MCAT Biology : Excretory and Digestive Systems
Study concepts, example questions & explanations for MCAT Biology
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Example Questions
Example Question #31 : Kidney And Nephron Physiology
Which of the following structures will be found in the renal medulla?
I. Glands that secrete aldosterone
II. Loop of Henle
III. Distal convoluted tubule
I and III
II only
I only
I and II
II only
Recall that the renal medulla is the inner portion of the kidney. A nephron spans both the renal cortex and the renal medulla. Structures such as the glomerulus (capillary bed), Bowman's capsule, and the proximal and distal convoluted tubules are found in the renal cortex, whereas the loop of Henle is found in the renal medulla. The collecting duct (the structure that transports urine to the renal pelvis) spans both the renal cortex and the renal medulla.
As mentioned above, distal tubules are found in the renal medulla and function to reabsorb sodium ions. Reabsorption of sodium ions inside the nephron (for example in the distal tubules) is facilitated by the hormone aldosterone. Aldosterone is a steroid hormone that is produced in glands inside the adrenal cortex (in the adrenal gland, rather than the kidney).
Example Question #482 : Biology
Which of the following is true regarding a nephron?
Nephrons are only found in the adrenal medulla
A nephron is the functional unit of a neuron
Filtration begins in nephrons’ capillary beds, called the collecting duct
Nephrons create urine, but they cannot store urine
Nephrons create urine, but they cannot store urine
A nephron is the functional unit of kidneys. It is the site of filtration, secretion, and reabsorption (processes essential for urine production).
Nephrons contain several structures that facilitate the proper excretion of waste through urine. A nephron contains structures that are found in both the adrenal medulla (inner region) and the adrenal cortex (outer region) of the kidneys; therefore, a single nephron spans both the adrenal medulla and the adrenal cortex. The first step in urine production occurs at the capillary beds of nephrons. Blood arrives at these capillary beds, known as the glomerulus, and initiates filtration. Filtration is the process by which potential waste products in the blood are filtered into the nephron, where they will ultimately become urine.
Remember that nephrons are the site of urine production; they do not store the urine. Once complete, urine exits the kidneys and is stored in the bladder. The bladder stores urine until it reaches the maximum capacity, causing smooth muscle around the organ to stretch. Once this maximum is reached the individual feels the urge to urinate, and the urine is excreted via the urethra.
Example Question #31 : Excretory System
In the urinary system, the ureter is most directly associated with the __________.
adrenal gland
liver
renal pelvis
renal vein
renal pelvis
The renal pelvis (hollow structure within the kidney) narrows to become the ureter, which leads to the bladder.
Example Question #32 : Kidney And Nephron Physiology
Which components of the nephron can be found in the renal medulla?
The loop of Henle and the collecting duct
The entire nephron can be found within the cortex of the kidney
The loop of Henle and the glomerulus
The proximal and distal convoluted tubules
The loop of Henle and the collecting duct
The loop of Henle descends into the medulla before ascending back into the cortex. The collecting duct, which ends the nephron, extends into the medulla.
Example Question #33 : Kidney And Nephron Physiology
Which of the following is true of a functioning kidney?
All blood solutes pass from the glomerulus into Bowman's capsule, adding to the volume of the filtrate
Only water can enter into Bowman's capsule by passive diffusion
Macromolecules, such as proteins, do not enter Bowman's capsule due to the impermeability of the podocyte membrane
Glucose, water, and ions permeate the visceral layer of Bowman's capsule to enter the blood vessels of the glomerulus
Macromolecules, such as proteins, do not enter Bowman's capsule due to the impermeability of the podocyte membrane
The visceral layer of Bowman's capsule is permeable to small blood solutes. Blood cells and most macromolecules remain in the blood stream.
One answer choice is nearly correct: "Glucose, water, and ions permeate the visceral layer of Bowman's capsule to enter the blood vessels of the glomerulus." While these solutes do in fact permeate the membrane, they exit the blood vessels of the glomerulus to enter Bowman's capsule.
Example Question #31 : Kidney And Nephron Physiology
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 statement(s) will contradict carbonic anhydrase inhibitors' usefulness in patients with hypertension?
The reabsorption of 
All of these
Water is only reabsorbed in the collecting tubule of the kidneys
None of these
The reabsorption of 
Water is only reabsorbed in the collecting tubule of the kidneys
In patients with hypertension, the blood volume is too high resulting in high blood pressure. carbonic anhydrase inhibitors will prevent water absorption by preventing sodium chloride reabsorption. As described from the passage, without sodium reabsorption at the proximal tubule, there will be no electrochemical drive for the reabsorption of water. carbonic anhydrase inhibitors mainly work on the proximal tubule where the majority of water reabsorption occurs.
Example Question #482 : Biology
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.
Based on the passage, which of the following statements, if true, would contradict the effectiveness of carbonic anhydrase inhibitors as a treatment?
The distal tubule of the kidney is impermeable to water
The proximal tubule of the kidney is impermeable to water
None of these
When sodium chloride is absorbed, the electric force created will pull magnesium with greater force than water
Even in a basic environment, sometimes an acidic molecule is able to retain it's proton
The proximal tubule of the kidney is impermeable to water
The proximal tubule has a high permeability for water. In patients with hypertension and/or heart failure, blocking the reabsorption of water at the proximal tubule will lower the blood's volume and blood's pressure. Therefore, if the proximal tubule is impermeable to water, then regulating the site with a carbonic anhydrase inhibitor has no purpose.
Example Question #1 : Excretory Regulation Mechanisms
Aldosterone is a key hormone used by the kidneys during urine formation.
What is the function of aldosterone in the kidneys?
Aldosterone increases the reabsorption of sodium from nephron filtrate
Aldosterone decreases the reabsorption of sodium from nephron filtrate
Aldosterone helps to decrease blood pressure
Aldosterone increases the amount of urine production
Aldosterone increases the reabsorption of sodium from nephron filtrate
Aldosterone increases the reabsorption of sodium from nephron filtrate.
The reabsorption of sodium leads to reabsorption of water, which makes the urine more concentrated. Increasing aldosterone production would lead to increased blood pressure, since more water is retained in the blood stream.
Example Question #31 : Excretory And Digestive Systems
What is the role of antidiuretic hormone (ADH)?
ADH decreases the reabsorption of water from the loop of Henle
ADH increases the reabsorption of water from the loop of Henle
ADH increases the reabsorption of water from the collecting duct
ADH decreases the reabsorption of water from the collecting duct
ADH increases the reabsorption of water from the collecting duct
Antidiuretic hormone, also known as vasopressin, increases the reabsorption of water from the collecting duct. It increases the permeability of the collecting duct, which allows water to be reabsorped and makes the urine more concentrated.
You can remember what antidiuretic hormone does by remembering that diuetics increase urine production; therefore an ANTIdiuretic will decrease urine production.
Example Question #3 : Excretory Regulation Mechanisms
Which of the following would most likely NOT happen in the excretory system if a person has not drunk water for an extended period of time?
Decrease in urine volume
Increase in blood volume
Decrease in sodium
Increase in aldosterone secretion
Increase in antidiuretic hormone secretion
Increase in blood volume
The signal to increase water reabsorption in the nephrons comes from antidiuretic hormones and aldosterone. The urine volume also decrease in an attempt to retain the fluids already present in the body. Since the body is trying to conserve the fluids it has and there are no incoming fluids, the blood volume should not increase.
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