human physiology: endocrine system

endocrine glands of the body

pituitary, thyroid, parathyroid, adrenal, and pineal

Gs

stimulates adenylyl cyclase to produce cAMP, which then triggers protein kinase A

Gq

triggers phospholipase C to derive PIP2 from the plasma membrane in order to produce second messengers IP3 and DAG

receptor tyrosine kinases

hormone receptor binding causes tyrosine kinases on each receptor to cross phosphorylate; phosphorylated tyrosines of the receptors serve as docks for relay proteins which then get activated via phosphorylation on their own tyrosine amino acids

receptor guanylyl cyclases

water-soluble hormones bind to receptors, which then dimerize; dimerization triggers guanylyl cyclase components of the receptors to produce cGMP, which then activates protein kinase G

janus kinase coupled receptors

a water-soluble hormone binds to the JAK receptor which then dimerizes with a neighbor and they cross phosphorylate each other; the active JAKs then phosphorylate a tyrosine in the cytosolic portion of the receptor; STAT proteins dock and get phosphorylated (activated) before entering the nucleus to alter gene transcription to produce a cellular response

tropins

hormones that act on endocrine glands or tissues to regulate the secretion of another hormone

hormone secretion can be regulated by

the nervous system, chemical changes in the blood, mechanical organ signals, or other hormones

infundibulum

stem structure that connects the pituitary gland to the hypothalamus

somatotrophs

APG cells that secrete growth hormones

gonadotrophs

APG cells that secrete folic stimulating hormone (FSH) and luteinizing hormone

thyrotrophs

APG cells that secrete TSH

corticotrophs

APG cells that secrete adrenocorticotropic hormone (ACTH)

lactotrophs

APG cells that secrete prolactin

hypothalamic-hypophyseal portal system

blood flows the hypothalamus into portal veins that take it to the anterior pituitary gland, allowing the hypothalamic hormones to act on the pituitary gland immediately and directly

pro-opiomelanocortin (POMC)

the precursor to a variety of peptides that impact various aspects of homeostasis like appetite, cortisol levels, pain signals, and hormones including ACTH

follicle stimulating hormone

development of eggs and secretion of estrogen in females; production of sperm in males

posterior pituitary gland

made of neurosecretatory cells, so it stores and releases hormones synthesized by APG

oxytocin

neurosecretatory cells of the hypothalamus secrete this in response to uterine distention to initiate labor

calcitonin

comes from parafollicular c cells in the thyroid gland to regulate blood calcium levels by inhibiting osteoclasts, which break down bone into calcium and phosphate components

hypothyroidism

deficiency in thyroid hormones causes by thyroid dysfunction, lack of TRH from the hypothalamus or TSH from the anterior pituitary gland, or lack of iodine in the blood

parathyroid glands

made up of parafollicular cells called chief cells and oxyphil cells, the parathyroid gland chief cells release PTH to increase levels of calcium, magnesium, and phosphate ions in the blood via bone respiration (breakdown)

antagonistic hormones in the endocrine system

insulin and glucagon, PTH and calcitonin,

adrenal cortex

produces steroid hormones mineralocorticoids, glucocorticoids, and androgens in the outer glomerulosa, middle fasciculata, and inner reticularis respectively

aldosterone

regulates blood pressure and blood volume through the RAA pathway in response to dehydration, hemorrhaging, or sodium deficiency; also regulates levels of K+, Na+, and H+ in the blood to prevent acidosis

glucocorticoid function

protein breakdown, neoglycogenesis, lipolysis, stress response/resistance, anti inflammatory, and immune response depression

glucocorticoid negative feedback cycle

low glucocorticoids stimulates the hypothalamus to release CRH, which triggers the release of ATCH from the anterior pituitary, which then causes the adrenal cortex to release glucocorticoids as a homeostatic response

adrenal medulla

modified sympathetic ganglion of the autonomic nervous system made of chromaffin cells, which synthesize and release epinephrine and norepinephrine to augment the fight or flight response of the sympathetic nervous system

