EXCRETORY SYSTEMEXCRETORY SYSTEM

EXCRETIONEXCRETION

The process of removal of The process of removal of metabolic wastes from the metabolic wastes from the

body.body.

OsmoregulationOsmoregulation

The process by which living The process by which living organisms maintain an osmotic organisms maintain an osmotic

pressure in the body by regulating pressure in the body by regulating the amount of water and salts.the amount of water and salts.

Kinds of wastes excretedKinds of wastes excreted Nitrogenous wastes: These are the major Nitrogenous wastes: These are the major

waste products formed during the waste products formed during the breakdown of extra amino acids and nucleic breakdown of extra amino acids and nucleic acids.acids.

Non- nitrogenous wastes: oxalic acid and Non- nitrogenous wastes: oxalic acid and lactic acid.lactic acid.

Excess chemicals: like drugs, vitamins, Excess chemicals: like drugs, vitamins, hormones, cholesterol etc.hormones, cholesterol etc.

Bile pigments: like bilirubin and biliverdin.Bile pigments: like bilirubin and biliverdin. Carbon dioxideCarbon dioxide Excess water.Excess water.

Classification of living Classification of living Organisms Organisms

((on the basis of type of on the basis of type of nitrogenous wastenitrogenous waste))Ammonotelic organisms:Ammonotelic organisms:

Organisms which excrete waste as Organisms which excrete waste as ammonia. ammonia.

Ammonia being highly toxic needs Ammonia being highly toxic needs large amount of water an immediate large amount of water an immediate expulsion.expulsion.

All aquatic animals are ammonotelic All aquatic animals are ammonotelic

Classification of living Classification of living Organisms Organisms

((on the basis of type of on the basis of type of nitrogenous wastenitrogenous waste))Ureotelic organisms: Ureotelic organisms:

Organisms which eliminate waste as urea.Organisms which eliminate waste as urea. Urea being less toxic than ammonia can Urea being less toxic than ammonia can

be retained for a longer time and also be retained for a longer time and also needs less dilution for elimination.needs less dilution for elimination.

Ammonia is converted to urea in the liver Ammonia is converted to urea in the liver in human beings.in human beings.

All animals dwelling in moderate All animals dwelling in moderate conditions are ureotelic.conditions are ureotelic.

Classification of living Classification of living Organisms Organisms

((on the basis of type of on the basis of type of nitrogenous wastenitrogenous waste))Uricotelic organisms:Uricotelic organisms:

Organisms which eliminate waste as uric Organisms which eliminate waste as uric acid.acid.

Uric acid being least toxic can be Uric acid being least toxic can be retained for a longer time and also needs retained for a longer time and also needs very less dilution for elimination.very less dilution for elimination.

Uric acid is eliminated as semi-solid Uric acid is eliminated as semi-solid waste.waste.

Birds, some desert animals are uricotelic.Birds, some desert animals are uricotelic.

Excretion in Unicellular Excretion in Unicellular organismsorganisms

No excretory organs presentNo excretory organs present Excretion by simple diffusion across Excretion by simple diffusion across

the plasma membrane.the plasma membrane. Cells have contractile vacuoles to Cells have contractile vacuoles to

collect and eliminate waste.collect and eliminate waste.

Excretion in Multicellular Excretion in Multicellular organismsorganisms

Sponges and coelentrates: no Sponges and coelentrates: no specific excretory organs.specific excretory organs.

Platyhelminthes: Flame cellsPlatyhelminthes: Flame cells Annelida: NephridaAnnelida: Nephrida Insects: malpighian tubules.Insects: malpighian tubules. Mollusca and all vertebrates: Kidneys Mollusca and all vertebrates: Kidneys

Excretory system in Human Excretory system in Human beingsbeings

The excretory system is made up ofThe excretory system is made up ofthe following parts:the following parts:KidneysKidneys A pair of bean shaped (reniform) organs A pair of bean shaped (reniform) organs

situated in the abdominal cavity.situated in the abdominal cavity. Left kidney lies at a higher level than the Left kidney lies at a higher level than the

right.right. The Renal artery carrying oxygenated blood The Renal artery carrying oxygenated blood

enters the kidney through the hilus.enters the kidney through the hilus. The renal artery drains the de-oxygenated The renal artery drains the de-oxygenated

blood from the kidney.blood from the kidney. Each kidney contains about 1 million Each kidney contains about 1 million

nephrons for filtering bloodnephrons for filtering blood

Structure of KidneyStructure of Kidney Each kidney is divided Each kidney is divided

into two parts:into two parts: (a) outer cortex(a) outer cortex (b) inner medulla(b) inner medulla The renal cortex consists The renal cortex consists

of the malpighian tubulesof the malpighian tubules The renal medulla The renal medulla

consists of the collecting consists of the collecting ducts of nephrons.ducts of nephrons.

