The pituitary gland ( and hypothalamus) Flashcards
What is the hypothalamus a part of?
the brain
How is the hypothalamus connected to the pituitary gland?
directly via stalk called the infundibulum
What is the infundibulum?
stalk connecting the hypothalamus and pituitary gland
How does the hypothalamus communicate with the anterior and posterior pituitary and what does this mean?
neural to posterior pituitary
endocrine to anterior pituitary
neuroendocrine function
What hormones are released from the hypothalamus? Why?
neuroendocrine
neural tissue
Where is the pituitary gland located?
in pocket of sphenoid bone directly below the hypothalamus
Give some examples of inputs to the hypothalamus
sleep hydration status puberty menstruation cold stress metabolic demand day/night breastfeeding pregnancy exercise
Give some examples of physiological mechanisms which the pituitary controls
water balance lactation parturition growth gonadal function thyroid function adrenal function metabolism
What is parturition?
The action of giving birth
The hypothalamus and anterior or posterior pituitary release both trophic and non-trophic hormones?
anterior
What are trophic hormones?
Hormones governing the release of another hormone
What type of hormones does the posterior pituitary release?
neurohormones from the hypothalamus
What type of hormones does the anterior pituitary release?
classic endocrine hormones
What do the trophic hormones from the hypothalamus govern?
release of anterior pituitary hormones
What do the non-trophic hormones from the hypothalamus govern?
travel to posterior pituitary and are released into the blood
What do all the trophic hormones released from the hypothalamus do when they reach the anterior pituitary?
bind to receptors and stimulate/inhibit release of AP hormones
Name the 5 hypothalamic releasing hormones
TSH CRH GHRH GnRH PRH
What are the 2 hypothalamic inhibiting hormones?
PIH eg dopamine
GHIH eg somatostatin
How are the hypothalamus and anterior pituitary connected?
hypothalamic-hypophyseal portal
tiny network of vessels
Where are the hormones released from neurosecretory neurons in the hypothalamus? (hypothalamus & ant. pituitary)
Median eminence
What is the tissue origin of the anterior and posterior pituitary?
anterior = epithelial posterior = neural
What are the other names for the anterior and posterior pituitary?
anterior = adenohypophysis posterior = neurohypophysis
What fraction of the gland does the anterior and posterior pituitary make up?
anterior is 2/3
How are the capillary beds in the hypothalamic-hypophyseal portal arranged?
2 capillary beds in series
What type of hormones does the hypothalamus produce that effects the anterior pituitary?
inhibiting or releasing hormones
trophic hormones
How many hormones are released from the anterior pituitary gland? What type of endocrine hormones?
6
peptides
How many of the 6 anterior pituitary hormones are trophic?
5
Name the 6 hormones the anterior pituitary produces
TSH LH FSH GH ACTH prolactin
What is the only non-trophic anterior pituitary hormones and what is its effect?
prolactin
DIRECTLY stimulates milk production from breast during lactation
3 integration centres of anterior pituitary feedback control
hypothalamus
anterior pituitary
target endocrine cell
What acts as the negative feedback signal in anterior pituitary feedback control?
hormones
Give an example of long loop feedback in anterior pituitary control
feedback from target endocrine cell to AP and hypothalamus
Give an example of short loop feedback in anterior pituitary control
feedback from AP to the hypothalamus
Advantage of anterior pituitary feedback control
links levels of sequential hormones together and tightly maintains plasma levels within the correct range
What are the 2 peptide neurohormones stored and released by the posterior pituitary?
vasopressin eg ADH
oxytocin
Where are the posterior pituitary neurohormones synthesised?
specific magnocellular neurons
Where are magnocellular neuronal cell bodies?
specific areas of the hypothalamus
How does the hormones travel from hypothalamus to posterior pituitary?
axons project down infundibulum to posterior pituitary
Do magnocellular neurons synapse?
no - terminals end directly on capillaries
Function of ADH
regulate water balance
Release of ADH is triggered by..
decrease bp/plasma volume
increase plasma osmolarity
Site/mode of action of ADH
kidney collecting ducts to increase water reabsorption
vascular smooth muscle to increase blood pressure
function of oxytocin
milk ejection and uterine contraction
release of oxytocin triggered by…
labour - baby’s head against the cervix
suckling
site/mode of action of oxytocin
milk ducts smooth muscle contracts and ejects milk
uterine smooth muscle contraction in child birth
Hyposecretion
too little hormones secreted
hypersecretion
too much hormone secreted
hyporesponsiveness
reduced response of target cell
hyperresponsiveness
increased response of target cell
primary endocrine disorders
defect in cells which secrete the hormone
secondary endocrine disorders
too much or little trophic hormone from pituitary gland
tertiary endocrine disorders
hypothalamic defects
3 causes of hyporesponsiveness
alterations in receptor for hormone
disordered post receptor events
failure of metabolic activation of hormone - if this is required
Possible cause of hyperresponsiveness
permissive effects
