Chapter 17: Endocrine System

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Hormone

chemical messenger secreted into bloodstream, stimulates response in another tissue or organ

Target Cells

have receptors for specific hormone

Endocrine Glands

produce hormones

Endocrine System

includes hormone producing cells in organs such as brain, heart and small intestine

Endocrine Glands

no ducts release hormones into tissue fluids, have dense capillary networks to distribute hormones

Intracellular Effects

alter target cell metabolism

Exocrine Glands

ducts carry secretion to body surface or other organ cavity, extracellular effects (e.g. digestive enzymes-food)

Electrical Impulses and Neurotransmitter, adapts

quickly to continual stimulation

Hormones in Blood adapt

slowly (days to weeks)

Speed and Persistence of Response of nervous system

reacts quickly (1-10 msec), stops quickly

Speed and Persistence of Response of endocrine system

reacts slowly (seconds to days), may continue long after stimulus stops

local

specific effects on target organs

general

widespread effects on many organs

Neuroendocrine Cells

neurons that secrete hormones into ECF

Several Chemicals Function as both as

neurotransmitters and hormones (norepinephrine)

Endocrine and Nervous system have

overlapping effects on same target cells

Systems regulate each other

neurons trigger hormone secretion, hormones stimulate or inhibit meurons

Hypothalamus

shaped like a flattened funne, forms floor and walls of third ventricle, regulates primitive functions from water balance (thirst and sweat) to sex drive (rage), works with (attached to) pituitary gland

Pituitary Gland (hypophysis)

suspended from hypothalamus by stalk (infundibulum), housed in bone (sella turcica) of the skull

Pituitary Lobes

anterior, posterior and middle

Pituitary Development

the anterio lobe (adenoshypopysis) derives from embryonic oral tissue (glandular-adeno, teh pars tuberalis (middle lobe) also derives from oral glandular tissue (pars intermedius in fetus), the posterior lobe (neurohypophysis) derives from neural (brain) tissue

Anterior Lobe

"tropic" hormones (meaning they target other endocrine glands) are released from the hypothalamus and carried to the pituitary by a portal (means venule to cap. to ven. or arteriole to cap. to art. ) capillary system, gonadotropins target gonads (testes and ovaries), FSH (follicle stimulating hormone) and LH (luteinizing hormone), TSH (thyroid stimulating hormone), ACTH ( adrenocorticotropic hormone

Non-tropic hormones

PRL (prolactin) and GH (growth hormone)

Posterior Lobe of pituitary gland

stores and releases OT (oxytocin) and ADH (antidiuretic hormone)

OT and ADH are produced

in the hypothalamus and transported down to the posterior lobe by hypothalamo-hypophyseal tract (axons- cell bodies in hypothal.)

Hypothalamo-hypophyseal portal system - anterior lobe control

releasing hormones and inhibiting hormones of hypothalamus, gonadotropin- releasing hormone (GNRH), thyrotropin- releasing hormone (TRH), corticotropin- releasing hormone (CRH), prolactin - releasing factor (PRF), Prolactin- inhibiting factor (PIF), GH- releasing hormone (GHRH), GH- inhibiting hormone (GHIH) - aka somatostatin

Hypothalamo-hypophyseal portal system - posterior lobe control

neuroendocrine reflexes, hormone release in response to nervous system signals-suckling infant stimulates nerve endings -> hypothalamus -> posterior lobe -> oxytocin milk ejection, hormone release in response to higher brain center- milk ejection reflex can be triggered by a baby's cry

Negative Feedback

increase target organ hormone levels inhibits release of tropic hormones (short and long "loop")

Positive Feedback

stretching of uterus increase OT release, causes stretch of uterus, increase OT release, etc... until delivery

FSH (follicle stimulating hormone)

ovaries, stimulates development of eggs and follicles, testes, stimulates production of sperm

LH (luteinizing hormone)

females, stimulates ovulation and corpus luteum to secrete progesterone, males, stimulates interstitial cells of testes to secrete testosterone

ACTH (adrenocorticopropic hormone)

regulates response to stress, effect on adrenal cortex and secretion of glucorticoids

PRL (prolactin)

female, milk synthesis, male, increase LH sensitivity, thus increase testosterone secretion

ADH (antidiuretic hormone)

targets kidneys to increase water retention, reduce urine (vasopressin- constricts blood vessels), also functions as neurotransmitter

OT (oxytocin)

labor contractions, lactation (letdown), possible role sperm transport, emotional bonding

GH ( growth hormone)

targets liver to produce somatomedins- increase mitosis + cellular differentiation for tissue growth,

Protein Synthesis

mRNA translated, increase DNA transciption for increase mRNA production, enhances amino acid transport into cells, decrease catobolism

