Pancreatic islets by scarce alpha, delta and PP cells in the periphery, human islets display alpha and beta cells in close relationship with each other throughout the cluster. Islets can influence each other through paracrine and autocrine communication, and beta cells are coupled electrically to six to seven other beta cells (but not to other cell types). The paracrine feedback system of the pancreatic islets has the following structure: A large number of G protein-coupled receptors (GPCRs) regulate the secretion of insulin, glucagon and somatostatin from pancreatic islets, and some of these GPCRs are the targets of drugs used to treat type-2
Apocrine sweat gland ducts. The tubules are wrapped in myoepithelial cells, which are more developed than in their eccrine gland counterparts. In hoofed animals and marsupials, apocrine glands act as the main thermoregulator, secreting watery sweat. For most mammals, however, apocrine sweat glands secrete an oily (and eventually smelly) compound that acts as a pheromone, territorial marker, and warning signal. Being sensitive to adrenaline, apocrine sweat glands are involved in emotional sweating in humans (induced by anxiety, stress, fear, sexual stimulation, and pain). In a five-month-old human fetus, apocrine glands are distributed all over the body; after a few weeks, they exist in