The wastage disposing system

There is no factory which can manufacture a product without generating any waste. This is true of our body which is a cellular factory too. And for other organisms as well. Wastes are generated at regular intervals from
the bodies of most organisms.

Excretion in Human Beings

• A number of reactions take place during various metabolic activities. Many useful substances and energy are produced.
• At the same time many other things happen such as, toxic wastes may be produced, water content
  may increase, ionic balance in the body may be disturbed.
• The wastep roducts include carbon dioxide, water, nitrogenous compounds like ammonia, urea, uric acid, bile pigments, excess salts etc.
• The most poisonous of all waste products of metabolism is Ammonia.

Excretory System in Human being

In human beings excretion mainly occurs through a urinary or excretory system consisting of a pair of kidneys, a pair of ureters, urinary bladder and urethra

Kidneys

In Human being there are a pair of bean-shaped, reddish brown structures in the abdominal cavity attached to dorsal body wall  one on either side of the back bone. The right kidney is placed slightly lower than the left kidney

The size of the kidney is 10 cm in length, 5-6 cm in breadth, and 4 cm in thickness. Each kidney is convex on the outer side and concave on the inner side. The position of the right kidney is lower than the left kidney
due to the presence of liver above.

• The inner side of each kidney has a fissure or hilus for the entry of a renal artery, exit of a renal vein and an ureter.
• Renal artery brings oxygenated blood loaded with waste products and renal vein carries deoxygenated blood. The waste products generated in various organs of the body are filtered and removed by the kidneys

the internal structure of the kidney:

Let us observe L.S of the kidney to know more about the internal structure. It shows two distinct regions. Dark colored outer zone called the cortex and pale inner zone called medulla.

• Each kidney is made up of approximately more than one million (1.3 to 1.8 million) microscopic and thin tubular functional units called nephrons or uriniferous tubules.

Structure of nephron

Each nephron has basically two parts. One is the malpighian body and other is renal tubule.
Malpighian body: It consists of a blind cup-shaped broader end of nephron called Bowman’s capsule and a bunch of fine blood capillaries called glomerulus.
The Bowman’s capsule and glomerulus together called Malpighian capsule or renal capsule. Glomerulus develops from afferent arteriole. It gives rise to an efferent arteriole.

Renal tubule: It has three parts. First or proximal convoluted tubule (PCT),
loop of Henle, which is U shaped, second or distal convoluted tubule (DCT).

• Distal convoluted tubules open into a collecting tube. Collecting tube form pyramids and calyces which open into the pelvis.
• Pelvis leads into the ureter. All the parts of the renal tubule are covered by a network of peritubular (around tube) capillaries formed from efferent arteriole.
• The peritubular capillaries join to form renal venule, which joins the other venules to form finally the renal vein.