SM02 Mini4 Flashcards
what is the embryologic origin of the adenohypophysis?
oral ectoderm
evaginates to form Rathke’s pouch
what is the embryologic origin of the neurohypophysis?
neural ectoderm
extension of hypothalamus
where is the pars tuberalis?
with the pars intermedia connects the adenohypophysis to the hypothalamus
what is the infundibulum?
the stalk that connects the pituitary gland to the hypothalamus
describe the hypophyseal portal system.
- hypothalamus secretes hormones into primary capillary plexus
- internal carotid artery→ superior hypophyseal artery→ primary capillary plexus (pars tuberalis)→ hypophyseal portal veins→ secondary capillary plexus (pars distalis)
where does the blood from the pituitary drain?
into the cavernous sinus
what does the inferior hypophyseal arteries supply?
the posterior pituitary or pars nervosa of the neurohypophysis
what cells of the adenohypophysis stain acidophilic?
(red/pink)
somatotrophs & mammotrophs
what does the somatotrophs produces & secrete?
growth hormone (somatotropin)
50% of cells in adenohypophysis
what does the mammotrophs produce & secrete?
prolactin
15% of cells in adenohypophysis
what cells of the adenohypophysis stain basophilic?
thyrotrophs
corticotrophs
gonadotrophs
what do the gonadotroph produce & secrete?
LH & FSH
most cells produce both, but some only produce one or the other
10% of cells in adenohypophysis
what do the corticotrophs produce and secrete?
proopiomelanocortin
which is then chopped into ACTH, lipotropin, MSH, & beta-endorphin
20% of cell in adenohypophysis
what is produced & secreted by the thyrotrophs?
TSH
5% of cells in adenohypophysis
what cells are found in the adenohypophysis?
- acidophils
- somatotrophs
- mammotrophs
- basophilic
- thyrotrophs
- corticotrophs
- gonadotrophs
- chromophobes
- folliculostellate cells
what is the function of folliculostellate cells?
support parenchyma or network of intercommunication w/each other
what is the function of the intermediate lobe of the pituitary gland?
none
vestigial in humans
colloid-filled cysts w/some scattered groups of basophilic cells
what cell type is this?
GH cells
what cell type is this?
TSH cells
what cell type is this?
adrenocorticotrophs
what cell type is this?
LH cells
what is the function of somatostatin in the pituitary?
inhibiting production & release of growth hormone
what is the function of dopamine in the pituitary?
inhibiting production & release of prolactin, which is otherwise constituitively released
what is the function of FSH?
promotes ovarian follicle development & estrogen secretion in women
stimulates spermatogenesis in men
what is the function of LH?
promotes ovarian follicle maturation & progesterone secretion in women
Leydig cell stimluation & androgen secretion in men
how is release of ACTH controlled?
via negative feedback
adrenal cortex hormones that are stimulated to release by corticotropin (ACTH) inhibits the release of ACTH by the pituitary & inhibits the release of CRH from teh hypothalamus
how is TSH controlled?
stimulated release by TRH
inhibited by T3 & T4 (thyroid hormones)→ these also inhibit the release of TRH
what are pituicytes?
supporting cells of the pars nervosa of the neurohypophysis
how are hormones released into the posterior pituitary?
neurons of the supraoptic & paraventricular nuclei of the hypothalamus extend unmyelinated axons
axons form hypothalamohypophyseal tract
axons terminate near fenestrated capillaries in pars nervosa
what are Herring bodies?
swellings of axons that contain hormones
what part of the brain lacks a BBB?
pineal gland
describe the embryologic development of the pineal gland.
- dorsal diverticulum of diencephalon during W10
- vesicular wall thickens, lumen occluded except at base of outpocket
- pineal recess communicates w/3rd ventricle
- formation of compact structure containing pinealocytes & glial-like interstitial cell
- both derived from neuroepithelial cells
- meninges envelop & invade to form connective tissue septa
which cells are responsible for melatonin production & secretion?
pinealocytes
what is brain sand?
corpora arenacea
calcified extracellular concteion of CaPO4 & CaCO3
what is used as a radiological marker in the pineal gland?
corpora arenacea
how can pinealocytes be identified?
accumulations of golden brown lipofuscin in their cytoplasm
how does melatonin get into the blood stream from pinealocytes?
via long cytoplasmic processes w/bulbous expansions that terminate near fenestrated capillaries
release is triggered by unmyelinated sympathetic nerve fibers from the superior cervical ganglion that enter pineal gland
describe the signaling pathway that inhibits melatonin release.
