland often causes hydrocephalushydrocephalushy-droh-SEF-uh-lusA buildup of too much cerebrospinal fluid inside the spaces (ventricles) of the brain.hydr/o watercephal/o head-us noun endingFull entry Close, a buildup of cerebrospinal fluidcerebrospinal fluidser-uh-broh-SPY-nul FLOO-idThe clear, watery fluid that bathes and cushions the brain and spinal cord.cerebr/o brainspin spine-al relating toFull entry Close in the brain (chapter 4).

5The thyroid gland

Its shape and its neighbors

The thyroid gland is shaped like a butterfly. It lies low in the front of the neck, on the front of the tracheatracheaTRAY-kee-uhThe windpipe: the tube that carries air from the throat to the lungs.Full entry Close, just under 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. Its right and left lobes are joined by a narrow middle band, the isthmus, which crosses the trachea between the second and fourth tracheal rings. It weighs about 20 grams and is the largest of the endocrine glandsendocrine glandEN-doh-krin GLANDA gland that releases hormones straight into the blood instead of through a tube or duct.endo- within-crine to secreteFull entry Close. It has a very rich blood supply.

About 30 percent of patients have a pyramidal lobe, a thin strip of thyroid tissue that runs upward from the isthmus. It is left over from the duct along which the thyroid moved down from the base of the tongue before birth.

The thyroid is crowded by structures the surgeon must protect.

• It lies under the thin strap muscles of the neck, on the trachea, and its lobes rest against the larynx, the trachea and the esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close. A band of tissue, the ligament of Berry, fixes it to the cricoid cartilagecartilageKAR-tih-lijFirm, smooth, rubbery tissue that cushions joints and gives shape to parts such as the ear, nose and windpipe.chondr/o cartilageFull entry Close and the trachea.
• The common carotidcarotidkuh-ROT-idHaving to do with the carotid arteries, the two large arteries on each side of the neck that carry blood to the head and brain.Full entry Close artery, the internal jugular veininternal jugular veinin-TUR-nul JUG-yuh-ler vaynA large vein deep on each side of the neck that carries blood from the brain, face and neck back toward the heart.Full entry Close and the vagus nervevagus 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 run up the neck beside each lobe.
• Two pairs of arteries feed it: the superior thyroid arteries, from the external carotid arteries, enter the upper poles, and the inferior thyroid arteries, from the thyrocervical trunks of the subclavian arteries, enter the lower part of the gland. Now and then a single extra artery, the thyroidea ima, rises from the aortic arch or the brachiocephalic artery to the bottom of the isthmus. Three pairs of veins drain it.
• The recurrent laryngeal nerve, a branch of the vagus nerve, runs up in the groove between the trachea and the esophagus, behind the thyroid, and works the muscles that move the vocal cords. Cutting one nerve leaves the voice hoarse; injuring both can close the airway.
• The external branch of the superior laryngeal nerve runs near the superior thyroid artery and works one small muscle of the larynx, the cricothyroid. Injury to it makes it hard to shout or to sing high notes.
• The parathyroid glandsparathyroid glandpair-uh-THY-royd glandOne of four small glands behind the thyroid that control the amount of calcium in the blood.para- besidethyr/o thyroid gland-oid likeFull entry Close lie on the back of the lobes.

Thyroid hormones and metabolism

The thyroid is built of tiny hollow sacs, the folliclesfollicleFOL-ih-kulA small sac or cavity in the body, such as the pocket a hair grows from or the sac in the ovary that holds an egg.Full entry Close, each full of a thick fluid, the colloid. The cells lining each follicle build the thyroid hormonesthyroid hormoneTHY-royd HOR-mohnA hormone made by the thyroid gland that controls how fast the body uses energy.Full entry Close in the colloid, and they need iodineiodineEYE-uh-dyneA mineral the thyroid gland uses to make thyroid hormone; it is also used to kill germs on the skin and in some contrast dyes.Full entry Close from food to do it. That is why iodine is added to table salt.

• Thyroxine (T4) carries four iodine atoms. It is the main hormone the gland makes.
• TriiodothyronineT3tee-THREETriiodothyronine: the more active of the two main thyroid hormones, or the blood test that measures it.Full entry Close (T3) carries three. It is the stronger of the two, and many body cells turn T4 into T3 by removing one iodine.

The hormones wait in the colloid until TSHthyroid-stimulating hormoneTHY-royd STIM-yuh-lay-ting HOR-mohnA hormone from the pituitary gland that tells the thyroid to make thyroid hormone; its blood level is the main thyroid test.Full entry Close releases them into the blood. There, more than 99 percent of them ride on carrier proteins, and only the small free share enters the cells.

T4 and T3 set the body's 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, the pace of the chemical work in its cells.

• They raise the basal metabolicmetabolicmet-uh-BOL-ikRelating to metabolism, the chemical processes that turn food into energy and build and break down substances in the body.metabol change-ic relating toFull entry Close rate, the energy the body burns at rest, so cells use more oxygen and fuel and give off more heat.
• They are needed for growth and for the development of the brain and nerves before birth and in childhood.
• They make the heart and blood vessels more sensitive to epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close and norepinephrinenorepinephrinenor-ep-ih-NEF-rinA hormone and nerve messenger that narrows blood vessels and raises blood pressure, also given as an IV drug.Full entry Close, so too much thyroid hormone speeds the heart, strengthens the beat and raises the blood pressure.

