When a vessel is damaged, chemicals are released from the vessel walls that attract platelets to the site of the damage. As they accumulate, more chemicals that attract more platelets to the area until the bleeding stops. This represents ________ feedback, with the platelets acting as the ________.
A. positive; effectors
B. negative; integrating center
C. negative; sensors
D. positive; integrating center
Answer: D
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Accommodation of the lens occurs when
A. the lens becomes more spherical. B. parasympathetic axons stimulate the ciliary muscles. C. ciliary muscles contract. D. the ciliary body moves closer to the lens. E. All of these choices are correct.
Muscle tissue possesses contractility, also known as the ability to ________.
A. swell B. mutate C. shorten D. strengthen
Eileen is a strict vegan and therefore eats no animal products. She develops an anemia that her doctor thinks is caused by a nutritional deficiency. Which of the following is the likeliest candidate?
A) iron deficiency B) vitamin B12 deficiency C) lack of intrinsic factor D) vitamin K deficiency E) vitamin B6 deficiency
At rest, skeletal muscles receive approximately what percentage of blood pumped by the heart?
A. About 25% B. About 10% C. About 2% D. About 75% E. About 50%