Chap. 15 CHEMICAL REGULATION ENDOCRINE GLANDS 269 



Cholecystokinin and Delivery of Bile. Acid food from the stomach stimu- 

 lates other lining cells of the duodenum to secrete this hormone into the 

 blood. This stimulates the muscles of the gallbladder to contract and pour 

 bile into the intestine. 



Enterogastrone, the Antiulcer Hormone. After partly digested food or 

 chyme leaves the stomach, the secretion of gastric juice and the contractions 

 of its muscles are slowed or stopped. Nervous mechanisms are probably 

 involved, but experiments have shown that such rest periods of the stomach 

 are caused by enterogastrone. Its production in the walls of the intestine is 

 stimulated by the arrival of the food, mainly by the neutral fat. 



Enterocrinin. Extracts made from intestinal lining will stimulate the release 

 of secretion stored in the lining. The hormone is called enterocrinin. 



Pituitary Gland 



Appearance, Position, and Parts. The human pituitary gland (hypophysis) 

 is the size and shape of a large pea. It is located almost exactly in the center 

 of the head in a cradlelike space on the floor of the cranium above the soft 

 palate (Figs. 15.13, 15.14). It is formed by two outgrowths, an anterior part 

 which grows upward from the roof of the embryonic mouth and becomes 

 the pars anterior, pars tuberalis, and pars intermedia, and a posterior part 

 formed by a downgrowth of the developing brain which becomes the pars 

 nervosa. It remains permanently connected with the brain by the pituitary 

 stalk through which it is well supplied with blood vessels and nerves. 



The early anatomists named the gland pituitary (L., pituitarius, phlegm) 

 because they thought that its nearness to the nasal cavities meant that it 

 poured a secretion into them. It is commonly known as the master gland 

 since it regulates growth, controls other endocrine glands, and affects tissues 

 and organs. With some variations in structure it is present in the vertebrates 

 from the lower fishes through the mammals. 



Functions of the Pars Anterior. Although the manufacture of as many as 

 10 to 15 hormones has been attributed to the pars anterior, the most recent 

 evidence indicates that it probably produces seven. Three of them influence the 

 development and function of the reproductive organs, the ovaries, testes, 

 and the mammary glands. Three of its other hormones affect metabolism, 

 stimulating growth, regulating the thyroid gland and the cortices of the 

 adrenal glands (Table 15.1). The seventh, not completely estabhshed, may be 

 associated with the formation of red blood cells. All of them are proteins; 

 three are glycoproteins, i.e., combinations of a carbohydrate and a protein; 

 and three are simple proteins. Several have been extracted in fairly pure 

 form, but none has been synthesized. It is now believed that the influence of 

 the pars anterior on carbohydrate and fat metabolism which was formerly 

 assigned to hormones called diabetogenic, pancreatrophic, parathyrotrophic. 



