Page 165 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)

Resistance to blood flow

4
law R= 8η 1/4 r R= resistance η= viscosity of blood 1= length of blood vessel r= radius of blood vessel
 Resistance ➔ directly proportional to viscosity (η) of the blood and length (1) of the blood vessel
 Resistance ➔ inversely proportional to fourth power of the vessel radius
Factor
• (If radius decrease to 1/2 ➔ resistance increase by 16 • If radius increase 2-fold ➔ resistance decreased to 1/16

fold)

Radius 1 2 1/2

Resistance R 1/16 16
Blood flow F 16 1/16

Blood Pressure [Resistance to blood flow]

I. Series resistance يلاوتلا ىلع ةم و اقم

It’s The blood vessels are arranged in series (i.e. blood flows sequentially عباتتلاب from one to the next )

• Each organ ➔ supplied with by a major artery, major vein:
▪ Blood flows from the major artery ➔ to smaller arteries ➔ to arterioles➔ to capillaries ➔ to
Example
Venules ➔ to the major vein
▪ The total resistance of the system = the Sum of the individual resistance
✓ Arterioles have the greatest resistance in the series (lowest BP)
✓ The total blood flow through each level is the same.
 blood flow through the renal artery = blood flow through all the renal capillaries = blood flow
NB
through the renal vein
• As blood flows through the series of blood vessels➔ the pressure decreases
• resistance increase by going away from heart

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