Endocrine System PP part 2

thyroid gland

butterfly-shaped gland located inferior to larynx and anterior to trachea

right and left lateral lobes connected by an isthmus

-some glands also have a pyramidal lobe projecting from the isthmus

follicular cells are stimulated by TSH to produce

thyroxine (tetraiodothyronine, T4) and triiodothyronine T3 known as thyroid hormones

parafollicular cells produce hormone

calcitonin to help regulate calcium homeostasis

T3 and T4 synthesis and secretion process

iodide trapping

synthesis of TGB

oxidation of iodide

iodination of tyrosine

coupling of T1 and T2

pinocytosis and digestion of colloid

secretion of thyroid hormones

transport in blood

thyroid hormones

increase basal metabolic rate BMR

help maintain normal body temp

stimulate protein synthesis

increase the use of glucose and fatty acids for atp production

thyrotropin-releasing hormone TRH from hypothalamus and thyroid-stimulating hormone TSH from ant pituitary stimulate

synthesis and release of thyroid hormones in a 5 step process

synthesis and release of thyroid hormones 5 step process

low blood levels of T3 and T4 or low metabolic rate stimulates release of TRH

TRH, carried by portal veins to ant pituitary, stimulates release of TSH by thyrotrophs

TSH released into blood stimulates thyroid follicular cells

T3 and T4 released into blood by follicular cells

elevated T3 inhibits release of TRH and TSH (neg feedback)

located on posterior aspect of each lobe of thyroid gland

2 parathyroid glands

one inf and one super

parathyroid glands have 2 types of cells

chief cells (principal cells)

oxyphil cells

chief cells of parathyroid glands

produce parathyroid hormone PTH/parathormone

oxyphil cells parathyroid glands

function is not known in normal parathyroid glands, but secrete excess PTH in cases of parathyroid cancer

calcitonin

produced by thyroid gland

works with PTH and calcitriol to regulate calcium homeostasis

calcium homeostasis

high calcium in blood- thyroid gland releases calcitonin to inhibit osteoclasts

low calcium in blood- parathyroid gland releases PTH to release calcium from bone ecm

low calcium in blood- PTH stimulates kidneys to release calcitriol to stimulate increased absorption of calcium from foods

parathyroid gland hormone

parathyroid hormone PTH

from chief cells

low blood calcium stimulates

high blood calcium inhibits

increases blood calcium and magnesium levels

decreases blood hydrogen phosphate level

promotes formation of calcitriol

adrenal glands

suprarenal glands

on top of each kidney

covered by a connective tissue capsule

two regions of adrenal glands

outer cortex

inner medulla

outer cortex 3 histological regions

zona glomerulosa

zona fasciculata

zona reticularis

zona glomerulosa

secretes hormones mineralocorticoids used to regulate mineral homeostasis

zona fasciculata

secretes hormones glucocorticoids that affect glucose homeostasis

zona reticularis

secretes weak androgens (hormones with masculinizing effects)

aldosterone

major mineralocorticoid secreted by adrenal gland

helps regulate sodium and potassium homeostasis

glucocorticoids

cortisol (hydrocortisone)- most produced

cortisone

corticosterone

secretion of glucocorticoids is regulated by

negative feedback

glucocorticoids help control

protein breakdown

glucose formation

lipolysis

resistance to stress

inflammation

immune responses

major androgen secreted by adrenal cortex

dehydroepiandrosterone DHEA

DHEA

in males, after puberty, testosterone is secreted in much larger quantities so DHEA has virtually no effect

in females, DHEA and other adrenal androgens play a major role in promoting libido and are converted to estrogens

in menopausal women all female estrogens come from adrenal androgens

adrenal medulla is stimulated by

sympathetic preganglionic neurons of ANS

Chromaffin cells

secrete epinephrine and norepinephrine

both are involved in fight-or-flight response

adrenal cortex hormones

mineralocorticoids (mainly aldosterone)

glucocorticoids (mainly cortisol)

androgens (mainly dehydroepiandrosterone)

mineralocorticoids source

zona glomerulosa cells

glucocorticoids source

zona fasciculata cells

androgens source

zona reticularis cells

mineralocorticoids control of secretion

increased blood K+ level and angiotensin II stimulate secretion

glucocorticoids control of secretion

acth stimulates release

corticotropin-releasing hormone promotes acth secretion in response to stress and low blood levels of glucocorticoids

