Excretion in animals :

The biologica process of remova of harmfu nitrogenous wastes from the body is called excretion.

The waste products in animals include :

(i) Nitrogenous compounds like ammonia, urea and uric acid.

(ii) Carbon dioxide and water.

(iii) Excess salts and vitamins.

(iv) Unwanted medicines

  

Ammonotelic organisms are those which excrete ammonia. e.g. most aquatic animals.

Ureotelic organisms are those which excrete urea. e.g. sharks, frogs, mammals.

Uricotelic organisms are those which excrete uric acid. e.g. birds, insects, land snails, many reptiles

Excretory Organs/Structures in Animals :-

Human Excretory system :

• Human excretory system consists of :-

-A pair of kidneys

-A pair of ureters.

-Urinary bladder

-Urethra

KIDNEY :

• The main excretory organ of our body are kidneys.

Colour -Dark red

Shape -Bean shaped

Weight -125_170 gms.

  

Size -10 cm length, 5 cm breadth, 3 cm thickness.

Position -Located lateraly either sides of vertebra column.

Externa Structure :-

• Each kidney is surrounded and covered by a tough, fibrous, capsule of connective tissues. This capsule is called rena capsule.

• Latera surfaces of kidney are convex while media surfaces are concave.

• On the inner border of each kidney is a depression called hilum/hilus.

The human kidney are not located at similar positions due to presence of liver above right kidney, so that the right kidney get slightly lower position.

Interna Structure :

• The interna structure of kidneys can be divided into two parts.

• Its outer part is called cortex and inner part is called medulla.

• Nephron is the structura and functiona unit of excretion.

• A nephron consists of a long coiled tubule differentiated into proxima nephron, loop of Henle and
dista nephron. The latter opens into the collecting tubule.

• At the proxima end of the nephron, a double walled cup shaped structure is present called Bowman's capsule.

• It consists of network of capillaries called glomerulus.

• One end of the glomerulus is attached to rena artery and the other end to the rena vein.

• In the glomesrulus, blood comes in through afferent arteriole and blood is drained out through efferent arteriole.

• Glomerulus and Bowman capsule are collectively called Malpighian body or rena corpuscle.

  

• The function of glomerulus is to filter the blood passing through it. This process is called ultrafiltration. 

Rena Columns

HUMAN KIDNEY

Structure of Nephron :-

Nephron is the structura and functiona unit of kidney, which is about 3 cm long and 20-60 mm in diameter. Each kidney has about one million nephrons in humans.

A nephron can be divided into three regions :

(I) Proxima nephron (Bowman's capsule + Proxima convoluted tubule)

(II) Loop of Henle (Ascending + Descending limb)

(III) Dista nephron (Dista convoluted tubule which opens into collecting duct)

(I) Proxima nephron : Nephron tubule is closed at its proxima (starting) end but its dista end is open and continues into the loop of Henle. At the proxima or closed end the nephron is expanded and curved inwardly to form a double walled cup shaped Bowman's capsule. Within the Bowman's capsule a network or tuft of capillaries is present, it is called glomerulus. Diameter of afferent arteriole is greater than efferent arteriole.

Malpighian corpuscle : Glomerulus and its surrounding Bowman's capsule together form this specialised structure.

(II) Loop of Henle : It starts after the proxima convoluted tubule, It ends before the dista convoluted tubule. This hairpin like loop has a descending limb, followed by an ascending limb.

(III) Dista nephron : The ascending limb of Henle's loop merges into dista convoluted tubule.

The dista convoluted tubules of a number of adjacent nephrons open into a common collecting duct or tubule.

Ureter :

• The collecting ducts open into the ureter.

• Each ureter originate from interior part of kidney.

• The anterior part of the ureter is broad, like a funne and called pelvis and its posterior part is in the form of long tubule.

Urinary Bladder :

• Each ureter opens into the urinary bladder.

• The structure of urinary bladder is muscular sac like and pear shaped.

• Its wal is flexible, it collect urine when necessary by the contraction of muscles, the urine is excreted through urethra.

Urethra :

• It is a muscular and tubular structure, which extends from the urinary bladder to the outside. It carries the urine to the outside.

Micturition :

• Micturition is the term used for urination. (Passing out of urine)

Functions of Kidney :

-Regulation of water and electrolyte balance. (Osmoregulation)

-Regulation of acid base balance.

