Histology of Endocrine Organs Flashcards
How does the endocrine sys vary from the nervous sys?
nervous = needs membrane depolarization; quick and short-lived
endocrine = distributed throughout body, bind to spec receptors; slower but longer
*some neurons secrete hormones*
What are the 3 classes of hormones?
peptide/proteins: largest class (GH, PTH)
biogenic amines: produced by altering specific AAs (Thyroid hormone, epinephrine)
steroid hormones: lipids derived from cholesterol (estrogen, testosterone)
What are teh 3 stimuli controlling hormone release?
humoral = release controlled by monitoring levels of ions and nutrients
neuronal = release stimulated by nerve signals
hormonal = release caused by hormone by another endocrine organ or cell
What embryonic tissue are endocrine glands derived from?
ectoderm
How are endocrine glands generally organized?
epitheliod cells arranged as cords/follicles and some as isolated individual cells
*well vascularized
Where is the hypothalamus located?
below thalamus
behind optic chiasma
surrounding the 3rd ventricle
Upon which bone does the pituitary gland sit?
hypophyseal fossa of the sphenoid bone
How is the pituitary gland attached to the hypothalamus?
by thin stalk = infundibulum
How are the hypothalamus and the posterior pituitary connected?
hypothalamus produces oxytocin and ADH –> stored and released by the post pit
What are the direct targets of hypothalamic hormones?
releasing and inhibiting hormones –> ant pit
oxytocin and ADH –> post pit –> kidney and uterus
sympathetic innervation –> adrenal medulla
What are the 5 main organs indirectly influenced by the hypothalamus?
thyroid
adrenal cortex
mammary gland
gonads
bone
What is the basic embryologic origin of the pituitary?
ectodermal placode –> rathke’s pouch at 3 weeks –> near final location by 8 weeks
infundibulum forms post pit and infundibular stalk
rathke’s pouch forms rest of pituitary
What types of cells make up the posterior pituitary?
axons from hypothalamus and support/glial cells
(axons carry ADH and oxytocin)
What is the pars distalis?
Pars nervosa?
pars distalis = anterior pituitary
pars nervosa = posterior pituitary
What are the major cell types in the anterior pituitary?
somatotrophic (GH)
thyrotropic (TSH)
corticotropic (ACTH and MSH)
gonadotropic (FSH and LH)
mammotropic (prolactin)
What cells are acidophils in the ant pit?
somatotrophs
mammotrophs
What cells are basophils (stain dark purple) in the ant pit?
corticotrophs
thyrotrophs
gonadotrophs
What is the pars intermedia?
btw pars distalis and pars nervosa
function unknown
small basophils and colloid-filled follicles lined by cuboidal epithelium
What cell types are found in the pars nervosa?
unmyelinated axons
herring bodies in axons = expanded nerve terminals storing ADH/oxytocin
pituicytes (glial-like)
fenestrated capillaries
What are the 2 parts of the infundibulum?
neural portion = connecting pars nervosa and hypothalamus; unmyelinated axons
adenohypophysis = surrounding pars tuberalis enveloping infundibular stalk; cuboidal cells arranged in cords
What makes up the hypophyseal portal system?
superior hypophyseal artery –> goes to stalk –> capillary bed to pick up hormones from hypothalamus –> hypophyseal portal vs –> secondary capillary plexus in ant pit to get hormones from ant pit
What is the blood supply like in the posterior pituitary?
inferior hypophyseal artery goes in –> ADH and oxytocin go into fenestrated capillaries (single capillary bed) –> blood goes out through single vein
What is gigantism?
excess production of GH due to tumor
if before growth plates close –> can grow to 8 feet tall
if after plates close –> enlargement of extremities and organs
What are pituitary dwarfs?
hyposecretion of GH –> normal body proportion, but rarely exceed 4 feet tall
Where is the pineal gland?
out pocketing of diencephalon’s roof of 3rd ventricle
covered in pia mater
What does the pineal gland produce?
melatonin
serotonin
What cells make up the pineal gland?
pinealocytes
neuroglia
calcified granular material (brain sand) = important marker for midline brain
What vessels supply the thyroid?
superior thyroid vessels
inferior thyroid vessels
What characterizes the histology of the thyroid?
follicles = simple cuboidal to columnar epithelium surrounding colloid
How does the thyroid store hormones and why is this distinct?
thyroglobulin = storage form of T3 and T4
stored in colloid = outside the cell
only gland to store hormone outside the cell
How does thyroid histology vary based on activity?
follicular cells look more columnar if synthesizing or secreting a lot (more active)
How is thyroid hormone synthesized?
thyroglob synthesized in RER –> glycosylated in the golgi –> secreted by exocytosis into lumen of follicle
How is thyroid hormone secreted?
iodinated apical surface –> T3 and T4 bound to thyroglobulin –> TSH stim endocytosis of thyroglob –> T3 and T4 freed –> released from basal surface of follicle cell into circulation
What are parafollicular C cells?
cells in thyroid that lie just outside follicles; stain lighter
secrete calcitonin –> lowers calcium levels thru kidneys, osteoclasts, and osteoblasts
What is the basic hypothalamic-ant pit-thyroid axis?
Stimulus (low body temp) –> hypothalamus secretes thyroitropin-releasing hormone (TRH) –> ant pit releases TSH –> follicular cells release TH –> act on target cells –> heat production in target cells sensed by hypothalamus –> TRH reduced
TH also blocks interactions of TRH on ant pit
Where are parathyroid glands located?
What do they do?
on posterior surface of the thyroid gland
release PTH –> regulates serum calcium and phosphate levels
What are the cell types in the parathyroid?
chief/ principle cells: release PTH, smaller and stain darker
oxyphil cells: function unknown, darker and stain lighter
How is calcium regulated by PTH?
blood levels drop below 9.6 mg/dL –> PTH released
osteoclasts –> resorb bone and release its calcium stores
kidneys –> reabsorb Ca; convert Vit to calcitriol –> increases Ca absorption by intestines
blood Ca increases –> further PTH inhibited
What are the zones of the adrenal gland from superficial to deep and what do they release?
capsule
zona glomerulosa: mineralcorticoids (aldosterone)
zona fasciculata: glucocorticoids
zona reticularis: androgens
adrenal medulla: NE and Epi
What types of cells release epi and NE?
chromaffin cells in medulla = clusters of large, spherical cells
epi cells = smaller w/ lighter granules
norepi cells = larger with darker granules
What is Cushing’s syndrome caused by?
hypersecretion of glucorticoids
either ACTH-secreting pit tumor or tumor in adrenal cortex
What is addison’s disease?
hyposecretion of usually both glucocorticoids and mineralcorticoids
What is the endocrine portion of the pancreas?
pancreatic islets = lightly stained blobs amongst acini
What are the cell types in the endocrine pancreas?
alpha cells: secrete glucagon
beta cells: secrete insulin
delta cells: secrete somatostatin
F cells: secrete pancreatic polypeptide
What does somatostatin do?
released by pancreatic delta cells –> slows release of insulin and glucagon
stimulated by high levels of nutrients in blood
What does pancreatic polypeptide do?
secreted by pancreatic F cells –> inhibits release of somatostatin
How is the pancreas supplied with blood?
dual supply: acinar and insuloacinar
blood goes thru insuloacinar –> capillaries leaving islets go to acini –> hormones have local action on acini
independent acinar vascular sys also supplies acini
