Endocrinology 2 - The Hypothalamo-adenohypophysial Axis Flashcards
Describe the position of the pituitary gland.
It is attached to the base of the brain within a bony dip called the sella turcica (turkish saddle).
What is another name for the pituitary gland?
The hypophysis
Describe the growth of the pituitary gland.
- The anterior gland is formed from upward growth from the buccal cavity, called the Rathke’s pouch.
- The posterior pituitary is produced from a downward growth from the base of the brain.
- These growths combine to make one gland.
What is another name for the anterior pituitary gland?
Adenohypophysis
What is another name for the posterior pituitary gland?
Neurohypophysis
Describe the structure of the adenohyphosis in relation to the relevant surrounding structures.
- The hypothalamic nuclei have projections called the hypothamaic neurones. These neurones may go to the posterior pituitary or the median eminence, if they have shorter axons.
- The body of the anterior pituitary is the pars distalis, while the pars tuberalis wraps around the pituitary stalk.
Describe the structure of the blood system in the anterior pituitary.
- The median eminence contains the primary capillary plexus, which is fenestrated.
- The secondary capillary plexus is in the anterior pituitary, and is also fenestrated.
- These are connected by the long portal veins.
- Blood enters the median eminence via the superior hypophysial artery, and exits the anterior pititary via the cavernous sinus.
Describe the general process of granule release from the anterior pituitary.
- The hypothamaic neurone is stimulated to release neurosecretin, hormones that enter the primary capillary plexus via fenestrations.
- This travels down the long portal veins to the secondary capillary plexus.
- Here they stimulate release of hormones from granules by exocytosis
List the 5 types of adenohypophysial cells and what they produce.
- Somatotrophs produce growth hormone/ somatotrophin
- Lactotrophs produce prolactin
- Thyrotrophs produce thyroid stimulating hormone/ thyrotrophin
- Gonadotrophs produce LH and FSH
- Corticotrophs produce adrenocorticotrophic hormone
What are the protein adenohypophysial hormones (more than 50aa)?
- Growth hormone/ somatotrophin
- Prolactin
What are the glycoprotein adenohypophysial hormones, and what is their structure?
- Glycoprotein hormones have alpha and beta subunits - the alpha subunit is common in these hormones.
- Thyroid stimulating hormone/ thyrotrophin
- The gonadotrophs - LH and FSH
What does LH and FSH stand for?
Luteinising hormone and follicle stimulating hormone.
What are the polypeptide hormones?
Adenocorticotrophic hormone
Which hypothalamic hormones regulate the production of growth hormone/ somatotrophin?
- Growth hormone releasing hormone (GHRH) is stimulatory
- Somatostatin is inhibitory.
Which hypothalamic hormones regulate the production of prolactin?
- Dopamine is the primary hormone, and it is inhibitory. Prolactin is under negative control - low levels of dopamine mean more prolactin
- Partially controlled by thyrotropin releasing hormone (stimulatory)
Which hypothalamic hormones regulate the production of thyroid stimulating hormone?
- Thyrotrophin releasing hormone (stimulatory)
Which hypothalamic hormones regulate the production of LH and FSH?
Gonadotrophin releasing hormone (GnRH) (stimulatory)
Which hypothalamic hormone regulates the production of ACTH?
- Mainly controlled by corticotrophin releasing hormone (stimulatory)
- Also controlled by vasopressin (stimulatory)
What are the target cells of growth hormone?
General body tissues, especially the liver.
What are the target cells of prolactin?
Breasts in lactating women.
What are the target cells of thyrotrophin?
Thyroid
What are the target cells of the gonadotrophs?
Testes and ovaries
What are the target cells of the corticotrophin?
Adrenal cortex
What happens following somatotrophin binding to GH receptors on the liver?
- The liver produces somatomedins (in adults primarily IGF I, in foetuses IGF II)
- These mediate the effects of GH in the body tissues.
What are the effects of growth hormone?
- May be direct or indirect via IGF I
- Stimulation of amino acid transport into cells, and therefore protein synthesis.
- Increase gluconeogenesis
- Stimulate lipolysis and therefore fatty acid production
- Increase cartilaginous growth and somatic cell growth
How does negative feedback of GH occur?
- Somatotrophin affects the hypothalamus.
- Somatomedins directly feedback to the anterior pituitary, and indirectly effects the hypothalamus to reduce GHRH
List the factors that stimulate somatotrophin production.
- Sleep
- Stress
- Oestrogen
- Exercise
- Fasting
- Amino acids
- Ghrelin (from the stomach)
Describe the neuroendocrine reflex arc in milk production.
- Suckling on the breast stimulates tactile receptors.
- This suppresses the hypothalamic dopaminergic neurones via the afferent neural pathway.
- This reduces dopamine production
- Prolactin production increases, and as a result milk production occurs.
