Excretory Products & their Elimination Class 11 Notes Biology

 Page 1


Points To Remember
Ammonotelism : 
The animals which excrete ammonia are called ammonotelic and excretion 
of ammonia is known as ammonotelism eg. Amoeba, sycon, hydra, liver fluke, 
tapeworm, Leech, Prawn, bony fishes etc.
Ureotelism :
excretion of urea is known as ureotelism and the animals which excrete 
urea are ureotelic animals eg. mammals, many terrertrial amphibians and marine 
fishes  and sting rays etc.
uricotelism :
Excretion of uric-acid is known as uricotelism and the animals are called 
uricotelic eg. most insects, land snails, lizards, snakes and birds.
Nephrons :
The structural and functional unit of kidneys. Each kidney contains about 
one million of nephrons.
Structure of Nephron :
A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal 
Convoluted Tubule). JG A (Juxaglomerular Apparatus), DCT (Distal Convoluted 
Tubule) and  the collecting duct. (Refer fig., 19.3, page 292 (NCERT Text Book 
of Biology for Class XI)
Structure of Kidney :
Size 10-12 cm in length, 5-7 cm in width, 2-3 cm thick, average weight 
about 120-170 g.
? The blood vessels, ureter and nerves enter in the kidney through hilum
(a notch).
Page 2


Points To Remember
Ammonotelism : 
The animals which excrete ammonia are called ammonotelic and excretion 
of ammonia is known as ammonotelism eg. Amoeba, sycon, hydra, liver fluke, 
tapeworm, Leech, Prawn, bony fishes etc.
Ureotelism :
excretion of urea is known as ureotelism and the animals which excrete 
urea are ureotelic animals eg. mammals, many terrertrial amphibians and marine 
fishes  and sting rays etc.
uricotelism :
Excretion of uric-acid is known as uricotelism and the animals are called 
uricotelic eg. most insects, land snails, lizards, snakes and birds.
Nephrons :
The structural and functional unit of kidneys. Each kidney contains about 
one million of nephrons.
Structure of Nephron :
A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal 
Convoluted Tubule). JG A (Juxaglomerular Apparatus), DCT (Distal Convoluted 
Tubule) and  the collecting duct. (Refer fig., 19.3, page 292 (NCERT Text Book 
of Biology for Class XI)
Structure of Kidney :
Size 10-12 cm in length, 5-7 cm in width, 2-3 cm thick, average weight 
about 120-170 g.
? The blood vessels, ureter and nerves enter in the kidney through hilum
(a notch).
? The outer layer of kidney is a tough capsule.
? The outer zone of kidney is cortex and the inner is medulla.
? The medulla is divided into few conical masses (medullary pyramids)
projecting into calyces.
? The cortex extends between medullary pyramids called columns of Bertini.
Refer figure 19.2, page 292 (NCERT—Class XI Biology)
Glomerular Filtration :
The filtration of blood in glomerulus, about 1100-1200 ml of blood is filtered 
by the kidney per minute.
Glomerular Filtration Rate (GFR) :
The amount of filtrate formed by the kidney per minute is called GFR. In a 
healthy individual it is about, 125 ml/minute, i.e. 180 litres per day.
Types of Nephrons :
(i) Juxtamedullary Nephron—About 15% of total nephrons, Glomeruli are 
found in inner region of cortex, large in size, long loop of Henle and found 
deep in medulla, associated with vasa recta control plasma volume when 
water supply is short.
 (ii) Cortical Nephron—About 85% of total nephron mainly lie in renal cortex, 
glomeruli found in outer cortex, short loop of Henle, extends very little in 
medulla. They do not have vasa recta or vasa recta is highly reduced.
Functions of Tubules :
 (i) PCT—absorption of all essential nutrients and 70-80% of electrolytes and 
water, helps to maintain the pH and ionic balance of body fluids by selective 
secretion of H
+
, ammonia and K
+
 into filtrate.
 (ii) Henele’s Loop—reabsorption in this segment is minimum, it plays a 
significant role in maintenance of higher molarity of medullary interstitial 
fluid.
