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Biology 232
Human Anatomy and Physiology
Chapter 18 Lecture Outline
ENDOCRINE SYSTEM – regulates body functions
endocrine glands – ductless glands; secrete products into interstitial fluid
(pituitary, thyroid, parathyroid, adrenals, pineal)
hormones – products of endocrine glands and cells; usually diffuse into
capillaries and circulate in blood
endocrine cells – found in many tissues and organs
hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver,
small intestine, skin, heart, adipose tissue, placenta
COMPARISON OF NERVOUS AND ENDOCRINE REGULATION
Nervous System
synaptic communication - neurotransmitter released at a specific site
postsynaptic cell (muscle, gland, neuron) must have correct receptors
rapid onset of response (milliseconds)
short duration – local inactivation of neurotransmitter
direct communication – electrical synapses at gap junctions
Endocrine System
endocrine communication - hormones released in bloodstream
diffuse - targets any body tissues with correct receptors
onset of response may take seconds to hours
longer duration – hormone inactivated by liver or excreted by kidneys
paracrine communication (local hormones) – hormones released in
interstitial fluid target neighboring cells with correct receptors
HORMONE FUNCTION
hormone receptors – cell proteins or glycoproteins on specific target cells
bind specific hormones and alter cell structure or function
Chemical Classes of Hormones – determines how the hormone functions
lipid soluble hormones – receptors inside target cells
steroid hormones – derived from cholesterol
sex hormones – androgens, estrogens
adrenal cortex hormones – mineralocorticoids, glucocorticoids
calcitriol
thyroid hormones – amino acid derivatives (tyrosine + iodines)
T3 and T4
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water-soluble hormones – receptors in plasma membrane of target cells
amino acid hormones – derived from amino acids
catecholamines – epinephrine, norepinephrine
melanin
peptide hormones – amino acid chains and proteins
many (eg. insulin, human growth hormone, oxytocin, etc.)
eicosanoid hormones – derived from arachadonic acid (fatty acid)
prostaglandins and leukotrienes
usually act as local hormones
act on receptors on inner cell membrane
Hormone Transport in the Blood
water-soluble hormones – free in blood plasma
relatively short-acting
broken down by liver, kidneys or enzymes
lipid-soluble hormones – bound to transport proteins from liver
3 advantages:
increases solubility in blood plasma
slows down breakdown and excretion
provides hormone reserve in bloodstream
free fraction (small percentage of unbound hormone)
these are the only active form of hormones
Mechanisms of Hormone Action – various target cells can respond differently to
the same hormone depending on the receptor
lipid-soluble hormones – intracellular receptor
receptor in cytoplasm or nucleus of target cell
1) free hormone diffuses into cell through lipid bilayer
2) in target cell, hormone binds to and activates receptors
3) receptor-hormone complex turns genes on or off
4) alters gene expression – synthesis of a protein
enzyme – alters target cell function
structural protein – alters target cell structure
water-soluble hormones – receptors in outer cell membrane
(eicosanoids – inner cell membrane)
first messenger (hormone) activates a second messenger inside cell
1) hormone binds receptor at surface of plasma membrane
2) hormone-receptor complex activates a G protein, which activates
membrane enzymes
3) enzymes activate a second messenger (eg. cAMP, cGMP, Ca+2)
4) second messenger alters enzyme within target cell
turns enzymes on or off = alters cell function
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amplification – one hormone may activate thousands of second
messengers
cascade effect – more than one enzyme pathway may be activated
one hormone can alter multiple cell functions
Target Cell Response – depends on 3 factors:
1) hormone concentration
2) number of hormone receptors
down-regulation - decrease number of receptors; decreases sensitivity
when excess hormone is present
up-regulation – increase number of receptors; increases sensitivity during
hormone deficiency
3) influence of other hormones
antagonistic effect – one hormone opposes the action of another
net result depends on balance of opposing hormones
synergistic effect – effect of 2 hormones is greater than sum of those
hormones acting alone
permissive effect – the action of one hormone is required for the proper
function of another hormone