-Regulation of blood pressure.

-Excretion of metabolic waste and foreign chemicals.

Physiology of Excretion :-

• The impure blood enters to each kidney through rena artery.

• The afferent arterioles which is branch of rena artery provides blood to the glomerulus.

• Glomerulus is a group of blood capillaries formed by division of afferent arterioles located in Bowman capsule.

• The arterioles which carry blood away from glomerulus are called efferent arterioles.

• The radius of afferent arterioles is greater than that of efferent arterioles so the pressure in glomerulus increases. Which is necessary for ultrafiltration.

• Due to the blood pressure, from the blood of afferent arteriole, water, glucose, urea, uric acid and some salt filter in Bowman capsule through ultra-filtration.

• It also contains glucose, amino acid and some usefu salts along with filtrate.

• This liquid from the Bowman capsule moves through the glandular part of the nephron.

• From where glucose, usefu salt and some part of water is reabsorbed. The amount of water reabsorbed depends on how much excess water there is in the body and on how much of dissolved waste there is to be excreted.

• The remaining liquid now contain only waste materia is called urine.

• The urine from the nephron is collected in urinary bladder through ureter.

• Urine is stored in the urinary bladder unti the pressure of the expanded bladder leads to the urge to pass it out through the urethra.

• By the contraction of muscles of urinary bladder, the urine passes out of the body when necessary.

• Al the systems of our body keep the interna environment stable even on the changing conditions of externa environment.

• This activity is called homeostatic activity.

• Usually the homeostatic activities are performed by excretory organ.

• They not only excrete out salts and nitrogenous waste products but also perform important role of water balance.

The process of maintaining the right amount of water and proper ionic balance in the body is called osmoregulation.

Urea is always formed in liver through Ornithine cycle.

Urine Formation (Uropoiesis) :-

It involves three processes : glomerular filtration (ultrafiltration), tubular reabsorption and tubular secretion.

(i) Ultrafiltration :-

Walls of glomerulus and Bowman's capsule are thin and semipermeable membrane. In the glomerulus there are many minute pores are present.

Afferent arteriole is wider and releases the blood into glomerulus, whereas efferent arteriole is narrow. Thus, there is development of high blood pressure.

Due to this pressure, separation of small, selective molecules ions from the large molecules in the blood occurs and called ultrafiltration. Fluid which is filtered out from the blood is called as glomerulus filterate / capsuler filtrate / ultrafiltrate.

(ii) Tubular Reaborption :-

The ultrafiltrate contains salts, glucose, amino acids, urea, uric acid and large amount of water.

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

(iii) Tubular secretion :-

It is remova of wastes from the surrounding blood capillaries into the glomerular filtrate.

Glomerular filtrate entering collecting duct is called urine. Urine composition is different from filtrate by the loss as wel as gain of many substances during the course of nephrons.

Chemica composition of urine :

• Urine is slightly acidic liquid, light yellow in colour.

• The healthy human being has 95% water, 5% urea, uric acid and salts of phosphoric acid.

• A young and healthy person excretes 1.5-1.8 litres urine per day.

• This quantity may increase due to intake of tea, coffee, wine etc.

Regulation of excretion :

Following two hormones regulate the functions of kidney :

(i) Anti Diuretic Hormone (ADH)/Vasopressin

It is secreted by pituitary gland, it promates the reabsorption of water through nephrons. (DCT part)

(ii) Aldosterone :- It is secreted by Adrena gland.

Aldosterone promotes the reabsorption of salts (Na+) in the nephron (DCT part) i.e. it checks the loss of Na+ ions through urine.

Role of lungs in excretion

Human lungs eliminate around 18 of CO2 per hour and about 400m of water per day in norma resting condition. Water loss via the lungs is smal in hot humid climate and large in cold dry climates.

Role of skin in excretion :

Human possess two types of glands :

(1) Sweat glands : These excrete sweat, Sweat contain 99.5%, Water, NaCl, Lactic acid, Urea, Amino acid and glucose.

(2) Sebaceous glands : These secrete sebum which contain waxes, sterols, other hydrocarbons and fatty acids.

