After reading this chapter, you should be able to:
Describe anatomic connections between the hypothalamus and the pituitary gland and their functional significance.
List the factors that control water intake, and outline the way in which they exert their effects.
Describe the synthesis, processing, storage, and secretion of the 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.
Name the hypophysiotropic hormones, and outline the effects that each has on anterior pituitary function.
List body temperature-regulating mechanisms, and describe the way in which they are integrated under hypothalamic control to maintain normal body temperature.
Discuss the pathophysiology of fever.
Many of the complex autonomic mechanisms that maintain the chemical constancy and temperature of the internal environment are integrated in the hypothalamus. The hypothalamus also functions with the limbic system as a unit that regulates emotional and instinctual behavior.
HYPOTHALAMUS: ANATOMIC CONSIDERATIONS
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.
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. 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.
RELATION TO THE PITUITARY GLAND
There are neural connections between the hypothalamus and the posterior lobe of the pituitary gland and vascular connections between the hypothalamus and the anterior lobe. The posterior pituitary is made up in large part of the endings of axons that arise from cell bodies in the supraoptic and paraventricular nuclei and pass to the posterior pituitary (Figure 17–1) via the hypothalamohypophysial tract. The anterior and intermediate lobes of the pituitary arise from an evagination from the roof of the pharynx (see Chapter 18). Few, if any, nerve fibers pass to the anterior pituitary from the hypothalamus. Rather, the portal hypophysial vessels form a direct vascular link. A network of fenestrated capillaries called the primary plexus lies on the ventral surface of the hypothalamus (Figure 17–1). Capillary loops also penetrate the median eminence. The capillaries drain into the portal hypophysial ...