unit 15 Flashcards
what are endocrine glands
tissues in which hormone secreting cells make up most of the parenchyma
where are hormones exerting endocrine action released
into the interstitial and then enter the blood stream for transport
where are aggregates of secretory cells embedded
in highly vascularized CT, no ducts are associated with secretory cells
what is different about secretory cells
resemble epithelial cells but lack free surface
how are secretory cells usually arranged
into cords or clusters and surrounded by an extensive capillary network
where are secretory cells derived from
most from CNS, neural crest, or gut tube epithelium, a few have mesenchymal origin
what are the four types of hormones
glycoproteins (mostly water-soluble)
protein or peptide (water)
amino acid derivatives (water)
steroids (lipid)
anterior pituitary
composed of glandular, densely packed epithelium
derived from ectoderm
stains darkly
not directly attached to the hypothalamus
aka adenohypophysis
posterior pituitary
composed of neural secretory tissue
derived from neuroectoderm
less cellular, appears streaky, stains lightly
directly attaches to the hypothalamus
aka neurohypophysis
pituitary development
regions of the posterior pituitary
pars nervosa - larger portion
infundibulum - continuous with median eminence
anterior pituitary regions
pars distalis
pars intermedia
pars tuberalis
pars distalis
bulk of anterior pituitary, arises from thickened anterior wall of Rathke’s pouch
composed of strongly staining secretory cells surrounded by fenestrated capillaries and minimal CT with reticular fibers
pars intermedia
thin remnant of posterior wall of Rathke’s pouch, abuts the pars distalis
pars tuberalis
sheath of tissue around infundibulum, developed from thickened lateral wall of Rathke’s pouch
what are the 3 cell types found in pars distalis
acidophils (40%), basophils (10%), chromophobes (50%)
what are chromophobes
heterogeneous group of cells including stem/progenitor cells and degranulated acidophils & basophils
what are the two types of acidophils
somatotrophs and lactotrophs
somatotrophs
secrete somatotropin (aka GH)
GH increases metabolic rate, induces liver to produce insulin-like growth factor 1 (IGF-1), stimulate bone and muscle growth
what affects somatotrophs
stimulated by GHRH, inhibited by somatostatin
lactotrophs
secrete prolactin
promotes androgen secretion in males and mammary gland development/lactation in female
large polygonal cells with oval nuclei
what affects lactotrophs
no dedicated releasing hormone, various factors promote secretion though
dopamine inhibits secretion
what do acidophils contain
cytoplasmic secretory vesicles containing peptide! hormone product
what are the 3 types of basophils
corticotrophs, gonadotrophs, thyrotrophs
corticotrophs
synthesize POMC, precursor to ACTH
ACTH stimulates synthesis & release of hormones from adrenal cortex
what affects corticotrophs
secretion stimulated by CRH, inhibited by high plasma cortisol levels
gonadotrophs
secrete FSH and LH
stimulate follicle growth, ovulation, sex hormone production
gonadotrophs location
small oval cells with round eccentric nuclei, scattered throughout pars distalis
what affects gonadotrophs
secretion stimulated GnRH, inhibited by high plasma levels of sex hormones
thyrotrophs
secrete thyrotropin (TSH), acts on follicular cells of the thyroid gland to stimulate production of thyroid hormones
what affects thyrotrophs
secretion stimulated by TRH, inhibited by high plasma thyroid hormone levels
pars intermedia
contains colloid-filled cysts (Rathke cysts) lined by cuboidal cells and clusters of basophil-like cells
what are Rathke cysts
remnants of Rathke pouch
pars tuberalis
highly vascular area containing large vessels if the hypothalamohypophyseal portal system with associated small clusters/cords of cells associated with BVs
contains nests of squamous cells and small follicles lined by cuboidal cells
what does the superior hypophyseal portal system supply directly
pars tuberalis, infundibulum, median eminence (contains termini of neurosecretory neurons producing releasing inhibitory hormones
what does the superior hypophyseal artery form
primary fenestrated capillary plexus
where does the primary capillary plexus drain
hypophyseal portal veins
what do hypophyseal portal veins form
secondary capillary plexus in pars distalis
what surrounds acidophils, basophils, chromophobes
fenestrated capillaries
what acts on pars distalis
releasing/inhibitory hormones
where does the secondary capillary plexus drain
into hypophyseal veins
is the posterior lobe of pituitary an endocrine gland
NO
what is the infundibulum continuous with? what does it contain?
median eminence
axons of hypothalamic neurosecretory cells traveling as hypothalamic hypophyseal tract
what does the pars nervosa contain
axons and termini of hypothalamic neurosecretory cells; axons terminate near capillaries of capillary plexus of nervosa
where are peptide hormones produced? what is well developed in these cells?
in supraoptic nucleus and paraventricular nucleus cell bodies
Nissl bodies are well developed
where are peptide hormones packed into? how are they transported?
into secretory granules
transported along axons and stored near and at axon termini in pars nervosa
what are accumulations of secretory granules in the pars nervosa seen as
visible distentions, Herring or neurosecretory bodies, along axons and at termini
axons appear as streaks
what are Herring bodies
groups of secretory vesicles containing granules of antidiuretic hormone (vasopressin) or oxytocin
what are pituicytes
neuroglia cells that surround and support axons extending from hypothalamus
most abundant in pars nervosa
have round/oval nucleus
irregularly shaped cells with many branches
antidiuretic hormone or vasopressin
increases permeability of collecting tubules to water and has an arteriolar vasoconstrictive action
mediated by cAMP
where does pars nervosa receive blood from?
what do these arteries form?
