40 - Respiratory physiology. External respiration. Functional organisation of the airways, lungs and thoracic cage. Mechanics of breathing. Intrapleural and intrathoracic pressure. The effect of surfactant. Protective reflexes – cough and sneeze.

sections

respiratory physiology

expiration

respiration

external respiration

mechanism of breathing

intrapleural/intrathoracic pressure

pulmonary surfactant

cough reflex

sneezing

respiratory physiology

• Two lungs, consist of tiny air-containing sacs called alveoli-

• The alveoli are the sites of gas exchange with the blood.- about 300million in lung

• bronchioles- pathway for air from the external environment to the alveoli and back.

• Inspiration is the movement of air from the external environment through the airways to the alveoli during breathing.

expiration

is the process of breathing out—pushing air from the lungs back into the atmosphere.

respiration

Respiration is the process whereby oxygen and carbon dioxide diffuse in and out of the blood. Respiration is known as gas exchange, occurs in two areas of the body. (lungs - external respiration, body tissue - internal respiration)

external respiration

• External respiration refers to gas exchange across the respiratory membrane in the lungs between alveoli and venous blood (deoxygenated blood).

• As venous blood flows through the pulmonary capillaries

• oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar gas.

• Each gas diffuses down its own partial pressure gradient - that is, from a high to low partial pressure.

mechanism of breathing

Inspiration:

1. intercostal muscles contract

2. sternum moves up and out

3. ribs move up and out

4. diaphragm flattens

5. increase volume of thoracic cavity

6. pressure in thoracic cavity decreases

7. air is drawn into thoracis cavity

Expiration:

1. intercostal muscles relax

2. sternum moves down and in

3. ribs move down and in

4. diaphragm relaxes forms bell shape

5. decrease volume of thoracic cavity

6. pressure in thoracic cavity increases

7. air is expelled from thoracis cavity

intrapleural/intrathoracic pressure

• pressure in the pleural cavity - usually the pressure is slightly less than the atmospheric pressure

• if the pleural cavity is ruptured the intrapleural pressure becomes equal or exceeds the atmospheric pressure -> pneumothorax

• pressure depends on the ventilation phase, atmospheric pressure, and the volume of the intrapleural cavity

pulmonary surfactant

• A fluid made up of a mixture of phospholipids, proteins and calcium ions

• Secreted by the alveolocyte type 2 cells and helps to reduce tension at the surface of the lungs.

• makes it easier for the lungs to stretch.

• A deep breath causes more surfactant to be secreted due to the stretching of the alveolcyte type 2 cells.

• Functions of surfactant:

  • Increases lung SA and lung compliance

  • Prevents collapsing of small alveoli

  • Reduces fluid filtration- to prevent swelling

cough reflex

• body rids the lower respiratory tract of any irritant that enters through the air

• or any fluids and solids that may spill into the respiratory tract.

• The lower respiratory tract (trachea, bronchi and bronchioles) is lined with epithelium that contains sensory receptors -pulmonary irritant receptors

• Inflammation and mucus hypersecretion can trigger coughing.

• triggered by any irritation of the upper respiratory tract

sneezing

• Sneezing is body’s way of removing irritants from the nose.

• A sneeze is an involuntary and powerful expulsion of air.