Question

If blood vessel resistance is proportional the inverse of the vessel radius, what would the magnitude of difference between a blood vessel with radius R versus a blood vessel with radius 2R? 2. a. Which of these would be better for oxygen transport, why?

Answer 1

Question: If blood vessel resistance is propotional to the inverse of the vessel radius, what would the magnitude difference between a blood vessel with radius R versus blood vessel wtih radius 2R?

Resistance to blood flow in a vessel are determined by 3 factors:

1. Vessels diameter or radius

2. Vessel length

3. Viscosity of blood.

Of all the determinants above Vessels diameter or radius is significat quanittatively and physiologically because the vessel diameter changes due to the contraction of vascular smooth muscle in the vessel wall. And also very small changes in the diameter lead to significant change in resistance.

Vessel resistance (R) is directly proportional to the length (L) of the vessel and the viscosity (?) of the blood, and inversly proportional to radius to the fouth power r⁴.  

R ? ?L/r⁴

Changes in diameter and radius and directly proportional to eachother. Therefore 2 fold increse in radius decreses the resistance by 16 fold. Thus vessel resistance is senseitive to change in radius.

Question - Which one of there is better for oxygen transport and Why

Since the flow rate is naturally higher with a bigger radius and resistance is low, there is more oxygen supply and thus vessels with bigger diameter or radius are better for oxygen transport. Blood vessel with 2R is better for oxygen transport than R.

Question - What are the two factors that trigger the relaxatio of precapillary sphincters?

1. Local metabolites such as Lactic acid, adenosine, carbon dioxide, hydrogen ions and potassium ions.

2. tissue hypoxia

3. incresed local blood pressure

Question: Give three examples of local metabolites that may be related

Local metabolites- Lactic acid, adenosine, carbon dioxide, hydrogen inos and potassium ions.

Question: Why can veins get away with having much tinner and less muscular wall compared to arteries?

The arteries have a thicker tunica media comared to veins, the tunica media contain smooth muscle cells. The arteries recieve blood from the heart at a high pressure and thus a thicker wall is necessary to sustain that pressure. Whereas veins have thinner walls and lesser smooth muscle cell in the tunica media as they the blood flows at a lower pressure and lower resistance compared to that of arteries.

Question: What problem this imposes?

Since there is less resistance and less pressure compared to arteries, it can cause venous stasis in the lower limbs and pedal edema. It may also be a contributing factor for varicose veins, congestive cardiac failure and pedal edema in sedentary and obese individuals.