The Kidneys
Shaped like giant beans, the kidneys are the fluid regulators of the body. They produce urine and regulate blood. Most people are born with a pair of kidneys, located at the lower back wall of the abdomen, one on each side of the spine. Each kidney is roughly 5 inches (13 cm) long and 3 inches (8 cm) wide.
The Structure of the Kidneys
Weighing in at roughly 5 ounces (141 g) each, the kidneys receive about 20 percent of the blood pumped from the heart. The blood is delivered to the kidneys via the renal arteries and returned to general circulation by the renal veins. Each kidney produces urine and sends them through tubes called ureters into the bladder, located near the pelvis. Each kidney has its own ureter. The bladder will store the urine until the body expels it through the urethra and out of the body.
The Many Functions of the Kidneys
The kidneys play a large role in maintaining the body’s homeostasis, or balance. Their main function is to regulate fluids within the body. The kidneys do this by producing urine, which results in:
- Regulating blood volume. By removing excess fluid from the body, the kidneys maintain healthy levels of plasma necessary for healthy blood flow to other organs.
- Maintaining proper pH. By regulating ions, the kidneys keep blood from turning too acidic or basic.
- Regulating blood pressure. By balancing solute levels in the fluid surrounding blood cells, the kidneys help maintain healthy blood pressure.
- Balancing chemicals in the body. The kidneys help balance levels of sodium, potassium, calcium, and other ions in the body. They also regulate glucose levels.
- Filtering out waste and toxins. The kidneys filter out waste and toxins into the urine for excretion.
- Producing red blood cells. By secreting erthryopoietin, the kidneys stimulate production of red blood cells in bone marrow.
Structure of the nephron
- The nephron is the main filtration structure in the kidney being responsible for filtration and reabsorption.
- Over 1 million nephrons are typically present in one human kidney.
- Ultra-filtration occurs at the interface of the Glomerulus and the Bowman’s Capsule where high-pressure forces liquid and waste products (e.g. urea) through the capsule. Due to the fine filtering mechanism, proteins and cells within the blood are retained and smaller molecules are able to pass.
- Some important molecules, like glucose that pass through in the filtrate are selectively reabsorbed from the Tubule (Distal and Proximal) of the nephron back in to the blood. This is an active process, involving energy, but it worthwhile due to the importance of the compounds being retained.
- Any substances, not reabsorbed, flow through into the connecting duct and ultimately are excreted from the body via the bladder.
