Q.5 Describe urinary system of humans. Also describe the structure of nephron?
Answer:
Urinary system of Humans
The excretory system of humans is also called the urinary system. It is formed of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
Kidneys
Kidneys filter blood to produce urine.
Ureters
The ureters carry urine from kidneys to urinary bladder.
Bladder
The bladder temporarily stores urine until it is released from body.
Urethra
Urethra is the tube that carries urine from urinary bladder to the outside of body.

Structure of kidney
(i) Colour and shape
Kidneys are dark-red bean shaped organs.
(ii) Size
Each kidney is 10 cm long, 5cm wide and 4 cm thick.
(iii) Weight
Each kidney weighs about 27 grams.
(iv) Location
They are placed against the back wall of abdominal cavity just below diaphragm, one on either side of vertebral column. They are protected by the last 2 ribs. The left kidney is a little higher than the right.
(v) Hilus
The concave side of kidney faces vertebral column. There is a depression, called hilus, near the centre of the concave area of kidney. This is the area of kidney through which ureter leaves kidney and other structures including blood vessels, lymphatic vessels and nerves enter and leave kidney.
(vi) Renal cortex
The longitudinal section of kidney shows two regions. Renal cortex is the outer part of kidney and it is dark in colour.
(vii) Renal medulla
Renal medulla is the inner part of kidney and is pale red in colour.
(viii) Pyramids
Renal medulla consists of several cone-shaped areas called renal pyramids.
(ix) Renal pelvis
Renal pyramids project into a funnel – shaped cavity called renal pelvis, which is the base of ureter.

Structure of nephron
The functional unit of the kidney is called nephron. There are over one million nephrons in each kidney.
Parts of Nephron
There are two parts of a nephron:
1. Renal corpuscle
2. Renal tubule
1. Renal corpuscle
The renal corpuscle is not tubular and has two parts:
i) Glomerulus
It is a network of capillaries.
(ii) Bowman’s capsule
Bowman’s capsule is a cup-shaped structure that encloses glomerulus.

2. Renal tubule
Renal tubule is the part of nephron which starts after Bowman’s capsule. It is sub – divided into following parts:
(i) Proximal convoluted tubule.
First portion of renal tubule is called proximal convoluted tubule.
(ii) Loop of Henle
Next portion is U-shaped and is called the loop of Henle..
(iii) Distal convoluted tubule
The last portion of renal tubule is the distal convoluted tubule.
(iv) Collecting ducts and Papillary ducts
The distal convoluted tubule of many nephrons open in a single collecting duct. Many collecting ducts join together to form several hundred papillary ducts which drain into renal pelvis.