Chapter 4: Urinary System of Man

Select the correct answer:

1. Excretion of hypotonic urine in humans is associated best with the

A. glomerular capsule

B. proximal convoluted tubule

C. loop of the Henle

D. distal convoluted tubule

Answer: C. loop of the Henle

Explanation: The loop of Henle establishes a concentration gradient in the medulla, which allows for the production of either concentrated or dilute (hypotonic) urine depending on the body's hydration status.

2. The walls of the ............... are made more or less permeable to water, depending on the need to conserve water:

A. ureter

B. urethra

C. fibrous capsule

D. collecting duct

Answer: D. collecting duct

Explanation: The permeability of the collecting duct to water is regulated by antidiuretic hormone (ADH). When ADH is high, the duct becomes more permeable, allowing water reabsorption and producing concentrated urine.

3. Which of the following will cause a decrease in ADH production?

A. dehydration

B. an increase in osmotic pressure of blood

C. drinking water

D. abnormally low blood pressure

Answer: C. drinking water

Explanation: Drinking water increases blood volume and decreases blood osmolarity, which inhibits ADH secretion, leading to the production of dilute urine.

4. The function of glomerulus and Bowman's capsule of the nephron is to

A. reabsorb water into the blood

B. eliminate ammonia from the body

C. reabsorb salts and amino acids

D. filter the blood and capture the filtrate

Answer: D. filter the blood and capture the filtrate

Explanation: The glomerulus and Bowman's capsule together form the renal corpuscle, which is responsible for filtering blood and collecting the filtrate.

5. In man, glucose is present in blood plasma but not in urine. This is because glucose molecules are

A. actively transported from the proximal convoluted tubule to blood capillaries

B. oxidized to supply energy for ultrafiltration

C. stored in the kidney

D. too large to enter Bowman's capsule

Answer: A. actively transported from the proximal convoluted tubule to blood capillaries

Explanation: Glucose is completely reabsorbed from the proximal convoluted tubule by active transport. It is not normally found in

urine.

6. Evidence for glomerular filtration in the kidney could be obtained by comparing the sizes of the molecules present in Bowman's capsule with those in the

A. afferent blood vessel

B. collecting duct

C. loop of Henle

D. proximal tubule

Answer: A. afferent blood vessel

Explanation: Comparing the composition of blood in the afferent arteriole with the filtrate in Bowman's capsule would show which molecules are filtered and which are retained.

7. The site and principal mechanism for the passage of glucose into the bloodstream in the human kidney is the

A. collecting duct, by active secretion

B. glomerulus, by selective reabsorption

C. glomerulus, by ultrafiltration

D. proximal convoluted tubule, by selective reabsorption

Answer: D. proximal convoluted tubule, by selective reabsorption

Explanation: Glucose is reabsorbed from the proximal convoluted tubule into the blood by active transport (secondary active transport with sodium).

8. A drug reduces mitochondrial activity in kidney nephrons. Which chemical will be present in increased amounts in the urine?

A. ammonia

B. glucose

C. uric acid

D. urea

Answer: B. glucose

Explanation: Reabsorption of glucose requires ATP produced by mitochondria. If mitochondrial activity is reduced, glucose reabsorption is impaired, leading to glucosuria (glucose in urine).

9. The water content of human blood is regulated by ADH. In which part of the nephron does regulation occur?

A. ascending limb of loop of Henle

B. descending limb of the loop of Henle

C. Bowman's capsule

D. proximal convoluted tubule

Answer: B. descending limb of the loop of Henle

Explanation: ADH primarily affects the collecting duct, but the descending limb of the loop of Henle is also involved in water reabsorption. The question may be slightly off, as ADH acts on the collecting duct. However, among the options, the descending limb is the site of passive water reabsorption. The best answer is the collecting duct, but since it's not an option, the descending limb is the closest.

10. The reason why the right kidney is slightly lower than the left is

A. the left kidney is bigger than right

B. considerable space occupied by the heart

C. considerable space occupied by the liver on the right side

D. the right kidney is bigger than the left

Answer: C. considerable space occupied by the liver on the right side

Explanation: The liver occupies a large space in the upper right abdomen, pushing the right kidney slightly lower than the left.

