Pituitary Gland Flashcards
What is a Peptide Hormone?
Synthesised as prohormones requiring more processing to activate.
Receptor : membrane receptors
What is a Steroid Hormone?
Synthesised from cholesterol
Receptor: bind to intracellular targets ( travel through blood with protein )
Peptide Hormone Storage?
Stored in vesicles ( regulatory secretion )
Steroid Hormone storage?
Released immediately and not stored ( constitutive secretion )
Where does the Pituitary gland sit and what is above it?
Part of sphenoid bone : Sella turcica
Above is Optic chiasm and Hypothalamus
The Anterior pituitary has to be told what to do by the hypothalamus by neurones. What neurones?
Hypothalamic Parvocellular neurones:
Short neurones which terminate on median eminence
Release hypothalamic factors into capillary plexus in median eminence
Factors get into capillary because they are leaky and carried down by portal circulation to A-pituitary
What five types of cells make up the anterior pituitary?
Samototrophs Lactotrophs Corticotrophs Thyrothrophs Gonadotrophs
( these cells make the ANTERIOR pituitary distinct from hypothalamus )
Cells regulated by the hypothalamic factors
Hypothalamo-pituitary portal system 4 steps using Thyroxine hormone release example
Hypothalamis –> A Pituitary –. thyroid gland
1 - Axon terminals of hypothalamic neurosecretory cells release Thyrotrophin Releasing Hormone - TRH into Hypothalamo-hypophysial portal system
2 - TRH travels in the portal to A-pituitary
3 - TRH stimulates the release of Thyroid Stimulating Hormone from A-pituitary thyrotrophs
4 - TSH leaves the gland via the blood to travel to the thyroid gland to stimulate Thyroid hormone release - Thyroxine
What hormones are made from each of the anterior pituitary cells?
S - growth hormone L - Prolactin T - Thyroid stimulating hormone G - LH + FSH C - Adrenocorticotrophic hormone
What is special about the growth hormone?
Growth Hormone releasing hormone ( on switch )
Somatostatin ( off switch )
Only hormone which can be turned on and off
Which A-Pituitary Hormone(s) has an inhibited control?
Prolactin = inhibited by Dopamine
Which A-pituitary Hormone(s) has releasing control ?
- TSH = thyrotrophin releasing hormone
- LH/FH = Gonadotrophin releasing hormone
- ACTH, corticotrophin = corticotrophin releasing hormone
Where do each of the A-pituitary hormones target?
Growth H- liver/ body tissue Prolactin - Lactating breasts Thyrotrophin - Thyroid Gonadotrophins - testes/ovaries Adrenocorticotrophic hormone - Adrenal Cortex
Why may Px with problem with pituitary gland not have hormonal problems?
Nearby structures may be affected:
e.g. bitemporal hemionopia ( because of pituitary tumour squashing optic chiasm - where medial retinae cross )
What is the role of the A-pituitary in milk production?
What does mechanical stimulation of the nipple cause?
Activates afferent pathways ascending to hypothalamus inhibiting dopamine release
∴ Less inhibition of A-pituitary Lactotrophs
Increased plasma prolactin = milk secretion in mammary glands
( regulated by prolactin via dopamine ) .
What 2 different ways does growth hormone exert growth?
Directly to receptors on muscle, bone etc
Indirectly to liver receptors. this stimulates IGF 1 production which travels to muscle, bone IGF 1 receptors
What causes gigantism?
A pituitary tumour makes too much growth hormone - growth in height
ONLY happens before puberty is finished
What is Acromegaly and what are its characteristics?
Excess growth hormone ( after puberty )
Coarsening of facial features ( Macroglossia, Prominent nose ) Prognathism Increased hand/feet size Sweatiness Headache
NO increased height
What are the Posterior pituitary hormones?
Two hormones:
Arginine vasopressin ( Anti-diuretic hormone )
Oxytocin
How is the Posterior pituitary different to anterior?
Anatomically continuous with hypothalamus : neuronal tissue no endocrine tissue
What are the Hypothalamic magnocellular neurons?
Long neurones - originate in supraoptic (AVP) and paraventricular (oxytocin) nuclei
Nuceli –> Stalk –> P-pituitary
What are the roles of ADH?
stimulation of water reabsorption in renal collecting duct = concentrated urine
Vasoconstrictor - V1 receptor
Stimulates ACTH release from A-pituitary
How does AVP concentrate urine?
AVP binds to ( a ) causing a cascade of ( b ) –> Adenylate cyclase –> ( c ) –> protein kinase A –> ( d ) = reabsorbs water
fill in gaps
a - V2 receptor
b - G proteins
c - cAMP
d - Aquaporins
What are the physiological actions of oxytocin?
Contraction for Delivery of baby : When time for delivery Myometrial cells in uterus contract due to oxytocin
Contraction for Milk ejection :
Myoepithelial cells contract due to oxytocin
