There are two kidneys in the human body, one on each side of the abdomen above the level of the belly button and towards the back. While the kidneys are part of the urinary system, they are closely linked to the circulatory system. Blood is carried through a complex system within the kidney where blood chemistry is regulated. The kidneys are so efficient that only one is necessary for survival.
The renal artery carries blood to the kidney where it branches into many smaller arteries within the kidney. These arteries carry blood to the nephrons, the functional units of the kidneys. Blood then travels through many small veins that merge to form the renal vein, which returns the blood to the heart.
Blood Volume and Pressure
Blood volume and blood pressure are directly related. If blood sodium levels are high, an increase in body fluid volume will increase, including blood volume. Higher blood volume leads to an increase in blood pressure. The kidneys remove sodium from the blood leading to a decrease in body fluid volume and blood pressure.
The kidneys remove metabolic waste from the blood. Urea is produced during cellular catabolism and is removed by the kidneys and excreted in the urine.
Regulation of pH
The kidneys help maintain the body's normal pH level by removing acid from the blood. The kidneys also reabsorb bicarbonate, a buffer.
The kidneys are responsible for the excretion of certain hormones into the blood. Erythropoietin stimulates red blood cell production. Specialized cells in the kidneys release renin in response to low blood pressure. Renin is a hormone that leads to an increase in blood pressure.
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