Expansion
Oxytocin and antidiuretic hormone, made in the hypothalamus and stored in the posterior lobe
Expansion
Both are nonapeptides synthesised in hypothalamic neurones and transported down axons bound to neurophysin:
- Antidiuretic hormone (vasopressin): mainly from the supraoptic nucleus
- Oxytocin: mainly from the paraventricular nucleus
Oxytocin actions
- Uterine contraction in labour, an example of positive feedback, since cervical stretch stimulates release which increases contraction (the Ferguson reflex)
- Milk ejection (let-down), by contracting myoepithelial cells; triggered by suckling and conditionable by the infant’s cry
Antidiuretic hormone acts on V2 receptors for water reabsorption and V1 for vasoconstriction.
Two structural consequences follow from the posterior lobe being neural: it has no portal blood supply, receiving a direct arterial supply instead, and pituitary infarction (Sheehan syndrome) or surgery affects the anterior lobe far more than the posterior. Conversely, damage high in the stalk or hypothalamus causes diabetes insipidus, while a low stalk section may not, since hormone can still leak from the cut end.