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Excretory Products and their Elimination Class 11 Notes Biology Chapter 19
Topics and Subtopics in for Class 11 Biology Chapter 19 Excretory Products and their Elimination:
|Section Name||Topic Name|
|19||Excretory Products and their Elimination|
|19.1||Human Excretory System|
|19.3||Function of the Tubules|
|19.4||Mechanism of Concentration of the Filtrate|
|19.5||Regulation of Kidney Function|
|19.7||Role of other Organs in Excretion|
|19.8||Disorders of the Excretory System|
NCERT SolutionsClass 11 BiologyBiology Sample Papers
Excretion is the removal of nitrogenous waste products and other metabolites from the animal body which is normally associated with the process of maintenance of osmibtic concentrations, i.e., osmoregulation within the body.
Both excretion and osmoregulation are important for the maintenance of homeostasis, i.e., for keeping the internal environment of the body constant that is necessary for normal life processes.
Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by animals. These substances get accumulated in the animal body either by metabolic activities or by other means like excess ingestion.
Topic 1 Excretion: Major Products, Human System and Uropoiesis
Types of Nitrogenous Excretion
Depending upon the nature of excretory product, animals exhibit different processes of nitrogenous excretion.
These are described as follows
(i) Ammonotelism Ammonia is the most toxic form of nitrogenous waste, it requires large amount of water for its elimination. The organism that excrete ammonia are called ammonotelic and this , process to eliminate ammonia is known as ammonotelism.
Examples of ammonotelic animals are Many bony fishes, aquatic amphibians and aquatic insects. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions.
Kidneys does not play any significant role in its removal.
(ii) Ureotelism The process of excreting urea is called ureotelism. Animals, which does not live in high abundance of ‘water convert ammonia produced in the body into urea (in the liver) and release into the blood, which is filtered and excreted out by the kidneys.
Examples of ureotelic animals are Mammals, many terrestrial amphibians and marine fishes.
(iii) Uricotelism The process of excreting uric acid is called uricotelism. Uric acid, being the least toxic nitrogenous waste can be removed with a minimum loss of water from the animal body.
Thus, it is excreted in the form of pellet or paste (i.e., semi-solid form). Normally, the animals which live in desert exhibit uricotelism.
Examples of uricotelic animals are Reptiles, birds, land snails and insects.
Some animals perform dual excretion, i.e., two modes of excretion. For example, Earthworms excrete ammonia when sufficient water is available, while it excretes urea in drier surroundings.
Other examples are lung fishes, Xenopus, crocodiles, etc.
Different animal groups have a variety of excretory structures (organs) to perform the process of excretion. In most of the invertebrates, these structures are simple tubular form, whereas, vertebrates have complex tubular organs called kidneys.
Some of these structures are mentioned below in the given table
Excretory Organs and Main Nitrogenous Wastes of Different Animal Croups
Human Excretory System
Human excretory system consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra, these are described below in detail
These are reddish brown, bean-shaped structures situated between the levels of last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity. –
Kidneys are mesodermal in origin as they developed from mesodermal nephrostomes or mesomeres (ciliated structures, functional in embryonic conditions).
Position of Kidneys
The kidneys are located below the diaphragm on the left and right sides. The right kidney is lower and smaller than the left kidney because the liver takes up much space of the right side.
Each kidney of an adult human measures. 10-12 cm in length, 5-7 cm in width, 2-3 cm in thickness with an average weight of 120-170 gm (i.e., 150 gm in males and about 135 gm in females).
Structure of Kidney
Structure of kidney can be studied well under two heads, i.e., external as well as internal structure.
These are described below as
The outer surface of each kidney is convex and inner surface is concave, where it has a notch called hilum, through, which the supply of blood occurs, i.e., renal artery and renal vein, pass in and out of the kidneys along with the ureter and the nerve supply of kidney.
If we look from outside to inside, three layers cover the kidneys, i.e., renal fascia (outermost), the adipose layer and then renal capsule (innermost layer). These coverings protect the kidneys from external shocks and injuries.
The LS of a mammalian kidney seems to have of an outer cortex and inner medulla.
Inside the kidney, the ureter is expanded as a funnel-shaped cavity called pelvis. The free end of pelvis has number of cup-like cavities called calyces (sing, calyx) major and minor.
Medulla projects into the calyces as conical processes, called renal pyramids or medullary pyramids. The tip of pyramids are called renal papillae. The cortex spreads in between medullary pyramids as renal columns called columns of Bertini.
Each kidney is composed of numerous (nearly one million) complex tubular structure called nephrons, which are the functional units of kidney.
Structure of Nephron Uriniferous Tubule
Each nephron consists of two parts, i.e., the Malpighian body or renal corpuscle and the renal tubule.
i. Malpighian Body or Renal Corpuscle
Glomerulus along with Bowman’s capsule is called the Malpighian body or renal corpuscle which filters out large solutes from the blood and delivers small solutes to the renal tubule for modification.
* Glomerulus It is a tuft of capillaries formed by the afferent arteriole (a fine branch of renal artery).
The afferent arteriole is short and wide that supplies blood to the glomerulus, while, the efferent arteriole is narrow and long carrying blood away from the glomerulus.
Differences between Afferent Arteriole and Efferent Arteriole
ii. Bowman’s Capsule (Glomerular capsule) It is a double walled cup-like structure that surrounds the glomerulus. The outer parietal wall which is composed of flattened (squamous) cells and the inner visceral wall is composed of a special type of less flattened cells, called podocytes.
iii. Renal Tubules
Just below the glomerulus, the tubule has a very short neck.
