19 Excretory Products and Their Elimination - SelfStudys

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y The process of removing waste products produced in the cells of living organism is called excretion. It is an essential process in all forms of the life.

y It involves elimination of metabolic wastes like ammonia, urea, uric acid etc. from the tissues. It is of the following types:

(i) Ammonotelism ² The process of excretion of ammonia is called

ammonotelism. ² Ammonia is highly toxic. So, needs more water for

getting excreted. ² The animals which excrete ammonia are called

ammonotelic animals. ² E.g. Aquatic invertebrates, bony fishes, aquatic

amphibians, tadpoles, aquatic insects etc.

(ii) Ureotelism ² The process of excretion of urea is called ureotelism. ² In liver, ammonia is converted into less toxic urea (for

conservation of water). This is called Ornithine cycle. ² Ammonia in liver → Urea ² Urea is less toxic. So, requires moderate quantity of

water for excretion. ² The animals which excrete urea are called ureotelic

animals. ² E.g. Terrestrial and semi-aquatic amphibians (frogs,

toads etc.), cartilaginous fishes, aquatic or semi-aquatic reptiles (alligators, turtles) etc.

(iii) Uricotelism ² The process of excretion of uric acid is called

uricotelism. ² Uric acid is least toxic. It is eliminated with the least

loss of water, as pellets or paste.

² It is insoluble in water. So water is not required for excretion.

² The animals which excrete urea are called uricotelic animals.

E.g. Birds, terrestrial reptiles, insects, land snails and some land crustaceans.

(iv) Aminotelism ² The process of excretion of excess amino acid is called

aminotelism. ² The animals which excrete amino acids are called

aminotelic animals. E.g. Some molluscs (Unio, Limnaea) and some

echinoderms (Asterias).

(v) Guanotelism ² The process of excreting guanine is called

guanotelism. ² The animals, which excrete guanine, are called

guanotelic animals. E.g. Spiders

SOME EXCRETORY ORGANS IN ANIMALS

Excretory organ Animals

Protonephridia(flame cells)

Flatworms, rotifers, someAnnelids and cephalochordate.

Nephridia Annelids

Malpighian tubules Insects

Antennary or green glands Crustaceans

Kidneys Higher animals

Chapter

19 Excretory Products and Their Elimination

Excretory Products and Their Elimination 415

HUMAN EXCRETORY SYSTEMThe parts involved in the process of excretion are called excretory system.

It includes a pair of kidneys, one pair of ureters, a urinary bladder and a urethra.

Posterior vena cavaDorsal aorta

Urethra

Urinary bladder

Ureter

Renal artery

Renal vein

Hilus

Left kidney

Fig. Urinary system

Structure of Kindney

y Kidneys are reddish brown, bean-shaped structures situated between the levels of last thoracic and 3rd lumbar vertebra.

y Each kidney is about 10-12 cm in length, 5-7 cm in width, and 2-3 cm in thickness.

y In adult male, the average weight of kidney is 150 gms, and in the adult female is about 135 gms.

y Each kidney is enclosed in a tough, three-layered fibrous capsule.

y On the concave side of kidney, there is an opening called hilum or hilus through which blood vessels, nerves, lymphatic ducts and ureter enter the kidney.

y Hilum leads to funnel shaped cavity called renal pelvis with projections called calyces.

y Each kidney has an outer dark region called cortex and inner lighter region called medulla.

y The medulla is divided into a number of conical projections called renal pyramids (medullary pyramids) projecting into the minor calyces. Minor calyces lead into major calyces.

y The major calyces open into a funnel shaped structure called renal pelvis which in turn leads into the ureter.

y Between the medullary pyramids, the substance of cortex extends into the medulla as renal columns called Columns of Bertini.

y Each kidney has nearly one million tubular nephrons.

Renalsinus Fibrous capsule

(covering kidney)

Fibrous capsule(covering renal sinus)

Renal cortex

Renal medulla

Renal pyramid

Renal column

Kidney lobe

Hilum

Fig. Longitudinal section of Kidney

Nephron y Nephrons are the structural and functional units of kidney. y Each kidney contains about one million of nephrons.

Structure of Nephron y Each nephron has two parts: Malpighian corpuscles and

renal tubule. 1. Malpighian corpuscle (Renal corpuscle): It comprises

Glomerulus and Bowman’s capsule. Malpighian body= Glomerulus + Bowman’s capsule (i) Glomerulus: It is a tuft of capillaries formed by afferent

arteriole (a fine branch of renal artery). Blood from the glomerulus is carried away by an efferent arteriole. Glomerular filtration takes place in the glomerulus.

(ii) Bowman’s capsule (Glomerular capsule): It is a double layered cup-shaped structure. Its lumen is continuous with the narrow lumen of the renal tubule. The two layers of Bowman’s capsule are outer parietal layer and inner visceral layer.

2. Renal tubule: It begins with a double walled cup-like Bowman’s capsule, which encloses the glomerulus.

² The tubule continues with proximal convoluted tubule (PCT), Henle’s loop and distal convoluted tubule (DCT).

(a) Proximal convoluted tubules (PCT): It is present in cortex region of kidney and is convoluted. It is lined by cuboidal epithelial cells bearing a brush border of microvilli.

(b) Henle’s loop: It is hairpin-shaped and runs straight in the renal medulla. It has descending and ascending limbs. The upper part of the descending limb is the thick segment that has the same diameter as that of the PCT. The distal part of the descending limb is the thin segment. The ascending limb also has thin segment and a thick segment. ² Loop of Henle is long in mammals and birds which

secrete hypertonic urine but is short or absent in other vertebrates like reptiles.

(c) Distal convoluted tubules (DCT): It is convoluted and is again present in cortex. It is lined by cuboidal epithelial

BIOLOGY416

cells with few microvilli. Many DCTs of many nephrons open into collecting duct, lined by columnar epithelium.

(d) Collecting duct: Collecting duct extends from cortex to inner parts of medulla. They converge and open into the renal pelvis through medullary pyramids in the calyces. ² The collecting ducts unit to form still larger ducts called

ducts of Bellini. y Malpighian body (Renal corpuscle), PCT and DCT are

situated in renal cortex. Loop of Henle dips into medulla. y The efferent arteriole emerging from glomerulus forms a fine

capillary network (peritubular capillaries) around the renal tubule. A minute vessel of this network runs parallel to the Henle’s loop forming a ‘U’ shaped vasa recta.

Types of NephronsNephrons are of two types: (i) Cortical nephrons: They form about 85% of total nephrons.

They mainly lie in the renal cortex. Their glomeruli are found in the outer cortex. In this, the Henle’s loop is short and extends only very little into the medulla.

Vasa recta is absent or highly reduced. (ii) Juxtamedullary nephrons: They form about 15% of total

nephrons. Their glomeruli are found in the inner margin of the cortex, near its junction with the medulla. In this, Henle’s loop is long and runs deep into medulla. Vasa recta are present.

Both arteriole and distal tubule has specialized cells: ² Juxtaglomerular cells (JG) – These are smooth muscle

cells surrounding the afferent and efferent artioles. They are composed of granules containing renin. These cells act as mechanoreceptors that sense the blood pressure in the arteriole.

