The superior portion of the esophagus contains smooth muscle in its wall.
Answer the following statement true (T) or false (F)
False
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During contraction of heart muscle cells ________.
A) the action potential is initiated by voltage-gated slow calcium channels B) some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores C) the action potential is prevented from spreading from cell to cell by gap junctions D) calcium is prevented from entering cardiac fibers that have been stimulated
Why is oxygen able to diffuse out of the bloodstream and into the peripheral tissues passively?
A) Oxygen has the unique ability to diffuse in or out of any tissue at any time. B) The plasma has higher quantities of dissolved proteins. C) There is a lower concentration of oxygen in the tissues than in the bloodstream. D) There is a higher concentration of oxygen in the tissues than in the bloodstream. E) None of the answers are correct.
ATP metabolism normally provides ________ percent of the ATP demands of a resting cell.
A) 25 B) 50 C) 70 D) 95 E) 100
Helper T (TH) cells recognize antigens when they are bound to a(n) ________
A) hapten B) natural killer cell C) major histocompatibility complex (MHC) protein D) immunoglobulin E) basophil