Fluid excretion

Blood enters each kidney from its renal artery, a major branch of the aorta, the body's main artery.

Once inside the kidney, the blood passes through a set of filtering systems called nephrons. These are the main functioning units of the kidney. Each kidney contains more than 1 million such units, each consisting of a tuft of small blood vessels, called a glomerulus, and some tubules. Although most nephrons measure 50 to 55 mm in length, the nephrons with renal corpuscles located within the cortex near the medulla are longer than the nephrons with renal corpuscles in the cortex nearer to the exterior of the kidney.

First, the blood passes through the glomerulus. The blood cells, proteins, large particles, and some of the water remain in the bloodstream. Everything else, including a large volume of water, filters out and passes into the tubule.

In the tubule, an important process occurs to control what will be excreted in the urine and what will be reabsorbed into the blood. Waste products (urea, creatinine, and uric acid) and excess salts, water, and calcium remain within the tubule. The other substances are absorbed. These absorbed substances are then returned to the bloodstream. Thus, the composition of the urine is determined by both the need to get rid of unwanted substances and the need to retain other substances.

The urine that has remained in the tubule emerges from its lower end, enters the ureter, and goes to the bladder, where it is stored. When the nerves of the bladder signal a feeling of fullness, the urine is avoided through the urethra.

Ex. 23. Read and translate the following words:

Adjacent; maintain; urea; erythropoiesis; cushion; cardiac output; interlobar; papillae; arcuate artery; radial artery; arteriole; peritubular; glomerule; link.

Ex. 24. Read the following text: