1. Breathing Mechanisms

2. Processes of Respiration
1) Pulmonary Ventilation
(Air moves in and out of lungs)
2) External Respiration
(Exchange of gas between lungs and blood)
3) Respiratory Gas Transport
4) Internal Respiration
(Exchange of gas between blood and cells)

3. Pulmonary Ventilation
Breathing, or ventilation, is the movement of air from outside the body into and out of the bronchial tree and alveoli
The actions providing these air movements:
- Inspiration = inhalation
- Expiration = exhalation

4. Inspiration
Atmospheric pressure due to the weight of air is the force that moves air into the lungs
The pressure on the inside of the lungs and alveoli (intrapulmonary pressure) and on the outside are about the same
If the pressure inside the lungs and alveoli decreases below air pressure, atmospheric pressure will push outside air into the airways.

5. Fig

6. Cause of decrease in intrapulmonary pressure:
Phrenic nerves stimulate contraction of the diaphragm – diaphragm moves downward enlarging thoracic cavity
The external intercostal muscles may be stimulated, raising the rib cage and sternum, enlarging thoracic cavity
Both of these actions will cause the lungs to expand and decrease intrapulmonary pressure as long as both the pleural membranes move together
The water based serous fluid of the pleural cavity ensures that the two membranes are held together

7. Fig

8. Expiration
As the diaphragm and intercostal muscles relax following inspiration, the elastic tissues cause the lungs and thoracic cavity to ‘recoil’ and return to their original shapes.
The surface tension of the alveolar linings causes them to decrease in size
Both of these actions cause the intrapulmonary pressure to increase (above atmospheric pressure) causing air to be forced out.

9. Fig ab

10. Forced Expiration
If respiratory passageways are narrowed by spasms of the bronchioles (asthma) or clogged with mucus/fluid (pneumonia), respiration becomes an active process.

11. Collapsed Lung
The alveoli are so elastic that they attempt to recoil at the end of exhalation
In order to prevent this, there is a small amount of pressure in the pleural cavity that acts as a “suction” to keep the alveoli slightly inflated
If air enters the pleural cavity it will cause the lung to collapse

12. Respiratory volumes
Tidal volume (TV) – volume of air that enters/leaves during a single respiratory cycle (resting tidal volume – 500mL)
Inspiratory reserve volume (IRV)– the additional air that enters during forced inspiration (3100mL)
Expiratory reserve volume (ERV)– the additional air that is expelled during forced expiration (1200mL)
Residual volume (RV)– volume of air that continually remains in lungs (approx. 1200mL)

13. Vital Capacity
Total amount of exchangeable air
IRV + TV + ERV

15. Respiration & Transport

16. Alveoli
The aveoli carry on the vital process of exchanging gases between the air and the blood
Each aveolus wall consists of simple squamous epithelium, as is the network of capillaries that surrounds each aveolus.
The area between each aveolus and capillary is referred to as the respiratory membrane

17. Diffusion of Gases
The gases found in air (Nitrogen, Oxygen, Carbon Dioxide) will diffuse across the respiratory membrane from an area of high pressure to an area of low pressure
The gases will then dissolve in the plasma portion of blood.

18. High Altitude Sickness
The efficiency of gas exchange is decreased because of the low atmospheric pressure at high altitudes

19. Oxygen Transport
Over 98% of oxygen that blood transports is carried on the iron-containing protein hemoglobin.
Once combined, the two weakly bonded molecules form oxyhemoglobin, which will release oxygen when it reaches areas of low oxygen concentration.
It will also release oxygen in areas of extremely high Carbon Dioxide levels

20. Carbon Dioxide Transport
Carbon Dioxide is a waste product of cellular activities, so it will diffuse from the tissues into the blood.
It will be transported in one of three ways:
1) dissolved in the plasma
2) bonding with hemoglobin to form carbaminohemoglobin
3) Formation of bicarbonate ions (HCO3-) in the plasma

21. Carbon Monoxide Poisoning
Carbon Monoxide (CO) competes vigorously with oxygen for the same binding sites on hemoglobin
In fact, it binds more easily
Causes inadequate oxygen delivery (hypoxia)

22. Control of Respiration

23. Control of Respiration
The basic rhythm of respiration is controlled by groups of neurons in the brain stem.
The area from which nerve impulses are sent to respiratory muscles is called the Respiratory Center, which is functionally divided into three areas:

24. Medulla Centers “Pacemaker” – sets the basic breathing rhythm
1. Self-exciting inspiratory center
Impulses travel along the phrenic and intercostal nerves to excite the diaphragm and external intercostal muscles
Expiratory center
Inhibits the pacemaker in a rhythmic way

25. Pons centers
Neurons of the pons that control the breathing rate by transmitting inhibitory impulses to the inspiratory area so that the lungs to not become too full of air
Smooth out the rhythm set by the medulla

26. Regulation of Respiratory Center
Chemosensitive areas – monitor concentration of dissolved gases in blood and CSF
The inflation reflex – the stretch of lung tissue indicate the necessity of breathing
Emotional upset
Conscious control
Body movement
Temperature (Increase body temperature, increase respiration)
Blood pressure (increase in blood pressure will decrease respiration rate)

27. Regulation of Bronchiole size
Bronchoconstriction :
caused by parasympathetic NS and mediators of allergic reactions (histamine)
Bronchodilation:
caused by sympathetic NS and epinephrine
Asthma attack – increased mucous and smooth muscle spasms