Explain how the sympathetic nervous system influences blood distribution and blood pressure.

The sympathetic nervous system is a part of the autonomic nervous system which is responsible for the body's 'fight or flight' response. It is activated in situations of stress, danger, or increased physical activity, which leads to a series of physiological changes that help to prepare the body. In relation to the cardiovascular system, the sympathetic nervous system plays a significant role in controlling blood distribution and blood pressure.

The sympathetic nervous system influences blood distribution by controlling the degree of constriction and dilation of blood vessels. It does this by releasing the neurotransmitters norepinephrine and epinephrine (adrenaline). When the sympathetic nervous system is activated, these neurotransmitters bind to alpha and beta receptors on the smooth muscle cells of blood vessel walls. This binding causes the smooth muscle cells to contract, resulting in vasoconstriction. Vasoconstriction narrows the blood vessels, restricting blood flow to certain areas of the body, like the skin and digestive organs, while increasing blood flow to other areas, like the muscles and brain, which are more crucial during the 'fight or flight' response.

The sympathetic nervous system also affects blood pressure by controlling heart function. Norepinephrine and epinephrine stimulate the cardiac muscle cells, increasing the heart rate and the force of heart contractions. These changes result in an increase in cardiac output, or the amount of blood pumped by the heart per minute. An increase in cardiac output contributes to a higher blood pressure.

The combined effects of constriction of blood vessels and increased cardiac output result in an overall increase in blood pressure. The sympathetic nervous system helps to maintain adequate blood flow to vital organs during periods of increased stress or physical activity. At the same time, it also ensures that blood pressure does not reach dangerously high levels by triggering mechanisms such as the baroreceptor reflex, which helps to adjust blood pressure according to the body's needs.

Overall, the sympathetic nervous system influences blood distribution and blood pressure by regulating the constriction and dilation of blood vessels and by controlling heart function. During the 'fight or flight' response, the sympathetic nervous system directs blood flow to vital organs and tissues, while increasing cardiac output, leading to an overall elevation in blood pressure. This physiological adaptation ensures the body is prepared for the challenges it may face during periods of stress or increased physical activity.