Kidneys- Filtration units of our body
The kidneys maintain water volume and balance as well as regulate blood composition.
Structure of urinary system
Kidneys are two bean – shaped organs, each about the size of your fist,10 cm long
and 6 cm wide, located on either side of the backbone, just below the rib cage and
protected by the last two ribs. Kidneys weigh about 0.5 percent of total body weight.
The right side kidney is at a slightly lower level than the left one. Kidneys receive
the blood from the renal artery, process it, return the processed blood to the body
through the renal vein and remove the wastes and other unwanted substances in the
A tube, the ureter, arises from the notch (hilum) in the
median surface of each kidney and connects behind with the urinary bladder in the
lower part of the abdomen. The front end of the ureter is somewhat expanded into
the kidney and is called the pelvis. Urine flows from the kidneys
through the ureters to the urinary bladder. In the bladder, the
urine is stored until it is excreted from the body through the urethra. The kidney
is the only organ of the body in which two capillary beds, in series, connect arteries
with veins. This arrangement is important for maintaining a constant blood flow
through and around the nephron despite fluctuations in systemic blood pressure.
Structure of Kidney:
A longitudinal section of the kidney shows the following parts:
- Renal capsule: a thin, outer membrane that helps protect the kidney.
- Cortex: a lightly colored outer region.
- Medulla: a darker, reddish – brown, inner region composed of a
finely striped substance arranged in several pyramids. The apex of each pyramid
(papilla) projects into the pelvis of the kidney.
- Renal pelvis: a flat, funnel shaped cavity that collects the urine
into the ureters.