11. Which of the following is known as the functional unit of the kidney and is found in the cortex?

A. calyces

B. renal pyramids

C. nephrons

D. medulla

Answer: C. nephrons

Explanation: The nephron is the functional unit of the kidney. The renal corpuscles (Bowman's capsules) are located in the cortex, while the loops of Henle extend into the medulla.

12. This artery passes blood to the kidney

A. common iliac

B. cystic

C. renal

D. coeliac

Answer: C. renal

Explanation: The renal artery supplies oxygenated blood to the kidney.

13. Which structure carries urine from the kidneys to the bladder?

A. nephron

B. ureter

C. bladder

D. urethra

Answer: B. ureter

Explanation: The ureters are muscular tubes that transport urine from the kidneys to the urinary bladder.

14. The blood vessel which carries blood to the glomerulus is the

A. renal artery

B. afferent arteriole

C. renal vein

D. peritubular capillaries

Answer: B. afferent arteriole

Explanation: The afferent arteriole brings blood into the glomerulus for filtration. The efferent arteriole carries blood away.

15. The basic unit of the renal system is the

A. cortex

B. neuron

C. nephron

D. medulla

Answer: C. nephron

Explanation: The nephron is the structural and functional unit of the kidney, responsible for filtering blood and forming urine.

16. The centre of the kidney where urine collects before leaving the kidneys is the

A. glomerulus

B. proximal tubule

C. distal tubule

D. renal pelvis

Answer: D. renal pelvis

Explanation: The renal pelvis is the funnel-shaped cavity that collects urine from the collecting ducts and passes it into the ureter.

17. An organ or structure that is not a component of the urinary system is the:

A. urethra

B. urinary bladder

C. ureter

D. adrenal gland

Answer: D. adrenal gland

Explanation: The adrenal glands are endocrine glands located on top of the kidneys. They are not part of the urinary system.

18. All of the following belong to the urinary system except:

A. urethra

B. ureter

C. bladder

D. prostate

Answer: D. prostate

Explanation: The prostate is a male reproductive organ. It is not part of the urinary system, although it surrounds the urethra.

19. What portion of the nephron extends into the medulla?

A. nephron loop

B. proximal convoluted tubule

C. distal convoluted tubule

D. papillary duct

Answer: A. nephron loop

Explanation: The loop of Henle (nephron loop) extends from the cortex into the medulla and back to the cortex.

20. Fibrous connective tissue that surrounds each kidney is the:

A. cortex

B. hilum

C. medulla

D. renal capsule

Answer: D. renal capsule

Explanation: The renal capsule is a tough, fibrous layer that surrounds the kidney, providing protection and support.

1. Name the organs of the urinary system and write their major functions.

Answer: The organs of the urinary system are:

Kidneys: Filter blood to remove waste products and excess water, forming urine. They also regulate blood pressure,

electrolyte balance, and red blood cell production. Ureters: Muscular tubes that transport urine from the kidneys to the urinary bladder. Urinary Bladder: A muscular sac that stores urine temporarily until it is expelled. Urethra: A tube that carries urine from the bladder to the outside of the body.

2. Describe glomerular filtration.

Answer: Glomerular filtration is the first step in urine formation. It occurs in the renal corpuscle (glomerulus and Bowman's capsule). Blood enters the glomerulus via the afferent arteriole under high pressure. This pressure forces water, ions, glucose, amino acids, and small waste products through the filtration membrane into Bowman's capsule. Blood cells and large proteins are too large to pass and remain in the blood. The resulting fluid is called filtrate. The filtration rate is regulated by blood pressure and the diameter of the afferent and efferent arterioles.

3. Describe the countercurrent multiplier mechanism.

Answer: The countercurrent multiplier mechanism is a process in the loop of Henle that creates a concentration gradient in the renal medulla. The descending limb is permeable to water but not to solutes, so water leaves as the filtrate descends. The ascending limb is impermeable to water but actively transports sodium and chloride out. This creates a high solute concentration in the medulla, which allows the collecting duct to reabsorb water and produce concentrated urine. The vasa recta (blood vessels) act as a countercurrent exchanger to maintain the gradient.

