NEET Biology: Human Physiology · Chapter 3

Excretory Products and their Elimination

What to remember

Nitrogenous waste type matches habitat: ammonia (ammonotelic) in water animals, urea (ureotelic) in mammals, uric acid (uricotelic) in reptiles, birds and insects.
Each kidney has about one million nephrons. A nephron = renal corpuscle (glomerulus + Bowman's capsule) + renal tubule (PCT, loop of Henle, DCT). DCTs open into collecting ducts.
Urine formation has three steps: glomerular filtration (GFR about 125 mL/min, about 180 L/day), selective reabsorption (about 99% of filtrate) and tubular secretion. Urine volume is about 1 to 1.5 L/day.
The countercurrent mechanism of the loop of Henle and vasa recta builds an osmolarity gradient from about 300 mOsmol/L (cortex) to about 1200 mOsmol/L (inner medulla). ADH, the renin-angiotensin-aldosterone system and ANF regulate kidney function.

Nitrogenous wastes and excretory structures

Breakdown of proteins and nucleic acids produces ammonia, which is highly toxic and needs a lot of water for removal. Animals have three strategies.

Type	Main waste	Water needed	Examples
Ammonotelic	Ammonia	Very large	Bony fishes, aquatic amphibians, aquatic insects
Ureotelic	Urea	Moderate	Mammals, many terrestrial amphibians, marine fishes
Uricotelic	Uric acid	Very little (pellet or paste)	Reptiles, birds, land snails, insects

Ammonia is excreted as ammonium ions by diffusion across body surfaces or gill surfaces. Kidneys play only a minor role in ammonotelic animals. In ureotelic animals, ammonia produced by metabolism is converted to urea in the liver. Urea is released into the blood and filtered by the kidneys. Some urea is retained in the kidney matrix, where it helps to keep a high osmolarity. Uric acid is the least toxic and needs the least water, so water loss is minimal.

Excretory structures differ across animal groups.

Structure	Animals	Note
Protonephridia (flame cells)	Flatworms (Platyhelminthes), rotifers, some annelids, Amphioxus	Excretion and osmoregulation
Nephridia	Earthworm and other annelids	Remove nitrogenous wastes, maintain fluid and ion balance
Malpighian tubules	Insects such as cockroach	Remove nitrogenous wastes and help osmoregulation
Antennal (green) glands	Crustaceans such as prawn	Excretion and osmoregulation

Human excretory system and the kidney

The human excretory system has a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

Kidneys are reddish brown and bean shaped. They lie between the levels of the last thoracic and the third lumbar vertebra, close to the dorsal inner wall of the abdominal cavity. An adult kidney is about 10 to 12 cm long, 5 to 7 cm wide and 2 to 3 cm thick. It weighs about 120 to 170 g.

The inner concave surface has a notch called the hilum. The renal artery, renal vein, nerves and the ureter pass through it.
Inside the hilum is a broad funnel-shaped renal pelvis with projections called calyces.
A tough capsule covers the kidney.
The kidney has an outer cortex and an inner medulla.
The medulla is divided into conical masses called medullary pyramids, which project into the calyces.
The cortex extends between the pyramids as renal columns (columns of Bertini).

The nephron

Each nephron has two parts: the glomerulus and the renal tubule. The glomerulus is a tuft of capillaries formed by the afferent arteriole. Blood leaves it by the efferent arteriole. The renal tubule begins with the double-walled cup-like Bowman's capsule, which surrounds the glomerulus. Glomerulus and Bowman's capsule together form the renal (Malpighian) corpuscle.

Flow of filtrate: Bowman's capsule → proximal convoluted tubule (PCT) → loop of Henle (descending limb, then ascending limb) → distal convoluted tubule (DCT) → collecting duct → renal pelvis through the medullary pyramids.

Part	Location	Epithelium
Renal corpuscle, PCT, DCT	Cortex	PCT: simple cuboidal with brush border
Loop of Henle	Dips into the medulla	Mostly squamous
Collecting duct	Cortex to medulla	Cuboidal

The brush border of the PCT increases the surface area for reabsorption.

There are two types of nephrons.

