(e) The renal pelvis is a cuplike cavity for the collection of urine that
empties into a ureter. As the pelvis extends from the kidney, it tapers into a funnel-like
convolution and then imperceptibly into the ureter.
c. Function. The kidneys eliminate the nitrogenous waste products of
metabolism and help maintain the constant chemical composition of the blood. They
excrete from about 1,000 to 1,800 cubic centimeters of urine in 24 hours. The glomeruli
and the tubules of the nephrons perform different functions in the production of urine.
(1) The glomeruli act as filters. Dissolved substances and water pass
through the capillary walls into the capsule. Blood pressure provides the force
necessary for filtration.
(2) The tubules transform the filtrate into urine. Tissue examination of the
tubules shows a great diversity of structure of the epithelium which lines them. It is
quite conceivable that some portions of the tubules absorb certain substances from the
filtrate while others secrete. The chemical and water constituents of the blood are kept
at a constant level by the functioning of the tubules. Radiopaque organic iodine
compounds, when injected intravenously, are normally excreted by the tubules with the
3-15. THE URETERS
The ureters are the two tubes which carry urine from the kidneys to the urinary
bladder (figure 3-8). Their upper portions are continuous with the renal pelvis. The
ureter proper is from 24 to 30 centimeters (10 to 12 inches) in length and varies in
caliber from about 1 centimeter proximally to 1 millimeter at the entrance of the urinary
bladder. Extending from its corresponding kidney, each ureter passes downward, one
on either side of the vertebral column, behind the peritoneum, to the pelvic brim. After
crossing the pelvic brim, the ureter passes along the lateral wall of the pelvic cavity and
curves downward, forward, and inward along the floor of the pelvic cavity, entering the
posterior portion of the urinary bladder. The wall of each ureter consists of an inner
mucous coat, a layer of muscles, and an outer fibrous coat.