Excertory System

1. Excretory System
Excretory: - It is the Biological process by which an organism gets rids of excess or toxic metabolic wastes. In humans such wastes may accumulate as urine, Nitrogen, sweat, or tears.
The elimination of faeces (Egestion) is not an excretory process. Because the faeces materials is not the product made by the human body, Only the materials arising from the metabolic activities within the body are considered as excretory products.

 Main aim of excretion is to maintain a constant chemical composition called Homeostasis. Organism maintain this process by four main types :-
a) Buffering
b) Storage
c) Feedback control
d) Excretion
 The major excretory Product is CO2, Which is originated from the organic molecules.

Note: - In kangaroo rat water formed after cellular respiration is used as a source of fluid so, It didn’t required too much water and can be easily inhabit in desert like area.



2. Excretory Organ

Excretory Organ: - These are those organs which help in the excretion in different animals to maintain constant internal environment (Homeostasis). To achieve this organ must have a controlled over removal of each nitrogenous wastes
The major functions of the excretory system are as follow:-
 Maintenance of proper concentration of solutes.
 Maintenance of proper body volume (Water content)
 Removal of metabolic end product
 Removal of foreign substances.

Morphologically and functionally there are great varieties of excretory organs :-

Functionally grouped into two types:-
I. Generalized Types
II. Specialized Types

Generalized Types Specialized types
Contractile Vacoule e.g Protozan Gills (Fishes)
Nephridial Organs e.g Invertebrates Rectal Gland
Malphighian Tubles e.g Insects Salt Gland
Kidney e.g Vertebrate Liver and Intestine




Morphological Group into following types:-
1) Non Demonstrated
2) Contractile Vacuole
3) Nephridial Organs
4) Malpighian Tubules
5) Kidneys


1. Non Demonstrated: - No specific excretory organ have been identified e.g. in coelenterates and echinoderms.

2. Contractile vacuole: - In the freshwater protozoan and sponges, Contractile vacuole has been found to carry out the function of excretion. Being freshwater, Hyper osmotic are said to perform primary function of osmotic and volume regulation.

3. Nephridial organs: - Simplest type of excretory systems, occur in Platy helminthes (Flat worms) rotifers, larvae, in planaria. The most common type in invertebrate of simple or branching tubes that open to the outside through a pore known as nephridial pores. There are two major types:-

Mechanism: - Excretory wastes formed inside the body by metabolic activity, diffuses from parenchyma to mesenchyma and then into the flame cell by the process similar to ultrafiltration. Useful material are absorbed finally urine is formed and released through the excretory pores. Fresh water platy helminthes have more flame cell as compared to the to marine.They are then removed from the body by the following route:-

Excretory pores----Parenchyme---mesenchyma--------flame cell----capillaries---vessels--- Excretory pores.

i. Protonephridium
ii. Metanephridium



A. Protonephridium:-
 Protonephridium are also known as flame cells(Network of closed tubules)
 These are modified mesenchymal cells
 Mainly Found in the animals which lack true body cavity (Coelum)
 An Animal may have two or more protonephridium, extensively branched. The closed end has several long cilia inside.
 If there is single cilium the terminate cell is known as Solenocyte(e.g Amphioxus);if there are numerous cilium projecting into lumen the structure is called a Flame cell.(Because the tuft of cilia resembling like flame of the candle).
 Flame cells are present in the Flatworm, where excess of water are swept out by the cilia.
 Function of ultra filtration is reported into protonephridium but it is involved in the osmoregulation.
B. Protonephridium:-
 These are unbranched and inner end are open into the coelomic cavity
 Found only in the animals with coelom.
 Fluid from coelom drain into nephridium and it passes down through the nephridium
 It act as Filtration reabsorbtion kidney
 Fluid expelled out of the body surface comprises water, nitrogenous wastes(NH3) and urea in land forms and salts

4. Malpighian Tubules: - The excretory system of insects like cockroach and locust, consist of tubules known as Malphigian Tubules. It is the main excretory organ in the urictelic.


 These may number anywhere from two to several hundred
 Each malipighian tubules is approximately 25mm in length and is lined with glandular epithelium
 Each tubules opens into the intestine between the midgut and hind gut: the other end in blind
 The blind end of the tubule lies with the rectum.
 Potassium is actively secreted into lumen of the tubule.
 Free ends of malipighian tubules float in the haemolymph, which extract wastes from haemolymph by active transport. CO2 and water enter by diffusion.
 It took part in both excretion and the osmoregulation.
 Urine consist of only nitrogenous wastes in the form of uric acid and some extra salt.

