OxytocinOxytocin

Oxytocin is a strong stimulant of uterine Oxytocin is a strong stimulant of uterine contractioncontraction

Regulated by a positive feedback mechanism Regulated by a positive feedback mechanism to oxytocin in the blood to oxytocin in the blood

This leads to increased intensity of uterine This leads to increased intensity of uterine contractions, ending in birthcontractions, ending in birth

Oxytocin triggers milk ejection (“letdown” Oxytocin triggers milk ejection (“letdown” reflex) in women producing milkreflex) in women producing milk

OxytocinOxytocin

Synthetic and natural oxytocic drugs are used Synthetic and natural oxytocic drugs are used to induce or hasten laborto induce or hasten labor

Plays a role in sexual arousal and satisfaction Plays a role in sexual arousal and satisfaction in males and nonlactating femalesin males and nonlactating females

Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH) ADH helps to avoid dehydration or water ADH helps to avoid dehydration or water

overloadoverload Prevents urine formationPrevents urine formation

Osmoreceptors monitor the solute Osmoreceptors monitor the solute concentration of the bloodconcentration of the blood

With high solutes, ADH preserves waterWith high solutes, ADH preserves water With low solutes, ADH is not released, thus With low solutes, ADH is not released, thus

causing water loss causing water loss Alcohol inhibits ADH release and causes Alcohol inhibits ADH release and causes

copious urine outputcopious urine output

Thyroid GlandThyroid Gland The largest endocrine gland, located in the The largest endocrine gland, located in the

anterior neck, consists of two lateral lobes anterior neck, consists of two lateral lobes connected by a median tissue mass called the connected by a median tissue mass called the isthmusisthmus

Composed of follicles that produce the Composed of follicles that produce the glycoprotein thyroglobulinglycoprotein thyroglobulin

Colloid (thyroglobulin + iodine) fills the lumen Colloid (thyroglobulin + iodine) fills the lumen of the follicles and is the precursor of thyroid of the follicles and is the precursor of thyroid hormonehormone

Other endocrine cells, the parafollicular cells, Other endocrine cells, the parafollicular cells, produce the hormone calcitoninproduce the hormone calcitonin

Thyroid GlandThyroid Gland

Figure 16.8

Thyroid hormone – major metabolic hormoneThyroid hormone – major metabolic hormone Thyroglobulin- synthesized by the follicle cells Thyroglobulin- synthesized by the follicle cells

and secreted into the colloid of the folliclesand secreted into the colloid of the follicles Consists of two related iodine-containing Consists of two related iodine-containing

compoundscompounds TT44 – thyroxine; has two tyrosine molecules plus four – thyroxine; has two tyrosine molecules plus four

bound iodine atomsbound iodine atoms TT33 – triiodothyronine; has two tyrosines with three – triiodothyronine; has two tyrosines with three

bound iodine atomsbound iodine atoms

Thyroid HormoneThyroid Hormone

Effects of Thyroid HormoneEffects of Thyroid Hormone TH:TH:

Elevates rates of oxygen and energy consumptionElevates rates of oxygen and energy consumption Increases heart rate and force, resulting in a rise in Increases heart rate and force, resulting in a rise in

blood pressureblood pressure Increases sensitivity to sympathetic stimulationIncreases sensitivity to sympathetic stimulation Maintains normal sensitivity of respiratory centers Maintains normal sensitivity of respiratory centers

to changes in O2 and CO2to changes in O2 and CO2 Stimulates red blood cell formationStimulates red blood cell formation Stimulates activity in other endocrine tissuesStimulates activity in other endocrine tissues Accelerates turnover of minerals in bonesAccelerates turnover of minerals in bones Directs maturation and development of developing Directs maturation and development of developing

childrenchildren

Synthesis of Thyroid HormoneSynthesis of Thyroid Hormone

Thyroglobulin is synthesized and dischargedThyroglobulin is synthesized and discharged Iodides (IIodides (I––) are oxidized to iodine (I) are oxidized to iodine (I22), and ), and

releasedreleased Iodine attaches to tyrosine, mediated by Iodine attaches to tyrosine, mediated by

peroxidase enzymes, forming Tperoxidase enzymes, forming T11

(monoiodotyrosine, or MIT), and T(monoiodotyrosine, or MIT), and T22

(diiodotyrosine, or DIT)(diiodotyrosine, or DIT)

Synthesis of Thyroid HormoneSynthesis of Thyroid Hormone

Iodinated tyrosines link together to form TIodinated tyrosines link together to form T33

and Tand T44

Colloid is then brought into the cell and Colloid is then brought into the cell and combined with a lysosome, where Tcombined with a lysosome, where T33 and T and T44

are cleaved and diffuse into the bloodstreamare cleaved and diffuse into the bloodstream

