Excretion is the elimination of metabolic wastes like Some amount of urea may be retained in the kidney matrix
ammonia, urea, uric acid etc. from the tissues. of some animals to maintain a desired osmolarity.
3. Uricotelism: Process of excretion of uric acid. It is water
Types of excretion
insoluble & less toxic. So, water is not needed for excretion.
1. Ammonotelism: Process of excretion of NH3.
Uricotelic animals: Insects, some land crustaceans, land
Ammonotelic animals: Aquatic invertebrates, aquatic
snails, terrestrial reptiles & birds.
insects, bony fishes, aquatic amphibians etc.
Ureotelism & uricotelism are needed for water conservation.
NH3 is highly toxic. So, excretion needs excess of water.
NH3 is readily soluble in water and is excreted by Some excretory organs in animals
diffusion through body surface or gill surfaces (in fishes) • Protonephridia (flame cells): In Flatworms, rotifers,
as ammonium ions. some annelids & cephalochordate (Amphioxus).
Kidneys do not play any significant role in its removal. Protonephridia are primarily for osmoregulation.
2. Ureotelism: Process of excretion of urea. • Nephridia: In Annelids. Help in the removal of
Ureotelic animals: Cartilaginous fishes, terrestrial & nitrogenous wastes and osmoregulation.
semi-aquatic amphibians (frogs, toads etc.), aquatic & • Malpighian tubules: In Insects. Help in the removal of
semi-aquatic reptiles (alligators, turtles), mammals etc. nitrogenous wastes and osmoregulation.
In liver, NH3 is converted into less toxic urea. So, it needs • Antennal or green glands: In Crustaceans (prawn etc.)
only moderate quantity of water for excretion. • Kidneys: In higher animals.
HUMAN EXCRETORY SYSTEM
It includes kidneys, ureters, urinary bladder & urethra. o Glomerulus: A tuft of
Structure of Kidney capillaries formed by
afferent arteriole (a
- Reddish brown,
fine branch of renal
bean-shaped
artery). Blood from
structures situated
glomerulus is carried
between the levels of
away by efferent
last thoracic & 3rd
arteriole.
lumbar vertebra.
o Renal tubule: It
- Length: 10-12 cm,
begins with a double
width: 5-7 cm,
walled cup-like
thickness: 2-3 cm.
Bowman’s capsule,
Average weight:
which encloses the glomerulus.
120-170 gm.
Glomerulus + Bowman’s capsule = Malpighian body
- It is enclosed in a
- The tubule continues with proximal convoluted tubule
tough, 3-layered fibrous renal capsule.
(PCT), Henle’s loop & distal convoluted tubule (DCT).
- On the concave side of kidney, there is an opening (hilum
- Henle’s loop is hairpin-shaped. It has descending and
or hilus) through which blood vessels, nerves, lymphatic
ascending limbs.
ducts and ureter enter
- The DCTs of many nephrons open into a collecting duct.
the kidney.
Collecting duct extends from cortex to inner parts of
- Hilum leads to funnel
medulla. They converge and open into the renal pelvis
shaped cavity called
through medullary pyramids in the calyces.
renal pelvis with
- Malpighian body (Renal corpuscle), PCT and DCT are
projections called
situated in renal cortex. Loop of Henle dips into medulla.
calyces.
- The efferent arteriole forms a fine capillary network
- A kidney has outer
(peritubular capillaries) around the renal tubule. A
cortex & inner medulla.
minute vessel of this network runs parallel to Henle’s loop
- Medulla has few conical projections called medullary
forming a ‘U’ shaped vasa recta.
pyramids (renal pyramids) projecting into the calyces.
Types of nephrons
- Cortex extends in between the medullary pyramids as renal
columns (Columns of Bertini). 1. Cortical nephrons (85%): In this, the Henle’s loop is
- Each kidney has nearly one million tubular nephrons. short and extends only very little into the medulla. Vasa
recta is absent or highly reduced.
Nephron
2. Juxtamedullary nephrons (15%): In this, Henle’s loop
- Nephrons are the structural & functional units of kidney. is long and runs deep into medulla. Vasa recta present.