 (iii) DCT—conditional reabsorption of Na
+
 and water takes place here, 
reabsorption of HCO
3
–
 and selective secretion of H
+
 and K
+
 and ammonia 
to maintain the pH and sodium-potassium balance in blood.
 (iv) Collecting duct—Large amount of water is absorbed from this region to 
produce concentrated urine, it plays a role in maintenance of  pH and ionic 
balance of blood by selective secretion of H
+
 and K
+
 ions.
Page 3


Points To Remember
Ammonotelism : 
The animals which excrete ammonia are called ammonotelic and excretion 
of ammonia is known as ammonotelism eg. Amoeba, sycon, hydra, liver fluke, 
tapeworm, Leech, Prawn, bony fishes etc.
Ureotelism :
excretion of urea is known as ureotelism and the animals which excrete 
urea are ureotelic animals eg. mammals, many terrertrial amphibians and marine 
fishes  and sting rays etc.
uricotelism :
Excretion of uric-acid is known as uricotelism and the animals are called 
uricotelic eg. most insects, land snails, lizards, snakes and birds.
Nephrons :
The structural and functional unit of kidneys. Each kidney contains about 
one million of nephrons.
Structure of Nephron :
A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal 
Convoluted Tubule). JG A (Juxaglomerular Apparatus), DCT (Distal Convoluted 
Tubule) and  the collecting duct. (Refer fig., 19.3, page 292 (NCERT Text Book 
of Biology for Class XI)
Structure of Kidney :
Size 10-12 cm in length, 5-7 cm in width, 2-3 cm thick, average weight 
about 120-170 g.
? The blood vessels, ureter and nerves enter in the kidney through hilum
(a notch).
? The outer layer of kidney is a tough capsule.
? The outer zone of kidney is cortex and the inner is medulla.
? The medulla is divided into few conical masses (medullary pyramids)
projecting into calyces.
? The cortex extends between medullary pyramids called columns of Bertini.
Refer figure 19.2, page 292 (NCERT—Class XI Biology)
Glomerular Filtration :
The filtration of blood in glomerulus, about 1100-1200 ml of blood is filtered 
by the kidney per minute.
Glomerular Filtration Rate (GFR) :
The amount of filtrate formed by the kidney per minute is called GFR. In a 
healthy individual it is about, 125 ml/minute, i.e. 180 litres per day.
Types of Nephrons :
(i) Juxtamedullary Nephron—About 15% of total nephrons, Glomeruli are 
found in inner region of cortex, large in size, long loop of Henle and found 
deep in medulla, associated with vasa recta control plasma volume when 
water supply is short.
 (ii) Cortical Nephron—About 85% of total nephron mainly lie in renal cortex, 
glomeruli found in outer cortex, short loop of Henle, extends very little in 
medulla. They do not have vasa recta or vasa recta is highly reduced.
Functions of Tubules :
 (i) PCT—absorption of all essential nutrients and 70-80% of electrolytes and 
water, helps to maintain the pH and ionic balance of body fluids by selective 
secretion of H
+
, ammonia and K
+
 into filtrate.
 (ii) Henele’s Loop—reabsorption in this segment is minimum, it plays a 
significant role in maintenance of higher molarity of medullary interstitial 
fluid.
 (iii) DCT—conditional reabsorption of Na
+
 and water takes place here, 
reabsorption of HCO
3
–
 and selective secretion of H
+
 and K
+
 and ammonia 
to maintain the pH and sodium-potassium balance in blood.
 (iv) Collecting duct—Large amount of water is absorbed from this region to 
produce concentrated urine, it plays a role in maintenance of  pH and ionic 
balance of blood by selective secretion of H
+
 and K
+
 ions.
Steps of Urine Formation
1. Gromerular Filtration—Blood is filtered by glomerulus through three
membranes i.e., endothelium of blood vessel, filtration slits of Bowman’s
capsule and basement membrance between these two layers. This filt ration is
called ultrafiltration as all constituents of plasma comes into filterate except
proteins.
2. Reabsorption—90% of filtrate is reabsorbed by the renal tubules by active
or passive mechanism.
