Ch 17 Endocrine System

they both specialize in communication and coordination; the endocrine system uses hormones while the nervous system uses neurotransmitters

what are similarities and differences between the endocrine and nervous systems?

gap junctions

pores in cell membrane allow signaling molecules, nutrients, and electrolytes to move from cell to cell (electrical synapses)

neurotransmitters

released from neurons to travel across synaptic cleft to second cell

paracrines

secreted into tissue fluids to affect nearby cells (occurs within a tissue)

hormones

chemical messengers that travel in the bloodstream to other tissues and organs

endocrine system

glands, tissues, and cells that secrete hormones

endocrinology

the study of the endocrine system and the diagnosis and treatment of its disorders

endocrine glands

organs that are traditional sources of hormones (goes into bloodstream)

hormones

chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ, often a considerable distance away

exocrine glands

have ducts; carry secretion to an epithelial surface or the mucosa of the digestive tract; has extracellular effects (food digestion); digestive and respiratory

endocrine glands

no ducts; contain dense, fenestrated capillary networks which allow easy uptake of hormones into the bloodstream; intracellular effects such as altering target cell metabolism

they release hormones, release bile into ducts, release albumin and blood-clotting factors into blood that are not hormones

why do liver cells defy rigid classification?

1) nervous: reacts and stops quickly; response declines in response to long term stimuli and it adapts quickly; it is targeted and specific to one organ 2) endocrine: reacts slowly and effect may continue for days or longer; response persists and it adapts slowly; it has general, widespread effects to many organs

compare the nervous and endocrine systems

norepinephrine, dopamine, and antidiuretic hormone

examples of chemicals that function as both hormones and neurotransmitters

both systems can have similar effects on target cells (norepinephrine and glucagon both cause glycogen hydrolysis in liver); the two systems can regulate each other (neurotransmitters can affect glands, and hormones can affect neurons); neuroendocrine cells share characteristics with both systems (neuron-like cells that secrete oxytocin into blood)

examples of how the nervous and endocrine system have similar effects or work together

target organs or cells

those organs or cells that have receptors for a hormone and can respond to it; some possess enzymes that convert a circulating hormone to its more active form

shaped like a flattened funnel; forms floor and walls of third ventricle; regulates primitive functions from water balance and thermoregulation to sex drive and childbirth; many of its functions are carried out by the pituitary gland

explain characteristics of the hypothalamus

infundibulum

stalk that attaches the pituitary gland to the hypothalamus

adenohypophysis (anterior) and neurohypophysis (posterior)

what are the two structures with independent origins and separate functions of the pituitary gland?

anterior pituitary gland

has two capillary beds (one in hypothalamus attaches to one in this by portal venules); three-quarters of the pituitary

hypothalamic hormones regulate the anterior pituitary gland’s cells; hypothalamic releasing and inhibiting hormones travel from the hypothalamus to the anterior pituitary; different hormones are then secreted by the anterior pituitary; so it **makes** and **releases** hormones

describe the anterior pituitary gland’s role in hormones

posterior pituitary gland

has nerve tissue and is not a true gland (one-quarter of the pituitary)

nerve cell bodies in the hypothalamus pass down the stalk as hypothalamo-hypophysal tract and end in the posterior lobe (axons go from the hypothalamus to the posterior); hypothalamic neurons secrete hormones that are stored in the posterior until they are released into the blood; so they don’t make but only **store** and **release** hormones; has quick release because it is regulated by nervous tissue

describe the posterior pituitary gland’s role in hormones

8; 6 regulate the anterior pituitary; 2 are released into capillaries in the posterior pituitary

how many hormones are produced in the hypothalamus?

PIH inhibits secretion of prolactin and somatostatin inhibits secretion growth hormone and thyroid-stimulating hormone by the anterior pituitary

what does PIH and somatostatin do?

oxytocin (OT)

stored and released by the posterior pituitary; paraventricular nuclei of the hypothalamus produce it

antidiuretic hormone (ADH)

stored and released by posterior pituitary; supraoptic nuclei of the hypothalamus produce it; causes you to not urinate

6

anterior pituitary synthesizes and secretes how many principal hormones?

follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

what are the two gonadotropin hormones that target gonads that are also anterior pituitary hormones?

follicle-stimulating hormone (FSH)

stimulates secretion of ovarian sex hormones, development of ovarian follicles, and sperm production; an anterior pituitary hormone

luteinizing hormone (LH)

stimulates ovulation, stimulates corpus luteum to secrete progesterone, stimulates testes to secrete testosterone; an anterior pituitary hormone

thyroid-stimulating hormone (TSH)

stimulates secretion of thyroid hormone; an anterior pituitary hormone

adrenocorticotropic hormone (ACTH)

stimulates adrenal cortex to secrete glucocorticoids; an anterior pituitary hormone

