Page 193 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Gas exchange  when the surface area for diffusion is maximized and the thickness of the barrier to

diffusion is minimized.

the surface area of the interface the thickness of the interface

 There are 300 million alveoli in the lungs. blood–gas interface consists of the alveolar

 The walls of each alveolus are completely lined epithelium, capillary endothelium, and

with capillaries (1000 capillaries per alveolus) interstitium  0.5um

 300 billion pulmonary capillaries.
 vast surface area for gas exchange of

2
approximately 70 m .
Gas transport in blood

a. Once oxygen has diffused from the alveoli into pulmonary circulation  must be transported in

the blood to cells that need it.

b. Once carbon dioxide has diffused from the tissues into the systemic circulation  must be

transported to the lungs, where it can be eliminated.
1- Transport of oxygen.

Oxygen is carried in the blood in two forms:

Physically dissolved Chemically combined with hemoglobin

 Oxygen is poorly soluble in plasma   Most of the oxygen in the blood (98.5%).

only 3 ml of oxygen is physically  Each Hb can bind 4 oxygen molecules.
dissolved in 1 l of blood.

 A blood volume of 5 l  15 ml of
The binding of oxygen to hemoglobin:
oxygen is in the dissolved form.
a. As PO2  (as in the lungs)  more O2 will
NB
combine with Hb.
 The normal rate of oxygen
b. When PO2  (as in the tissues consuming it) 
consumption: at rest 250 ml/min.
Hb releases the O2.
During exercise, oxygen consumption
 Each gram of Hb can combine with up to 1.34 ml of
may increase to 3.5 - 5.5 l/min.
oxygen.
 amount of dissolved oxygen is
 In a healthy individual, there is 15 g of hemoglobin
insufficient to meet needs of tissues.
per 100 ml of blood.

 oxygen content of the blood is 20.1 ml O2/100 ml

blood:

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