Excretory system in humans – Diagram, Parts and Function

Excretory system in humans beings

The excretory system in humans being gathers and drains out the wastes from the body. The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

The waste substances dissolved in the blood are carried to the kidneys for filtration. During the filtration of blood, many useful things also get filtered along with the waste things. They are reabsorbed and the waste products are dissolved in water to form urine.

Urine contains 95 per cent water, 2.5 per cent urea and 2.5 per cent other wastes. Urine is collected from the kidneys by two tubes called ureters that open into a muscular bag called the urinary bladder. When the bladder gets full, urine is passed out through the urethra.

In case both kidneys of a person fail to work, blood is cleaned by a process called dialysis and a more permanent solution is kidney transplantation.

Extra salts are also removed from our skin in the form of sweat. Sweat also helps to keep the body cool in summer.

The Main Parts of the excretory system in humans

There is the following main excretory system in humans:

• Kidneys
• Renal Arteries
• Renal vein
• Ureters or Excretory tubes
• Urinary bladder
• Urethra

Kidneys

Each kidney is bean-shaped, reddish-brown in colour and is located in the abdomen, one on either side of the backbone. It is about 12 cm long, about 6 cm thick and weighs about 150 gm.

• The study of the kidney is called Nephrology.
• Doctor of the kidney called Nephrologist.
• The Left kidney is located a little higher than the right kidney.
• Colour of natural kidney = Reddish Brown
• Weight of kidney = 170 gram
• The shape of kidney = Bean shape
• Location of kidney = Peritoneal / Pectorial cavity.
• The cell of kidney = Nephron
• In 1 kidney = 1 million nephron present
• Kidney works on ultrafiltration process.

The renal artery brings in the impure blood containing waste substances into the kidneys.

The renal vein carries away the cleansed blood from the kidneys.

Renal Arteries

Two renal arteries regularly transport blood to each of the kidneys.

Renal vein

Two renal veins return useful nutrients back into the bloodstream after filtering the useless materials in the kidneys.

Ureters 

Ureters are the thin muscular tubes coming out from each kidney that opens into the urinary bladder. It is ducted which drain out urine from the kidneys.

Urinary bladder

The urinary bladder is a pear-shaped reservoir that stores urine before being discharged to the outside.

Urethra

The urethra is a muscular tube that arises from the neck of the bladder and conducts the urine to the outside through an opening at its end, the urinary opening.

The function of the Kidney

• The kidney regulates the water balance and osmotic pressure of the blood.
• It regulates the pH of the blood.
• Kidney removes the poisonous substances like urea, other waste salts and excess water from the blood and excretes them in the form of yellowish liquid known as urine.

Function of Urine

• Each kidney has large numbers of these filtration units known as nephrons.
• The nitrogenous waste like urea or uric acid is removed from blood in the kidney, thus kidneys are the basic filtration units.
• Some substances in the initial filtrate such as glucose, amino acids, salts & a major amount of water are selectively reabsorbed as the urine flows along the tube. This depends on how excess water is there in the blood and on how much-dissolved waste is there to be excreted.
• The formation of urine in each kidney enters a long tube, the ureter which connects the kidneys with the urinary bladder.
• It is stored in the urinary bladder until the pressure of the expanded bladder leads to pass out through the urethra.

Nephron

Each nephron functions as an independent unit and produces a minuscule quantity of human urine.

The nephron is the structure and functional unit of the kidneys. Each kidney is made up of a large number of excretory filtration units known as nephrons or uriniferous tubules.

• It consists of a long coiled tubule whose one end is connected to the double-walled cup-shaped structure of Bowman’s capsule and its other end to urine- collecting duct of a kidney.
• The Bowman’s capsule contains a bundle of blood capillaries which is called the glomerulus.
• The function of the glomerulus is to filter the blood passing through it.
• The function of the tubular part of the nephron is to allow selective reabsorption of the useful substance into the blood capillaries.

Process of Excretion

Ultrafiltration: Ultrafiltration is the first step in clearing the blood. This occurs in the glomerulus. It is also known as ultrafiltration.

Reabsorption: The ultrafiltration contains glucose, salts, amino acid, urea acid and a large amount of water.

Glucose, amino acid, salts and water are reabsorbed by various parts of the nephron and finally, they enter into the surroundings blood capillaries.

Tubular secretion: It is the removal of wastes from the surrounding blood capillaries into the glomerular filtrate.

Artificial Kidney

Infection, injuries or restricted blood flow to kidneys reduce the normal activity of kidneys.

This led to the accumulation of poisonous wastes in the body, which can even lead to death.

It is a device to remove nitrogenous waste products from the blood through dialysis.

During the procedure of dialysis, the patient’s blood is passed through these tubes.

As the blood passes, the waste products from the blood move into a dialyzing fluid by diffusion and purified blood is pumped back into the patient’s body.

This dialysis unit allows the blood to run along one side of a cellophane membrane and dialysis fluid in opposite direction.

Dialysis

Dialysis is the procedure used in the artificial kidney to replace a non-functional or damaged kidney. In the process, the blood of the patient is allowed to pass through the long cellulose tubes dipped in a tank containing dialyzing solution having the same ionic concentration as plasma. The waste substances diffuse out of the blood into the tank and clean blood is returned back into the patient through a vein.

Excretory system in animals

• Fishes and other aquatic animals excrete their waste product in gaseous form like ammonia.
• Birds and reptiles excrete uric acid, and mammals excrete urea.
• There are no special excretory organs in lower animals like hydra, amoeba, and sponges.

Excretion in Plant

• The plant produces a number of waste products during its life process.
• It can rid of excess water by transpiration.
• The main waste products produced by the plant are carbon dioxide, water vapour and oxygen.
• Many plants waste products are stored in cellular vacuoles.
• Other types of waste products are stored as resins and gums, especially in old xylem.
• Plants release some waste substances into the soil around them.

Frequently Asked Questions (FAQ) of Excretory System in humans

1. What is excretion?

Answer: The process of eliminating the waste products of metabolism (such as carbon dioxide, salts, urea, and uric acid) and other non-useful substances is known as excretion. The kidney is one of the main excretory systems in humans.

2. What is the major excretory product in human beings?

Answer: Human beings excrete urea as a major metabolic waste.

3. What is Osmoregulation?

Answer: Osmoregulation is the maintenance of water and ionic content of the body.

     4.  What is the smallest unit of the human excretory system?

Answer: Nephron is the smallest unit of the human excretory system.

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