4. Name the parts of a nephron and trace the blood supply to the nephron.

Answer: The parts of a nephron are:

1. Renal Corpuscle: Bowman's capsule and glomerulus.

2. Proximal Convoluted Tubule (PCT).

3. Loop of Henle: Descending and ascending limbs.

4. Distal Convoluted Tubule (DCT).

5. Collecting Duct. Blood Supply: Blood enters the kidney via the renal artery, which branches into segmental arteries, interlobar arteries, arcuate arteries, and interlobular arteries. The interlobular arteries give rise to the afferent arteriole, which supplies the glomerulus. Blood leaves the glomerulus via the efferent arteriole, which forms the peritubular capillaries and vasa recta. These vessels surround the tubules for reabsorption and secretion. Blood then drains into the interlobular veins, arcuate veins, interlobar veins, and finally the renal vein.

5. Name general processes which are involved with urine formation?

Answer: Urine formation involves three main processes:

1. Glomerular Filtration: Blood is filtered in the glomerulus, producing filtrate.

2. Tubular Reabsorption: Useful substances (water, glucose, amino acids, ions) are reabsorbed from the filtrate back into the blood in the tubules.

3. Tubular Secretion: Waste products and excess ions are secreted from the blood into the tubular fluid. These processes ensure that waste products are excreted while essential substances are conserved.

6. Describe urinary tract infection.

Answer: A urinary tract infection (UTI) is an infection of any part of the urinary system, most commonly the bladder (cystitis) and urethra (urethritis). It is usually caused by bacteria, especially E. coli from the digestive tract. Symptoms include a burning sensation during urination, frequent urge to urinate, cloudy or bloody urine, and pelvic pain. UTIs are more common in women due to a shorter urethra. Treatment involves antibiotics and increased fluid intake.

7. Name three urinary tract infections and bacteria responsible.

Answer: Three urinary tract infections and their causative bacteria:

1. Cystitis (bladder infection): Escherichia coli (most common), Staphylococcus saprophyticus.

2. Urethritis (urethra infection): Neisseria gonorrhoeae, Chlamydia trachomatis.

3. Pyelonephritis (kidney infection): E. coli, Proteus mirabilis, Klebsiella pneumoniae. These infections can cause pain, fever, and urinary symptoms.

8. What are the causes of kidney failure?

Answer: Kidney failure can be caused by:

Acute Kidney Injury (AKI): Sudden damage due to dehydration, severe infection, blood loss, medication, or obstruction. Chronic Kidney Disease (CKD): Gradual loss of function due to diabetes, hypertension, glomerulonephritis, polycystic kidney disease, or long-term use of certain drugs. Other causes: Autoimmune diseases, genetic disorders, and toxic exposure. Kidney failure leads to the accumulation of waste products and fluid imbalance.

9. By what physical processes do solutes enter or leave the blood during dialysis?

Answer: During dialysis, solutes move between the blood and dialysate by two physical processes:

1. Diffusion: Solutes move from an area of higher concentration to lower concentration. Waste products like urea, creatinine, and excess potassium diffuse from the blood into the dialysate.

2. Ultrafiltration: Water and dissolved solutes are forced across the semipermeable membrane by a pressure gradient. This removes excess fluid from the blood. These processes mimic the filtering and reabsorbing functions of the kidney.

10. Why do blood and dialysis flow in opposite direction?

Answer: Blood and dialysate flow in opposite directions (countercurrent flow) to maximize the concentration gradient across the semipermeable membrane. This maintains a high concentration difference along the entire length of the dialyzer, allowing for efficient diffusion of waste products from the blood into the dialysate. If they flowed in the same direction, equilibrium would be reached quickly, and less waste would be removed.

11. Suggest two problems that might occur if the dialysate was pure water.

Answer: If the dialysate were pure water, two problems would occur:

1. Hemolysis: Red blood cells would swell and burst due to osmosis, as water would move into the blood cells.

2. Electrolyte Imbalance: Essential ions (e.g., sodium, potassium, calcium) would diffuse out of the blood into the pure water, leading to dangerous electrolyte deficiencies. Therefore, dialysate must contain physiological concentrations of electrolytes.

12. Why women are more likely to acquire UTI as compared to men?

Answer: Women are more likely to acquire UTIs because their urethra is shorter (about 4 cm) and closer to the anus, making it easier for bacteria from the digestive tract to enter the urinary tract. Additionally, the female urethra lacks the antibacterial properties of prostatic fluid found in males. Sexual activity can also introduce bacteria into the urethra. Hormonal changes during pregnancy and menopause can further increase susceptibility.