inferior hypophyseal and trabecular arteries
capillary plexus in pars nervosa
how do hormones released by Herring bodies enter the blood circulation
through capillary plexuses of inferior hypophyseal and trabecular arteries
where does the pineal gland develop from
neuroectoderm of the posterior roof of diencephalon and remains attached via a small stalk
what does the pineal gland do
relates light intensity/duration to endocrine activity, regulates circadian rhythm
produces melatonin
what covers the pineal gland
capsule of pia mater
CT trabeculae extend from capsule into substance of gland, divide into lobules
pinealocytes
melatonin producing cells, arranged in clumps/cords within lobules
interstitial glial cells
closely resemble astrocytes, have elongated nuclei that stain more heavily the pinealocytes
found in perivascular areas and between groups of pinealocytes
corpora arenacea
brain sand
calcified concretions
thyroid gland structure
2 lobes connected via isthmus, surrounded by thin fibrous capsule which send septa deeply into gland
hormones produced by thyroid
thyroid hormones T3, T4- control basal metabolic rate
calcitonin - helps regulate calcium and phosphate metabolism
thyroid follicle
spherical, cyst like structures lined by simple epithelium (follicular epithelium)
structural and functional unit of thyroid
what surrounds each follicle
a thin layer of CT containing fenestrated capillaries, epithelium ranges from cuboidal to low columnar
what is colloid
gel-like material in center of follicle
T3 and T4 bound to thyroglobulin, a glycoprotein that is most abundant component of colloid
how does the thyroid store its secretory products
extracellularly
colloid volume/follicle size…
inversely correlated with follicle activity
thyroid follicular cells
synthesize and secrete T4 and T3 in response to TSH from pituitary
thyroid follicular cell structure
apical surface lines follicular lumen, in contact with colloid
basal surface rests on basal lamina adjacent to surrounding CT
lateral surface contains tight junctions
range from squamous to low cuboidal/columnar
abundant vesicles at apical surface and in apical cytoplasm
where do cells reabsorb colloid? secrete T3/T4?
apical surface
basal surface
thyroid follicular cells at EM level
apical rER, supranulcear golgi
apical microvilli
colloid resorption droplets
many lysosomes
where are parafollicular cells located
found at periphery of follicle in interfollicular stroma, individually or in small clusters
what do parafollicular cells contain
small, dense secretory granules containing calcitonin
what is calcitonin secretion stimulated by
directly by high levels of calcium in blood, acts to decrease calcium concentration in blood
parathyroid glands
4 glands embedded in posterior thyroid, encased in thin capsule which invaginates creating poorly defined lobules
how are parathyroid cells organized
into cords/clusters surrounded by reticular fibers, BV, lymphatics, nerves
what do parathyroid cells secrete
parathyroid hormone, maintains optimal concentrations Ca in blood and interstitial fluid
stimulated by declining serum calcium levels
released by exocytosis
oxyphil cells
round large cells with relatively smaller nucleus, acidophilic cytoplasm
found singly or in clusters
function unclear
adrenal glands
paired organs covered with dense CT capsule
parenchyma composed of secretory cells, stroma mostly reticular fibers, fibroblasts, microvasculature
adrenal cortex
originates from mesoderm, parenchymal cells synthesize and secrete steroid hormones
adrenal medulla
derived from neural crest
produced catecholamines
3 concentric zones of adrenal cortex
zona glomerulosa
zona fasciculata
zona reticularis
zona glomerulosa
small columnar/pyramidal cells organized into tightly packed ovoid clusters surrounded by capillaries
hormones secrete mineralocorticoids
mineralocorticoids
regulate Na and K homeostasis
principle secretion is aldosterone (increases Na resorp, stimulates K excretion)
regulated by renin-angiotensin aldosterone system
zona fasciculata
long cords 1-2 cell layers thick, large columnar or pyramidal cells separated by sinusoidal capillaries
abundant cytoplasmic lipid droplets that give cells a vacuolated appearance
zona fasciculata hormones
secrete glucocorticoids in response to ACTH from pituitary which regulates gluconeogenesis and glycogenesis
principle secretion is cortisol
zona fasciculata function
control carbohydrate, fat, and protein metabolism
zona reticularis
smaller cells with deeply stained nuclei, arranged in network of irregular cords surrounded by wide capillaries
cells often dark, contain few lipid droplets in cytoplasm
zona reticularis hormones
secrete weak androgens (DHEA, DHEAS, and androstenedione)
secrete some glucocorticoids, responsive to ACTH
zona reticularis function
weak, masculinizing hormones
adrenal medulla
derived from neural crest
functions as a modified sympathetic ganglion
chromaffin cells
epitheliod (columnar) secretory cells that produce catecholamines, surrounded by capillaries
secrete epinephrine mostly, some norepinephrine
modified postgang symp neurons
innervated by myelinated, pregang symp nerve terminals
ganglion cells
large round cells with prominent nuclei, found in clusters
axons extend to adrenal cortex and impact secretory activity, blood vessels and splanchnic nerves
how are the effects of epinephrine mediated
by adrenergic receptors, multiple alpha and beta adrenergic receptors expressed in different target tissues
what do the suprarenal arteries give rise to
short cortical and long medullary arteries
short cortical arteries
form fenestrated arterial capillary plexus in subcapsular space and zona glomerulus
converge into cortical sinusoidal capillaries that traverse zona fasciculata, drain into fenestrated venous capillary plexus in zona reticularis and medulla
long medullary arteries
traverse cortex and form sinusoidal capillaries in medulla to provide arterial blood
what drains into central adrenomedullary veins? why are they unusual?
cortical and medullary capillary plexuses
tunica media contains abundant SM cells, contraction enhances efflux of hormones into circulation
secretory cells and vasculature
