pituitary gland Flashcards
what is a hormone
a chemical messenger
carried from the organ where they are produced to the organ which they affect by means of the blood stream
what are the 2 types of hormones
steroid and peptide
what is the synthesis of peptide hormones
synthesised as prohormones requiring further processing eg cleavage to activate
how are peptide hormones stored
in vesicles (regulatory secretion) - needs to be triggered to be released
what are receptors for peptide hormones
bind to receptors on cell membranes and transduce signals using secondary messenger systems
how are steroid hormones synthesised
in a series of reactions from cholesterol
how are steroid hormones stored
they aren’t ahahaha
they are released immediately
what are receptors for steroid hormones
they bind to intracellular receptors to change gene expression directly
what is another name for the anterior pituitary gland
adenohypophysis
where is the anterior pituitary gland derived from
an upgrowth from the oral ectoderm of the primitive oral cavity called Rathke’s pouch
it has epithelial origin
what is another name for the posterior pituitary gland
neurohypophysis
where is the posterior pituitary derived from
formed from a downgrowth of the diencephalon that forms the floor of the 3rd ventricle
neural origin
what regulates anterior pituitary function
hypothalamic parvocellular neurons
describe hypothalamic parvocellular neurons
short
terminate on median eminence
what do hypothalamic parvocellular neurons do
release hypothalamic releasing or inhibiting factors into the capillary plexus in median eminence
these factors are carried by portal circulation to anterior pituitary
is the anterior pituitary anatomically distinct from the hypothalamus
heck yea
what are the 5 endocrine cells in the anterior pituitary (some losers cry to god..)
somatotrophs lactotrophs corticotrophs thyrotrophs gonadotrophs
how are these endocrine cells regulated
regulated by hypothalamic releasing/inhibiting factors via hypophyseal-pituitary portal system
STEPS for release of hormone via hypothalamo-pituitary portal system
1) axon terminals of hypothalamic neurosecretory cells release hormones (RHs and IHs) into the hypothalamo-pituitary portal system
2) the RHs and IHs travel in the portal system to the anterior pituitary
3) the RHs and IHs stimulate or inhibit the release of hormones from anterior pituitary cells
4) anterior pituitary hormones leave the gland via the blood
summary of STEPS for hormone release
hypothalamus > portal system > anterior pituitary > blood > target tissue/organ/cell
STEPS for thyroid hormone production
1) axon terminals of hypothalamic neurosecretory cells release thyrotrophin releasing hormone (TRH) into hypothalamo-hypophysial portal system (connects brain and anterior pituitary)
2) TRH travels in the portal system to the anterior pituitary
3) TRH stimulates the release of thyroid stimulating hormone (thyrotrophin) from anterior pituitary thyrotrophs
4) TSH leaves the gland via the blood to travel to the thyroid gland to stimulate thyroid hormone release (thyroxine)
summary of thyroid hormone production
hypothalamus has cells > release TRH > travels in portal to AP > stimulates TSH release > in blood to thyroid gland > stimulates thyroxine release
hypothalamo-pituitary regulation (the 5 cells and their pre releasing things)
released by hypothalamic neurosecretory cells > released by anterior pituitary cells
GHRH > growth hormone
somatostatin > inhibitory effects on growth hormone (not released by AP)
dopamine > inhibitory effect on prolactin (^dopamine = less prolactin)
thyrotrophin releasing hormone > thyroid stimulating hormone (TSH) - thyrotrophin
gonadotrophin releasing hormone > LH and FSH
corticotrophin releasing hormone > adrenocorticotrophic hormone (ACTH, corticotrophin)
what are the target cells for growth hormone
general body tissues (particularly the liver)
target cells for prolactin
breasts (lactating women)
target cells for thyroid stimulating hormone (TSH)
thyroid gland
target cells for gonadotrophins (LH and FSH)
testes (male)
ovaries (female)
target cells for adrenocorticotropic hormone (ACTH)
adrenal cortex
where does the pituitary gland sit
in the sella turcica of the sphenoid bone
what is a bitemporal hemianopia and what is it caused by
visual loss at the outer part of both visual fields
fibres from the nasal (medial) retinae cross at the optic chiasm
compression of the optic chiasm by a pituitary tumour/suprasellar tumour prevents transmission of sensory information from lateral (temporal) visual fields to the occipital lobe
what is the mechanism of growth hormone action
growth hormone (somatotrophin) is secreted by somatotrophs
acts on body tissues > growth and development and also
tells the liver to secrete insulin like growth factor (somatomedin) - IGF1 and IGF2 which leads to growth and development
what is acromegaly
excess growth hormone
symptoms of acromegaly
coarsening of facial features macroglossia - enlargement of tongue prominent nose large jaw - prognathism increased hand and feet size sweatiness headaches
what 2 hormones does the posterior pituitary store
AVP (arginine vasopressin) aka anti diuretic hormone
oxytocin
is the posterior pituitary anatomically continuous with the hypothalamus
no sir
describe hypothalamic magnocelullar neurons
- long, originate in the supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei
- nuclei > stalk > posterior pituitary
does the posterior pituitary make hormones
nope
it does not make hormones itself
it stores AVP and oxytocin produced in the hypothalamus
STEPS for regulation of the posterior pituitary gland
1) two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to the posterior pituitary
2) excitation of these hypothalamic magnocellular neurons stimulates release of AVP or oxytocin into the posterior pituitary where they diffuse into blood capillaries
3) then leave the posterior pituitary via the blood
physiological actions of vasopressin
anti diuretic hormone
(diuresis = production of urine)
main physiological action = stimulation of water reabsorption in renal collecting duct
CONCENTRATES urine
what are the receptors for vasopressin
act on the V2 receptor in the kidney
also a vasoconstrictor (via V1 receptor)
stimulates ACTH release from anterior pituitary
2 physiological actions of oxytocin
milk ejection
delivery of baby
summarise the process of milk ejection
oxytocin acts on breasts during lactation
acts on myoepithelial cells
contraction
milk ejection
summarise the process of delivery of baby
oxytocin acts on the uterus at parturition
acts on myometrial cells
contraction
delivery of baby
STEPS for lactation (role of anterior pituitary)
1) mechanical stimulation of nipple and surrounding area activates afferent pathways
2) afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
(less dopamine = more prolactin)
3) less dopamine in the hypothalamic pituitary portal system causes less inhibition of anterior pituitary lactotrophs - can now produce prolactin
4) increased plasma prolactin increases milk secretion in mammary glands
STEPS for lactation (role of posterior pituitary)
1) mechanical stimulation of nipple and surrounding area activates afferent pathways
2) afferent signals integrated in the hypothalamus and stimulate oxytocin releasing neuron activity
3) action potentials travel down oxytocin neurons and oxytocin is secreted into the bloodstream
4) increased plasma oxytocin increases milk ejection in mammary gland
