DAY TWENTY TWO
Excretory
Products and
their Elimination
Learning & Revision for the Day
u Modes of Excretion u Osmoregulation and u Role of Other Organs
u Human Excretory System Regulation of Kidney in Excretion
Functions Disorders of Excretory System
u Urine Formation in Kidney u
Excretion is the process of removal of nitrogenous wastes from the body. The organs
involved in excretion are called excretory organs. There are different types of excretory
products or waste materials in different animals.
Modes of Excretion
There are mainly three types of modes of excretion
1. Ammonotelic Excretion It is found in aquatic animals like protozoans (e.g. Amoeba
and Paramecium), sponges (e.g. Sycon), coelenterates (e.g. Hydra), aquatic arthropods
(e.g. prawn), most aquatic molluscs (e.g. Pila), bony fishes (e.g. Labeo) and frog’s
tadpole larva.
l
Ammonia as a waste product is most toxic because of high pH and high solubility
in water, so large amount of water is required for its excretion.
l
It is released through general body surface into surrounding water.
2. Ureotelic Excretion It is found in those animals, which can take in water and can
retain considerable amounts of urea in their blood.
l
It is a common method of excretion in human, whales, seals, camels, kangaroo,
toads, frogs, sharks, etc.
l
Urea formation in liver cells of mammals was studied by Krebs and Henseleit.
l
Urea is formed in liver by detoxification of ammonia through ornithine cycle and
transported in the blood by plasma.
l
A person, who takes large amount of protein in his diet will excrete more urea. A
person having no food and water will have more urea in his blood. It requires less
water for excretion.
, 3. Uricotelic Excretion It is found in birds, land reptiles Nephron
(snakes and lizards), insects, snails, etc.
It is the structural and functional unit of kidney. These are
l
In this, the main nitrogenous waste is uric acid. also called as renal tubules or uriniferous tubules. There are
l
Uric acid is least soluble in water and is less toxic. about one million nephrons in each kidney. Each nephron is
l
It is excreted in solid crystal forms and formed from about 6 cm long.
ammonia in the liver of uricotelic animals and It is differentiated into four regions
Malpighian tubules in insects. l
Bowman’s capsule is double-walled cup and is lined by
thin flat cells called podocytes. It contains a group of
Human Excretory System capillaries called glomerulus. Glomerulus in the kidney
It consists of the following parts acts as a dialysing bag.
1. Kidneys (two)
l
Proximal Convoluted Tubule (PCT) is highly coiled
(convoluted) tubular structure. It is about 12-24 mm in
2. Ureters (two) length. Almost whole of vitamins, glucose, amino acids,
3. Urinary bladder (one) sodium and potassium, etc., are reabsorbed by active
4. Urethra (one) transport.
l
Henle’s loop is U-shaped segment. Loop of Henle is long
1. Kidneys in mammals and birds, which secrete hypertonic urine,
l
These are bean-shaped, chocolate brown structures lying in but short in other vertebrates like reptiles, etc.
the abdomen, one on each side of the vertebral column just l
Distal Convoluted Tubule (DCT) is connected to the
below the diaphragm. collecting duct. In this, active reabsorption of some Na +
l
The left kidney is placed a little higher than the right kidney takes place. It is impermeable to H2O. The DCTs of
(but reverse in rabbit). many nephrons open into a straight tube called collecting
duct, where large amounts of water could be reabsorbed.
l
Concavity of kidney called hilum or hilus is always inwardly
directed. 2. Ureters
l
These form the urine and control osmotic pressure within
These are two narrow tubes arising from the hilum. Each of
the organism with respect to external environment.
which is about 30 cm in length. These bring the urine
l
The functions and structure of kidney, with its different downwards and open into urinary bladder.
parts and their organisation is given in the figure below
Minor calyces
3. Urinary Bladder
Fine branches originating It temporarily stores the urine. Each ureter opens in urinary
from major calyx.
Renal fascia bladder. It can hold about 0.5-1.0 L of urine. It is absent in
Renal column of
Outermost, anchor Bertini birds. In both reptiles and birds, ureters and rectum open
kidney to
abdominal wall.
Projections of cortex into a common sac called cloaca.
into medulla.
Adipose capsule Major calyx
Branches of renal pelvis.
4. Urethra
Fat layer which
protects the kidney. Renal hilum A muscular and tubular structure, which extends from neck
123
Renal The larger blood
artery
vessels (renal artery
of bladder to outside.
Renal capsule and renal vein) In females, this tube is small and serve as a passage of urine
Innermost, fibrous connecting the
connective tissue Renal kidney to the major only. In males, it is long and function as a common passage
lining of kidney. vein abdominal blood for urine and spermatic fluids.
vessels pass in
Renal cortex and out.
Outer dark region. Renal pelvis Urine Formation in Kidney
Renal medulla Proximal part of ureter,
Medulla is sub-divided breaks into 2-3 branches The process of urine formation is called uropoiesis. Urine is
into number of towards kidney formed by mechanism of glomerular filtration, reabsorption
conical areas to form Renal papilla called major calyx. and secretion as described below
medullary pyramids. Serves as the opening of medullary
pyramids in the lumen of minor calyx. 1. Glomerular Filtration The glomerular capillary blood
Longitudinal section of kidney pressure causes filtration of blood through three layers,
i.e. the endothelium of glomerular blood vessels, the
NOTE
Aorta brings oxygenated blood to kidneys whereas inferior epithelium of Bowman’s capsule and a basement
vena cava carries deoxygenated blood from kidneys. membrane between these two layers.
