Textbook Question
Net hydrostatic pressure forces water ____ a capillary; net osmotic pressure reabsorbs water _____ a capillary.
(a) into, out of
(b) out of, into
(c) out of, out of
(d) into, into
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19. The Blood Vessels
Introduction to Hemodynamics
Problem 15
Textbook Question
The hydrostatic pressure gradient drives water _____ capillaries, and the colloid osmotic pressure draws water ____ capillaries.
a. out of; out of
b. out of; into
c. into; out of
d. into; into
Verified step by step guidance1
Understand the concept of hydrostatic pressure: Hydrostatic pressure is the force exerted by a fluid due to its weight. In the context of capillaries, it pushes water and solutes out of the capillaries into the surrounding interstitial space.
Understand the concept of colloid osmotic pressure: Colloid osmotic pressure, also known as oncotic pressure, is generated by plasma proteins (like albumin) in the blood. It pulls water back into the capillaries from the interstitial space.
Analyze the relationship between these pressures: Hydrostatic pressure and colloid osmotic pressure work in opposite directions. Hydrostatic pressure drives water out of the capillaries, while colloid osmotic pressure draws water into the capillaries.
Apply this understanding to the question: The hydrostatic pressure gradient drives water out of the capillaries, and the colloid osmotic pressure draws water into the capillaries.
Review the answer choices: Based on the explanation, the correct answer is 'b. out of; into,' as hydrostatic pressure pushes water out and colloid osmotic pressure pulls water in.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrostatic Pressure Gradient
The hydrostatic pressure gradient refers to the pressure exerted by a fluid at rest due to the force of gravity. In the context of capillaries, this pressure drives water out of the capillaries into the surrounding tissues, facilitating the exchange of nutrients and waste products. Understanding this concept is crucial for analyzing fluid movement in the circulatory system.
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Colloid Osmotic Pressure
Colloid osmotic pressure is the pressure exerted by proteins, primarily albumin, in the blood plasma that attracts water into the capillaries. This pressure counteracts hydrostatic pressure and is essential for maintaining fluid balance within the vascular system. It plays a key role in determining the direction of water movement across capillary membranes.
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Capillary Dynamics
Capillary dynamics involves the processes that govern the movement of fluids and solutes across capillary walls. It is influenced by both hydrostatic and colloid osmotic pressures, which together determine whether water moves into or out of the capillaries. A solid grasp of these dynamics is necessary for understanding physiological processes such as tissue perfusion and edema.
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