The TRH, TSH and thyroid chain in the feedbackfeedbackFEED-bakInformation about a result that is sent back to change what happens next, in the body or between people.Full entry Close figure controls the output. A blood test for TSH is the single best test of thyroid function. Because of negative feedback, a high TSH means the gland is underactive, and the pituitary is pushing it harder; a low TSH means the gland is overactiveoveractivityoh-ver-ak-TIV-ih-teeMore activity than normal, in a person, an organ or a body system.Full entry Close.

When the diet lacks iodine, the thyroid cannot make enough hormone, the pituitary keeps sending more TSH, and the gland swells. An enlarged thyroid is called a goitergoiterGOY-terAn enlarged thyroid gland, seen or felt as a swelling at the front of the neck.Full entry Close. A goiter can also come with an overactive gland.

Calcitonin

Scattered between the follicles are the parafollicular cells, or C cells. When the blood calcium rises, they release calcitonincalcitoninkal-sih-TOH-ninA hormone made by the thyroid gland that lowers blood calcium; a lab-made form is used as a drug.Full entry Close, which lowers it: it slows the bone cells that break down bone (osteoclastsosteoclastOS-tee-oh-klastA bone cell that breaks down and removes old bone tissue.oste/o bone-clast something that breaksFull entry Close), cuts the absorptionabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close of calcium in the gut and increases the calcium lost in the urine.

Calcitonin usually does little to keep the calcium steady; parathyroid hormoneparathyroid hormonepar-uh-THY-royd HOR-mohnA hormone from the parathyroid glands in the neck that raises the calcium level in the blood.para- besidethyr/o thyroid-oid resemblingFull entry Close does most of that work. A drug form of calcitonin is used for weak, thin bones (osteoporosisosteoporosisos-tee-oh-puh-ROH-sisA condition in which bones lose density and become thin, weak and easy to break.oste/o bonepor/o pore, small opening-osis abnormal conditionFull entry Close), and a high blood level can mark a medullarymedullamuh-DUL-uhThe inner part of an organ; most often the medulla oblongata, the lowest part of the brainstem.Full entry Close thyroid cancer.

6The parathyroid glands and calcium

Where they are

The parathyroid glandsparathyroid glandpair-uh-THY-royd glandOne of four small glands behind the thyroid that control the amount of calcium in the blood.para- besidethyr/o thyroid gland-oid likeFull entry Close are small, oval, yellow to brownish glands, each about the size of a lentil, on the back of the thyroid lobes. A thick capsule of connective tissueconnective tissuekuh-NEK-tiv TISH-ooBody tissue that supports, binds together and protects other tissues and organs.Full entry Close separates them from the thyroid, and fat often covers them.

• Most people have four: two upper glands near the upper poles of the thyroid and two lower glands near the lower poles. The lower ones vary more in where they sit.
• Some people have more, and glands can sit away from the thyroid, lower in the neck or in the upper chest (the superior mediastinum). The Core Curriculum lists four to six glands; one reference gives a range of 2 to 12, with about 90 percent of people having four.
• Both the upper and the lower glands get their blood from the inferior thyroid artery.

They are hard to tell apart from a lobule of fat, a lymph nodelymph nodelimf nohdA small, bean-shaped organ of the immune system that filters lymph fluid and holds white blood cells.Full entry Close or a small thyroid nodulenoduleNOD-yoolA small, firm, rounded lump of tissue that can be felt or seen, in or under the skin or in an organ.Full entry Close, and during thyroid surgery they can be damaged, removed by accident or cut off from their blood supply.

Parathyroid hormone and blood calcium

Calcium is needed for muscles to contract, for nerves to send signals and for blood to clot, so its level in the blood is held in a narrow range.

When the blood calcium falls, the chief cells of the parathyroid glands release parathyroid hormoneparathyroid hormonepar-uh-THY-royd HOR-mohnA hormone from the parathyroid glands in the neck that raises the calcium level in the blood.para- besidethyr/o thyroid-oid resemblingFull entry Close (PTH), also called parathormone. It raises the calcium in three ways.

1. Bone: it makes osteoclastsosteoclastOS-tee-oh-klastA bone cell that breaks down and removes old bone tissue.oste/o bone-clast something that breaksFull entry Close break down bone matrix and free calciumionized calciumEYE-uh-nized KAL-see-umA blood test for the free, active form of calcium that is not bound to proteins.Full entry Close into the blood, and it slows the cells that lay calcium down in bone.
2. Kidneys: it makes the kidneys take back more calcium from the urine, and it makes them produce calcitriolcalcitriolkal-sih-TRY-olThe active form of vitamin D, given as a drug to raise calcium absorption or, as an ointment, for psoriasis.Full entry Close, the active form of vitamin D.
3. Gut: calcitriol makes the intestine absorbabsorptionub-ZORP-shunThe taking in of a substance, such as a drug or a nutrient, into the bloodstream.Full entry Close more calcium from food.

As the calcium rises, PTH release slows, by negative feedbackfeedbackFEED-bakInformation about a result that is sent back to change what happens next, in the body or between people.Full entry Close. PTH and calcitonincalcitoninkal-sih-TOH-ninA hormone made by the thyroid gland that lowers blood calcium; a lab-made form is used as a drug.Full entry Close pull in opposite directions, and together they keep the calcium steady.