Feature	Cortical nephron	Juxtamedullary nephron
Loop of Henle	Short, enters medulla only a little	Long, runs deep into the medulla
Vasa recta	Absent or reduced	Well developed
Role in concentrating urine	Small	Major

The efferent arteriole forms a fine network of peritubular capillaries around the tubule. A minute vessel from this network runs parallel to the loop of Henle and is called the vasa recta.

Urine formation

Urine formation involves three processes in different parts of the nephron.

1. Glomerular filtration. Blood is filtered by the glomerulus (ultrafiltration). The filtering membrane has three layers: the endothelium of glomerular capillaries, the basement membrane, and the epithelium of Bowman's capsule made of podocytes. Podocytes leave minute gaps called filtration slits. All plasma constituents except proteins (and blood cells) pass into the capsule.

GFR is about 125 mL/min, which is about 180 L/day.
The kidneys receive about 1100 to 1200 mL of blood per minute, about one-fifth of the cardiac output.
Only about 1.5 L of urine is formed per day, so most of the filtrate is reabsorbed.

2. Tubular reabsorption. About 99% of the filtrate is reabsorbed. Active transport (glucose, amino acids, Na⁺) and passive transport (nitrogenous wastes, water) both occur.

3. Tubular secretion. Cells of the tubule add H⁺, K⁺ and ammonia to the filtrate. This helps to maintain ionic and acid-base balance of the blood.

Segment	Main events
PCT	Reabsorption of nearly all essential nutrients, and about 70 to 80% of electrolytes and water. Secretion of H⁺ and ammonia. Helps to maintain the pH and ionic balance of body fluids.
Descending limb of loop of Henle	Permeable to water, almost impermeable to electrolytes. Filtrate becomes more concentrated as it moves down.
Ascending limb of loop of Henle	Impermeable to water, allows transport of electrolytes. Filtrate becomes dilute as it moves up.
DCT	Conditional reabsorption of Na⁺ and water. Reabsorption of HCO₃⁻. Selective secretion of H⁺, K⁺ and NH₃.
Collecting duct	Large amount of water reabsorbed to give concentrated urine. Allows a small amount of urea into the medullary interstitium. Secretes H⁺ and K⁺ to maintain pH and ionic balance.

Concentration of the filtrate

Mammals can produce urine that is concentrated. Human kidneys can produce urine about four times as concentrated as the initial filtrate. This depends on the loop of Henle and the vasa recta, which work as a countercurrent system.

Countercurrent means that the flow in the two limbs of the loop (and in the two limbs of the vasa recta) is in opposite directions.
The interstitial fluid of the medulla has an osmolarity gradient. It is about 300 mOsmol/L in the cortex and increases to about 1200 mOsmol/L in the inner medulla.
The gradient is caused mainly by NaCl and urea.
NaCl is transported by the ascending limb of the loop of Henle to the interstitium. It is exchanged with the descending limb of the vasa recta, and returns to the interstitium by the ascending limb of the vasa recta.
A small amount of urea enters the thin segment of the ascending limb of the loop of Henle. It is carried back to the interstitium by the collecting duct.
Because of this gradient, water moves out of the collecting duct and the filtrate is concentrated as it passes through the medulla.

Value	Figure
Osmolarity of cortex interstitium	about 300 mOsmol/L
Osmolarity of inner medulla	about 1200 mOsmol/L
GFR	about 125 mL/min
Filtrate formed per day	about 180 L
Urine per day	about 1 to 1.5 L
Urea excreted per day	about 25 to 30 g

Regulation of kidney function

Hypothalamus and ADH. Osmoreceptors in the body sense changes in blood volume, body fluid volume and ionic concentration. Excess loss of body fluid activates them. They stimulate the hypothalamus to make the neurohypophysis release ADH (antidiuretic hormone). ADH increases water reabsorption in the later parts of the tubule and prevents diuresis (large urine volume). When the fluid volume rises, osmoreceptors are switched off and ADH release is reduced. ADH also constricts blood vessels and raises blood pressure.

Juxtaglomerular apparatus (JGA). The JGA is a special region formed by the cells of the DCT (macula densa) and the modified cells of the afferent arteriole (JG cells) at the point where the DCT passes close to them. A fall in glomerular blood flow, blood pressure or GFR activates the JG cells to release renin.

