Download EXCRETORY SYSTEM

EXCRETORY SYSTEM
EXCRETION
The process of removal of
metabolic wastes from the body.
Osmoregulation
The process by which living organisms
maintain an osmotic pressure in the
body by regulating the amount of
water and salts.
Kinds of wastes excreted
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Nitrogenous wastes: These are the major waste
products formed during the breakdown of extra
amino acids and nucleic acids.
Non- nitrogenous wastes: oxalic acid and lactic
acid.
Excess chemicals: like drugs, vitamins,
hormones, cholesterol etc.
Bile pigments: like bilirubin and biliverdin.
Carbon dioxide
Excess water.
Classification of living Organisms
(on the basis of type of nitrogenous
waste)
Ammonotelic organisms:
 Organisms which excrete waste as
ammonia.
 Ammonia being highly toxic needs large
amount of water an immediate expulsion.
 All aquatic animals are ammonotelic
Classification of living Organisms
(on the basis of type of nitrogenous
waste)
Ureotelic organisms:
 Organisms which eliminate waste as urea.
 Urea being less toxic than ammonia can be
retained for a longer time and also needs less
dilution for elimination.
 Ammonia is converted to urea in the liver in
human beings.
 All animals dwelling in moderate conditions are
ureotelic.
Classification of living Organisms
(on the basis of type of nitrogenous
waste)
Uricotelic organisms:
 Organisms which eliminate waste as uric
acid.
 Uric acid being least toxic can be retained
for a longer time and also needs very less
dilution for elimination.
 Uric acid is eliminated as semi-solid waste.
 Birds, some desert animals are uricotelic.
Excretion in Unicellular organisms
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No excretory organs present
Excretion by simple diffusion across the
plasma membrane.
Cells have contractile vacuoles to collect
and eliminate waste.
Excretion in Multicellular organisms
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Sponges and coelentrates: no specific
excretory organs.
Platyhelminthes: Flame cells
Annelida: Nephrida
Insects: malpighian tubules.
Mollusca and all vertebrates: Kidneys
Excretory system in Human beings
The excretory system is made up of
the following parts:
Kidneys
 A pair of bean shaped (reniform) organs situated
in the abdominal cavity.
 Left kidney lies at a higher level than the right.
 The Renal artery carrying oxygenated blood
enters the kidney through the hilus.
 The renal artery drains the de-oxygenated blood
from the kidney.
 Each kidney contains about 1 million nephrons
for filtering blood
Structure of Kidney
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Each kidney is divided
into two parts:
(a) outer cortex
(b) inner medulla
The renal cortex consists
of the malpighian tubules
The renal medulla
consists of the collecting
ducts of nephrons.
Ureters
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A pair of distensible tubes arising from
hilus.
Ureters carry urine by peristaltic
movements, from the kidneys and drain it
into the urinary bladder.
Urinary Bladder
 A pear shaped muscular bag lies in the lower
abdominal cavity and is the structure for
temporary storage of urine.
Urethra
 Tube that takes urine from the bladder to the
outside.
 Its opening is guarded by a ring of muscles
called the urethral sphincter.
 Urethra is separate in females but common with
the reproductive tract in males.
The Nephron
Nephron
Def: The fundamental structural
and functional unit of the
excretory system (kidneys)
Structure of a nephron
A nephron is made up of two main
parts:
Malpighian body
Renal tubule
Malpighian Body:
Also called renal corpuscle.
It is made up of a cup shaped
structure called the Bowman’s capsule
which contains a bunch of fine blood vessels or
capillaries arising from the Afferent arteriole (a
branch of the renal artery). This bunch is called
Glomerulus.
The bunch comes out of the Bowman’s capsule
as a narrower efferent arteriole.
The Bowman’s Capsule and the Glomerulus
make up the Malpighian Body, which is the main
filtering unit of the kidneys.
Renal Tubule:
 It has three parts – (a) Proximal Convoluted
tubule, (b) Loop of Henle and (c) Distal
convoluted Tubule
 DCT opens into the collecting ducts that give
rise to pyramids called renal pyramids.
 Pyramids form calyces which open into the
pelvis.
 Pelvis leads into the ureter.
 All the parts of the renal tubule are covered by a
network of capillaries called Peri-tubular
capillaries, formed from the efferent arteriole
Mechanism of Urine formation
It has 4 major components:
1. Glomerular filtration: Due to the difference in the
diameter of the afferent and efferent arterioles the
amount of blood entering the glomerulus is much more
than the volume of blood leaving it.
This leads to the development of a pressure.
This pressure leads to the filtration of blood.
The glomerular filtrate so obtained contains glucose,
ions, vitamins, amino acids, uric acid, Sodium,
Potassium, Chloride, bicarbonates and water.
The volume of Glomerular filtrate is 125 ml/ min
Mechanism of Urine formation
2. Reabsorption:
Glomerular filtrate passes through the PCT.
As it travels down the renal tubule useful
substances like glucose, amino acids, vitamins c,
calcium, Potassium, Sodium, Chloride,
bicarbonates and water (75%) are absorbed into
the Peri-tubular capillaries. The reabsorption is
either active or passive
Mechanism of Urine formation
3. Tubular Secretion:
Occurs mostly in the DCT and some in
PCT.
It is an active process, in which blood
capillaries secrete waste products into the
renal tubule.
These waste products include urea, uric
acid, creatinine, extra salts.
Mechanism of Urine formation
4. Concentration of Urine:
 Most of the water (70%) in the glomerular
filtrate is re-absorbed into the peritubular
network from the PCT and some (10 %) by
osmosis from Loop of Henle.
 The Anti- Diuretic Hormone from the Pituitary
also regulated the concentration of urine.
When more water is taken in ADH is released to
absorb more water from the nephrons.
Low ADH production leads to discharge of
frequent and highly diluted urination (Diabetes
insipidus)
Composition of Urine
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Transparent, amber coloured (due to
urochrome)
96% Water
2.5% organic substances (urea, uric acid,
creatine, water soluble vitamins, hormones,
oxalates)
1.5 % inorganic solutes (sodium, chloride,
phosphate, sulphate, magnesium, calcium,
iodine)
Micturition
The process of excreting urine.
Micturition can be voluntary as
well as involuntary.
Functions of kidneys
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Removal of waste products
Maintaining water balance.
Elimination of excess water soluble
substances.
Regulation of salts content.
Maintenance of pH.
Regulation of blood pressure.
Accessory Excretory Organs
Skin as an Excretory organ
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Contains sweat and sebaceous glands.
Secrete sweat and wax or sebum.
Liver as an Excretory organ
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Extra amino acids are deaminated and
toxic ammonia converted to urea.
Degrades hemoglobin into bilirubin and
biliverdin
Passes cholesterol, excess vitamins, drugs
for elimination.
Dialysis
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The process of filtering blood artificially using a
dialysis machine is called dialysis.
Dialysis involves separation of smaller solutes or
ions from larger particles, using an ultrafilter.
Blood from an artery or a vein fitted to a pump
and mixed with heparin (anti-coagulant) is
cooled to 0 deg. C and passes through
cellophane tubes for filtration.
The filtered blood is returned into another vein.
The whole process takes 3-4 hours.