MCAT Biology : Excretory System
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Example Question #51 : Excretory System
Listed below are four structures that participate in urine storage and elimination.
1. Ureter
2. Urethra
3. Renal pelvis
4. Bladder
Which of the following is the correct order of urine flow after it exits the collecting duct?
3, 1, 4, 2
4, 2, 3, 1
2, 1, 3, 4
2, 3, 1, 4
3, 1, 4, 2
After exiting the collecting duct, urine enters the renal pelvis. The renal pelvis is part of the ureter and is found inside the medulla of the kidney. Numerous collecting ducts will pool into the renal pelvis, allowing urine to accumulate. After it exits the kidney (via the renal pelvis), urine enters the ureter where it is pushed towards the urinary bladder. In the bladder, urine is stored until it reaches a maximum threshold pressure and volume. Once this maximum is reached, the individual feels the urge to urinate and the process of urination begins. During urination, the urine is propelled via smooth muscle contraction from the urinary bladder to the urethra, and excreted from the body.
Example Question #52 : Excretory System
The basement membrane that separates the glomerular capillary from Bowman's capsule is negatively charged. What is the purpose of this?
To prevent proteins from entering the filtrate
To generate an electrical gradient for increased ion flow
To attract positvely charged substances
To increase hydrostatic pressure within the glomerular capillary
To decrease osmotic pressure within Bowman's capsule
To prevent proteins from entering the filtrate
The basement membrane is negatively charged in order to repel other negatively charged substances, specifically proteins. This is important because it ensures that proteins don't enter the filtrate, which is eventually excreted as urine. Old or malfunctioning proteins can be broken down, and their amino acids can often be recycled. Excretion of protein molecules would be extremely unfavorable.
Example Question #53 : Excretory System
Kidney stones are crystals that most commonly form from calcium and uric acid. They are typically found in the ureters, but they can form in the calyces, the collecting ducts, or even in the nephrons themselves. Suppose an obstructive kidney stone is found in a nephron. Which of the following would occur?
Increased membrane fluidity
Increased glomerular filtration rate
Increased clearance rate
Decreased membrane fluidity
Decreased glomerular filtration rate
Decreased glomerular filtration rate
An obstructive kidney stone in a nephron would impact bulk forces and filtration. Specifically, it would affect the hydrostatic pressure in Bowman's capsule. As a result, the glomerular filtration rate would decrease due to increased hydrostatic pressure in the capsule opposing filtration. Consequenty, fluid would be prevented from being filtered out of the kidney.
Example Question #504 : Biology
Which of the following correctly depicts the order of liquid waste elimination?
Papillary duct, calyces, urinary bladder, micturition
Papillary duct, urinary bladder, calyces, micturition
Micturition, calyces, urinary bladder, papillary duct
Papillary duct, calyces, micturition, urinary bladder
Papillary duct, calyces, urinary bladder, micturition
The papillary duct forms from collecting ducts in the kidney, where it travels to the calyces in the renal pelvis and then out of the kidney (via the ureter) to the bladder. Here, it is stored until micturition (urination).
Example Question #52 : Excretory System
Which of the following is not true of the function and/or structure of the rectum?
The rectum forces waste into the anal canal by use of internal and external sphincter muscles
The rectum precedes the anal canal and acts as temporary storage for feces
The rectum makes up part of the lower gastrointestinal tract and shortens as waste is forced into the anal canal
The rectum contains stretch receptors in walls that signal the urge to defecate
The rectum forces waste into the anal canal by use of internal and external sphincter muscles
While internal and external sphincter muscles are used to expel waste, these are located in the anal canal, not the rectum. The rectum precedes the anal canal and serves as storage; it signals the nervous system when it is full and defecation is needed.
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