\-tropic

hormone that causes another gland to make another hormone

prolactin (PRL)

after birth, stimulates mammary glands to synthesize milk; an anterior pituitary hormone

growth hormone (GH)

stimulates mitosis and cellular differentiation; an anterior pituitary hormone

antidiuretic hormone (ADH) and oxytocin (OT)

what are the two hormones produced in the hypothalamus and transported to the posterior pituitary? the hormone is released when hypothalamic neurons are stimulated

antidiuretic hormone (ADH)

increases water retention, thus reducing urine volume, and preventing dehydration; it is also called vasopressin because it can cause vasoconstriction

oxytocin (OT)

surge of hormone released during sexual arousal and orgasm; promotes feelings of sexual satisfaction and emotional bonding between partners; stimulates labor contractions during childbirth; stimulates flow of milk during lactation; may promote emotional bonding between lactating mother and infant

no; it is regulated by the hypothalamus, other brain areas, and feedback from target organs

is the rate of pituitary secretion constant?

in times of stress, the hypothalamus triggers the release of ACTH; during pregnancy, the hypothalamus triggers prolactin secretion

examples of how brain monitors conditions and influences anterior pituitary accordingly

neuroendocrine reflexes; ex: hypothalamic osmoreceptors trigger release of ADH when they detect a rise in blood osmolarity; ex: infant suckling triggers hypothalamic response to release oxytocin

what is the posterior pituitary controlled by?

negative feedback

increased target organ hormone levels inhibit release of hypothalamic and/or pituitary hormones

thyroid hormone inhibits release of TRH by the hypothalamus and of TSH by the anterior pituitary

example of negative feedback in control of pituitary secretion

oxytocin is involved in a positive feedback loop; in response to uterine contractions, oxytocin is released, which leads to more contractions

example of positive feedback in control of pituitary secretion

widespread effects on body tissues (especially cartilage, bone, muscle, and fat)

what does growth hormone (GH) have effects on?

growth hormone

what induces the liver to produce growth stimulants?

insulin-like growth factors (IGF-I) or somatomedins (IGF-II)

what are two growth stimulants?

prolongs the action of GH

what does IGF-I do?

hormone half life

the time required for 50% of the hormone to be cleared from the blood; GHs is 6 to 20 minutes and IGF-Is is about 20 hours

protein synthesis increases

boosts transcription and translation; increases amino acid uptake into cells; suppresses protein catabolism; proteins involved with blood clotting (function of growth hormone)

lipid metabolism increases

stimulates adipocytes to catabolize fats (protein-sparing effect) (function of growth hormones)

carbohydrate metabolism affected by growth hormones

glucose-sparing effect, mobilizing fatty acids reduces dependence of most cells on glucose, freeing more for the brain; stimulates glucose secretion by liver

electrolyte balance

promotes Na+, K+, and Cl- retention by kidneys, enhances Ca2+ absorption in intestine; makes electrolytes available to growing tissues

secretion high during first 2 hours of sleep; can peak in response to vigorous exercise; activates ghrelin which is released by the empty stomach; levels decline gradually with age;

when are growth hormone levels low or high?

lack of protein synthesis contributes to aging of tissues and wrinkling of skin; the body becomes less bone and muscle and more fat

what occurs with less and less growth hormone as you age?

pineal gland

attached to roof of third ventricle beneath the posterior end of the corpus callosum; after the age of 7, it undergoes involution and is only a tiny mass of shrunken tissue in adults

may synchronize physiological function with 24-hour circadian rhythms of daylight and darkness (it synthesizes melatonin from serotonin during the night and this fluctuates seasonally with changes in day length); may also influence timing of puberty in humans

what are functions of the pineal gland?

seasonal affective disorder

occurs in winter or northern climates; influenced by melatonin production from the pineal gland; symptoms: depression, sleepiness, irritability, and carbohydrate craving

2 to 3 hours of exposure to bright light each day

what can reduce melatonin levels and the symptoms of SAD?

exposing ganglion cells to bluelight

what can cause the pineal gland to think you are in the sunlight?

endocrine, lymphatic, immune

what are the three systems that the thymus plays a role in?

thymus

it is a bilobed gland in the mediastinum superior to the heart that goes through involution after puberty

site of maturation of T cells that are important in immune defense; secretes hormones (thymopoietin, thymosin, and thymulin) that stimulate development of other lymphatic organs and activity of T lymphocytes

what are some functions of the thymus?

lots of T lymphocytes in reserve in infants; less T lymphocytes in reserve and more adipose and scar tissue in geriatric individuals

difference in the thymus between infants and geriatric individuals?

thyroid gland

largest gland that is purely endocrine; it is composed of two lobes and an isthmus below the larynx; is dark reddish brown in color due to a rich blood supply

thyroid follicles

sacs that make up most of thyroid; they contain protein-rich colloid and follicular cells (simple cuboidal epithelium) line them

thyroxine (T4 because of four iodine atoms) and triiodothyronine (T3)

what does the thyroid gland secrete in response to TSH?

