LEC61: Endrocrine II Flashcards
components of endocrine II
1) thyroid, C (parafollicular) cells
2) parathyroid
3) adrenal- cortex & medulla
4) pancrease- islets of langerhans
5) diffuse endocrine system
where is thyroid gland?
extends from middle of thyroid cartilage > tracheal rings 3-4
has R and L lobes, connected by CT fiber, isthmus, at tracheal ring 1 level
covered by capsule
what are thyroid follicles? contain what? how many are there ?how long do their contents last for?
structural unit of lobules of thyroid gland
20 million follicles/lobe of thyroid gland
store sufficient thyroid hormone to last for 3 months
what is in lumen of thyroid follicles?
thyroglobulin
what is this? what is in center?
what are these
thyroid gland’s lobes, lobucles, follicles
what is thyroglobulin?
high molecular weight (660 kda) tyrosine-rich glycoprotein
iodinated
for storage of thyroid hormones in lumen of follicles
forms of thyroid hormones? and what are thyroid hormones?
T3, triiodothyronine
T4, tetraiodothyronine (thyroxine)
are iodine-containing tyrosine molecules
4 stages of synthesis/storage of thyroid hormones by follicular cells
1) follicular cells synthesize thyroglobulin
2) iodide pump at basal plasma membrane uptakes iodide from the blood
3) thyroid peroxidase oxidizes iodide to iodine, at apical plasma membrane
4) tyrosine residues of thyroglobulin in lumen of follicles are iodinated to form T4 and T3
TSH funciotn re: forming T3 and T4
TSH controls process of thyroglobulin > T4 and T3
how does T3 triiodothyronine form
1 molecule monoiodotyrosine + 1 molecule diiodotyrosine = triiodothyronine, T3
how does thyroxine, T4, form?
1 molecule diiodotyrosine + 1 molecule diiodotyrosine = T4, thyroxine
what regulations thyroid hormone production?
hypothalamus, anteiror pituitary, and feedback mechanism
difference btwn T3, T4?
T3 acts more rapidly, more potent than T4
T4 represents 90% of circulating thyroid hormone
both regulate basal metabolic rate
both influence body growth & maturation, including nerve tissue
describe feedback loop of TRH, TSH, T3 and T4
neural stimulus > hypothalamus
hypothalamus produces TRH, acts on anterior pituitary
anterior pitutary secretes TSH
TSH acts on thyroid to make T3 and T4
T3 and T4 effect target tissues
T3 and T4’s production by thyroid acts as negative feedback on hypothalamus and anteiror pituitary
what is thyroid c cell
aka parafollicular cells
neuroendocrine cells in the thyroid with primary function to secrete calcitonin
comprise 0.1% of mass of thyroid
derived from neural crest
what is this, what is its fxn
thyroid c cells aka parafollicular cells
secrete calcitonin
what is arrow pointing to
thyroid c cells aka parafollicular cells
secrete calcitonin
best way to identify c cells?
immunohistochemistry with antibody made against calcitonin, which localizes C cell since C cell makes concitonin
what is this
immunostaining for C cells using calcitonin ab
what is in the granules
calcitonin
c cells/parafollicular cells of thyroid gland
when is calcitonin secreted & what is its effect?
is stimulated by high blood calcium levels
suppresses osteoclast activity on bone resorption, so lowers blood calcium levels
opposses action of parathyroid hormone (which raises blood calcium levels)
what type of molecule is calcitonin?
a polypeptide
how many parathyroid glands?
4
ID the parathyroid glands
where is parathyroid
parathyroid is embedded under capsule of thyroid
chief cells fxn
secrete the parathyroid hormone
oxyphil cells are?
2nd type of cells in parathyroid
do not make hormone
appear during puberty, their # increases with aging
2 types of cells in parathyroid
1) chief cells
2) oxyphil cells
identify these cells
chief cells, oxyphil cells of parathyroid gland
in older people, what types of cells in parathyroid?
chief cells, oxyphil cells, but also FAT cells
what is this? ID diff structures
older person’s parathyroid, with fat cells taking up 40%
what does parathyroid hormone do? how?
parathyroid hormone raises blood calcium levels. by
1) promotes calcium abroption from intestine, mediated by vitamin D synthesis
2) increases reabsorption of calcium from kidney tubules
3) stimulates bone resorption by osteoclasts w/ release of calcium
4) increases calcium release from bony matrix, due to osteocytic osteolysis
how many adrenal glands?