It is evident by the fact that out of 180L of filtrate formed per day only 1.5
L of urine released.
3. Secretion—Tubular cells secrete H
+
, K
+
, ammonia into the urine. It maintains
acid-base balance of body fluids.
Mechanism of concentration of the Filtrate (Countercur-
rent Mechanism) :
Refer fig 19.6 page 296 (NCERT-Class XI Biology)
? This mechanism is said to be countercurrent mechanism because the out
flow (in the ascending limb) runs parallel to and in the opposite direction of
the inflow (in the descending limb).
? NaCl is transported by the ascending limb of Henle’s loop which is exchanged
with the descending limb of vasa-recta.
? NaCl is returned to the interstitium by the ascending portion of vasa recta.
? Henle’s loop and vasarecta as well as  the counter current in them help to
maintain an increasing osmolality towards the inner medullary interstitium
i.e., from 300 mosmol/L in cortex to about 1200 mosmol/L in inner medulla.
? Small amount  of urea enter, the thin segment of ascending limb of Henle’s
loop which is transported back to the interstitium by the collecting tubule.
? This mechanism helps to maintain a concentration gradient in the medullary
tubule interstitium.
? It helps in an easy passage of water from the collecting tubule to concentrate
the filtrate i.e. urine.
Anti Diuretic Hormone (ADH) Controls the urine formation when there
is less blood volume due to excessive loss of fluid from the body, osmoreceptors 
send the signal to hypothalamus to release ADH which in turn facilitates water 
reabsorption thus preventing diuresis (increase in frequency of urination)
Page 4


Points To Remember
Ammonotelism : 
The animals which excrete ammonia are called ammonotelic and excretion 
of ammonia is known as ammonotelism eg. Amoeba, sycon, hydra, liver fluke, 
tapeworm, Leech, Prawn, bony fishes etc.
Ureotelism :
excretion of urea is known as ureotelism and the animals which excrete 
urea are ureotelic animals eg. mammals, many terrertrial amphibians and marine 
fishes  and sting rays etc.
uricotelism :
Excretion of uric-acid is known as uricotelism and the animals are called 
uricotelic eg. most insects, land snails, lizards, snakes and birds.
Nephrons :
The structural and functional unit of kidneys. Each kidney contains about 
one million of nephrons.
Structure of Nephron :
A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal 
Convoluted Tubule). JG A (Juxaglomerular Apparatus), DCT (Distal Convoluted 
Tubule) and  the collecting duct. (Refer fig., 19.3, page 292 (NCERT Text Book 
of Biology for Class XI)
Structure of Kidney :
Size 10-12 cm in length, 5-7 cm in width, 2-3 cm thick, average weight 
about 120-170 g.
? The blood vessels, ureter and nerves enter in the kidney through hilum
(a notch).
? The outer layer of kidney is a tough capsule.
? The outer zone of kidney is cortex and the inner is medulla.
? The medulla is divided into few conical masses (medullary pyramids)
projecting into calyces.
? The cortex extends between medullary pyramids called columns of Bertini.
Refer figure 19.2, page 292 (NCERT—Class XI Biology)
Glomerular Filtration :
The filtration of blood in glomerulus, about 1100-1200 ml of blood is filtered 
by the kidney per minute.
Glomerular Filtration Rate (GFR) :
The amount of filtrate formed by the kidney per minute is called GFR. In a 
healthy individual it is about, 125 ml/minute, i.e. 180 litres per day.
Types of Nephrons :
(i) Juxtamedullary Nephron—About 15% of total nephrons, Glomeruli are 
found in inner region of cortex, large in size, long loop of Henle and found 
deep in medulla, associated with vasa recta control plasma volume when 
water supply is short.
 (ii) Cortical Nephron—About 85% of total nephron mainly lie in renal cortex, 
glomeruli found in outer cortex, short loop of Henle, extends very little in 
medulla. They do not have vasa recta or vasa recta is highly reduced.
Functions of Tubules :
 (i) PCT—absorption of all essential nutrients and 70-80% of electrolytes and 
water, helps to maintain the pH and ionic balance of body fluids by selective 
secretion of H
+
, ammonia and K
+
 into filtrate.
