Circulatory System Structure and Blood Flow Dynamics (3B) - Bio & Biochem

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

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

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

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

3. What is the main physiological purpose of arterioles?

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

4. How does total peripheral resistance change when arterioles vasoconstrict?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

12. What is the valve between the left atrium and left ventricle?

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

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

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

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

    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.

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

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

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

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

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

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

18. Which heart chamber directly pumps blood into the aorta?

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

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

    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.

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

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

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

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

22. What is the valve between the right atrium and right ventricle?

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

23. What is the primary physiological purpose of capillaries?

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

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

    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.

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

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

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