Physiology 1 - The Pituitary

Question 1

Describe the anatomy of the pituitary gland?

Answer 1

Split into 2 parts:
Anterior Pituitary (Adenohypophysis) which is a true endocrine gland of epithelial origin

Posterior Pituitary (Neurohypophysis) which is derived from neural tissue

Question 2

How is the pituitary gland related to the hypothalamus?

Answer 2

Its physically connected by:

1) Pituitary Stalk (of which the post. pituitary is an extension)
2) Hypothalamo-Hypophyseal portal system to the ant pituitary

The hypothalamus controls what hormones are released by the pituitary gland

Question 3

What is another word for the pituitary stalk?

Answer 3

The Infandibulum

Question 4

Whats the function of the hypothalamo-hypophyseal portal system?

Answer 4

Carried trophic hormones from the hypothalamus to the anterior pituitary

Question 5

How do trophic hormones from the hypothalamus enter the hypothalamo-hypophyseal portal system?

Answer 5

Neurons of the hypothalamus release them at the median eminence into the bloodstream.

Question 6

What is the function of the infandibulum?

Answer 6

It carries neurohormones from the hypothalamus to the posterior pituitary where they are stored before released into the general blood supply

Question 7

What is a trophic hormone?

Answer 7

One which modulates the release of other hormones from its target tissue

Question 8

What is a neurohormone?

Answer 8

Hormones produced by nerve axons and released into the blood

Question 9

What hormones are released from the hypothalamus?

Answer 9

Trophic hormones that travel to the anterior pituitary

Non-trophic hormones released into the blood via the post. Pituitary

Question 10

Specifically what trophic hormones are released from the hypothalamus?

Answer 10

Releasing:

• Thyrotrophin releasing hormone (TRH)
• Corticotrophin “ (CRH)
• Growth Hormone “ (GHRH)
• Gonadotrophin “ (GnRH)
• Prolactin “ (PRH)

Inhibiting:

• Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
• Prolactin Inhibiting Hormone (PIH) aka Dopamine

Question 11

What physical class of hormone are the hypothalamic trophic hormones?

Answer 11

Entirely Peptide hormones

Except for dopamine (Prolactin Inhibiting Hormone) which is a catecholaamine

Question 12

What hormones are released from the Adenohypophysis?

Answer 12

• Thyrotrophin (Thyroid stimulating - TSH)
• Corticotrophin (Adrenocorticotrophic - ACTH)
• Gonadotrophins (Follicle Stimulatin - FSH & Luteinising - LH)
• Growth Hormone (GH)
• Prolactin

Question 13

What class of hormones are the Adenohypophysis hormones?

Answer 13

They’re all peptides

5 Are trophic, only prolactin is non-trophic

Question 14

So far the pituitary hormones are classed as:

Answer 14

Hypothalamus:

• Excretes 5 releasing trophic hormones
• 2 Inhibiting Trophic hormones
• Some Non-trophic hormones

Ant. Pituitary:

• 5 Trophic hormones
• 1 (Prolactin) non-trophic hormone

All so far are peptides except for Dopamine (Prolactin inhibiting hormone) released from the hypothalamus

Question 15

What -ve feedback mechanisms are involved in control of pituitary hormones?

Answer 15

Short Feedback Loop:
Trophic hormones released from the pituitary inhibit the hypothalamus

Long Feedback Loop:
Non-trophic hormones released from the final endocrine gland inhibit the ant pituitary

These mechanisms tightly control appropriate plasma levels of hormones

Question 16

So far we know the posterior pituitary releases Neurohormones produced in the hypothalamus, how are they made and released?

Answer 16

Peptide Neurohormones produced in the magnocellular neurons of the hypothalamus.

They travel down axons in the infandibulum and are stored in the post pituitary.

Activity in these neurons releases them into the blood

Question 17

What peptide neurohormones are released from the post. Pituitary?

Answer 17

Oxytocin

Vasopressin (ADH)

Question 18

Describe the mechanisms behind vasopressin?

Answer 18

Vasopressin or ADH regulates water balance.

Its released in response to low plasma volume, low BP and high plasma osmolarity.

It increases water reabsorption at the kidney collecting duct & vasoconstricts to raise BP

Question 19

Describe the mechanisms behind Oxytocin?

Answer 19

Oxytocin triggers milk ejection & uterine contraction in response to suckling & labour respectively

It causes milk duct and uterine smooth muscle to contract