objective 3-physiology of pleura

8/8/2019 Objective 3-Physiology of Pleura

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Objective 3: Physiology of Pleura

The lungs

y The lungs are vital organs.y The main function of the lung is gas exchange.y

Other functions of the lung:y Excretory function,waste gases are carried by blood traveling the veins to the

lungs where respiration takes place.

y Homeostatic function ,adjust PH of the blood by altering the pressure of CO2.y Synthesis of surfactanty Metabolic functions:-y Activation and inactivation of biological substancesy Conversion of angiotensin 1>>>angiotensin 11 since the lung is rich in

angiotensin converting enzyme.

y Inactivation of substances like serotonin, epinephrine and prostaglandins.y So the lung must be protected by the pleura


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Pleura

y Each lung is enclosed in a double walled sac called the pleura.y Both layer of pleura is formed of serous membraney The portion that adheres to the thoracic cavity is parietal pleuray The portion which covers the lung is the visceral layery Between the two layers of pleura a space called intra pleural space

Respiratory Pressures

Two types of pressures are exerted in thoracic cavity and the lungs during the process of

respiration:

1. Intrapleural pressure or intrathoracic pressure2. Intraalveolar pressure or intrapulmonary pressure

Intrapleural Pressure

Definition:

y The pressure existing in pleural cavity, that is, in between the visceral and parietallayers of pleura.

y It is exerted by the suction of thr fluid that lines the pleural cavity.y It is also called intrathoracic pressure since it is exerted in the whole of thoracic

cavity.

Normal values:

y The respiratory pressures are always expressed in relation to atmospheric pressurewhich is 760 mmHg.

y Intrapleural pressure is always negative.Phase Intrapleural Pressure/Intrathoracic Pressure

Inspiration -6 mmHg (760-6=754 mmHg)

Expiration -2 mmHg (760-2=758 mmHg)

Cause for Negative Intrapleural Pressure

y Lack of air in the pleural cavityy Surface tension of the fluid lining the alveolar wally Elastic recoil lf the lung which continuously pulls the visceral pleura away from the

parietal pleura.N.B ve force is a suction force.

Measurement:

Intrapleural pressure is measured by:

Direct method: Introducing a needle into the pleural cavity and connecting the needle to a

mercury manometer

Indirect method: Introducing a esophageal balloon, which is connected to a manometer


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Significance of Negative Intrapleural Pressure

y It helps expansion of the lung.y Helps venous return to the heart.y Helps blood flow through pulmonary vessels.y Helps lymphatic flow in the thoracic duct

Intraalveolar Pressure

Definition:

y The pressure existing in the alveoli of the lungs is called the intraalveolar pressure.y It is also known as intrapulmonary pressure.

Normal values:

y Normally, intraalveolar pressure is equal to the atmospheric pressur which is 760mmHg.

y It becomes negative during inspiration and positive during expiration.Phase Intraalveolar Pressure/Intrapulmonary Pressure

Inspiration -4 mmHg(760 4 =756 mmHg)

Expiration +4 mmHg(760+4=764 mmHg)

Significance of intraalveolar pressure

y The pressure in alveoli causes flow of air in and out of alveoli. During inspiration,since the pressure in the alveoli is negative, the atmospheric air enters the alveoli,

and, as the intrathoracic pressure becomes positive during expiration, the air is

expelled out of alveoli.

y The intraalveolar pressure also helps in the exchange of gases between the alveolarair and the blood.

Transpulmonary Pressure

The pressure difference between alveoli and outer surface of lungs or the difference

between intraalveolar pressure and intraplural pressure is called the transpulmonary

pressure. It is the measure of elastic forces in lungs, which is responsible for the collapsing

tendency of lungs.

objective 3-physiology of pleura

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