Left Kidney Revealing Calyx and Renal Pyramid: This is a cross-section of the left kidney showing the calyces pryamids and urethra; the vasculature has been omitted. The calyces are the areas in the kidney that collect urine emptying from the papilla of the renal pyramids. They converge into the renal pelvis which connects with the ureter where urine will continue to travel to the bladder and then out of the body by expulsion through the urethra.
The human kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water everyday. These wastes are passed out of the body as urine. If the kidneys did not remove them these wastes would build up in the blood and damage the body. Damage to the kidneys can also occur in people who have had diabetes for many years particularly if the diabetes is not well controlled.
The kidneys are bean-shaped organs that serve several essential regulatory roles in vertebrate animals. They remove excess organic molecules (e.g., glucose) from the blood, and it is by this action that their best-known function is performed: the removal of waste products of metabolism (e.g., urea, though 90% of this is reabsorbed along the nephron.) They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure (via maintaining salt and water balance). They serve the body as a natural filter of the blood, and remove water soluble wastes, which are diverted to the urinary bladder. In producing urine, the kidneys excrete wastes such as urea and ammonium, and they are also responsible for the reabsorption of water, glucose, and amino acids. The kidneys also produce hormones including calcitriol, erythropoietin, and the enzyme renin, the last of which indirectly acts on the kidney in negative feedback.
Located at the rear of the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary bladder.
Renal physiology is the study of kidney function, while nephrology is the medical specialty concerned with kidney diseases. Diseases of the kidney are diverse, but individuals with kidney disease frequently display characteristic clinical features. Common clinical conditions involving the kidney include the nephritic and nephrotic syndromes, renal cysts, acute kidney injury, chronic kidney disease, urinary tract infection, nephrolithiasis, and urinary tract obstruction. Various cancers of the kidney exist; the most common adult renal cancer is renal cell carcinoma. Cancers, cysts, and some other renal conditions can be managed with removal of the kidney, or nephrectomy. When renal function, measured by glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not normally harmful, kidney stones can be painful, and repeated, chronic formation of stones can scar the kidneys. The removal of kidney stones involves ultrasound treatment to break up the stones into smaller pieces, which are then passed through the urinary tract. One common symptom of kidney stones is a sharp to disabling pain in the medial/lateral segments of the lower back or groin.
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