Anterior, Intermediate, and Posterior Pituitary

Question 1

What differentiates a tropic hormone from a trophic hormone?

Answer 1

Tropic: stimulates a specific target gland to secrete a different set of hormones
Trophic: Affects the growth, nutrition, or function of another endocrine gland/cell

Question 2

What 3 components make up a pre-prohormone?

Answer 2

1. Signal peptide
2. Hormone
3. Cryptic peptide

Question 3

What components make up a prohormone? What was lost from the pre-prohormone?

Answer 3

Prohormones have hormone and cryptic peptide components, the signal peptide has been cleaved from the pre-prohormone.

Question 4

Where is the cryptic peptide cleaved off a prohormone, producing the mature hormone?

Answer 4

At dibasic Lysine/Arginine sites.

Question 5

What is the full name for POMC?

Answer 5

Pro-opiomelanocortin.

Question 6

Which lobes of the pituitary express pro-opiomelanocortin (POMC)?

Answer 6

The anterior lobe and the intermediate lobe, but not the posterior lobe.

Question 7

What POMC product is produced in the intermediate pituitary? What enzyme cleaves POMC to produce this?

Answer 7

Melanocyte stimulating hormone (MSH). Produced from the cleavage of POMC by prohormone convertase 2 (PC2).

Question 8

What POMC product is produced in the anterior pituitary? What enzyme cleaves POMC to produce this?

Answer 8

Adrenocorticotropic hormone (ACTH). Produced from the cleavage of POMC by prohormone convertase 1 (PC1).

Question 9

What product of POMC cleavage in the pituitary is also produced in the skin? What does this stimulate?

Answer 9

Melanocyte stimulating hormone (MSH) is also produced in the skin and stimulates the production of melanin for skin pigmentation.

Question 10

What major endocrine function is controlled by the secretion of adrenocorticotropic hormone (ACTH) (Hint: tropic effect)?

Answer 10

Steroid secretion (glucocorticoids, mineralocorticoids, androgens) from the adrenal cortex.

Question 11

What kind of receptors do POMC cleavage products bind to?

Answer 11

Melanocortin G-protein coupled receptors (GPCRs).

Question 12

What trophic effect can ACTH have on the adrenal cortex?

Answer 12

Crucial for the development of the adrenal cortex.

Question 13

When a melanocortin (POMC product) binds a GPCR, what kind of Galpha subtype is activated? What does this stimulate?

Answer 13

Galpha-s. Activates adenylyl cyclase (AC) to stimulate protein kinase A (PKA).

Question 14

What is the function of the melanocytes in mammals? How are they stimulated?

Answer 14

Stimulated by melanocyte stimulating hormone (MSH), they release melanin which protects skin cells from UV radiation damage.

Question 15

What is the function of the melanophores in amphibian or aquatic organisms? What stimulates this?

Answer 15

Stimulated by melanophore releasing hormone (MSH), they release pigment used for adaptive colour change/camouflage.

Question 16

How do radiotrophic fungi use melanin?

Answer 16

As a photosynthetic pigment which allows them to absorb gamma rays just as plants absorb sunlight for energy.

Question 17

How do microbes use melanin?

Answer 17

As protection from high temperature and chemical stresses.

Question 18

Besides production of melanin or pigment in the skin, what other role does melanocyte stimulating hormone (MSH) have?

Answer 18

Contributes to appetite regulation/suppression in the hypothalamus.

Question 19

How does the mechanism of stimulation by the hypothalamus differ for the anterior pituitary and the posterior pituitary?

Answer 19

Ant. Pit.: signalled by the arrival or hormones along the hypophyseal portal veins
Pos. Pit.: signalled by hormone-containing neurons which project from the hypothalamus

Question 20

What other names are often used to refer to vasopressin (VP)?

Answer 20

Arginine vasopressin (AVP) or antidiuretic hormone (ADH).

Question 21

How are vasopressin and oxytocin related?

Answer 21

They share structural homology except in 2 positions where the amino acids are different.

Question 22

What are the 2 main functions of vasopressin?

Answer 22

1. Osmoregulation (water balance)

2. Pressure regulation (vasoconstriction).

Question 23

What are the 3 main functions of oxytocin in women?

Answer 23

1. Uterine contraction
2. Milk ejection
3. Mother-offspring bonding

Question 24

In what way is oxytocin released from the posterior pituitary?

Answer 24

Secreted in pulses.

Question 25

What role does oxytocin play in the stress response?

Answer 25

Helps to inhibit adrenocorticotropic hormone (ACTH) release, calming after a stress response.

Question 26

How does vasopressin act as an osmoregulator in the kidney? What kind of receptor does it bind to?

Answer 26

Binds to a GPCR, signals the cells to express more aquaporins for greater water reabsorption.

Question 27

How does vasopressin regulate blood pressure?

Answer 27

By acting on blood vessels to constrict smooth muscle (the same pathway as for oxytocin).

Question 28

How is vasopressin involved in the stress response?

Answer 28

Signals the anterior pituitary to upregulate the secretion of adrenocorticotropic hormone (ACTH).

Question 29

What disease is cause by a lack of vasopressin? What are the symptoms of this disease?

Answer 29

Diabetes insipidus. Causes major excretion of very dilute urine. Causes excessive thirst and dehydration.

Question 30

What are the 3 major causes of diabetes insipidus?

Answer 30

1. Hypothalamic defect (no vasopressin production_
2. Nephrogenic (no uptake of vasopressin in the nephron)
3. Gestational (increased degredation)

Question 31

What hormone is responsible for pair bonding in the female prairie vole? What about the male?

Answer 31

Female: oxytocin
Male: vasopressin