(30 points) A car accident victim arrives int he emergency room. He has lost a l

Question

(30 points) A car accident victim arrives int he emergency room. He has lost a lot of blood due to his injuries and is in hypovolemic shock. a. How and why would this loss of blood affect his Mean Arterial Pressure and blood flow rate? Apply the formulas for the factors that affect MAP and flow rate to explain. You may want to return to the diagram provided for your assignment on blood flow to answer this question. b. Describe two homeostatic regulatory mechanisms that would be employed by his body as he is losing blood to counteract the effects of his blood loss. Include mechanisms influencing both the heart and blood vessels when answering this question. c. The emergency room staff have determined that he will need to be given a blood transfusion in order to save his life and restore homeostasis. His blood has been typed and he has been found to have Type AB- blood. Explain what that means in terms of antigens and antibodies. There has been a huge demand for blood supplies that day, and no Type AB- blood is available. What other blood types could be given to the patient and why?

Explanation / Answer

Hypovolemic shock

Hypovolemic shock occurs when more than 20 percent (one-fifth) of body’s blood or fluid supply is lost. Due to severe fluid loss, it is impossible for the heart to pump a sufficient amount of blood to the body. Hypovolemic shock can lead to organ failure.

Part A answer:

As blood volume decreases blood flow rate as well as blood pressure also decreases. Mean arterial pressure or MAP is the average pressure in a arteries during one cardiac cycle. MAP is a better indicator of perfusion to vital organs in comparison to only systolic blood pressure. MAP can be calculated approximately by adding the diastolic pressure to one-third of systolic pressure minus the diastolic pressure as given in equation:

MAP = diastolic BP + ((systolic-diastolic BP) / 3)

Among five variables which affect MAP and flow rate cardiac output, compliance, volume of the blood, viscosity of the blood, blood vessel length and diameter.

Below is the mathematical approach which shows relation between blood flow rate and different factors:

Blood flow = ? ?P r48??

Where ? s the Greek letter pi, and its value is 3.14

?P is the difference in pressure.

r4 represents the radius of the vessel to the fourth power.

? is the Greek letter eta and shows the viscosity of the blood.

? is the Greek letter lambda and shows the length of a blood vessel.

Part B answer:

Loss of blood results in drop in cardiac output as reflected by falling systolic blood pressure further results in decrease in pressure in the carotid bodies and aortic arch. The body has a number of compensatory mechanisms that become activated in an attempt to restore arterial pressure and blood volume back to normal.

Baroreceptor: Decrease in pressure triggers baroreceptors. Baroreceptors are inhibitory stretch-sensitive receptors that constantly measure arterial pressure. Decrease in arterial pressure sensed by baroreceptor activates sympathetic nervous system and then this result in initiation of neural and hormonal cascade to restore pressure back to normal. This direct neural and hormonal activation increase the heart rate and myocardial contractility and also increase vascular resistance through vasoconstriction. The diastolic blood pressure is an indirect measure of peripheral vascular resistance; thus, as the vessels constrict and vascular resistance increases, the diastolic blood pressure is maintained.

Chemoreceptor: Vasoconstriction causes reduced organ blood flow and reduced arterial pressure which results in to systemic acidosis. Systemic acidosis is sensed by chemoreceptors. The chemoreceptors further activates the sympathetic adnergic system thereby further supporting baroreceptor reflex.

Part C answer

Glycoproteins are expressed on red blood cells and difference in the terminal residue of sugar attached to these glycoproteins distinguish the A and B blood group antigens. A person lacking one or both of these antigens will have serum antibodies to these antigens. A type A individual has anti-B antibodies; a type B individual has anti-A; and a type O individual thus has anti-A and anti-B, while type AB has neither anti-A nor anti-B antibodies. As patient has AB blood blood group does not have antibodies against A as well as B antigen can receive blood from any group (with AB being preferable), but cannot donate blood to any group other than AB. They are known as universal recipients.

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