Too much or too little parathyroid hormone

• Hyperparathyroidismhyperparathyroidismhy-per-pair-uh-THY-roy-diz-umOveractivity of the parathyroid glands, which make too much parathyroid hormone.hyper- excessivepara- besidethyroid -ism conditionFull entry Close: when the trouble starts in the glands themselves, it is most often a single benign tumor of one gland, an adenomaadenomaad-uh-NOH-muhA tumor of gland tissue that is not cancer.aden/o gland-oma tumorFull entry Close (80 to 85 percent of these cases), less often an enlargement of all four glands, and rarely a cancer. The high calcium thins the bones so they break easily, forms kidney stoneskidney stoneKID-nee STOHNA hard, pebble-like lump of minerals that forms inside the kidney.Full entry Close, and causes muscle weakness, tiredness, belly pain and changes in mood.
• Hypoparathyroidismhypoparathyroidismhy-poh-pair-uh-THY-royd-iz-umA condition in which the parathyroid glands make too little parathyroid hormone.hypo- below, too littlepara- besidethyr/o thyroid gland-oid like-ism conditionFull entry Close: most often the result of thyroid surgery that injures the parathyroid glands or cuts off their blood supply. The low calcium makes nerves and muscles fire too easily: numbness and tingling, twitching, cramps and muscle spasmsspasmSPAZ-umA sudden, involuntary tightening of a muscle or of the muscle in a hollow organ or tube.Full entry Close, a state called tetanytetanyTET-uh-neeInvoluntary muscle cramps and spasms that come from nerves firing too easily.Full entry Close. Severe cases can bring on seizuresseizureSEE-zherA sudden burst of abnormal electrical activity in the brain that changes movement, feeling, behavior or awareness.Full entry Close and spasm of 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 that blocks breathing, and can be fatal.

7The adrenal glands

Where they sit

The two adrenal glandsadrenal glanduh-DREE-nul GLANDOne of two small glands that sit on top of the kidneys and make hormones such as cortisol, aldosterone and epinephrine.ad- toward, nearren/o kidney-al relating toFull entry Close sit on top of the kidneys, which is why they are also called the suprarenal glands. They lie behind 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, 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, inside the same fasciafasciaFASH-ee-uhA sheet or band of tough connective tissue that covers and separates muscles and organs.fasci/o bandFull entry Close as the kidneys (Gerota fascia). The right gland is triangular and lies against 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. The left gland is crescent-shaped and lies behind the stomach and 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.

They have one of the richest blood flows in the body. Arteries reach them from the inferior phrenic arteries, the aorta and the renal arteries. The right adrenaladrenaluh-DREE-nulHaving to do with the adrenal glands, the two small glands that sit on top of the kidneys.ad- nearren/o kidney-al relating toFull entry Close vein is short and drains straight into the inferior vena cava; the left drains into the left renal vein.

Each gland is two glands in one.

• The adrenal cortexadrenal cortexuh-DREE-nul KOR-teksThe outer layer of each adrenal gland, which makes the steroid hormones cortisol and aldosterone.ad- nearren kidney-al relating tocortex outer layer (Latin, bark)Full entry Close, the outer layer, is glandular tissue that makes steroidsteroidSTAIR-oydA fat-based chemical built from cholesterol; the group includes hormones such as cortisol and estrogen, and many drugs.ster/o solid-oid likeFull entry Close hormones.
• The adrenal medullaadrenal medullauh-DREE-nul meh-DUL-uhThe inner part of each adrenal gland, which releases epinephrine and norepinephrine.medulla inner part (Latin for marrow)Full entry Close, the inner core, is modified nerve tissue that makes catecholaminescatecholaminekat-uh-KOH-luh-meenAny of a group of hormones and neurotransmitters, mainly epinephrine, norepinephrine and dopamine, that act in the body's stress response.Full entry Close.

The adrenal cortex

The cortexcortexKOR-teksThe outer layer of an organ, especially the folded gray outer layer of the brain.cortic/o cortex, outer layerFull entry Close has three zones, and each makes its own group of steroids.

ACTHadrenocorticotropic hormoneuh-dree-noh-kor-tih-koh-TROH-pik HOR-mohnA hormone from the pituitary gland that tells the adrenal glands to make cortisol.adren/o adrenal glandcortic/o cortex, outer layer-tropic stimulatingFull entry Close from the anterior pituitary drives the release of cortisol and the androgens. The chain runs CRHCRHsee-ar-aych (said as letters)Corticotropin-releasing hormone: a hormone from the hypothalamus that signals the pituitary gland to release ACTH.Full entry Close from the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close, ACTH from the pituitary, then cortisol, and a high cortisol level switches the chain off. Aldosterone is also released when the potassium is high, the sodium is low or the blood pressure falls; a fall in pressure works through a hormone chain that starts in the kidneys (chapter 8).

Steroid drugs such as prednisoneprednisonePRED-nih-soneA corticosteroid drug taken by mouth to reduce inflammation and calm the immune system.Full entry Close, dexamethasonedexamethasonedek-suh-METH-uh-zohnA strong, long-acting corticosteroid drug that reduces inflammation and calms the immune system.Full entry Close and hydrocortisonehydrocortisonehy-droh-KOR-tih-soneA corticosteroid drug that is the same as the body's own cortisol, given by mouth, IV, on the skin or rectally.Full entry Close copy cortisol. They are used to calm inflammation, in a joint, in the lungs or on the skin, and to prevent the rejection of a transplanted organ. Taken for a long time, they shut down the patient's own adrenal cortex, a point that matters on the day of surgery. Chapter 12 teaches them as drugs.