Renin → converts angiotensinogen to angiotensin I → angiotensin II.

Angiotensin II is a strong vasoconstrictor. It raises glomerular blood pressure and thus GFR.
Angiotensin II also stimulates the adrenal cortex to release aldosterone.
Aldosterone increases reabsorption of Na⁺ and water from the distal part of the tubule. This raises blood volume and blood pressure.

ANF (atrial natriuretic factor). An increase in blood flow to the atria of the heart releases ANF. It causes vasodilation and lowers blood pressure. It acts as a check on the renin-angiotensin mechanism.

Micturition and the role of other organs

Urine formed by the nephrons passes to the renal pelvis, then the ureter, then the urinary bladder. It is stored in the bladder until a voluntary signal comes from the central nervous system (CNS).

Micturition reflex: the bladder fills → stretch receptors in the bladder wall send signals to the CNS → the CNS sends motor signals → the smooth muscle of the bladder contracts and the urethral sphincter relaxes → urine is released. The neural mechanism that causes release of urine is called the micturition reflex. The act of passing urine is micturition.

Normal urine is light yellow, watery, slightly acidic (about pH 6.0) and has a characteristic odour. Presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine is a sign of diabetes mellitus.

Other organs also remove wastes.

Organ	Substances removed
Lungs	CO₂ (about 200 mL per minute) and a significant amount of water
Liver	Bile pigments (bilirubin, biliverdin), cholesterol, degraded steroid hormones, vitamins and drugs, in bile
Skin: sweat glands	Sweat with NaCl, small amounts of urea and lactic acid
Skin: sebaceous glands	Sebum with sterols, hydrocarbons and waxes

Disorders of the excretory system

Uremia: accumulation of urea in the blood. It may lead to kidney failure.
Haemodialysis: used for uremic patients. Blood is taken from an artery, heparin (an anticoagulant) is added, and the blood is pumped into the dialysing unit (artificial kidney). The unit has a coiled cellophane tube surrounded by dialysing fluid. This fluid has the same composition as plasma except for the nitrogenous wastes. The cellophane membrane is porous, so wastes move out along the concentration gradient. The cleared blood is returned to a vein after adding anti-heparin.
Kidney transplantation: the final method for kidney failure. A functioning kidney from a donor, preferably a close relative, is used to reduce the chance of rejection by the immune system of the recipient.
Renal calculi: stones or insoluble masses of crystallised salts (such as oxalates) formed within the kidney.
Glomerulonephritis: inflammation of the glomeruli of the kidney.

NEET traps

1. Ureotelic versus uricotelic: mammals make urea; birds and reptiles make uric acid. Marine fishes are ureotelic; bony fishes are ammonotelic.
2. Urea is made in the liver, not in the kidney. The kidney only filters it.
3. Protonephridia (flame cells) are in flatworms; nephridia are in earthworm; Malpighian tubules are in insects; antennal glands are in prawn.
4. Descending limb is permeable to water; ascending limb is impermeable to water. Do not reverse them.
5. Filtrate is hypertonic at the bottom of the loop of Henle and becomes dilute in the ascending limb.
6. Vasa recta is well developed in juxtamedullary nephrons and reduced or absent in cortical nephrons.
7. ADH acts on the later parts of the tubule (DCT and collecting duct) to increase water reabsorption. Aldosterone acts on the distal part to increase Na⁺ (and water) reabsorption. ADH comes from the neurohypophysis; aldosterone from the adrenal cortex.
8. ANF lowers blood pressure (vasodilation); angiotensin II raises it (vasoconstriction).
9. GFR is about 125 mL/min (180 L/day), but urine is only about 1.5 L/day. Do not confuse filtrate with urine.
10. The filtration barrier lets plasma proteins stay in the blood. Proteins and blood cells in urine are a sign of damage.