- light signals conducted to suprachiasmatic nucleus (SCN) in hypothalamus by retinohypothalamic tract
- intermediolateral cell column of thoracic spinal cord via hypothalamospinal tract
- preganglionic fibers to superior cervical ganglion
- postganglionic sympathetic fibers from superior cervical ganglion
- unmyelinated ends enter pineal gland
- inhibits melatonin release
- meltonin simtulated release in darkness
what stimulates melatonin release?
in the dark, postganglionic sympathetic neurons release norepinephrine
activates beta adrenergic receptors
increase in N-acetyltransferase activity
stimulates melatonin synthesis & release
why is melatonin only made in the pineal gland?
only location of hydroxyindole-O-methyltransferase
the enzyme needed to synthesize melatonin
where are the islets of Langerhans found?
scattered among the pancreati acini
what does the ventral diverticulum of the foregut give rise to?
common bile duct
gallbladder
liver
ventral pancreatic anlage
what is the ventral pancreatic anlage?
becomes a portion of the head of the pancreas & uncinate portion of the pancreasw/its ductal system
where is the minor papilla derived from?
dorsal anlage
how is the main pancreatic duct formed?
fusion of the duct systems from teh dorsal and ventral pancreatic anlages
what is a distinguishing characteristic of teh exocrine pancreatic glands?
presence of centroacinar cell in center of acinus
3-4 form the beginning of the duct system from teh acinus
usually seen w/in an acinus
how do pancreatic acini stain?
blue at the base due to high RNA & nuclei content
pink at their apex due to high zymogen protein content in granules
which cells have secretin receptors?
centroacinar cells
describe the flow of pancreatic exocrine products.
- acinar cells
- acinar tubules
- intralobular ducts (intercalated ducts)
- interlobular ducts
- main pancreatic duct (duct of Wirsung)
what type of cells line the main pancreatic duct?
single layer of cuboidal duct cells
function of pancreatic acinar cells
production & secretion of amylase, lipase, reibonuclesase, deoxyribonuclease, trypsinogen, chymotrypsin, procarboxypeptidase, elastase
pancreatic enzyme release is stimulated by?
cholecystokinin (from duodenum) & ACh (from parasympathetic fibers)
function of the pancreatic ductal cells
production & secretion of bicarbonate-rich alkaline fluid
how can the cells found in the islet of Langerhans be differentiated?
they must be stained for their products (in granules)
in order of predominance, what are the different cell types in the islets of Langerhans?
beta cells
alpha cells
delta cells
which cell type is typically found in the periphery of the islet of Langerhans?
alpha cells
how are the islets of Langerhans supplied with blood?
via insuloacinar portal system
describe the embryologic origin of the thyroid gland.
- forms late in W4 from endoderm at floor of pharynz by the foramen cecum on developing tongue
- descends in front of gut as bilobed diverticulum
- connected to tongue via thryoglossal duct
- final position in W7
what are the hormones produced by the follicular cells & parafollicular cells?
follicular (thyroid) cells: T3 & T4
parafollicular cells: calcitonin
what are the distinguish features between parafollicular and follicular cells?
folliular cells are arranged around the colloid & in single (simple) squamous to columnar
parafollicular cells stain lighter & have secretory granules of calcitonin & have no contact w/colloid
what are parafollicular cells derived from?
neural crest cells
migrated from ultimobranchial body of 4th pharyngeal arch
what stimulates calcitonin release?
high blood serum levels of Ca2+
where & how does calcitonin exert its effects?
on osteoclasts
- inhibit bone reabsorption
- increase Ca2+ retention by bones
- decrease Ca2+ & PO42- levels in blood
where are TSH receptors found?
on the basal surface of follicular cells
what is thyroglobulin?
precursor protein of thyroid hormones
synthesized in rER
post-translationally glycosylated in rER & Golgi
released via exocytosis into lumen of follicle
how is iodide brought into follicular cells?
Na+/I- symporter on basal surface of follicular cells
how does iodide get into the lumen of the follicle?
via pendrin
an I-/Cl- antiporter in the apical surface of follicular cells
why is H2O2 needed in the follicular lumen?
for function of thyroid peroxidase on the apical surface of follicular cells to oxidize iodide to iodine
iodine is more reactive form for conjugation into hormone
how is T3 formed?
couple of one MIT & one DIT
how is T4 formed?
coupling of two DITs
describe the pathway of thyroid hormone release.
- TSH stimulates endocytosis of iodinated TGB into follicular cells
- lysosomal pathway
- endosome fuses w/lysosome
- TGB degraded into aa, carbs, free MIT, free DIT, T3, T4
- all released into cytosol
- MIT & DIT reused
- T3 & T4 enter capillary at basal surface
- transepithelial pathway
- TGB binds transmembrane megalin
- transported directly from apical to basal surfaces
- usually only seen in pathological conditions
what causes the most severe cretinism?
maternal hypothyroidism
b/c fetal thyroid doesn begin to function until W14
cause of cretinism
congenital hypothyroidism
hyposecretion of thyroid hormones during fetal life or infancy