13. Write the differences between:

(a) osmoregulation and osmoreceptors

Answer: Osmoregulation is the process of maintaining water and electrolyte balance. Osmoreceptors are sensory receptors that detect changes in osmotic pressure.

(b) ammonotelic and ureotelic

Answer: Ammonotelic animals excrete ammonia; ureotelic animals excrete urea.

(c) ureteric and uretotelic

Answer: Ureteric refers to the ureter; ureotelic refers to excretion of urea.

(d) proximal and distal convoluted tubule

Answer: PCT is in the cortex, reabsorbs most nutrients; DCT is in the cortex, involved in secretion and reabsorption of ions. (e) afferent and efferent arterioles

Answer: Afferent brings blood to the glomerulus; efferent carries blood away. (f) hypercalcemia and hyperuricemia

Answer: Hypercalcemia is high calcium in blood; hyperuricemia is high uric acid in blood. (g) extracorporeal shock wave lithotripsy and percutaneous nephrolithotripsy

Answer: ESWL uses shock waves to break stones; PCNL uses a surgical instrument through a small incision. (h) chronic renal failure and acute renal failure

Answer: Chronic is gradual and irreversible; acute is sudden and potentially reversible.

(i) peritoneal dialysis and haemodialysis

Answer: Peritoneal uses the peritoneum as a filter; hemodialysis uses an artificial membrane. (j) renal cortex and renal medulla

Answer: Cortex is the outer region; medulla is the inner region. (k) vasodilation and vasoconstriction

Answer: Vasodilation widens blood vessels; vasoconstriction narrows them.

(l) dialyzer and dialysate

Answer: Dialyzer is the artificial kidney machine; dialysate is the fluid used in dialysis.

1. Discuss relationship between excretory products and habitats.

Answer: The type of nitrogenous waste excreted by an organism is closely related to its habitat and the availability of water. This relationship is a key concept in comparative physiology.

1. Ammonotelic Excretion (Ammonia):

Habitat: Aquatic animals (bony fishes, aquatic amphibians, aquatic invertebrates). Product: Ammonia (NH₃). Relationship: Ammonia is highly toxic and requires a large amount of water for dilution. Aquatic animals have access to abundant water, so they can excrete ammonia directly across their gills or body surface. This is energy-efficient because ammonia is formed directly from protein metabolism without additional conversion.

2. Ureotelic Excretion (Urea):

Habitat: Terrestrial animals (mammals, adult amphibians, cartilaginous fishes). Product: Urea (CO(NH₂)₂). Relationship: Urea is less toxic than ammonia and requires less water for excretion. It is synthesized in the liver from ammonia and carbon dioxide. This adaptation allows terrestrial animals to conserve water. However, urea production requires energy (ATP).

3. Uricotelic Excretion (Uric Acid):

Habitat: Birds, reptiles, insects, and land snails. Product: Uric acid (C₅H₄N₄O₃). Relationship: Uric acid is relatively non-toxic and insoluble in water, so it can be excreted as a semi-solid paste with minimal water loss. This is crucial for animals in dry environments (deserts) or those that lay shelled eggs (birds and reptiles), as it allows them to conserve water. Uric acid production is energetically expensive.

4. Other Excretory Products:

Amino acids: Some aquatic animals excrete amino acids. Trimethylamine oxide: Marine fishes excrete this to maintain osmotic balance.

In summary, the type of nitrogenous waste is an adaptation to the availability of water in the habitat. Aquatic animals excrete ammonia, terrestrial animals excrete urea or uric acid, depending on their water conservation needs. This relationship illustrates the principle of evolutionary adaptation to environmental challenges.

2. Describe the structure and function of human kidney.

Answer: The kidneys are paired, bean-shaped organs located in the posterior abdominal wall. They are the primary organs of the urinary system, responsible for filtering blood, removing waste, and maintaining homeostasis.

External Structure:

Renal Capsule: A tough, fibrous outer covering. Hilum: A concave notch on the medial side where the renal artery, renal vein, and ureter enter and exit. Renal Cortex: The outer region, containing renal corpuscles and convoluted tubules. Renal Medulla: The inner region, containing renal pyramids (loops of Henle and collecting ducts). Renal Pelvis: A funnel-shaped cavity that collects urine and connects to the ureter.

