2. (30 points) During capillary exchange, fluid leaves and is reabsorbed by bloo

Question

2. (30 points) During capillary exchange, fluid leaves and is reabsorbed by blood capillaries.

- 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.

- What happens to the excess fluid that is filtered and not reabsorbed by the capillaries?

- 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.

- 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.

- 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.

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Explanation / Answer

The fluid that enters the glomerular capsule is called ultrafilterate because it is formed under pressure- the hydrostatic pressure of blood. This process is similar to the formation of tissue fluid by other cappillary bed in the body in response to the Starling forces.The force favouring filtration is opposed by counterforce developed by hydrostatic pressure of fluid in glomerular capsule. Also since the protein concentration of the tubular fluid is low( less than 2 to 5 mg per 100 ml) compared that of plasma (6 to 8 g per 100 ml), the greater colloid osmotic pressure of plasma promotes the osmotic return of filtered water. When these opposing pressures are subtracted from the hydrostatic lressure of glomerular capillaries, a net filteration pressure is only about 10 mmHg is obtained. Beacause glomerular capillaries are extremely permeableand having an extensive surface area, this modest net filteration pressure produces an extraordinarily large volume of filterate. The Glo.erular filterate is the volume of filterate produced by both kidneys per minute. GFR varies from 115 ml per minute in women to 125 ml in men per minute. This is equivalent to 7.5L per hour or 180L per day (about 45 gallons).

The extra fluid filtered from capillaries and not reabsorbed are remained in interstitial space for osmotic balance, ionic balance.

Congestive heart failure is the chronic progression condition that affects the pumping power of your heart muscle.

CHF decreases the GFR as well as reabsorption rate of capillary bed.

Left CHF- Left side of heart brings oxygen rich blood from the lungs through the left atrium to the left ventricle then out into your body. when the left side of your heart is damaged or cant pump the blood it has to do work harder to send blood through your body. This causes fluid to build up in your body (edema), specially the lungs, that is why shortness of breathe is the most common symptom of it.

Right CHF- Right side of heart usually becomes weaker in response to failure on left side. The right side of the heart brings the circulated blood from the body and send it to the lungs for oxygen. When the left side of heart weakens, the right one has to work harder to compensate . again as the heart muscles looses strength, blood and fluid become backed up in the body. You may experience swelling (edema) and trouble in catching your breathe.

Edema due to liver abnormality or protein malnutrition- Chirrhosis slows the slows the normal flow of blood through the liver, thus increasing pressure in the vein that brings blood from the intestines and spleen to the liver. Portal hypertension cam cause fluud to accumulate in the legs(edema) and in abdomen (ascites).

Reason of swollen bellies due to malnutrition(kwashiorkar)- In kwashiorkar for instance, calorie intake of children affected is fine in that is it is not lacking in the energy needed by the body for the metabolic processes. However the diet is lacking certain nutirient, particularly proteins. Proteins in the body are responsible for making the osmotic balance besides their structural roles. Proteins are macromolecule means they are large in size and not easy to transport through cell membranes. The protein can pass through tge membrane through mechaniatic procedure otherwise found in blood stream or lymph. Presence of proteins in lymphatic system leads to higher osmotic pressure aa compared to water in gut this hypertonicity leads the fluid to flow from gut to lymph fluid and then blood stream. This leads to distenSion of abdomen.

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