Page 192 - Physiology and Pathophysiology MNU 2024-2025 نظرى

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

External  Supplied by the intercostal nerves.

intercostal  When contract  the ribs are lifted upward & outward   horizontal
muscles dimension of the thoracic cavity   thoracic volume.

Accessory  Located mainly in the neck.

inspiratory  Raise the sternum & elevate the first two ribs  the upper portion of the

muscles: thoracic cavity is enlarged.

2- Expiration
During normal, quiet breathing During exercise or voluntary hyperventilation

Passive  no active muscle contraction is required. Active process because a larger volume of air

must be exhaled more rapidly.

a. Relaxation of diaphragm: a. The muscles of the abdominal wall:

Passively returns to its original preinspiration Contraction  pushes inward on the abdominal

position under the ribs. contents   abdominal pressure  the
diaphragm is pushed upward more rapidly &

b. Relaxation of the external intercostal more forcefully toward its preinspiration

muscles position.

Allows the rib cage to fall inward and downward.
b. The internal intercostal muscles:
These movements   thoracic volume.
Contraction  pulls the ribs inward &

downward.

Pulmonary pressures

Changes in thoracic volume & lung volume  changes in pressures within the airways  create the
pressure gradients responsible for airflow in & out of the lungs.

Gas exchange

Occurs at the blood–gas interface where the alveoli and the pulmonary capillaries come together.
a. Inspired oxygen moves from the alveoli into the capillaries.

b. Carbon dioxide moves from the capillaries into the alveoli for elimination by expiration.

• Oxygen & carbon dioxide ➔move across the blood–gas interface by simple diffusion  from an

area of high concentration to an area of low concentration.
According to Fick's law of diffusion:

The amount of gas that moves across the blood–gas interface is:
a. proportional to the surface area of the interface

b. inversely proportional to thickness of the interface.

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