Attached to each Bowman’s capsule is a long, thin tubule with three distinct regions.
These regions are described as follows
(a) Proximal Convoluted Tubule (PCT) Behind the neck, it makes few coils and is restricted to the cortical region of the kidney.
(b) Henle’s Loop It is quite narrower and U-shaped (or hair pin-shaped) having a descending limb that ends into the medulla and an ascending limb that extends back from the medulla into the cortex.
Differences between Descending Limb and Ascending Limb of Henle’s Loop
* Peritubular Capillary Network (PTCN), is formed when a minute vessel of peritubular capillaries runs parallel to the loop of Henle forming a U-shaped vasa recta.
* All these capillaries join to form renal venules, which join to form a renal vein that opens into the inferior vena cava.
Types of Nephrons
Based on the location in the kidney, nephrons are of following two types
1. Cortical Nephrons
In majority of nephrons, the loop of Henle is too short and extends only very little into the medulla i.e., lie in the renal cortex. Such two nephrons are called cortical nephrons.
In some of the nephrons, the loop of Henle is very long and runs deep into the medulla. These nephrons are called juxtamedullary nephrons.
The cortical nephron forms about 80% of the total nephron count while rest 20% are the juxtamedullary nephron.
Functions of Kidney
Following functions are served by kidney
(i) Regulation of water and electrolyte balance.
(ii) Regulation of arterial pressure.
(iii) Excretion of metabolic waste and foreign chemicals.
(iv) Secretion of hormones like renin.
The pelvis of each kidney is continued as a ureter and emerges out at hilus. Ureter is a long and muscular tube. Ureters of both sides extend posteriorly and open into the urinary bladder.
3. Urinary Bladder
It is a thin-walled, pear-shaped, white transparent sac present in the pelvic cavity. It temporarily stores the urine.
It is a membranous tube, which conduct urine to the exterior. The urethral sphincters keep the urethra closed except during voiding of urine.
The formation of urine is the result of the following processes
1. Glomerular Filtration
The first step of urine formation is the filtration of blood, which is carried out by the glomerulus. That’s why this step is called glomerular filtration.
Kidneys filter about 1100-1200 mL of blood per minute, which constitute roughly l/5th of the blood pumped out by each ventricle of the heart in a minute.
The glomerular capillary bloodpressure causes filtration of blood through three layers, i.e.,
(i) the endothelium of glomerular blood vessels.
(ii) the epithelium of Bowmans capsule.
(iii) a basement membrane (present between the above mentioned two layers).
The podocytes (epithelial cells of Bowman’s capsule) are arranged in such a manner so, as to leave some minute spaces called filtration slits or slit pores.
On account of the high pressure in the glomerular capillaries, the substances are filtered through these pores into the lumen of the Bowman’s capsule (but the RBC, WBC and plasma proteins having high molecular weight are unable to pass out).
That’s why this process of filtration through glomerular capillaries in the Bowman’s capsule is known as ultra filtration and the filtrate is called glomerular filtrate or primary urine.
It is hypotonic to urine that is actually excreted. Basic function of nephron is to clear out the plasma from unwanted substrates and also maintain the osmotic concentration of the blood plasma. Thus, the fluid coming out is known as urine, whose formation occurs inside the kidney.
Glomerular Filtration Rate The amount of the filtrate formed by the kidneys per minute is called Glomerular Filtration Rate (GFR). In a healthy person it was found approximately 125 mL/min, i.e., 180 L/day.
GFR is regulated by one of the efficient mechanism carried out by Juxtaglomerular Apparatus (JGA).
JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact.
This apparatus includes
(i) granular juxtaglomerular cells in the afferent arteriole.
(ii) macula densa cells of DCT.
(iii) agranular lacis cells situated in between the above two.
A fall in GFR can activate the JG cells to release renin, which can stimulate the glomerular blood flow and thereby, the GFR back to I normal.
2. Selective Reabsorption
This is the second step in the formation of urine from filtrate. The urine released is 1.5 L as compared to the volume of the filtrate formed per day (180 L). It suggests that as much as 99% of the material in the filtrate is reabsorbed by the renal tubules. Thus, the process is called reabsorption.
Depending upon the types of molecules being reabsorbed, movements into and out of epithelial cells in different segments of nephron occur either by passive transport or active transport.
These are described as follows
(i) Water and urea, are reabsorbed by passive transport (i.e., water is reabsorbed by osmosis and urea by simple diffusion).
(ii) Glucose and amino acids are reabsorbed by active transport.
(iii) The reabsorption of Na+, occurs both by passive and active transport.
3. Tubular Secretion
It is also an important step in urine formation. Certain chemicals in the blood that are not removed by filtration from the glomerular capillaries are removed by this process of tubular secretion. It helps in the maintenance of ionic and acid-base balance of body fluids by removing chemicals like foreign bodies, ions (K+, H+, NH–) and molecules (medicines), etc., that are toxic at elevated levels.
Difference between the Tubular Reabsorption and Tubular Secretion
Functions of the Tubules
When the glomerular filtrate/primary urine passes through renal tubule, water and different materials of filtrate reabsorb at various places.
