Chapter 9 The Endocrine System

Biology 112Tri-County Technical College

Pendleton, SC

Hormones are flowing…Hormones are chemical substances secreted into extracellular fluid that regulate activity of other cellsHormones circulate to all organs but affect ONLY certain tissue cells/organs referred to as its TARGET CELLS/ORGANS

Target MUST have specific protein receptors on its plasma membrane or interior to which hormone can attach

Hormones, cont.Reproduction, growth & development, body’s defenses against stressors, electrolyte, water, & nutrient balance of blood, regulating metabolism & energy balanceTypically one or more of following occur as result of hormone action:

changes in PM permeability/electrical statesynthesis of proteins or regulatory moleculesactivation/inactivation of enzymesstimulation of mitosis/meiosis

Getting there

Steroid hormones able to diffuse across PMNonsteroid hormones require membrane receptors and utilize signal-transduction mechanism (second messengers)One of three mechanisms responsible for stimulating endocrine gland

HORMONALHUMORALNEURAL

Hormonal Action, Visual

Stimulation, Visual

Been there…done that

Hormonal secretion triggered by some internal/external stimulusRising hormone levels inhibit further hormone release even while promoting responses in target organsWOW!!! Negative feedback model again**End product controls the rate of the reaction or event

Endocrine Glands

Endocrine glands (ductless) release their secretions into blood or lymphEndocrine glands have a very rich blood supplyHypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads (testes/ovaries)

Location, Visual

Pituitary Gland

Pituitary gland about the size of a grape and hangs by a stalk from inferior surface of hypothalamus of the brain

surrounded by “turk’s saddle” of sphenoid bone

Has two functional lobesAnterior pituitary arises from glandular tissuePosterior pituitary arises from nervous tissue

Anterior hormones: growth hormone (GH), prolactin (PRL), follicle-stimulating (FSH), luteinizing (LH), Thyroid stimulating (TSH) and Adrenocorticotropic (ACTH)

Pituitary, cont.

Growth hormone and prolactin exert their major effects on nonendocrine targetsFSH, LH, TSH, and ACTH are all TROPHIC hormonesTrophic hormone is hormone that regulates the activity of another ENDOCRINE glandAll anterior pituitary hormones are proteins/peptides; act through 2nd messengers; are regulated by hormonal stimuli, and operate via negative feedback mechanism (in most cases)

Anterior Pituitary, Visual

Growth HormoneGH is protein-sparing & anabolic hormone causing amino acids to build into proteinsStimulates MOST target cells to grow in size and divideCauses fats to be broken down for energySpares body’s supply of glucose thereby helping to maintain blood sugar homeostasis

Pituitary AbnormalitiesHyposecretion of GH during childhood leads to pituitary dwarfism

body proportions fairly normal but person is living miniature (adult height ~ 4 feet)

Hypersecretion during childhood leads to gigantism

individual becomes extremely tall (8-9 feet)

If hypersecretion occurs after long bone growth ended = acromegaly

lower jaw and bony ridges under eyebrow enlarge as does hands and feet; thickening of soft tissue leads to coarse/malformed facial features

Most hypersecretion of endocrine glands caused by tumors of affected gland

Prolactin

Abbreviated as PRLProtein hormone whose only known target in humans is the breastAfter childbirth, it stimulates and maintains milk production by mother’s breastsIts function is males is NOT known

Same song, different verse…

Adrenocorticotrophic hormone = ACTHRegulates activity of the cortex portion of the adrenal glandThyroid-stimulating hormone = TSHTSH also known as thyrotropic hormone (TH)Influences growth and activity of the thyroid gland

Follicle Stimulating Hormone

Abbreviated as FSHRegulates activity of gonads (ovaries/testes)In females, FSH stimulates follicle development in ovaries

As follicles mature, they produce estrogen and eggs are readied for ovulation

In males, FSH stimulates sperm development by the testes

Luteinizing Hormone

Abbreviated LHIn females, LH triggers ovulation of egg from ovaryAlso causes ruptured follicle to become corpus luteum

LH then stimulates corpus luteum to produce progesterone and some estrogen

In men, LH is referred to as interstitial cell-stimulating hormone (ICSH)

stimulates testosterone production by interstitial cells

Pituitary and Sterility

Hyposecretion of FSH or LH leads to sterility in both males and femalesHypersecretion does NOT appear to cause any problem(s)Some drugs used to produce fertility stimulate release of FSH and LH

Multiple births fairly common after their administration

Anterior Pituitary/Hypothalamus

Pituitary used to be called “master gland”Release of pituitary’s hormones controlled by releasing and inhibiting hormones produced by hypothalamusHypothalamus releases these regulatory hormones into portal circulation which connects blood supply of hypothalamus with that of anterior pituitary