One-liners

1. Ammonia is the most toxic and uric acid the least toxic nitrogenous waste.
2. Insects excrete uric acid through Malpighian tubules.
3. The kidney lies between the last thoracic and third lumbar vertebra.
4. The hilum is the notch where the renal artery, renal vein and ureter pass.
5. Renal columns are cortical extensions between the medullary pyramids.
6. Glomerulus plus Bowman's capsule is the renal corpuscle.
7. Podocytes form the epithelium of Bowman's capsule.
8. The PCT has a brush border of cuboidal cells.
9. GFR is about 125 mL/min or about 180 L/day.
10. Nearly all glucose and amino acids are reabsorbed in the PCT.
11. Medullary osmolarity rises from about 300 to about 1200 mOsmol/L.
12. JG cells release renin when GFR falls.
13. Aldosterone is released from the adrenal cortex.
14. The micturition reflex is started by stretch receptors in the bladder wall.
15. Heparin is added to blood before haemodialysis and anti-heparin after it.

Practice questions

Which of the following animals is ureotelic?
1. Birds
2. Mammals
3. Bony fishes
4. Insects
Answer
B. Mammals
Mammals convert ammonia to urea in the liver and excrete urea. Birds and insects excrete uric acid; bony fishes excrete ammonia.
The excretory organs of the cockroach are
1. Nephridia
2. Antennal glands
3. Flame cells
4. Malpighian tubules
Answer
D. Malpighian tubules
Insects such as the cockroach remove nitrogenous wastes through Malpighian tubules.
Antennal (green) glands are the excretory structures of
1. Earthworm
2. Cockroach
3. Prawn
4. Planaria
Answer
C. Prawn
Crustaceans such as prawns excrete through antennal or green glands.
The notch on the inner concave surface of the kidney through which the renal artery, renal vein and ureter pass is the
1. Hilum
2. Renal column
3. Calyx
4. Renal pelvis
Answer
A. Hilum
The hilum is the notch on the concave surface of the kidney where vessels, nerves and the ureter enter or leave.
The extensions of the renal cortex between the medullary pyramids are called
1. Renal pelvis
2. Calyces
3. Renal columns
4. Renal papillae
Answer
C. Renal columns
The cortex extends between the pyramids as renal columns (columns of Bertini).
Which pair of structures lies in the renal cortex?
1. Loop of Henle and collecting duct
2. Vasa recta and loop of Henle
3. Descending limb and ascending limb of the loop
4. Bowman's capsule and PCT
Answer
D. Bowman's capsule and PCT
The renal corpuscle (glomerulus and Bowman's capsule) and the PCT are in the cortex. Loop of Henle and vasa recta dip into the medulla.
About how much glomerular filtrate is formed by both kidneys of a healthy adult per day?
1. 18 L
2. 180 L
3. 1.5 L
4. 1800 L
Answer
B. 180 L
GFR is about 125 mL/min, which is about 180 L/day.
The epithelial cells of Bowman's capsule that leave filtration slits are the
1. Podocytes
2. Juxtaglomerular cells
3. Endothelial cells
4. Macula densa cells
Answer
A. Podocytes
Podocytes form the epithelium of Bowman's capsule and are arranged to leave filtration slits.
Which substance is reabsorbed by active transport in the nephron?
1. Water
2. Glucose
3. Nitrogenous wastes
4. Urea
Answer
B. Glucose
Glucose, amino acids and Na⁺ are actively reabsorbed. Nitrogenous wastes and water are reabsorbed passively.
Which part of the loop of Henle is impermeable to water but allows transport of electrolytes?
1. Ascending limb
2. Descending limb
3. Collecting duct
4. Proximal convoluted tubule
Answer
A. Ascending limb
The ascending limb is impermeable to water, so the filtrate becomes dilute as electrolytes leave it.
The osmolarity of the interstitial fluid in the inner medulla is about
1. 300 mOsmol/L
2. 2400 mOsmol/L
3. 600 mOsmol/L
4. 1200 mOsmol/L
Answer
D. 1200 mOsmol/L
The gradient rises from about 300 mOsmol/L in the cortex to about 1200 mOsmol/L in the inner medulla.
The hormone released from the neurohypophysis that prevents diuresis is
1. ANF
2. Aldosterone
3. ADH
4. Renin
Answer
C. ADH
ADH increases water reabsorption in the later parts of the tubule and prevents diuresis.
Renin is released by
1. JG cells
2. Podocytes
3. Macula densa
4. PCT cells
Answer
A. JG cells
