LEC36: Endocrine System I Flashcards
what’s within endocrine II?
thyroid, C (parafollicular) cells, parathyroid, adrenal - cortex & medulla, pancreas - islets of langerhans, diffuse endocrine system
what is within endocrine I
pituitary, hypothalamus, pineal
exocrine duct formation and release
downgrowth of epithelium into CT > duct forms at surface > contents release from duct, at epithelium surface
endrocine duct formation
proliferation of cells, downgrowth into CT > breaks from epithelium > follicular endocrine gland forms w/ cord of cells/capillaries surrounding
endocrine follicle structure
ring of endocrine cells divided by epithelial cells in center; lumen in center; capillaries infiltrate CT between follicles
hormone defn
chemical substances synthesized by endocrine cells and secreted
3 ways hormones can effect cells once secreted
1) into bloodstream > distant target cells
2) into tissue space > adjacent or nearby target cell
3) onto own cell surface > own target cells
why hormones synthesized/secreted?
1) to influence metabolic activities of target cells
2) in conjunction w/ nervous system, coordinate & integrate fxns of all physiological systems
hormonal signaling mechanisms (3)
1) endocrine signaling
2) paracrine signaling
3) autocrine signaling
how endocrine signaling works
endocrine follicle gland has lumen, blood vessel goes through > hormone secreted into blood > attaches to membrane receptor or receptor in cytosol at distant target cell > tells distant cell to make hormone
i.e. pituitary hormones
how do paracrine signals work
endocrine cell inside hormone travels through CT > effect nearby cell, a few cells away from endocrine cell > hormone sits on membrane receptor to tell target cell to produce
i.e. somatostatin inhibits insulin secretion in islets of langerhans
how does autocrine signaling work
hormone/growth factor sits on membrane receptor of its own cell
i.e. insulin, TGF-beta
chemically, hormone types (3)
1) peptides and glycoproteins
2) steroids
3) amino acids
examples of peptides, glycoproteins hormones
hormones of pituitary, parathyroid, C cells of the thyroid, islets of Langernas and GI tract
examples of steroid hormones
hormones of adrenal cortex, ovary and testis
examples of amino acid (tyrosine) hormones
hormones of thyroid, adrenal medulla
hormonal distinguishment by morphology (2)
1) peptide/glyprotein hormone producing cells contain granules (electron dense on EM!), which store hormones
2) steroid hormone-producing cells store and release hormones into circulation right away (eosinophilic stain!), no granules for storage
endocrine glands whose sole functions are hormone production
pituitary, pineal, thyroid, parathyroid, adrenal
endocrine tissues found in association w/ organs which have other functions
pancreas, ovary, testis, kidney, liver
ovary’s exocrine function
release of ovum
testis’s endocrine and exocrine functions
endocrine: testosterone
exocrine: sperm
kidney’s endocrine and exocrine functions
endocrine: make renin, prostaglandins
exocrine: renal tubule absorption/reabsorption into tubules
liver’s endocrine and exocrine functions
endocrine: makes glucose amino acid albumin, > circulation
exocrine: makes many metabolites which > metabolism, secrete bile to gall bladder
diffuse endocrine system
endocrine tissue > single hormone-producing cells diffusely scattered in digestive, respiratory systems
where is pituitary located
beneath floor of III ventricle, connected to hypothalamus
where is diencephalon, what does it consist of?
between forebrain and midbrain
forms wall of ventricle or cisterna
consists of thalamus, hypothalamus, epithalamus
which part of thalamus and of hypothalamus forms floor of III ventricle?
ventral part of thalamus
median eminence of hypothalamus
where does floor of III ventricle extend into?
site of pituitary gland
why is pituitary gland “master” gland?
although tiny, it controls most of endocrine functions of the body
where does pituitary gland sit?
in hypophyseal fossa, a bony depression of the sella turcia (hump) of the sphenoid bone (in middle cranial fossa)
where is median eminence of hypothalamus, what does it connect to?