Lipid Metabolism

stimulates FFA and glycerol release, protein sparing

Carbohydrate Metabolism

glucose sparing effect- glucose stored as glycogen

Electrolyte Balance

promotes NA+, K+, Cl- retention, Ca2+ absorption

GH levels - childhood

bone, cartilage and muscle growth

GH levels - adulthood

declines with age

Pituitary disorders

hypopituitarism, panhypopituitarism, diabetes insipidus and hyperpituitarism

Hypopituitarism

pituitary dwarfism, childhood decrease GH

Panhypopituitarism

complete cessation of pituitary secretion, causes broad range of disorders

Diabetes Insipidus

decrease ADH, 10x normal urine output

Hyperpituitarism

Childhood- gigantism, adult - acromegaly (thickening of bones, soft tissues of hands, feet and face)

Pineal Gland

peak secretion 1-5 yr. olds, by puberty 75% lower, produces serotonin by day, converts it to melatonin at night

Thymus

location: mediastinum, superior to heart, shrinks (involution) after puberty, secretes hormones that regulate development and later activation of T-lymphocytes (immune cells)

Thyroid Gland

largest endocrine gland, anterior and lateral sides of trachea, 2 large lobes connected by isthmus, filled with colloid and lined with simple cuboidal epith. (follicular cells) that secretes 2 hormones, T3 + T4- T4 (tetraiodothyronine-thyroxine)- T3 (triiodothyronine- more powerful, but less abundant

TH Effects

body's metabolic rate and O2 consumption, calorigenic effecct- increase heat production, heart rate and contraction strength, respiratory rate

Parafollicular Cells

produce calcitonin that blood Ca2+, promotes Ca2+ deposition and bone formation especially in children

Thyroid Gland Disorders

congenital hypothyroidism, myxedema, endemic goiter, toxic goiter

Congenital Hypothyroidism (decrease TH)

infant suffers

Myxedema

adult hypothyroidism, decrease TH

Endemic Goiter

goiter- enlarged thyroid gland

Toxic Goiter

(graves disease)- antibodies mimic TSH, increase TH, exophthalmos (bulgiing of the eyeballs)

Parathyroid Glands

secrete PTH (parathyroid hormone)- blood Ca2+, decrease Ca2+ absorption, decrease Ca2+ urinary excretion and incrase bone resorption (destruction); hypoparathyroid vs. hyperparathyroid

Adrenal Glands

Adrenal Medulla, Adrenal Cortex

Adrenal Medulla

sympathetic ganglion innervated by sympathetic preganglionic fibers- stimulation causes release of (nore-) epinephrine

Adrenal Cortex

3 layers: (outer) zona glomerulosa, (middle) zona fasciculata, (inner) zona reticularis; secrete corticosteriods

Mineralocorticoids (zona glomerulosa) control

electrolyte balance, aldosterone promotes Na+ retention and K+ excretion

Corticosteroids

glucocorticoids (zona fasciculata- response to ACTH), especially cortisol, stimulates fat + protein catabolism, glucaneogenesis (from a.a's + FA's and release of fatty acids and glucose into blood to repair damaged tissues

Sex Steroids

(zona reticularis)- androgens (male hormones), including DHEA (other tissues convert to testosterone) and estrogen (important after menopause)

Adrenal Gland Disorders

Pheochromocytoma, cushing syndrome, adrenogenital syndrome, addison disease

Pheochromocytoma

tumor of adrenal medulla, with hypersecretion of (nor-) epinephrine, causes increase BP, increase metabolic rate, hyperglycemia, glycosuria, nervosuness, indigestion, sweating

Cushing Syndrome (adrenal tumor, excess ACTH)

causes hyperglycemia, hypertension, weakness, edema, muscle, bone loss with fat deposition shoulders + face

Adrenogenital Syndrome (AGS)

androgen hypersecretion cuases enlargement of penis or clitoris and prematrue onset of puberty, prenatal AGS in girls can result in masculinized genitals (photo), AGS in women can result in deep voice, beard, body hair

Addison Disease

hyposecretion of glucocorticoids and mineralocorticoids by adrenal cortex, hypoglycemia, Na+ and K+ imbalances, dehydration, hypotension, weight loss, weakness, causes increase pituitary ACTH secretion, stimulates melanin synthesis and bronzing of skin

Pancrease

retroperitoneal, inferior and dorsal to stomach

Mostly exocrine gland with pancreatic islets of endocrine cells that produce:

insulin, glucogan, somatostatin

Insulin (from B cells)

secreted after a meal with carbohydrates raises glucose blood levels, stimulates glucose and amino acid uptake, nutrient strage effect (stimulates glycogen/ stored glucose, fat and protein synthesis), antagonizes glucagon

Glucagon (from a cells)

secreted in very low carbohydrate and high protein diet or fasting, stimulates glycogenolysis (breakddown of glycogen into glucose), fat catabolism (release of FFA's) and promotes absorption of amino acids for gluconegensis (forming gluc, from fat and/ or protein)

Somatostatin

(growth hormone- inhibiting hormone, from delta () cells), secreted with rise in blood glucose and smino acids after a meal, paracrine secretion- modulates secretion of a + b cells

Diabetes Mellitus: signs and symptoms

poyuria (excess urine output), polydipsia (excess thirst), polyphagia (excess hunger), hyperglycemia, glycosuria, ketonuria (ketones are a product of fat catab.)