Regulation of Hormone Secretion
neural stimuli –endocrine cell stimulated by neuron at neuroglandular junction
humoral stimuli – endocrine cell stimulated by changes in composition of blood
or interstitial fluid
hormonal stimuli – presence or absence of another hormone stimulates endocrine
cell
negative feedback – most endocrine cells are inhibited as their products or effects
increase (eg. high thyroid hormone levels inhibit thyroid gland secretion)
HYPOTHALAMUS AND PITUITARY GLAND – function together to regulate most
aspects of growth, development, metabolism, and homeostasis
HYPOTHALAMUS – integrates nervous and endocrine systems
neurosecretory cells – specialized neurons which produce hormones
release hormones in interstitial spaces when stimulated by a nervous
impulse or humoral receptors
hormones stored by posterior pituitary
antidiuretic hormone (ADH)
oxytocin
produced by neuron cell bodies in hypothalamus
hormone vesicles travel down axons in infundibulum to posterior
pituitary
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regulatory hormones – regulate anterior pituitary
releasing hormones – stimulate anterior pituitary
inhibiting hormones – inhibit anterior pituitary
produced by neurons in hypothalamus and released in interstitial
space
hypophyseal portal system – system of 2 capillary networks
which delivers hormones secreted by the hypothalamus to
the anterior pituitary
autonomic motor neurons
sympathetic stimulation of adrenal medulla
secretion of epinephrine and norepinephrine into blood stream
PITUITARY GLAND (HYPOPHYSIS) – inferior to hypothalamus in hypophyseal
fossa of sella turcica (sphenoid bone)
infundibulum – stalk attaching pituitary to hypothalamus
2 lobes of pituitary:
1) Anterior Pituitary – adenohypophysis (glandular hypophysis)
produces and secretes 7 hormones
tropins – hormones that regulate other endocrine glands or tissues
thyrotropin – thyroid-stimulating hormone (TSH)
regulates thyroid
corticotropin – adrenocorticotropic hormone (ACTH)
regulates adrenal cortex
gonadotropins – follicle-stimulating hormone (FSH)
luteinizing hormone (LH)
both regulate gonads (testes and ovaries)
mammotropin – prolactin (PRL)
regulates mammary glands
somatotropin – growth hormone (GH)
regulates most body tissues
melanotropin – melanocyte-stimulating hormone (MSH)
regulates melanocytes
secretion of these hormones is regulated mainly by hypothalamic releasing
and inhibiting hormones
2) Posterior Pituitary – neurohypophysis (neural hypophysis)
modified axon terminals – stores hormones from hypothalamus and
releases them in response to nervous stimulation
pituicytes – specialized neuroglia of posterior pituitary
hypothalamohypophyseal tract – axon tract from hypothalamus to
posterior pituitary (in infundibulum)
2 stored hormones:
oxytocin
antidiuretic hormone (ADH) – also called vasopressin
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Hormones of Anterior Pituitary
1) thyroid-stimulating hormone (TSH) – (thyrotropin)
stimulates thyroid to produce and secrete T3 and T4
promoted by a thyrotropin-releasing hormone (TRH) [from hypothalamus]
inhibited by negative feedback of T3 and T4
2) adrenocorticotropic hormone (ACTH) - (corticotropin)
stimulates adrenal cortex to produce and secrete glucocorticoids
promoted by corticotropin-releasing hormone (during stress)
inhibited by negative feedback of glucocorticoids
3) follicle-stimulating hormone (FSH) – (gonadotropin)
female – stimulates ovaries to produce egg follicles and estrogen
male – stimulates testes to produce sperm
promoted by a gonadotropin-releasing hormone (GnRH)
inhibited by negative feedback of sex hormones
4) luteinizing hormone (LH) - (gonadotropin)
female – stimulates ovaries to ovulate and maintain pregnancy
male – stimulates testes to secrete testosterone
promoted by gonadotropin-releasing hormone (GnRH)
inhibited by negative feedback of sex hormones
5) prolactin (PRL) – (mammotropin)
stimulates mammary glands to produce and secrete milk
permissive and synergistic effects of other hormones required:
estrogens, progesterone, glucocorticoids, GH, T4, insulin, oxytocin
promoted by prolactin-releasing hormone (PRH)
inhibited by prolactin-inhibiting hormone (PIH)
6) growth hormone (GH) – (somatotropin)
stimulates cells in most body tissues and organs
causes cell growth, division, breakdown of energy stores
insulinlike growth factors – hormones produced by liver in response to
GH; target other body tissues
increase protein synthesis = growth
promoted by growth hormone-releasing hormone (GHRH)
inhibited by growth hormone-inhibiting hormone (GHIH)
gigantism – hypersecretion of GH during childhood
pituitary dwarfism – hyposecretion of GH during childhood
acromegally – hypersecretion of GH during adulthood
7) melanocyte-stimulating hormone (MSH)
from pars intermedia – fetal pituitary lobe which atrophies
function unknown
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Hormones of Posterior Pituitary – produced by hypothalamus
neuroendocrine reflexes – hormones are released due to neural impulses
1) oxytocin
stimulates uterine wall muscles to contract during delivery,
and mammary glands to eject milk
promoted by sensory stimuli:
stretch of the cervix
suckling of an infant
positive feedback loop – hormone release continues until sensory
stimulus stops (birth, or infant stops suckling)
2) antidiuretic hormone (ADH)
vasopressin – regulates blood volume and pressure
promoted by:
high blood osmotic pressure (detected by osmoreceptors in
hypothalamus)
low blood pressure (detected by baroreceptors in blood vessels)
low blood volume
target organs:
kidneys – excrete less water from blood = less urine produced
sweat glands – decrease sweating
arterioles – constrict = increases blood pressure
diabetes insipidus – hyposecretion of ADH or nonfunctional
ADH receptors
excess urine output = thirst, dehydration
THYROID GLAND
Anatomy of the Thyroid
inferior to larynx; lateral and anterior to trachea
right and left lateral lobes – connected by isthmus
thyroid follicles – contain colloid (large quantity of stored form of
thyroid hormones T4 & T3)
follicular cells (simple cuboidal epithelium)
produce thyroid hormones - T4 and T3
parafollicular cells (C cells) – produce calcitonin
Production of Thyroid Hormones
follicular cells actively transport iodide ions from blood into cell
follicular cells synthesize thyroglobulin (large glycoprotein) and secrete it
into follicle lumen
iodides react with tyrosines (amino acid) on thyroglobulin
T4 = tyrosine + 4 iodides (tetraiodothyronine) [thyroxine]
T3 = tyrosine + 3 iodides (triiodothyronine)
hormones stored in follicle as colloid (thyroglobulin molecules)
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secretion of thyroid hormones
endocytosis of colloid into follicular cells
lysosomes digest colloid and cleave off molecules of T4 and T3
T4 and T3 diffuse into interstitial fluid and into bloodstream (90% T4)
thyroxine-binding globulin (TBG) – blood transport protein for T4 & T3
T4 and T3 released as free fraction is used up
Functions of Thyroid Hormones
target – most cells of body
increases basal metabolic rate – oxygen consumption at rest after
overnight fast
increase cellular metabolism – more ATP production, protein synthesis,
glycolysis, and more sodium/potassium pumps
calorigenic effect – body temperature rises
upregulate beta receptors for catecholamines – increase heart rate and
force, increase blood pressure
participate in growth – especially nervous tissue
Regulation of Thyroid Hormones
1) low T4 and T3 in blood
2) hypothalamus secretes thyrotropin-releasing hormone (TRH)
3) anterior pituitary secretes TSH
4) thyroid production and secretion of T4 and T3 increases
5) negative feedback inhibition by T3
(increased ATP demands increase thyroid activity)
Thyroid Disorders
hypothyroidism – reduced secretion
congenital (at birth) – mental retardation (cretinism)
myxedema (adult) – edema, low heart rate and body temperature,
weakness, weight gain
hyperthyroidism – increased secretion
high heart rate and blood pressure
elevated body temperature, nervousness
weight loss, increased appetite
goiter – enlarged thyroid; various causes
hyperthyroidism
dietary iodine deficiency
Function of Calcitonin – from parafollicular (C) cells of thyroid
lowers blood calcium (increases bone density)
targets – osteoclasts – inhibits bone resorption
kidneys – increases excretion of calcium ions in urine
promoted by high blood calcium
inhibited by low blood calcium
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PARATHYROID GLANDS
Anatomy of the Parathyroids
attached to posterior surface of thyroid lobes
4 glands – superior and inferior glands on each side
chief cells – produce parathyroid hormone (PTH)
oxyphil cells – function unknown
Parathyroid Hormone – major regulator of calcium level in blood
increases blood calcium
targets:
osteoclasts – stimulates resorption of bone, which releases calcium
into blood
osteoblasts – inhibits calcification of bone
kidneys – decreases calcium excretion in urine
stimulates production of calcitriol – increases absorption of
dietary calcium
promoted by low blood calcium
