Baroregulatory afferent fibres arise in low-pressure receptors that are sited in the atria of the heart and the great veins of the chest, and in high-pressure receptors that are present in the carotid body and arch of the aorta. These fibres terminate in a group of nuclei within the brainstem. They then relay in the posteromedial nucleus of the hypothalamus before ending in the paraventricular and supraoptic nuclei. The potent stimulatory effect of vomiting on vasopressin release is probably mediated by the vagus nerve. It remains unclear whether the effects of hypoglycaemia are monitored by a hypothalamic glucostat and whether an angiotensin sensor exists to appreciate changes in blood angiotensin concentration. The release of oxytocin by suckling is a neurohormonal reflex, the afferent fibres being carried by the vagus nerve from the breast.