The adrenal medulla

The medullamedullamuh-DUL-uhThe inner part of an organ; most often the medulla oblongata, the lowest part of the brainstem.Full entry Close is really part of the sympathetic nervous systemsympathetic nervous systemsim-puh-THET-ik NER-vus SIS-tumThe branch of the autonomic nervous system that gets the body ready for stress or danger ("fight or flight").Full entry Close (chapter 4). Its large chromaffin cells release epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close (adrenaline) and norepinephrinenorepinephrinenor-ep-ih-NEF-rinA hormone and nerve messenger that narrows blood vessels and raises blood pressure, also given as an IV drug.Full entry Close (noradrenaline) into the blood, about four parts epinephrine to one of norepinephrine. These hormones are catecholamines, a group that also includes dopaminedopamineDOH-puh-meenA natural brain chemical, also given as an IV drug that raises blood pressure and makes the heart pump harder.Full entry Close.

Sympathetic nerves fire the medulla in danger or sudden stress, and the hormones arrive within seconds. This is the fight-or-flight response.

• The heart beats faster and harder, and the blood pressure rises.
• The airways widen, and more blood goes to the muscles, the heart and the brain.
• Blood vessels to the gut, the kidneys and the skin narrow, and digestion slows.
• The liver turns glycogen into glucose, so the blood sugar rises. The pupils widen and the mouth goes dry.

Epinephrine is also a drug you will handle at the field. A little of it is mixed with local anestheticslocal anestheticLOH-kul an-es-THET-ikA drug that blocks feeling in one part of the body without making the person unconscious.Full entry Close such as lidocainelidocaineLY-doh-kaynA local anesthetic that numbs an area, also given by IV to treat some fast, abnormal heart rhythms.Full entry Close; it narrows the small vessels, so the numbing drug stays where it was injected and lasts longer, and the tissue bleeds less. Chapter 12 teaches its safe use.

8The pancreatic islets and blood sugar

Most 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 makes digestive juice (chapter 7). Scattered through it are tiny clusters of hormone-making cells, the pancreatic islets, or islets of Langerhans, which release their hormones into the blood.

Each islet holds four 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.
• 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.
• Delta cells, about 4 percent, make somatostatin, which holds back the release of both insulin and glucagon. The hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close, the stomach and the intestine make somatostatin too.
• PP cells, about 1 percent, make pancreatic polypeptide, which seems to play a part in appetite.

Glucose is the body's preferred fuel, and the brain depends on a steady supply. The body keeps the blood glucose, or blood sugar, at about 70 to 100 mg/dL, and it stores extra glucose in the liver and the muscles as glycogenglycogenGLY-kuh-jenThe stored form of glucose, kept mainly in the liver and muscles.glyc/o sugar-gen producingFull entry Close. Insulin and glucagon work as a seesaw to hold it there.

• When the blood sugar rises, as after a meal, the beta cells release insulin. Insulin lets most body cells, above all muscle and fat cells, take glucose in; it makes the liver store glucose as glycogen; and it helps the body build fat and protein. The blood sugar falls. The brain, the liver, the kidneys and red blood cells take up glucose without needing insulin.
• When the blood sugar falls, as during fasting or hard exercise, the alpha cells release glucagon. Glucagon makes the liver break glycogen back down into glucose and build new glucose from amino acidsamino aciduh-MEE-noh AS-idOne of the small building blocks that join together in chains to make proteins.Full entry Close and glycerol. The blood sugar rises.

Each hormone is held in check by negative feedbackfeedbackFEED-bakInformation about a result that is sent back to change what happens next, in the body or between people.Full entry Close: a falling blood sugar turns off insulin, and a rising one turns off glucagon. CortisolcortisolKOR-tih-solA steroid hormone made by the adrenal glands that helps control blood sugar, blood pressure, stress and inflammation.Full entry Close, epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close and growth hormonegrowth hormoneGROHTH HOR-mohnA hormone from the pituitary gland that drives growth in children and helps control body build and metabolism in adults.Full entry Close also raise the blood sugar, which is why stress pushes it up.

Diabetes mellitus

In diabetes mellitus ("honey-sweet"), the blood sugar stays too high, a state called hyperglycemiahyperglycemiahy-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, because the body makes too little insulin or its cells do not respond to it.

• Type 1: the immune system destroys the beta cells, so the body makes little or no insulin. The patient needs insulin by injection or pump for life. It usually starts young and makes up a small share of cases.
• Type 2: the cells resist insulin, the pancreas makes more to keep up, and in time the beta cells wear out. It makes up about 90 to 95 percent of cases and is linked to excess weight and too little activity. Diet, exercise and pills often control it, and some patients need insulin.

The early signs are passing large amounts of urine (polyuriapolyuriapol-ee-YOOR-ee-uhPassing an abnormally large amount of urine, usually more than about 2.5 to 3 liters a day in an adult.poly- many, muchur/o urine-ia conditionFull entry Close), great thirst (polydipsiapolydipsiapol-ee-DIP-see-uhExtreme thirst, with drinking much more fluid than usual.poly- many, much-dipsia thirstFull entry Close) and hunger (polyphagia): the extra glucose spills into the urine and pulls water with it.

