EXCRETORY

The Excretory System
Excretion
Excretion is the removal of harmful and unwanted substances, especially nitrogenous wastes from the
body.
Substances to Rid Off
Carbon Dioxide and Water  Carbon dioxide is eliminated through the

lungs.
 Water becomes part of the rest of the
water in the body.
Nitrogenous Metabolic Wastes  Urea is excreted through the kidneys.
Excess Salts  Salts are excreted through the kidneys.
Water  The excess quantity of water is removed
through the kidneys.
Bile Pigments  Some of the bile pigments are excreted
in the urine.
The Excretory Organs
1. The Kidneys  Primary excretory organ.
 Excrete sweat which contains nitrogenous

2. Sweat Glands
waste.
 Sweat is excreted only when required, i.e. for
cooling the body.
3. The Lungs  Carbon dioxide is expired by the lungs.
The Urinary System
The human urinary system consists of

1. A pair of kidneys
2. A pair of ureters
3. Urinary bladder
4. Urethra
Human Urinary System
A Pair of Kidneys  Dark red, bean shape, 10 cm long, 6 cm wide.

 The right kidney is slightly lower in position due to the
presence of the liver.
 The renal artery supplies oxygenated blood to the
kidneys.
 The renal veins take away deoxygenated blood from the
kidneys.
A Pair of Ureters  Ureters are tube-like structures which arise from the
notch, i.e. the hilum of each kidney.
 The ureters connect behind with the urinary bladder.
 The ureters carry the urine produced to the urinary
bladder.
Urinary Bladder  Muscular sac-like structure.

 It stores urine temporarily.
Urethra  Short muscular tube which expels urine out of the body.
 It is long in males and very short in females.
 The opening is guarded by sphincters which open at the
time of urination.
Internal Structure of the Kidneys
L.S. of Kidney
 The longitudinal section of the kidneys shows two regions—an outer dark cortex and an inner lighter
medulla.
 The medulla is composed of conical pyramids.
 The apex of each pyramid, i.e. papilla, projects into the pelvis.
Uriniferous Tubule
Uriniferous Tubule
The kidneys have an enormous number of uriniferous tubules.
They are also known as nephrons, renal tubules or kidney tubules.
Uriniferous tubules are the structural and functional units of the kidneys.
Malpighian Tubule
Bowman’s Capsule Proximal Convoluted Loop of Distal Convoluted

Tubule (PCT) Henle Tubule (DCT)
 It is a thin-walled, cup-  It is also known as  It is the U-  It is the end part of

like depression. the first convoluted shaped the kidney tubule.
 A knot-like mass of blood tubule. middle part  It opens into the
capillaries called  It is the first part of of the collecting duct.
glomerulus is located in the convoluted region tubule.
the concave depression of the tubule.
of the Bowman’s capsule.  PCT lies in the
 The Bowman’s capsule cortex.
and the glomerulus
together are called
Malpighian tubule or
renal tubule.
Blood Supply to the Kidneys

Dorsal aorta  renal artery  afferent arteriole  glomerulus  efferent arteriole 
secondary capillary network (vasa recta)  renal vein  posterior vena cava
Formation of Urine
The process of urine formation occurs in two major steps:
Ultrafiltration Reabsorption
 Due to the hydrostatic pressure built in  The glomerular filtrate passes down the
the glomerulus, the liquid part of the tubule; water and other substances
blood filters out from the glomerulus and required by the body are reabsorbed.
passes into the Bowman’s capsule.  This entire process is called selective
 This filtration under extraordinary force reabsorption.
is called ultrafiltration.  Potassium ions and certain substances
 The filtrate is known as glomerular such as penicillin are passed into the urine
filtrate. through the distal convoluted tubule.
 The cells of the walls of DCT are involved
in bringing back into the renal tubule
potassium ions and other substances;
hence, this process is known as tubular
secretion.
Part of the Renal Tubule Activity
Glomerulus Ultrafiltration
Bowman’s Capsule Receives glomerular filtrate
Proximal Convoluted Tubule (PCT) Reabsorbs water, glucose, sodium and
chloride ions
Loop of Henle Absorption of water and sodium ions
Distal Convoluted Tubule (DCT) Reabsorption of chloride ions and water
Urine Excretion
 The filtrate left after reabsorption and tubular secretion is called urine.
 The urine passes from the collecting duct to the pelvis of the kidneys. From there, it is sent to the
urinary bladder through the ureters.
 By relaxing the sphincters present at the opening of the urethra, the urine is expelled from the body.
This process is known as micturition or urination.
Physical Properties of Urine

 Colour: Yellow. It is due to urochrome.
 Volume: 1 to 1.5 litres. However, the volume can vary depending on the liquid intake of the person.
 pH: 5 to 8. Slightly acidic.
 Odour: Faint smell. It is ammonia-like due to bacterial activity.
 Specific gravity: 3 to 1.035
 Urine is made of 95% of water and 5% of solid wastes.
Abnormal Constituents in Urine

1. Haematuria: Due to infection in the urinary tract, kidney stone or tumour, blood passes out with urine.
2. Glycosuria: Excess glucose passes out with urine due to diabetes mellitus.
3. Due to anaemia, hepatitis or liver cirrhosis, bile is passed out in the urine.
Regulation of Urine Output
The water content in urine is controlled by Anti-diuretic Hormone (ADH).
Reduction in the secretion of ADH results in more production of urine. This condition is called diuresis.
Substances which increase the production of urine are called diuretics.
Osmoregulation
While removing urea from the blood, the kidneys also regulate the composition of blood, i.e. the water and
salt concentration in the blood. This function is called osmoregulation.
Drinking enough water helps the kidneys to function properly.
In summer, we lose a considerable amount of water through perspiration which makes the urine thicker
and concentrated. Hence, the kidneys have to reabsorb more water from the urine.
Artificial Kidney
 If one kidney is damaged or removed, the other kidney alone is capable of fulfilling the excretory needs
of the patient.
 However, the failure of both kidneys would lead to death.
 Such a patient undergoes dialysis. The dialysis machine is an artificial kidney in which the patient’s
blood is led from the radial artery through the machine where excess salts and urea are removed.
 The purified blood returns to a vein in the same arm.

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EXCRETORY

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The Excretory System

Substances to Rid Off

Carbon Dioxide and Water  Carbon dioxide is eliminated through the

The Excretory Organs

1. The Kidneys  Primary excretory organ.

 Excrete sweat which contains nitrogenous

The human urinary system consists of

Human Urinary System

A Pair of Kidneys  Dark red, bean shape, 10 cm long, 6 cm wide.

Urinary Bladder  Muscular sac-like structure.

Bowman’s Capsule Proximal Convoluted Loop of Distal Convoluted

 It is a thin-walled, cup-  It is also known as  It is the U-  It is the end part of

Blood Supply to the Kidneys

The process of urine formation occurs in two major steps:

Physical Properties of Urine

Abnormal Constituents in Urine

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