androgens control of secretion

acth stimulates secretion

adrenal medulla hormones

epinephrine and norepinephrine from chromaffin cells

epinephrine and norepinephrine control of secretion

sympathetic preganglionic neurons release acetylcholine which stimulates secretion

mineralocorticoids principal actions

increase blood levels of sodium and water

decrease blood level of potassium

glucocorticoids principal actions

increase protein breakdown except in liver

stimulate gluconeogenesis and lipolysis, provide resistance to stress, dampen inflammation, depress immune responses

androgens principal actions

assist in early growth of axillary and pubic hair in both sexes

in females, contribute to libido and are source of estrogens after menopause

epinephrine and norepinephrine principal actions

enhance effects of sympathetic division of autonomic nervous system ANS during stress

pancreas

in curve of duodenum

is both endocrine and exocrine gland

acini

clusters that almost all exocrine cells of pancreas are arranged in

what do acini produce

digestive enzymes that are delivered to gi tract through ducts

scattered among acini are clusters of endocrine tissue called

pancreatic islets/islets of Langerhans

pancreatic islets contain

secretin cells

islets 4 types of cells that secrete dif hormones

alpha a cells

beta b cells

delta d cells

f cells

alpha cells secrete

glucagon

beta cells secrete

insulin

delta cells secrete

somatostatin

f cells secrete

pancreatic polypeptide

pancreatic islet hormones

glucagon

insulin

somatostatin

pancreatic polypeptide

glucagon control of secretion

decreased blood level of glucose, exercise, and mainly protein meals stimulate secretion

somatostatin and insulin inhibit secretion

glucagon principal actions

raises blood glucose level by accelerating breakdown of glycogen into glucose in liver (glycogenolysis), converting other nutrients into glucose in liver (gluconeogenesis), and releasing glucose into blood

insulin control of secretion

stimulates secretion:

increased blood level of glucose, acetylcholine (released by parasympathetic vagus nerve fibers)

arginine and leucine (2 amino acids)

glucagon

GIP

GH

ACTH

inhibits secretion:

somatostatin inhibits secretion

insulin principal actions

lowers blood glucose level by accelerating transport of glucose into cells, converting glucose into glycogen (glycogenesis), and decreasing glycogenolysis and gluconeogenesis

increases lipogenesis and stimulates protein synthesis

secretion of insulin and glucagon are controlled by

negative feedback

glucagon negative feedback loop

low blood glucose stimulates alpha cells to secrete glucagon

glucagon acts on liver cells to convert glycogen into glucose and to form glucose from lactic acid and certain amino acids

glucose released by liver cells raises blood glucose level to normal

if blood glucose continues to rise, hyperglycemia inhibits release of glucagon

insulin negative feedback loop

high blood glucose stimulates beta cells to secrete insulin

insulin acts on various body cells

blood glucose level falls

if blood glucose continues to fall hypoglycemia inhibits release of insulin

insulin acts on various body cells to

accelerate facilitated diffusion of glucose into cells

speed conversion of glucose into glycogen

increase uptake of amino acids and increase protein synthesis

speed synthesis of fatty acids

gonads

ovaries and testes

gonads produce

gametes

oocytes and sperm

ovaries produce

two estrogens- estradiol and estrone

progesterone

relaxin

inhibin

testes produce

testosterone

ovarian hormones

estrogens and progesterone

relaxin RLX

inhibin

estrogens and progesterone

together with gonadotropic hormones of ant pituitary, regulate female reproductive cycle, maintain pregnancy, prepare mammary glands for lactation, and promote development and maintenance of female secondary characteristics

relaxin RLX principal actions

increases flexibility of pubic symphysis during pregnancy

helps dilate uterine cervix during labor and delivery

inhibin principal actions

inhibits secretion of FSH from ant pituitary

testicular hormones

testosterone

inhibin

testosterone principal actions

stimulates descent of testes before birth

regulates sperm production

promotes development and maintenance of male secondary sex characteristics

inhibin principal actions

inhibits secretion of FSH from ant pituitary

pineal gland

attached to roof of third ventricle of brain and secretes melatonin

melatonin

helps to regulate body’s biological clock

thymus

behind sternum between lungs

produces thymosin, thymic humoral factor THF, thymic factor TF, and thymopoietin

thymosin, thymic humoral factor THF, thymic factor TF, thymopoietin

these hormones promote maturation of immune system’s T cells