Over the years, a high blood sugar damages blood vessels and nerves. That leads to heart attacksmyocardial infarctionmy-oh-KAR-dee-ul in-FARK-shunDeath of part of the heart muscle because its blood supply is blocked; a heart attack.my/o musclecardi/o heart-al having to do withinfarct area of dead tissueFull entry Close and strokes, kidney failurerenal failureREE-nul FAYL-yerLoss of the kidneys' ability to filter waste and extra fluid from the blood.ren kidney-al relating toFull entry Close, blindness, poor blood flow to the legs, and loss of feeling in the feet (neuropathyneuropathynoo-ROP-uh-theeDamage to or disease of one or more nerves, most often the nerves of the hands and feet.neur/o nerve-pathy diseaseFull entry Close). Together these raise the risk of injury, infection and tissue death, and lead to many toe, foot and leg amputationsamputationam-pyoo-TAY-shunThe removal of all or part of a limb or other body part, by surgery or by injury.Full entry Close.

Without insulin, cells burnburnBURNAn injury to the skin or deeper tissues caused by heat, chemicals, electricity, radiation or friction.Full entry Close fat for fuel, and acids called ketonesketoneKEE-tohnAn acid made by the liver when the body burns fat for energy instead of glucose.Full entry Close build up in the blood. This ketoacidosisketoacidosiskee-toh-as-ih-DOH-sisA state in which ketones build up in the blood and make it too acidic.ket/o ketoneacid acid-osis abnormal conditionFull entry Close can lead to comacomaKOH-muhA deep state of unconsciousness in which a person cannot be woken and does not respond with purpose.Full entry Close and death if it is not treated.

The opposite problem, hypoglycemiahypoglycemiahy-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, a blood sugar that is too low, most often comes from too much insulin. The patient becomes anxious, sweaty, shaky, hungry and weak, with a fast heart rate; as the brain runs short of glucose, they become confused and may have seizuresseizureSEE-zherA sudden burst of abnormal electrical activity in the brain that changes movement, feeling, behavior or awareness.Full entry Close or lose consciousness. A very high and a very low blood sugar can look alike, so the cause is checked quickly and treated.

9The thymus and other hormone makers

The thymus

The thymusthymusTHY-musA small gland in the upper chest, behind the breastbone, where T cells (a kind of white blood cell) mature.Full entry Close lies in the mediastinum, in the upper front of the chest behind the sternum. It is large and active in infancy and childhood and shrinks with age.

Its hormones, the thymosins, help T 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, the immune cells that mature in the thymus, to develop. Chapter 5 teaches the thymus as lymphoid tissue, and chapter 10 teaches immunityimmunityih-MYOO-nih-teeThe body's ability to resist or fight off a particular infection or disease.immun/o protection-ity stateFull entry Close.

A thymectomy removes the thymus. It is done for a tumor of the thymus, a thymoma, and for myasthenia gravismyasthenia gravismy-us-THEE-nee-uh GRAV-isA long-term autoimmune disease in which antibodies block the signals passing from nerves to muscles.my/o muscle-asthenia weaknessgravis seriousFull entry Close, an autoimmune diseaseautoimmune diseaseaw-toh-ih-MYOON dih-ZEEZA disease in which the immune system attacks the body's own healthy tissue.auto- selfimmune protectedFull entry Close that weakens the muscles; thymomas are often found together with it. The classic approach is through the split sternum (a median sternotomy), and less invasive approaches go through a partial sternotomy, through the neck, or through small chest incisions with a thoracoscope or a robot. Chapter 41 teaches it.

Other organs that make hormones

10When glands make too much or too little

Most endocrineendocrineEN-doh-krinRelating to the glands that release hormones straight into the blood, or to those hormones.endo- withincrin/o to secreteFull entry Close diseases come from a gland making too much of its hormone (hypersecretion) or too little (hyposecretion). The prefix "hyper-" means above normal and "hypo-" means below normal, so hyperthyroidismhyperthyroidismhy-per-THY-roy-diz-umA condition in which the thyroid gland makes too much thyroid hormone.hyper- above, overthyr/o thyroid gland-ism conditionFull entry Close is an overactive thyroid and hypothyroidismhypothyroidismhy-poh-THY-roy-diz-umA condition in which the thyroid gland makes too little thyroid hormone.hypo- below, underthyr/o thyroid gland-ism conditionFull entry Close an underactive one. Too little is often treated by replacing the hormone; too much, with drugs that lower it or by removing the gland.

11Hormones and surgery

The stress of surgery

The body treats an operation as an injury. Nerve signals from the cut tissue reach the hypothalamushypothalamushy-poh-THAL-uh-musA small area at the base of the brain that controls body temperature, hunger, thirst, sleep and many hormones.hypo- belowthalamus inner chamber (a part of the brain)Full entry Close, which turns on the pituitary and the adrenal glandsadrenal glanduh-DREE-nul GLANDOne of two small glands that sit on top of the kidneys and make hormones such as cortisol, aldosterone and epinephrine.ad- toward, nearren/o kidney-al relating toFull entry Close, and the blood fills with cortisolcortisolKOR-tih-solA steroid hormone made by the adrenal glands that helps control blood sugar, blood pressure, stress and inflammation.Full entry Close, catecholaminescatecholaminekat-uh-KOH-luh-meenAny of a group of hormones and neurotransmitters, mainly epinephrine, norepinephrine and dopamine, that act in the body's stress response.Full entry Close, 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 growth hormonegrowth hormoneGROHTH HOR-mohnA hormone from the pituitary gland that drives growth in children and helps control body build and metabolism in adults.Full entry Close.

