hypothalamus
Think of the hypothalamus as the brain's thermostat-and-control-panel for the body's internal world. It is a small region at the base of the brain, no bigger than an almond, yet it watches over body temperature, hunger, thirst, sleep, and stress, and then quietly adjusts the body's hormones to keep everything in balance.
Anatomically the hypothalamus sits below the thalamus and just above the pituitary gland, to which it is connected by a stalk. It is the meeting point of the nervous system and the endocrine system: its neurons sense signals from blood and brain, then respond by firing nerve impulses or by secreting tiny amounts of hormones. These hormones travel a short distance to control the pituitary gland, which in turn commands many other glands.
The hypothalamus contains clusters of specialized neurons. Some make releasing and inhibiting hormones (such as GnRH, TRH, CRH, GHRH, and somatostatin) that are delivered to the anterior pituitary through a private set of blood vessels. Others make oxytocin and vasopressin, sending them down their long axons into the posterior pituitary for release into the bloodstream.
Because it integrates so many functions, damage to the hypothalamus can disrupt growth, reproduction, water balance, appetite, and the body's stress response all at once. This makes it a small structure with outsized clinical importance.
When you become dehydrated, osmoreceptors in the hypothalamus detect the rise in blood concentration, trigger thirst, and stimulate vasopressin release to make the kidneys conserve water.
The hypothalamus links a sensed need (low water) to a hormonal response.
The hypothalamus is part of the brain (neural tissue), not a classic gland made of glandular epithelium. It acts as an endocrine organ through its neurosecretory neurons.