What is the primary purpose of autoregulation in tissues?
To increase systemic blood pressure in response to low oxygen levels.
To regulate perfusion through signals from the central nervous system.
To adjust blood flow based on local chemical and pressure signals.
To ensure constant blood flow regardless of local metabolic activity.
The Correct Answer is C
A. To increase systemic blood pressure in response to low oxygen levels: Systemic blood pressure regulation is primarily controlled by the autonomic nervous system and endocrine responses, not by tissue-level autoregulation. Autoregulation acts locally rather than influencing overall systemic pressure.
B. To regulate perfusion through signals from the central nervous system: While the CNS can influence vascular tone via sympathetic output, autoregulation is independent of central input. It relies on local factors within the tissue to adjust blood flow to meet metabolic demands.
C. To adjust blood flow based on local chemical and pressure signals: Autoregulation ensures that tissue perfusion matches local needs by responding to changes in oxygen, carbon dioxide, pH, and local blood pressure. Vasodilation or vasoconstriction occurs directly within the tissue’s arterioles to maintain optimal nutrient and oxygen delivery.
D. To ensure constant blood flow regardless of local metabolic activity: Autoregulation does not override metabolic demands; instead, it fine-tunes blood flow according to local chemical and pressure cues. Constant flow regardless of tissue activity could lead to hypoxia or excess perfusion, which autoregulation prevents.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. They have tight junctions only: While fenestrated capillaries do have tight junctions between endothelial cells, this feature is not unique to them. Continuous capillaries also have tight junctions, so this does not differentiate fenestrated capillaries.
B. They have large intercellular clefts: Large intercellular clefts are characteristic of sinusoidal capillaries, not fenestrated ones. Fenestrated capillaries have small pores rather than wide gaps between cells.
C. They are found only in the brain: Fenestrated capillaries are not restricted to the brain. In fact, the brain predominantly contains continuous capillaries that form the blood-brain barrier. Fenestrated capillaries are common in organs with high rates of filtration or absorption, such as the kidneys, intestines, and endocrine glands.
D. They contain large pores (fenestrations): Fenestrated capillaries have specialized pores in the endothelial cells called fenestrations, which allow rapid exchange of water, solutes, and small molecules between blood and tissues. These fenestrations make them more permeable than continuous capillaries while maintaining selective barrier properties.
Correct Answer is B,A,D,C
Explanation
In a major hemorrhage, the sympathetic nervous system is rapidly activated in response to decreased circulating blood volume and falling arterial pressure. Baroreceptors in the carotid sinus and aortic arch detect reduced stretch and trigger increased sympathetic outflow from the medulla. This results in the release of catecholamines, primarily norepinephrine and epinephrine, which cause tachycardia, increased myocardial contractility, and peripheral vasoconstriction. Vasoconstriction shunts blood away from nonessential organs such as the skin and gastrointestinal tract toward vital organs like the brain and heart. Additionally, sympathetic stimulation promotes venoconstriction, which helps increase venous return and temporarily supports cardiac output. These compensatory mechanisms aim to maintain blood pressure and tissue perfusion until volume can be restored.
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