Chapter Summary

• Endocrine cells secrete chemical signals that induce responses in other cells that have receptors for those molecules. In some cases endocrine cells are aggregated into endocrine glands.

• Hormones are endocrine signals that are secreted from a cell, circulate in the blood, and bind to target cells distant from the secreting cell. Review Figure 40.1

• Hormones fall into three general categories: protein and peptide hormones, steroid hormones, and amine hormones. Peptide and protein hormones and some amine hormones are water-soluble; steroid hormones and some amine hormones are lipid-soluble. Review Figure 40.2

• Receptors for water-soluble hormones are located on the cell surface. Receptors for most lipid-soluble hormones are inside the cell.

• The same hormone can cause different responses in different target cells. Review Figure 40.3

• The chemical structures of hormones are highly conserved. Through evolution, however, hormones acquire different functions in different animal groups. Review Figure 40.4

• In humans, the major endocrine glands are distributed around the body. Review Figure 40.5, Activity 40.1

• The pituitary gland is the interface between the nervous and endocrine systems. The anterior pituitary develops from embryonic mouth tissue; the posterior pituitary develops from the developing brain. Review Figure 40.6, Focus: Key Figure 40.7

• The posterior pituitary secretes two neurohormones: antidiuretic hormone (ADH) and oxytocin. The anterior pituitary secretes tropic hormones (thyrotropin, adrenocorticotropin, luteinizing hormone, and follicle-stimulating hormone) as well as growth hormone, prolactin, endorphins, enkephalins, and melanocyte stimulating hormone.

• The anterior pituitary is controlled by neurohormones produced by cells in the hypothalamus and transported through portal blood vessels to the anterior pituitary. See Animation 40.1

• Hormone release is controlled in part by negative feedback loops.

• The hormone irisin may mediate effects of exercise on the brain. Review Investigating Life: How Could Irisin Mediate the Benefits of Exercise on Cognition?

• Pioneering experiments in illustrating hormonal action showed that two hormones, PTTH and ecdysone, control molting in arthropods. A third hormone, juvenile hormone, prevents maturation. Review Figure 40.8, Animation 40.2

• Sex hormones (androgens in males, estrogens and progesterone in females) control sexual development, secondary sexual characteristics, and reproductive functions. Review Figures 40.9, 40.10

• The thyroid gland is controlled by thyroid-stimulating hormone (TSH, also called thyrotropin) and secretes thyroxine, which controls cell metabolism. Review Figure 40.11

• The level of calcium in the blood is regulated by three hormones. Calcitonin from the thyroid lowers blood calcium by promoting bone deposition. Parathyroid hormone (PTH) raises blood calcium by promoting bone turnover and decreasing calcium excretion. Calcitriol promotes calcium absorption from the digestive tract. Review Figure 40.13, Animation 40.3

• The pancreas secretes three hormones. Insulin stimulates glucose uptake by cells and lowers blood glucose. Glucagon raises blood glucose, and somatostatin slows the rate of nutrient processing. Review Figure 40.14

• The adrenal gland has two portions, one within the other. The inner portion, the adrenal medulla, releases epinephrine and norepinephrine in response to stress. The outer portion, the adrenal cortex, produces three classes of corticosteroids: glucocorticoids, mineralocorticoids, and small amounts of sex steroids. Review Figure 40.16

• Aldosterone is a mineralocorticoid that stimulates the kidneys to conserve sodium and excrete potassium. Cortisol is a glucocorticoid that is released in response to stressful stimuli but acts more slowly than the hormones of the adrenal medulla.

• The pineal gland releases melatonin, a hormone involved in controlling biological rhythms.