between/just posterior to optic chiasma
connects by stalk to pituitary gland
2 parts of pituitary gland
1) adenohypophysis, anterior pituitary, aka pars distalis - glandular
2) neurohypophysis, posterior pituitary, aka pars nervosa
pars distalis means
hormones of anterior pituitary
pars distalis contains
most endocrine cells of pituitary
pars nervosa means
hormones of posterior pituitary
parts of anterior pituitary
1) pars distalis
2) pars tuberalis
3) pars intermedia
parts of posterior pituitary
1) pars nervosa
2) infundiibulum
3) median eminence
what does posterior pituitary (neurohypophysis) develop from
nervous tissue of hypothalamus
what does anterior pituitary (adenohypophysis) develop from
ectoderm of roof of the mouth
how does pituitary gland develop?
1) hypothalamus invaginates, grows down toward rathke’s pouch of fossa, becomes stalk, while neurectoderm tissue of roof of mouth grows toward hypoficial fassa
2) rathke’s pouch approaches pars nervosa; pouch space becomes narrow, forms pars distalis and pars intermedia
what does pars nervosa develop from?
distal end of hypothalamus
what does rathke’s pouch become?
anterior part: anterior part of pars distalis
posterior part: pars intermedia
where does rathke’s pouch develop from?
roof of the mouth
what is between pars nervosa and pars distalis?
pars intermedia
how/where does pituitary gland connect to the hypothalamus?
pars nervosa connects to stalk to hypothalamus
functional and physical connection
how/why do pars nervosa and pars distalis stain differently?
pars distalis stains darker b/c has endocrine cells
characteristics of pars distalis
1) endocrine cell clusters
2) reticular fibers, Type III collagen, support
3) FENESTRATED/SINUSOIDAL CAPILLARIES throughout for rapid diffusion of hormones into circulation
chromophils
affinity for dye
1) acidophils- affinity for acidic dye
2) basophils- affinity for basic dyes
chromophobes
degranulated acidophils/basophils, granules don’t stain by antibodies
how many populations/types of endocrine cells are there
5
how would you localize endocrine hormones
immunocytochemical staining
make an antibody against a hormone, localize it
why 6 hormones but 5 cell types
because both FSH and LH expressed by 1 cell type, gonadotrophs
6 hormones localizable with immunocytochemical staining
growth hormone, prolactin, corticotropin (ACTH), thyrotropin (TSH), follicle stimulating hormone (FSH), luteinizing hormone (LH)
how can you tell anterior pituitary cell in EM?
anterior pituitary hormones are stored in granules, which has marker that stains positively
how are endocrine cell types named?
for the hormones they secrete
acidophils of pars distalis?
1) somatotrophs
2) mammatrophs
what do somatotrophs secrete, what proportion is this of all pars distalis?
growth hormone (GH) 50%
what do mammatrophs secrete, what proportion is this of all pars distalis?
prolactin
20%
basophils of pars distalis?
1) corticotrophs
2) thyrotrophs
3) gonadotrophs
what do corticotrophs secrete, what proportion is this of all pars distalis?
corticotropin (ACTH)
20%
what do thyrotrophs secrete, what proportion is this of all pars distalis?
thyrotropin (TSH)
5%
what do gonadotrophs secrete, what proportion is this of all pars distalis?
1) follicle stimulating hormone (FSH)
2) luteinizing hormone (LH)
5%
how are pars distalis hormones controlled?
secretion of pars distalis hormones controlled by HYPOTHALAMUS via HYPOTHALAMIC RELEASING or INHIBITING HORMONES
function of hypophyseal (pituitary) portal system?
in pituitary gland
provides anatomical-function link between hypothalamus & pars distalis of anteiror pituitary
blood supply to pituitary gland?
inferior & superior hypophyseal artery - branchs of coratid
how does hypophyseal portal system work
inferior/superior hypophyseal arteries enter pituitary gland at pars distalis
> break into vein, venule
> go to endocrine cells of pars distalis, surround capillaries
> hormones > circulation
what do neurosecretory cells in hypothalamus do?
control pars distalis hormone secretion by making releasing and inhibiting hormones
what do releasing and inhibiting hormones of hypothalamus neurosecretory cells target?
anterior pituitary hormones
therefore effect target organ cells
what are the hypothalamic hormones?
