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Kidneys and Associated Structures
Human body has two dark brown, bean shaped kidneys in the abdominal region, one on either side of the vertebral column. The right kidney is a little lower than the left one. The outer surface of kidney is convex while the inner surface is concave. The following structures are attached with kidneys.
A tube which arises from each kidney and enters in urinary bladder is called ureter. It transports urine from kidneys to urinary bladder. Urinary bladder is a muscular sac which collects urine from both ureers. A fine tube through which urine is released from urinary bladder to the outside is called Urethra.
Internal Structure of Kidney.
Internally, each kidney is divided into three regions renal cortex, renal medulla and renal pelvis. Renal Cortex is the outermost region. Renal Medulla is the middle region which is divided into conical masses called Renal pyramids. Renal Pelvis is the inner area where urine is drained.
The urine from renal pelvis moves into ureter.
Nephron.
Nephrons are the functional units of the kidneys. They are the tubules where urine is formed.
There are over one million Nephrons in each kidney. Each Nephron has two parts, renal corpuscle and renal tubule.
Renal Corpuscle
It is the first part of Nephron. It consists of two structures glomerulus and Bowman's capsule. Glomerulus is a tuft of blood capillaries formed by the division of small arteries. Bowman's capsule is a cup shaped structure enclosing glomerulus.
Renal Tubule.
This part of Nephron starts after Bowman's capsule. The first coiled part of renal tubule is called proximal tubule. The next part is U shaped and is called Loop of Henle. The last part of the renal tubule is again coiled and is called Distal Tubule.
The distal tubules of many Nephrons open in a collecting duct. Many collecting ducts join and drain into renal pelvis.
Function of Kidneys
Blood carries wastes materials from the body to the kidneys. Inside the kindneys, blood reaches the capillaries of glomerulus.
Here, most of the water and wastes materials are filltered from the blood into the Bowman's capsule as filtrate. This filtrate which moves into the renal tubule of nephron also contains some useful substances. During its passage towards the collecting duct, 99% of the filtrate (Containing useful substances) is reabsorbed into the blood in capillaries around renal tubule. During this reabsorption, more waste materials are absorbed from blood capillaries into the renal tubule filtrate. Now, the filtrate in renal tubule is the Urine which moves into collecting ducts and then into renal pelvis.
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