THE UROGENITAL SYSTEM 



307 



blood pressure in the glomerulus is considerably greater than that in 

 capillaries generally, so that filtration through the glomerular capillaries is 

 increased. The. renal veins parallel the arteries and receive the same 

 names. Lymphatics and sympathetic nerves are abundant. 



Ureters. The renal ducts or ureters convey the excretions of the 

 kidneys to the bladder. Each ureter is a tube about a quarter of an 

 inch in diameter and about twelve inches long. Within the sinus of 

 the kidney, each ureter enlarges into a renal pelvis, which fills the sinus 

 and branches into the renal calyces. The human kidney has two major 

 calyces, superior and inferior, and each of these subdivides again into three 

 to five minor calyces. Each of the minor calyces is connected with one 



PROXIMAL CONVOLUTED TUBULE 



COLLECTING TUBULE 



GLOMERULUS 



A. CORTEX B. MEDULLA 



Fig. 273. — Sections of the human kidney. Section A is taken from the region of the 

 cortex, B from the medulla. Glomeruli which are abundant in the cortex are lacking in 

 the medulla. (Redrawn from Bremer after Schaper.) 



or more renal papillae and in this way receives the urine from the col- 

 lecting tubules. The two ureters open into the bladder on its posterior 

 surface, about an inch from the beginning of the urethra. Three layers 

 appear in a cross section of an ureter, an inner mucosa of transitional 

 epithelium, a muscularis coat of longitudinal and circular muscles, and an 

 outer adventitia of loose connective tissue. 



The Bladder. The bladder is a muscular sac, the shape and size of 

 which vary greatly since, when distended with urine, it may increase 

 twenty to thirty times its size when empty. A median connective-tissue 

 ligament, the urachus, a rudiment of the embryonic allantoic stalk, extends 

 from the bladder to the umbiUcus. 



The lining of the bladder is a layer of transitional epithelium capable 

 of great distension. Next to this is a layer of loose connective tissue 

 with many elastic fibers. The greater portion of the thickness of the 

 wall of the bladder is, however, a coat of smooth muscle fibers arranged 



