Our Essential Kidneys

• The two kidneys of the human body have a variety of important biological functions. Buried deep within the cavity of the abdomen, the kidneys work continuously to balance the fluids on the body, filter the blood and rid the body of waste. The kidneys are so vital to the function of the human body that there are two. If one kidney no longer works, the body is able to survive using the remaining kidney.
  
  The kidney's functions are carried out using an intricate filtration system located in a portion of the kidney called the nephron. The nephrons are made of tubes surrounded by tiny blood vessels which pass the blood through a filtration system in the kidney and into the kidney tubing. The filtering process takes place in structures called the renal corpuscles. As the blood flows into the kidney area it is shuttled into a region of high pressure called the glomerulus, which surrounds the corpuscles. This high pressure area moves small objects such as water, glucose, electrolytes and urea into the tubing of the corpuscles while large molecules like hemoglobin stay in the blood stream. The resulting liquid is then moved on through the kidneys for further processing.
  
  

The Renal Tubules

• After the initial processing in the renal corpuscles the filtered material then moves to a structure of the kidney called the renal tubules. In the tubules water, electrolytes, urea, minerals and amino acids are transported back into the blood stream according to the current needs of the body. The highest volume of reabsorption occurs in the tubules where over 99% of the filtrate is returned to the blood stream. Chlorine ions, water and urea are all pushed back into the blood stream if the concentration is greater in the filtrate than in the blood stream. Sodium ions and other electrolytes are actively moved back into the blood if needed, even if they are in low concentration in the filtered fluid. The concentration of sodium and electrolytes are controlled by hormonal signals.
  
  

The Collecting Ducts

• After the fluid has passed through the renal tubules it moves into collecting ducts for the final stages of filtration. The collecting ducts absorb additional water, electrolytes and ions. A great extent of the material reabsorbed in the collecting ducts is controlled by hormones. For example, sodium ions are moved back into the blood stream based on the levels of the hormone aldosterone and water reabsorption is regulated by vasopressin. Ions such as potassium and hydrogen are moved from the blood stream into the collecting ducts in order to maintain the pH in the body. At the final point in the kidneys only waste products, excess electrolytes and water remain. Once the urine is formed it is moved out of the kidneys and through a tube called the ureter before traveling to the urinary bladder.