Endocrinology 2 - The Hypothalamo-adenohypophysial Axis

Question 1

Describe the position of the pituitary gland.

Answer 1

It is attached to the base of the brain within a bony dip called the sella turcica (turkish saddle).

Question 2

What is another name for the pituitary gland?

Answer 2

The hypophysis

Question 3

Describe the growth of the pituitary gland.

Answer 3

• 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.

Question 4

What is another name for the anterior pituitary gland?

Answer 4

Adenohypophysis

Question 5

What is another name for the posterior pituitary gland?

Answer 5

Neurohypophysis

Question 6

Describe the structure of the adenohyphosis in relation to the relevant surrounding structures.

Answer 6

• 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.

Question 7

Describe the structure of the blood system in the anterior pituitary.

Answer 7

• 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.

Question 8

Describe the general process of granule release from the anterior pituitary.

Answer 8

• 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

Question 9

List the 5 types of adenohypophysial cells and what they produce.

Answer 9

• Somatotrophs produce growth hormone/ somatotrophin
• Lactotrophs produce prolactin
• Thyrotrophs produce thyroid stimulating hormone/ thyrotrophin
• Gonadotrophs produce LH and FSH
• Corticotrophs produce adrenocorticotrophic hormone

Question 10

What are the protein adenohypophysial hormones (more than 50aa)?

Answer 10

• Growth hormone/ somatotrophin

- Prolactin

Question 11

What are the glycoprotein adenohypophysial hormones, and what is their structure?

Answer 11

• Glycoprotein hormones have alpha and beta subunits - the alpha subunit is common in these hormones.
• Thyroid stimulating hormone/ thyrotrophin
• The gonadotrophs - LH and FSH

Question 12

What does LH and FSH stand for?

Answer 12

Luteinising hormone and follicle stimulating hormone.

Question 13

What are the polypeptide hormones?

Answer 13

Adenocorticotrophic hormone

Question 14

Which hypothalamic hormones regulate the production of growth hormone/ somatotrophin?

Answer 14

• Growth hormone releasing hormone (GHRH) is stimulatory

- Somatostatin is inhibitory.

Question 15

Which hypothalamic hormones regulate the production of prolactin?

Answer 15

• 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)

Question 16

Which hypothalamic hormones regulate the production of thyroid stimulating hormone?

Answer 16

• Thyrotrophin releasing hormone (stimulatory)

Question 17

Which hypothalamic hormones regulate the production of LH and FSH?

Answer 17

Gonadotrophin releasing hormone (GnRH) (stimulatory)

Question 18

Which hypothalamic hormone regulates the production of ACTH?

Answer 18

• Mainly controlled by corticotrophin releasing hormone (stimulatory)
• Also controlled by vasopressin (stimulatory)

Question 19

What are the target cells of growth hormone?

Answer 19

General body tissues, especially the liver.

Question 20

What are the target cells of prolactin?

Answer 20

Breasts in lactating women.

Question 21

What are the target cells of thyrotrophin?

Answer 21

Thyroid

Question 22

What are the target cells of the gonadotrophs?

Answer 22

Testes and ovaries

Question 23

What are the target cells of the corticotrophin?

Answer 23

Adrenal cortex

Question 24

What happens following somatotrophin binding to GH receptors on the liver?

Answer 24

• The liver produces somatomedins (in adults primarily IGF I, in foetuses IGF II)
• These mediate the effects of GH in the body tissues.

Question 25

What are the effects of growth hormone?

Answer 25

• 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

Question 26

How does negative feedback of GH occur?

Answer 26

• Somatotrophin affects the hypothalamus.

- Somatomedins directly feedback to the anterior pituitary, and indirectly effects the hypothalamus to reduce GHRH

Question 27

List the factors that stimulate somatotrophin production.

Answer 27

• Sleep
• Stress
• Oestrogen
• Exercise
• Fasting
• Amino acids
• Ghrelin (from the stomach)

Question 28

Describe the neuroendocrine reflex arc in milk production.

Answer 28

• 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.