Excretion It involves the removal of harmful metabolic

wastes from the body of organisms by

various processes.

Excretion in humans

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The excretory system consists of- a pair of

kidneys, a pair of ureters, a urinary bladder,

and a urethra.

• Nitrogenous wastes such as urea and

uric acid are removed

• Nephron- basic filtration unit

• Main components of the nephron -

glomerulus, Bowman's capsule, renal tube

• The process of Removing of nitrogenous

wastes through artificial kidney is called

dialysis.

rNitrogenous waste products

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Other Excretory Organs

Apart from the above-mentioned organs,

there are other organs that perform

excretion. They are:

Skin

The skin is the largest organ in the

body. Its primary function is to

protect the different organs of the

body. In addition, the skin excretes

sweat. In particular, the skin

eliminates compounds like NaCl,

some amount of urea etc.

Lungs

Lungs are the primary respiratory organs.

They help take in oxygen and expel carbon

dioxide. But, in this process, they also

eliminate some amount of water in the

form of vapour.

Liver

This organ has an important function

in excreting waste from the body. It is

the first line of defence when it

comes to hormones, fats, alcohol,

and drugs. In fact, most drugs

undergo first-pass metabolism in this -organ. t

The kidneys also eliminate a

few drugs. Furthermore, the liver

eliminates excess fats and

cholesterol. This is essential to

maintain the health of the body.

Excretion in human beingi

0 A pair of kidneys, a pair of ureters, a urinary bladder and a urethra constitutes the human excretory system.

° Kidneys are present on either side of the backbone in the abdomen.

° Kidneys produce urine and urine from kidney passes through the ureters into the urinary bladder and remains stored their until it is released through the urethra.

Ureters

There is one ureter that comes out of

each kidney as an extension of the

renal pelvis. It is a thin muscular tube

that carries urine from the kidneys to

the bladder.

Urinary Bladder

The bladder is a sac-like structure.

And a smooth muscle layer lines it. It

stores the urine until micturition.

Furthermore, Micturition is the act of

expelling urine from the body. The

bladder receives urine from the

ureters, one from each kidney. In

addition, the level of placement of

the bladder in the body differs in

men and women.

Urethra

The urethra is a tube that arises from

the urinary bladder. Its function is to

expel the urine outside by

micturition. In addition, it is shorter

in females and longer in males.

Furthermore, in males, it functions as

a common path for sperms and

urine. Also, sphincter guards the

opening of the urethra.

The nephron is the functional unit of a

kidney. In fact, each kidney consists of

millions of nephrons. They all function

together to filter blood and expel waste

products. It consists of the following parts:

• Bowman's capsule- It is the first

part of the nephron. It is a cup­

shaped structure and receives the

blood vessels. Glomerular

filtration occurs here. The blood

cells and proteins remain in the

blood.

f--- Glomerulus

'--- Bowmons c.opsufe

Proximal t ubule

Loop of Henle--

Distal t ubuf e

~ Collecting duct

• Proximal Convoluted Tubule­

The Bowman's capsule extends

downwards to form the proximal

tubule. Water and reusable

materials from the blood are now

reabsorbed back into it.

• The loop of Henle- The proximal

tubule leads to the formation of a

u-shaped loop called the Loop of

Henle. It has three parts: the

descending limb, the u-shaped

bend, and the ascending limb. It is

in this area in which urine

becomes concentrated as water is

reabsorbed. The descending limb

is permeable to water whereas the

ascending limb is impermeable to

it.

• Distal Convoluted Tubule- The

Loop of Henle leads into the distal

convoluted tubule. It is where the

kidney hormones cause their

effect.

• Collecting Duct- The Distal

Convoluted Tubule of each

nephron leads to the collecting

ducts. The collecting ducts

together form the renal pelvis.

Functions of the Excretory System

The excretory system performs many

functions such as:

• Eliminating waste products such

as urea, uric acid ammonia, and

other chemical products via urine.

• Maintaining the osmotic level of

blood and plasma

• Maintaining the electrolyte

balance in the body

Excretion in Rlants

0 Oxygen, a waste product of photosynthesis is released.

0 Excess water is removed by transpiration.

0 Some waste products may get stored in the leaves which fall off.

0 Many waste products are stored in vacuoles.

0 Some waste products are stored as resins and gums in old xylem.

o Plants excrete some waste materials into the soil around them.

What you have learnt

• Movement of various types can be taken as an indication of life.

• The maintenance of life requires processes like nutrition, respiration, transport of materials within the body and excretion of waste products.

• Autotrophic nutrition involves the intake of simple inorganic materials from the environment and using an external energy source like the Sun to synthesis complex high-energy organic material.

• Heterotrophic nutrition involves the intake of complex material prepared by other organisms.

• In human beings, the food eaten is broken down by various steps along the alimentary canal and the digested food is absorbed in the small intestine to be sent to all cells in the body.

• During the process of respiration, complex organic compounds such as glucose are broken down to provide energy in the form of ATP. ATP is used to provide energy for other reactions in the cell.

• Respiration may be aerobic or anaerobic. Aerobic respiration makes more energy available to the organism.

• In human beings, the transport of materials such as oxygen, carbon dioxide, food and excretory products is a function of the circulatory system. The circulatory system consists of the heart, blood and blood vessels.

• In highly differentiated plants, transport of water, minerals, food and other materials is a function of the vascular tissue which consists of xylem and phloem.

• In human beings, excretory products in the form of soluble nitrogen compounds are removed by the nephrons in the kidneys.

• Plants use a variety of techniques to get rid of waste material. For example, waste material may be stored in the cell­vacuoles or as gum and resin, removed in the falling leaves, or excreted into the surrounding soil.