Excretory
Products and
their Elimination
Learning & Revision for the Day
u Modes of Excretion u Osmoregulation and u Role of Other Organs
u Human Excretory System Regulation of Kidney in Excretion
Functions Disorders of Excretory System
u Urine Formation in Kidney u
Excretion is the process of removal of nitrogenous wastes from the body. The organs
involved in excretion are called excretory organs. There are different types of excretory
products or waste materials in different animals.
Modes of Excretion
There are mainly three types of modes of excretion
1. Ammonotelic Excretion It is found in aquatic animals like protozoans (e.g. Amoeba
and Paramecium), sponges (e.g. Sycon), coelenterates (e.g. Hydra), aquatic arthropods
(e.g. prawn), most aquatic molluscs (e.g. Pila), bony fishes (e.g. Labeo) and frog’s
tadpole larva.
l
Ammonia as a waste product is most toxic because of high pH and high solubility
in water, so large amount of water is required for its excretion.
l
It is released through general body surface into surrounding water.
2. Ureotelic Excretion It is found in those animals, which can take in water and can
retain considerable amounts of urea in their blood.
l
It is a common method of excretion in human, whales, seals, camels, kangaroo,
toads, frogs, sharks, etc.
l
Urea formation in liver cells of mammals was studied by Krebs and Henseleit.
l
Urea is formed in liver by detoxification of ammonia through ornithine cycle and
transported in the blood by plasma.
l
A person, who takes large amount of protein in his diet will excrete more urea. A
person having no food and water will have more urea in his blood. It requires less
water for excretion.
, 3. Uricotelic Excretion It is found in birds, land reptiles Nephron
(snakes and lizards), insects, snails, etc.
It is the structural and functional unit of kidney. These are
l
In this, the main nitrogenous waste is uric acid. also called as renal tubules or uriniferous tubules. There are
l
Uric acid is least soluble in water and is less toxic. about one million nephrons in each kidney. Each nephron is
l
It is excreted in solid crystal forms and formed from about 6 cm long.
ammonia in the liver of uricotelic animals and It is differentiated into four regions
Malpighian tubules in insects. l
Bowman’s capsule is double-walled cup and is lined by
thin flat cells called podocytes. It contains a group of
Human Excretory System capillaries called glomerulus. Glomerulus in the kidney
It consists of the following parts acts as a dialysing bag.
1. Kidneys (two)
l
Proximal Convoluted Tubule (PCT) is highly coiled
(convoluted) tubular structure. It is about 12-24 mm in
2. Ureters (two) length. Almost whole of vitamins, glucose, amino acids,
3. Urinary bladder (one) sodium and potassium, etc., are reabsorbed by active
4. Urethra (one) transport.
l
Henle’s loop is U-shaped segment. Loop of Henle is long
1. Kidneys in mammals and birds, which secrete hypertonic urine,
l
These are bean-shaped, chocolate brown structures lying in but short in other vertebrates like reptiles, etc.
the abdomen, one on each side of the vertebral column just l
Distal Convoluted Tubule (DCT) is connected to the
below the diaphragm. collecting duct. In this, active reabsorption of some Na +
l
The left kidney is placed a little higher than the right kidney takes place. It is impermeable to H2O. The DCTs of
(but reverse in rabbit). many nephrons open into a straight tube called collecting
duct, where large amounts of water could be reabsorbed.
l
Concavity of kidney called hilum or hilus is always inwardly
directed. 2. Ureters
l
These form the urine and control osmotic pressure within
These are two narrow tubes arising from the hilum. Each of
the organism with respect to external environment.
which is about 30 cm in length. These bring the urine
l
The functions and structure of kidney, with its different downwards and open into urinary bladder.
parts and their organisation is given in the figure below
Minor calyces
3. Urinary Bladder
Fine branches originating It temporarily stores the urine. Each ureter opens in urinary
from major calyx.
Renal fascia bladder. It can hold about 0.5-1.0 L of urine. It is absent in
Renal column of
Outermost, anchor Bertini birds. In both reptiles and birds, ureters and rectum open
kidney to
abdominal wall.
Projections of cortex into a common sac called cloaca.
into medulla.
Adipose capsule Major calyx
Branches of renal pelvis.
4. Urethra
Fat layer which
protects the kidney. Renal hilum A muscular and tubular structure, which extends from neck
123
Renal The larger blood
artery
vessels (renal artery
of bladder to outside.
Renal capsule and renal vein) In females, this tube is small and serve as a passage of urine
Innermost, fibrous connecting the
connective tissue Renal kidney to the major only. In males, it is long and function as a common passage
lining of kidney. vein abdominal blood for urine and spermatic fluids.
vessels pass in
Renal cortex and out.
Outer dark region. Renal pelvis Urine Formation in Kidney
Renal medulla Proximal part of ureter,
Medulla is sub-divided breaks into 2-3 branches The process of urine formation is called uropoiesis. Urine is
into number of towards kidney formed by mechanism of glomerular filtration, reabsorption
conical areas to form Renal papilla called major calyx. and secretion as described below
medullary pyramids. Serves as the opening of medullary
pyramids in the lumen of minor calyx. 1. Glomerular Filtration The glomerular capillary blood
Longitudinal section of kidney pressure causes filtration of blood through three layers,
i.e. the endothelium of glomerular blood vessels, the
NOTE
Aorta brings oxygenated blood to kidneys whereas inferior epithelium of Bowman’s capsule and a basement
vena cava carries deoxygenated blood from kidneys. membrane between these two layers.
