Patterns and Processes of LifePatterns and Processes of Life

Chapter 17Chapter 17

The Endocrine SystemThe Endocrine System

Membrane receptors facilitate the coordination of gene expression and key developmental events.

Figure 17.2

The nervous system carries signals between the brain and the rest of the body at speeds of up to 150 m/sec!

Figure 17.4

Figure 17.5

Chemical signaling by hormones: (a) Endocrine hormones are produced by cells of endocrine glands and transported by the blood to target cells. (b) Some hormones are released by neurosecretory cells, which function in both the nervous and endocrine systems. (c) A few hormones are secreted over short distances through tissue fluid.

The mechanism of peptide hormones(1) Peptide hormones are produced by an endocrine gland and carried by the blood. (2) Receptors on the plasma membrane of a target cell bind with the hormone. The hormone itself does not enter the cell. (3) An enzyme in the plasma membrane changes ATP to cyclic AMP (cAMP). The cAMP molecule is the “second messenger,” carrying the hormone’s signal through the cell. (4) Enzymes are activated, triggering a series of reactions. (5) These reactions bring about the changes controlled by the hormone.

Figure 17.7

The mechanism of steroid hormones(1) Steroid hormones are released by endocrine cells and carried by the blood. (2) Because of their size and structure, steroid hormones enter the cell. (3) The hormones enter the nucleus, where they bind to receptor molecules. The hormone-receptor complex binds to DNA and regulates gene expression. (4) If the gene is “switched on” it will be transcribed and translated to protein. (5) The protein made in this way is the effect of the hormone’s release.

Figure 17.8

The hormones controlling insect development(a) Hormones secreted by the brain and prothoracic gland: Neurosecretory cells in the brain produce brain hormone (BH), which is stored and released by a gland just behind the brain. BH’s main target is the prothoracic gland, which produces molting hormone (MH), also called ecdysone. The corpus allatum produces juvenile hormone (JH). (b) Hormones’ effects on development of Cecropia moth: Development is the result of interactions between JH and MH. MH is produced to stimulate growth and molting. When JH concentrations are high, a molt produces a larger larva. When JH level drops, the larva molts and becomes a pupa. At this point, JH production stops and the moth develops its adult organs and emerges from the pupa.

Figure 17.10

The hypothalamus and pituitary control and coordinate endocrine function.

Figure 17.12

The anterior pituitaryNeurosecretory cells of the hypothalamus produce releasing and inhibiting hormones (red dots). These hormones enter capillaries in the hypothalamus, move through portal vessels and reach their target cells via a second capillary system in the anterior lobe of the pituitary. Endocrine cells in the anterior pituitary secrete hormones which are carried to other endocrine glands in the body.

Figure 17.13

The posterior pituitaryNeurosecretory cells of the hypothalamus are connected directly to the posterior pituitary. These cells produce ADH and oxytocin, which are stored in and released by the posterior pituitary.

Figure 17.14