Question

A milkman is very upset one morning as his cow refuses to give any milk. The milkman's wife gets the calf from the shed. On feeding by the calf, the cow began expressing sufficient milk.

Describe the role of endocrine gland and pathway associated with this response?

Answer 1

Suckling by the calf creates a neuroendocrine reflex which results in increase of oxytocin from the neurohypophysis. Oxytocin is synthesised in the hypothalamus in specific nuclei, the paraventricular nucleus and the supra optic nucleus (a cluster of nerve cells in the brain is often called a nucleus).

Neurons in this region (hypothalamic nuclei) synthesise the oxytocin precursor and packages it into vesicles. The oxytocin concentration in the blood normally begins increasing within 1-2 min, after the udder stimulation.

It brings about contraction of smooth muscles of the udder resulting in the milk flow. A direct infra-udder function of oxytocin like hormone would do the same function.

It can be summarised as follows

Udder (suckling stimulus) $\Rightarrow$ Brain (hypothalamus) $\Rightarrow$ Neurohypophysis $\Rightarrow$ Blood (oxytocin) $\Rightarrow$ Udder (smooth muscles) $\Rightarrow$ Milk flow.