MCAT Biology : Excretory and Digestive Systems
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Example Questions
Example Question #41 : Excretory And Digestive Systems
The juxtaglomerular cells of the nephron regulate __________.
blood pressure
blood osmolarity
blood pH
urine acidity
blood osmolarity
Juxtaglomerular cells respond to low levels of sodium and secrete renin in response, which results in the release of aldosterone from the adrenal cortex. Aldosterone, as a result, will increase sodium reabsorption from the collecting duct. This will in turn increase blood pressure, however, the direct role of the cells themselves is to regulate blood osmolarity.
Example Question #1 : Excretory Regulation Mechanisms
The effect of the hormone vasopressin (ADH) on the kidney is best described by which of the following?
It increases water reabsorption in the afferent convoluted tubule
It increases sodium reabsorption in the distal convoluted tubule
It decreases the glomerular filtration rate
It increases the permeability of the collecting duct to water
It increases the permeability of the collecting duct to water
Vasopressin acts on the collecting duct in order to increase its permeability to water. This results in more water being reabsorbed, and increases blood pressure.
Example Question #6 : Excretory Regulation Mechanisms
Which of the following conditions would you not predict in a severely dehydrated patient?
Antidiuretic hormone (ADH) would be elevated
Aldosterone would be elevated
Renin would be secreted at low levels
The collecting ducts would be permeable to water
Renin would be secreted at low levels
In a severely dehydrated patient, the kidneys will be acting to preserve water in the body. Renin is secreted by the kidneys, and is the starting enzyme for a cascade that stimulates the release of aldosterone. Aldosterone raises the blood pressure of the body by acting on the distal tubule, and antidiuretic hormone (ADH) is responsible for making the collecting ducts permeable to water, thus concentrating the urine. Because of this, we would expect that renin levels would be higher than normal in a dehydrated patient.
Example Question #7 : Excretory Regulation Mechanisms
Which of the following is the function of aldosterone?
Sodium excretion
Sodium and water retention
Water retention
Sodium and water excretion
Sodium retention
Sodium and water retention
Aldosterone is released from the adrenal cortex and acts on nephrons to increase water and sodium retention. Aldosterone directly affects the synthesis of sodium ion channels and sodium-potassium pump proteins in the nephron, actively leading to sodium retention and indirectly leading to water retention based on increased blood osmolarity. Antidiuretic hormone (ADH), on the other hand, works by just retaining water without directly affecting sodium retention.
Example Question #8 : Excretory Regulation Mechanisms
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 doctor is examining a patient in a dialysis center. She notices that the patient's blood pressure is high. A common treatment of high blood pressure is a class of drugs called ACE inhibitors. After administering an ACE inhibitor, which of the following is likely to be true?
Angiotensin I levels will immediately decrease
Renin levels will remain elevated
Renin levels will immediately decrease
Sodium reabsorption in the distal tubule will increase
Aldosterone levels will remain high
Renin levels will remain elevated
The passage outlines the role of angiotensin converting enzyme (ACE) in the renin-angiotensin-aldosterone system (RAAS). Because ACE inhibitors act on the enzyme that converts angiotensin I to angiotensin II, we would expect renin and angiotensin I to remain high because they are present before the ACE step in the RAAS pathway. The hormones present after ACE action, including angiotensin II and aldosterone, however would decrease with ACE inactivation, as would sodium reabsorption. The result is generally lower blood pressure.
We can see that inhibiting the action of ACE would cause buildup of renin and angiotensin I, and a decrease in angiotensin II, which would result in a failure to retain water.
Example Question #9 : Excretory Regulation Mechanisms
What substance is produced by the juxtaglomerular apparatus in the kidney to help regulate blood volume and pressure?
Aldosterone
Angiotensin II
Angiotensinogen
Renin
Renin
The juxtaglomerular apparatus in the distal tubule monitors the filtrate that passes by to sense increases or decreases in blood volume. Granular cells in the apparatus secrete the enzyme renin, which initiates a cascade that ultimately produces aldosterone. Remember that aldosterone acts on the distal tubule to stimulate sodium reabsorption and potassium secretion.
Secretion of renin allows the conversion of angiotensinogen to angiotensin I. Angiotensin-converting enzymes (ACE) change angiotensin I to angiotensin II in the lungs, which then stimulates the adrenal cortex to release aldosterone and increase blood volume.
Example Question #47 : Excretory System
Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:
A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.
In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride 
When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more 
Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.
Which of the following side effects is/are expected in a drug that overstimulates carbonic anhydrase?
I. Increased in the blood's pH
II. Increased in the urine's pH
III. Increased bicarbonate level in the blood
I and II
II only
I and III
I only
I, II, and III
I and III
As mentioned from the passage, carbonic anhydrase inhibitors will alkalize the urine and make the blood more acidic. Therefore, the opposite will occur if one were to overstimulate the enzyme.
Example Question #491 : Biology
The process of excretion officially begins after the collecting duct since the collecting duct is the last point of reabsorption.
Urine passes through all of the following structures except the __________.
urethra
vasa recta
renal pelvis
ureters
vasa recta
The path of urine excretion from the body, after filtrate passes through the collecting ducts of the nephrons, begins in the renal pelvis. The renal pelvis collects the concentrated filtrate and transfers it to the bladder via the ureters. During urination, the bladder contracts, and urine exits the body through the urethra.
Vasa recta are capillaries found near nephrons within the kidneys.
Example Question #501 : Biology
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.
After exiting the nephron, urine is transported to the urinary bladder by which structure?
Distal tubule
Loop of Henle
Urethra
Ureter
Collecting duct
Ureter
The ureters extend from the kidneys to the urinary bladder, where urine is stored until it can be excreted from the body.
The loop of Henle, distal tubule, and collecting duct are all considered parts of the nephron and are involved in filtration and concentration of urine. After passing through the collecting duct, urine enters the ureters for transport to the bladder. From the bladder, urine enters the urethra before expulsion from the body.
Example Question #42 : Excretory And Digestive Systems
A certain individual is born with a mutation that resulted in the lack of a bladder. How will this affect the individual?
Urination will remain voluntary, but its frequency will increase
Urination will become involuntary and its frequency will increase
Urination will remain voluntary, but its frequency will decrease
Urination will become involuntary and its frequency will decrease
Urination will become involuntary and its frequency will increase
The urinary bladder is an important structure in humans that stores urine until urination. The walls of the bladder contain both smooth and somatic muscle. The smooth muscle serves to detect the degree of stretch of pressure in the bladder, stimulating the sensation of a full bladder and the need for urination. The somatic muscle allows for actual contraction of the bladder, making urination a voluntary process.
Without a bladder, the urine from the kidneys would continuously flow to the ureter and, subsequently, to the urethra where it would be excreted. Due to this continuous flow, urine would not be stored, and the person will have to urinate constantly. This means that without a urinary bladder, urination will become involuntary and the individual will urinate constantly (urination frequency will increase dramatically).
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