suprachiasmatic nucleus

the body’s internal biological clock located in the hypothalamus that establishes circadian (daily) rhythms (theoretically) in sync with the light/dark cycle based on visual input relayed to the retinohypothalamic tract

pineal gland

secretes melatonin, which is derived from tryptophan, to induce sleep, protect against free radicals, and regulate circadian rhythms

pancreas

the endocrine portion has cells called pancreatic leaflets that secrete hormones as part of the endocrine system: alpha cells secrete glucagon, beta cells secrete insulin, and delta cells secrete somatostatin

insulin uptake

insulin binds to an insulin receptor tyrosine kinase, cross phosphorylation occurs, insulin receptor substrates bind to the active (phosphorylated) sites and then trigger intracellular pathways for glucose transporters to bring glucose into the cell, thus lowering blood sugar levels

insulin functions

glycogenesis to turn glucose into glycogen in liver and skeletal muscle cells, inhibit catabolic processes that release glucose (glycogenolysis), and promote synthesis of triglycerides and proteins from preexisting fatty acids and amino acids

glucagon

targets hepatocytes to break down large glycogen molecules into smaller, usable glucose molecules through catabolic processes and the Gs adenylyl cyclase cAMP pathway

glucagon function

antagonistic functions to insulin, so glucagon forms glucose from non-carb sources and breaks down triglycerides and proteins into smaller components

stomach

produces ghrelin for stimulating appetite and gastrin for digestive juice secretion and digestive motility

skin and kidneys

contribute to the absorption of the active form of vitamin D3 as cholecalciferol and calcitriol are produced by the respective organs; vitamin D is crucial for calcium absorption into the blood stream

placenta

serves as the site of nutrient and waste exchange between the mother and the fetus during pregnancy and secretes several hormones involved in child development and mammary preparation

cause of craving for salty foods

an excess of aldosterone is released in response to low sodium levels in the blood

somatostatin

is released by delta cells of the pancreas and inhibits secretion of glucagon, insulin, and growth hormones. also slows nutrient absorption during digestion. can inhibit and be inhibited by the pancreatic polypeptide.

go to G protein IP3 receptors on the uterus, mammary glands, and kidneys for water reabsorption

oxytocin and ADH

FSH, LH, ATCH, TSH, CRH, PTH, calcitonin, glucagon

go adenylyl cyclase cAMP receptor

atrial natriuretic peptide hormone (ANP)

binds to guanylyl cyclase cGMP receptor; secreted by the heart to prevent high BP → goes to kidney cells and circulatory cells to regulate BP and BV by excretion of sodium and excess juices through urinary system and inhibits na+ reabsorption

insulin

goes to tyrosine kinase receptor on skeletal muscle cells, liver cells, beta pancreatic cells, cardiac cells, and adipose cells

prolactin, GH

go to janus kinase STAT receptor on mammary cells and chondrocytes respectively

glucocorticoids, aldosterone, cortisol, T3 and T4; estrogen, testosterone, and progesterone

go to steroid receptors on every cell; the gonads

placenta hormones

estrogen, progesterone, and relaxin

adipose tissue hormone

leptin, which triggers satiety cues

digestive endocrine secretions

gastrin for stomach acid, CCK for bile secretion, ghrelin for appetite, and secretin for pancreatic enzyme flow

testosterone

descent of testes before birth, sperm production, secondary male sex characteristics

inhibin

inhibits secretion of FSH in both males and females

relaxin

encourages relaxation of the uterus so that it is easier for a fertilized egg to implant in the uterine wall

estrogen types

estradiol and estrone

androgen insensitivity syndrome

there is an absence/deficiency of testosterone and DHT receptors in a genetically male embryo, leading to internal testes and female appearance

hyperglycemia

triggers beta cell secretion of insulin to promote glucose uptake and glycogenesis; hypoglycemia inhibits insulin release and stimulates glucagon to keep blood sugar from dropping excessively

