After reading this chapter, you should be able to:
Describe the anatomic connections between the hypothalamus and the pituitary gland and the functional significance of each connection.
Define the role of the hypothalamus in producing and secreting hormones of the posterior pituitary.
Discuss the effects of vasopressin, the receptors on which it acts, and how its secretion is regulated.
Discuss the effects of oxytocin, the receptors on which it acts, and how its secretion is regulated.
Outline the hypophysiotropic hormones, and the effect each has on anterior pituitary function.
List the temperature-regulating mechanisms, and describe the way in which they are integrated under hypothalamic control to maintain normal body temperature in both cold and heat stress.
Explain how the hypothalamus regulates water intake, and outline how thirst is regulated
Discuss the pathophysiology of fever.
The hypothalamus regulates complex autonomic mechanisms that maintain the chemical constancy of the internal environment, and regulates metabolic endocrine processes to control body temperature and satiety. It synthesizes and secretes hypothalamic hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus also functions with the limbic system as a unit that regulates emotional and instinctual behavior.
HYPOTHALAMUS: ANATOMIC CONSIDERATIONS
The hypothalamus (Figure 17–1) is located in the lower part of the brain above the pituitary gland (Chapter 16, Figure 16–3) and releases hormones directly into the hypophysial portal system, which carries them directly to the pituitary gland. The hypothalamus is the portion of the anterior end of the diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei. It is divided into a variety of nuclei and nuclear areas.
Human hypothalamus, with a superimposed diagrammatic representation of the portal hypophysial vessels.
AFFERENT & EFFERENT CONNECTIONS OF THE HYPOTHALAMUS
The principal afferent and efferent neural pathways to and from the hypothalamus are mostly unmyelinated. Many connect the hypothalamus to the limbic system. Important connections also exist between the hypothalamus and nuclei in the midbrain tegmentum, pons, and hindbrain.
Norepinephrine-secreting neurons with their cell bodies in the hindbrain end in many different parts of the hypothalamus (see Figure 7–2). Paraventricular neurons that secrete oxytocin and vasopressin project in turn to the hindbrain and the spinal cord. Neurons that secrete epinephrine have their cell bodies in the hindbrain and end in the ventral hypothalamus.
An intrahypothalamic system is composed of dopamine-secreting neurons that have their cell bodies in the arcuate nucleus and end on or near the capillaries that form the portal vessels in the median eminence. Serotonin-secreting neurons project to the hypothalamus from the raphe nuclei.
RELATION TO THE PITUITARY GLAND