1. (30 points) A car accident victim arrives int he emergency room. He has lost
ID: 3523463 • Letter: 1
Question
1. (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?
2. (20 points) Kwashiorkor is a condition that occurs due to insufficient protein in the diet. It develops in malnourished children in poverty stricken nations. One major symptom of this condition is a swollen abdomen due to fluid build-up (also known as ascites). Ascites also occurs in people with cirrhosis of the liver as the hepatocytes are destroyed.
a. Describe what happens normally to balance fluid loss with recovery as blood flows through capillaries throughout the body.
b. Explain why ascites will develop in these malnourished children and those with cirrhosis of the liver. Apply the pressures associated with fluid exchange at capillary beds to your explanation.
3. (20 points) A patient with congestive heart failure is suffering from poor cardiac output. Her ejection fraction is 40%. As a result, her organs are poorly perfused with oxygenated blood and she tires easily.
a. What is ejection fraction, how is it calculated, and how does her ejection fraction compare to that of a normal, healthy heart?
b. Cardiac output may be improved by increasing the strength of ventricular contractility. Explain how contractility could be increased in cardiac muscle cells. Focus on how muscle fibers produce tension and how that tension can be increased during muscle contraction. (Hint: Ca2+ ions are important here).
4. (20 points) An individual stands up rapidly from a lying position and becomes light-headed due to a drop in blood pressure in the brain. This is known as postural hypotension. The body responds by triggering the baroreceptor reflex that targets the heart and blood vessels.
a. Explain how heart rate could be increased due to the baroreceptor reflex. Include which cells are involved and the electrical changes that occur in the cells to influence heart rate. Make sure to discuss what is happening at the cellular level and focus on specific ions/gated ion channels that affect membrane potential.
b. Explain how blood vessels would be affected by the baroreceptor reflex and why this would help alter blood pressure. What cells are functioning as the effectors in this mechanism and what are they doing?
5. (30 points) Valvular stenosis and valvular regurgitation are diseases of the heart valves that can affect blood flow and cardiovascular function.
a. Explain how heart valves normally work to ensure single-direction blood flow and why that is important to normal cardiovascular function. Include an explanation of the forces involved in causing the valves to open and close.
b. Describe how either of these conditions in the mitral valve would affect blood flow and cardiac output.
c. These conditions may lead to secondary pulmonary hypertension (high blood pressure in the pulmonary circuit) and pulmonary edema (fluid build up in and around the lungs). Explain why these secondary diseases would occur and why they would occur in the pulmonary, rather than the systemic, circuit. Incorporate factors that affect blood flow and pressure, as well as capillary exchange, in your answer.
Explanation / Answer
1. (a) Mean arterial pressure(MAP)= (SBP +2DBP)/ 3. Here, SBP is systolic blood pressure and DBP is diastolic blood pressure. Because of blood loss, SBP and DBP would decrease, hence MAP would also decrease.
Blood flow rate can also be called cardiac output(CO). CO= Stroke volume* heart rate. Stroke volume is the amount of blood ejected by heart per beat. Heart rate is the number of beats per minute. Since blood is lost from the body, less amount is left for the heart to pump, decreasing heart rate. Less amount is ejected by the heart per beat, decreasing stroke volume. Thus CO or blood flow rate decreases.
(b) Baroreceptor reflxes- Baroreceptors are present in walls of blood vessels and heart chambers. They respond when they are streched and this happens in presence of blood. They send electrical impulses to cardiovascular center to regulate blood flow. During blood loss, impulse transmission is decreased and sympathetic stimulation of heart decreases, leading to increase in the cardiac output. Blood vessels are also sympathetically stimulated, which causes their constriction. Hence, this leads to an increase in blood pressure.
Renin Angiotensin Aldosterone Mechanism- When blood flow decreases, cells in juxtaglomerular apparatus of kidneys secrete renin. Renin converts angiotensinogen into active angiotensin I, which is converted to angiotensin II inside lungs. Angiotensin II acts a vasoconstrictor, leading to rise in blood pressure. It also increases sodium and water reabsorption in the body by stimulating release of aldosterone. This increases blood volume, thus also blood pressure and rate.
(c) AB- blood group means that there is a presence of A and B antigens and absence of Rh factor. The patient can receive blood from people with blood groups A-, B- and O-. (AB- also, but according to the question, that is not available). If any other blood type is transfused, agglutination reaction would occur due to the presence of antibodies. This occurs between similar antigen and antibody. For example, antibody is B for antigen A and A for antigen B. Hence these to groups cannot donate or receive group from each other. If someone would give B type blood to A type person, the anti A antibodies will attack the A type cells. Similarly, antibodies would be formed in an Rh- person against the blood of an Rh+ person, irrespective of the blood type, whether it is A,B, AB or O. So in this case, only Rh- blood can be transfused.
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