A. The respiratory system provides oxygen for the blood and eliminates carbon dioxide

B. Pathway of air
    1. Nasal cavity and oral cavity

    2. Pharynx

    3. Larynx

    4. Trachea

    5. Right and Left Primary Bronchi

    6. Secondary bronchus

    7. Tertiary bronchus

    8. Bronchioles

    9. Alveoli

C. The exchange of gases between the respiratory system and  blood    occurs at
        the  alveoli .  The exchange occurs by simple diffusion .  This means that it
        is essential for the alveoli to maintain a higher concentration of oxygen and a lower
        concentration of carbon dioxide then the blood.  These levels are maintained through ventilation.

D. Mechanics of breathing

    1. Diaphragm: sheet of muscle between abdominal and thoracic cavity

    2. External intercostal muscles: muscles between ribs

    3. Boyle's Law: increase volume, decrease pressure and vice versa

    4. recall how fluids (and air) like to move - areas of  high pressure to areas of  low     pressure.

    5. Inspiration

        a. during inspiration the diaphragm and the intercostal muscles contract

            1). the diaphragm moves down

        b. The movements of the diaphragm and rib cage increase the volume of the thoracic cavity
 
 
 

        c. Inside the thoracic cavity are the pleural cavities.  Inside the pleural cavity are the lungs.
                As the thoracic cavity expands the pleural cavity and lungs also expland.  Expansion
                of the lungs causes the pressure in the lung to decrease  .

        d. This decrease in pressure means that the air pressure in the lungs is lower
                than atmospheric pressure.

        e. This difference in pressure allows the air to move from an area of high pressure (ATM) to an area of lower concentration (lungs)

        f. This movement of air is called inspiration

    6. Expiration

        a. The diaphragm and external intercostals relax

            1). The diaphragm moves up

            2). the relaxation of the intercostals causes ribcage to move down and in

        b. The movements of the diaphragm and rib cage decreases the volume of the thoracic cavity

        c. As the volume of the lungs decrease the air pressure in the lungs increases

        d. This forces air out of the lungs

        e. This movement of air out of the lungs is called expiration

E. Rate of respiration

    1. The normal rhythm of respiration is controlled by the interaction of the respiratory control
            centers in the brain.

        a. The inspiratory and expiratory centers located in the medulla oblongata.

        b. The pneumotaxic (increases rate of respiration) and apneustic (increases depth of respiration) centers located in the pons.

    2. The impulses to the muscles originate in the inspiratory centers.

    3. When these impulses reach the diaphragm and intercostal muscles inspiration begins.

    4. As air moves into the lungs the bronchioles will increase in diameter

    5. In the bronchioles there are stretch receptors.  These receptors transmit impulses to the inspiratory center that inhibit the inspiratory center.

    6. The impulses to the diaphragm and intercostals stop.  Without an impulse the diaphragm
            and intercostals relax  and  expiration begins.

    7. With expiration the air leaves the lungs and bronchioles.  The walls of the bronchioles
            are no longer stretched and the stretch receptors stop sending inhibitory impulses.
            The impulses to the diaphragm and intercostals begins again restarting inspiration.

    8.  This is normal  unconscious breathing.  Since the muscles of respiration are
            muscles and these types of muscles are skeletal muscles we can override
            the automatic rhythm of respiration.

F. Increase in Respiratory Rate due to increased activity

    1. Increased activity or decreased ventilation will cause increased levels of CO₂

    2. As more carbon dioxide is produced more hydrogen ions are produced.

                CO₂ + H₂0 <----> H₂CO₃  <---->  HCO₃^-  + H⁺

    3. This causes the pH of the blood to go down (become more acidic).

    4. The increased levels of carbon dioxide are detected by chemoreceptors in the medulla
            while the decreased pH is detected by chemoreceptors in the  aorta  and carotid
            sinuses.  These chemoreceptors stimulate the respiratory center in the medulla
            oblongata and the result is an increase in the rate of respiration.
 

Useful link:

Human Physiology: Respiratory System

Control of Breathing

Regulation of Respiration

Breathing Mechanics

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