- Each nephron has 2 parts: Glomerulus & Renal tubule.
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ammonia, urea, uric acid etc. from the tissues. of some animals to maintain a desired osmolarity.
3. Uricotelism: Process of excretion of uric acid. It is water
Types of excretion
insoluble & less toxic. So, water is not needed for excretion.
1. Ammonotelism: Process of excretion of NH3.
Uricotelic animals: Insects, some land crustaceans, land
Ammonotelic animals: Aquatic invertebrates, aquatic
snails, terrestrial reptiles & birds.
insects, bony fishes, aquatic amphibians etc.
Ureotelism & uricotelism are needed for water conservation.
NH3 is highly toxic. So, excretion needs excess of water.
NH3 is readily soluble in water and is excreted by Some excretory organs in animals
diffusion through body surface or gill surfaces (in fishes) • Protonephridia (flame cells): In Flatworms, rotifers,
as ammonium ions. some annelids & cephalochordate (Amphioxus).
Kidneys do not play any significant role in its removal. Protonephridia are primarily for osmoregulation.
2. Ureotelism: Process of excretion of urea. • Nephridia: In Annelids. Help in the removal of
Ureotelic animals: Cartilaginous fishes, terrestrial & nitrogenous wastes and osmoregulation.
semi-aquatic amphibians (frogs, toads etc.), aquatic & • Malpighian tubules: In Insects. Help in the removal of
semi-aquatic reptiles (alligators, turtles), mammals etc. nitrogenous wastes and osmoregulation.
In liver, NH3 is converted into less toxic urea. So, it needs • Antennal or green glands: In Crustaceans (prawn etc.)
only moderate quantity of water for excretion. • Kidneys: In higher animals.
HUMAN EXCRETORY SYSTEM
It includes kidneys, ureters, urinary bladder & urethra. o Glomerulus: A tuft of
Structure of Kidney capillaries formed by
afferent arteriole (a
- Reddish brown,
fine branch of renal
bean-shaped
artery). Blood from
structures situated
glomerulus is carried
between the levels of
away by efferent
last thoracic & 3rd
arteriole.
lumbar vertebra.
o Renal tubule: It
- Length: 10-12 cm,
begins with a double
width: 5-7 cm,
walled cup-like
thickness: 2-3 cm.
Bowman’s capsule,
Average weight:
which encloses the glomerulus.
120-170 gm.
Glomerulus + Bowman’s capsule = Malpighian body
- It is enclosed in a
- The tubule continues with proximal convoluted tubule
tough, 3-layered fibrous renal capsule.
(PCT), Henle’s loop & distal convoluted tubule (DCT).
- On the concave side of kidney, there is an opening (hilum
- Henle’s loop is hairpin-shaped. It has descending and
or hilus) through which blood vessels, nerves, lymphatic
ascending limbs.
ducts and ureter enter
- The DCTs of many nephrons open into a collecting duct.
the kidney.
Collecting duct extends from cortex to inner parts of
- Hilum leads to funnel
medulla. They converge and open into the renal pelvis
shaped cavity called
through medullary pyramids in the calyces.
renal pelvis with
- Malpighian body (Renal corpuscle), PCT and DCT are
projections called
situated in renal cortex. Loop of Henle dips into medulla.
calyces.
- The efferent arteriole forms a fine capillary network
- A kidney has outer
(peritubular capillaries) around the renal tubule. A
cortex & inner medulla.
minute vessel of this network runs parallel to Henle’s loop
- Medulla has few conical projections called medullary
forming a ‘U’ shaped vasa recta.
pyramids (renal pyramids) projecting into the calyces.
Types of nephrons
- Cortex extends in between the medullary pyramids as renal
columns (Columns of Bertini). 1. Cortical nephrons (85%): In this, the Henle’s loop is
- Each kidney has nearly one million tubular nephrons. short and extends only very little into the medulla. Vasa
recta is absent or highly reduced.
Nephron
2. Juxtamedullary nephrons (15%): In this, Henle’s loop
- Nephrons are the structural & functional units of kidney. is long and runs deep into medulla. Vasa recta present.
- Each nephron has 2 parts: Glomerulus & Renal tubule.
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