A fall in GFR activates the juxtaglomerular (JG) cells of the afferent arteriole to release renin.
Stretch receptors in the wall of the urinary bladder send signals to the
1. Kidney
2. Adrenal gland
3. Ureter
4. Central nervous system
Answer
D. Central nervous system
The signals go to the CNS, which sends motor signals back in the micturition reflex.
Which substance is added to blood before it enters the dialysing unit in haemodialysis?
1. Aldosterone
2. Anti-heparin
3. Heparin
4. Renin
Answer
C. Heparin
Heparin is an anticoagulant added before dialysis. Anti-heparin is added before the blood returns to the vein.
Inflammation of the glomeruli of the kidney is called
1. Uremia
2. Glomerulonephritis
3. Gout
4. Renal calculi
Answer
B. Glomerulonephritis
Glomerulonephritis is inflammation of the glomeruli.
Given below are two statements: Statement I: Uric acid excretion needs the least amount of water. Statement II: Most terrestrial reptiles excrete ammonia.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
C. Statement I is correct but Statement II is incorrect
Uric acid is excreted as pellet or paste with minimal water loss. Reptiles are uricotelic, not ammonotelic.
Given below are two statements: Statement I: The filtrate becomes more concentrated as it moves down the descending limb of the loop of Henle. Statement II: The filtrate becomes dilute as it moves up the ascending limb.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
A. Both Statement I and Statement II are correct
The descending limb is permeable to water and the ascending limb is not, so both statements are correct.
Given below are two statements: Statement I: The vasa recta is well developed in cortical nephrons. Statement II: Juxtamedullary nephrons have long loops of Henle that run deep into the medulla.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
D. Statement I is incorrect but Statement II is correct
The vasa recta is absent or reduced in cortical nephrons. Juxtamedullary nephrons have long loops.
Given below are two statements: Statement I: Aldosterone is secreted by the adrenal medulla. Statement II: ADH is released from the neurohypophysis.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
D. Statement I is incorrect but Statement II is correct
Aldosterone comes from the adrenal cortex. ADH is stored and released by the neurohypophysis.
Which of the following statements are correct? 1. Angiotensin II is a vasoconstrictor. 2. ANF causes vasodilation. 3. Renin is secreted by the macula densa cells.
1. 1 and 3 only
2. 1 and 2 only
3. 2 and 3 only
4. 1, 2 and 3
Answer
B. 1 and 2 only
Angiotensin II constricts vessels and ANF dilates them. Renin comes from JG cells, not the macula densa.
Given below are two statements: Statement I: Urea is synthesised in the tubules of the kidney. Statement II: Birds are ureotelic.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
B. Both Statement I and Statement II are incorrect
Urea is made in the liver, and birds are uricotelic. Both statements are incorrect.
Which of the following statements are correct? 1. Plasma proteins are present in the glomerular filtrate. 2. Podocytes form filtration slits. 3. The basement membrane is a layer of the filtration membrane.
1. 1 and 2 only
2. 1 and 3 only
3. 1, 2 and 3
4. 2 and 3 only
Answer
D. 2 and 3 only
Proteins are not filtered. Podocyte slits and the basement membrane are parts of the filtration membrane.
Given below are two statements: Statement I: The collecting duct reabsorbs a large amount of water when concentrated urine is formed. Statement II: The collecting duct allows a small amount of urea to enter the medullary interstitium.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
A. Both Statement I and Statement II are correct
Both are functions of the collecting duct and help to maintain medullary osmolarity.
Which of the following statements are correct? 1. Lungs remove CO₂ and a significant amount of water. 2. The liver removes bilirubin and biliverdin through bile. 3. Sebaceous glands secrete sweat containing NaCl and lactic acid.
1. 2 and 3 only
2. 1 and 3 only
3. 1 and 2 only
