KIDNEYS AND URINARY SYSTEM
WHERE IN THE BODY?
Y
our body makes wastes and unwanted substances that it must remove. Some of this waste comes out of the end of the digestive tract and is called solid waste. The other main kind is liquid waste, called urine. Urine is created a very different way than solid waste. It is made, not from digestive leftovers, but by filtering the blood.
The parts of the urinary system are inside the lower body or abdomen. The kidneys are at the upper rear, on either side of the backbone behind the lower ribs. The bladder is the lowest part of the abdomen, between the hips.
• See pages 38–39 for information on DIGESTION.
KIDNEYS – SIZE AND SHAPE • The right kidney is usually about 0.4–0.6 in. lower than the left one. kidney
kidney
• Average kidney measurements are 4.3 in. high, 2.3 in. wide, and 1.1 in. from front to back.
MAIN PARTS OF THE KIDNEY Cortex Outer layer, formed mainly of microscopic blood vessels from the filtering units, called nephrons.
• Each kidney is shaped like a bean with a slight indent on one side.
• In a woman, the typical weight of the kidneys is 4.5–4.9 ounces.
bladder
• In a man, the typical weight is 4.9–5.2 ounces.
Medulla Inner layer, formed mainly from the tiny tubes of the nephrons.
The kidneys’ huge blood supply can be seen by the size of the renal arteries (red) and veins (blue). The pale ureter tubes lead down to the bladder.
Renal pelvis Space in the middle of the kidney where urine collects.
KIDNEY MICROFILTERS
Bowman’s capsule glomerulus
Each kidney contains about one million microscopic filters, called nephrons. • Each nephron begins with a tiny tangle or knot of the smallest blood vessels, called capillaries, known as the glomerulus. • Waste substances and water squeeze out of the glomerulus into a cup-shaped part around it, called Bowman’s capsule. The work of the kidney takes place in the nephrons.
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• The wastes and water then flow through a microscopic tube, the renal tubule, where some water, minerals, and salts are taken back into the blood. • All the tiny tubules of all the nephrons in one kidney, straightened out and joined end to end, would stretch 62 miles. • The end result is urine, which is mostly water containing dissolved wastes like urea and ammonia.