inhibited by high blood calcium
Regulation of Blood Calcium Level – negative feedback loops by blood calcium
directly to thyroid and parathyroid
1) low blood calcium stimulates parathyroid gland secretion of PTH
(also inhibits calcitonin)
2) PTH targets osteoclasts, osteoblasts, and kidneys
3) blood calcium increases
4) high blood calcium stimulates thyroid secretion of calcitonin
(also inhibits PTH)
5) calcitonin targets osteoclasts and kidneys
6) blood calcium decreases
Parathyroid Disorders
hypoparathyroidism – causes low blood calcium
tetany and spasms – spontaneous depolarization of neurons and
muscle cells
hyperparathyroidism – causes excess blood calcium
fragile bones, kidney stones, lethargy, and weakness
ADRENAL GLANDS
Anatomy of Adrenals – superior to each kidney; pyramidal shape; covered by
connective tissue capsule
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2 functional regions of adrenal gland:
adrenal cortex – peripheral 80-90% of gland
3 zones – 3 hormones:
zona glomerulosa (outer) – mineralocorticoids
zona fasciculata (middle) – glucocorticoids
zona reticularis (inner) – androgens
adrenal medulla – modified sympathetic ganglion
central 10-20% of gland
neuroendocrine cells – produce epinephrine and norepinephrine
stimulated by sympathetic ANS
(review effects of sympathetic nervous system)
Adrenal Cortical Hormones
1) Mineralocorticoids – electrolyte and water homeostasis
aldosterone – main mineralocorticoid produced
increases blood Na+ and water, decreases blood K+
(increases blood pressure)
targets - kidneys (sweat, salivary, digestive glands) – decreases excretion
of Na+, increases excretion of K+
promoted directly by low blood Na+ or high blood K+
Regulated by renin-angiotensin-aldosterone (RAA) pathway
1) decreased blood volume and pressure
2) kidneys secrete renin (enzyme) into blood
3) renin converts angiotensinogen (plasma protein from liver) into
angiotensin I
4) enzyme in lung capillaries converts angiotensin I to angiotensin II
5) angiotensin II promotes aldosterone secretion by adrenal cortex
6) aldosterone promotes Na+ and water reabsorption in kidneys
7) blood volume and pressure increase
2) Glucocorticoids – regulate metabolism and resistance to stress
cortisol (hydrocortisone) – main glucocorticoid
(also cortisone and corticosterone)
Regulation of Secretion
1) low glucocorticoids in blood
2) corticotropin- releasing hormone (CRH) from hypothalamus
3) ACTH from anterior pituitary
4) zona fasciculata secretes more glucocorticoids
5) high glucocorticoids cause negative feedback
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Effects of Glucocorticoids (stress hormones)
resistance to stress – mobilize energy and substrates; increase
blood pressure, increase appetite
protein breakdown (muscles) mobilizes amino acids
lipolysis – breakdown and metabolism of fats
glucose synthesis and glycogen storage in liver
spares glucose for use of neural tissues
anti-inflammatory effects – inhibit white blood cells, reduce
swelling and pain, slows healing
depression of immune responses
Cushing’s syndrome – hypersecretion of glucocorticoids
loss of muscle, redistribution of fat (buffalo hump, pendulous
abdomen), poor healing, infections, hypertension, weakness
3) Androgens – masculinizing sex hormones
effects:
puberty in boys and girls – participate in growth spurt; growth of
axillary and pubic hair
adult males – small quantity relative to testicular androgens
females – libido (sex drive), anabolic effects (increase muscle and bone
mass), body tissues convert to estrogens
(only source of estrogen after menopause)
THE STRESS RESPONSE
stressor – physical or emotional disturbance that threatens equilibrium
general adaptation syndrome (GAS) – body changes due to stress, controlled
mainly by the hypothalamus
3 phases:
1) alarm phase – immediate sympathetic nervous response initiated by
hypothalamus
rapid energy mobilization to brain, heart, skeletal muscles
reduced non-essential functions
activates RAA pathway – aldosterone maintains blood pressure
decreases urine production
2) resistance phase – longer-lasting hormonal response initiated by hypothalamic
releasing hormones
CRH – ACTH – cortisol
GHRH – GH
TRH – TSH – T4 & T3
1) mobilizes lipids and proteins for energy
2) glucose-sparing for use by nervous tissues
3) synthesis of glucose from other molecules
4) maintains blood volume and pressure – supplies nutrients to tissue
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3) exhaustion phase – prolonged exposure to cortisol and other stress hormones
