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Robert B.
Professor of Physiology
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Health and Medicine
TutorMe
Question:

Which of the following parameters decreases the stroke volume of the left ventricle?

Robert B.
Answer:

a) Increased contractility b) Increased preload c) Increased afterload d) Decreased aortic pressure e) Increased compliance of the aorta Answer = C

Biomedical Science
TutorMe
Question:

PO2 in the arterial blood is around 95mm Hg and in the venous blood it is around 40mm Hg. PCO2 in the arterial blood is around 40mm Hg and in the venous blood it is around 46 mm Hg. CO2 only increase 6 mm Hg from arterial to venous blood while O2 decreases nearly 60 mm Hg from arterial to venous blood. What is the most important reason for this disparity?

Robert B.
Answer:

The difference observed is due to CO2¬ being transported mainly as bicarbonate in venous blood rather than dissolved in the plasma. Upwards of 80% of CO2 is transported as bicarbonate. This is possible because when CO2 mixes with H2O in the presence of the enzyme carbonic anhydrase, it creates carbonic acid (H2CO3). Carbonic acid dissociates to form bicarbonate (HCO3-) and a hydrogen ion (H+). The equation moves to the right during internal respiration (gas exchange between blood and tissue) and moves to the left during external respiration ( gas movement between blood and lungs).

Biology
TutorMe
Question:

A college student takes an exam in his favorite subject (Biology) and afterwards wants to celebrate with some with friends. They go out to a local pizza joint and slap each other high fives, celebrating their successful completion of the exam. While eating the pizza, one of the biology students starts to think about all the processes that are going on in their body in order to break down and obtain energy from the pizza. Please describe the metabolic pathways that the glucose molecules from the pizza go through. Include what enters and exits the various pathways, as well as where the pathways are located inside the cell. Don't get bogged down with minutia; think big picture.

Robert B.
Answer:

The pizza is broken down into lipids, amino acids (building blocks of proteins) and carbohydrates, and these various parts are imported into the cell. The carbohydrates are imported into the cell as glucose which then enters the pathway of glycolysis. Through the action of various enzymes, 10 steps later the and a single glucose molecule, 2 ADP and 2NAD+ are transformed into 2 molecules of pyruvate, 2 ATP, and 2 NADH. Glycolysis occurs in the cytoplasm (space inside cell not occupied by organelles )/cytosol (liquid solution in the cytoplasm) and not in any specific organelle. The ATP is used ubiquitously inside the cell as a source of energy, the NADP heads to the ETC (electron transport chain), and pyruvate enter eithers the pyruvate dehydrogenase pathway if oxygen is available at the ETC. If oxygen is NOT available, pyruvate enters the fermentation pathway (anaerobic respiration) which occurs in the cytoplasm and yields 2 ATP and 2 Lactate. Since aerobic respiration is far more energetically efficient, if oxygen is available as a final electron acceptor in the ETC, pyruvate will move into the pyruvate dehydrogenase pathway which is located in the mitochondria. Pyruvate is then converted to Acetyl CoA which enters the citric acid cycle (CAC), also located in the mitochondria. Acetyl CoA (two are produced per 1 glucose molecule) enters the CAC along with oxidized electron carriers and the products of the CAC are reduced electron carries in the form of 1 ATP, 3 NADH, and 1 FADH2 per acetyl CoA. CO2 is also produced as a byproduct of acetyle CoA oxidation and this is where the CO2 we breath comes from. Now, the reduced electron carriers go to the electron transport chain (ETC) where oxidative phosphorylation occurs.

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