pituitary gland Flashcards by Rumaysa Ahmed

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

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what are the 2 types of hormones

steroid and peptide

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what is the synthesis of peptide hormones

synthesised as prohormones requiring further processing eg cleavage to activate

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how are peptide hormones stored

in vesicles (regulatory secretion) - needs to be triggered to be released

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what are receptors for peptide hormones

bind to receptors on cell membranes and transduce signals using secondary messenger systems

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how are steroid hormones synthesised

in a series of reactions from cholesterol

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how are steroid hormones stored

they aren’t ahahaha

they are released immediately

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what are receptors for steroid hormones

they bind to intracellular receptors to change gene expression directly

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what is another name for the anterior pituitary gland

adenohypophysis

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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

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what is another name for the posterior pituitary gland

neurohypophysis

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where is the posterior pituitary derived from

formed from a downgrowth of the diencephalon that forms the floor of the 3rd ventricle
neural origin

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what regulates anterior pituitary function

hypothalamic parvocellular neurons

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describe hypothalamic parvocellular neurons

short

terminate on median eminence

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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

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is the anterior pituitary anatomically distinct from the hypothalamus

heck yea

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what are the 5 endocrine cells in the anterior pituitary (some losers cry to god..)

somatotrophs
lactotrophs
corticotrophs
thyrotrophs
gonadotrophs

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how are these endocrine cells regulated

regulated by hypothalamic releasing/inhibiting factors via hypophyseal-pituitary portal system

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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