The result is the stress response.

• The heart rate and blood pressure rise.
• The liver pours out glucose while the cells respond less to 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 the blood sugar rises, even in patients without diabetes. The bigger the operation, the greater this insulin resistanceinsulin resistanceIN-suh-lin rih-ZIS-tunsA state in which the body's cells respond poorly to insulin, so more insulin is needed to move glucose into them.Full entry Close.
• Muscle protein is broken down for fuel, which can slow healing.
• Cortisol held high for a long time weakens the 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 fight infection.

Bleeding adds to it. In a heavy bleed, 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 releases vasopressinvasopressinvay-zoh-PRES-inA man-made form of antidiuretic hormone, given by IV mainly to raise blood pressure in shock.Full entry Close, glucagon, cortisol, epinephrineepinephrineep-ih-NEF-rinA hormone and drug, also called adrenaline, that raises heart rate and blood pressure and opens the airways.Full entry Close and norepinephrinenorepinephrinenor-ep-ih-NEF-rinA hormone and nerve messenger that narrows blood vessels and raises blood pressure, also given as an IV drug.Full entry Close. At first they help, by raising the cardiac outputcardiac outputKAR-dee-ak OWT-putThe amount of blood the heart pumps out in one minute.Full entry Close and narrowing the vessels so blood goes to the heart and brain. Chapter 11 teaches shockshockshokA life-threatening state in which blood flow is too low to bring enough oxygen to the body's tissues.Full entry Close.

Enhanced recovery after surgery (ERAS) pathways are built to lower the body's stress response to an operation. The CDC's guideline for preventing surgical site infection calls for controlling the blood sugar around surgery, with a target below 200 mg/dL, in patients with and without diabetes.

The patient with a gland disorder

Diabetes, thyroid disorders and adrenaladrenaluh-DREE-nulHaving to do with the adrenal glands, the two small glands that sit on top of the kidneys.ad- nearren/o kidney-al relating toFull entry Close insufficiencyinsufficiencyin-suh-FISH-un-seeA state in which an organ or part does not work well enough to meet the body's needs.in- notsufficient enoughFull entry Close (Addison diseaseAddison diseaseAD-ih-sun dih-ZEEZA condition in which the adrenal glands do not make enough cortisol and often not enough aldosterone.Full entry Close) are among 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 disorders that change how a patient goes through surgery.

Diabetes. 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 slows wound healingwound healingwoond HEE-lingThe body's process of repairing damaged skin and tissue.Full entry Close and raises the risk of a surgical site infection, so the patient's blood sugar is checked before, during and after surgery. Surgery upsets both the patient's meals and their insulin doses. A patient with diabetes should be the first case of the day, so they can get back to their usual meals as soon as possible. In a long case, the team pads pressure points with extra care, because poor circulation and lost feeling put the skin at risk.

An overactive thyroidhyperthyroidismhy-per-THY-roy-diz-umA condition in which the thyroid gland makes too much thyroid hormone.hyper- above, overthyr/o thyroid gland-ism conditionFull entry Close. Before planned surgery, drugs bring the thyroid hormonethyroid hormoneTHY-royd HOR-mohnA hormone made by the thyroid gland that controls how fast the body uses energy.Full entry Close levels back to normal (a euthyroid state). These patients have a higher risk of heart rhythm problems, such as atrial fibrillationatrial fibrillationAY-tree-ul fib-rih-LAY-shunAn irregular heart rhythm in which the upper chambers of the heart quiver instead of beating in an organized way.atri/o atrium (upper heart chamber)fibrill/o small fibers, quivering-ation processFull entry Close.

The danger is thyroid storm (thyrotoxic crisiscrisisKRY-sisA time when a person's usual ways of coping fail and they cannot manage a stressful event.Full entry Close): a sudden release of a large amount of thyroid hormone, which can be set off by a stress such as surgery. The patient develops a high fever, a very fast heart rate, high blood pressure, vomiting or diarrhea, agitation and confusion, and may have seizuresseizureSEE-zherA sudden burst of abnormal electrical activity in the brain that changes movement, feeling, behavior or awareness.Full entry Close or slip into a comacomaKOH-muhA deep state of unconsciousness in which a person cannot be woken and does not respond with purpose.Full entry Close. A calm, quiet room helps prevent it. If it happens, the team gives oxygen, fluids and drugs and cools the patient.

An underactive thyroidhypothyroidismhy-poh-THY-roy-diz-umA condition in which the thyroid gland makes too little thyroid hormone.hypo- below, underthyr/o thyroid gland-ism conditionFull entry Close. These patients are at risk of breathing failure around surgery. A rare and dangerous form, myxedema coma, mostly affects people older than 75.

A large goitergoiterGOY-terAn enlarged thyroid gland, seen or felt as a swelling at the front of the neck.Full entry Close or thyroid nodulenoduleNOD-yoolA small, firm, rounded lump of tissue that can be felt or seen, in or under the skin or in an organ.Full entry Close can press on the tracheatracheaTRAY-kee-uhThe windpipe: the tube that carries air from the throat to the lungs.Full entry Close or push it aside and make the breathing tube hard to place, so the difficult airway cart is brought into the room before inductioninductionin-DUK-shunThe starting of a process on purpose, such as bringing on labor or putting a client under anesthesia.Full entry Close.