TT44 and T and T33 bind to thyroxine-binding globulins (TBGs) bind to thyroxine-binding globulins (TBGs)

produced by the liverproduced by the liver Both bind to target receptors, but TBoth bind to target receptors, but T33 is ten times more is ten times more

active than Tactive than T44

Peripheral tissues convert TPeripheral tissues convert T44 to T to T33

Mechanisms of activity are similar to steroidsMechanisms of activity are similar to steroids Regulation is by negative feedback Regulation is by negative feedback Hypothalamic thyrotropin-releasing hormone (TRH) Hypothalamic thyrotropin-releasing hormone (TRH)

can overcome the negative feedback can overcome the negative feedback

Transport and Regulation of THTransport and Regulation of TH

A peptide hormone produced by the A peptide hormone produced by the parafollicular, or C, cellsparafollicular, or C, cells

Lowers blood calcium levels in childrenLowers blood calcium levels in children Antagonist to parathyroid hormone (PTH)Antagonist to parathyroid hormone (PTH)

CalcitoninCalcitonin

Calcitonin targets the skeleton, where it:Calcitonin targets the skeleton, where it: Inhibits osteoclast activity (and thus bone Inhibits osteoclast activity (and thus bone

resorption) and release of calcium from the bone resorption) and release of calcium from the bone matrixmatrix

Stimulates calcium uptake and incorporation into Stimulates calcium uptake and incorporation into the bone matrixthe bone matrix

Regulated by a humoral (calcium ion Regulated by a humoral (calcium ion concentration in the blood) negative feedback concentration in the blood) negative feedback mechanismmechanism

CalcitoninCalcitonin

Parathyroid GlandsParathyroid Glands

Tiny glands embedded in the posterior aspect Tiny glands embedded in the posterior aspect of the thyroidof the thyroid

Cells are arranged in cords containing oxyphil Cells are arranged in cords containing oxyphil and chief cellsand chief cells

Chief (principal) cells secrete PTHChief (principal) cells secrete PTH PTH (parathormone) regulates calcium PTH (parathormone) regulates calcium

balance in the bloodbalance in the blood

Parathyroid GlandsParathyroid Glands

Figure 16.11

PTH release increases CaPTH release increases Ca2+2+ in the blood as it: in the blood as it: Stimulates osteoclasts to digest bone matrix and Stimulates osteoclasts to digest bone matrix and

inhibits osteoblastsinhibits osteoblasts Enhances the reabsorption of CaEnhances the reabsorption of Ca2+2+ and the and the

secretion of phosphate by the kidneyssecretion of phosphate by the kidneys Increases absorption of CaIncreases absorption of Ca2+2+ by intestinal mucosal by intestinal mucosal

Rising CaRising Ca2+2+ in the blood inhibits PTH release in the blood inhibits PTH release

Effects of Parathyroid HormoneEffects of Parathyroid Hormone

Effects of Parathyroid HormoneEffects of Parathyroid Hormone

Figure 16.12

Adrenal glands – paired, pyramid-shaped Adrenal glands – paired, pyramid-shaped organs atop the kidneysorgans atop the kidneys

Structurally and functionally, they are two Structurally and functionally, they are two glands in oneglands in one Adrenal medulla – neural tissue that acts as part of Adrenal medulla – neural tissue that acts as part of

the SNSthe SNS Adrenal cortex – glandular tissue derived from Adrenal cortex – glandular tissue derived from

embryonic mesodermembryonic mesoderm

Adrenal (Suprarenal) GlandsAdrenal (Suprarenal) Glands

Adrenal CortexAdrenal Cortex Synthesizes and releases steroid hormones Synthesizes and releases steroid hormones

called corticosteroidscalled corticosteroids Different corticosteroids are produced in each Different corticosteroids are produced in each

of the three layersof the three layers Zona glomerulosa – mineralocorticoids Zona glomerulosa – mineralocorticoids

(chiefly aldosterone)(chiefly aldosterone) Zona fasciculata – glucocorticoids Zona fasciculata – glucocorticoids

(chiefly cortisol)(chiefly cortisol) Zona reticularis – gonadocorticoids Zona reticularis – gonadocorticoids

(chiefly androgens)(chiefly androgens)

Adrenal CortexAdrenal Cortex

Figure 16.13a, b

Regulate electrolytes in extracellular fluidsRegulate electrolytes in extracellular fluids Aldosterone – most important Aldosterone – most important

mineralocorticoid mineralocorticoid Maintains NaMaintains Na++ balance by reducing excretion of balance by reducing excretion of

sodium from the bodysodium from the body Stimulates reabsorption of NaStimulates reabsorption of Na++ by the kidneys by the kidneys

