MULTICELLULAR ANIMALS 205 



gans. The hormones from the posterior lobe aflfect the muscles of 

 the walls of the blood vessels, causing contraction, affect similar 

 types of muscles in the reproductive system, apparently are also con- 

 cerned in the activity of the kidneys, and have still other effects. 



The Pancreas. The pancreas varies in form among vertebrates. 

 In Man it is a large lobed gland located posterior to the stomach. It 

 contains two sorts of tissues. One type is glandular tissue which 

 secretes the pancreatic juice that is employed in digestion. These 

 secretions are passed to the duodenum by means of the pancreatic 

 duct opening with the bile duct from the liver. In the mammalian 

 pancreas the other type of tissue is scattered as islets among the 

 tissue concerned with digestive enzyme production. The products 

 of these islets are passed directly into the blood as in other endocrine 

 glands. The islet hormone is known as insulin and regulates the 

 sugar content of the blood. We have seen how the liver converts 

 the digested starches into glycogen, the so-called animal starch, and 

 stores it within the liver cells. We have also noted that this starch, 

 glycogen, is again converted into a sugar and released into the 

 blood for the use of muscles and other tissues. Insulin appears to be 

 the chemical agent which controls this release of sugar into the 

 blood. Deficiency in the activity of the pancreas brought about by 

 disease or degeneration of the islets produces a serious condition 

 known as diabetes mellitus, which is characterized by a constant 

 loss of sugar from the blood into the urine, with resulting break- 

 down of body functions. A remedy, at least temporary, is afforded 

 by the administration of insulin. 



The Adrenals. The adrenals are glands located very near the 

 kidneys, in mammals just anterior and slightly medial. Each 

 adrenal consists of two portions which secrete different hormones. 

 The central or medullary portion of the gland secretes adrenalin, 

 a substance that affects blood pressure, causes an output of muscle 

 sugar from the liver into the blood in emergencies, and affects the 

 sympathetic nervous system which in turn affects many automati- 



