c) How going from laying to standing affects arterial blood pressure in the head region?
When we are laying down the Mean Arterial Pressure (MAP) is at the same level of the heart which is about 100 mm Hg. When we try to stand up from the lying position, our head is placed above our heart and gravity starts to pull the blood back downwards to our heart and feet. Return of venous blood is reduced and this leads to a decrease in cardiac stroke volume and decline in mean arterial pressure which is reduced to 60-70 mm Hg. This decreases the flow of blood to head. In response to this reduction in arterial blood pressure in the brain, parasympathetic nervous system is withdrawn and sympathetic nervous system is activated to pump more blood to head region via increased heart rates.
d) How the baroreceptors reflex explains the higher HRs during standing
When a person stands up, baroreceptor reflexes are rapidly activated to restore arterial pressure so that mean arterial pressure normally is not reduced by more than a few mmHg when a person is standing compared to lying down. However, in order to maintain this normal mean arterial pressure, the person who is standing upright has increased systemic vascular resistance (sympathetic mediated), decreased venous compliance (due to sympathetic activation of veins), decreased stroke volume (due to decreased preload), and increased heart rate (baroreceptor-mediated tachycardia).
c) How going from laying to standing affects arterial blood pressure in the head region?
When we are laying down the Mean Arterial Pressure (MAP) is at the same level of the heart which is about 100 mm Hg. When we try to stand up from the lying position, our head is placed above our heart and gravity starts to pull the blood back downwards to our heart and feet. Return of venous blood is reduced and this leads to a decrease in cardiac stroke volume and decline in mean arterial pressure which is reduced to 60-70 mm Hg. This decreases the flow of blood to head. In response to this reduction in arterial blood pressure in the brain, parasympathetic nervous system is withdrawn and sympathetic nervous system is activated to pump more blood to head region via increased heart rates.
d) How the baroreceptors reflex explains the higher HRs during standing
When a person stands up, baroreceptor reflexes are rapidly activated to restore arterial pressure so that mean arterial pressure normally is not reduced by more than a few mmHg when a person is standing compared to lying down. However, in order to maintain this normal mean arterial pressure, the person who is standing upright has increased systemic vascular resistance (sympathetic mediated), decreased venous compliance (due to sympathetic activation of veins), decreased stroke volume (due to decreased preload), and increased heart rate (baroreceptor-mediated tachycardia).