Posterior Pituitary

Posterior pituitary (neural tissue) STORES two hormones produced by hypothalamusOxytocin and antidiuretic hormone (ADH)Both are peptide hormonesProduced in hypothalamus

Transported along axons of hypothalamic neurosecretory cells to posterior pituitary for storage

Released into blood in response to nerve impulses from the hypothalamus

Posterior Pituitary, Visual

OH!!! for Oxytocin

Released in significant amounts only during childbirth and in nursing womenStimulates powerful contractions of the uterine muscles during labor, sexual relations, and when female is nursingAlso causes milk ejection (letdown reflex) in nursing womenNatural/synthetic oxytocic drugs (pitocin) used to induce/hasten labor, stop postpartum bleeding, and stimulate milk ejection reflex

Antidiuretic Hormone

Diuresis is urine productionAntidiuretic is chemical that inhibits and/or prevents urine productionADH causes kidneys to reabsorb more water from forming urine

Results in urine volume DECREASE and blood volume INCREASE

In large amounts, ADH increases blood pressure by causing constriction of arterioles (small arteries)ADH sometimes called VASOPRESSIN

Diabetes InsipidusHyposecretion of ADH leads to condition of excessive urine output called diabetes insipidusIndividuals with this problem are continually thirsty and drink large amounts of water

Thyroid GlandThyroid located at base of throat, inferior to Adam’s apple where easily palpatedLarge gland of two lobes joined by central mass called isthmusInternally, composed of hollow structures called follicles which store sticky colloidal material

Thyroid iodine-containing hormone derived from colloid

Produces 2 active hormones: T3 and T4Also produces calcitonin (thyrocalcitonin)

Thyroid, Visual

T3 and T4

Thyroid hormone (body’s major metabolic hormone) actually two iodine-containing hormonesTetraiodothyronine (thyroxine or T4)Triiodothyronine (T3)Thyroxine (T4) is major hormone secreted by thyroid folliclesMost T3 formed at target tissues by conversion of T4 to T3

The T’s, cont.Both are very similar—two tyrosine amino acids linked by either 3 or 4 iodine atomsControls rate at which glucose is converted to chemical energy and heatEVERY cell in body is target for thyroid hormoneAlso important for normal tissue growth and development especially in reproductive and nervous systems

Remember it well…

GOITER is enlargement of thyroid glandcaused by diet deficient in iodine

TSH keeps calling for thyroxine and thyroid gland continues to enlarge to make more…Only peptide part of molecule is made but without iodine it is NONFUNCTIONAL

fails to provide negative feedback to inhibit TSH release

Uncommon in US today because of iodized salt

Cretinism, Myxedema, and more

Cretinism results in dwarfism where adult body proportions remain childlikeCaused by hyposecretion of throxine in early childhoodUntreated leads to mental retardation, scanty hair, and very dry skinDiscovered early, HR can prevent signs and symptoms of deficiency

C, M, and more…cont.Myxedema caused by hyposecretion of thryoxine during adulthoodMental and physical sluggishness, puffiness of face, fatigue, poor muscle tone, low body temperature, obesity, and dry skinOral thyroxine is prescribedHYPERTHYROIDISM usually results from tumor of thyroid gland = extreme overproduction of thyroxine

C, M, and more…cont.

High metabolic rate, intolerance of heat, rapid heart beat, weight loss, nervous and agitated behavior, & inability to relaxGrave’s disease is one form of hyperthyroidismMay also cause thyroid to enlarge & eyes to bulge or protrude anteriorly in condition called exophthalmos

CalcitoninCalcitonin (thyrocalcitonin) is second major hormone of the thyroid glandDecreases blood calcium levels by causing calcium to be deposited in boneAntagonistic to parathyroid hormoneMade by “C cells” found in connective tissue between folliclesReleased into blood in response to >ing levels of blood calciumBelieved calcitonin production is meager or absent in elderlyCalcitonin is hypocalcemic hormone; < calcium in blood

Calcium Homeostasis, Visual

Parathyroid GlandsAre tiny masses of glandular tissue found on posterior surface of thyroid glandTypically 2 on each lobe (8 reported)Secrete parathyroid hormone (PTH) or parathormone**Most important regulator of calcium ion (Ca2+) in bloodCalcium levels drop below certain level, parathyroids release PTH which stimulates bone destruction cells (osteoclasts)

Parathyroids, cont.Osteoclasts break down bone matrix and increase blood levels of calcium**PTH is hypercalcemic hormone because it acts to > blood levels of calciumAnother example of negative feedbackPTH also stimulates kidneys and intestine to absorb MORE calcium from forming urine and foodstuff

Hypo versus Hypercalcemia

Hypocalcemia can be caused by hypoparathyroidism (poor diet, lack of vitamin D, and/or renal failure)Blood calcium levels drop too low, neurons become extremely irritable/overactiveNeurons deliver impulses to muscles at such rapid rate that muscles go into uncontrollable spasms (tetany)Convulsions, intestinal cramps, weak heartbeat, cardiac arrhythmias, osteoporosis (what a lesson)

Hypo/Hyper, cont.

