I Need Help with this Question for anatomy and physiology?

Question

Mrs. Johnson is brought to the emergency room after being involved in an auto accident. She is hemorrhaging and has a rapid, thready pulse. But her blood pressure is still within normal limits. Describe the compensatory mechanisms that are maintaining her blood pressure in the face of blood loss?

Answer 1

your question refers to the following physiology equation:

mean arterial pressure (MAP) = cardiac output (CO) * total peripheral resistance (TPR)

MAP=CO*TPR

MAP=diastolic pressure + .333(systolic-diastolic) or the average pressure in the arterial system. the difference between the MAP and the average venous pressure is the driving force for blood through capillaries

CO = stroke volume x heart rate. stroke volume represents the volume of blood the heart is able to pump with each beat.

TPR refers to the sum total of vascular resistance to the flow of blood in the systemic circulation. Because of their small radii, arterioles provide the greatest resistance to blood flow in the arterial system.

there are multiple factors that affect each of the three terms above. i will try to focus on them one at a time. in hemorrhage, there is a sudden decrease in blood volume. the body compensates to maintain tissue oxygenation by a number of mechanisms.

if the body detects a sudden decrease in blood volume this will lead to a decrease in central venous pressure which will lead a decrease in preload to the heart (the volume of blood the heart sees just prior to systolic contraction) so the stroke volume will decrease. to maintain a constant cardiac output by the equation above, the body will increase the heart rate by increasing the sympathetic nervous system input to the heart to increase the heart rate.
in addition to the increase in heart rate, the body maintains and increases the TPR through the sympathetic nervous system as well. the sympathetic nervouse system innvervates the arterioles (not the parasympathetic except the penis where it results in erections) in humans. since the arterioles play the major contributing role to TPR, in the setting of acute blood loss the sympathetic nervous system releases norepinephrine which causes vasoconstriction of the arterioles and an increase in TPR.

if both CO and TPR are increased then the MAP will be compensated for to a certain degree. of course, if her fluid status and hemorrhage aren't addressed the body will no longer be able to maintain such a work state and she will go into a state of hypovolemic shock.

i think that up front, upon initial presentation, it would be too soon for her kidneys to start holding onto fluid by sodium reabsorption, but for hypovolemia that occurred in a slower clinical scenario like protracted vomiting or diarrhea, then her kidneys would try to hold on to sodium to help hold on to water.

Answer 2

My Answer is the Same as Troy Above. I Have Some Question if Fluid Retention is Immediate, but don't Know for Sure.

Answer 3

vasoconstriction, increased cardiac output (rate, contractility), decreased urine output (increased water reabsorption)

Answer 4

you didn't state rather she was conscious or unconscious...