² Macula densa – These are distal tubule cells that act as chemoreceptors or osmoreceptors that respond to changes in solute concentration of filtrate in distal tubule.

Fig. Juxtaglomerular and cortical nephrons

Functions of Excretory System

y Filters waste products from blood - The excretory system eliminates in the urine different waste products such as ammonia and urea (both formed when amino acids are broken down), and uric acid (formed when nucleic acids are broken down).

y Regulates ion levels in the plasma - The excretory system also regulates ion levels in the plasma by regulating the amount of sodium, potassium, chloride and other ions lost in the urine.

y Regulates blood pH - The excretory system regulates blood pH by regulating the number of H+ and bicarbonate ions (HCO3

2-) lost in the urine. y Conserves valuable nutrients - At the same time, the

excretory system makes sure that glucose, amino acids and other valuable nutrients are not lost from the urine.

y Regulates blood volume - The excretory system regulates blood volume by:

y Releasing renin, a hormone that after a series of reactions eventually restricts salt and water loss at the kidneys.

y Adjusting the volume of water lost in the urine y Regulates RBC production - If oxygen levels in the blood

are low, the kidneys release erythropoietin, a hormone that stimulates the hemocytoblasts (stem cells in the bone marrow) to increase red blood cell formation. Having more RBCs allows the blood to transport more oxygen.

y Stores urine - The bladder stores the urine until it is convenient to excrete it.

y Excretes urine - The urethra transports urine from the urinary bladder to the outside of the body.

Urine Formation (Physiology of Kidney)Urine formation includes three processes: Glomerular filtration, reabsorption and secretion.

(i) Glomerular filtration (ultra filtration) y Ultrafiltration is an entirely passive process. y In glomerular capillaries of Bowman’s capsule, the blood

pressure is about twice as that in other capillary network. It is because efferent arteriole is narrower than afferent arteriole.

y The glomerular capillary blood pressure causes filtration of blood through 3 layers, i.e., endothelium of glomerular blood vessels, epithelium of Bowman’s capsule and a basement membrane between these two layers.

y The epithelial cells (podocytes) of the Bowman’s capsule are arranged in an intricate manner so as to leave some minute spaces called filtration slits (slit pores).

y Thus, almost all constituents of the blood plasma except the proteins are filtered into the lumen of the Bowman’s capsule through its walls.

y About 15-25% of the water and solutes are removed from the blood plasma that flows through glomerulus.

y The amount of the filtrate formed in all the nephrons of both the kidneys per minute is called Glomerular filtration rate (GFR).

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y In a healthy individual, it is about 125 mL/minute. y Glomerular filtrate contains a large amount of water, glucose,

amino acids, sodium, potassium, urea, uric acid, ketone bodies, and large amounts of water.

y Normal GFR = 125 ml/minute, i.e., 180 litres/day. y About 1100-1200 ml of blood is filtered by the kidneys per

minute which constitute 1/5th of the blood pumped out by each ventricle of the heart in a minute.

(ii) Tubular Reabsorption y From the Bowman’s capsule, the glomerulus filtrate enters

the proximal convoluted tubule. y The process of absorption of selected materials from the

filtrate into the blood of the peritubular capillaries or vasa recta is termed as tubular resorption.

y Even though 180 litres of glomerular filtrate is produced daily, about 99% of this is reabsorbed by the renal tubules.

y So normal volume of urine released is 1.5 litres. y Substances like glucose, amino acids, Na+, etc. in the filtrate

are reabsorbed actively whereas the nitrogenous wastes are absorbed by passive transport.

y Passive reabsorption of water occurs in the initial segments of the nephron.

y PCT reabsorbs most of the nutrients, and 70-80% of electrolytes and water. Simple cuboidal brush border epithelium of PCT increases surface area for reabsorption.

y In loop of Henle, minimum reabsorption takes place. It maintains high osmolarity of medullary interstitial fluid.

y The descending limb is permeable to water but almost impermeable to electrolytes. This concentrates the filtrate.

y The ascending limb is impermeable to water but allows transport of electrolytes. So, the filtrate gets diluted.

y In DCT, conditional reabsorption of Na+ and water takes place.

y Collecting duct extends from cortex to inner parts of medulla. It reabsorbs large amount of water to concentrate urine. It also allows passage of small amounts of urea into medullary interstitium to keep up the osmolarity.

(iii) Tubular Secretion y Tubular secretion is the opposite of tubular reabsorption. It

occurs as: ² Creatinine, pigments, drugs along with hydrogen ions

and ammonia are actively secreted into the filtrate in the PCT from the interstitial fluid.

² Urea enters the filtrate by diffusion in the thin segment of the ascending limb of loop of henle.

² Potassium, hydrogen ions, ammonia, HCO32- ions are

secreted by active transport into the filtrate in DCT. y Maximum hydrogen ions secretion occurs in the PCT. The

removal of H+ ions and NH3 from the blood in the PCT and DCT helps to maintain the pH of the blood between 6 to 8.

y Thus, we can say, the cells of the renal tubule performs two functions:

² It removes substances from the filtrate by the process of reabsorption and send them to the blood capillaries and

² Excrete additional wastes from the blood stream into the filtrate by secretion.

Functions of Tubules y 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.

y Henle’s Loop: Reabsorption in this segment is minimum. It plays a significant role in maintenance of high osmolarity of medullary interstitial fluid.

y DCT: Conditional reabsorption of Na+ and water takes place here. Reabsorption of HCO3

- and selective secretion of H+ and K+ and ammonia takes place to maintain the pH and sodium-potassium balance in blood.

y 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.

Mechanism of the Concentration of the Filtrate (Counter Current Mechanism)

y The counter current mechanism operating inside the kidney is the main adaptation for the conservation of water.

y There are two counter current mechanisms inside the kidneys: Henle’s loop and vasa rectae. They both help to concentrate the urine. Henle’s loop is a U-shaped part of the nephron, while the vasa recta are an efferent arteriole, which forms a capillary network around the tubules inside the renal medulla. It runs parallel to Henle’s loop and is U-shaped.

y The flow of filtrate in the two limbs of Henle’s loop and the flow of blood through the two limbs of vasa recta are in opposite directions (i.e. in a counter current pattern).

y The proximity between the Henle’s loop and vasa recta, as well as the counter current in them help to maintain an increasing osmolarity towards the inner medullary interstitium, i.e., from 300 mOsmolL–1 in the cortex to about 1200 mOsmolL–1 in the inner medulla.

y This gradient is mainly caused by NaCl and urea. y NaCl is transported by ascending limb of Henle’s loop that

is exchanged with descending limb of vasa recta. NaCl is returned to interstitium by ascending limb of vasa recta.

y Similarly, small amount of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule.

y The above described transport of substances facilitated by Henle’s loop and vasa recta is called Counter current mechanism. This helps to maintain a concentration gradient in the medullary interstitium. Presence of such

BIOLOGY418

interstitial gradient helps in an easy passage of water from collecting tubule thereby concentrating the filtrate (urine).

y Human kidneys produce urine four times concentrated than the initial filtrate formed.

