Multiple Choice
The only vessels that provide direct access to nearly every cell in the body are the __________.
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19. The Blood Vessels
Capillaries
Problem 7
Textbook Question
The local control of blood flow due to the action of precapillary sphincters is:
(a) Vasomotion
(b) Autoregulation
(c) Selective resistance
(d) Turbulence
Verified step by step guidance1
Step 1: Understand the role of precapillary sphincters. These are small muscular rings located at the entrance of capillary beds that regulate blood flow into the capillaries by contracting or relaxing.
Step 2: Define the term 'vasomotion'. Vasomotion refers to the rhythmic contraction and relaxation of precapillary sphincters, which causes intermittent blood flow through capillaries.
Step 3: Review the other options: 'Autoregulation' refers to the ability of tissues to regulate their own blood flow based on metabolic needs; 'Selective resistance' is not a standard term in this context; 'Turbulence' refers to irregular blood flow patterns, not controlled by sphincters.
Step 4: Connect the concept of local control of blood flow by precapillary sphincters to the term that best describes this action, which is the rhythmic opening and closing of these sphincters.
Step 5: Conclude that the correct term describing the local control of blood flow by precapillary sphincters is 'vasomotion'.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Precapillary Sphincters and Local Blood Flow Control
Precapillary sphincters are rings of smooth muscle located at the entrance of capillary beds. They regulate blood flow into capillaries by contracting or relaxing, thus controlling the distribution of blood to tissues based on local metabolic needs.
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Vasomotion
Vasomotion refers to the rhythmic contraction and relaxation of precapillary sphincters and small blood vessels. This process causes intermittent blood flow through capillary beds, allowing fine-tuned local regulation of blood supply.
Autoregulation
Autoregulation is the ability of tissues to maintain a relatively constant blood flow despite changes in arterial pressure. It involves mechanisms like myogenic responses and metabolic factors but is broader than the specific action of precapillary sphincters.
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