These are given below in the following manner
i. Proximal Convoluted Tubule (PCT)
The epithelial cells of the PCT have numerous microvilli (simple cuboidal brush-border epithelium) which increase the surface area available for reabsorption.
The process of reabsorption mostly (65%) takes place within PCT (i.e., nearly all of the essential nutrients, 70-80% of electrolytes and water). PCT also helps in the absorption of HCO– from the filtrate.
Selective secretion of hydrogen ions, ammonia and potassium ions takes place here to maintain the pH and ionic balance of the body fluids. The filtrate is considered isotonic to blood plasma.
ii. Henle’s Loop
Reabsorption in Henle’s loop is minimum, besides it, this plays an important role in maintaining the high osmolarity of medullary interstitial fluid. Two portions of Henle’s loop, play different role in osmoregulation such as
a. Descending Limb of Loop of Menu?
Water is reabsorbed here due to increasing osmolarity of interstitial fluid but, sodium and other electrolytes are not reabsorbed here. This concentrates the filtrate as it moves down.
b. Ascending Limb of Loop of Menu?
This segment is impermeable to water but permeable to K+,Cl– and Na+ and partially permeable to urea. Thus, in the thick ascending limb of the loop of Henle Na+, K+, Mg2+ and Cl– are reabsorbed.
Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.
iii. Distal Convoluted Tubule (DCT)
Active reabsorption of sodium ions from the filtrate (under the influence of aldosterone) takes place. Water is also reabsorbed here under the influence of Antidiuretic Hormone (ADH).
With associated secretion of potassium (K+), hydrogen (H+) ions, NH–, some Cl– (chloride) ions and HCO– are also reabsorbed here. It is necessary to maintain the pH and sodium-potassium balance in blood. This makes the filtrate isotonic to blood plasma.
This duct extends from the cortex of the kidney to the inner parts of the medulla and is highly permeable to water. Thus, a considerable amount of water is reabsorbed here under the influence of ADH to produce concentrated filtrate. Sodium is also reabsorbed here under the influence of aldosterone.
CT (Collecting Tubule) allows passage of small amounts of urea into the medullary interstitium to maintain the osmolarity. It also plays an important role in the maintenance of pH and ionic balance of blood by the selective secretion of H+ and K+ ions.
Therefore, the filtrate is now called urine. Thus, urine is isotonic to medullary fluid and hypertonic to blood.
Concentrations of important ions and other substances in the blood are controlled by regulating water levels.
Topic 2 Excretion : Various Controlling Mechanisms and Disorders
Counter Current Mechanism
Kidney of higher vertebrates (such as mammals, birds including man) has the ability of absorbing more and more water from tubular filtrate (in the Henle’s loop region) to make the urine more concentrated.
This can be achieved by a special mechanism known as counter current mechanism and also known as urine concentration mechanism.
(i) Henles loop and vasa recta (capillary loop) play an important role in this mechanism. The flow of filtrate in the limbs of Henle’s loop is in opposite directions and thus, forms a counter current. The flow of blood with in the two limbs of vasa recta also occur in the counter current pattern.
(ii) The osmolarity (i.e., number of Osmols of solute per litre) of renal cortical interstitium is the same (300 m Osmol/ L) as in other tissues, but that of the interstitium of renal medulla is hypertonic with a gradient of hyperosmolarity from renal cortex to the tips of medullary papillae.
The hyperosmolarity of medullary interstitium near the tips of the papillae is as high as 1200-1450 m Osmol/L.
The gradient of increasing hyperosmolarity of medullary interstitium is maintained by a counter current mechanism and the proximity between the Henle’s loop and vasa recta.
This gradient is mainly caused by NaCl and urea. The transport of these substances is facilitated by the special arrangement of Henle’s loop and vasa recta.
There are two aspect of this mechanism
(i) Counter current multiplication (by the Henle’s loop).
(ii) Counter current exchange (by the vasa recta).
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 medullary interstitium by the ascending part of vasa recta. But, contrarily, the water diffuses into the blood of ascending limb of vasa recta and is carried away into the general.blood circulation.
Permeability to urea is found only in the deeper parts of thin ascending limb of Henle’s loops and collecting ducts.
Urea diffuses out of the collecting ducts and enters into the thin ascending limb. A certain amount of urea recycled in this way is trapped in medullary interstitium by the collecting tubule. Thus, collecting tubule also play a minor role in the process (as shown in the figure above).
The counter current mechanism helps in the maintenance of a concentration gradient in the medullary interstitium.
Presence of such gradient helps in an easy passage of water from the collecting tubule resulting in the formation of concentrated urine (filtrate), i.e., nearly four times concentrated than the initial filtrate formed.
Regulation of Kidney Functions
To maintain homeostasis, the regulation of water and solute contents of the body fluids is performed by the kidneys. The vertebrate kidney is very flexible in its functioning. It excretes larger quantities of dilute urine when water is abundant in the body tissues and small amounts of concentrated urine when there is shortage of water.
Hormones acts as an important signalling molecules in controlling the regulatory processes in the kidneys. The functioning of the kidneys is efficiency monitored and regulated by hormonal feedback mechanisms involving hypothalamus, JGA (Juxtaglomerular Apparatus) and to a certain extent, the heart.
Regulation of the functioning of kidneys can be discussed under the following headings
Regulation by the Hypothalamus
Excessive loss of fluid from the body activates osmoreceptors, which stimulate the hypothalamus to release ADH or vasopressin form the neurohypophysis. ADH facilitates water reabsorption from posterior parts of tubule. An increase in body fluid volume can switch off the osmoreceptors and suppresses the ADH release to complete the feed back. ADH also causes constrictory effects on blood vessels.