Route: - Excertory wastes--- malipighian tubules----luman of malipighian tubules---Hind gut—Reabosroption of salts and water in rectum----Outside.

5. Antennal Gland or Green Gland: - These are the excretory organ of the crustaceans (Prawn) of phylum Arthropods. These are one pair of pear shaped structure for excerption and osmoregulation.
 Green lies as the base of the antennae and open out.
 They draw water and dissolved substances from the haemolymph into their end sac by ultrafiltration
 Much of salt is reabsorbed by the active Transport. The remaining fluid called Urine. Flows into bladder.
 A Large quantity of dilute urine is passed out through the uterus and renal aperture.
 Excretory Matter mainly consists of ammonia but some urea and amino acid are also present.
 Ammonia is largely secreted by the gills, Therefore excretory organs regulates water, ions and other metabolites.

6. Kidney: - Kidney is the major excretory and osmoregulatory organs of vertebrates. Mammalian(Human beings) Urinary system of consists of the following main organs:
1. Two Kidney
2. Two Urethra
3. Bladder
4. Urethra
Kidney: - The kidneys are the bean shaped organs toward the back of our body just above the waist. Every person has two kidneys. The blood is constantly passing through our kidneys. The renal artery brings in the dirty blood into the kidneys.
The function of the kidney is to remove the poisonous substance urea other wastes salts and excess water from the blood and excrete them in the form of yellowish liquid called Urine.




 Kidneys cleaned our blood by filtrating it to remove unwanted substances present it.
 The cleaned blood is carried away from the kidneys by the renal vein.
 Thee urethra, one from each kidney opens into urinary bladder.
 Urethras are the tubes which carry urine from the kidney to the bladder.
 Urine is stored in the bladder, which after some time passed out from the body through the penis.

Structure of kidney: - Each kidney is made up of large number of excretory units called nephrons. The nephrons has a cup shaped bag at its upper end which is called Bowman’s Capsule.The lower end of Bowman’s Capsule is tube shaped and it is called a Tubule.

• The Bowman’s capsule and the Tubules together make a Nephron. One end of the tubule is connected to the Bowman’s capsule and to its other end is connected to urine collecting ducts of the kidney.
• The Bowman’s capsule contains a bundle of blood capillaries which is called Glomerulus.
• One end of the glomerulus is attached to the renal artery which brings the dirty blood containing the urea waste into it. The other end of glomerulus comes out of bowman’s capsule as a blood capillary surround the tubule of nephron and finally joins a renal vein.
• The function of glomerulus is to filter the blood passing through it. Only the small molecules of substances present in the blood like glucose, amino acid, urea and water etc. pass through the glomerulus.
• The large molecules like protein and blood cell cannot pass out through the glomerulus capillaries and hence remain behind in the blood.
• The function of the tubules of nephron is to allow the selective reabsorption of the useful substances like glucose, amino acid, urea and water etc.But the wastes materials like urea doesn’t reabsorbed..

Working of humans Kidney: - The dirty blood containing waste like urea enters the glomerulus. Which filter this blood, during filtration the substances like glucose, amino acid, and urea and water etc. present in the blood pass into Bowman’s capsule and then enter the tubule of nephron. Reabsorption takes place through the blood capillaries surrounding the tubule. Only the wastes substances urea some unwanted salt and excess water remain behind in the tubule. The liquid left behind in the tubule is known as Urine. Nephron then carries this urine into the collecting duct of the kidney from where it is carried to urethra.

Accessory Excretory Structure: - 1.Specialized Epithelial structures known as sweat gland are located in the skin. In humans these sweat gland are present everywhere mainly in the palm and the soles of feet. Since these are activated by the ANS as in excessive fear produces sweat. Sweat is a source of abundant water loss but it may contain salts (NaCl, K+ Mg2+ ions) and urea.

2. Tears, which are produced by the lacrimal gland from the outer corner of the eye, also constitute a minute excretory product. The AIDS virus has been found in the tears. A major function of the tears of course is lubrication moistening of the surface of the eye.