4. 1, 2 and 3
Answer
C. 1 and 2 only
Sweat is secreted by sweat glands. Sebaceous glands secrete sebum with sterols, hydrocarbons and waxes.
Given below are two statements: Statement I: Renal calculi are caused by inflammation of the glomeruli. Statement II: Uremia is the accumulation of glucose in the blood.
1. Both Statement I and Statement II are correct
2. Both Statement I and Statement II are incorrect
3. Statement I is correct but Statement II is incorrect
4. Statement I is incorrect but Statement II is correct
Answer
B. Both Statement I and Statement II are incorrect
Renal calculi are stones of crystallised salts such as oxalates. Uremia is accumulation of urea in blood.
Assertion (A): Birds can conserve water because they excrete uric acid. Reason (R): Uric acid is excreted as a pellet or paste with very little water.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
A. Both A and R are true and R is the correct explanation of A
Uric acid needs minimal water for removal, which explains water conservation.
Assertion (A): ADH prevents diuresis. Reason (R): ADH is released from the adrenal cortex.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
C. A is true but R is false
ADH increases water reabsorption, so A is true. It comes from the neurohypophysis, so R is false.
Assertion (A): The descending limb of the loop of Henle actively transports NaCl to the interstitium. Reason (R): The ascending limb of the loop of Henle is impermeable to water.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
D. A is false but R is true
The descending limb is almost impermeable to electrolytes. The ascending limb transports electrolytes and is impermeable to water.
Assertion (A): Ureotelic animals need a moderate amount of water for excretion. Reason (R): Urea is synthesised in the liver.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
B. Both A and R are true but R is not the correct explanation of A
Both are true, but the liver site of synthesis does not explain the water requirement.
Assertion (A): Urine volume per day is much smaller than the volume of glomerular filtrate. Reason (R): About 99% of the filtrate is reabsorbed in the tubules.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
A. Both A and R are true and R is the correct explanation of A
About 180 L is filtered but only about 1.5 L is passed as urine because of reabsorption.
Assertion (A): The cells of the proximal convoluted tubule have no brush border. Reason (R): The brush border increases the surface area for reabsorption.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Answer
D. A is false but R is true
PCT cells have a brush border, so A is false. R is a correct statement of its role.
Match List I with List II. List I: a. Planaria b. Earthworm c. Cockroach d. Prawn List II: i. Antennal glands ii. Malpighian tubules iii. Protonephridia iv. Nephridia
1. a-i, b-ii, c-iii, d-iv
2. a-iii, b-ii, c-iv, d-i
3. a-iii, b-iv, c-ii, d-i
4. a-iv, b-iii, c-ii, d-i
Answer
C. a-iii, b-iv, c-ii, d-i
Planaria has flame cells (protonephridia), earthworm nephridia, cockroach Malpighian tubules and prawn antennal glands.
Match List I with List II. List I: a. PCT b. Descending limb c. Ascending limb d. Collecting duct List II: i. Impermeable to water; filtrate becomes dilute ii. Brush border; reabsorbs most nutrients iii. Permeable to water; filtrate becomes concentrated iv. Water reabsorbed to give concentrated urine
1. a-iii, b-ii, c-i, d-iv
2. a-ii, b-iii, c-i, d-iv
3. a-iv, b-iii, c-i, d-ii
4. a-ii, b-i, c-iii, d-iv
Answer
B. a-ii, b-iii, c-i, d-iv
PCT has a brush border (ii); descending limb is water permeable (iii); ascending limb is impermeable to water (i); collecting duct gives concentrated urine (iv).
Match List I with List II. List I: a. ADH b. Aldosterone c. Renin d. ANF List II: i. JG cells ii. Neurohypophysis iii. Adrenal cortex iv. Atria of the heart
1. a-ii, b-iii, c-i, d-iv
2. a-iii, b-ii, c-i, d-iv
3. a-i, b-iii, c-ii, d-iv
4. a-ii, b-iii, c-iv, d-i
Answer
A. a-ii, b-iii, c-i, d-iv
ADH comes from the neurohypophysis, aldosterone from the adrenal cortex, renin from JG cells and ANF from the atria.
