The hypothalamus-adenohypophysial axis Flashcards
What is the bony dip the pituitary gland lies in called?
Sella Turcica
Rough size of pituitary gland
Thumbnail size
How many lobes make up the pituitary gland?
2
Anterior and Posterior
What is the anterior lobe in the pituitary gland called?
Adenohypophysis
What is the posterior lobe in the pituitary gland called?
Neurohypophysis
Embryological origin of adenohypophysis
Upward growth derived from part of Buccal cavity- Rathke’s pouch
Embryological origin of neurohypophysis
Downward growth from base of brain
Which is the secretory lobe of the pituitary gland?
Adenohypophysis
Which is the neural lobe of the pituitary gland, made up of nerve axons derived from base of brain?
Neurohypophysis
What is a collection of neural cell bodies?
Nuclei
Where do hypothalamic nuclei send axons to in pituitary gland?
LONG: Down pituitary stalk to neurohypophysis
SHORT: To median eminence
What can median eminence communicate with?
Systemic circulation
What is the Pars Distalis?
Body of anterior pituitary
What is the Pars Tuberalis?
Part of anterior pituitary which wraps around pituitary stalk
How is the anterior pituitary gland regulated?
Via the bloodstream- a special circulation
= Hypothalamic- hypophyseal portal circulation
Where is the median eminence?
Between the pituitary stalk and the hypothalamus.
What are the 2 areas of the brain that are useful anatomical markers for distinguishing the posterior pituitary from the anterior?
Anterior - Optic chiasma
Posterior - Mammilary body
Describe the hypothalamic– hypophyseal portal circulation
Blood supplied by superior hypophyseal artery
Enters 1st plexus in median eminence
Travels down long portal vein
Enters 2nd plexus in anterior pituitary
Plexus
Cluster of capillaries
How does the hypothalamic-hypophyseal portal circulation allow communication with anterior pituitary
Capillary walls are fenestrated (leaky)
Hormone from hypothalamic neurone can enter at 1st plexus
Hormone leaks out at 2nd plexus and acts on anterior pituitary target cells
What do short hypothalamic neurones which terminate in the median eminence lie on?
The surface of the primary capillary plexus
Name 5 adenohypophysial cells
Somatotrophs Lactotrophs Thyrothrophs Gonadotrophs Corticotrophs
What do somatotrophs produce?
Somatotrophin
Growth hormone
What do lactotrophs produce?
Prolactin
What do thyrotrophs produce?
Thyroid stimulating hormone
=TSH/ Thyrotrophin
What do gonadotrophs produce?
Luteinising Hormone (LH) Follicle Stimulating Hormone (FSH)
What do corticotrophs produce?
Adrenocorticotropic Hormone
=ACTH/ Corticotrophin
Most hormones are made from longer precursors called
Pro-hormones
Enzymatic cleavage of pro-hormone yields
Bioactive hormone
What are adenohypophysial hormones stored in?
Secretory granules
What are the longest adenohypophysial hormones?
Protein hormones:
Somatotrophin
Prolactin
What are adenohypophysial glycoprotein hormones
TSH
LH
FSH
What are the shortest adenohypophysial hormones?
Polypeptide hormones:
ACTH
Which hypothalamic hormones regulate production of somatotrophin?
Growth hormone releasing hormone (GHRH)
Somatostatin (SS)
Which hypothalamic hormones regulate production of Prolactin?
Dopamine
Thyrotrophin releasing hormone (TRH)
Which hypothalamic hormones regulate production of TSH?
Thyrotrophin releasing hormone (TRH)
Which hypothalamic hormones regulate production of LH and FSH?
Gonadotrophin releasing hormone (GnRH)
Which hypothalamic hormones regulate production of ACTH?
Corticotrophin releasing hormone (CRH)
Vasopressin (VP)
Which hypothalamic hormones are inhibitory?
Somatostatin
Dopamine
How are hypothalamic hormones (and hence anterior pituitary hormones) released?
In a pulsatile fashion
Which is the dominant hypothalamic hormone in regulation of somatotrophin?
GHRH
As SS is a short polypeptide (minor in comparison)
Which is the dominant hypothalamic hormone in regulation of prolactin?
Dopamine
What are the main targets of growth hormone?
General body tissue Particularly liver (causes secretion of IGF 1 and 2)
What are the main targets of Prolactin?
Breasts in lactating women
What is the main target of thyrotrophin?
Thyroid
What are the main targets of gonadotrophins?
Testes (men)
Ovaries (women)
What is the main target of corticotrophin?
Adrenal cortex
Why does growth hormone stimulate liver to make IGF 1 and 2?
They are somatomedins (mediate growth)
IGF 1 also has indirect effect on growth (has anabolic and metabolic effects)
What are the indirect effects on growth caused by IGF 1?
Stimulation of aa transport into cells and protein synthesis
Increased gluconeogenesis
Stimulation of lipolysis leading to increased fatty acid production
Increased cartilaginous and somatic cell growth
What is the “on” switch for growth hormone?
GHRH
What is the “off” switch for growth hormone?
Somatostatin
What does dopamine constantly inhibit?
Production of prolactin by lactotrophs in anterior pituitary
What do you need to increase prolactin?
Reduction in dopamine
What is prolactin essential for?
Milk production
How is prolactin regulated?
By neuro-endocrine reflex arc
What is the neuro-endocrine reflex arc in a breast feeding woman?
- Neural part- suckling stimulates neuronal tactile receptors
- Feedback to hypothalamic dopamineuric neurones
- Suppresses dopamine
- Less inhibition of prolactin
- More prolactin released
- Formation of milk in breast
