Question

A person hemorrhages. What effects will this have on the Cardiovascular and renal systems? (MAP has just decreased dramatically, how will your body attempt to fix that?) Your answer should include an illustration of the negative feedback loop and you will need to explain how cardiac output, total peripheral resistance and fluid volume can affect MAP. . As always, feel free to include illustrations, but I want explanation as well. For each effector in your drawing, choose one arrow, (label each one you choose, a, b, c, and d), and explain the relationships and physiological functions that cause that arrow (how does the box before the arrow cause the box after the arrow).

Answer 1

1. Cardiac output = Heart rate X stroke volume

Blood pressure = Cardiac output x systemic vascular resistance

Cardiac output decides Systolic blood pressure and systemic vascular resistance Diastolic blood pressure.

2. Changes in blood volume affect arterial pressure by changing cardiac output.

3. An decrease in blood volume decreases central venous pressure. This decreases right atrial pressure,

right ventricular end-diastolic pressure and volume.

4. This decrease in ventricular preload decreases ventricular stroke volume by the Frank-Starling

mechanism.

Systemic vascular resistance (SVR) also known as Total peripheral resistance (TPR) refers to the resistance to

blood flow offered by all of the systemic vasculature.

Mechanisms that cause vasoconstriction increase SVR, hence it will also increase the blood pressure  and those mechanisms that cause vasodilation decrease SVR, hence also decrease the blood pressure.

Although SVR is primarily determined by changes in blood vessel diameters, changes in blood viscosity also affect SVR.

Compemsatory mechanism for haemorrhage --

On Cardiovascular System

Reduced blood volume after hemorrhage decreases venous return, ventricular filling and cardiac output.

In severe hemorrhage, there is fall in blood pressure also, However, when blood loss is slow or less, the arterial blood pressure is not affected much.

Mechanism involved in maintenance of blood pressure:

i. Usually when arterial blood pressure increases, the carotid and aortic baroreceptors are stimulated and send impulses to brain resulting in decrease in blood pressure. During hemorrhage when the arterial blood pressure falls, baroreceptors become inactivated and stop discharging impulses.

ii. This increases the vasomotor tone leading to vasoconstriction. This type of reflex vaso constriction occurs in all regions of the body except brain and heart.

iii. Vasoconstriction results in increase in the peripheral resistance

iv. Loss of blood also causes reflex constriction of veins

\v. Venoconstriction enhances the venous return, ventricular filling and stroke volume

vi. Thus, because of increased peripheral resistance and stroke volume the arterial blood pressure is restored

On Renal System -

Constriction of afferent and efferent arterioles of kidneys after hemorrhage decreases the glomerular filtration rate (GFR) very much. Therefore, the urinary output decreases.

Compemsatory mechanism by RAAS -