2
what are parts of adrenal gland, what are their embryologic origins?
cortex- arises from mesoderm
medulla- arises from neural crest
ID diff structures
adrenal gland- cortex (mesoderm), medulla (neural crest), cortex
zones of adrenal cortex and their secretions?
zona glomerulosa: mineralcorticoids (aldosterone)
zona fasiculata: glucocorticoids (cortisol)
zona reticularis: androgens
what is this
zones of the adrenal cortex
what is glucocorticoid secretion mediated by, how does it work?
renin-angiotensin-aldosterone system mediates secretion
decreased bp acts on kidney distal tubules, causes decreased [Na]
decreased [Na] causes kidney to secrete renin
renin acts on other systems, to produce angiotensin II, vascoconstrictor
angiotensis II acts on zona glomerulosa to stimulate aldosterone secretion
aldosterone goes to kidney tubules to increase Na reabsorption in tubules
Na reabsorption in kidney tubules > increased bp!
what is this
zona fasiculata of adrenal cortex
secrete glucocorticoids (cortisol)
notice fenestrated capillaries lining columns on both sides b/c ENDOCRINE secretion
what regulations glucocorticoid production? how does it work?
hypothalamis, anterior pituitary, feedback mechanism
hypothalamus secretes CRH. this acts on anterior pituitary.
anterior pituitary releases ACTH into circulation
ACTH in circulation causes adrenal cortex to secrete glucocorticoids
glucocorticoids’ secretion has negative feedback on hypothalamus and anterior pituitary
glucocorticoids’ function?
regulate carbohydrate, protein, fat metabolism
what is this? what does it secrete?
zona reticularis
secretes androgens
what factors influence histology of adrenal cortex?
stress - if high stress, acts on hypothalamis, which acts on pituitary to release ACTH; cortex becomes hypertrophied
what factors influence histology of adrenal medulla?
none! adrenal medulla is not affected by factors like stress
what is this
adrenal cortex hypertrophy b/c of stress
how do steroid producing cells present?
have characteristic organelles - lipid droplets, mitochondria, SER - but don’t store hormones
what organelles are involved w/ steroid synthesis in adrenal cortex? what do they do?
mitochondrion- form intermediates from cholesterol, pass to smooth ER; after processing in smooth ER, forms steroid hormones like aldosterone, cortisol, which > circulation
smooth ER- processes intermediates
“shuttle mechanism” of mitochondrion > smooth ER > mitochondrion
physical relationship btwn adrenal cortex & medulla?
not actually connected
what are medullary cells considered?
modified postganglionic sympathetic neurons
what is this
adrenal cortex’s zona reticularis, adrenal medulla
what are these? fxn?
adrenal medulla cells
synthesize catecholamines, which stain brown when exposed to chromium, so call medullary cells “chromaffin” cells
lighter= epinephrine (aka A cells, 80%), darker= norepinephrine (aka N cells, 20%)
what mediates catecholamine secretion?
when does it occur?
what division of autonomic system is release pt of?
what does it lead to?
1) mediated by preganglion sympathetic fibers that innervate chromaffin cells
2) occurs in resposne toa acute fear, stress
3) constitutes “fight or flight” response - sympathetic
4) leads to increased bp, faster heart rate, faster breathing rate, elevated blood glucose levels
blood supplies to adrenal medulla?
1) long cortical arteries- supply bed directly to medulla
2) short cortical arteries- carry glucocorticoids from cortex to medulla; pass through zona glomerulosa, zona fasiculata, zona reticularis before > adnreal medulla
what converts norepinephrine > epinephrine?
glucocorticoids
via methylation
parts of pancreas?
head, neck, body, tail
islet of langerhans, function?
endocrine part of pancreas
how many islets of langerhans in pancreas? where are they?
> 1 million islets in pancreas
more islets in tail of pancreas
islets comprise 2% of pancreatic mass
each islet contains ~3000 endocrine cells
what is this
islets of langerhans
what types of cells islets of langerhans contain?
1) beta-cells: insulin-producing cells, lower blood glucose
2) alpha-cells: glucagon-producing cells, raise blood glucose
3) delta-cells: somatostatin, inhibits insulin and/or glucagon secretion via paracrine mechanism
4) PP cells: pancreatic polypeptide cells, inhibits pancreatic enzyme secretion
beta cells of islet of langerhans
produce insulin
alpha cells of islet of langerhans
raise blood glucose
triple IF staining of islet of langerhans
beta cells-green
alpha cells-red
delta cells-blue
what is diffuse endocrine system
endocrine cells scattered diffusely in GI tract, ie in villi and crypt of small intestine
2 types of enteroendocrine cells
endocrine cells of the GI tract and pancreas (islet of langerhans)
open type: microvilli on lumen of intestine
closed type
in both types, cells released into bloodstream or tissue space, not through apex of cell into intestinal lumen
enteroendocrine cell (jejunum)
gastrin location, action
antrum
increase HCl
somatostatin location, action
antrum
decrease gastrin
CCK location, action
duodenum, jejunum
increase pancreatic enzymes
secretin location, action
duodenum, jejunum
increase pancreatic bicarbonate & water
where are enteroendocrine cells in GI tract?
antrum, duodenum/jejunum
relationship/mechanism of action btwn somatostatin & gastrin?
somatostatin inhibits gastrin release
by paracrine mechanism
where and how is appetite controlled?
satiety center of hypothalamus
GI hormones act on satiety center of hypothalamus, affect appetite
what increases appetite?
ghrelin - stomach
what decreases appetite?
leptin - stomach
CCK - duodenum, jejunum
glucagon-like peptide - ileum, colon
PYY - distal ileum, colon
