Passage
The heart is a muscular organ comprising four chambers, two atria and two ventricles, that function synergistically to pump blood through a vast, closed network of blood vessels. The chambers are separated by membranous muscular barriers known as septa. Oxygenated blood returning from the lungs via the pulmonary veins fills the left atrium and enters the left ventricle, which then pumps the blood into the systemic arteries to supply other organs in the body. By contrast, deoxygenated blood returning from systemic veins first enters the right atrium, then the right ventricle, and is ultimately siphoned into the pulmonary arteries leading to the lungs. The necessary oxygen, nutrient, and waste exchange occurs between the thinnest blood vessels (capillaries) and neighboring tissues of the systemic and pulmonary circuits.Blood flow throughout the circulatory system is dictated by blood (hydrostatic) pressure, vascular resistance (force opposing blood flow through a vessel), and cardiac output (blood volume expelled from the ventricles per unit time). When blood traverses a vessel, it exerts hydrostatic pressure on the vessel walls, which results in the forced movement of fluid out of the vessel and into the interstitial space. The circulating plasma proteins cause the osmotic pressure within the vessel to be higher than that of the interstitial fluid. In turn, osmotic pressure causes fluid to flow from the interstitial space into the blood vessel, opposing hydrostatic pressure.Cardiac output depends in part on heart rate, which is tightly regulated by the sinoatrial (SA) and atrioventricular (AV) nodes, specialized groups of self-depolarizing cells located in the upper right atrial wall and lower interatrial septum, respectively. Action potentials (APs) generated by SA nodal cells stimulate atrial contraction as they travel to the AV node. The AV node delays AP transmission to ventricular cells, ensuring ventricular filling is complete prior to heart contraction.A 63-year-old male patient collapsed while exercising and was hospitalized. The patient presented with an elevated heart rate, low systemic blood pressure, and abnormally low blood oxygen levels. In addition, x-rays revealed excess fluid in his lungs.
-Given the information in the passage, the excess fluid in the patient's lungs is most likely caused by which of the following at the pulmonary sites of gas exchange?

Question

Passage
The heart is a muscular organ comprising four chambers, two atria and two ventricles, that function synergistically to pump blood through a vast, closed network of blood vessels.  The chambers are separated by membranous muscular barriers known as septa.  Oxygenated blood returning from the lungs via the pulmonary veins fills the left atrium and enters the left ventricle, which then pumps the blood into the systemic arteries to supply other organs in the body.  By contrast, deoxygenated blood returning from systemic veins first enters the right atrium, then the right ventricle, and is ultimately siphoned into the pulmonary arteries leading to the lungs.  The necessary oxygen, nutrient, and waste exchange occurs between the thinnest blood vessels (capillaries) and neighboring tissues of the systemic and pulmonary circuits.Blood flow throughout the circulatory system is dictated by blood (hydrostatic) pressure, vascular resistance (force opposing blood flow through a vessel), and cardiac output (blood volume expelled from the ventricles per unit time).  When blood traverses a vessel, it exerts hydrostatic pressure on the vessel walls, which results in the forced movement of fluid out of the vessel and into the interstitial space.  The circulating plasma proteins cause the osmotic pressure within the vessel to be higher than that of the interstitial fluid.  In turn, osmotic pressure causes fluid to flow from the interstitial space into the blood vessel, opposing hydrostatic pressure.Cardiac output depends in part on heart rate, which is tightly regulated by the sinoatrial (SA) and atrioventricular (AV) nodes, specialized groups of self-depolarizing cells located in the upper right atrial wall and lower interatrial septum, respectively.  Action potentials (APs) generated by SA nodal cells stimulate atrial contraction as they travel to the AV node.  The AV node delays AP transmission to ventricular cells, ensuring ventricular filling is complete prior to heart contraction.A 63-year-old male patient collapsed while exercising and was hospitalized.  The patient presented with an elevated heart rate, low systemic blood pressure, and abnormally low blood oxygen levels.  In addition, x-rays revealed excess fluid in his lungs.
-Given the information in the passage, the excess fluid in the patient's lungs is most likely caused by which of the following at the pulmonary sites of gas exchange?

Quizplus · Accepted Answer

11ecba2d_1039_2de0_a3bf_3576bc3eb187_MD0008_00 According to the passage, blood flowing through vessels exerts hydrostatic pressure on the walls, forcing some fluid from the vessel into the interstitial space. In addition, circulating plasma proteins cause osmotic pressure (eg, solute concentration) within blood vessels to be higher than that of the interstitial fluid. Fluid generally flows from areas of low to high osmotic pressure; therefore, blood osmotic pressure tends to draw fluid into blood vessels from the interstitial space, opposing hydrostatic pressure and minimizing fluid loss from blood vessels. In addition, lymph vessels generally collect any excess fluid forced from blood vessels (ie, known as lymph when flowing through the lymphatic system), ultimately returning it to the bloodstream. As blood flow through a capillary increases, hydrostatic pressure exerted on the vessel walls also increases, leading to a higher rate of fluid leakage from the capillary into the interstitial space. If the rate of fluid leakage from capillaries exceeds the rate at which fluid is taken up by surrounding blood and lymph vessels, a higher volume of leaked fluid can build up in associated tissues (ie, edema). X-rays revealed that the patient has excess fluid in his lungs (ie, pulmonary edema), a condition that may hinder oxygen and carbon dioxide exchange at the alveoli. Pulmonary edema would be due to an increased volume of blood flowing through pulmonary capillaries (Choice D), which causes an increase in hydrostatic pressure exerted on capillary walls. High hydrostatic pressure would increase the rate of fluid leakage into the interstitial space surrounding pulmonary capillaries, causing excess fluid accumulation in the lungs. (Choices A and B) Increased protein concentration in blood flowing through pulmonary capillaries would increase blood osmotic pressure. Because fluid generally flows from low to high osmotic pressures, higher blood osmotic pressure would tend to pull more fluid into pulmonary capillaries from the interstitial space, decreasing (not increasing) pulmonary fluid accumulation. In addition, decreased osmotic pressure of interstitial fluid surrounding pulmonary capillaries would increase the flow of fluid into the capillaries, decreasing (not increasing) fluid accumulation in the lungs. Educational objective: Blood flowing through capillaries exerts hydrostatic pressure on the vessel walls that forces some fluid from the vessel into the interstitial space. In contrast, circulating proteins in the bloodstream cause osmotic pressure in the blood to be higher than that of the interstitial fluid, drawing fluid from the interstitial space into the capillary.