Role of liver in excretion :

Liver is the main site for elimination of cholesterol, bile pigments (bilirubin & biliverdin), inactivated products of steroid hormones, some vitamins and many drugs. Bile carries these materials to the intestine from where they are excreted with the faeces.

ARTIFICIA KIDNEY OR HAEMODIALYSIS

Kidney dialysis also known as haemodialysis or rena dialysis, is a medica treatment used to remove nitrogenous waste materials from the blood of patients lacking kidney function or kidney failure, due to infections, injury or restricted blood flow to kidneys. In this procedure, the blood is circulated through a machine known as artificia kidney or dialyser that removes wastes and excess fluid from the bloodstream.

The blood from an artery is pumped through a dialyser or artificia kidney, where it flows through a semipermeable membrane which are made up of cellophane tubes. The cellophane tubes remain suspended in a tank filled with dialysing fluid which has same osmotic pressure as blood and has the same composition as that of blood plasma but it lacks nitrogenous wastes. When the blood of the patient is passed through the cellophane tubes, the dialysis fluid passing on the other side of the membrane removes unwanted elements in the blood by diffusion. The blood is then returned to the body through a vein.

Main difference of kidney & dialysis is that there is no reabsorption in dialysis. In kidney, initia filtrate is about 180 daily but actua excretion is only a litre or two a day.

* Anuria :- No production of urine

* Polyuria :- Excess production of urine. More urine formation takes place due to less secretion of ADH. Due to less secretion of ADH, the amount of water increases in the urine. So, the patient feels thirsty again and again. This disease is called Diabetes inspidus.

* Glycosuria :- Excretion of glucose through urine. This sign is present in Diabetes mellitus. This disease is caused mainly due to less secretion of insulin.

* Uremia :- Excess of urea in blood is termed as uremia.

* Calculi and cast :- It is also termed as Kidney-stone. Due to deposition of Calcium-oxalate in the kidney, stone is formed. Sometimes, calcium - phosphate and calcium-sulphate are also found. These are insoluble-salts. Normally, these are not excreted by the urine.

* Haematuria :- Excretion of blood through urine.

* Diuresis :- The process of excess formation of urine in the kidney's is termed as diuresis.

* The urine on standing gives a pungent smell. It is due to conversion of urea into ammonia by bacteria

* The volume of urine produced per day wil increase on a cold day, due to ¯ADH secretion.

* If one kidney is removed, the remaining one enlarges and performs function of both kidneys.

* Rena failure : It is a syndrome characterised by rena dysfunction, oliguria, anuria, sudden rise in metabolic waste products like urea & creatinine in blood (uremia) . It is either of acute (sudden onset) or chronic (slow onset) nature.

* Diabetic nephropathy : It is a complication due to diabetes mellitus where the kidney progressively gets damaged leading to death ultimately due to rena failure.

* Pale yellow colour of urine is due to the Urochrome pigment. It is formed in the blood due to the reduction of Haemoglobin. So in the body of a healthy anima urochrome is found in a very less amount.

                                         EXCRETION IN PLANTS

Excretion : The process of remova of toxic waste products from the body of an organism is known as excretion.

The main waste products produced by plants are carbon dioxide, water vapour and oxygen.

CO2 and water are produced as wastes during respiration by plants.

CO2 produced during respiration in day time is al used by the plant itself in photosynthesis. Plants excrete oxygen as a waste only during day time.

The gaseous wastes of respiration and photosynthesis in plants are removed through the stomata in leaves and lenticels in woody stem and released to the air.

Oxygen is produced as a waste during photosynthesis.

Plants get rid of excess water by transpiration.

Many plant waste products are stored in cellular vacoules.

Plants also store some of the waste products in their body parts (leaves, bark and fruits).

e.g. Tannins, essentia oils, latex, gums, resins.

Tea leaves, amla, beta nut and bark of tree contain tannins.

Leaves of Eucalyptus, lemon, tulsi, contain essentia oils.

Leaves of yellow oleander contain latex.

Gums are found in babu tree.

Resins are found in stem of conifers.

Quinine and morphine are medicines derived from alkaloid stored in Cinchona bark and Opium fruits respectively.

Caffeine found in coffee seeds and nicotine in tobacco leaves are also alkaloids.

Calcium Oxalate crystals accumulate in some tubers like Yam (zamikand).