Which statement about simple diffusion is correct?
It uses the Na+/K+ pump.
It moves molecules down their concentration gradient without energy.
It is the main mechanism for glucose absorption.
It requires a specific receptor for each solute.
The Correct Answer is B
A. It uses the Na+/K+ pump: This pump is an example of primary active transport, which requires ATP to move ions against their concentration gradients. Simple diffusion is a passive process that occurs spontaneously without the use of molecular pumps. It relies on kinetic energy rather than metabolic energy.
B. It moves molecules down their concentration gradient without energy: This is the fundamental definition of passive transport across a semi-permeable membrane. Molecules naturally migrate from areas of high concentration to areas of low concentration until equilibrium is reached. No cellular energy or ATP is consumed during this process.
C. It is the main mechanism for glucose absorption: Glucose is a large, polar molecule that cannot easily pass through the lipid bilayer via simple diffusion. It requires secondary active transport (SGLT) and facilitated diffusion (GLUT) to enter and exit renal cells. Its absorption is strictly carrier-mediated in the nephron.
D. It requires a specific receptor for each solute: Receptors and carrier proteins are characteristics of facilitated diffusion and active transport. Simple diffusion involves the movement of small, non-polar, or lipid-soluble substances directly through the phospholipid bilayer. It is characterized by a lack of specificity and saturation.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Reduced blood pressure: While a significant loss of fluid through high GFR can eventually lower blood volume, an increase in GFR is often a result of high blood pressure. High GFR itself does not immediately reduce pressure through a primary mechanism. It is a consequence of hemodynamics rather than a cause.
B. No change in urine volume: Renal physiology dictates that an increase in the filtered load typically results in a higher volume of fluid entering the tubules. Unless tubular reabsorption increases proportionally, the final urine volume must change. The volume of filtrate directly influences the volume of the end product.
C. Decreased urine production: This would only occur if the tubular reabsorption rates significantly exceeded the increased rate of filtration at the glomerulus. Under standard physiological conditions, a higher GFR provides more substrate for excretion. Decreased production is associated with low GFR or high ADH levels.
D. Increased urine production: A higher GFR elevates the volume of ultrafiltrate entering the proximal convoluted tubule each minute. This overwhelms the standard reabsorptive capacity of the nephrons, leading to a greater volume of fluid reaching the collecting ducts. Consequently, the total daily urine output increases significantly.
Correct Answer is D
Explanation
A. Hormones reduce the need for filtration during low activity: The metabolic need to clear wastes and maintain electrolyte balance is continuous. While hormones like ANP or Angiotensin II can modulate GFR, they do not eliminate the baseline requirement for stable filtration. Stability is maintained by local mechanisms.
B. The liver compensates for changes in renal pressure: The liver is not involved in the autoregulation of renal blood flow or glomerular pressure. Renal autoregulation is an intrarenal process that occurs independently of other organ systems. The kidney manages its own perfusion through local vascular responses.
C. Blood volume stays constant regardless of physical activity: Physical activity causes significant shifts in blood volume due to sweating and fluid redistribution to muscles. Despite these systemic changes, the kidney utilizes autoregulation to protect the glomerulus from fluctuations. Stable volume is a result, not the cause.
D. Intrinsic controls like myogenic and tubuloglomerular feedback adjust afferent arteriole tone: Autoregulation allows the kidney to maintain a constant GFR across a wide range of systemic blood pressures (80-180 mmHg). The myogenic response and feedback from the macula densa adjust afferent resistance to keep glomerular pressure steady.
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