UretersUreters

A pair of distensible tubes arising A pair of distensible tubes arising from hilus.from hilus.

Ureters carry urine by peristaltic Ureters carry urine by peristaltic movements, from the kidneys and movements, from the kidneys and drain it into the urinary bladder.drain it into the urinary bladder.

Urinary BladderUrinary Bladder A pear shaped muscular bag lies in the A pear shaped muscular bag lies in the

lower abdominal cavity and is the structure lower abdominal cavity and is the structure for temporary storage of urine.for temporary storage of urine.

UrethraUrethra Tube that takes urine from the bladder to Tube that takes urine from the bladder to

the outside.the outside. Its opening is guarded by a ring of muscles Its opening is guarded by a ring of muscles

called the urethral sphincter.called the urethral sphincter. Urethra is separate in females but common Urethra is separate in females but common

with the reproductive tract in males. with the reproductive tract in males.

The NephronThe Nephron

NephronNephron

DefDef: The fundamental : The fundamental structural and functional unit structural and functional unit

of the excretory system of the excretory system (kidneys)(kidneys)

Structure of a nephronStructure of a nephron

A nephron is made up of two main A nephron is made up of two main parts:parts:

Malpighian bodyMalpighian bodyRenal tubuleRenal tubule

Malpighian Body:Malpighian Body:Also called renal corpuscle.Also called renal corpuscle.

It is made up of a cup shaped It is made up of a cup shaped structure called the structure called the Bowman’s capsuleBowman’s capsule

which contains a bunch of fine blood which contains a bunch of fine blood vessels or capillaries arising from the vessels or capillaries arising from the Afferent arteriole Afferent arteriole (a branch of the renal (a branch of the renal artery). This bunch is called artery). This bunch is called GlomerulusGlomerulus..The bunch comes out of the Bowman’s The bunch comes out of the Bowman’s capsule as a narrower capsule as a narrower efferent arteriole.efferent arteriole.The Bowman’s Capsule and the Glomerulus The Bowman’s Capsule and the Glomerulus make up the make up the Malpighian BodyMalpighian Body, which is the , which is the main filtering unit of the kidneys.main filtering unit of the kidneys.

Renal Tubule:Renal Tubule: It has three parts – It has three parts – (a) Proximal Convoluted (a) Proximal Convoluted

tubule, (b) Loop of Henle and (c) Distal tubule, (b) Loop of Henle and (c) Distal convoluted Tubuleconvoluted Tubule

DCT opens into the DCT opens into the collecting ductscollecting ducts that that give rise to pyramids called give rise to pyramids called renal pyramids. renal pyramids.

Pyramids form Pyramids form calyces calyces which open into the which open into the pelvis.pelvis.

PelvisPelvis leads into the ureter. leads into the ureter. All the parts of the renal tubule are covered All the parts of the renal tubule are covered

by a network of capillaries called by a network of capillaries called Peri-Peri-tubular capillariestubular capillaries, formed from the efferent , formed from the efferent arteriolearteriole

Mechanism of Urine Mechanism of Urine formationformation

It has 4 major components:It has 4 major components:1. Glomerular filtration:1. Glomerular filtration: Due to the difference in the Due to the difference in the

diameter of the afferent and efferent arterioles the diameter of the afferent and efferent arterioles the amount of blood entering the glomerulus is much amount of blood entering the glomerulus is much more than the volume of blood leaving it.more than the volume of blood leaving it.This leads to the development of a pressure.This leads to the development of a pressure.

This pressure leads to the filtration of blood.This pressure leads to the filtration of blood.

