7- Nephrons - Filtration and Reabsorption Basics

Source: https://www.youtube.com/watch?v=OEzKQmqV2WQ

Answer: B. Nephron

Explanation: The nephron is the structural and functional unit of the kidney responsible for filtration, reabsorption, secretion, and urine formation.

What is the functional unit of the kidney?

A. Glomerulus
B. Nephron
C. Bowman’s capsule
D. Collecting duct

Answer: B. Renal cortex and medulla

Explanation: Nephrons extend through both the renal cortex (Bowman’s capsule, convoluted tubules) and the renal medulla (loop of Henle and collecting duct).

In which part of the kidney are most nephrons located?

A. Renal pelvis
B. Renal cortex and medulla
C. Ureter
D. Calyx

Answer: B. Filtration of blood plasma

Explanation: The glomerulus filters blood plasma into Bowman’s capsule, forming filtrate while retaining blood cells and large proteins.

What is the main function of the glomerulus?

A. Reabsorption of nutrients
B. Filtration of blood plasma
C. Secretion of ADH
D. Storage of urine

Answer: C. 20%

Explanation: About 20% of the plasma that enters the glomerulus passes through as filtrate.

Approximately what percentage of plasma entering the glomerulus is filtered into Bowman’s capsule?

A. 5%
B. 10%
C. 20%
D. 50%

Answer: C. Filtrate

Explanation: Once plasma is filtered into Bowman’s capsule, it is referred to as filtrate, not blood plasma or urine yet.

The fluid that enters Bowman’s capsule is called:

A. Plasma
B. Lymph
C. Filtrate
D. Urine

Answer: B. Reabsorption of water and nutrients

Explanation: The PCT reabsorbs about two-thirds of filtered water and most nutrients like glucose, amino acids, and vitamins.

What is the primary function of the proximal convoluted tubule (PCT)?

A. Filtration
B. Reabsorption of water and nutrients
C. Active secretion of waste
D. Storage of urine

Answer: B. Water

Explanation: The descending limb allows water to diffuse out via osmosis due to the high salt concentration in the medulla.

The descending limb of the nephron loop is primarily permeable to:

A. Sodium ions
B. Water
C. Glucose
D. Proteins

Answer: B. Impermeable to water

Explanation: The ascending limb is impermeable to water but actively transports sodium and chloride ions out, maintaining medullary salinity.

The ascending limb of the nephron loop is:

A. Permeable to water
B. Impermeable to water
C. Only permeable to glucose
D. Responsible for urine storage

Answer: B. Active transport of Na⁺ and Cl⁻ in the ascending limb

Explanation: Sodium and chloride ions are actively pumped out of the ascending limb, producing the medulla’s high salt concentration.

What process creates the salty environment in the renal medulla?

A. Osmosis
B. Active transport of Na⁺ and Cl⁻ in the ascending limb
C. Filtration in the glomerulus
D. Diffusion of glucose

Answer: C. Antidiuretic hormone (ADH)

Explanation: ADH (antidiuretic hormone or vasopressin) increases water permeability, allowing reabsorption when the body is dehydrated.

Which hormone regulates water reabsorption in the distal convoluted tubule and collecting duct?

A. Insulin
B. Aldosterone
C. Antidiuretic hormone (ADH)
D. Epinephrine

Answer: D. Urine becomes more concentrated

Explanation: ADH increases water reabsorption, concentrating urine and reducing urine volume.

What happens when ADH secretion increases?

A. More urine is produced
B. Urine becomes more dilute
C. Less water is reabsorbed
D. Urine becomes more concentrated

Answer: B. Dilute and light-colored

Explanation: Without ADH, water is not reabsorbed, producing large volumes of dilute urine.

In the absence of ADH, urine will be:

A. Concentrated and dark
B. Dilute and light-colored
C. Full of proteins
D. Acidic

Answer: B. Afferent arteriole

Explanation: The afferent arteriole delivers blood into the glomerulus, while the efferent arteriole carries it away.

Which blood vessel brings blood to the glomerulus?

A. Renal vein
B. Afferent arteriole
C. Efferent arteriole
D. Pulmonary vein

Answer: C. Red blood cells

Explanation: Red blood cells and large proteins are too big to pass through the glomerular filtration membrane.

Which of the following substances normally does NOT pass into the filtrate?

A. Glucose
B. Amino acids
C. Red blood cells
D. Water

Answer: C. Hydrostatic pressure (blood pressure)

Explanation: Blood pressure forces plasma through the glomerular capillaries into Bowman’s capsule — this is glomerular filtration.

What drives filtration at the glomerulus?

A. Active transport
B. Osmotic pressure
C. Hydrostatic pressure (blood pressure)
D. Hormonal stimulation

Answer: C. Collecting duct

Explanation: The collecting duct gathers filtrate from multiple nephrons and delivers it toward the calyces and renal pelvis.

Which structure collects urine from many nephrons?

A. Proximal tubule
B. Loop of Henle
C. Collecting duct
D. Glomerulus

Answer: B. To filter blood, reabsorb needed substances, and form urine

Explanation: The nephron filters blood, reabsorbs essential molecules, and removes wastes in the form of urine.

