MCAT Biology : Kidney and Nephron Physiology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #11 : Kidney And Nephron Physiology

Which of the following would be a symptom associated with diabetes mellitus?

Possible Answers:

More concentrated urine

Less-frequent urination

Increased urine volume

Decreased urine volume

Correct answer:

Increased urine volume

Explanation:

Diabetes mellitus is the product of decreased insulin effectiveness in the body. As a result, blood glucose levels are extremely high. When filtrate enters the nephron through Bowman's capsule, glucose is generally transported as well. In a healthy individual, this glucose is rapidly removed from the filtrate in the proximal convoluted tubule. In a diabetes patient, however, the level of glucose in the filtrate can overwhelm the reabsorption of the tubule, resulting in glucose in the urine. This increases urine osmolarity, causing the filtrate to retain water. The result is an increase in urine volume, resulting in more frequent urination.

Example Question #461 : Biology

Which of the following sections of the nephron does not change the osmolarity of the filtrate?

Possible Answers:

Acending loop of Henle

The distal tubule

The collecting duct

The proximal tubule

Descending loop of Henle

Correct answer:

The proximal tubule

Explanation:

The purpose of the proximal tubule is to reduce the amount of filtrate in the nephron. The proximal tubule does alter the solute concentrations in the filtrate, but it does not alter the osmolarity of the filtrate. This is because the proximal tubule is where reabsorption of solutes, proteins, and glucose takes place. Meanwhile, drugs and toxins are being secreted into the filtrate. Essentially, the volume of filtrate in the proximal tubule decreases, but the filtrate remains isotonic to the blood.

Example Question #11 : Kidney And Nephron Physiology

The descending loop of Henle in the nephron is permeable to which of the following substances?

Possible Answers:

Albumin

Water

Sodium

Potassium

All of these

Correct answer:

Water

Explanation:

The descending loop of Henle is responsible for the first step in urine concentration. Due to the high concentration of salt in the space surrounding the descending limb of the loop of Henle, water flows out of the tubule, concentrating the filtrate. The descending limb is impermeable to sodium, potassium, and albumin (the principle protein component in blood).

Example Question #14 : Kidney And Nephron Physiology

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

A nephrologist is studying a glomerulus, and notes that it is actively filtering blood normally. Which of the following blood vessels contributes most to maintaining appropriate pressure in the glomerulus?

Possible Answers:

Fenestrated capillaries

Unfenestrated capillaries

Arteries

Arterioles

Veins

Correct answer:

Arterioles

Explanation:

The glomerulus is a capillary bed. Afferent arterioles carry blood to enter the glomerulus, and efferent arterioles carry blood away from the glomerulus after filtration. Both types of arteriole are able to tighten and relax to modulate pressure within the glomerulus, driving filtration. Though fenestrated capillaries form the glomerulus itself, these vessels cannot regulate flow and pressure because they have no smooth muscle.

Example Question #12 : Kidney And Nephron Physiology

Which of the following is not a function of the kidney?

Possible Answers:

Excrete nitrogenous waste

Maintain water balance

Control blood pH

Gluconeogenesis

Correct answer:

Gluconeogenesis

Explanation:

The kidney is responsible for excreting nitrogenous waste produced by the urea cycle, maintaining water balance (and thus blood pressure), maintaining salt concentrations in the blood, and controlling blood pH by excreting or retaining protons. Blood flows into the nephrons through the glomerulus and is pushed into Bowman's capsule. The filtrate then flows through the proximal tubule, the main site for most reabsorption of glucose, proteins, and electrolytes. From the proximal tubule it enters the loop of Henle, where salt and water balance is regulated via the ion gradient in the extracellular space of the renal medulla. Finally, the filtrate enters the distal tubule and collecting duct, where salt, water, and proton balance is further regulates.

The liver is responsible for gluconeogenesis and glycogen storage.

Example Question #11 : Kidney And Nephron Physiology

The distal tubule is responsible for secreting all of the following electrolytes except __________.

Possible Answers:

calcium ions

potassium ions

protons

bicarbonate ions

Correct answer:

calcium ions

Explanation:

The distal tubule of the nephron is responsible for reabsorbing sodium and calcium and secreting potassium, hydrogen, and bicarbonate. Remember that aldosterone is responsible for increasing reabsorption of sodium and increasing excretion of potassium.

Example Question #12 : Kidney And Nephron Physiology

In a healthy individual, which of the following is filtered into the glomerular capsule in the nephron?

Possible Answers:

Platelets

Hemoglobin

Red blood cells

White blood cells

Glucose

Correct answer:

Glucose

Explanation:

The glomerulus is the capillary bed of the afferent arterioles, which filter the blood and allows the nephron to concentrate waste into urine. Glucose is a sugar is filtered into the glomerular capsule. It is, however, quickly reabsorbed back into the bloodstream in the proximal convoluted tubule, and returned to the efferent arterioles. In a healthy individual, the nephron will be able to reabsorb all the glucose that gets filtered into the glomerular capsule.

Example Question #13 : Kidney And Nephron Physiology

The main function of the Loop of Henle is to __________.

Possible Answers:

establish a concentration gradient

absorb sodium

reabsorb water

secrete potassium

Correct answer:

establish a concentration gradient

Explanation:

The main function of the Loop of Henle is to establish a concentration gradient so that water can be reabsorbed from the collecting duct and avoid being lost as urine. Although the ascending limb does absorb water, this water would be lost as urine if it were not for the concentration gradient established in the medulla of the kidney. Neither sodium nor potassium is absorbed in the Loop of Henle.

Example Question #471 : Biology

What of the following are not involved in the flow of filtrate through nephrons?

Possible Answers:

Renal artery

Proximal convoluted tubule

Collecting duct

Ascending Loop of Henle

Correct answer:

Renal artery

Explanation:

The correct path of filtrate through a nephron starts in the renal corpuscle, which is comprised of the glomerulus and Bowman's capsule. Filtrate then passes through the proximal convoluted tubule, where the majority of reabsorption takes place. It then travels through the descending and ascending limbs of the Loop of Henle, creating the counter current multiplier gradient that will allow urine to be concentration in the collecting duct. From the Loop of Henle, filtrate enters the distal convoluted tubule for final reabsorption before entering the collecting duct and being trasported to the bladder.

The renal artery is used to carry blood into the kidneys. Filtrate originates from the renal artery, but it is not a part of the nephrons.

Example Question #472 : Biology

What is the main function of the Loop of Henle within each nephron?

Possible Answers:

The Loop of Henle is the site at which the hormone vasopressin takes its greatest effect

The Loop of Henle creates a countercurrent multiplier system

The Loop of Henle is the primary site of glucose and amino acid reabsorption

The Loop of Henle contains Bowman's capsule, which is where filtrate first enters the nephron

Correct answer:

The Loop of Henle creates a countercurrent multiplier system

Explanation:

The Loop of Henle creates a countercurrent multiplier system. As the filtrate descends through the Loop of Henle, water leaves the filtrate and is reabsorbed, making the filtrate very concentrated. When the Loop of Henle ascends, salt ions leave the filtrate and are reabsorbed making the filtrate less concentrated. This creates a strong concentration of ions in the interstitial fluid toward the bottom of the loop, as compared to the concentration at the top. When filtrate flows down the collecting duct, this gradient helps concentrate the urine by removing water.

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