One substance has no membrane transporters to move it but can diffuse freely through open leak channels if there is a concentration gradient. Initially, this substance's concentrations in the filtrate and extracellular fluid are equal. Later, however, the active transport of Na+ and other solutes creates a gradient by removing water from the lumen of the tubule where it is located. What substance
is this?
A) urea
B) glucose and calcium
C) glucose
D) glucose, calcium, and urea
E) calcium
A) urea
Anatomy & Physiology
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Which of the following connective tissue cells produces collagen?
A) adipocytes B) fibroblasts C) macrophages D) mast cells E) lymphocytes
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The corticospinal pathway begins in which area of the brain?
A) somatosensory cortex B) primary motor cortex C) midbrain D) vestibular nuclei E) red nuclei
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Which muscle cells have the greatest ability to regenerate?
A) no muscle can regenerate B) smooth C) skeletal D) cardiac
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What is the name of the superior opening into the stomach?
A. Gastric portal B. Esophageal constrictor C. Ileal papilla D. Cardiac orifice E. Pyloric sphincter
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