Endocrinology 2 - Adenohypophysial System

Question 1

What is the Sella Turcica and why is it important from a clinical point of view?

Answer 1

Sella Curcica - Bony cavity in which the pituitary is attached to. It is important because any possible tumour will protrude out towards the brain (unless very malignant and gets through bone).

Question 2

What are the 2 types of tissue that the pituitary is derived from?

Answer 2

Glandular Tissue - Buccul cavity which extends and starts growing upwards in the embryo = Adenohypophysis.
Nervous Tissue - downwards movement of tissue from hypothalamus = Neurohypophysis.

Question 3

What are Hypothalamic Nuclei?

Answer 3

Bundles of neurones in the hypothalamus.

Question 4

What is the Median Eminence?

Answer 4

The region that lies between the pituitary stalk and the hypothalamus. Some axons from the hypothalamic nuclei terminate here. Has lots of capillaries (Primary Capillary Plexus)that receive blood from the superior hypophysial artery. It is outside the blood brain barrier = capillaries are fenestrated.

Question 5

How is the anterior pituitary controlled by the hypothalamus? (Hypothalamo-hypophysial axis)

Answer 5

1. Hypothalamic nuclei activated - release neurosecretions that are hormones to median eminence.
2. Hormones travel in hypothalamo-adenohypophysial to anterior pituitary.
3. Bind to target cell receptors - adenohypophysial cells release hormones into blood.

Question 6

What kind of hormone are adenohypophysial hormones?

Answer 6

They are protien/polypeptide hormones. Proteins, Glycoproteins (made of alpha and beta subunits) and polypeptides.

Question 7

List the adenohypophysial hormones and their target cells

Answer 7

Somatotrophin - General tissue + liver
Prolactin - Breasts ( lactating women)
Thyrotrophin - Thyroid
Gonadotrophin - Testes (men) + Ovaries (women)
Corticotrophin - Adrenal cortex

Question 8

What are the actions of Somatotrophin?

Answer 8

Works on many tissues = increases metabolic actions (Direct effect).
The liver is the main target = binds to receptors on hepatocytes and stimulates production of IGF I + II that are important for growth (Indirect effect).

Question 9

What are the metabolic actions of Somatotrophin? (5)

Answer 9

1. Stimulates AA transport in cells.
2. Stimulates protein synthesis.
3. Increased cartilaginous growth.
4. Stimulation of lipid metabolism = increased fatty acid production.
5. Decreased glucose use = increased blood glucose concentration.

Question 10

What increases somatotrophin levels? (8)

Answer 10

1. Somatotrophin releasing hormone (Growth hormone releasing hormone.
2. AA - when you have a meal you get lots of AA = increase protein synthesis.
3. Hypoglycemia - to increase blood glucose level.
4. Exercise.
5. Stress.
6. Oestrogen,
7. Sleep
8. Ghrelin

Question 11

What are inhibitors of Somatotrophin? (3)

Answer 11

1. Somatostatin (pituitary).
2. Somatotrophin (hypothalamus).
3. IGF I (Pituitary - direct, hypothalamus - indirect)

Question 12

What are the effects of Prolactin? (4)

Answer 12

1. Breast lactogenesis (main effect).
2. Inhibits LH release.
3. Sexual behaviour reduced.
4. Immune system (e.g. increased T-cells).

Question 13

What are the steps for prolactin control?

Answer 13

1. Baby suckling breasts.
2. Stimulates tactile receptors on nipple.
3. Nerve to hypothalamus.
4. Thyrotrophin releasing hormone (dopaminergic neurones inhibited).
5. Prolactin release.