The kidneys are important to the body’s production of urine. They also play a role in regulating important components in the blood.
Oxygenated blood comes to the kidneys from the right and left renal arteries off the abdominal aorta. Deoxygenated blood leaves the kidneys via the right and left renal veins that run into to the inferior vena cava.
The kidneys are highly complicated “filtration factories.” Inside each kidney, the renal arteries branch into smaller and smaller parts until they make contact with the core structural and functional units of the kidney, the nephrons.
The nephrons include tiny coiled tubes of capillaries and their associated tubules. Each kidney has approximately 1 million of them. The nephrons regulate waste, water, and other materials in the blood and urine to adjust to the body’s changing needs.
Other important parts of the kidney include:
- Renal pyramids: cone-shaped lobes consisting of parallel segments of nephrons
- Calyx: cup-like structures that help collect urine from the hilar tip of each renal pyramid on its way to the renal pelvis
- Renal pelvis: funnel-shaped, first portion of the ureter in the kidney
- Hilum: the section that’s the entry and exit points of the kidney for the renal veins, renal arteries, and ureter located on the medial side of the kidney
Within each nephron is a small sac of capillaries called the glomerulus that’s surrounded by Bowman’s capsule.
In these capillaries, under tight pressure, materials are constantly being filtered out of the blood. The pressure in each glomerulus is higher than in any other capillary. Each glomerulus needs that pressure to actively filter foreign particles out of the body.
Because of their need for high pressure, the kidneys also help control blood pressure by producing renin.
Renin helps increase the blood pressure and retain sodium in the bloodstream, which leads to water retention. Both the resulting arterial constriction and sodium and water retention help restore normal blood pressure if it dips.
The kidneys also regulate the production of red blood cells. When the kidneys don’t get enough oxygen, their distress call comes in the form of production of erythropoietin. Erythropoietin is a hormone that stimulates the bone marrow to produce more oxygen-carrying red blood cells.
After the kidneys have performed their cleansing function, the filtered, deoxygenated blood leaves the kidneys through the renal vein, moves up the inferior vena cava, and returns to the heart.