Internal Structure (Nephron):

The nephron is the functional unit of the kidney. Each kidney contains about 1 million nephrons. Renal Corpuscle: Bowman's capsule and glomerulus. Site of filtration. Proximal Convoluted Tubule (PCT): Site of reabsorption of glucose, amino acids, and ions. Loop of Henle: Creates a concentration gradient in the medulla.

Distal Convoluted Tubule (DCT): Regulates pH and electrolyte balance. Collecting Duct: Reabsorbs water (under ADH control) and transports urine to the renal pelvis.

Functions:

1. Excretion: Removal of waste products (urea, creatinine, uric acid).

2. Regulation of Water and Electrolytes: Maintains fluid and electrolyte balance.

3. Regulation of Blood Pressure: Via renin-angiotensin-aldosterone system.

4. Regulation of Red Blood Cell Production: Secretes erythropoietin.

5. Regulation of Acid-Base Balance: Excretes H⁺ and reabsorbs HCO₃⁻.

6. Vitamin D Activation: Converts vitamin D to its active form.

In summary, the kidney is a complex organ with a highly organized structure that performs vital homeostatic functions.

3. Describe the structure of human nephron.

Answer: The nephron is the structural and functional unit of the kidney. Each human kidney contains approximately 1 million nephrons. A nephron consists of a renal corpuscle and a renal tubule.

1. Renal Corpuscle:

Glomerulus: A network of capillaries derived from the afferent arteriole. It is the site of filtration. Bowman's Capsule: A double-walled, cup-shaped structure that surrounds the glomerulus. The inner wall (visceral layer) is made of podocytes, and the outer wall (parietal layer) is simple squamous epithelium. The space between them collects the filtrate.

2. Renal Tubule:

Proximal Convoluted Tubule (PCT): Coiled tube in the cortex. It is lined with cuboidal epithelial cells with microvilli (brush

border) for reabsorption. Loop of Henle: A U-shaped tube extending into the medulla. It has a descending limb (permeable to water) and an ascending limb (impermeable to water, active transport of salts). Distal Convoluted Tubule (DCT): Coiled tube in the cortex. It is lined with cuboidal cells without microvilli. It is involved in secretion and reabsorption of ions. Collecting Duct: Receives fluid from multiple nephrons and carries it to the renal pelvis. It is lined with cuboidal or columnar cells and is regulated by ADH.

3. Juxtaglomerular Apparatus:

Located at the junction of the DCT and the afferent arteriole. It consists of juxtaglomerular cells (secrete renin) and macula densa (detects NaCl concentration).

In summary, the nephron is a highly specialized structure with distinct regions for filtration, reabsorption, secretion, and concentration of urine.

4. Discuss the 'urine formation' and mechanism of urine concentration in man.

Answer: Urine formation involves three main processes: glomerular filtration, tubular reabsorption, and tubular secretion.

1. Glomerular Filtration:

Blood enters the glomerulus via the afferent arteriole under high pressure. Water, ions, glucose, amino acids, and small waste products are filtered into Bowman's capsule. Blood cells and large proteins remain in the blood. The filtrate is similar to plasma but without proteins.

2. Tubular Reabsorption:

As the filtrate flows through the tubules, useful substances are reabsorbed into the blood. PCT: Reabsorbs about 65% of water, glucose, amino acids, and ions (Na⁺, K⁺, Cl⁻) by active transport and osmosis. Loop of Henle: Creates a concentration gradient in the medulla. Descending limb reabsorbs water; ascending limb reabsorbs salts. DCT: Reabsorbs ions and water (under hormonal control). Collecting Duct: Reabsorbs water (under ADH control) and urea.

3. Tubular Secretion:

Substances are secreted from the blood into the tubular fluid. H⁺ and K⁺ are secreted into the DCT and collecting duct to regulate pH and electrolyte balance. Ammonia is secreted into the PCT. Drugs and toxins are secreted into the PCT.

Mechanism of Urine Concentration:

The loop of Henle acts as a countercurrent multiplier, creating a high osmolarity in the medulla. The collecting duct is permeable to water (due to ADH), so water is reabsorbed by osmosis as the fluid passes through the concentrated medulla. This produces concentrated urine.