 (ii) Henele’s Loop—reabsorption in this segment is minimum, it plays a 
significant role in maintenance of higher molarity of medullary interstitial 
fluid.
 (iii) DCT—conditional reabsorption of Na
+
 and water takes place here, 
reabsorption of HCO
3
–
 and selective secretion of H
+
 and K
+
 and ammonia 
to maintain the pH and sodium-potassium balance in blood.
 (iv) Collecting duct—Large amount of water is absorbed from this region to 
produce concentrated urine, it plays a role in maintenance of  pH and ionic 
balance of blood by selective secretion of H
+
 and K
+
 ions.
Steps of Urine Formation
1. Gromerular Filtration—Blood is filtered by glomerulus through three
membranes i.e., endothelium of blood vessel, filtration slits of Bowman’s
capsule and basement membrance between these two layers. This filt ration is
called ultrafiltration as all constituents of plasma comes into filterate except
proteins.
2. Reabsorption—90% of filtrate is reabsorbed by the renal tubules by active
or passive mechanism.
It is evident by the fact that out of 180L of filtrate formed per day only 1.5
L of urine released.
3. Secretion—Tubular cells secrete H
+
, K
+
, ammonia into the urine. It maintains
acid-base balance of body fluids.
Mechanism of concentration of the Filtrate (Countercur-
rent Mechanism) :
Refer fig 19.6 page 296 (NCERT-Class XI Biology)
? This mechanism is said to be countercurrent mechanism because the out
flow (in the ascending limb) runs parallel to and in the opposite direction of
the inflow (in the descending limb).
? NaCl is transported by the ascending limb of Henle’s loop which is exchanged
with the descending limb of vasa-recta.
? NaCl is returned to the interstitium by the ascending portion of vasa recta.
? Henle’s loop and vasarecta as well as  the counter current in them help to
maintain an increasing osmolality towards the inner medullary interstitium
i.e., from 300 mosmol/L in cortex to about 1200 mosmol/L in inner medulla.
? Small amount  of urea enter, the thin segment of ascending limb of Henle’s
loop which is transported back to the interstitium by the collecting tubule.
? This mechanism helps to maintain a concentration gradient in the medullary
tubule interstitium.
? It helps in an easy passage of water from the collecting tubule to concentrate
the filtrate i.e. urine.
Anti Diuretic Hormone (ADH) Controls the urine formation when there
is less blood volume due to excessive loss of fluid from the body, osmoreceptors 
send the signal to hypothalamus to release ADH which in turn facilitates water 
reabsorption thus preventing diuresis (increase in frequency of urination)
Micturition :
The expulsion of urine from the urinary bladder is called micturition. It is 
a reflex process but can be controlled voluntarily up to some extent in grown up 
children and adults.
? The CNS (Central Nervous System) sends the signal which cause the
stretching of the urinary bladder when it gets filled with urine.
? In response, the stretch receptors on the walls of the bladder sends signals
to the CNS.
? The CNS passes on motor message to initiate the contraction of smooth
muscles of the bladder and simultaneous relaxation of the urethral sphincter 
causing the release of urine.
? An adult human excretes on an average 1 to 1.5 Litres res of urine per day.
? On an average 25-30 gram of urea is excreted out per day.
Renin Angiotensin System
         Fall in GFR
    ?  Renin from JG cells
            Angiotensinogen ?  Angiotensin I ? Angiotensin II
  ? Acts on
Adrenal Cortex
  ? Secretes aldosterone
Reabsorption from DCT
  ?
Increase in GFR
Role of other organs in excretion :
? Lungs—removes CO
2
 (18L/day) and water.
? Liver—secretes bilirubin, biliverdin etc. helps to eliminate these substances
along. with cholesterol, vitamins, drugs and degraded steroid hormones
through digesive wastes.
? Sweat and sebaceous glands—These glands of skin help to eliminate small
amount of urea, NaCl and lactic acid etc. through sweat while sebaceous
glands help to eliminate some substances like steroids, hydrocarbons and
waxes through sebum.