The The glomerular filtrateglomerular filtrate so obtained contains so obtained contains glucose, ions, vitamins, amino acids, uric acid, glucose, ions, vitamins, amino acids, uric acid, Sodium, Potassium, Chloride, bicarbonates and Sodium, Potassium, Chloride, bicarbonates and water.water.The volume of Glomerular filtrate is The volume of Glomerular filtrate is 125 ml/ min125 ml/ min

Mechanism of Urine Mechanism of Urine formationformation

2. Reabsorption:2. Reabsorption: Glomerular filtrate passes through the PCT.Glomerular filtrate passes through the PCT.

As it travels down the renal tubule useful As it travels down the renal tubule useful substances like glucose, amino acids, substances like glucose, amino acids, vitamins c, calcium, Potassium, Sodium, vitamins c, calcium, Potassium, Sodium, Chloride, bicarbonates and water (75%) are Chloride, bicarbonates and water (75%) are absorbedabsorbed into the Peri-tubular capillaries. into the Peri-tubular capillaries. The The reabsorption is either active or passivereabsorption is either active or passive

Mechanism of Urine Mechanism of Urine formationformation

3. Tubular Secretion:3. Tubular Secretion:Occurs mostly in the DCT and some Occurs mostly in the DCT and some in PCT.in PCT.It is an It is an active processactive process, in which blood , in which blood capillaries secrete waste products capillaries secrete waste products into the renal tubule.into the renal tubule.These waste products include urea, These waste products include urea, uric acid, creatinine, extra salts.uric acid, creatinine, extra salts.

Mechanism of Urine Mechanism of Urine formationformation4. Concentration of Urine:4. Concentration of Urine:

Most of the water (70%) in the glomerular Most of the water (70%) in the glomerular filtrate is re-absorbed into the peritubular filtrate is re-absorbed into the peritubular network from the PCT and some (10 %) by network from the PCT and some (10 %) by osmosis from Loop of Henle.osmosis from Loop of Henle.

The The Anti- Diuretic HormoneAnti- Diuretic Hormone from the Pituitary from the Pituitary also regulated the concentration of urine.also regulated the concentration of urine.When more water is taken in ADH is released When more water is taken in ADH is released to absorb more water from the nephrons. to absorb more water from the nephrons. Low ADH production leads to discharge of Low ADH production leads to discharge of frequent and highly diluted urination frequent and highly diluted urination (Diabetes insipidus)(Diabetes insipidus)

Composition of UrineComposition of Urine Transparent, amber coloured (due to Transparent, amber coloured (due to

urochrome)urochrome) 96% Water96% Water 2.5% organic substances (urea, uric acid, 2.5% organic substances (urea, uric acid,

creatine, water soluble vitamins, creatine, water soluble vitamins, hormones, oxalates)hormones, oxalates)

1.5 % inorganic solutes (sodium, chloride, 1.5 % inorganic solutes (sodium, chloride, phosphate, sulphate, magnesium, calcium, phosphate, sulphate, magnesium, calcium, iodine)iodine)

MicturitionMicturition

The process of excreting The process of excreting urine.urine.

Micturition can be voluntary Micturition can be voluntary as well as involuntary.as well as involuntary.

Functions of kidneysFunctions of kidneys

Removal of waste productsRemoval of waste products Maintaining water balance.Maintaining water balance. Elimination of excess water soluble Elimination of excess water soluble

substances.substances. Regulation of salts content.Regulation of salts content. Maintenance of pH.Maintenance of pH. Regulation of blood pressure.Regulation of blood pressure.

Accessory Excretory OrgansAccessory Excretory Organs

Skin as an Excretory organSkin as an Excretory organ Contains sweat and sebaceous Contains sweat and sebaceous

glands.glands. Secrete sweat and wax or sebum.Secrete sweat and wax or sebum.

Liver as an Excretory organLiver as an Excretory organ Extra amino acids are deaminated Extra amino acids are deaminated

and toxic ammonia converted to and toxic ammonia converted to urea.urea.

Degrades hemoglobin into bilirubin Degrades hemoglobin into bilirubin and biliverdinand biliverdin

Passes cholesterol, excess vitamins, Passes cholesterol, excess vitamins, drugs for elimination.drugs for elimination.

DialysisDialysis The process of filtering blood artificially using a The process of filtering blood artificially using a

dialysis machine is called dialysis.dialysis machine is called dialysis. Dialysis involves separation of smaller solutes Dialysis involves separation of smaller solutes

or ions from larger particles, using an ultrafilter.or ions from larger particles, using an ultrafilter. Blood from an artery or a vein fitted to a pump Blood from an artery or a vein fitted to a pump

and mixed with heparin (anti-coagulant) is and mixed with heparin (anti-coagulant) is cooled to 0 deg. C and passes through cooled to 0 deg. C and passes through cellophane tubes for filtration. cellophane tubes for filtration.

The filtered blood is returned into another vein.The filtered blood is returned into another vein. The whole process takes 3-4 hours. The whole process takes 3-4 hours.