The Pitutuitar...fuck it, gland.

Question 1

You can think of the posterior pituitary as an extension of this organ:

Answer 1

Hypothalamus. The posterior pituitary gland is composed of axons whose cell bodies are in the hypothalamus. The axons terminate at a capillary bed where they release the hormones (oxytocin and ADH) that they produced.

Question 2

How are trophic hormones transported from the hypothalamus to the anterior pituitary to signal for release of other hormones?

Answer 2

Hypothalamo-pituitary portal system/Long portal vessel

Question 3

Name the two nuclei of the hypothalamus responsible for synthesis of oxytocin and ADH.

Answer 3

Supraoptic- Oxytocin and paraventricular nuclei- ADH. Which nucleus produces which hormone is still being debated as there is cross production, etc.

Question 4

Describe the function of oxytocin and the positive feedback mechanism that is classically associated with this hormone (few positive feedback mechanisms in hormone action).

Answer 4

Oxytocin stimulated contraction of smooth muscles of a pregnant uterus and of myoepithelial cells in the mammary gland (to secrete milk). The dilation of the cervix (via stretch receptors) in turn stimulates the production of oxytocin by the hypothalamus. Touch receptors on the nipple also positively feed back on the production of oxytocin as a baby feeds.

Question 5

Describe the action of ADH.

Answer 5

Regulates body retention of water (increases water channels in the walls of kidney tubules (DCT & CD).
Also causes increased contractility of arterial smooth muscle, increasing resistance and thus BP in times of hypotension.

Question 6

Describe the structure, synthesis, and secretion of OT and ADH.

Answer 6

They are nonapeptides (9 amino acids long), w/ -S-S- bridge, similar structures, overlapping activities.
Synthesized as much larger molecules: pro-pressophysin & pro-oxyphysin.
They are stored in granules (polar), with neurophysins* I & II.
They are secreted when action potentials when action potentials reach the nerve terminals; analogous to neurotransmitter release. They are secreted together with their respective neurophysins*.
*Neurophysins are carrier proteins which transport the hormones oxytocin and vasopressin to the posterior pituitary from the paraventricular and supraoptic nucleus of the hypothalamus.

Question 7

Describe the two conditions that independently stimulate paraventricular nucleus synthesis of ADH.

Answer 7

1) Drop in ECF (plasma) volume [dehydration, hemorrhage] –> ^ ADH secretion
2) Rise in osmolarity sensed by hypothalamus [dehydration] –> ^ ADH secretion

Question 8

List the 6 hormones secreted by the anterior pituitary and their common chemical structure and composition.

Answer 8

GH, Prolactin, ACTH, LH, FSH, TSH

All are peptide hormones (polar).

Question 9

Describe the unique relationship between ACTH and melanocyte stimulating hormone.

Answer 9

The structure of MSH lies within the ACTH molecule. So excess ACTH (Addison’s disease) causes hyperpigmentation.

Question 10

Describe which cells (basophils vs acidophils) within the anterior pituitary (pars distalis) secrete which hormones.

Answer 10

Basophils: FSH, LH, TSH, ACTH
Acidophils: GH, PRL

**The cells that secrete GH & PRL (acidophils) make up the bulk of the anterior pituitary mass (~70%)

Question 11

Due to similarities in structure and function, test assays need to measure which subunit (alpha or beta) of TSH, LH, & FSH in order to distinguish them?

Answer 11

Beta. The beta subunit of one hormone is dominant when compared to the alpha of another, in terminal function.