1) GH-releasing hormone
2) corticotropin-releasing hormone
3) TSH-releasing hormone
4) gonadotropin-releasing hormone
5) dopamine
6) somatostatin
GH-releasing hormone function?
stimulates GH release
corticotropin-releasing hormone function?
stimulates ACTH release
TSH-releasing hormone function?
stimulates TSH release
gonadotropin-releasing hormone function?
stimulates FSH and LH release
dopamine function?
INHIBITS prolactin release - unique b/c inhibition!
somatostatin function?
aka global inhibitor - always inhibits, wherever it acts
INHIBITS GH release
ex: inhibits glucose release in pancreas
when is pars intermedia well pronounced?
in animals, not in humans
what does pars intermedia secrete
2 types of melanocyte-stimulating hormone:
B-MSH: skin pigmentation
A-MSH: anti-appetite
what are melanocyte-stimulating hormones product of?
pro-opiomelanocortin (POMC)
what do pars intermedia granules and corticotrophs both synthesize
pro-opiomelanocortin
what can pro-opiomelanocortin split into
1) ACTH
2) lipotropins for lipid metabolism
3) endorphins for endogenous opioids
4) MSHs B and A for skin pigmentation and anti-appetite
what hormones does pars nervosa secrete
1) antidiuretic hormone (ADH; vasopressin)
2) oxytocin
what do pars nervosa hormones bind to
a carry protein neurphysin
what produces ADH?
neurons in the supraoptic nuclei of the hypothalamus
what produces oxytocin?
neurons in the paraventricular nuclei of the hypothalamus
what is the hypothalamohypophyseal tract
axon tract that carries hormones (ADH, oxytocin) from neuron of hypothalamus to pars nervosa of pituitary
ADH function?
water absorption in collecting ducts, convoluted tubules of kidneys
oxytocin functions?
1) acts on myoepithelial contraction- physically expelling milk from mammary glands
2) uterine contraction
what are pituicytes?
neuroglia - supporting cells of hypothalamo-hypophyseal tract
what is hypothalamo-hypophyseal tract made of
100,000 unmyelinated axons
what are herring bodies
swellings along axon of hypothalamo-hypophyseal tract; collecting sites of granules of hormones ADH and oxytocin, which bind in herring bodies to neurophysin
what controls release of ADH/oxytocin, where are they released?
into blood
caused by neurostimuli from hypothalamus > hormone released from granule > down axon terminal > circulation
neurosecretion defn
how oxytocin/ADH released because their release from herring bodies controlled by neurostimuli
where is pineal gland
it is a diverticulum of posterior diencephalon, at posterior end of III ventricle
what covers pineal gland?
pia mater
structures of pineal gland?
lobules separated by CT septa; neuroglial cells (pinealocytes) inside lobules; corpora arenacea outside
corpora arenacea- where and what is it?
outside pineal gland
extracellular calcified bodies containing CaPO4, MgPO4, carbonate in an organic matrix
increase with age
what controls day/night cycle (diurnal rhythms) of the body?
melatonin, “hormone of the darkness”
why is melatonin “hormone of the darkness”?
synthesis induced by darkness and suppressed by light
what is melatonin synthesized from?
the amino acid tryptophan, via serotonin
what effect does melatonin have on reproduction?
has anti-reproductive effects by decreasing gonadotropin (FSH, LH) release
relationship between melatonin and jet lag?
use of melatonin may help counteract drowsiness, disorientation related to jet lag because helps reacclimate to correct time zone
what happens if remove pineal gland from animal?
gonadotropin production increases
reproductive organs enlarge
