The Hypothalamo-Adenohypophysial Axis Flashcards
Where does the pituitary gland lie in the brain and under which structure?
At the base of the brain in the sella turcica
Directly under the hypothalamus
What is the function of the hypothalamus?
Regulates the endocrine system
Which ventricle does the hypothalamus lie around?
The third ventricle
How do the two lobes of the pituitary gland develop?
Anterior (adenohypophysis) - ‘grows up’ and attaches to base of the brain
Posterior (neurohypophysis) - ‘grows down’ and attaches to the anterior lobe, consists mainly of nerve axons and terminals
What is the region between the hypothalamus and the pituitary gland called?
Region of median eminence
What are the hypothalamic nuclei?
Clusters of nerve cell bodies in the hypothalamus
Two types of neurones in the hypothalamic nuclei?
Neurones that pass through the region of median eminence and terminate at the neurohypophysis (posterior pituitary)
Neurones that terminus at the region of median eminence
Artery supplying region of median eminence?
Superior hypophysial artery
Process of neurosecretion into the hypothalamo-hypophysial portal system and to target cells?
Hypothalamic neurone is activated, hypothalamic neurosecretion occurs
Neurosecretion released into fenestrated primary capillary plexus in the region of median eminence
Neurosecretions travel by long portal veins and secondary capillary plexus to anterior pituitary target cells
What happens when neurosecretions reach the anterior pituitary cells?
Stimulates adenohypophysial hormone release into the CAVERNOUS SINUS and then into general circulation via the jugular veins
General process of adenohypophysial hormone production and packaging?
Enzymes cleave prohormones to produce bioactive hormone
Hormones stored in secretory granules
2 protein adenohypophysial hormones?
Somatotrophin - produced by somatotrophs
Prolactin - produced by lactotrophs
2 glycoprotein adenohypophysial hormones?
Thyrotrophin - thyrotrophs
Gonadotrophins (LH and FSH) - gonadotrophs
Polypeptide adenohypophysial hormone?
Corticotrophin (ACTH) - corticotrophs
What molecules stimulate and inhibit release of somatotrophin?
Somatotrophin releasing hormone - stimulates release
Somatostatin - inhibits release
What molecules stimulate and inhibit release of prolactin?
Thyrotrophin releasing hormone - stimulates release
Dopamine - inhibits release
What molecule stimulates thyrotrophin release?
Thyrotrophin releasing hormone - stimulates release
What molecule stimulates LH and FSH (gonadotrophins) release?
Gonadotrophin releasing hormone - stimulates release
What molecule stimulates corticotrophin release?
Corticotrophin releasing hormone - stimulates release
Vasopressin - also stimulates release (secondary)
Which tissues do the 5 main adenohypophysial hormones act on?
Somatotrophin - general body tissue, especially liver Prolactin - breasts (lactating women) Thyrotrophin - thyroid Gonadotrophin - testes, ovaries Corticotrophin - adrenal cortex
Effect of somatotrophin binding to receptors on the liver?
Release of SOMATOMEDINS (IGF I, IGF II)
Effect of somatotrophin binding to general body tissues?
Increased growth and development
Somatomedin metabolic effects?
Amino acid transport into cells
Protein synthesis
Lipid metabolism leading to increased fatty acid production
Insulin resistance - decreased glucose utilisation and increased blood glucose concentration
Increased cartilage growth
Which molecules negatively feedback on somatotrophin production?
Somatotrophin and somatomedin release both themselves inhibit further somatotrophin production
Somatostatin also inhibits release
Somatotrophin releasing hormone stimulates somatotrophin release, what other conditions stimulate its release?
Sleep (stage 3/4) Stress Oestrogens Exercise Gasting/hypoglycaemia Amino acids Ghrelin (from stomach)
Prolactin main physiological effect?
Breast lactogenesis in lactating women
Secondary effects of prolactin?
Increased LH receptors in gonads
Increase Na+/water reabsorption
Steroidogenesis
Immunological effects, stimulates T cells
What is prolactin release stimulated by and what is the mechanism resulting in release?
Suckling stimulates tactile receptors in breast nipple
Afferent signals stimulate release of TRH and inhibit release of dopamine
These increase prolactin release
Prolactin stimulates milk production by endocrine efferent neural pathway
This is an example of a NEUROENDOCRINE REFLEX ARC