T4 and T3

these increase the metabolic rate, O2 consumption, heat production (calorigenic effect), appetite, growth hormone secretion, alertness, reflex speed

calcitonin

what do parafollicular (C or clear) cells secrete with rising blood calcium? (in thyroid)

stimulates osteoblast activity and bone formation in children

what does calcitonin do?

four

how many parathyroid glands are partially embedded in the posterior surface of the thyroid gland

secrete parathyroid hormone which increases blood Ca2+ levels; this promotes synthesis of calcitriol, increases absorption of Ca2+, decreases urinary excretion, and increases bone resorption

what do parathyroid glands do?

adrenal medulla

inner core, 10 to 20% of adrenal gland; it has dual nature acting as an endocrine gland and a ganglion of the sympathetic nervous system

adrenal medulla

consists of modified sympathetic postganglionic neurons called chromaffin cells

it releases catecholamines (epinephrine and norepinephrine) and a trace of dopamine directly into the bloodstream → these cause blood glucose and lipid levels to increase (physical activity)

what happens when the adrenal medulla is stimulated?

increase alertness and prepare body for physical activity (mobilize high energy fuels, lactate, fatty acids, and glucose; glycogenolysis and gluconeogenesis by liver boost glucose levels; epinephrine inhibits insulin secretion and so has a glucose-sparing effect so muscles use fatty acids and save glucose for the brain); increase blood pressure, heart rate, blood flow to muscles, pulmonary airflow, and metabolic rate; decreases digestion and urine production

what are the effects of catecholamines?

if no physical activity, it can cause lipid build up in the blood vessels; lipids go from the limbs and redeposit in the abdomen

what can occur when constantly dumping catecholamines (stress response hormones) into the bloodstream?

adrenal cortex

this surrounds the adrenal medulla and secretes several corticosteroids (hormones) from three layers of glandular tissue

zona glomerulosa

outer layer of adrenal cortex; cells are arranged in rounded clusters; secretes mineralocorticoids that regulate the body’s electrolyte balance

zona fasciculata

middle layer of adrenal cortex; cells are arranged in fascicles separated by capillaries; secretes glucocorticoids and androgens

zona reticularis

inner layer of adrenal cortex; cells are in a branching network; secretes glucocorticoids and sex steroids

glucocorticoids

regulate blood glucose

androgens

regulate sex hormones

mineralocorticoids

steroid hormones that regulate electrolyte balance

aldosterone

a mineralocorticoid; stimulates Na+ retention and K+ excretion; water is retained with sodium by osmosis so blood volume and blood pressure is maintained

ultimately have the same effect of causing us to retain water but ADH causes us to retain water directly while water is retained with sodium via osmosis with aldosterone

compare aldosterone and antidiuretic hormone (ADH)

glucocorticoids

secreted by zona fasciculata and reticularis in response to ACTH; they regulate metabolism of glucose and other fuels

cortisol and corticosterone

stimulate fat and protein catabolism, gluconeogenesis (glucose from amino acids and fatty acids) and release of fatty acids and glucose into blood; adapt to stress and repair tissues; anti-inflammatory effect that if long term can lead to immune suppression

glucocorticoids

help body adapt to stress and repair tissues; has anti-inflammatory effect that becomes immune suppression with long term use

sex steroids

secreted by zona fasciculata and zona reticularis (besides glucocorticoids)

androgens

set libido throughout life; larger role in prenatal male development (include DHEA which other tissues convert into testosterone)

DHEA

precursor to testosterone

estradiol

small quantity from adrenals, but this becomes important after menopause for sustaining adult bone mass

form of estrogen (1 of 3 forms); most potent one with the most effect on metabolism; helps to regulate mammary and uterine lining development; low levels of estradiol are associated with osteoporosis in post menopausal women

functions/characteristics of estradiol

no

are the medulla and cortex of the adrenal gland functionally independen?

cortisol

medulla atrophies without the stimulation of what?

chromaffin cells

some of these from the medullary origin extend into the cortex; they stimulate the cortex to secrete corticosteroids when stress activates the sympathetic nervous system

both

is pancreas endocrine or exocrine?

glucagon

secreted by A or alpha cells