? Saliva—It  can help to eliminate small amount of nitrogenous wastes.
Page 5


Points To Remember
Ammonotelism : 
The animals which excrete ammonia are called ammonotelic and excretion 
of ammonia is known as ammonotelism eg. Amoeba, sycon, hydra, liver fluke, 
tapeworm, Leech, Prawn, bony fishes etc.
Ureotelism :
excretion of urea is known as ureotelism and the animals which excrete 
urea are ureotelic animals eg. mammals, many terrertrial amphibians and marine 
fishes  and sting rays etc.
uricotelism :
Excretion of uric-acid is known as uricotelism and the animals are called 
uricotelic eg. most insects, land snails, lizards, snakes and birds.
Nephrons :
The structural and functional unit of kidneys. Each kidney contains about 
one million of nephrons.
Structure of Nephron :
A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal 
Convoluted Tubule). JG A (Juxaglomerular Apparatus), DCT (Distal Convoluted 
Tubule) and  the collecting duct. (Refer fig., 19.3, page 292 (NCERT Text Book 
of Biology for Class XI)
Structure of Kidney :
Size 10-12 cm in length, 5-7 cm in width, 2-3 cm thick, average weight 
about 120-170 g.
? The blood vessels, ureter and nerves enter in the kidney through hilum
(a notch).
? The outer layer of kidney is a tough capsule.
? The outer zone of kidney is cortex and the inner is medulla.
? The medulla is divided into few conical masses (medullary pyramids)
projecting into calyces.
? The cortex extends between medullary pyramids called columns of Bertini.
Refer figure 19.2, page 292 (NCERT—Class XI Biology)
Glomerular Filtration :
The filtration of blood in glomerulus, about 1100-1200 ml of blood is filtered 
by the kidney per minute.
Glomerular Filtration Rate (GFR) :
The amount of filtrate formed by the kidney per minute is called GFR. In a 
healthy individual it is about, 125 ml/minute, i.e. 180 litres per day.
Types of Nephrons :
(i) Juxtamedullary Nephron—About 15% of total nephrons, Glomeruli are 
found in inner region of cortex, large in size, long loop of Henle and found 
deep in medulla, associated with vasa recta control plasma volume when 
water supply is short.
 (ii) Cortical Nephron—About 85% of total nephron mainly lie in renal cortex, 
glomeruli found in outer cortex, short loop of Henle, extends very little in 
medulla. They do not have vasa recta or vasa recta is highly reduced.
Functions of Tubules :
 (i) PCT—absorption of all essential nutrients and 70-80% of electrolytes and 
water, helps to maintain the pH and ionic balance of body fluids by selective 
secretion of H
+
, ammonia and K
+
 into filtrate.
 (ii) Henele’s Loop—reabsorption in this segment is minimum, it plays a 
significant role in maintenance of higher molarity of medullary interstitial 
fluid.
 (iii) DCT—conditional reabsorption of Na
+
 and water takes place here, 
reabsorption of HCO
3
–
 and selective secretion of H
+
 and K
+
 and ammonia 
to maintain the pH and sodium-potassium balance in blood.
 (iv) Collecting duct—Large amount of water is absorbed from this region to 
produce concentrated urine, it plays a role in maintenance of  pH and ionic 
balance of blood by selective secretion of H
+
 and K
+
 ions.
Steps of Urine Formation
1. Gromerular Filtration—Blood is filtered by glomerulus through three
membranes i.e., endothelium of blood vessel, filtration slits of Bowman’s
capsule and basement membrance between these two layers. This filt ration is
called ultrafiltration as all constituents of plasma comes into filterate except
proteins.
2. Reabsorption—90% of filtrate is reabsorbed by the renal tubules by active
or passive mechanism.
It is evident by the fact that out of 180L of filtrate formed per day only 1.5
L of urine released.
3. Secretion—Tubular cells secrete H
+
, K
+
, ammonia into the urine. It maintains
acid-base balance of body fluids.