Long-term steroidssteroidSTAIR-oydA fat-based chemical built from cholesterol; the group includes hormones such as cortisol and estrogen, and many drugs.ster/o solid-oid likeFull entry Close. A patient who has taken steroid drugs for more than about 3 weeks may have a shut-down adrenal cortexadrenal cortexuh-DREE-nul KOR-teksThe outer layer of each adrenal gland, which makes the steroid hormones cortisol and aldosterone.ad- nearren kidney-al relating tocortex outer layer (Latin, bark)Full entry Close that cannot make the extra cortisol the stress of surgery calls for. The result can be an adrenal crisis, with a dangerous fall in blood pressure. So the patient's steroid use is found out before surgery. The usual dose is kept up, and whether an extra stress dose of steroid is added is decided for each patient, from how much steroid they take and for how long, and from the type and length of the operation. A stress dose for every patient on steroids is no longer the routine.

Thyroid and parathyroid surgery

Surgeons remove all or part of the thyroid for a known or suspected cancer, for a goiter that presses on the airway or the esophagusesophagusih-SOF-uh-gusThe muscular tube that carries food and liquid from the throat to the stomach.esophag/o esophagusFull entry Close, and for some patients with an overactiveoveractivityoh-ver-ak-TIV-ih-teeMore activity than normal, in a person, an organ or a body system.Full entry Close gland, such as in Graves diseaseGraves diseaseGRAYVZ dih-ZEEZAn autoimmune disease in which antibodies make the thyroid gland overactive.Full entry Close. Parathyroidparathyroid glandpair-uh-THY-royd glandOne of four small glands behind the thyroid that control the amount of calcium in the blood.para- besidethyr/o thyroid gland-oid likeFull entry Close tissue is removed for hyperparathyroidismhyperparathyroidismhy-per-pair-uh-THY-roy-diz-umOveractivity of the parathyroid glands, which make too much parathyroid hormone.hyper- excessivepara- besidethyroid -ism conditionFull entry Close. When the disease starts in the glands themselves, its cause is most often a single adenomaadenomaad-uh-NOH-muhA tumor of gland tissue that is not cancer.aden/o gland-oma tumorFull entry Close.

Chapter 32 teaches the operations: the thyroidectomythyroidectomythy-roy-DEK-tuh-meeSurgery to remove all or part of the thyroid gland in the neck.thyr/o thyroid-ectomy surgical removalFull entry Close, the hemithyroidectomy, which removes one lobe with the isthmus, and the parathyroidectomy. The anatomy in this chapter explains their three chief complications: injury to the recurrent laryngeallarynxLAIR-inksThe voice box: the part of the airway in the neck, above the windpipe, that holds the vocal cords.laryng/o larynxFull entry Close nerve, a low blood calcium and a hematomahematomahee-muh-TOH-muhA collection of blood, often clotted, that has leaked out of the blood vessels into the tissue.hem/o blood (here as hemat-)-oma swelling or massFull entry Close in the neck.

• The recurrent laryngeal nerve. The surgeon finds the nerve and protects it, often with a nerve monitor built into the breathing tube. Because the nerve controls the voice, the patient's voice is checked before surgery as a baseline. A nerve injured on one side leaves the voice hoarse; injury to both sides can block the airway and call for an emergency tracheotomytracheotomytray-kee-OT-uh-meeThe surgical cut made into the windpipe through the front of the neck.trache/o windpipe-tomy cutting, incisionFull entry Close.
• Low calcium. If the parathyroid glands are removed or lose their blood supply, PTHparathyroid hormonepar-uh-THY-royd HOR-mohnA hormone from the parathyroid glands in the neck that raises the calcium level in the blood.para- besidethyr/o thyroid-oid resemblingFull entry Close falls and so does the blood calcium. After a total thyroidectomytotal thyroidectomyTOE-tul thy-roy-DEK-tuh-meeSurgery to remove the whole thyroid gland.thyroid thyroid gland-ectomy surgical removalFull entry Close or a parathyroidectomy, the calcium reaches its lowest point 48 to 72 hours after surgery. Early signs are numbness and tingling of the fingers, toes and lips. Tapping over 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 makes the face muscles twitch (a positive Chvostek signChvostek signVOS-tek sineA twitch of the muscles of the face when the facial nerve, just in front of the ear, is tapped.Full entry Close), and a blood pressure cuff pumped up on the arm makes the hand and wrist spasmspasmSPAZ-umA sudden, involuntary tightening of a muscle or of the muscle in a hollow organ or tube.Full entry Close (a positive Trousseau signTrousseau signtroo-SOH SINEA spasm of the hand and wrist that appears when a blood pressure cuff on the upper arm is kept inflated for a few minutes.Full entry Close). TetanytetanyTET-uh-neeInvoluntary muscle cramps and spasms that come from nerves firing too easily.Full entry Close can follow, with spasms of the hands and feet, seizures and stridorstridorSTRY-derA high-pitched, harsh sound made while breathing, usually heard when breathing in.Full entry Close, the harsh, high-pitched sound of a narrowed airway, which can be fatal.
• A neck hematoma. Bleeding under the closed wound can press on the trachea. That is why the back table stays sterile until the patient has been extubated and has left the room, and a tracheotomy tray stays close by.

