Function of the respiratory system
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Function of the Respiratory System. Oversees gas exchanges between the blood and external environment Exchange of gasses takes place within the lungs in the alveoli Passageways to the lungs purify, warm, and humidify the incoming air. Upper Respiratory Tract. Figure 13.2. The Nose.

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Function of the respiratory system
Function of the Respiratory System

  • Oversees gas exchanges between the blood and external environment

  • Exchange of gasses takes place within the lungs in the alveoli

  • Passageways to the lungs purify, warm, and humidify the incoming air

The nose
The Nose

  • Air enters the nose through the external nares (nostrils). The openings are guarded by hairs that prevent the entrance of large particles.

  • The interior of the nose consists of a nasal cavity divided into right and left portions by a nasal septum.

Anatomy of the nasal cavity
Anatomy of the Nasal Cavity

  • Lateral walls have projections called conchae

    • Increases surface area

    • Increases air turbulence within the nasal cavity

  • The nasal cavity is lined with Pseudostratified Columnar Epithelium that is rich in Goblet Cells. It functions to:

    • Moisten and Warm the air

    • Mucous traps incoming foreign particles. Cilia move the entrapped particles toward the pharynx and are swallowed.

Paranasal sinuses
Paranasal Sinuses

  • Cavities within bones surrounding the nasal cavity

    • Frontal bone

    • Sphenoid bone

    • Ethmoid bone

    • Maxillary bone

Paranasal sinuses1
Paranasal Sinuses

  • Function of the sinuses

    • Lighten the skull

    • Act as resonance chambers for speech

    • Produce mucus that drains into the nasal cavity


  • Enlargement in the airway at the top of the trachea. Serves as a passageway for air and houses the vocal cords.

  • Vocal Cords

  • Composed of muscle and elastic fibers. Create vocal sounds when air is forced between them causing vibrations in the air column above.


  • The windpipe is about 12.5 cm in length and about 2.5 cm in diameter.

  • It extends from the larynx downward until it divides into the right and left bronchi.

  • It is supported by C-Shaped cartilage rings to keep it from collapsing under negative pressure.

  • The trachea divides at the level of the 5th thoracic vertebrae into the Right and Left Primary Bronchi.

  • Each primary bronchus soon divides into Secondary Bronchi.

  • These secondary bronchi divide again and again into smaller and smaller branches. The smallest are bronchioles.

  • Bronchioles give rise to thin tubes called Alveolar Ducts which terminate in groups of microscopic chambers called Alveoli.


  • Terminal bronchioles end in alveoli

Figure 13.5a


  • Each alveoli is surrounded by a capillary network and is the site of oxygen and carbon dioxide exchange with the blood.

  • There are about 300 million alveoli in each lung.


  • Soft, spongy, cone-shaped organs located in the thoracic cavity. Covered by two serous membranes, the Pleura.

  • Visceral Pleura attached to the surface of each lung.

  • Parietal Pleura attached to the wall of the thoracic cavity.

  • Pleural Cavity. Space between the pleural layers contains serous fluid that lubricates the lungs when breathing.

Breathing pulmonary ventilation
Breathing (Pulmonary Ventilation)

  • Movement of air from outside of the body into (Inspiration) and out of (Expiration) of the lungs.

  • Inspiration – The diaphragm contracts increasing the volume of the thoracic cavity. This reduces the air pressure in the lungs below atmospheric pressure. Air is forced into the lungs.

  • Expiration – Diaphragm relaxes. Recoil of elastic tissues in and around the lungs returns lung volume to normal. This raises the air pressure inside the lungs above atmospheric pressure forcing air out of the lungs.

Respiratory volumes and capacities
Respiratory Volumes and Capacities

  • Tidal Volume – Air that enters the lungs during a normal quiet inspiration. (500 cc)

  • Inspiratory Reserve Volume – Quantity that enters the lungs in addition to tidal volume during forced inspiration. (3100 cc)

  • Expiratory Reserve Volume – Quantity in addition to tidal volume that is expelled out of the lungs during forced expiration. (1200 cc)

  • Residual Volume – Volume that remains in the lungs at all times even after forced expiration. (1200 cc)

  • Vital Capacity – Maximum volume of air that can be exhaled after taking the deepest breath possible. Equal to TV + IRV + ERV. (4800 cc)

  • Total Lung Capacity – Total volume of air that the lungs can hold. Equal to VC + RV. (6000 cc)

Control of breathing
Control of Breathing

  • Breathing is controlled by a group of neurons in the pons and medulla called the Respiratory Center.

  • Neurons in these areas emit impulses that contract the diaphragm, increase the force of breathing and control the rate of breathing.

Rate and depth stimuli
Rate and Depth Stimuli

  • High concentrations of CO2 and H+ ions stimulate chemoreceptors in the medulla to increase breathing rate.

  • Low O2 concentration stimulate chemoreceptors in the Aorta and Carotid arteries to stimulate the medulla to increase breathing rate.

  • Fear and pain increase breathing rate.

  • Stimulation of stretch receptors when the lungs are overstretched will cause the depth of breathing to decrease.

  • Rate and depth of breathing can be consciously controlled.

Exchange of gases
Exchange of Gases

  • In order for Oxygen and Carbon Dioxide to be exchanged between the atmosphere and blood, they must diffuse across the Respiratory Membrane.

  • The respiratory membrane consists of the wall of the alveolus (simple squamous epithelium), the wall of the capillary (simple squamous epithelium), and a common basement membrane between them.

Gas transport in the blood
Gas Transport in the Blood

  • Oxygen transport in the blood

    • Inside red blood cells attached to hemoglobin (oxyhemoglobin [HbO2])

    • A small amount is carried dissolved in the plasma. (1.5%)

Gas transport in the blood1
Gas Transport in the Blood

  • Carbon dioxide transport in the blood

    • Most is transported in the plasma as bicarbonate ion (HCO3–). (70%)

    • A small amount is carried inside red blood cells on hemoglobin, but at different binding sites than those of oxygen. (23%)

    • The rest (7%) as a gas dissolved in the plasma

Internal respiration
Internal Respiration

  • Exchange of gases between blood and body cells

  • An opposite reaction to what occurs in the lungs

    • Carbon dioxide diffuses out of tissue to blood

    • Oxygen diffuses from blood into tissue

Internal respiration1
Internal Respiration

Figure 13.11