hypothalamic pituitary gland system Flashcards by Issy Garratt

what is the hypothalamic pituitary system

coordinates the endocrine system

organises hormonal responses to stimuli from higher brain centres

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what does the hypothalamic pituitary system respond to

external environment changes
- temp, food, stressors
internal environment
- hormones, feedback signals, salt balance, BP, heart rate, pregnancy, trauma, disase

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what is the pitiutary gland

also called hypophysis
sits in a bony cavity called sella turnica
2 distinct lobes with reoles

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what is the anterior pituitary gland

adrenohypophysis
well vascularised glandular tissue
contailss 5 types of secretory ceclls
NO nerve fibres

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what is the posterior pituitary

brain-like tissue

secretes 3 principle neuro-hormones

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what are the 5 secretory cells in the ant-pit

acidophiles
- somatrophs
- mannotrophs/lactotrophs
basohils
- gonadaotrophs
- thyrotrophs
- corticotrophs

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examples of single polypeptide hormones

ATCH
GH
PRL

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examples of multi-subunit polypeptide chain hormones

LH
FSH
TSH

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what is a multi-subunit polypeptide chain hormone

common alpha subunit

but different beta subunits that give the hormones their biological specificity

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what is the hypothalamus

regulatory centre

recieved nerve fibres from other areas of the brain and sends signal down to pituitary

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what type of neurones innervate the pos pit from the hypothalamus

magnocellular peptidogeric neurones

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what type of neruones innervate the ant.pit from the hypothalamus

hypothalamic parvocellular peptidergic neurones

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what is a petidergic neurone

make a chemical messernger which is a peptide

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what do hypothalamic parvocellular neurones do

terminate by the median eminence stimulating hormones in a pulsatile way

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describe the hypophseal portal system of the ant-pit

neurones from hypothalamus release peptide near the median eminence
hypophyseal arteries form a capillary plexus to the portal vein which takes the peptides to the ant-pit
the peptides reach the second plexus
peptide act as ligands on ant-pit cells using GPCRs
2nd messengers made- TRH, GnRH, GHRH ( releasin hormone RH)

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describe the anatomy of the pos pit

magnocellular neurones from the hypothalamus send axons down and directly terminate in the pos pit

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key difference between pos and ant pit

pos has direct neuronal innervation

ant doesnt, uses circulation system

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parvocellular hypothalamic neurones

ant-pit
control the 5 secretory cell types
each neurone produces a neuropeptide to act on receptors of each cell type

what are the hypothalamic releasing hormones

TRH
thryotrophin RH
GnRH
gonadotrophin RH
CRH
cortiocotrophin RH
GHRH
Growth hromone RH

what is the HPA axis

hypothalamic-pituitary axis
eg. cortisol production controls its own secretion, elevated levels can act to inhibit both the pituitary and hyothalamus fro releasing CRH and ATCH

what is pan-hypopituitaryism

disease
loss of multiple endocrine cells in pit
deficient in hormones

what can pan-hypopiuitaryism be caused by

a space occupying non-functional tumour

how is pan-hypopitiutaryism treated

with steriods to replace what the target gland would make in response to the lost pit hormones
eg gonadalstreiods

what are the main hormones of the pos pit

oxytocin and vasopressin

features of magnocellular neurones

send axons down to pit and directly innervate the pos pit | takes up precurosr peptide hormones and makes pre-prohormones which are then released

how are neurohormones released

action potential arrives wave of depolarisation influx of NA ions calcium channels opens drives exocytosis of granules containing oxytocin or vasopressin membrane repaptures the granule and everything is restored back to normal

whats the role of oxytocin

promotes childbirth/partuition and the milk ejection reflex

whats the role of vasopressin

reduced water excretion by the kidney

what is an analogue

a synthetic version of the hormone used clincially | eg. oxytocin analogues used to promote childbirth

stimulus for vasopressin

increased osmotic pressure in blood, picked up by osmoreceptors fall in blood volume detected by baroreceptors

actions of vasopressin

allows more aquaporins on nephron, more permeable to water | restore the blood volume to correct level, more water resorbed

describe the process of ADH secretion

- high blood osmoticpressure stimulates hypothalamic neurones - osmoreceptors active neurosecretory cells to syntheise ADH in hypothalamus - nerve impluses allow ADH to be reelased in pos pit blood stream - ADH goes and has effects on target tissues low blood osmolarity inhibits all this acitivty reducing ADH secretion

disorders of vasopressin

``` hypersecretion = tooo much fluid retention, decreases osmolarity patients need to limit fluid intake hyposecretion = too little ADH diabetes insipidus ```

what is the neuroendocrine reflex

oxytocin sensory cells in nipple convey stimulus to brain via mechanoreceptors synpases contact mangocellular neurones and oxytocin is made the hormone reaces the myo-epithelial cells leading to muscle contraction, pressure and he milk is ejected

role of the mammory gland

globular gland structure epithelial cells make the milk a reticular netrowrk and corrdianted activity with cells allow the mypepithelila cells to respond to oxytocin and rlease the milk

whats stimulates milk production

prolactin

what stimulates milk release

oxytocin

what is the pregnant rat model

nipple transducers measured hormone levels there was a burst of activity as the pups attach the intramammory pressure also increased just after the hormone burst

how does the milk ejection relfex work

positive feedback, more nipple stimulates equals more oxytocin and more milk

furguson reflex

tactile stimulation of the reproductive tract leads to oxytocin release shwon in sheeo and orfan lambs

describe the oxytocin pathway

nipple stimuli sensed by mechanoreceptors this is sent as a neuronal imput to the hypothalamus which releses down axons into pos pit oxytocin oxytocin rleased into blood stream and this targets myoepithelila cells of breast tissue milk ejected

what kind of receptor does oxytocin use

GPRC

how is positive feedback used in oxytocin

the foetus drops lower into the uterus leading to cervial stretch this positively leads to oxytocin release and uterine contractions the loop stops when the uterus is not stretched any more and the foetus is delivered