Question

1. In which vertebrate group is double circuit circulation first seen, and what advantage does it confer?

2. Describe how various methods of capillary exchange are able to move materials between the circulatory system and the target cells.

3. How do hydrostatic pressure, osmotic pressure, and their interaction in the capillary network contribute to material exchange in the body?

4. Relate the length of the Loops of Henle in a vertebrate species to its habitat. How does the length affect its functioning?

Answer 1

Answer 1 ) Amphibians were the first vertebrates to have a double circulatory system. The first circuit circulates blood between the heart and lungs also known as pulmonary circulation. The blood is pumped to the lungs thus receiving oxygen and releasing carbon dioxide simultaneously. The second circuit circulates blood between the heart and the rest of the body also known as systemic circulation. This circuit provides blood to rain and body parts. There are several advantages of double circuit circulation – maintenance of higher blood pressure, greater flow to tissues, and efficient supply of oxygen to different tissues of the body.

Answer 2) Capillaries are the most critical part of the circulatory system which helps in delivering nutrients and oxygen to cells. The capillaries have a diameter of 8-10 micrometer. Dissolved nutrients such as amino acids, glucose and vitamins enter the tcells by active transport. Carbon dioxide and other waste molecules from the cells to the interstitial fluids. There are four ways in which capillaries exchange solutes :

1. Simple diffusion occurs for small lipid soluble molecues and gases. Which move directly through endothelial cells.
2. Vesicular transport occurs for lipid insoluble molecules
3. Intercellular clefts allow passage of small molecules between endothelial cells
4. Fenestration where large molecules pass through

Answer 3) Exchange of materials between cells and surrounding fluid occurs via the interplay of two forces (pressures). Hydrostatic pressure is the pressure of fluid (blood) enclosed in a given space (blood vessels or heart chamber). The capillary hydrostatic pressure drives the fluid out of the capillaries into the tissues.

Osmotic pressure – as the solutes diffuse into the interstitial fluid from the blood, osmotic pressure pushes the fluid back into the blood. Osmotic pressure thus allows reabsorption of solutes. Osmoticc pressure is determined by concentration gradients in the blood and tissue fluid.

The interaction between hydrostatic and osmotic pressures is known as the net filtration pressure. Filtration occurs at the arterial end where the capillary hydrostatic pressure is greater than blood colloidal osmotic pressure. No net movement of fluid occurs near the midpoint as the two pressures are equal. At the venous end, reabsorption takes place as blood colloidal pressure is greater than capillary hydrostatic pressure.

Answer 4) Henle’s loop helps in concentrating the urine. In deserts the primary requirement is water absorption and retention. Desert animals such as kangaroo rat and rodents have long loops of Henle allowing greater water retention and concentration of urine. On the other hand animals such as beavers living in habitats with little dancer of desiccation have shorter loops which produce a dilute urine.