MineralocorticoidsMineralocorticoids

Aldosterone secretion is stimulated by:Aldosterone secretion is stimulated by: Rising blood levels of KRising blood levels of K++

Low blood NaLow blood Na++

Decreasing blood volume or pressureDecreasing blood volume or pressure

MineralocorticoidsMineralocorticoids

The Four Mechanisms of The Four Mechanisms of Aldosterone SecretionAldosterone Secretion

Renin-angiotensin mechanism – kidneys Renin-angiotensin mechanism – kidneys release renin, which is converted into release renin, which is converted into angiotensin II that in turn stimulates angiotensin II that in turn stimulates aldosterone release aldosterone release

Plasma concentration of sodium and potassium Plasma concentration of sodium and potassium – directly influences the zona glomerulosa – directly influences the zona glomerulosa cellscells

ACTH – causes small increases of aldosterone ACTH – causes small increases of aldosterone during stressduring stress

Atrial natriuretic peptide (ANP) – inhibits Atrial natriuretic peptide (ANP) – inhibits activity of the zona glomerulosaactivity of the zona glomerulosa

Major Major Mechanisms Mechanisms

of of Aldosterone Aldosterone

SecretionSecretion

Figure 16.14

Glucocorticoids (Cortisol)Glucocorticoids (Cortisol)

Help the body resist stress by:Help the body resist stress by: Keeping blood sugar levels relatively constantKeeping blood sugar levels relatively constant Maintaining blood volume and preventing water Maintaining blood volume and preventing water

shift into tissueshift into tissue Cortisol provokes:Cortisol provokes:

Gluconeogenesis (formation of glucose from Gluconeogenesis (formation of glucose from noncarbohydrates)noncarbohydrates)

Rises in blood glucose, fatty acids, and amino Rises in blood glucose, fatty acids, and amino acidsacids

Excessive Levels of Excessive Levels of GlucocorticoidsGlucocorticoids

Excessive levels of glucocorticoids:Excessive levels of glucocorticoids: Depress cartilage and bone formationDepress cartilage and bone formation Inhibit inflammationInhibit inflammation Depress the immune systemDepress the immune system Promote changes in cardiovascular, neural, and Promote changes in cardiovascular, neural, and

gastrointestinal functiongastrointestinal function

Gonadocorticoids (Sex Gonadocorticoids (Sex Hormones)Hormones)

Most gonadocorticoids secreted are androgens Most gonadocorticoids secreted are androgens (male sex hormones), and the most important (male sex hormones), and the most important one is testosteroneone is testosterone

Androgens contribute to:Androgens contribute to: The onset of pubertyThe onset of puberty The appearance of secondary sex characteristicsThe appearance of secondary sex characteristics Sex drive in females Sex drive in females

Androgens can be converted into estrogens Androgens can be converted into estrogens after menopauseafter menopause

Adrenal MedullaAdrenal Medulla

Made up of chromaffin cells that secrete Made up of chromaffin cells that secrete epinephrine and norepinephrineepinephrine and norepinephrine

Secretion of these hormones causes:Secretion of these hormones causes: Blood glucose levels to riseBlood glucose levels to rise Blood vessels to constrictBlood vessels to constrict The heart to beat fasterThe heart to beat faster Blood to be diverted to the brain, heart, and Blood to be diverted to the brain, heart, and

skeletal muscleskeletal muscle

Adrenal MedullaAdrenal Medulla

Epinephrine is the more potent stimulator of Epinephrine is the more potent stimulator of the heart and metabolic activitiesthe heart and metabolic activities

Norepinephrine is more influential on Norepinephrine is more influential on peripheral vasoconstriction and blood pressureperipheral vasoconstriction and blood pressure

A triangular gland, which has both exocrine A triangular gland, which has both exocrine and endocrine cells, located behind the and endocrine cells, located behind the stomach stomach

Acinar cells produce an enzyme-rich juice Acinar cells produce an enzyme-rich juice used for digestion (exocrine product)used for digestion (exocrine product)

Pancreatic islets (islets of Langerhans) produce Pancreatic islets (islets of Langerhans) produce hormones (endocrine products)hormones (endocrine products)

The islets contain two major cell types:The islets contain two major cell types: Alpha (Alpha () cells that produce glucagon) cells that produce glucagon Beta (Beta () cells that produce insulin) cells that produce insulin

PancreasPancreas

A polypeptide hormone that is a potent A polypeptide hormone that is a potent hyperglycemic agenthyperglycemic agent