“Cushing-like” symptoms - muscle wasting, immune failure, poor healing
high blood pressure
electrolyte imbalances – low K+
exhaustion of adrenal cortex – inability to produce glucocorticoids
lack of available energy sources, especially glucose
Pancreatic Islets
pancreas – between stomach and sm. intestine; exocrine and endocrine functions
99% acinar cells – exocrine cells producing digestive enzymes
1% pancreatic islets (islets of Langerhans) – produce hormones
Cell Types in Pancreatic Islets
alpha (A) cells – about 15%; secrete glucagon (increases blood glucose)
beta (B) cells – about 80%; secrete insulin (decreases blood glucose)
delta (D) cells – about 5%; secrete somatostatin (GHIH)
inhibits glucagon and insulin release; slows nutrient absorption
from GI tract
F cells – remainder; secrete pancreatic polypeptide
inhibits gallbladder contraction
regulates digestive enzyme secretion
Regulation and Effects of Glucagon – increases blood glucose
hypoglycemia (low blood glucose) stimulates alpha cells to produce
and secrete glucagon
main target - liver
promotes glycogenolysis (glycogenbroken down to glucose)
promotes gluconeogenesis (lactic acid and amino acids converted
to glucose)
other target – adipocytes
stimulates lipolysis (fat breakdown for energy)
decreases glucose consumption
glucagon secretion also stimulated by sympathetic activity
inhibited by increases glucose, insulin, somatostatin from D cells
Regulation and Effects of Insulin – decreases blood glucose
hyperglycemia (high blood glucose) stimulates beta cells to produce
and secrete insulin
targets – most body cells
promotes uptake of glucose by body cells by stimulating
synthesis of glucose transporter proteins
promotes use of glucose for ATP synthesis
promotes protein synthesis
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liver – promotes glycogenesis (excess glucose stored as glycogen)
adipocytes – promotes triglyceride synthesis
insulin secretion also stimulated by:
parasympathetic activity
some amino acids and glucose in small intestine (eating)
Pancreatic Islet Disorders
Diabetes mellitus – inability to produce or respond to insulin
Signs and symptoms:
cells can’t take in or use glucose for energy
hyperglycemia
glucosuria – glucose in urine
polyuria – excessive urine production
polydipsia – excessive drinking
polyphagia – excessive eating
lipolysis – atherosclerosis and cardiovascular disease
ketoacidosis – high blood ketones from fatty acid
breakdown
2 Types of Diabetes Mellitus
type I (insulin dependent) – destruction of beta cells
juvenile diabetes - usually develops when young
can’t produce enough insulin
insulin injections required to prevent death
type II (non-insulin dependent) – insulin levels normal or
high, but target cells don’t respond
down-regulation of insulin receptors on target cells
usually in obese, over age 40
may be managed with diet and exercise
insulin shock – hypoglycemia due to overdose of insulin or not
eating; deprivation of glucose to brain causes convulsions,
loss of consciousness, shock, and death
Pineal Gland – part of epithalamus; regulated by light and darkness
Cell Types:
neurons, neuroglia
pinealocytes – secrete melatonin mainly in darkness
functions:
biological clock (circadian rhythm) – sleep and awakening cycles
seasonal affective disorder (SAD) – winter depression
less daylight = more melatonin production
may inhibit reproductive functions
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Thymus – lies over base of heart
participates in immune system
hormones promote maturation of lymphocytes
Eicosanoids – local hormones in most tissues; derived from arachadonic acid released
by damaged cell membranes
2 families:
prostaglandins (PGs) – broad physiological effects
participate in inflammation, fever, and pain – inhibited by
NSAIDS (non-steroidal anti-inflammatory drugs)
thromboxane – participates in blood clotting
leukotrienes (LTs) – promote inflammation and chemotaxis of white
blood cells
Other Endocrine Cells
GI tract
GIP – promotes insulin secretion
Kidneys
erythropoietin (EPO) – red blood cell formation
calcitriol (vitamin D) – dietary calcium and phosphorus absorption
Heart
atrial natriuretic peptide (ANP) – decreases blood pressure
Adipose tissue
leptin – suppresses appetite
Placenta
Ovaries and Testes
sex hormones – androgens, estrogens, others
Growth Factors – mitogenic (promote cell division)
many act locally promoting tissue development, growth, and repair
tumor angiogenesis factors (TAFs) – promote capillary growth, regeneration, and
wound healing
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