If a parathyroid gland is found on the removed thyroid, it is saved and reimplanted (chapter 32). A patient whose whole thyroid is removed takes thyroid hormone, levothyroxinelevothyroxinelee-voh-thy-ROK-seenA man-made form of the thyroid hormone thyroxine (T4), taken to replace hormone the thyroid does not make.Full entry Close, for life.

Thyroidectomy32 instruments · 1 photoPro Hemithyroidectomy48 instruments Parathyroidectomy27 instruments · 1 photo

Adrenal surgery

An adrenalectomy removes one or both adrenal glands, for a tumor that makes too much hormone, such as a pheochromocytoma, a tumor making cortisol (Cushing syndromeCushing syndromeKUSH-ing SIN-drohmA condition caused by too much cortisol in the body over a long time.Full entry Close) or one making aldosteronealdosteroneal-DOS-tuh-rohnA hormone from the adrenal glands that makes the kidneys keep sodium and water and get rid of potassium.aldo- from aldehyde (a chemical group)-sterone steroid hormoneFull entry Close, or for cancer. It is usually done laparoscopically, which means less harm and a shorter hospital stay than an open operation; for one gland, the patient lies on the side or on the back. Chapter 34 teaches it.

A pheochromocytoma makes the case dangerous.

• Before surgery, the patient takes drugs that block the effects of the catecholamines, the alpha blockerblockerBLOK-erA drug that stops a receptor or channel in the body from being activated, so the usual effect does not happen.Full entry Close first and then the beta blockerbeta blockerBAY-tuh BLOK-erA drug that blocks the effects of adrenaline on beta receptors, slowing the heart rate and lowering blood pressure.Full entry Close.
• During surgery, 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 watches the blood pressure continuously through an arterial linearterial linear-TEER-ee-ul lineA thin catheter placed in an artery, often in the wrist, to measure blood pressure all the time and draw blood.Full entry Close. Handling the tumor can release a flood of catecholamines and send the blood pressure soaring, so the surgeon ties off the adrenal vein early.
• Once the tumor is out, the catecholamines fall away. The blood pressure can drop sharply, and so can the blood sugar, so the patient goes to intensive care to be watched.

After a tumor that made too much cortisol is removed, the other adrenal gland may have been shut down and cannot keep up, so steroids are given during and after surgery and tapered slowly. A patient who loses both adrenal glands needs glucocorticoidcorticosteroidkor-tih-koh-STER-oydA drug that acts like the hormones of the adrenal glands, used mainly to calm inflammation and the immune system.cortic/o cortex (the outer layer of the adrenal gland)-oid likeFull entry Close and mineralocorticoidmineralocorticoidmin-er-uh-loh-KOR-tih-koydA steroid hormone, or a drug that acts like one, that makes the kidneys keep sodium and water and remove potassium.mineral saltscortic/o cortex-oid likeFull entry Close replacement for life.

Laparoscopic Adrenalectomy28 instruments · 2 photos

Pituitary surgery

Most pituitary tumors are removed through the nose and the sphenoid sinussinusSY-nusA hollow space in the body, most often one of the air-filled spaces in the skull bones around the nose.Full entry Close, a transsphenoidal hypophysectomy, with an endoscopeendoscopeEN-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 or a microscope. A large or complex tumor may need a craniotomycraniotomykray-nee-OT-uh-meeSurgery in which a piece of the skull is removed to reach the brain, and usually put back at the end.crani/o skull-tomy cutting intoFull entry Close instead. The sella may be packed with a small graftgraftGRAFTTissue or a man-made material moved into place in surgery to replace or repair a damaged part.Full entry Close of fat or muscle so cerebrospinal fluidcerebrospinal fluidser-uh-broh-SPY-nul FLOO-idThe clear, watery fluid that bathes and cushions the brain and spinal cord.cerebr/o brainspin spine-al relating toFull entry Close cannot leak. Chapter 42 teaches it.

The gland's work explains what the team watches for afterward.

• Diabetes insipidusdiabetes insipidusdy-uh-BEE-teez in-SIP-ih-dusA disorder of antidiuretic hormone: the body makes too little of it, or the kidneys do not respond to it.Full entry Close: the loss of ADHantidiuretic hormonean-tee-dy-yoo-RET-ik HOR-mohnA hormone from the pituitary gland that tells the kidneys to hold on to water, making the urine more concentrated.anti- againstdiuretic making urineFull entry Close, or swelling around the gland, can cause a flood of dilute urine.
• Vision: a hematoma can press on the optic nervesoptic nerveOP-tik nervThe nerve that carries visual signals from the back of the eye to the brain; the second cranial nerve.Full entry Close or the optic chiasm.
• A leak of cerebrospinal fluid.
• Lost hormones: when the whole gland is removed, the patient needs thyroid hormone, sex hormones and glucocorticoids for life.

The pancreas at surgery

Removing part 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, as in a Whipple procedure for pancreatic cancer (chapter 32), can leave the patient making too little insulin, so the blood sugar must be watched. For some patients with type 1 diabetestype 1 diabetesTYPE WUN dy-uh-BEE-teezA form of diabetes in which the pancreas makes little or no insulin because the immune system has destroyed the cells that make it.Full entry Close, a pancreas transplant or a transplant of islets alone can let the body make insulin again; during a pancreas transplant, the anesthesia provider checks the blood sugar throughout.

Pancreaticoduodenectomy (Whipple)40 instruments · 2 photos

Check yourself5 quick questions

Free for everyone. Pick an answer for each, then check them all at once.

In the ORWhere you'll use this