Its major target is the liver, where it promotes:Its major target is the liver, where it promotes: Glycogenolysis – the breakdown of glycogen to Glycogenolysis – the breakdown of glycogen to

glucoseglucose Gluconeogenesis – synthesis of glucose from lactic Gluconeogenesis – synthesis of glucose from lactic

acid and noncarbohydratesacid and noncarbohydrates Release of glucose to the blood from liver cellsRelease of glucose to the blood from liver cells

GlucagonGlucagon

A protein consisting of two amino acid chains A protein consisting of two amino acid chains linked by disulfide bondslinked by disulfide bonds

Synthesized as part of proinsulin and then Synthesized as part of proinsulin and then excised by enzymes, releasing functional excised by enzymes, releasing functional insulininsulin

Insulin:Insulin: Lowers blood glucose levelsLowers blood glucose levels Enhances transport of glucose into body cellsEnhances transport of glucose into body cells Counters metabolic activity that would enhance Counters metabolic activity that would enhance

blood glucose levelsblood glucose levels

InsulinInsulin

The insulin receptor is a tyrosine kinase The insulin receptor is a tyrosine kinase enzymeenzyme

After glucose enters a cell, insulin binding After glucose enters a cell, insulin binding triggers enzymatic activity that:triggers enzymatic activity that: Catalyzes the oxidation of glucose for ATP Catalyzes the oxidation of glucose for ATP

productionproduction Polymerizes glucose to form glycogenPolymerizes glucose to form glycogen Converts glucose to fat (particularly in adipose Converts glucose to fat (particularly in adipose

tissue)tissue)

Effects of Insulin BindingEffects of Insulin Binding

Regulation of Blood Glucose Regulation of Blood Glucose LevelsLevels

Figure 16.18

The The hyperglycemic hyperglycemic effects of effects of glucagon and glucagon and the the hypoglycemic hypoglycemic effects of effects of insulininsulin

Results from hyposecretion or hypoactivity of Results from hyposecretion or hypoactivity of insulininsulin

The three cardinal signs of DM are:The three cardinal signs of DM are: Polyuria – huge urine outputPolyuria – huge urine output Polydipsia – excessive thirstPolydipsia – excessive thirst Polyphagia – excessive hunger and food Polyphagia – excessive hunger and food

consumptionconsumption Hyperinsulinism – excessive insulin secretion, Hyperinsulinism – excessive insulin secretion,

resulting in hypoglycemiaresulting in hypoglycemia

Diabetes Mellitus (DM)Diabetes Mellitus (DM)

T1DMT1DM

Type 1 Diabetes Mellitus: Insulin DependentType 1 Diabetes Mellitus: Insulin Dependent Is characterized by inadequate insulin production Is characterized by inadequate insulin production

by the beta cellsby the beta cells Patients require multiple injections or infusions of Patients require multiple injections or infusions of

insulin dailyinsulin daily Accounts for 5-10% of cases; often develops in Accounts for 5-10% of cases; often develops in

childhoodchildhood

T2DMT2DM

Type 2 Diabetes Mellitus: Non-Insulin Type 2 Diabetes Mellitus: Non-Insulin DependentDependent The most common form of diabetesThe most common form of diabetes Most patients produce normal amounts of insulin, Most patients produce normal amounts of insulin,

but the tissues do not respond; sometimes called but the tissues do not respond; sometimes called insulin resistanceinsulin resistance

Is associated with obesityIs associated with obesity Weight loss through diet and exercise is an Weight loss through diet and exercise is an

effective treatmenteffective treatment

Diabetes MellitusDiabetes Mellitus

Complications of untreated or poorly managed Complications of untreated or poorly managed diabetes:diabetes: Kidney degenerationKidney degeneration Retinal damageRetinal damage Early heart attackEarly heart attack Peripheral nerve problemsPeripheral nerve problems Peripheral nerve damagePeripheral nerve damage

Diabetes Mellitus (DM)Diabetes Mellitus (DM)

Figure 16.19

Paired ovaries in the abdominopelvic cavity Paired ovaries in the abdominopelvic cavity produce estrogens and progesteroneproduce estrogens and progesterone

They are responsible for: They are responsible for: Maturation of the reproductive organsMaturation of the reproductive organs Appearance of secondary sexual characteristicsAppearance of secondary sexual characteristics Breast development and cyclic changes in the Breast development and cyclic changes in the

uterine mucosauterine mucosa

Gonads: FemaleGonads: Female

Testes located in an extra-abdominal sac Testes located in an extra-abdominal sac (scrotum) produce testosterone(scrotum) produce testosterone