Fig. Diagrammatic representation of a nephron and vasa recta showing counter current mechanisms

Osmoregulation: Osmoregulation is a homeostatic mechanism that regulates the optimum temperature of water and salts in the tissues and body fluids. It maintains the internal environment of the body by water and ionic concentration.

Regulation of the Kidney Function

y It is done by hormonal feedback mechanisms involving the hypothalamus, Juxta Glomerular Apparatus (JGA) and the heart.

y Changes in blood volume, body fluid volume and ionic concentration activate Osmoreceptors in the body.

(i) Regulation by ADH (vasopressin)

y Antidiuretic hormone or ADH plays an important role in regulation.

y When body fluid level decreases, the osmoreceptors stimulate the hypothalamus to release antidiuretic hormone (ADH), which helps in water re-absorption and prevents diuresis. ADH prevents diuresis by facilitating water reabsorption from DCT and collecting duct.

y A further increase in body fluid volume can turn off the osmoreceptors. This inhibits the ADH release, which in turn completes the feedback.

y ADH constricts the blood vessels and causes blood pressure to increase, which in turn increases glomerular blood flow and therefore GFR.

(ii) Regulation by Juxta Glomerular Apparatus (JGA) (Renin-Angiotensin mechanism)

y Juxtaglomerular apparatus is a microscopic structure located between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron.

y It plays a role in regulating the renal blood flow and glomerular filtration rate.

y A fall in glomerular blood flow/glomerular blood pressure/GFR activates the JG cells to release renin.

y Renin converts angiotensinogen in blood to angiotensin I and further to angiotensin II (a vasoconstrictor).

Angiotensinogen Renin → Angiotensin I → Angiotension II

y Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and thereby GFR. Angiotensin II also stimulates the adrenal cortex of the adrenal gland to produce aldosterone. Angiotensin II increases glomerular blood pressure and thereby GFR. It also activates adrenal cortex to release Aldosterone.

y Aldosterone increases the rate of absorption of sodium ions and water from the distal convoluted tubule and the collecting duct. This also leads to an increase in blood pressure and glomerular filtration rate. This mechanism, known as renin-angiotensin mechanism, ultimately leads to an increased blood pressure.

Fig. Renin – Angiotensin mechanism

3. Regulation by Atrial-natriuretic Factor (ANF) y ANF check on the renin- angiotensin mechanism. y An increase in blood flow to the atria of the heart causes the

release of Atrial Natriuretic Factor (ANF). y ANF causes vasodilation (dilation of blood vessels) and

thereby decreases the blood pressure.

Micturition y Micturition is the process by which the urine from the urinary

bladder is excreted. y As the urine accumulates, the muscular walls of the bladder

expand. As a result, the stretch receptors on its wall send impulses to CNS. The CNS passes on motor messages. It

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causes the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing micturition (release of urine). The neural mechanism causing micturition is called the micturition reflex.

y An adult human excretes 1 to 1.5 litres of urine (25-30 gm urea) per day.

y Urine is a light yellow coloured watery fluid, slightly acidic (pH-6.0) and has a characteristic odour. Various conditions can affect the characteristics of urine.

y Analysis of urine helps in clinical diagnosis of many metabolic disorders and malfunctioning of the kidney.

Example: ² Glycosuria: Presence of glucose in urine is known as

glycosuria. ² Ketonuria: Presence of high ketone bodies in urine is

called ketonuria. ² Diabetes mellitus: Glucouria and ketonuria in urine

indicates diabetes mellitus.

Role of Lungs, Liver and Skin in Excretion y Liver, lungs, and skin also play an important role in the

process of excretion. ² Lungs: Lungs help in the removing waste materials

such as carbon dioxide (18 litres/day) from the body. ² Liver: Liver is the largest gland in vertebrates. It helps in

the excretion of cholesterol, steroid hormones, vitamins, drugs, and other waste materials through bile. Urea is formed in the liver by the ornithine cycle. Ammonia – a toxic substance – is quickly changed into urea in the liver and hence eliminated from the body. Liver also changes the decomposed haemoglobin pigment into bile pigments called bilirubin and biliverdin.

² Skin (Sweat and sebaceous glands): Skin has many glands which help in excreting waste products through pores. It has two types of glands – sweat and sebaceous glands.

♦ Sweat glands are highly vascular and tubular glands that separate the waste products from the blood and excrete them in the form of sweat. Sweat excretes

excess salt and water from the body. ♦ Sebaceous glands are branched glands that secrete

an oily secretion called sebum. ² Saliva eliminates small amounts of nitrogenous

wastes.

Disorders of Excretory System (i) Uremia: Accumulation of urea in blood which may lead

to kidney failure. The accumulation of urea in blood due to malfunctioning

of kidney is known as uremia. It may lead to kidney failure. (ii) Renal calculi: The formation of insoluble mass of

crystallised salts (oxalates or phosphates of calcium within the kidney is known as renal calculi.

(iii) Glomerulonephritis: The inflammation of glomeruli of kidney is known as glomerulonephritis.

Artificial Kidney/ Hemodialysis y In patients with uremia, urea is removed by hemodialysis. y The dialyzing unit contains a coiled cellophane tube

surrounded by dialyzing fluid having same composition of plasma except the nitrogenous wastes.

y Blood drained from a convenient artery is pumped into dialyzing unit after adding an anticoagulant like heparin.

y The porous cellophane membrane of the tube allows the passage of molecules based on concentration gradient.

y As nitrogenous wastes are absent in dialyzing fluid, these substances freely move out, thereby clearing the blood.

y The cleared blood is pumped back to the body through a vein after adding anti-heparin to it.

Kidney Transplantation y It is the ultimate method in the correction of acute renal

failures. A functioning kidney is taken from a donor. y It is better to receive kidney from a close relative to minimize

chances of rejection by immune system of host.

420 BIOLOGY

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421Excretory Products and their Elimination

1. The Glomerulus along with Bowman’s capsule is called(a) Column of Bertini (b) Renal capsule(c) Malpighian tubule (d) None of these

2. Which of the following is not the part of renal tubule?(a) Henle’s loop (b) Glomerulus(c) Bowmans’s capsule (d) Collecting tubule

3. Waste products of adenine and guanine metabolism areexcreted by man as(a) Ammonia (b) Urea(c) Uric acid (d) Allantois

4. A man takes large amount of protein. He is likely to excretemore amount of(a) water (b) glucose(c) urea and uric acid (d) salts

5. In man, the urea is mainly produced in(a) Liver (b) Kidneys(c) Gall bladder (d) Spleen

6. Aquatic reptiles are(a) Ammonotelic (b) Ureotelic over land(c) Ureotelic (d) Ureotelic in water

7. Which one is not correct ?(a) Humans - Uriotelic (b) Birds - Uricotelic(c) Lizards - Uricotelic (d) Whale - Ammonotelics

8. Which of the following animal dose not excrete nitrogen asurea?(a) Tadpole (b) Frog(c) Toad (d) Elesmobranch fish

9. Uric acid is the chief nitrogenous component of the excretoryproducts of(a) Man (b) Earthworm(c) Cockroach (d) Frog

10. Which of the following hormone is secreted from kidney?(a) ANF (b) Erythropoetin(c) Rennin (d) Aldosterone

11. The appearance of albumin in the urine is most likely due to(a) Increase in the blood pressure(b) Decrease in the blood osmotic corpuscles(c) Damage to the Malpighian corpuscles(d) Damage to the proximal convoluted tubules