This causes an increase in blood pressure, which in turn increase the glomerular blood flow and thereby the GFR (Glomerular Filtration Rate).
Regulation by the Juxtaglomerular Apparatus (JGA)
As blood pressure/glomerular blood flow /GFR decreases, the cells of the JGA release the enzyme renin.
Renin converts angiotensinogen in blood to Angiotensin I and Angiotensin II (active form). This mechanism is generally known as the Renin-angiotensin mechanism.
Angiotensin has following effects
(a) Raises blood pressure by constricting blood vessels (being a powerful vasaconstrictor) and thereby, GFR.
(b) Activates the adrenal cortex to release aldosterone.
(c) Aldosterone causes reabsorption of Na+ and water from the distal parts of the tubule. This also leads
to an increase in blood pressure and GFR.
Regulation by the Heart
Atrial Natriuretic Factor (ANF) produced by the atria of heart can cause vasodilation (dilation of blood vessels) and thereby, decrease the blood pressure.
ANF inhibits NaCl reabsorption and concentration of urine.
Urine is produced and drained continuously by the nephron into the renal pelvis from here, it is carried down to the ureters and then into the urinary bladder.
The bladder serves to store the urine temporarily till a voluntary signal is given by the Central Nervous System (CNS). As urine collects, the muscular walls of the bladder distend to accommodate it. .
The stretch receptors on the walls of the bladder set up reflexes (send signals to the (CNS) by stimulating the sensory nerve ending in the bladder). It causes an urge to pass out urine.
The act of expulsion of urine involves the coordinated contraction (as CNS passes on motor messages) of the smooth muscle of the bladder wall and simultaneous relaxation of the internal and external urethral sphincters. The process of release of urine is called micturition and the neural mechanism causing it is called the micturition reflex.
Alcohol inhibits the release of ADH and caffeine interferes with ADH action and sodium reabsorption. Thus, both of these artificially dilute the urine and are called diuretics. Urination is a reflex response in babies, but is controlled consciously in older children and adults.
An adult man normally passes about 1-1.5 L of urine per day.
Composition Urine normally contains, water 95%, salts 2%, urea 2.6%, uric acid 0.3%, traces of creatinine, creatine, ammonia, etc.
Colour Pale yellow, due to pigment urochrome produced by the breakdown of haemoglobin.
pH Ranges from 4.5-8.2, average pH 6.0 (i.e., slightly acidic).
Odour Unpleasant, if allowed to stand imparts strong smell like, ammonia.
Least concentration of urea is found in renal vein because urea is excreted through urine formed in kidney. On an average, 25-30 g of urea is excreted out per day. Highest concentration of urine is found in hepatic vein because urea is synthesised in liver.
Analysis of urine helps in clinical diagnosis of many metabolic disorders as well as malfunctioning of the kidney.
For example, presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine are indicative of diabetes mellitus and presence of protein, blood and pus in the urine is called proteinuria, haematuria and pyuria respectively.
Role of Other Organs in Excretion
Other than the kidneys, there are some accessory excretory organs also that help in the elimination of excretory wastes.
These are described as follows
Carbon dioxide and water are the waste products formed in respiration. Lungs remove the CO2 and some water as vapour in the expired air. About 18 L of CO2 per hour and 400 mL of water per day are eliminated by human lungs.
It changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile pigments, i.e., bilirubin and biliverdin. These pigments passes into the alimentary canal with the bile for elimination in the faeces. The liver also excretes cholesterol, steroid hormones, certain vitamins and drugs via bile.
Liver deaminates the excess and unwanted amino acids, producing ammonia, which is quickly combined with CO2 to form urea in urea cycle or Ornithine cycle, which is further removed by the kidneys.
The sweat and sebaceous glands in the skin can eliminate certain substances through their secretions.
(i) Sweat Glands The secretion of sweat glands (sweat) is an aqueous fluid containing NaCl, lactic acid, small amounts of urea, amino acids and glucose. Control of sweat lost is an example of homeostasis control, for regulating the body temperature (i.e., to facilitate a cooling effect on the body surface).
(ii) Sebaceous Glands Sebum from sebaceous glands eliminates sterols, fatty acids, waxes and hydrocarbons. This secretion is mainly meant for protective oily covering of the skin.
Epithelial cells of colon excrete excess salts of calcium, magnesium and iron along with faeces.
5. Salivary Glands
Heavy metals and drugs are excreted in the saliva.
Important Metabolic Wastes and Substances Excreted from the Body
Disorders of the Excretory System
Malfunctioning of kidneys can lead to several disorders of the excretory system.
Some of these are as follows
(i) Uremia It is the presence of an excessive amount of urea in the blood. Urea is highly harmful as it poisons the cells at high concentration and may lead to kidney failure.
(ii) Kidney Failure (renal failure) Partial or total inability of kidneys to carry on excretory and salt-water regulatory functions is called renal or kidney failure.
(iii) Renal Calculi It is the formation of stone or insoluble mass of crystallised salts (calcium, magnesium, phosphates and oxalates etc.), formed within the kidney.
(iv) Glomerulonephritis It is the inflammation of glomeruli of kidney.