Osmotic Diuresis

blood glucose levels rise above transport maximum of kidney tubules, glucose remains (spills") in urine, osmolarity of blood increase and draws water in, this also increase urine osmol., drawing water into urine

Type I

(insulin- dependent diabetes mellitus- IDDM)- 10% of cases ("juvenile" onset), some cases have autoimmune destruction of b cells, diagnosed about age 12, treated with diet, excercise, monitoring of blood glucose and periodic injections of insulin or insulin pump

Typ II

(non-insulin- dep, diab. mell. - NIDDM) - 90% of cases ("adult onset), insulin resistance: failure of target cells to respond to insulin, 3 major risk factors are heredity, age (40+) and obesity, reated with weight loss program of diet and exercise, oral medication improve insulin secretion or target cell sensitivity

Acute Pathology

cells cannon absorb glucose, rely on fat proteins (weight loss + weakness)

Fat Catabolism

increase FFA's in blood and ketone bodies

Ketonuria

(ketones in urine) promotes osmotic diuresis, loss of Na+ and K+

Ketoacidosis

occurs as ketones decrease blood pH: if continued causes dyspnea (hyperventilating to try and get rid of acid) and eventually diabetic coma

Chronic Pathology

chronic hyperglycemia leads to neuropathy and cardiovascular damage, damage to retina and kidneys (common in type I), atherosclerosis leading to heart failure (common in type II), and gangrene

Hyperinsulinism

from excess insulin injection or pancreatic islet tumor, causes hypoglycemia, weakness and hunger, triggers secretion of epinephrine, GH and glucagon, side effects: anxiety, sweating and increase HR

Insulin Shock

uncorrected hyperinsulinism with disorientation, convulsions or unconsciousness

Granulosa Cells

wall of ovarian follicle- produces estradial, increases during first half of menstrual cycle

Corpus Luteum

follicle remnant after ovulation produces progesterone for at 12 days after ovulation or several weeks with pregnancy (eventually disintegrates)

Functions of estrogens and progesterone

development of female reproductive system and physique, regulate menstrual cycle, sustain pregnancy, prepare mammary glands for lactation

Both granulosa cells and corpus secrete and suppresses

inhibin and FSH secretion (neg. feedback)

Interstitial (leydig) cells (between seminiferous tubules)

produce testosterone

Functions (of testosterone)

developement of male reproductive system and physique, sustains sperm production and sex drive

Sustentacular (sertoli) Cells

secrete inhibin: suppresses FSH secretion, stabilizes sperm production rates

Heart

atrial natruicetic peptide (ANP)- decrease blood volume + decrease (blood pressure) BP, from increase Na+ and H2O loss by kidneys

Calcitriol

Ca2+ and phosphate: increase absorption, decrease loss for bone deposition (formation)

Erythropoietin

stimulates bone marrow to produce (red blood cells) RBC's

Stomach and Small intestines

enteric hormones (cordinate digestive motility (movement) and secretion)

Liver

angiotensinogen (a prohormone-precursor of angiotenisn II, a vasoconstrictor), erythropoietin (15%), and somatomedins- mediate action of GH

Placenta

secretes estrogen, progesterone and others (to regulate pregnancy and stimulate development of fetus and mammary galnds)

Steroids

derived from cholesterol (sex steroids, corticosteroids, etc...)

Peptides and glycoproteins

OT, ADH; all releasing and inhibiting hormones of hypothalamus; most of anterior pituitary hormones

Monoamines (biogenic amines)

derived from the amino acid tyrosine (catecholamines (morepinephrine, epinephrine, dopamine) and thyroid hormones)

Eicosonoids

important family of paracrine (not produced in neurons or transported in blood-travel short distance) secretions, derived from arachidonic

Lipoxygenase

converts arachidonic acid to leukotrienes that mediate allergic and inflammatory reactions

Cyclooxygenase

converts arachidonic aciid to prostacyclin

Prostacyclin

produced by blood vessel walls, inhibits blood clotting and vasoconstriction

Thromboxones

produced by blood platelets after injury, they override prostacyclin and stimulate vasoconstriction and clotting

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