In summary, urine formation involves filtration, reabsorption, and secretion, and its concentration is regulated by the countercurrent mechanism and ADH.

5. What are kidney stones? Discuss the causes and treatment of kidney stones?

Answer: Kidney stones (renal calculi) are hard, crystalline deposits that form in the kidneys from minerals and salts in the urine.

Causes:

Dehydration: Low water intake leads to concentrated urine, promoting stone formation. Diet: High intake of oxalate (spinach, nuts), calcium, or animal protein. Obesity: Increased risk. Medical Conditions: Hyperparathyroidism, gout, urinary tract infections, and certain metabolic disorders. Medications: Some diuretics and calcium supplements. Genetics: Family history.

Types of Stones:

Calcium oxalate: Most common. Uric acid: Associated with gout. Struvite: Associated with UTIs. Cystine: Genetic disorder.

Symptoms:

Severe pain in the back and side (renal colic). Pain radiating to the lower abdomen and groin. Blood in urine (hematuria). Nausea and vomiting. Frequent urination.

Treatment:

Conservative: Drinking plenty of water, pain relievers, and medications to help pass the stone. Extracorporeal Shock Wave Lithotripsy (ESWL): Uses shock waves to break stones into smaller pieces. Ureteroscopy: A scope is passed through the urethra to remove or break the stone. Percutaneous Nephrolithotomy (PCNL): Surgical removal of large stones through a small incision in the back. Prevention: Staying hydrated, dietary changes, and medications.

In summary, kidney stones are a common and painful condition. Treatment depends on the size and type of stone. Prevention is key.

6. What is renal dialysis? Describe the two types of renal dialysis.

Answer: Renal dialysis is a medical procedure that replaces the function of the kidneys when they fail. It removes waste products and excess fluid from the blood.

1. Hemodialysis:

Procedure: Blood is pumped from the patient's body through a dialyzer (artificial kidney). The dialyzer contains a semipermeable membrane. Dialysate (a fluid with physiological concentrations of electrolytes) flows on the other side of the membrane. Waste products diffuse from the blood into the dialysate. The cleaned blood is returned to the body. Duration: Usually 3-4 hours, three times a week. Access: Requires a vascular access (fistula, graft, or catheter). Advantages: Efficient, performed in a clinic. Disadvantages: Requires frequent visits, dietary restrictions.

2. Peritoneal Dialysis:

Procedure: Dialysate is introduced into the peritoneal cavity (abdomen) through a catheter. The peritoneum acts as a natural semipermeable membrane. Waste products diffuse from the blood into the dialysate. After a dwell time, the fluid is drained. Types: Continuous Ambulatory Peritoneal Dialysis (CAPD) and Automated Peritoneal Dialysis (APD). Advantages: Can be done at home, continuous. Disadvantages: Risk of infection (peritonitis), less efficient than hemodialysis.

In summary, renal dialysis is a life-saving treatment for kidney failure. Hemodialysis and peritoneal dialysis are the two main types,

each with its own advantages and disadvantages.

7. What is kidney transplantation? Describe principles of kidney transplant. What are the problems associated with kidney transplant?

Answer: Kidney transplantation is the surgical placement of a healthy kidney from a donor into a patient with end-stage kidney failure.

Principles:

1. Donor Selection: The donor can be living (related or unrelated) or deceased. The donor kidney must be a good match for blood type and tissue type (HLA antigens) to minimize rejection.

2. Recipient Preparation: The recipient undergoes evaluation to ensure they are fit for surgery and to identify any contraindications.

3. Surgical Procedure: The donor kidney is placed in the recipient's iliac fossa. The renal artery and vein are connected to the recipient's iliac vessels, and the ureter is connected to the bladder.

4. Immunosuppression: The recipient must take immunosuppressive drugs for life to prevent rejection.

Problems Associated:

Rejection: The immune system may attack the donor kidney (hyperacute, acute, or chronic rejection). Infection: Immunosuppressive drugs increase the risk of infections. Side Effects of Drugs: Hypertension, diabetes, and kidney damage. Surgical Complications: Bleeding, infection, and blood clots. Organ Shortage: There is a shortage of donor kidneys.

In summary, kidney transplantation is the best treatment for end-stage kidney failure, but it requires careful donor-recipient matching and lifelong immunosuppression. It carries risks of rejection and infection.