Artificial kidney (haemodialyser) is a machine that is used to filter the blood (to remove urea and other nitrogenous wastes) of a person, whose kidneys are damaged.
The process is called haemodialysis.
The outline details of apparatus and the process are as follow
(i) It works on the principle of dialysis (i.e., diffusion of small solute molecules through a semipermeable membrane (cellophane).
(ii) Blood of the patient is pumped from one of the arteries into the dialysing unit (haemodialyser) after cooling it to 0°C and mixing with an anticoagulant (heparin).
(iii) Haemodialyser is a cellophane tube suspended in a dialysing fluid (salt-water solution) of the same composition as that of plasma except the nitrogenous wastes (urea).
(iv) Pores of the cellophane tube allow the passage of molecules based on concentration gradient. Nitrogenous wastes like urea, uric acid, creatinine,excess salts and excess H+ ions easily get diffuse from the blood into the surrounding solution. Thus, the blood is cleared of nitrogenous waste products without loosing plasma proteins.
(v) The blood thus, purified, is warmed to body temperature, checked to ensure that it is isotopic to the patients blood. Now, the blood is mixed with an anti-heparin to restore its normal clotting power and then pumped back to the body of patient through a vein, usually the radial vein.
Kidney (Rena!) Transplantation
Grafting a kidney from a compatible donor to restore kidney functions in a recipient suffering from kidney failure is called renal or kidney transplantation. It is an ultimate method in the correction of acute renal failures.
A living donor can be used in a kidney transplant. It may be an identical twin, a sibling or a close relative to minimize the chances of rejection by the immune system of the host. To prevent the rejection of transplanted kidney, special drugs are also used, which suppress the recipients immune system.
CBSE Class 11 Biology Chapter-19 Important Questions
1 Marks Questions
1.In which part of nephron filtration takes place?
2.What difference is observed in the ascending and descending limb of Henle’s loop witch reference to permeability of water?
Ans. Ascending limp of Henle’s loop is impermeable to water. Descending limb of Henle’s loop is permeable to water.
3.What is the PH of urine.
Ans. It is slightly acidic, PH – 6.0
4.Name the three kinds of nitrogen excretion.
Ans.(a) Ammonotelism (b) Ureotelism (c) Uricotelism
5.What are podocytes?
Ans. Epithelial cells of Bowman’s capsule are called podocytes.
6.Besides water, name any two constituents of human sweat.
Ans. Sodium chloride and urea.
7.What happens is glomerulonephritis?
Ans. Inflammation of glomeruli of kidney.
8.Name the excretory organ of cockroach.
Ans. Malphigian tubules.
9.Name the hormone which controls the concentration of sodium in the body.
Ans. Aldosterene is a hormone which controls concentration of sodium in the body.
10.Which gland secrete sebum?
Ans. The sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum,
11.One part of loop of Henle is impermeable to water, Name it.
Ans. Ascending limb
12.Besides water, name any two constituents of human sweat.
Ans. Sodium chloride, Iactic acid, glucose (any two).
13.Explian the function of vasa rectae.
Ans. It helps to retain reabsorbed ions and urea in the interstitial fluid of the medulla, to maintain its high osmotic pressure.
14.Name two types of nephrons found in human kidney.
Ans. (i) Juxta medullary nephron (ii) Cortical nephron.
15.Define GPR (Glomerular Filtration Rate)
Ans. The amount of filtrate formed by the kidney per minute.
16.The mechanism of is also known as counter current mechanism justify the statement.
Ans. (in the ascending limb) the out flow runs parallel to and in the opposite direction of the inflow in the descending limb.
17.What Is maturation?
Ans. the act of passing out urine from urinary bladder.
18.Write the function of enzyme ‘renin’ produced by kidney.
Ans. Renin is used to convert angiotensinogen to angiotensin.
19.Name the excretory product of (i) reptiles (ii) Prawns.
Ans.(i) Uric acid (ii) Ammonia.
2 Marks Questions
1.Differentiate between Rennin and Renin?
|1.||Secreted from the peptic cell or gastric glands in stomach.||Secreted from the juxtaglomerular cells of afferent renal artery in the renal cortex of kidney.|
|2.||The rennin is proteolysis enzyme.||Renin is a hormone but it acts as enzyme also.|
|3.||Helpful in the digestion of milk of protein.||Converts angiotensinogen into angiotensin – II|
|4.||Released in inactive form.||Released in active form.|
2.What are the two intrinsic mechanisms that provide auto regulation of glomerular filtrate? Explain any one of these.
Ans. Two intrinsic mechanisms that provide autoregulation, Myogenic mechanism and Juxtaglomerular apparatus (JGA) JGA – A special cellular apparatus is located in kidney where DCT passes close to Bowman’s capsule between afferent and efferent arterioles. The JGA cells secrete rennin that modulate blood pressure there by regulating renal flow and GFR.
3.How is the permeability of the distal convoluted tubule and the collecting tubule controlled for regulating the water content inside the body?
Ans. 1) When the water content inside the body is low, the osmorecepters stimulates theadenohypophysis to releases vasopressin / ADH.
2) Vasopressin / ADH render the DCT and collecting tubule permeable to water. So, water is reabsorbed.
3) When the water content in the body is normal, there is no release of ADH.
4) The tubule is impermeable to water and water is eliminated in the urine.
4.Kidneys do not play a major role in excretion in ammonotelic animals Justify.
