2. (30 points) During capillary exchange, fluid leaves and is reabsorbed by bloo
ID: 3479255 • Letter: 2
Question
2. (30 points) During capillary exchange, fluid leaves and is reabsorbed by blood capillaries.
a. Describe the normal forces (pressures) that determine the net filtration rate and how changes in those forces lead to changes from net filtration to net reabsorption as blood travels through a typical capillary bed.
b. What happens to the excess fluid that is filtered and not reabsorbed by the capillaries?
c. Explain what congestive heart failure is and how it affects filtration during capillary exchange. Contrast the effects of right and left sided congestive heart failure.
d. What force (pressure) has become imbalanced in the capillaries that leads to edema as a result of congestive heart failure? Explain why such a change would lead to edema.
e. Liver disease can also lead to edema, particularly in the abdomen, where the accumulation of fluid is called ascites. A similar problem can arise in people suffering from malnutrition where protein consumption is limited. You may have seen pictures of children with swollen bellies in textbooks. Explain how this edema can arise in terms of an imbalance in the forces associated with capillary exchange.
Explanation / Answer
Blood in the capillaries continuously exchange substances with the liquid outside these blood vessels, called interstitial fluid. This dynamic displacement of materials between the interstitial fluid and the blood is named capillary exchange.
This movement, often referred to as bulk flow, involves two pressure-driven mechanisms:
1) Hydrostatic pressure and
2)Osmotic pressure.
Hydrostatic Pressure:
The primary force driving fluid transport between the capillaries and tissues is hydrostatic pressure.
Blood hydrostatic pressure is the force exerted by the blood confined within blood vessels or heart chambers. Even more specifically, the pressure exerted by blood against the wall of a capillary is called capillary hydrostatic pressure (CHP), and is the same as capillary blood pressure.
As fluid exits a capillary and moves into tissues, the hydrostatic pressure in the interstitial fluid correspondingly rises. This opposing hydrostatic pressure is called the interstitial fluid hydrostatic pressure (IFHP).
Generally, the CHP originating from the arterial pathways is considerably higher than the IFHP, because lymphatic vessels are continually absorbing excess fluid from the tissues. Thus, fluid generally moves out of the capillary and into the interstitial fluid.
This process is called filtration.
Osmotic Pressure:
The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries—is called osmotic pressure . Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in.
B) EDEMA:
If the excess fluid that is filtered and not reabsorbed by the capillaries it leads to “edema.”
C) Congestive heart failure:
Signs/Symptoms
Left-Sided Heart Failure
Right-Sided Heart Failure
Pitting Edema (Legs, Hands)
Mild to moderate.
Moderate to severe
Fluid Retention
Pulmonary edema (fluid in lungs) and pleural effusion (fluid around lungs).
Abdomen (ascites).
Organ Enlargement
Heart.
Liver. Mild jaundice may be present.
Neck Veins
Mild to moderate raised jugular venous pressure (JVP).
Severe jugular venous pressure (JVP). Neck veins visibly distended.
Shortness of Breath
Prominent dyspnea. Paroxysmal nocturnal dyspnea (PND).
Dyspnea present but not as prominent.
d) CAUSES OF EDEMA:
Hydrostatic and osmotic pressures become imbalanced in the capillaries which leads to edema.
E) ASCITES:
When excess fluid accumulates within the peritoneal space (space between the abdominal wall and organs), this is termed "ascites."
Ascites is the accumulation of protein-containing (ascitic) fluid within the abdomen. Many disorders can cause ascites,
The increase in portal blood pressure and decrease in albumin (a protein that is carried in the blood) may be responsible in forming the pressure gradient and resulting in abdominal ascites.
Other factors that may contribute to ascites are salt and water retention.
The swollen belly is the result of not only that enlarged liver, but also the loss of muscle mass, which leads to weak abdominal muscles. Together with a weakened lymphatic system that is unable to keep up with the body’s liquid wastes, when those wastes accumulate in the abdomen, the belly becomes distended.
Signs/Symptoms
Left-Sided Heart Failure
Right-Sided Heart Failure
Pitting Edema (Legs, Hands)
Mild to moderate.
Moderate to severe
Fluid Retention
Pulmonary edema (fluid in lungs) and pleural effusion (fluid around lungs).
Abdomen (ascites).
Organ Enlargement
Heart.
Liver. Mild jaundice may be present.
Neck Veins
Mild to moderate raised jugular venous pressure (JVP).
Severe jugular venous pressure (JVP). Neck veins visibly distended.
Shortness of Breath
Prominent dyspnea. Paroxysmal nocturnal dyspnea (PND).
Dyspnea present but not as prominent.
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