12. The blood constituents that remain unchanged in quantityafter circulating through the kidney are(a) Urea and glucose (b) Glucose and proteins(c) Urea and proteins (d) Urea and uric acid

13. Due to insufficient filtration in the Bowman's capsule, all arelikely to happen except(a) Accumulation of fluid in the body(b) Increase in blood pressure(c) Increase in blood urea level(d) Loss of glucose through urine

14. Kidney crystals are solid clusters of(a) Calcium nitrate and uric acid(b) Phosphate and uric acid(c) Calcium carbonate and uric acid(d) Calcium metabisulphite and uric acid

15. The glomerular filtrate consists of(a) Urea, sodium chloride, fibrinogen and water(b) Glucose, amino acids, urea, oxytocin and calcitonin(c) Both (a) and (b)(d) Urea, glucose, salts and water

16. "Columns of Bertini" in the kidney of mammals are formed asthe extension of(a) Medulla into cortex (b) Cortex into medulla(c) Medulla into pelvis (d) Pelvis into ureter

17. The liquid which is collected in the cavity of Bowman's capsuleis(a) Concentrated urine(b) Blood plasma minus blood proteins(c) Glycogen and water(d) Sulphates and water

18. Juxta glomerular apparatus is formed by cellular modificationin the(a) Afferent arteriole and DCT(b) Efferent arteriole and PCT(c) Afferent arteriole and PCT(d) Efferent arteriole and DCT

19. In which part of excretory system of mammals can you firstuse the term 'urine' for contained fluid ?(a) Bowman's capsule (b) Loop of Henle(c) Collecting tubule (d) Urinary bladder

20. ADH influences water permeability in the(a) Proximal tubule (b) Distal tubule(c) Collecting tubule (d) Both (a) and (b)

21. The plasma resembles its composition to the filtrate producedby the glomerulus except the presence of(a) Glucose (b) Chloride(c) Amono acids (d) Proteins

22. When a person is suffering from poor renal reabsorption thenwhich of the following will not help in the maintenance ofblood volume(a) Decreased glomerular filtration(b) Increased ADH secretion(c) Decreased arterial pressure in kidney(d) Increased arterial pressure in kideny

23. In distal convoluted tubule of the nephrons.(a) Na reabsorption requires energy(b) Secretion of K ions does not require energy(c) Water reabsorption requires energy(d) Ammonia is secreted

422 BIOLOGY

24. Which of the following is totally reabsorbed in renal tubules ?(a) Na (b) K(c) H2O (d) C6H12O6

25. Part not belonging to uriniferous tubule is –(a) Glomerulus(b) Henle's loop(c) Distal convoluted tubule(d) Collecting duct

26. Reabsorption of chloride ions from glomerular filtrate inuriniferous tubule occurs by –(a) Active transport (b) Diffusion(c) Osmosis (d) Brownian movement

27. Which of the following set contains all groups of ureotelcanimals?(a) Marine fishes, amphibians and mammals(b) Bony fishes, mammals and terrestrial insects(c) Aquatic insects, amphibians and land snails(d) Bony fishes, aquatic amphibians and terrestrial

mammals28. The projections of renal pelvis are called

(a) Hiluses (b) Calyces(c) Medullary pyramids (d) Renal columns

29. Main functions of kidney is –(a) Passive absorption (b) Ultrafiltration(c) Selective reabsorption (d) Both b and c

30. In man the two kidneys lie –(a) At the level of ovaries(b) At the same level(c) Left kidney at a higher level than the right one(d) Right kidney at a higher level than the left one

31. Vasa rectae are peritubublar capillaries around –(a) Posterior part of alimentary canal(b) PCT(c) Loop of Henle(d) DCT

32. Glomerular filtration rate would be decreased by –(a) Constriction of the efferent arteriole(b) An increase in afferent arteriolar pressure(c) Compression of the renal capsule(d) An increase in renal blood flow

33. Duct of Bellini is concerned with –(a) Filtration of urine (b) Purification of urine(c) Conduction of urine (d) All the above

34. Which of the following is directly responsible for increasingglomerular blood pressure and hence GFR?(a) Aldosterone (b) ANF(c) Angiotensin II (d) Renin

35. Urine contains how much of water –(a) 96% (b) 90%(c) 70% (d) None of these

36. Which regulates reabsorption of salts from glomerular filtrate ?(a) Oxytocin (b) Vassopressin(c) Glucoorticoides (d) Mineral orticoids

37. A person who is on a long hunger strike and is surviving onlyon water, will have –(a) less amino acids in his urine(b) more glucose in his blood(c) less urea in his urine(d) more sodium in his urine

38. Liquid part of the blood having undergone ultrafiltration fromthe glomerulus and reaching Bowman's capsule normallywould not contain(a) Sugar (glucose) (b) Sodium chloride(c) Creatinine (d) Albumin

39. Find the incorrect statement regarding mechanism of urineformation in man(a) The glomerular filtration rate is about 125 ml per minute(b) The ultrafiltration is opposed by the colloidal osmotic

pressure of plasma(c) The counter current systems contribute in diluting the

urine(d) Aldosterone induces greater reabsorption of sodium

40. Other function performed by kidney apart from excretion is(a) Osmoregulation (b) Temperature regulation(c) Hormonal regualrtion (d) Spermatogenesis

41. Filtration pressure in human kidneys is about(a) + 15 mm Hg (b) + 70 mm Hg(c) + 45 mm Hg (d) +55 mm Hg

42. Presence of glucose in urine is called(a) Diabetes insipidus (b) Diabetes mellitus(c) Galactosemia (d) None of these

43. Which of the following is correct ?(a) Water reabsorption in descending limb of loop and

collecting duct are under similar conditions(b) Sodium reabsorption in ascending limb of loop and

collecting duct occur under similar conditions.(c) Water reabsorption in descending limb of loop and

collecting duct occur under different conditions.(d) None of these

44. Diameter of the renal afferent vessel is(a) Same as that of efferent(b) Smaller than that of efferent(c) Larger than that of efferent(d) There is no efferent vessel

45. Excretory products of mammalian embryo are eliminated by-(a) Placenta (b) Amniotic fluid(c) Allantois (d) Ureters

46. Effective filtration pressure in the glomerulus in kidney of manis about(a) + 75 mm Hg (b) + 10 mm Hg(c) + 35 mm Hg (d) + 50 mm Hg

47. Person suffering from muscular dystrophy eliminate in urine agreat amount of –(a) Glucose (b) Sulphate(c) Water (d) Creatinine