Ans. Kidneys do not play any significant role in elimination of ammonia –
(i) Ammonia is readily soluble in water and diffuses across the body surfaces.
(ii) Ammonia is excreted as ammonium ions through gill surface.
5.Define glomerular filtration rate. What is its value in a healthy human?
Ans. The amount of filtrate formed by kidneys per minute is known as Glomerular filtration rate. (GFR). In a healthy individual, GFR is approx. 125ml / minute i.e. 180 liters per day.
6.What is the significance of frog’s tadpole being ammonetelic and the adult frog being ureotelic?
Ans. Tadpole is ammonotelic, because excretion of ammonia requires a large volume of water, which the tadpole has in its surrounding. An adult frog is ureotelic because elimination of urea requires a moderate volume of water that is much less compared to ammonia.
7.Describe the blood vessels called vasa rectae found in relation to uriniferous tubules. What is their function?
Ans. Vasa recta are u–shaped, thin walled capillaries that arise from the efferent arteriole; they run parallel to Henle’s loop.
They retain the reabsorbed ions in the medullary tissue fluid and maintain its high osmolarity.
8.What is chief nitrogenaus waste product in birds? Give two advantages of this mode of excretion.
Ans. Chief mitrogenous waste product of bird is uric acid.
It is advantageous them as –
(i) Uric acid requires very little or no water for its elimination.
(ii) Uric acid is far less toxic and can be eliminated slowly.
9.Terrestrial animals are generally either ureotelic ar uric telic, Not ammonotelic. Why?
Ans. Ammonia is highly toxic and it has to eliminate as rapidly as it is formed.
– Land animals have an integument that is impervious to gas exchange.
– It requires a large volume of water needed for elimination
– They do not access to such a large volume of water needed for elimination of ammonia.
– So they are ureotelic or uricotelic.
10. Name two metabolic disorders which can be diagnosed by the analysis of urine.
Ans. Glycosuria, Ketonuria.
3 Marks Questions
1.Person suffering from very low blood pressure pass no urine why? What suggestion would you offer for the removal of waste products from the blood in such a situation.
Ans. It is because, the blood to pass through the glomerulus of the nephron must have required amount of pressure in it. If the pressure is not sufficient it will not flow through glomerulus and filtration would not the take place, hence no urine would be formed. This is quite harmful to the person as waste products go on accumulating in the body.
To avoid this, a person should be advised take sufficient amount of water and medicine to keep the blood pressure at optimum level.
2.Explain briefly how micturation is a reflex process; but is also under some voluntary control.
Ans. 1) Micturation is act of voiding urine
2)It accomplished by the simultaneous contraction of the smooth muscles of urinary bladder wall and the relaxation of the skeletal muscle sphincters around the opening of the bladder.
3)As the bladder wall becomes stretched due to accumulation of urine, the stretch receptors in the wall of the bladder generate nerve impulse that are carried to sense neurons to the spinal cord and brain produce the sensation of fullness.
4)But the sphincter muscles can also be relaxed voluntarily and there by the smooth muscles of the bladder are allowed to contract under autonomic control and the content of the bladder can be emptied.
3.Describe urea cycle.
Ans. It is called kreb’s Ornitnine cycle.
4. What is a dialysis machine? When is it needed?
Ans. Dialysis machine is also known as artificial kidney. It filters blood when the kidneys fail. In dialysis small solute moleclues diffuse through a semi permeable membrane as a substitute for glomerulus. It has a cellophane membrane where the blood of a patient is made to flow on one side of the membrane and the surrounding fluid on other side. The wastes from the blood move into the surrounding fluid though cellophane membrane. It is needed when kidney fails to work and urine is not formed.
5.Suppose the kidneys of a person are damaged, can you predict what is going to happen to him?
Ans. The kidneys are considered as master chemists of the body. If they are damaged, it would disturb the normal functioning of the life processes. Due to the effect of toxins produced by some bacteria the fillers of tiny uriniferous tubules are damaged. They become perforated with larger holes and allow blood cells, proteins also to pass through them along with the urea and water during filtration of blood in formation of urine. Thus urine contains the blood proteins etc. It is a serious disease.
6. How does liver both as a digestive as well as an excretory organ?
Ans. Liver serve as digestive organ – It secretes bile; bile helps in the digestion of fats.
Liver serve as excretory organ – It secretes following waste products in the bile; bilirubin, biliverdin (products of degradation of haemoglobin), cholesterol, inactivated steroid hormones, drugs, etc in the bile; these wastes are eliminated along with the digestive wastes or faecal matter.
7. Give three point of difference between rennin and Renin.
(i)It is a proteolytic enzyme
(ii) It helps in the digestion of milk proten casein
(iii) It is secreted as an inactive form prorennin which is activated to rennin by HCI.
(iv) Its secretion is stimulated by food.
(i)It is a hormone that acts as an enzyme.
(ii) It converts the protein angiotensinogen into angiotensin
(iii) It is secreted as rennin
(iv) It secretion is stimulated by a reduction of Na+level in tissue flunid. (—- any three)
5 Marks Questions
1. Describe briefly the structure and function of renal corpuscle.
Ans. Renal Corpuscle – It is the main excretory organ in the kidney. Nephrons are the functional units of kidney of renal corpuscle. There are about 102 million nephrons in each kidney in man.