Match List I with List II. List I: a. Lungs b. Liver c. Sweat glands d. Sebaceous glands List II: i. Sterols and waxes ii. CO₂ iii. NaCl and lactic acid iv. Bilirubin
1. a-iv, b-ii, c-iii, d-i
2. a-i, b-iv, c-iii, d-ii
3. a-ii, b-iv, c-iii, d-i
4. a-ii, b-iv, c-i, d-iii
Answer
C. a-ii, b-iv, c-iii, d-i
Lungs remove CO₂, the liver bilirubin, sweat glands NaCl and lactic acid, sebaceous glands sterols and waxes.
Match List I with List II. List I: a. Uremia b. Glomerulonephritis c. Renal calculi d. Glycosuria List II: i. Inflammation of glomeruli ii. Accumulation of urea in blood iii. Stones of crystallised salts iv. Glucose in urine
1. a-i, b-ii, c-iii, d-iv
2. a-iii, b-i, c-ii, d-iv
3. a-ii, b-iii, c-i, d-iv
4. a-ii, b-i, c-iii, d-iv
Answer
D. a-ii, b-i, c-iii, d-iv
Uremia is urea accumulation, glomerulonephritis is inflammation of glomeruli, calculi are crystal stones and glycosuria is glucose in urine.
Match List I with List II. List I: a. GFR b. Urine per day c. Cortex osmolarity d. Inner medulla osmolarity List II: i. About 300 mOsmol/L ii. About 1200 mOsmol/L iii. About 125 mL/min iv. About 1.5 L
1. a-i, b-ii, c-iii, d-iv
2. a-iii, b-iv, c-i, d-ii
3. a-iii, b-iv, c-ii, d-i
4. a-iv, b-iii, c-i, d-ii
Answer
B. a-iii, b-iv, c-i, d-ii
GFR is about 125 mL/min, urine about 1.5 L/day, cortex about 300 and inner medulla about 1200 mOsmol/L.
A person has a narrowed afferent arteriole and the glomerular filtration rate falls. Which substance is released first by the juxtaglomerular apparatus?
1. Renin
2. ADH
3. ANF
4. Insulin
Answer
A. Renin
A fall in GFR activates JG cells to release renin, which starts the renin-angiotensin-aldosterone chain.
A person drinks a large amount of water. What is the expected response?
1. ADH release rises and urine is concentrated
2. ADH release rises and urine is dilute
3. ADH release falls and a large volume of dilute urine is passed
4. ADH release falls and scanty concentrated urine is passed
Answer
C. ADH release falls and a large volume of dilute urine is passed
Rise in body fluid switches off osmoreceptors, ADH falls, less water is reabsorbed and urine is dilute and plentiful.
Glucose and ketone bodies are found in the urine of a patient. This is most likely a sign of
1. Renal calculi
2. Uremia
3. Glomerulonephritis
4. Diabetes mellitus
Answer
D. Diabetes mellitus
Glycosuria and ketonuria are signs of diabetes mellitus.
In a healthy adult the GFR is 125 mL/min and urine flow is about 1 mL/min. About what percentage of the filtrate is reabsorbed?
1. About 70%
2. About 80%
3. About 99%
4. About 50%
Answer
C. About 99%
124 of 125 mL is reabsorbed, which is about 99%.
In haemodialysis, urea moves from the patient's blood into the dialysing fluid mainly because
1. ADH acts on the dialysing unit
2. A concentration gradient across the porous membrane
3. Active transport by the cellophane membrane
4. Podocytes filter the blood in the unit
Answer
B. A concentration gradient across the porous membrane
The dialysing fluid has no nitrogenous wastes, so wastes diffuse out along the concentration gradient.
Suppose the ascending limb of the loop of Henle stopped transporting NaCl into the interstitium. Which result is expected?
1. The medullary osmolarity gradient falls and urine becomes less concentrated
2. GFR rises to 180 mL/min
3. Urine becomes more concentrated
4. Aldosterone release stops
Answer
A. The medullary osmolarity gradient falls and urine becomes less concentrated
NaCl from the ascending limb builds the medullary gradient. Without it, water cannot leave the collecting duct as well, so urine is less concentrated.
A drug blocks the formation of angiotensin II in a patient. Which effect is expected?
1. GFR rises sharply
2. More aldosterone is released
3. ANF release falls to zero
4. Less vasoconstriction and less aldosterone, so blood pressure falls
Answer
D. Less vasoconstriction and less aldosterone, so blood pressure falls
Without angiotensin II there is less vasoconstriction and less aldosterone, so less Na⁺ and water are reabsorbed and blood pressure falls.

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