48. Healthy human does not excrete out in his urine –(a) Uric acid (b) Alanine(c) Creatinine (d) B-complex vitamins

49. Urea from the blood can be removed by(a) Uraemia (b) Diuresis(c) Dialysis (d) Micturition

50. Ureters act as urogenital ducts in(a) human males(b) human females(c) both female and male frog(d) frog male

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1. Which one of the following statements is correct with respectto kidney functions?(a) When someone drinks lot of water,ADH release is

suppressed.(b) Exposure to cold temperature blood flow stimulates

formation of Angiotensin II.(c) An increase in glomerular blood flow stimulates formation

of Angiotensin II.(d) During summer when body loses lot of water by

evaporation, the release of ADH is suppressed.2. Which one of the following correctly explains the function of

a specific part of a human nephron ?(a) Podocytes: create minute spaces (slit pores) for the

filtration of blood into the Bowman’s capsule.(b) Henle’s loop: most of the reabsorption of the major

substances from the glomerular filtrate.(c) Distal convoluted tubule : reabsorption of K+ ions into

the surrounding blood capillaries.(d) Afferent arteriole: carries the blood away from the

glomerular towards renal vein.3. A large proportion of oxygen is left unused in the human blood

even after its uptake by the body tissues. This O2(a) acts as a reserve during muscular exercise.(b) raise the pCO2 of blood to 75 mm of Hg.(c) is enough to keep oxyhaemoglobin saturation at 96%.(d) helps in releasing more O2 to the epithelial tissues.

4. The principal nitrogenous excretory compound in humans issynthesised(a) in kidneys but eliminated mostly through liver(b) in kidneys as well as eliminated by kidneys(c) in liver and also eliminated by the same through bile(d) in the liver, but eliminated mostly through kidneys

5. Which one of the following statements in regard to theexcretion by the human kidneys is correct?(a) Descending limb of Loop of Henle is impermeable to water(b) Distal convoluted tubule is incapable of reabsorbing

HCO3(c) Nearly 99 per cent of the glomerular filtrate is reabsorbed

by the renal tubules(d) Ascending limb of Loop of Henle is impermeable to

electrolytes6. What will happen if the stretch receptors of the urinary bladder

wall are totally removed?(a) Micturition will continue(b) Urine will continue to collect normally in the bladder(c) There will be no micturition(d) Urine will not collect in the bladder

7. Lysozyme that is present in perspiration, saliva and tears,destroys

(a) certain types of bacteria(b) all viruses(c) most virus-infected cells(d) certain fungi

8. Bowman’s glands are located in the(a) anterior pituitary(b) female reproductive system of cockroach(c) olfactory epithelium of our nose(d) proximal end of uriniferous tubules.

9. In Ornithine cycle, which of the following wastes are removedfrom the blood?(a) CO2 and urea (b) Ammonia and urea(c) CO2 and ammonia (d) Urea and urine

10. A person is undergoing prolonged fasting. His urine will befound to contain abnormal quantities of:(a) fats (b) amino acids(c) glucose (d) ketones

11. In the kidney, glucose is mainly absorbed in(a) Loop of Henle(b) Proximal convoluted tubules(c) Distal convoluted tubules(d) Bowman's capsule

12. Which of the following is a metabolic waste of proteinmetabolism ?(a) NH3, urea and CO2(b) Urea, Oxygen and N2(c) Urea, ammonia and alanine(d) Urea, ammonia and creatinine

13. Occurence of excess urea in blood due to kidney failure is(a) Urochrome (b) Uraemia(c) Uricotelism (d) Ureotelism

14. If kidneys fail to reabsorb water, the effect on tissue would(a) Remain unaffected(b) Shrink and shrivel(c) Absorb water from blood plasma(d) Take more O2 from blood

15. Figure shown human urinary system with structures labelledA to D. Select option which correctly identifies them and givestheir characteristics and /or functions.

424 BIOLOGY

(a) B-pelvis-broad funnel shaped space inner to hilum,directly connected to loops of Henle.

(b) C-Medulla-inner zone of kidney and contains complexnephrons.

(c) D - Cortex - outer part of kidney and do not contain anypart of nephrons

(d) A-Adrenal gland - located at the anterior part of kidney.Secrete Catecholamines which stimulate glycogenbreakdown.

16. Select the option which shows correct matching of animalwith excretory organs and excretory product

Animal Excretory Excretoryorgans product

(a) Housefly Renal tubules Uric acid(b) Labeo (Rohu) Nephridial Ammonia

tubes(c) Salamander Kidney Urea(d) Peacock Kidney Urea

17. Refer the following diagram and identify the parts of a kidneyindicated

ABC

D

E

(a) A = cortex, B = nephron, C = pelvis, D= medulla,E = ureter

(b) A = cortex, B = medulla, C = nephron, D = pelvis,E = ureter

(c) A = nephron, B = cortex, C = medulla, D = ureter,E = pelvis

(d) A = nephron, B = cortex, C = medulla, D = pelvis,E = ureter

18. In the diagram of excretory system of humna beings givenbelow, different parts have been indicated by alphabets;choose the answer in which these alphabets have beencorrectly matched with the parts whcih they represent

B

A

F

C

D

E

(a) A = Kidney, B = Abdominal aorta, C = Ureters,D = Urinary bladder, E = Urethra, F = Renal pelvis

(b) A = Kidney, B = Abdominal aorta, C = Urethra,D = Urinary bladder, E = Ureters , F = Renal pelvis

(c) A = Kidney, B = Renal pelvis, C = Urethra, D = Urinarybladder, E = Ureters, F = Abdominal aorta

(d) A = Kidney, B = Abdominal aorta, C = Urethra,D = Urinary bladder, E = Renal pelvis, F = Ureters

19. Match Column I with Column IIColumn I Column II(Excretory organs) (Animals)

A. Nephridia 1. HydraB. Malpighian tubules 2. LeechC. Protonephridia 3. SharkD. Kidneys 4. Round worms

5. Cockroach(a) A ® 2; B ® 5; C ® 4; D ® 3(b) A ® 4; B ® 2; C ® 1; D ® 5(c) A ® 5; B ® 2; C ® 4; D ® 3(d) A ® 2; B ® 4; C ® 5; D ® 1

20. Match Column I with Column IIColumn I Column II

A. Ultrafiltration 1. Henle's loopB. Concentration of urine 2. UreterC. Transport of urine 3. Urinary bladderD. Storage of urine 4. Malpighian corpuscles

5. Proximal convolutedtubules

(a) A ® 4; B ® 1; C ® 2; D ® 3(b) A ® 4; B ® 3; C ® 2; D ® 1(c) A ® 5; B ® 4; C ® 1; D ® 3(d) A ® 5; B ® 4; C ® 1; D ® 2(e) A ® 4; B ® 1; C ® 3; D ® 2

21. Consider the following four statements (1-4) regarding kidneytransplant and select the two correct ones out of these.(1) Even if a kidney transplant is proper the recipient may

need to take immune suppresants for a long time.(2) The cell mediated immune response is responsible for

the graft rejection.(3) The B lymphocytes are responsible for rejection of the

graft.(4) The acceptance or rejection of a kidney transplant

depends on specific interferons.The two correct statements are:(a) (2) and (3) (b) (3) and (4)(c) (1) and (3) (d) (1) and (2)

22. Consider the following statements and select the correct onesout of these(1) Flame cells are excretory structures in flatworms.(2) Green glands are excretory organs in annelids.(3) Columns of Bertini are the conical projections of renal

pelvis into renal medulla between the renal pyramids.

