MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 3b Circulatory System Blood Flow

What this deck covers

This deck focuses on 3b Circulatory System Blood Flow, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which vessel type has the greatest total cross-sectional area in systemic circulation?

Answer: Capillaries. Capillaries' extensive branching results in the largest collective area, optimizing nutrient exchange.

Flashcard 2: Which vessel type has the lowest average blood velocity in systemic circulation?

Answer: Capillaries. Velocity is inversely proportional to cross-sectional area, minimizing speed in capillaries for diffusion.

Flashcard 3: What is the main physiological purpose of arterioles?

Answer: Major resistance vessels controlling tissue perfusion and $BP$. Arterioles regulate blood distribution and pressure via smooth muscle control of vessel diameter.

Flashcard 4: How does total peripheral resistance change when arterioles vasoconstrict?

Answer: Total peripheral resistance increases. Vasoconstriction reduces vessel radius, elevating resistance via Poiseuille's fourth-power relationship.

Flashcard 5: What is the main function of semilunar valves during ventricular diastole?

Answer: Prevent backflow from arteries into ventricles. Semilunar valves close to sustain arterial pressure and prevent blood from re-entering relaxed ventricles.

Flashcard 6: State the continuity equation relating flow, velocity, and cross-sectional area.

Answer: $Q = Av$. The continuity equation conserves volume flow by relating it to area and velocity.

Flashcard 7: If blood viscosity doubles and all else is constant, how does flow $Q$ change?

Answer: Flow decreases by a factor of $2$. Flow is inversely proportional to viscosity in Poiseuille's law, with other factors constant.

Flashcard 8: State Poiseuille's law for laminar flow through a cylindrical blood vessel.

Answer: $Q = \frac{\pi r^4 \Delta P}{8\eta L}$. Poiseuille's law quantifies how radius, viscosity, and length influence laminar flow in vessels.

Flashcard 9: State the relationship between flow, pressure difference, and resistance in hemodynamics.

Answer: $Q = \frac{\Delta P}{R}$. This equation, analogous to Ohm's law, describes blood flow driven by pressure against resistance.

Flashcard 10: Which heart chamber directly pumps blood into the pulmonary artery?

Answer: Right ventricle. The right ventricle pumps deoxygenated blood to the lungs for gas exchange via the pulmonary artery.

Flashcard 11: What is the formula for mean arterial pressure in terms of CO and TPR?

Answer: $MAP \approx CO \times TPR$. This approximation balances cardiac pumping with vascular resistance to determine arterial pressure.

Flashcard 12: What is the valve between the left atrium and left ventricle?

Answer: Mitral (bicuspid; left atrioventricular) valve. The mitral valve maintains forward flow of oxygenated blood from left atrium to ventricle during filling.

Flashcard 13: What is the valve at the outflow of the right ventricle into the pulmonary trunk?

Answer: Pulmonary semilunar valve. The pulmonary valve allows deoxygenated blood to exit the right ventricle while preventing backflow.

Flashcard 14: What is the primary functional difference between pulmonary and systemic circulation?

Answer: Pulmonary: gas exchange in lungs; Systemic: delivers $O_2$ to tissues. Pulmonary circulation facilitates oxygenation, while systemic circulation supplies oxygen and nutrients to body tissues.

Flashcard 15: If a vessel radius doubles, by what factor does resistance change (Poiseuille)?

Answer: Resistance decreases by a factor of $16$. Resistance varies inversely with radius to the fourth power per Poiseuille's law.

Flashcard 16: Which vessel type contains valves to prevent backflow, especially in the limbs?

Answer: Veins. Valves in veins counteract gravity and ensure unidirectional blood return to the heart.

Flashcard 17: If total cross-sectional area increases $4$-fold, how does velocity change (constant $Q$)?

Answer: Velocity decreases by a factor of $4$. For constant flow, velocity inversely scales with cross-sectional area per continuity equation.

Flashcard 18: Which heart chamber directly pumps blood into the aorta?

Answer: Left ventricle. The left ventricle pumps oxygenated blood throughout the body via the aorta to meet tissue demands.

Flashcard 19: What is the correct blood flow sequence from systemic veins to the aorta?

Answer: Venae cavae → RA → RV → pulmonary a. → lungs → pulmonary v. → LA → LV → aorta. This pathway ensures deoxygenated blood is oxygenated in the lungs before being pumped systemically.

Flashcard 20: What is the valve at the outflow of the left ventricle into the aorta?

Answer: Aortic semilunar valve. The aortic valve enables oxygenated blood to enter the aorta while preventing regurgitation into the left ventricle.

Flashcard 21: What is the main function of atrioventricular valves during ventricular systole?

Answer: Prevent backflow from ventricles into atria. Atrioventricular valves close to maintain pressure and ensure forward propulsion of blood into arteries.

Flashcard 22: What is the valve between the right atrium and right ventricle?

Answer: Tricuspid (right atrioventricular) valve. The tricuspid valve ensures unidirectional flow of deoxygenated blood from right atrium to ventricle.

Flashcard 23: What is the primary physiological purpose of capillaries?

Answer: Exchange of gases, nutrients, and wastes with tissues. Capillaries' thin endothelium and slow flow enable efficient diffusion across vessel walls.

Flashcard 24: What is the primary structural feature that distinguishes arteries from veins?

Answer: Arteries have thicker tunica media; veins have thinner walls and valves. Arteries require robust walls for high pressure, while veins use valves for low-pressure return flow.

Flashcard 25: If cardiac output increases $25\%$ with constant $TPR$, how does $MAP$ change?

Answer: $MAP$ increases by $25\%$. Mean arterial pressure directly proportional to cardiac output when resistance is unchanged.