Structure of nephron – The nephron is a thin, long, twisted tubular structure. The tubule of each nephron starts as a up – shaped called Bowman’s capsule. There is a globular tuft of capillaries in the hollow of the cup. The Bowman’s capsule and the glomerulus together form a globular body called the renal corpuscle. Blood enters the glomerular capillaries through an afferent arteriole and leaves the glomerulus through as efferent arteriole.
Urine is formed by the filtration of a protein free fluid from the glomerulus into lumen of the Bowman’s capsule.
There are 3 parts of a nephron –
(i) proximal nephron
(ii) hoop of Henle and
(iii) distal nephron.
A long highly coiled and tubule trusted starts form the neck of the Bowman’s capsule. It is called the PCT (Proximal Convoluted tubule). It continues into a thin–walled straight tubule, then loops like segment of the tubule is called the Henle’s loop. It has thin descending limb and thick ascending limb. The Henle’s loop continuous into another segment of coiled and twisted tubule called DCT (Distal convoluted tubule). The terminal part of DCT is a straight short tubule called the collecting duct. The collecting duct runs down to the medulla again conducting the collected urine towards the medulla.
The collecting ducts unite with each other in the medulla to form the larger ducts called Ducts of Bellini. These ducts rue through the renal pyramids and open into renal pelvis.
The efferent arteriole gives a capillary network around the tubule in the cortex. It also fives rise to some parallel wise, thin walled straight capillaries called vasa rectae. They help to maintain reabsorbed ions and urea in the intestinal fluid and maintain osmotic pressure in the kidney.
Functions – Various part of nephron perform deferent function but the main function is liberation of metabolic waste from the body and maintain osmotic pressure of fluid in the body.
2. Describe the mechanism of urine formation.
Ans. Urine formation involves three main processes –
(i)Glomerular filtration – A protein – free fluid is filtered from blood of glomerular capillaries into the lumen of Bowman’s capsule.
The filtration occurs through three layers,which form the filtration membrane; they are :
(i) Endothelium of glomerular capillaries
(ii) Epithelium of Bowman’s capsule.
(iii) Basement membrane between the two layers.
The epithelial cells or podocytes of the Bowman’s capsule are arranged in an intricate manner, to leave some filtration slits.
The blood is filtered so finely that the composition of filtrate is very similar to plasma except for the plasma proteins.
The glomerular filtrate rate is about (25ml / min)
Nearly 90% of the filtrate is reabsorbed in the renal tubule of the epithelial cells of the lining of renal tubule.
Certain substances like glucose, amino acids, Na+ ions, K+ ions and Ca2+ ions are reabsorbed actively.
Water is reabsorbed passively by osmosis.
Certain other substance like Cl– ions are absorbed passively.
(iii)Tubular secretion –
It is the process by which certain substances / ions like K+ and ammonia are directly secreted into the lumen of the nephron.
The step is important in urine formation, as it helps to maintain the ionic balance and PH of the body fluids.
3. Describe the renal excretory system of man.
Ans. The urinary system consist of following organs.
(a) A pair of kidneys
(b) A pair of ureters
(c) Urinary bladder
(d) Urethra kidney – The kidneys are located in the abdomen, one on each side of the vertebral column just below the diaphragm, which remains protected by last two pairs of ribs.. The left kidney is usually placed higher than right one. Each kidney is 10cm in length 5 cm in breadth and 4cm in thickness. Each kidney is somewhat bean shaped with concavity along the inner border. Blood vessels, nerves, lymph ducts and ureters enter the kidney at this point. In the gross anatomy of kidney, two regions can be clearly marked out. There are outer cortex and inner medulla.
Internal structure of kidney – Each kidney composed of several tiny units called nephrons or uriniferous tubule, all similar in structure and function. Each nephron is made up of vascular component, the glomerulus and tubular component, and surrounded by a network of capillaries. The tubule is composed of single layer of epithelial cells which differ in structure and function in different parts of the tubule. The tubule originates as a blind sac, which is known as Bowman’s capsule which is lined by a single layer of thin epithelial cells – Bowman’s capsule is ultimately associated with vascular glomerulus which protrudes into Bowman’s capsule and is completely covered by the linning of the capsule. The glomerulus is formed by afferent and efferent arteries. The afferent arterioles bring blood to the tubular and efferent arterioles takes blood away from the tubule. Due to this, the blood in the glomerulus is separated from the space within the capsule only by (a) a thin layer of a tissue composed of the single – celled capillary lining (b) a layer material called basement membrane and (c) the single celled lining of Bowman’s capsule. This extremely thin barrier permits the filtration of the fluid from the capillaries into Bowman’s capsule.
The glomerular capillaries combine together to form efferent arterioles which further divide into many capillaries distributed all over the surface of the tubule. These capillaries are termed as particular capillaries. These capillaries join together to form the venous channels which take blood away from the kidney. The tubule is divided into three pates – Proximal convoluted part in which Bowman’s capsule opens. The next part is Henle’s loop and last part is distal convoluted part which finally runs as a collecting duct.
Ureters – These are two tubes or about 30 cm long – one coming out from each kidney. They run downwards and open into urinary bladder.
Urinary bladder- It is a bag like structure where urine is stared. The bladder has three openings two of the ureters and one to urethra.
Urethra – the urethra is the passage through which urine is passed out.
NCERT TEXTBOOK QUESTIONS FROM SOLVED
1.Define Glomerular Filtration Rate (GFR).
Solution. The amount of filtrate formed by the kidneys per minute is called glomerular filtration rate (GFR). It is approximately 125 mL/min. in a healthy person.