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(a) (1) and (2) are correct (b) (2) and (3) are incorrect(c) (1) and (3) are correct (d) (1), (2) and (3) are correct

23. Which of the following statement (s) is/are true ?(1) Urine is hypertonic in distal convoluted tubule.(2) When the urine passes into collecting tubule, it becomes

hypotonic.(3) Urine is isotonic in proximal convoluted tubule.(4) Urine becomes more and more hypotoinic as it passes

through Henle's loop.(a) (1) and (4) (b) (1), (2) and (3)(c) (2) and (3) (d) (3) only

DIRECTIONS for Qs. 24 to 25: Each questions containSTATEMENT-1 (Assertion) and STATEMENT-2 (Reason). Eachquestion has 4 choices (a), (b), (c) and (d) out of which ONLY ONE iscorrect.

(a) Statement- 1 is True, Statement-2 is True, Statement-2 is acorrect explanation for Statement -1

(b) Statement -1 is True, Statement -2 is True ; Statement-2 is NOTa correct explanation for Statement - 1

(c) Statement - 1 is True, Statement- 2 is False(d) Both the Statements are False.24. Statement 1 : Urinary bladder and ureters are lined by

transitional epithelium.Statement 2 : Ureters carry the urine to urinary bladder whereit is stored temporarily.

25. Statement 1 : Hemodialysis can save and prolong the life ofuremic patients.Statement 2 : Waste products like urea can be removed fromthe blood by the process of hemodialysis.

Exemplar Questions

1. The following substances are the excretory products inanimals. Choose the least toxic form among them.(a) Urea (b) Uric acid(c) Ammonia (d) Carbon dioxide

2. Filtration of the blood takes place at(a) PCT (b) DCT(c) Collecting ducts (d) Malpighian body

3. Which of the following statement is intorrect?(a) ADH prevents conversion of angiotensinogen in blood

to angiotensin(b) Aldosterone facilitates water reabsorption(c) ANF enhances sodium reabsorption(d) Renin causes vasodilation

4. A large quantity of one of the following is removed from ourbody by lungs.(a) CO2 only (b) H2O only(c) CO2 and H2O (d) ammonia

5. The pH of human urine is approximately(a) 6.5 (b) 7(c) 6 (d) 7.5

6. Different types of excretory structures and animals are givenbelow. Match them appropriately and mark the correct answerfrom among those given below.

Excretory Structure/Organ AnimalsA. Protonephridia 1. PrawnB. Nephridia 2. CockroachC. Malpighian tubules 3. EarthwormD. Green gland or antennal gland 4. FlatwormsCodes

A B C D A B C D(a) 4 3 2 1 (b) 2 3 1 2(c) 4 3 1 2 (d) 2 3 2 4

7. Which one of the following statements is incorrect?(a) Birds and land snails are uricotelic animals(b) Mammals and frogs are ureotelic animals(c) Aquatic amphibians and aquatic insects are ammonotelic

animals(d) Birds and reptiles are ureotelic

8. Which of the following pairs is wrong?(a) Uricotelic — Birds(b) Ureotelic — Insects(c) Ammonotelic — Tadpole(d) Ureotelic — Elephant

9. Which one of the following statement is incorrect?(a) The medullary zone of kidney is divided into a few conical

masses called medullary pyramids projecting into thecalyces

(b) Inside the kidney the cortical region extends in betweenthe medullary pyramids as renal pelvis

(c) Glomerulus along with Bowman's capsule is called therenal corpuscle

(d) Renal corpuscle, Proximal Convoluted Tubule (PCT) andDistal Convoluted Tubule (DCT) of the nephron aresituated in the cortical region of kidney

10. The condition of accumulation of urea in the blood is termedas(a) renal calculi (b) glomerulonephritis(c) uremia (d) ketonuria

11. Which one of the following is also known as antidiuretichormone?(a) Oxytocin (b) Vasopressin(c) Adrenaline (d) Calcitonin

426 BIOLOGY

12. Match the following columns.Column I Column II

A. Proximal convoluted 1. Formation of concentratedtubule urine

B. Distal convoluted 2. Filtration of bloodtubule

C. Henle's loop 3. Reabsorption of 70-80% ofelectrolytes

D. Counter current 4. Ionic balancemechanisms

E. Renal corpuscle 5. Maintenance of concentrationgradient in medulla

CodesA B C D E A B C D E

(a) 3 5 4 2 1 (b) 3 4 1 5 2(c) 1 3 2 5 4 (d) 3 1 4 5 2

13. Match the following columns.Column I Column I

A. Glycosurea 1. Accumulation of uric acid in jointsB. Renal calculi 2. Inflammation in glomeruliC. Glomerular 3. Mass of crystallised salts within

nephritis the kidneyD. Gout 4. Presence of glucose in urineCodes

A B C D A B C D(a) 1 3 2 4 (b) 3 2 4 1(c) 4 3 2 1 (d) 4 2 3 1

14. We can produce a concentrated/dilute urine. This is specialmechanism. Identify the mechanism.(a) Reabsorption from PCT(b) Reabsorption from collecting duct(c) Reabsorption/Secretion in DCT(d) Counter current mechanism in Henle's loop/vasa recta

15. Dialysing unit (artificial kidney) contains a fluid which is almostsame as plasma except that it has(a) high glucose (b) high urea(e) no urea (d) high uric acid

NEET/AIPMT (2013-2017) Questions

16. Figure shown human urinary system with structures labelledA to D. Select option which correctly identifies them and givestheir characteristics and /or functions. [2013]

AB

CD

Kidney

Urinary bladder

(a) B-pelvis-broad funnel shaped space inner to hilum,directly connected to loops of Henle.

(b) C-Medulla-inner zone of kidney and contains complexnephrons.

(c) D - Cortex - outer part of kidney and do not contain anypart of nephrons

(d) A-Adrenal gland - located at the anterior part of kidney.Secrete Catecholamines which stimulate glycogenbreakdown.

17. Select the option which shows correct matching of animalwith excretory organs and excretory product

[NEET Kar. 2013]Animal Excretory Excretory

organs product(a) Housefly Renal tubules Uric acid(b) Labeo (Rohu) Nephridial tubes Ammonia(c) Salamander Kidney Urea(d) Peacock Kidney Urea

18. Which of the following causes an increase in sodiumreabsorption in the distal convoluted tubule? [2014](a) Increase in aldosterone levels(b) Increase in antidiuretic hormone levels(c) Decrease in aldosterone levels(d) Decrease in antidiuretic hormone levels

19. Which of the following does not favour the formation of largequantities of dilute urine? [2015 RS](a) Caffeine(b) Renin(c) Atrial-natriuretic factor(d) Alcohol

20. Removal of proximal convoluted tubule from the nephron willresult in: [2015 RS](a) More concentrated urine(b) No change in quality and quantity of urine(c) No urine formation(d) More diluted urine

21. Human urine is usually acidic because : [2015 RS](a) excreted plasma proteins are acidic(b) potassium and sodium exchange generates acidity(c) hydrogen ions are actively secreted into the filtrate.(d) the sodium transporter exchanges one hydrogen ion for

each sodium ion, in peritubular capillaries.22. In mammals, which blood vessel would normally carry largest

amount of urea? [2016](a) Renal Vein (b) Dorsal Aorta(c) Hepatic Vein (d) Hepatic Portal Vein

23. Which of the following statements is correct? [2017](a) The descending limb of loop of Henle is impermeable to

water.(b) The ascending limb of loop of Henle is permeable to water.(c) The descending limb of loop of Henle is permeable to

electrolytes.(d) The ascending limb of loop of Henle is impermeable to

water.

