6-Posterior pituitary gland

Question 1

Hormones

Answer 1

vasopressin and oxytocin

Question 2

Synthesis

Answer 2

Occurs in supraoptic and paraventricular nuclei
Hormones processed en route to produce active hormones (neurophysins)

Question 3

Oxytocin mechansim

Answer 3

Binds a GPCR (Gq)
Increases Pi turnover
Mobilisation of intracellular Ca

Question 4

Milk ejection

Answer 4

In mammary gland
Milk secreted into small sacs (alveoli)
surrounded by smooth muscle (myoepithelium)
Oxytocin receptors found in smooth muscle
Act of suckling on nipple picked up by sensory neurones via spinal reflex arc
stimulates oxytocin release
Contraction
Fear, anxiety, pain and alcohol can inhibit it

Question 5

Uterine smooth muscle contractions in birth

Answer 5

Increase in oxytocin receptors on smooth muscle
released when fetus stimulates cervix
enhances contractions
Pitocin (synthetic oxytocin) can be used if contractions not enough
If labour starts early, antagonists such as atosiban can be used
Pitocin can cause cerebral palsy as can starve baby of oxygen

Question 6

Maternal behaviour

Answer 6

Acts in mothers brain and gets to baby through milk

Question 7

Oxytocin in men

Answer 7

Present in sperm fluid
May facilitate sperm transport
Similar social effects

Question 8

Suppression

Answer 8

Acute stress, catecholamines released from adrenals
Reduces milk volume in cows
Sex steroids reduce production
Reason for big release at birth is decrease in progesterone

Question 9

Vasopressin mechanism

Answer 9

Binds receptors on collecting ducts on kidneys and promotes water reabsorption
Absence causes impermeability of tubules to water
Stimulates synthesis of aquaporins and insertion in kidney tubule
Decreases osmolality of urine
AQP-2 inserted in apical membrane
3&4 already inserted in basolateral membrane

Question 10

Activation

Answer 10

Sensed by hypothalamic osmoreceptors
Baroreceptors in aortic arch, left atrium and carotid sinus detect drop in blood volume
Both cause vasopressin release
Secretion increased by:
Angiotensin
Pain
Trauma
Nausea
Vomiting
Blood loss
Drugs like nicotine and morphine

Decreased by alcohol and caffeine

Question 11

Diabetes insipidus

Answer 11

Excess urine
Up to 16L per day
Treated with exogenous vasopressin

Hypothalamic diabetes insipidus caused by a deficiency in vasopressin secretion
caused by head trauma and hypothalamic tumours

Nephrogenic diabetes insipidus
Kidney insensitve to vasopressin
Mutation in vasopressin receptor/AQP-2 gene