Respiratory System

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The Respiratory System

At the end of this topic students will be able to:
• Compare the respiratory systems • Describe the mechanic of respiration - Air passage principals - Ventilation - Lung volume and respiration cycle - Respiration rate • Explain gas exchange - Partial pressure - Oxygen separation curve • Discriminate gas transportation - Oxygen and carbon dioxide

Respiration : - all processes that accomplish movement of O2 from the environment to the tissues - has 2 components : a) Cellular respiration ( in mitochondria): refers to intracellular metabolic processes C6H12O6 + O2 6CO2 + 6H2O b) External respiration : events involved in the exchange of O2 and CO2 between the external environment and cellular mitochondria

Function of respiration
1. Provides oxygen 2. Eliminates carbon dioxide 3. Regulates the blood’s hydrogen-ion concentration (pH) , because CO2 generates carbonic acid 4. Defends against microbes

Partial Pressure
• Atmospheric gas is a mixture of gas (79% N2, 20.9% O2, 0.03% CO2, H2O vapour, other gases and pollutants) • Altogether these gases exert a total atmospheric pressure of 760 mmHg • Partial pressure : The individual pressure exerted independently by a particular gas within a mixture of gases (Pgas)

Diversity of Gas Exchange Structures

Respiratory System of a Bony Fish

Human Respiratory System

Pathway of air: • nasal cavities (or oral cavity) pharynx trachea primary bronchi (right & left) secondary bronchi tertiary bronchi bronchioles alveoli (site of gas exchange)

The exchange of gases (O2 & CO2) between the alveoli & the blood occurs by simple diffusion: •O2 diffusing from the alveoli into the blood & CO2 from the blood into the alveoli. • Diffusion requires a concentration gradient. So, the concentration (or pressure) of O2 in the alveoli must be kept at a higher level than in the blood & the concentration (or pressure) of CO2 in the alveoli must be kept at a lower level than in the blood.

• Contraction of external intercostal muscles elevation of ribs & sternum increased front- to-back dimension of thoracic cavity lowers air pressure in lungs air moves into lungs • Contraction of diaphragm diaphragm moves downward increases vertical dimension of thoracic cavity lowers air pressure in lungs air moves into lungs


• relaxation of external intercostal muscles & diaphragm return of diaphragm, ribs, & sternum to resting position restores thoracic cavity to preinspiratory volume increases pressure in lungs air is exhaled


Pulmonary volumes and capacities• Spirometry is the study of lung ventilation. • A record of the air movement in and out of the lungs is called a spirogram which can be obtained by a device called a spirometer. • To describe events of pulmonary ventilation, the air in the lungs has been subdivided at different points on the diagram into 4 volumes and 4 capacities.


Dry spirometer

Wet spirometer


Pulmonary volumes
1. Tidal volume- the volume of air inspired or expired with each normal breath 2. Inspiratory reserve volume- the volume of air that can be inspired above the normal tidal volume 3. Expiratory reserve volume- the volume of air that can be expired by forced expiration after normal tidal expiration. 4. Residual volume- the volume of air remaining in lungs after forceful expiration

Pulmonary capacities
1. Inspiration capacity = Tidal Volume + Inspiratory Reserve 2. Functional residual capacity = Expiratory reserve + Residual Volume 3. Vital Capacity = Inspiratory reserve + Tidal Volume + Expiratory Reserve 4. Total Lung Capacity = Vital Capacity + Residual Volume

Gas Exchange
 Gas exchange at both the pulmonary capillary and tissue capillary levels involves simple passive diffusion of O2 and CO2 down partial pressure gradients.

the blood Oxygen is carried in blood: 1 - bound to hemoglobin (98.5% of all oxygen...
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