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EXERCISE - 1

1. (d) 2. (b)3. (c) Main sources of uric acid are purines. Purines like adenine

and Guanine change into xanthine which changes intouric acid. Guanine ¯Adenine ® xanthine ® uric acid

4. (c) Because they are they are the ultimate products of proteincatabolism.

5. (a) Ornithine cycle is a cyclic process of urea formation whichoperates in the mitochondria of liver cells and has beenstudied by kreb's and Henseleit.

6. (c) Ureotelic animals include mainly amphibians andmammals besides its annelids (earthworm) branch fishes(shark) and aquatic animals are ureotelic.

7. (d) Whale is ureotelic.8. (a) 9. (c) 10. (b)11. (c) Normally albumin can't pass out through the filtering

pores due to their large size but in some pathologicalconditions viz. anoxia or heart failure, the filtrationmembrane becomes damaged and filtering pores enlargein size, so that serum albumin passes out in the largestamount and appears in the urine.

12. (b) Proteins are not filtered through glomerulus and glucoseis totally reabsorbed in renal tubule.

13. (d) Insufficient filtration will increase the blood urea levelbecause all the quantity of urea produced by liver wouldnot be filtered through glomerular capsule. Loss ofglucose through urine always takes place due toinsufficient reabsorption.

14. (b) 15. (d)16. (b) The renal columns of Bertini is the part of cortex continued

inside medulla between pyramids.17. (b) 18. (a) 19. (c)20. (b) Antidiuretic hormone (ADH) produced by neurosecretory

cells in the paraventricular and supraoptic nuclei of thehypothalamus that stimulates water reabsorption from(in DCT part of nephron) kidney tubules into the bloodand vasocontraction of arterioles.

21. (d) Due to large size, protein can't be filtered through thefiltratrion slits. So they are absent in glomerular filtrate.

22. (d) Increased arterial pressure in kidney will promote thefiltration but the person is suffering from poor renalreabsorption, so the volume of glomerular filtrate andurine will increase and person would be unable to maintainthe volume of blood.

23. (a) Reabsorption of Na+ in the tubules is an active process.24. (d) 25. (d)26. (b) Reabsorption of chloride ions from glomerular filtrate in

uriniferous tubule occurs by diffusion.27. (a) 28. (b) 29. (d) 30. (c) 31. (c) 32. (c)33. (c) 34. (c) 35. (a)36. (d) Mineralo corticoids regulates reabsorption of salts from

glomerular filtrate.37. (c) 38. (d) 39. (c)40. (a) Besides removing the metabolic wastes and impurities

from the blood the kidney also perform the importantfunction of osmoregulation (regulation of osmolality) byregulating the amount of water in body fluids.

41. (a) Effective filtration pressure in man is + 15 mm Hg. In caseof horse and some other mammals it is + 25 mm Hg.

42. (d) 43. (a) 44. (c) 45. (a) 46. (b) 47. (d)48. (b) 49. (c)50. (d) In male frogs the sperms are carried through the ureters,

hence in male, ureters are called urinogenital ducts.EXERCISE - 2

1. (a) When some one drinks lots of water, release of ADH issuppressed.

2. (a) Podocytes are highly specialized cells with a complexcytoarchitecture plays a major role in establishing theselective permeability of glomerular filtration barrier.

3. (a) A large portion of oxygen is left unused in the humanblood even after its uptake by the body tissues. This O2acts as a reserve during muscular exercise.

4. (d) The principal nitrogenous excretory compound in humansis urea. It is synthesized in the mitochondrial matrix andcytosol of liver cells and eliminated through kidneys.

5. (c) Urine formation involves three main process called,glomerular filtration, reabsorption and secretion. Acomparison of the volume of the filtrate formed per day(which is 180 litres per day) with that of urine released(about 1.5 litres) suggest that nearly 99 percent of theglomerular filtrate is reabsorbed by the renal tubules. Thedescending limb of loop of Henle is permeable to waterbut impermeable to electrolytes. The ascending limb isimpermeable to water but allows transport of electrolytes.Reabsorption of sodium ions and water takes place indistal convoluted tubule.

6. (c) Micturition is same as urination. Urination or micturitionis the act of passing urine which is a reflex phenomenon.As urine accumulates in bladder the stretch receptors areactivated and pass the stimulus to the CNS. In the absenceof stretch receptors the urine would get collected andprobably overflow.

Hints & Solutions

428 BIOLOGY

7. (a) Lysozyme is an antibacterial agent which is secreted bythe major salivary glands.

8. (c) Bowman’s glands are located in the olfactory epitheliumof our nose.

9. (c) Urea NH2 – CO – NH2 is formed from two molecules ofammonia and one molecule of carbon dioxide. A moleculeof ammonia combines with carbondioxide to form carbonylphosphate. It reacts with ornithine to form citrulline.Citrulline accepts another molecule of NH4

+ giving riseto arginine. Arginine is hydrolysed into urea and ornithinewith the help of enzyme arginase.

10. (d) Under fasting conditions and in uncontrolled diabetes,the liver produces large amount of ketone bodies likeacetoacetate, dihydroxy butyrate. The presence of excessketone bodies in blood or urine is termed ketonemic andketonuria respectively.

11. (b) Complete reabsorption by active transport takes placesfor glucose in the proximal convoluted tubules.

12. (d) 13. (b) 14. (b)15. (d) A – Adrenal gland – located at the anterior part of kidney,

secrete Catecholamines which stimulate glycogenbreakdown.

16. (c) Salamander (Amphibia; Caudata) excrete urea by help ofkidneys.

17. (d) 18. (a) 19. (a) 20. (a)21. (d) Tissue and blood group matching are essential before

undertaking kidney transplant. Even if kidney transplantis proper, the recipient may need to take immunosuppresant all his/her life. The ability of body todifferentiate self and nonself and the cell-mediated immuneresponse is responsible for graft rejection.

22. (b)23. (d) The filtrate is isotonic to blood plasma (in proximal

convoluted tubule) and the filtrate becomes hypertonicto blood plasma (in descending limb of loop of Henle).The filtrate is hypotonic to blood plasma (in ascendinglimb of loop of Henle) in distal convoluted tubule. ADHmake the filtrate isotonic to blood plasma.

24. (b) Urinary bladder and ureters of excretory system are linedby transitional epithelium because it is a stretchableepithelium, hence the urinary bladder and ureters may beconsiderably stretched without getting torn when theyare filled with urine. Ureters are thin muscular tubes whichemerge from the hilum of each kidney. Urine enters theureters from the renal pelvis and is conducted along theureters by peristaltic waves on their walls. Ureters fromboth the kidneys finally open into urinary bladder whichis a hollow muscular sac. In this way urine from both thekidneys is drained into the urinary bladder which storesit temporarily.

