Page 167 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
I. Parallel resistance

• The blood flows to parallel vessels at the same time & BP more or less the

same in arteries
Ex: Systemic circulation

 Each organ is supplied by an artery that branches off the aorta.
 Each parallel artery receives a fraction of the total blood flow.
 Blood flow through the aorta ➔ equals blood flow through all the large
systemic arteries.
 The total resistance is less than the resistance of any of the individual
arteries.

 no loss of pressure ➔ i.e. the mean pressure in all major arteries equals
to the mean pressure in the aorta

Pressure profile in blood vessels

 As blood flows through the systemic circulation  Pressure decreases because of the

resistance to blood flow.

 Thus, pressure is highest in the aorta, large arteries & slowest in veins [loss Pressure by
distance]
Pressure is not constant due to heart sometime contract, sometime relax.
 Mean pressures in the systemic circulation are as follows:
Blood vessel Aorta Arterioles Capillaries Vena cava Right atrium

Mean pressure (mm Hg) 100 50 20 4 0 - 2

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