hypoglycemia

triggers alpha cell secretion of glucagon for glycogenolysis and gluconeogenesis in hepatocytes, causing blood sugar to rise; hyperglycemic conditions inhibit glucagon release and stimulate insulin release to regulate blood sugar levels

pancreatic islets/islets of langerhans

where pancreatic endocrine cells are

melatonin

secretion by the pineal gland is monitored by visual input into the suprachiasmatic nucleus of the hypothalamus; inhibits melanin and reproductive functions in animals in accordance with the seasons

dehydroepiandrosterone (DHEA)

adrenal androgen prominent in females as it is the source of libido and estrogens post menopause

renin-angiotensin-aldosterone secretion (RAAS) pathway

decrease in BP and BV due to dehydration, electrolyte deficiency, or hemorrhaging prompts liver to secrete angiotensinogen and juxtaglomerular cells of the kidneys to secrete renin → we now have angiotensin 1 which gets converted to angiotensin 2 by ACE in the lungs → angiotensin 2 causes aldosterone secretion by adrenal cortex to get kidneys to increase BV and sodium levels in the blood while also filtering out excess K+ and H+ into the urine; angiotensin 2 also prompts vasoconstriction of arterioles → BP and BV is normal

go find romance MEN and make good soup

glomerulosa → mineralcorticoids, fasciculata → glucocorticoids, reticular → androgens/sex hormones; the adrenal medulla secretes epinephrine and norepinephrine

blood calcium homeostasis

high ca levels trigger thyroid parafollicular cells to release calcitonin, which inhinits osteoclasts and thus lowers ca levels → low ca levels stimulate parathyroid chief cells to secrete PTH which promotes ca retention and secretion from bones into the blood stream; PTH also tells kidneys to release calcitriol which promotes ca absorption from food → ca level is high again

posterior pituitary gland hormones

oxytocin and antidiuretic hormone (ADH)

anterior pituitary gland hormones

growth, thyroid stimulating, adrenocorticotropic, prolactin, follicle stimulating, and luteinizing hormones

follicular thyroid cells synthesis process

produce T3 and T4 (triiodothyronine and thyroxine): iodide is picked up from the blood and transported into the colloid via thyroglobulin from the rough ER → iodide is oxidized into iodine and binds to tyrosine rings with thyroglobulin → MIT and DIT couple into T4 (monodeiodinization makes T3) → pinocytosis and digestion of colloid into the follicular cell before T3 and T4 enter the bloodstream with thyroxine-binding globulin for transport

T3 and T4 functions

initiate changes in gene transcription (protein synthesis especially), increase basal metabolic rate, regulate growth and development, and permissively enhance actions of catecholamines (NE, E, and dopamine)

T3/T4 secretion

T4 is secreted in a larger quantity than T3 but T3 is much more potent; T4 often gets converted into T3 in the liver and kidney

T3/T4 regulation

negative feedback! low T3/T4 levels stimulate TRH release by hypothalamus to get the anterior pituitary gland to secrete TSH to the thyroid, which then releases T3 and T4

vitamin D

enhances ca absorption in intestines: uv light creates cholecalciferol in the skin, which then gets converted into 25 hydroxycholecalciferol and then becomes calcitriol, the active form of vitamin D in the body

bone growth

occurs at epiphyseal plates thanks to osteoblasts. as bones get taller, osteoblasts thicken them to sustain strength (and also get stronger/thicker if you exercise!). insulin-like growth factors, GH, and sex hormones promote bone growth during childhood and puberty and bone remodeling during adulthood

stress response

short term/alarm reaction: epinephrine and norepinephrine from the adrenal medulla trigger sympathetic fight-or-flight responses

long term stress resistance reaction: cortisol from the adrenal cortex triggers lipid and protein catabolism to make glucose, GH tells the liver to metabolize lipids, and glucose is used to produce ATP thanks to the thyroid hormones