The pituitary gland (11) Flashcards
What is a hormone?
chemical messengers carried in the bloodstream to target organ
How are peptide hormones synthesised?
synthesised as prohormones- require further processing (e.g. cleavage) to be activated
How are peptide hormones stored?
stored in vesicles and only released in response to a signal (regulatory secretion)
How do peptide hormones work in terms of receptors?
bind to receptors on cell membrane and usually activate a secondary messenger system
How are steroid hormones synthesised?
made from precursor cholesterol in a series of reactions
How are steroid hormones stored?
released immediately (constitutive secretion)
How do steroid hormones work in terms of receptors?
bind to intracellular receptors- alter gene expression
Where is the pituitary gland located and what is its structure?
- pituitary gland hangs from infundibulum (stalk)
- sits in sella turcica of sphenoid bone
- anterior and posterior portions- posterior continuous with hypothalamus
- at front is optic chiasm
What are the 5 endocrine cell types in the anterior pituitary and what hormones do they produce?
- somatotrophs: produce growth hormone (somatotrophin)
- lactotrophs: produce prolactin
- thyrotrophs: produce thyroid stimulating hormone (TSH)
- gonadotrophs: produce luteinising hormone (LH) and follicle stimulating hormone (FSH)
- corticotrophs: produce adrenocorticotrophic hormone (ACTH)
How does the hypathalmo-pituitary portal system work?
- axon terminals of parvocellular neurons release hormones/factors (releasing/inhibitory) into median eminence- rich in blood vessels
- factors leak into portal system–> transported through blood stream into anterior pituitary
- factors bind to relevant anterior pituitary hormone cells (e.g. thyrotrophs)–> causes them to release their hormones into circulation
What hypothalamic factor regulates the production of prolactin?
dopamine- inhibiting, so less dopamine–> more prolactin
What 2 hypothalamic factors regulate the production of growth hormone?
growth hormone releasing hormone- releasing
AND
somatostatin- inhibiting
Where are the main target cells/receptors of growth hormone?
muscle tissue, bone, liver
Where are the main target cells of gonadotrophins (LH+FSH)?
ovaries and testes
Where are the main target cells of prolactin?
mammary glands
Where are the main target cells of corticotrophin?
adrenal gland- specifically adrenal cortex
Where are the main target cells of thyrotrophin?
thyroid gland
What happens when a pituitary tumour compresses the optic chiasm?
lose peripheral vision
‘bitemporal hemianopia’- common presentation
–> fibres from nasal retinae cross at the optic chiasm
–> tumour prevents transmission of sensory info from lateral visual fields to occipital lobe
What is the mechanism of milk production (a neuroendocrine reflex)?
- mechanical stimulation of nipple and surrounding area activates afferent pathways
- afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
- less dopamine in hypothalamic-pituitary portal system–> less inhibition of anterior pituitary lactotrophs
- more prolactin in plasma–> more milk secretion in mammary glands
What are the 2 ways in which growth hormone can stimulate growth?
GH binds to body tissues directly
BUT ALSO to GH receptors on liver–> causes production of insulin-like Growth Factor (IGF-1 and IGF-2)
so skeleton has IGF receptors and GH receptors
–> both leads to growth and development
What conditions are a result of too much growth hormone?
gigantism= children acromegaly= adults (can't get taller, but large jaw/prognathism, macroglossia, prominent nose, increased hand and foot size)
What are the posterior pituitary hormones?
arginine vasopressin (AVP/ADH) and oxytocin
How does regulation of the posterior pituitary gland work?
- 2 sets of distinct populations of hypothalamic neurosecretory cells producing AVP and oxytocin
- excitation of neuronal populations stimulates release of hormones–> transported into posterior pituitary
- diffuse into blood capillaries and leave via blood
What is the physiological action of vasopressin?
/Anti-Diuretic Hormone
*diuresis= production of urine
–> binds to V2 receptor in collecting duct–> stimulates intracellular cascade–> promotes Aquaporin-2 movement to membrane- then inserted–> water flows along conc. gradient (from urine) through collecting duct to Aquaporin 3–> water reabsorbed into plasma–> urine concentrated