Which of the following best describes the overall function of the nephron?

A. To store urine
B. To filter blood, reabsorb needed substances, and form urine
C. To secrete hormones
D. To regulate body temperature

Answer: C. Proximal convoluted tubule

Explanation: The PCT reabsorbs most nutrients and the majority of water filtered from the blood.

Where does most nutrient reabsorption occur?

A. Bowman’s capsule
B. Loop of Henle
C. Proximal convoluted tubule
D. Collecting duct

Answer: B. It filters almost everything, then reabsorbs what the body needs

Explanation: The kidney first filters many substances (even useful ones) and then selectively reabsorbs what is needed.

Which of the following is TRUE about the kidney’s “inefficient” design?

A. It filters only waste products
B. It filters almost everything, then reabsorbs what the body needs
C. It doesn’t perform reabsorption
D. It skips the filtration process

Answer: A. Collecting duct → Calyx → Ureter → Bladder

Explanation: Urine flows from the collecting duct → minor calyx → major calyx → renal pelvis → ureter → bladder.

Which of the following sequences correctly traces the flow of urine from the nephron onward?

A. Collecting duct → Calyx → Ureter → Bladder
B. Loop of Henle → Calyx → Ureter → Bladder
C. Bowman’s capsule → Calyx → Bladder
D. Collecting duct → Urethra → Calyx

Answer: C. 180 liters

Explanation: Roughly 180 liters of plasma are filtered through the glomeruli into Bowman’s capsules every 24 hours. Most of this fluid is reabsorbed; only about 1–2 liters become urine.

About how much blood plasma is filtered through the kidneys each day?

A. 18 liters
B. 80 liters
C. 180 liters
D. 800 liters

Answer: B. They are too large to pass through the filtration membrane

Explanation: The filtration membrane in the glomerulus has small pores that allow water and small solutes to pass but block large proteins and blood cells.

Why don’t red blood cells and plasma proteins enter the filtrate?

A. They are reabsorbed immediately
B. They are too large to pass through the filtration membrane
C. They are secreted later in the tubules
D. They dissolve in water

Answer: B. It drains blood away from the glomerulus

Explanation: The efferent arteriole carries blood away from the glomerulus and leads to the peritubular capillaries, where reabsorption occurs.

What is the function of the efferent arteriole?

A. It carries blood to the kidney
B. It drains blood away from the glomerulus
C. It delivers blood to the ureter
D. It filters plasma into Bowman’s capsule

Answer: C. Peritubular capillaries

Explanation: The peritubular capillaries (and the vasa recta in juxtamedullary nephrons) surround nephron tubules to allow reabsorption of water, ions, and nutrients back into the blood.

The network of capillaries surrounding the nephron tubules is called:

A. Vasa recta
B. Glomerulus
C. Peritubular capillaries
D. Cortical veins

Answer: B. Osmosis

Explanation: Osmosis moves water from areas of low solute concentration (filtrate) to high solute concentration (salty medulla/bloodstream).

Which process primarily drives water movement from the nephron into the blood?

A. Diffusion
B. Osmosis
C. Active transport
D. Secretion

Answer: B. Ascending limb of the loop of Henle

Explanation: The ascending limb uses ATP to actively pump sodium and chloride ions out, maintaining the medullary salt gradient necessary for water reabsorption.

Which portion of the nephron consumes the most energy (ATP)?

A. Bowman’s capsule
B. Ascending limb of the loop of Henle
C. Proximal convoluted tubule
D. Collecting duct

Answer: B. Proximal convoluted tubule

Explanation: Glucose and other nutrients are almost completely reabsorbed in the proximal convoluted tubule (PCT) under normal conditions.

Where is glucose normally reabsorbed in the nephron?

A. Bowman’s capsule
B. Proximal convoluted tubule
C. Loop of Henle
D. Collecting duct

Answer: C. Saturation of glucose transporters in the nephron

Explanation: When blood glucose levels exceed the renal threshold, glucose transporters in the PCT become saturated, and glucose spills into the urine (a condition known as glycosuria, common in diabetes mellitus).

If glucose appears in the urine, it most likely indicates:

A. Low blood sugar
B. Excessive ADH production
C. Saturation of glucose transporters in the nephron
D. Damage to the bladder

Answer: C. More water is reabsorbed, and urine becomes concentrated

Explanation: Dehydration triggers increased ADH release, making the distal tubule and collecting duct more permeable to water, concentrating the urine.

During dehydration, which of the following occurs?

A. ADH secretion decreases
B. Distal tubule and collecting duct become less permeable to water
C. More water is reabsorbed, and urine becomes concentrated
D. Urine output increases

Answer: C. Opposite flow of filtrate and blood to maximize exchange of solutes and water

Explanation: The countercurrent mechanism involves filtrate in the loop of Henle flowing in the opposite direction to blood in the vasa recta. This enhances exchange of salts and water, maintaining the medullary concentration gradient.

Which of the following best describes the countercurrent mechanism in the nephron loop?

A. Flow of filtrate in the same direction as blood flow
B. Active secretion of glucose
C. Opposite flow of filtrate and blood to maximize exchange of solutes and water
D. Direct hormone exchange between tubules