The pineal gland in humans is a clone-shaped structure of about 1 cm in length. It is located near the center of the brain. The pine clone-like organ consists of specialized secretory cells called pinealocytes, which synthesize the hormone melatonin and secrete it into the bloodstream by means of the surrounding cerebrospinal fluid. Melatonin has significant effects on reproduction and daily physiologic cycles, most notably the circadian rhythms.

Seasonal affective disorder (SAD) is a condition caused by the overproduction of melatonin, especially during the longer nights of winter. Its symptoms include tiredness, weight gain, sadness, profound depression, and oversleeping. Treatment of SAD thus should consist of exposure to bright lights for several hours each day to inhibit melatonin production. There is indication that melatonin plays a role in cancer inhibition (see Slide 19).

The pancreas has both exocrine and endocrine functions. The bulk of it is a ducted gland secreting digestive enzymes into the small intestine through the pancreatic duct. Its other function is achieved by means of its many small clusters of endocrine cells called islets of Langerhans. These islets consist of four types of cells called alpha, beta, delta, and gamma.

The alpha cells secrete glucagons, which mobilize glucose, fatty acids, and amino acids from stores into the blood in response to a low sugar level. The beta cells are responsible for the secretion of insulin which is needed to metabolize glucose. Patients are said to have diabetes mellitus if their pancreas does not make enough insulin to lower the blood sugar level, or if their muscle, fat, and liver cells do not respond to insulin’s normal function, or both.