The small intestine is one of many organs that has endocrine functions in addition to its more familiar roles in the body. By producing such hormones as intestinal gastrin, gastric inhibitory peptide (GIP), secretin, and cholecystokinin, the small intestine regulates the activities of neighboring digestive organs and their secretions.
The thymus gland secretes thymosin, a protein hormone that stimulates the maturation and differentiation of T-lymphocytes. These cells of the immune system provide cell-mediated immunity, which not only includes attacks on infectious agents, but on infected cells as well.
Other endocrine-producing structures include the pineal gland, the kidney, and the heart. In response to light stimuli entering the eye, the pineal gland (located in the brain) releases melatonin, which is believed to play a role in regulating daily circadian rhythms. The kidney regulates red blood cell production through the secretion of erythropoietin. The heart, by secreting atrial natriuretic factor (ANF), helps regulate blood pressure, salt, and water balance.
Thymosin can directly _____.
Select one of the following: