360 THE VERTEBRATE BODY 



or both. Weakened bones, tooth disintegration, and cyst formation on 

 the bones may indicate hyperfunction. 



The pancreas is interesting because it is both a duct and a ductless 

 gland at the same time. We have already learned that it secretes pan- 

 creatic juice which passes through the pancreatic duct to the duodenum. 

 In addition, it secretes an important hormone, insulin, that regulates 

 sugar metabolism and storage in the body. Histological studies of the 

 pancreas explain its dual function ; there are two distinct types of tissue. 

 Many small ducts can be seen lined with secretory cells that supply the 

 pancreatic juice for digestion, but in addition there are small islands of 

 cells having no connection with the ducts. These are the isles of 

 Langerhans which produce insulin. 



A person having a deficient supply of insulin develops a condition 

 known as diabetes. Because of the improper sugar metabolism the con- 

 centration of sugar in the blood becomes high and is removed by the 

 kidneys so that there will be sugar in the urine. If the deficiency is 

 great a person may go into a diabetic coma and die unless insulin is ad- 

 ministered. Unfortunately, insulin is destroyed by digestive juices and 

 must be administered by injection. However, diabetics soon overcome 

 the "needle complex" and can lead fairly normal lives by giving them- 

 selves regular injections of this hormone. They need to learn to regulate 

 the amount of insulin taken to correspond with the carbohydrate intake, 

 for too much insulin will cause insulin shock which is even more dan- 

 gerous than diabetic coma. 



The adrenal glands are a pair of small bodies lying just above the 

 kidneys. If one of these glands is cut in two it will be seen to consist of 

 two distinct portions, an outer bark, the cortex, and an inner marrow, 

 the medulla. These portions represent two entirely separate endocrine 

 glands. 



The medulla secretes the well-known hormone adrenalin, which has 

 several marked effects on the body. When injected into the body it 

 causes a shrinkage of the capillaries, elevation of the blood pressure, an 

 increase in heart beat, a decrease in blood-clotting time, an elevation of 

 the sugar content of the blood through its release from the liver, and an 

 increased muscular power and resistance to fatigue. Small quantities 

 are continually being released by this gland, but in times of emotional 

 stress extra quantities are released. This seems to be a body adjustment 

 which makes us ready for extra activity that may accompany emotional 

 stress : if we are angry, to fight ; if we are frightened, to run ; and so on. 

 Our body is keyed up for emergency action and in case we are injured 

 in the action the blood will clot more readily. Because of these effects 

 adrenalin is a valuable medical product. It may restore heart beat when 



