Respiratory System

Lungs

• Lungs are lateral to the heart

• Each is located in its own enclosed pleural cavity within the thoracic cavity

• Each lung is covered by a pleural membrane

• A pleural space lubricated with fluid also surrounds each lung

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Pathway of Air to the Lungs• Pharynx - throat (extends to

larynx)• Larynx - houses vocal chords -

leads to trachea • Trachea - air passes through this

tube on way to the lungs (windpipe)• Bronchi - branches of trachea

going to each lung • Bronchioles - smaller branches of

the bronchi• Alveoli - air sacs surrounded by

capillaries where oxygen is exchanged for CO2 - (blood returns to heart from here)

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Pathway of Air Into the Lungs

Can be divided into 2 zones:

• Conducting Zone

• Respiratory ZoneQuickTime™ and a

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Conducting Zone

• Nose, nasal cavity, pharynx, larynx, trachea, bronchi

• Function: warm, filter and moisten inspired air

• Mucous traps airborne pathogens and cilia propel matter into the pharynx to be swallowed

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Respiratory Zone

• Bronchioles, alveoli• Function: gas exchange

(CO2 enters alveoli from blood and O2 passes into blood from the alveoli)

• Capillaries surround each alveolus for efficient gas exchange

* In emphysema, the alveoli are damaged, reducing ability for gas exchange

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Mechanics of Breathing

• Diaphragm - muscle at the base of the lungs that regulates pressure within the pleural cavities by moving up and down

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Inspiration & Expiration(see Figure 22.13)

Inspiration (breathing in)• Diaphragm contracts and

moves down• Intercostal muscles contract

and expand ribcage• Volume of thoracic cavity is

increased as intrapulmonary (inside alveoli) pressure decreases

• Air moves into lungs because atmospheric pressure is greater than intrapulmonary pressure

Expiration (breathing out)• Diaphragm relaxes and

moves upwards• Intercostal muscles relax

and ribcage collapses• Volume of thoracic cavity

decreases as intrapulmonary pressure increases

• Air is forced out of lungs because atmospheric pressure is less than intrapulmonary pressure

Diaphragm movements

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Regulation of Breathing

• The medulla and pons contain respiratory centers that control breathing (figure 22.24)

• The depth and rate of breathing are controlled by CO2, O2 and pH (H+) concentrations in the blood

• CO2 levels are the strongest stimulus for breathing

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Chemoreceptors in aorta andcarotid arteries monitor bloodand send signals to respiratory centers in pons and medulla