25. (a) The blood urea level rises abnormally (uremia) in patientssuffering from renal failures. In uremia patients an artificialkidney is used for removing accumulated waste productslike urea from the blood by a process called hemodialysis.In this way, hemodialysis saves and prolongs the life ofmany uremic patients.

EXERCISE - 3

Exemplar Questions

1. (b) Uric acid is the least toxic. Insects, land tortoises, lizardsand birds change most of their nitrogenous waste intouric acid. It is the least toxic because it is insoluble inwater and is present in solid form, thus, contains leastwater. In birds, uric acid mixes with undigested food toform the bird dropping.Urea moves to blood for filtration and is eliminated withwater in urine via kidneys.Ammonia is very toxic and needs water for diffusion.Carbon dioxide excretion takes place through the lungs.

2. (d) Filtration of blood occurs at the Malpighian body.Malpighian body or corpuscle comprises of glomerulusand Bowman's capsule. Filtration of blood takes place inglomerulus through glomerular filtration in which bloodenters in the glomerules through an afferent arteriole andleaves it through efferent arteriole.

3. (a) ADH (Antidiuretic Hormone) or vasopressin is secretedby the posterior pituitary gland. It facilitates waterreabsorption from later parts of the tubule, and thusprevents diuresis.It regulates water excretion by increasing permeability ofthe collecting duct for water and salt by accelerating waterand ion transfer determined by the osmotic gradient.

4. (c) Human lungs remove large amounts of CO2 (18L / day)and also siginificant amount of water everyday.While respiration, CO2 alone cannot be eliminated fromthe body and the same holds true for H2O. Ammonia ishighly toxic, and thus it is immediately converted to non-toxic form.

5. (c) The pH of human urine is approximately 6.0.6. (a) 1. Praws possess green gland or antennal glands as

their excretory structures.2. Cockroaches possess Malpighian tubules as their

excretory structures.3. Earthworms possess nephridia as their excretory

structures.4. Flatworms possess protonephridia as their excretory

structures.7. (d) Birds and reptiles are uricotelic as they excrete

nitrogenous waste, uric acid in the form of pellet or pastewith minimal loss of water.

8. (b) Insects excrete nitrogenous wastes as uric acid hence areuricotelic. Ureotelic animals include mammals, adultamphibians and elasmobranchs.

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Thus, birds are uricotelic and tadpoles excret ammonia.Elephant being a mammal is ureotelic.

9. (b) Inside the kidney the cortical region extends between themedullary pyramids as renal columns and are calledcolumn of Bertini.

10. (c) Uremia is the accumulation of urea in blood. It occursdue to malfunctioning of kidney.Renal calculi refers to the formation of stones or insolublemass of crystallised salts (oxalates. etc) with in the kidney.Glomerulonephritis is the inflammation of glomeruli ofkidney.Ketonuria is a medical condition in which ketone bodiesare present in the urine. It is normally seen duringstarvation or more commonly in type 1 diabetes mellitus.

11. (b) Vasopressin is also known as Antidiuretic Hormone(ADH). It is secreted from the neurohypophysis of thepituitary and facilitates water reabsorption from the latterparts of the tubule, thereby preventing diuresis.Oxytocin hormone is produced by the hypothalamus andis stored and secrated by the posterior pituitary gland.Oxytocin stimulates contractions of uterus at the end ofpregnancy and contractions of mammary glands that helpin the flow of milk.Adrenaline is released by adrenal medulla at the time ofemergency, and hence has a role in 'fight or flight' reaction.Calcitonin is primarily produced in humans by theparafollicular cells of the thyroid. It acts to reduce bloodcalcium, levels opposing the effect of parathyroidhormone.

12. (b) Proximal convoluted tubule reabsorps about 70-80% ofelectrolytes.Distal convoluted tubule is involved in the secretion ofhydrogen, potassium ions and NH3 in order to maintainpH and sodium-potassium balance in the blood (ionicbalance).Henle's loop (the descending limb) is permeable to water,but almost impermeable to electrolytes. This concentratesthe urine as it moves down.Counter current mechanisms help to maintain aconcentration gradient in the medullary interstitium ofkidney.Renal corpuscle involves filtration of blood via theglomerulus and Bowman's capsule.

13. (c) Glycosurea/glucosuria is the presence of glucose in tneurine.Renal calculi is the formation of a mass of crystallisedsalts within the kidney.Glomerular nephritis is the inflammation of glomeruli ofthe kidney.Gout is the accumulation of uric acid crystals in jointscausing inflammation.

14. (d) Counter current mechanism in Henle's loop and vasa rectahelps to maintain concentration gradient in the medullaryinterstitum. Presence of such interstitial gradient helps

an easy passage of water from the collecting tubulethereby concentrating the urine.PCT helps in maintaining pH and ionic balance of thebody fluid by the secretion of H+, ammonia and potassiumions and reabsorbing 70-80% of electrolytes and water.Collecting duct helps in reabsorption of water to produceconcentrated urine and in maintaining osmolarity. It alsoplays a vital role in maintaining pH and ionic balance inblood by secreting H+ and K+ ions.DCT reabsorbs Na+ and water along with HCO3

–,maintaining pH and sodium-potassium/ionic balance inblood by selectively secreting hydrogen and potassiumions.

15. (c) Dialysis is a process for removing waste and excess waterfrom the blood and is used primarily as an artificialreplacement for lost kidney function in people with renalfailure.The dialysing unit has the same composition as that ofplasma except the nitrogenous waste (urea).

NEET/AIPMT (2013-2017) Questions

16. (d) A – Adrenal gland – located at the anterior part of kidney,secrete Catecholamines which stimulate glycogenbreakdown.

17. (c) Salamander (Amphibia; Caudata) excrete urea throughkidneys (mesonephric).

18. (a) Aldosterone hormone, released by the adrenal glands,helps the body regulate blood pressure. Aldosteronecauses the tubules of the kidneys to increase thereabsorption of sodium and water into the blood. Thisincreases the volume of fluid in the body, which alsoincreases blood pressure.

19. (b) The secretion of Renin is induced by decrease in bloodpressure and blood volume. It maintains the proper BPand BV. It has no role in the formation of large quantitiesof urine.

20. (d) Generally all of the essential nutrients and 70% to 80% ofelectrolytes and water are reabsorbed by this segment.Removal of proximal convolnted tubule from the nephronwill result in dilution of urine.

21. (c) Urine has acidic nature because hydrogen ions(H+) arecomponents of an acid which are secreted into the filtrate.

22. (c) Hepatic Vein, because the liver produces urea and otherwaste materials and then it pours it all in the right ventricleof the heart for oxygenation. The heart distributes theblood to various parts of the body from here. So theimpure blood brought by the Hepatic Vein and other bloodvessels get distributed through the aorta. This willautomatically imply that the Renal Artery will containlesser impure blood than the Hepatic Vein.

23. (d) Descending limb of loop of Henle is permeable to waterbut impermeable to electrolytes whereas ascending limbis impermeable to water but permeable to electrolytes.

19 Excretory Products and Their Elimination - SelfStudys

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