Exam 2 (Lecture 7) - Oxytocin, Prolactin, and ADH

Question 1

Describe how prolactin and oxytocin regulate milk synthesis and ejection and which factors trigger the release of these two hormones?

Answer 1

1) Prolactin (polypeptide)
- stimulates lactogenesis is secretory alveolar cells
- stimulated by TRH and estrogen (from suckling reflex)
- inhibited by dopamine, GAP, and GABA

2) Oxytocin (nanopeptide)
- triggers milk ejection by stimulating contraction of myoepithelial cells
- stimulated by the suckling reflex

Question 2

What is galactorrhea?

Answer 2

Secretion of milky fluid from the breast of males (or females)

Hypothyroidism > increase of TRH > increase of prolactin

Question 3

What are other functions of oxytocin and prolactin?

Answer 3

1) Oxytocin and Prolactin are the “mother love” hormones; stimulate maternal behavior and pair bonding

2) Oxytocin:
- facilitates contraction of uterine myometrial cells during labor (prostaglandins also involved)
- stimulates secretion of uterine prostaglandin F2-alpha (toward the end of pregnancy)
- stimulates contraction of smooth muscles of reproduction organs during copulation
- can stimulate ADH receptors; severe water retention when oxytocin used to induce labor

Question 4

What is ADH, which gland secretes it and what is its main function?

Answer 4

1) Anti-diuretic hormone (nanopeptide)
2) Secreted by the posterior pituitary
3) Primary Functions:
- inhibits diuresis and controls blood volume and pressure
- increases water reabsorption by incorporating aquaporins in the apical membrane
4) Secondary Functions:
- Constriction of systemic, coronary, and pulmonary vessels; dilation of cerebral and renal vessels
- in large amounts, stimulates ACTH

Question 5

By which cellular mechanisms does ADH achieve its physiological effect?

Answer 5

ADH increases water reabsorption by incorporation of aqua porins in the apical membrane

Question 6

What are the primary stimuli that trigger ADH secretion?

Answer 6

High plasma osmolarity (low blood volume); detected by osmoreceptors

Blood pressure signals conveyed directly to the brain

Question 7

What is diabetes insipidus and how can it be treated? At which level of water intake would you suspect diabetes insipidus?

Answer 7

1) A condition associated with insufficient ADH action

2) Patients produce large volumes of dilute (hypotonic), tasteless (insipid) urine (polyuria) and exhibit intense thirst (polydipsia)

3) Suspected when water consumption is greater than 100 mL/kg/day and urine production without glucose is greater than 50 mL/kg/day

4) Can be treated with desmopressin (a synthetic analog of ADH; no pressor effects)