Hypercalcemia results when calcium blood levels become too highCan be caused by hyperparathyroidism (cancer, vitamin D toxicity, calcium supplement overdose)Confusion, muscle pain, cardiac arrhythmias, kidney stones, fatigue, and calcification of soft tissueIs it catching…????

Adrenal GlandsAdrenal glands curve over top of kidneysEach is structurally/functionally two endocrine glandsLike pituitary, the adrenal has glandular (cortex) and neural (medulla) partsCentral medulla enclosed by adrenal cortex which contains three separate layers of cellsAdrenal cortex produces 3 major groups of STEROID hormones called corticosteroids

Adrenal Glands, cont.

Mineralocorticoids, Glucocorticoids, and sex hormonesMineralocorticoids, mainly aldosterone, produced by outermost adrenal cortex layerImportant in regulating mineral (salt) content of blood—especially [ ] of sodium and potassium ionsTheir target is kidney tubules that selectively reabsorb minerals or allow them to be flushed out in urine

Adrenal glands, cont.

Blood levels of aldosterone >, kidney tubule cells reclaim >ing amounts of sodium ions

Allows more potassium ions to be excreted in urine

When sodium reabsorbed, water followsResults in >ed blood volume and blood pressureMineralocorticoids help regulate both water and electrolyte balance in body fluids

Aldosterone Release, Visual

Adrenals and Glucocorticoids

Cortisone & Cortisol are 2 glucocorticoids produced by MIDDLE cortex layerPromote normal cell matabolism and help body resist long-term stressors primarily by >ing blood glucose levelsHigh levels of glucocorticoids in blood prompt body cells to convert fats and proteins to glucoseGlucocorticoids are hyperglycemic hormones

Glucocorticoids cont.

Help control inflammation by <ing edemaReduce pain by inhibiting pain-causing molecules called prostaglandinsOften prescribed for patients with rheumatoid arthritis to suppress inflammation**Glucocorticoids released from adrenal cortex in response to rising blood levels of ACTH

Adrenals and Sex hormones

Regardless of gender, adrenal cortex produces small amounts of both male and female sex hormones throughout lifeInnermost layer of adrenal cortex produces the bulk of the adrenal-produced sex hormonesAndrogens (male hormones) and some estrogen also produced

Addison’s Disease Addison’s disease caused by hyposecretion of adrenal cortex hormonesMajor sign is peculiar bronze skin toneAldosterone levels <; sodium & water lost from body = problems with electrolytes and water balance

causes muscles to become weak/shock possible

Low levels of glucocorticoids results in hypoglycemia = lessened ability to cope with stress (burnout) and suppression of immune system & increased susceptibility to infectionComplete lack of glucocorticoids=auf wiedersehen

Cushing’s Syndrome

Hypersecretion usually result of tumorIf tumor in middle cortex region, Cushing’s syndrome occursExcessive output of glucocorticoids results in “moon face” and appearance of “buffalo hump” of fat on upper backAlso high BP, hyperglycemia, and possible diabetes, weakening of bones, and severe depression of the immune system

Trying things on…Tumor in zona reticularis of cortex layer can cause excessive production of either androgens or estrogenIf androgen >s dramatically, produces symptoms of adrenogenital syndromeIn women=gradual development of male secondary sexual characteristics (body and facial hair, adipose tissue distribution, and muscular development)In estrogen >s, leads to gynecomastiaMale develops female secondary sexual characteristics

ANS and Adrenal MedullaAdrenal medulla (like posterior pituitary) develops from neural tissueWhen stimulated sympathetic NS neurons, its cells release 2 similar hormonesHormones called catecholaminesEpinephrine (adrenaline) & norepinephrine (noradrenaline)Sympathetic division called “fight or flight response” division of ANS> heart rate, blood pressure, blood glucose levels and dilation of small passageways of lungsBody better able to deal with short-term stressorCauses the “alarm” stage of the stress response

The PancreasPancreas located close to stomach in abdominal cavity and is MIXED gland (both endocrine & exocrine)Tiny masses of hormone-producing cells scattered among enzyme-producing cells

pancreatic islets (islets of Langerhans)

Islet cells produce insulin & glucagonBoth help regulate sugar (glucose) in blood but in opposite waysBeta cells produce insulin and Alpha cells produce glucagon

Pancreas, Visual

Release and Function of Insulin

High blood levels of glucose stimulate beta cells to produce insulinInsulin acts on ALL body cells and >s their ability to transport glucose across their PMsOnce inside, glucose used for energy or converted to glycogen or fat for storageInsulin sweeps glucose from blood=hypoglycemicBlood glucose levels fallinsulin release ends (classic negative feedback)

Insulin, cont.

