Posterior Pituitary

Question 1

What is the posterior pituitary?

Answer 1

direct extension of the hypothalamus

Question 2

Function of the posterior pituitary?

Answer 2

stores and secretes hormones that were synthesized by the hypothalamus - to affect parts directly

Question 3

What are the hormones of the posterior pituitary?

Answer 3

1. Antidiuretic hormone (ADH)/arginine vasopressin (AVP)

2. oxytocin

Question 4

Describe the structure of the hormones?

Answer 4

hormones are peptides consisting of 9 AA residues

Question 5

ADH mainly acts where?

Answer 5

on the collecting ducts of the kidney to prevent water excretion

Question 6

When is ADH secreted?

Answer 6

1. low blood volume

2. high blood osmolarity

Question 7

What is the effect of ADH secretion?

Answer 7

1. has vasoconstricting action that increase blood pressure thus decreasing blood osmolarity
2. retain water from urine

Question 8

ADH is synthesized by?

Answer 8

supraoptic vasopressinergic neurons

Question 9

ADH secretion is stimulated by?

Answer 9

raised osmolarity - low blood volume

Question 10

ADH secretion is inhibited by?

Answer 10

lowered osmolarity

Question 11

The target organ of ADH is?

Answer 11

the kidney

Question 12

What is the effect of ADH on the kidney?

Answer 12

increases the permeability of the collecting duct to reabsorb water

Question 13

When is oxytocin released?

Answer 13

when the baby suckles on the mothers breast

Question 14

Oxytocin is synthesized by?

Answer 14

paraventricular oxytocinergic neurons

Question 15

Oxytocin secretion is stimulated by?

Answer 15

1. stretch receptors in the nipple and cervix

2. estrogen

Question 16

How is oxytocin released?

Answer 16

1. stretch receptors in the nipple send signals to the brain via sensory nerves
2. the signal causes depolarization in the paraventricular neurons and oxytocin release from the posterior pituitary
3. Oxytocin reaches the myoepithelial cells of the breast which contract pushing milk out of the breast

Question 17

Oxytocin secretion is inhibited by?

Answer 17

stress

Question 18

The target organ for oxytocin is?

Answer 18

1. uterus

2. mammary glands

Question 19

What is the effect of oxytocin on the mammary glands?

Answer 19

smooth muscle contraction leading to milk ejection

Question 20

How can ADH deficiency be treated?

Answer 20

desmopressin - a long acting vasopressin analogue to control fluid loss

Question 21

What is the effect of oxytocin on the uterus?

Answer 21

smooth muscle contraction leading to birth

Question 22

Consequence of a deficiency of ADH?

Answer 22

diabetes insipidus - prevents osmotic control of the kidney leading to very dilute polyuria

Question 23

What are the signs and symptoms of deficiency of ADH?

Answer 23

1. polyuria - over 20L of urine can be passed per day
2. potentially fatal dehydration
3. constant thirst

Question 24

Deficiency of ADH can be caused by?

Answer 24

1. trauma
2. surgery
3. tumours

Question 25

Consequence of excess ADH secretion?

Answer 25

causes water retention resulting in hypoosmotic hypomatraemia (low sodium)

Question 26

Excess ADH can be caused by?

Answer 26

syndrome of inappropriate secretion of ADH (SIADH) 
can be caused by: 
1. neurological
2. endocrine 
3. malignant or infective diseases

Question 27

Name the symptoms of excess ADH?

Answer 27

symptoms progress from malaise and weakness to confusion and coma

Question 28

Consequence of a deficiency of oxytocin?

Answer 28

1. failure to progress in labour 2. difficulty with breast feeding