Testosterone:Testosterone: Initiates maturation of male reproductive organsInitiates maturation of male reproductive organs Causes appearance of secondary sexual Causes appearance of secondary sexual

characteristics and sex drivecharacteristics and sex drive Is necessary for sperm productionIs necessary for sperm production Maintains sex organs in their functional stateMaintains sex organs in their functional state

Gonads: MaleGonads: Male

Small gland hanging from the roof of the third Small gland hanging from the roof of the third ventricle of the brainventricle of the brain

Secretory product is melatoninSecretory product is melatonin Melatonin is involved with:Melatonin is involved with:

Day/night cyclesDay/night cycles Physiological processes that show rhythmic Physiological processes that show rhythmic

variations (body temperature, sleep, appetite)variations (body temperature, sleep, appetite)

Pineal GlandPineal Gland

ThymusThymus

Lobulated gland located deep to the sternum Lobulated gland located deep to the sternum Major hormonal products are thymopoietins Major hormonal products are thymopoietins

and thymosinsand thymosins These hormones are essential for the These hormones are essential for the

development of the T lymphocytes (T cells) of development of the T lymphocytes (T cells) of the immune systemthe immune system

Heart – produces atrial natriuretic peptide Heart – produces atrial natriuretic peptide (ANP), which reduces blood pressure, blood (ANP), which reduces blood pressure, blood volume, and blood sodium concentrationvolume, and blood sodium concentration

Gastrointestinal tract – enteroendocrine cells Gastrointestinal tract – enteroendocrine cells release local-acting digestive hormonesrelease local-acting digestive hormones

Placenta – releases hormones that influence Placenta – releases hormones that influence the course of pregnancythe course of pregnancy

Other Hormone-Producing Other Hormone-Producing StructuresStructures

Kidneys – secrete erythropoietin, which Kidneys – secrete erythropoietin, which signals the production of red blood cellssignals the production of red blood cells

Skin – produces cholecalciferol, the precursor Skin – produces cholecalciferol, the precursor of vitamin Dof vitamin D

Adipose tissue – releases leptin, which is Adipose tissue – releases leptin, which is involved in the sensation of satiety, and involved in the sensation of satiety, and stimulates increased energy expenditurestimulates increased energy expenditure

Other Hormone-Producing Other Hormone-Producing StructuresStructures

Developmental AspectsDevelopmental Aspects

Hormone-producing glands arise from all three Hormone-producing glands arise from all three germ layersgerm layers

Endocrine glands derived from mesoderm Endocrine glands derived from mesoderm produce steroid hormonesproduce steroid hormones

Endocrine organs operate smoothly throughout Endocrine organs operate smoothly throughout lifelife

Most endocrine glands show structural changes Most endocrine glands show structural changes with age, but hormone production may or may with age, but hormone production may or may not be affectednot be affected

Developmental AspectsDevelopmental Aspects

Exposure to pesticides, industrial chemicals, Exposure to pesticides, industrial chemicals, arsenic, dioxin, and soil and water pollutants arsenic, dioxin, and soil and water pollutants disrupts hormone functiondisrupts hormone function

Sex hormones, thyroid hormone, and Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of glucocorticoids are vulnerable to the effects of pollutantspollutants

Interference with glucocorticoids may help Interference with glucocorticoids may help explain high cancer rates in certain areasexplain high cancer rates in certain areas

Developmental AspectsDevelopmental Aspects

Ovaries undergo significant changes with age Ovaries undergo significant changes with age and become unresponsive to gonadotropinsand become unresponsive to gonadotropins

Female hormone production declines, the Female hormone production declines, the ability to bear children ends, and problems ability to bear children ends, and problems associated with estrogen deficiency (e.g., associated with estrogen deficiency (e.g., osteoporosis) begin to occurosteoporosis) begin to occur

Testosterone also diminishes with age, but Testosterone also diminishes with age, but effect is not usually seen until very old ageeffect is not usually seen until very old age

Developmental AspectsDevelopmental Aspects

GH levels decline with age and this accounts for GH levels decline with age and this accounts for muscle atrophy with agemuscle atrophy with age

Supplemental GH may spur muscle growth, Supplemental GH may spur muscle growth, reduce body fat, and help physiquereduce body fat, and help physique

TH declines with age, causing lower basal TH declines with age, causing lower basal metabolic ratesmetabolic rates

PTH levels remain fairly constant with age, and PTH levels remain fairly constant with age, and lack of estrogen in women makes them more lack of estrogen in women makes them more vulnerable to bone-demineralizing effects of vulnerable to bone-demineralizing effects of PTHPTH