Biology of Man 477 



known as appendicitis. Extending upward on the right side from the 

 cecum is the ascending colon. The transverse colon connects the latter 

 with the descending colon which descends down the left side of the lower 

 abdominal cavity. The sigmoid connects the lower end of the descending 

 colon with the rectum. The latter empties externally through the anus. 



(6) The liver is the largest gland in the body and is divided into the right 

 and left lobes. It is located just below the diaphragm and in the adult 

 weighs about 2.8 per cent of the total body weight. The liver arises 

 embryologically as an outgrowth of the duodenum and migrates to its 

 normal position below the diaphragm. The liver manufactures bile from 

 the red blood corpuscles and pours it into the gall bladder through the 

 cystic duct. The bile duct leads from the gall bladder to the duodenum. 



(7) The pancreas is an elongated organ, about two by six inches, which 

 lies between the stomach and the duodenum. In adult human beings it 

 weighs about 2/2 ounces. Certain cells of the pancreas secrete the pan- 

 creatic juice which is carried by the duct of Wirsung to the common bile 

 duct. In some cases the duct of Wirsung and the common bile duct 

 open separately into the duodenum. 



V. CIRCULATION IN MAN 



The circulatory system is a so-called "closed system" composed of a 

 heart, contractile arteries, capillaries, and veins. The muscular, cone- 

 shaped heart is about the size of a fist and is divided by a partition into 

 right and left sides. Each side is divided into an upper chamber called 

 the atrium (auricle)* and a lower, more muscular, ventricle. The very 

 muscular left ventricle pumps oxygenated blood (Figs. 237 to 241) 

 through the aorta (artery) to all parts of the body (except lungs). From 

 all parts of the body (except lungs) blood is carried back to the right 

 atrium through a series of veins. From the right atrium the blood passes 

 through the right atrioventricular valve (tricuspid valve) into the right 

 ventricle from which it is pumped through the pulmonary arteries to the 

 lungs where it is oxygenated. The blood is returned from the lungs by 

 pulmonary veins (two right and two left) to the left atrium, from which 

 it passes through the left atrioventricular valve (bicuspid valve) into the 

 left ventricle. The portion of the system which supplies the body is 

 called the systemic circulation and the part which carries blood to the 

 lungs to be oxygenated is the pulmonary circulation. These, however, 

 are all one complete circulation unit. 



*The terms atrium and auricle are sometimes used synonymously, as are auriculoventricular 

 and atrioventricular, although there are minor differences. Atria is the plural of atrium. 



