Question

1. What causes water to cross capillary beds from high to low hydrostatic?
2. What is the fluid movement when hydrostatic pressure exceeds colloid osmotic pressure at the arteriolar end of the capillary?
3. What is blood pressure equivalent to?
4. What is some of the fluid that is forced out of capillaries returned to the blood by?
5. What is the outward force that blood exerts on the walls of blood vessels?
6. Which neurotransmitter decreases heart rate, and thus cardiac output and blood pressure?

Answer 1

1. There is hydrostatic pressure and oncotic pressure. If hydrostatic pressure is more in the capillaries, the water will move through the endothelium into the interstitium. If it is less or relatively oncotic pressure is high, it will attract the fluid.
2. When hydrostatic pressure exceeds colloid pressure (oncotic pressure exerted by albumin), the hydrostatic pressure tends to move water out of the capillaries to maintain a balance. Therefore it will throw the fluid out of the capillaries.
3. Blood pressure is equivalent to Cardiac output x total peripheral Resistance. Cardiac output means the amount of blood pumped by heart in a minute. Total peripheral Resistance means the amount of Resistance exerted by the blood vessels on the blood flow
4. The fluid which is forced out of the capillaries go into the interstitium. The interstitium is connected to lymphatic vessels. These lymphatic vessels take up the excess fluid and through its vessels enter into the right atrium and thus the fluid returns to the blood.
5. It is called blood pressure because the force exerted by the flowing blood depends on the area. If the area is less, the force exerted will be more and if the area is more, the force exerted will be less. And force /area = pressure. Therefore it is blood pressure.
6. Heart rate is governed through the pacemakers like SA node. SA node is under control of both sympathetic and parasympathetic nervous systems. Sympathetic increase the firing of SA node and thus increase heart rate and parasympathetic decrease firing and cause decrease in heart rate. As heart rate is reduced, cardiac output is reduced (cardiac output= stroke volume x heart rate) and thus blood pressure is decreased. The neurotransmitter of Parasympathetic nervous system is ACETYLCHOLINE.