2.Explain the autoregulatory mechanism of GFR.
Solution. The kidneys have built-in mechanisms for the regulation of glomerular filtration rate. One such efficient mechanism is carried out by juxta glomerular apparatus (JGA). JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. A fall in GFR can activate the JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR back to normal.
3.Indicate whether the following statements are true or false.
(a) Micturition is carried out by a reflex.
(b) ADH helps in water elimination, making the urine hypotonic.
(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.
(d) Henle’s loop plays an important role in concentrating the urine.
(e) Glucose is actively reabsorbed in the proximal convoluted tubule.
Solution.(a) True (b) False (c) True (d) True (e) True
4.Give a brief account of the counter current mechanism.
Solution. The kidneys have a special mechanism for concentrating the urine, it is called counter current mechanism. The mechanism is said to be a counter current mechanism because the out flow (in the ascending limb) of Henle’s loop runs parallel to and in the opposite direction of the inflow (in the descending limb) and vasa recta. As the mechanism begins to function, the ascending limb of loop of Henle actively transports chloride and sodium ions out into the vasa recta from where it is secreted into the interstitial fluid. As a result the interstitial fluid around the loop of Henle contains large quantities of NaCl. The filtrate passes from the ascending limb of loop of Henle and enters a collecting duct. The collecting duct passes adjacent to the loop of Henle where the interstitial fluid contains large amounts of NaCl. The high osmotic pressure created by NaCl causes water to diffuse out of the collecting duct in the interstitial fluid and eventually to the blood of vasa recta. The filtrate becomes greatly concentrated and is now called urine. A similar counter current mechanism, operates between the interstitial fluid and blood passing through the vasa recta. As the blood capillary runs along the ascending limb of loop of Henle, NaCl diffuses out of the blood. The direction is reversed as the blood capillary passes along the descending limb of Henle. The blood flows in the vasa recta around the loop of Henle from ascending to the descending side while the fluid passing through the loop of Henle goes in the opposite direction. The arrangement helps to maintain the concentration gradient of NaCl.
The ‘overall function of counter current mechanism is to concentrate sodium chloride in the interstitial fluid and thereby cause water to diffuse out of the collecting ducts and concentrate the urine.
5.Describe the role of liver, lungs and skin in excretion.
Solution. Other than the kidneys, lungs, liver and skin also help in the elimination of excretory wastes. Lungs remove large amounts of C02 (18 litres/day) and also significant quantities of water every day. Liver secretes bile which contains substances like bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs. Most of these substances ultimately pass out along with digestive wastes. The sweat and sebaceous glands in the skin can eliminate certain substances through their secretions. Sweat produced by the sweat glands is a watery fluid containing NaCl, small amounts of urea, lactic acid etc. Sebaceous glands eliminate certain substances like sterols, hydrocarbons and waxes through sebum.
Solution. The process of passing out urine from the urinary bladder is called micturition. Urine formed by the nephrons is ultimately carried to the urinary bladder where it is stored. This causes stretching of the wall of bladder that leads to the stimulation of stretch receptors on the walls of the bladder. This sends signal to the CNS. The CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.
7.Match the items of column I with those of column II.
Column I Column II
(a) Ammonotelism (i)Birds
(b) Bowman’s capsule (ii)Water reabsorption
(c) Micturition (iii)Bony fish
(d) Uricotelism (iv)Urinary bladder
(e) ADH (v)Renal tubule
Solution. (a) – (iii), (b) – (v), (c) – (iv), (d) – (i), (e) – (ii)
8.What is meant by the term osmoregulation?
Solution. The regulation of water and solute contents of the body fluids by the kidney is called osmoregualtion.
9.Terrestrialanimalsaregenerallyeitherureotelic or uricotelic, not ammonotelic, why?
Solution. Ammonotelic animals are aquatic animals that excrete ammonia which is highly soluble in water, thus large amount of water is also excreted. Terrestrial animals cannot afford to lose such large quantities of water from their bodies as they live in environment having water scarcity. They, therefore, excrete either urea (ureotelic) or uric acid (uricotelic) as these are less soluble in water.
10. What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Solution. Juxta glomerular apparatus (JGA) is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. The JGA plays a complex regulatory role. A fall in glomerular blood flow/ glomerular blood pressure/GFR can activate the JG cells to release renin which converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby GFR. Angiotensin II also activates the adrenal cortex to release aldosterone. Aldosterone causes reabsorption of Na+ and water from the distal parts of the tubule. This also leads to an increase in blood pressure and GFR.
11 .Name the following.
(a) A chordate animal having flame cells as excretory structures.
(b) Cortical portions projecting between the medullary pyramids in the human kidney.
(c) A loop of capillary running parallel to the Henle’s loop.
Solution. (a) Cephalochordate – Amphioxus
(b) Columns of Bertini
(c) Vasa recta
12.Fill in the gaps.
(a) Ascending limb of Henle’s loop is________to water whereas the descending limb is________to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone________
(c) Dialysis fluid contains all the constituents as in plasma except________
(d) A healthy adult human excretes (on an average)________gm of urea/day.
(a) Ascending limb of Henle’s loop is impermeable to water whereas the descending limb is permeable to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone ADH.
(c) Dialysis fluid contains all the constituents as in plasma except nitrogenous wastes.
(d) A healthy adult human excretes (on an average) 25 – 30 gm of urea/day.