Insulin is ONLY hormone that <s blood glucose levelsIt is absolutely necessary for use of glucose by body cellsGlucagon, glucocorticoids, and epinephrine increase blood glucose levels and are hyperglycemic

Blood Glucose Regulation

Diabetes Millitus

Condition in which blood glucose levels rise to 600 mg/100 ml compared to normal of 80-100 mg/100 ml because of lack of insulinKidney tubules cannot absorb glucose fast enough so spills into urineAs glucose flushes from body, water follows leading to dehydrationCells cannot use glucose so fats/proteins broken down for energy=decline in body weightLoss of body proteins=decreased ability to fight infections

Diabetes Millitus, cont.Use of large amts. of fat for energy results in ketones in blood=acidosis as blood becomes more acidicUnless corrected=death3 cardinal signs of diabetes milliuts

Polyuria (excessive urination)Polydipsia (excessive thrist)Polyphagia (hunger)

Mild cases (Type II/adult onset) treated with special diets/oral meds to stimulate isletsType I (juvenile/brittle) requires insulin injections

Glucagon Function/Release

Glucagon released by alpha cells of isletsRelease stimulated by LOW blood levels of glucoseAction is basically hyperglycemicPrimary target organ is liver where stimulates breakdown of glycogen to glucose and its release into the blood

Pineal Gland/Body

Small, cone-like gland found in roof of 3rd ventricle of brainSecretes melatonin; >s at night; <s during dayPlays role in body’s day and night cycleMay be related to mating behavior and coordination of hormones of fertilityInhibits sexual maturation occurrence during childhood

Thymus GlandLocated upper thorax, posterior to sternumLarge in infants, decreases in size during adulthood—by old age just fibrous connective tissue and fatProduces thymosin which programs T cellsIn childhood, is “incubator” for maturation of T lymphocytes (WBCs important in immunity)

Ovaries

Paired, almond shaped organs located in pelvic cavityProduce estrogens and progesteroneEstrogens (estrone & estradiol) produced by Graafian follicles of ovary & stimulate development of secondary sexual characteristicsWork with progesterone to prepare uterus to receive fertilized eggresults in cyclic changes = menstrual cycle

Ovaries, cont.

Estrogens help maintain pregnancy and prepare breasts for lactation

placenta source at this time and not ovaries

Progesterone (with estrogen) bring about menstrual cyclesDuring pregnancy, quiets muscles of uterus to prevent abortionAlso assists in preparing breasts for lactation

Ovaries, cont.

Progesterone also secreted by corpus luteum

CL produces estrogen/progesterone in >ing amounts

Ovaries stimulated to release estrogen and progesterone in cyclic way by anterior pituitary gonadotropic hormones of FSH and LH

TestesTestes produce male sex hormones (androgens) of which testosterone is most importantTestosterone produced by interstitial cells of testes and causes development of adult male sex characteristicsPromotes growth/maturation of reproductive systemPromotes development of SSC’s such as growth of beard, development of heavy bones/muscles, lowering of voiceStimulates male sex drive

Testes, cont.

Testosterone necessary for continuous sperm production during adulthoodProduction is stimulated by LH from anterior pituitary glandIt’s the testosterone that killing us, guys, but what a Catch 22!!!

PlacentaFormed temporarily in uterus of pregnant womanHas role in respiratory, excretory, and nutrition delivery system for fetusAlso produces hormones that help maintain pregnancyHuman chorionic gonadotropin (hCG) produced by conceptus and then by fetal part of placentaFound only in urine of pregnant women/is basic for EPTs (monoclonal antibody technology)

Placenta, cont.

hCG stimulates corpus luteum to continue producing estrogen/progesterone so uterine lining NOT sloughed offIn 3rd month, placenta assumes job of production and ovaries become inactiveHuman placental lactogen (hPL) works with estrogen/progesterone to prepare breasts for lactationRelaxin causes mother’s pelvic ligaments & pubic symphysis to relax and become more flexible

Eases birth passage

Old dogs/children/WM wine

Endocrine system seems to work smoothly until old ageLate middle age = menopause for womenEstrogen deficiency can lead to arteriosclerois, osteoporosis, decreased skin elasticity, changes in operation of sympathetic nervous system, fatigue, nervousness, and mood changesFor most part, men produce testosterone throughout life

Watermelon wine, cont.Efficiency of endocrine system gradually declines in old ageTarget organs become less productiveGH declines = muscle atrophyMost older people = hypothyroidPineal gland calcifies and immune system becomes compromisedDecline in insulin production occurs and adult-onset diabetes common in elderly