Mechanism of concentration of the Filtrate (Countercur-
rent Mechanism) :
Refer fig 19.6 page 296 (NCERT-Class XI Biology)
? This mechanism is said to be countercurrent mechanism because the out
flow (in the ascending limb) runs parallel to and in the opposite direction of
the inflow (in the descending limb).
? NaCl is transported by the ascending limb of Henle’s loop which is exchanged
with the descending limb of vasa-recta.
? NaCl is returned to the interstitium by the ascending portion of vasa recta.
? Henle’s loop and vasarecta as well as  the counter current in them help to
maintain an increasing osmolality towards the inner medullary interstitium
i.e., from 300 mosmol/L in cortex to about 1200 mosmol/L in inner medulla.
? Small amount  of urea enter, the thin segment of ascending limb of Henle’s
loop which is transported back to the interstitium by the collecting tubule.
? This mechanism helps to maintain a concentration gradient in the medullary
tubule interstitium.
? It helps in an easy passage of water from the collecting tubule to concentrate
the filtrate i.e. urine.
Anti Diuretic Hormone (ADH) Controls the urine formation when there
is less blood volume due to excessive loss of fluid from the body, osmoreceptors 
send the signal to hypothalamus to release ADH which in turn facilitates water 
reabsorption thus preventing diuresis (increase in frequency of urination)
Micturition :
The expulsion of urine from the urinary bladder is called micturition. It is 
a reflex process but can be controlled voluntarily up to some extent in grown up 
children and adults.
? The CNS (Central Nervous System) sends the signal which cause the
stretching of the urinary bladder when it gets filled with urine.
? In response, the stretch receptors on the walls of the bladder sends signals
to the CNS.
? The CNS passes on motor message to initiate the contraction of smooth
muscles of the bladder and simultaneous relaxation of the urethral sphincter 
causing the release of urine.
? An adult human excretes on an average 1 to 1.5 Litres res of urine per day.
? On an average 25-30 gram of urea is excreted out per day.
Renin Angiotensin System
         Fall in GFR
    ?  Renin from JG cells
            Angiotensinogen ?  Angiotensin I ? Angiotensin II
  ? Acts on
Adrenal Cortex
  ? Secretes aldosterone
Reabsorption from DCT
  ?
Increase in GFR
Role of other organs in excretion :
? Lungs—removes CO
2
 (18L/day) and water.
? Liver—secretes bilirubin, biliverdin etc. helps to eliminate these substances
along. with cholesterol, vitamins, drugs and degraded steroid hormones
through digesive wastes.
? Sweat and sebaceous glands—These glands of skin help to eliminate small
amount of urea, NaCl and lactic acid etc. through sweat while sebaceous
glands help to eliminate some substances like steroids, hydrocarbons and
waxes through sebum.
? Saliva—It  can help to eliminate small amount of nitrogenous wastes.
Disorders of Excretory system :
? Uremia—The accumulation of urea in blood due to malfunctioning of kidney.
 Hemodialysis—The process; of removal of urea from the blood artificially.
In this process the blood from an artery is passed into dialysing unit after
adding an anticoagulant like heparin. The blood passes through coiled
cellophane tube surrounding by dialysing fluid. The nitrogenous wastes
from the concentration gradient and the blood becomes clear. This blood is
pumped back to the body through vein after adding anti-heparin to it.
? Renal calculi—The format ion of insoluble mass of crystallised salts (oxalates
or phosphates of calcium.
? Glomerulonephritis—Inflamation of glomeruli of kindney.
Kidney Transplantation 
? Kidney transplantation is done in a patient in which both the kidneys fail to work i.e.
at total failure of kidney. Kidney transplantation is the ultimate method for treatment
of renal failure. In case of kidney transplantation both the damaged kidneys of patient 
are removed by surgery. And a functional kidney from a healthy donar preferably
from close relative is taken and transplanted in the body of patient. After successful
transplantation the patient and donar can survive on one kidney.
Precautions taken for successful transplantation of Kidney :
1. Kidney should be taken from a healthy donor preferably from close relative.
2. Matching of blood group and other factor and compatibility should be done
carefully before transplantation.
3. The patient (recipient) has to take some prescribed medicines
immunosuppresses through out the life to suppress the immune system.