recap

40.2 recap

The pituitary is the interface between the nervous system and the endocrine system. The posterior pituitary releases two neurohormones, antidiuretic hormone (ADH) and oxytocin. The anterior pituitary, under the control of other neurohormones from the hypothalamus, releases four tropic hormones that control other endocrine glands. In addition, the anterior pituitary produces and releases five other hormones that act directly on non-endocrine tissues. The hypothalamus and pituitary are under negative feedback control by the hormones of their target glands.

learning outcomes

You should be able to:

  • Describe the relationships between the hypothalamus and the pituitary gland.

  • Explain developmental origins of the anterior pituitary and the posterior pituitary.

  • Explain how a negative feedback loop controls hormone secretion.

Question 1

Provide a developmental explanation of why posterior pituitary hormones are released from neurons and anterior pituitary hormones are released from epithelial cells.

During development, the posterior pituitary is derived from an outpocketing of the brain and the anterior pituitary is derived from an outpocketing of the embryonic mouth tissue. Thus the posterior pituitary is neural tissue, and it is nerve cells that produce and release the posterior pituitary hormones, which are neurohormones. The anterior pituitary comes from gut epithelium, and the secretory cells develop from gut epithelial cells.

Question 2

How do hypothalamic neurons control the release of hormones from the anterior pituitary?

Hypothalamic neurons release tiny quantities of releasing or release-inhibiting hormones that diffuse into portal blood vessels between the hypothalamus and the anterior pituitary. These hypothalamic hormones leave the portal capillaries in the anterior pituitary and diffuse to anterior pituitary cells that have receptors for those particular release or release-inhibiting hormones. Those anterior pituitary cells respond by changing the release of their hormones, which include four tropic hormones (thyrotropin, adrenocorticotropin, and the gonadotropins LH and FSH) and growth hormone.

Question 3

Explain what is meant by negative feedback in the hypothalamic control of endocrine function.

Negative feedback in the hypothalamic control of endocrine function involves the inhibitory effect of the end hormone on the hypothalamic production of the hypothalamic releasing (or release-inhibiting) hormone that controls the anterior pituitary cells that produce the tropic hormones controlling the cells or gland that produce and release the end hormone.

854

The hypothalamic and pituitary hormones and some of the endocrine glands they control are easy to conceptualize because they share common features in how they are organized and function. But the entire list of hormones is highly diverse, making generalizations difficult. We cannot consider all of the hormones in this chapter. Instead, we focus on hormones that have some common functions—one of which is the coordination of developmental processes.