Question

1. A decrease in plasma volume will decrease plasma hydrostsatic pressure. This can be detected by the cardiovascular baroreceptors which send a signal to the cardiovascular control center which sends nervous impulses to the arterioles to constrict. Constriction decreases flow to the capillary beds, in turn decreasing flow out of the capillaries at the capillary beds served by this arteriole. This prevents further decrease in plasma volume.

• Is this an osmotic mechanism?
• Is this a homeostatic mechanism?  
• Is it negative feedback? Positive feedback?
• Define each of these terms and explain your answer to each of these questions.

Answer 1

1. No, this is not an osmotic mechanism. Osmotic mechanism involve the movement of a fluid across a semipermeable membrane toward a higher concentration of solute.

2. Yes, this is homeostatic mechanism. Homeostasis is a phenomenon of natural resistance to change in the optimal conditions, and equilibrium involves many regulatory mechanisms. All homeostatic control mechanisms involves at least three interdependent components for the variable being regulated: a receptor, a control centre, and an effector. Here receptors involved are cardiovascular baroreceptors, control center is nervous system and effector is arterioles.

3. Negative feedback occurs when some function of the output of a system, process, or mechanism is fed back in a way that leads to reduce the fluctuations in the output, while positive feedback increases the fluctuations in the output.