Questions: Blood Vessel Anatomy and Circulatory Dynamics
3 questions to test your understanding
Score: 0 / 3
Question 1 Multiple Choice
According to Poiseuille's Law, if an arteriole's radius is reduced by half (e.g., due to vasoconstriction), by what factor does resistance to blood flow increase?
A2-fold
B4-fold
C8-fold
D16-fold
Poiseuille's Law states that resistance is proportional to 1/r⁴. If radius is halved (r → r/2), resistance becomes proportional to 1/(r/2)⁴ = 16/r⁴ — a 16-fold increase. This explains why even modest narrowing of blood vessels dramatically raises blood pressure and why arterioles are the primary site of vascular resistance control.
Question 2 True / False
Arteries usually carry oxygenated blood because their function is to deliver oxygen from the heart to the body's tissues.
TTrue
FFalse
Answer: False
Arteries are defined by direction of flow relative to the heart (away from it), not by oxygen content. The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs. Only after gas exchange in pulmonary capillaries does blood become oxygenated and return via the pulmonary veins.
Question 3 Short Answer
Why are capillaries, rather than arteries or veins, the primary site of gas and nutrient exchange with tissues?
Think about your answer, then reveal below.
Model answer: Capillaries have walls only one cell thick (simple squamous endothelium), blood moves slowly through them maximizing contact time, and their enormous total cross-sectional area provides vast surface for diffusion. Arteries and veins have thick walls that block exchange, and blood moves too quickly through them.
Exchange efficiency depends on diffusion distance, contact time, and surface area. Capillaries optimize all three: minimal wall thickness minimizes diffusion distance, slow velocity maximizes contact time, and the vast capillary network provides enormous surface area. Thick-walled arteries would block diffusion entirely.