I.        Major functions of the respiratory system.


A) Supplies body with O2 and disposes of CO2 (i.e., respiration and ventilation).

B) Houses olfactory (smell) receptors.

C) Provides sound and speech making organs and tissues.


II.       Functional process of respiration.


A) Pulmonary ventilation (generally known simply as ventilation).

a)  Moves air in and out of lungs so that it is continually refreshed.


B) External respiration.

a)  Gas exchange occurring between blood and air in the lung alveoli. (O2 is loaded into blood, CO2 is unloaded from blood.  Other gases also exchanged).


C) Transport of respiratory gases.

a)  O2 and CO2 transported between lungs and cellular tissue in the rest of the body.  Transport accomplished by blood in the cardiovascular system.


D) Internal respiration.

a)   Gas exchange at the systemic capillary level, i.e., between blood and the systemic cellular tissue.

III.      General and functional anatomy of the respiratory system.


A) Organs.                                                  Division of respiratory system by zones.                       

1)  Nose and nasal cavity.                

            2) Pharynx.       Conducting zone.

            3) Larynx.                                               Pathways where air travels to respiratory zone.

4)  Trachea.

5)  Bronchi (and branches).                                                                                                             

            6) Lungs.                                                 Respiratory zone.  Site of gas exchange in lungs.

            7) Alveoli.                                               Includes respiratory bronchioles, alveolar ducts, alveoli.


IV.     Individual organs.


A) Nose and nasal cavity.

1)  General functions.

a)  Airway, moistens and warms air, filters (cleans) air, resonating chamber for speech, houses olfactory (smell) receptors.

2)  Nasal cavity.

a)  Divided into right and left by nasal septum.

b) Vibrassae (nose hairs) filters large particles.

c)  Lined with mucous membrane.

1)  Olfactory mucosa house olfactory receptors.

2)  Respiratory mucosa.

a)  Muscous cells secrete mucus to trap small particles, viruses, etc.

b)  Serous cells secrete fluid containing digestive enzymes for bacteria.

3)  Paranasal sinuses.

a)  Sinuses (air filled cavities) surrounding nasal cavity that also have mucuos cells that trap particles, etc.


B) Pharynx (throat).

-   Connects nasal cavity to oral cavity and larynx and esophagus.

-   Is a common path for air and food.

1)  Nasopharynx (the upper section closest to nasal area).

a)  Only passes air.

b) Uvula prevents food from entering up the nasopharynx.

c)  Pharyngeal tonsils (adenoids) kill pathogens entering nasopharynx.

d) Auditory tube drains fluid from middle ear.

e)  Tubal tonsils kill pathogens before they enter auditory tube.

2)  Oropharynx (middle section near oral cavity).

a)  Passes food and air.

b) Has palatine and lingual tonsils.

c)  Structure allows high friction and chemical trauma (preliminary digestion of food).

3)  Laryngopharynx (distal section near larynx).

a)  Passes food and air.

b) Structure allows high friction and chemical trauma.


C) Larynx (voice box).  Between pharynx (laryngopharynx) and trachea.

1)  Functions.

a)  Provides an open airway.

b) Routes food to esophagus (digestive tract) and air to trachea (respiratory tract).

1)  superior opening is open during breathing and closed during swallowing.

c)  Houses vocal cords (vocal folds), thus produces sound (only part of the speech process).

2)  Structure.

a)  Nine cartilages and associated ligaments and membranes.

1)  Thyroid cartilage acts somewhat as a protective shield and has the laryngeal prominence (Adam’s apple).

2)  Epiglottis.

a)  Attached to tongue and thyroid cartilage.

b)  When swallowing larnyx is pulled up, epiglottis tips down, covering the                           laryngeal inlet to prevent food from entering the larynx.

     c)  The structure allows good speech, poor anti-choking features.

c)  Vocal ligaments.

1)  Form vocal cords (vocal folds).

2)  The glottis is the opening between vocal cords, is controlled by the laryngeal muscle.

3)  Sound production from vibration of vocal cords, but speech is aided by nasal                 and oral cavities, paranasal sinuses, lips, tongue, pharynx, soft palate.

4)  Closing of glottis (Valsalva’s maneuver) confines air to lower respiratory tract                 and is done in conjunction with increasing abdominal pressure.


D) Trachea (windpipe).

1)  Descends from larynx and divides into the two primary bronchi.

2)  Is mobile; stretches, recoils, moves side to side.

3)  Structure.

a)  Horseshoe shaped rings of hyaline cartilage connected by connective tissue; keeps              trachea from collapsing while maintaining flexibility.

b) Trachealis muscle. Between open ends of cartilage rings on posterior side of trachea.

1)  Contraction decreases tracheal size, helps expel material during coughing and                 sneezing by accelerating the air.

c)  Carina.

1)  A ridge on the distal tracheal cartilage marking the end of trachea and starting point of the primary bronchi.

2)  Is very sensitive to irritants, thus often originates the cough reflex.

3)  Lined with mucous membrane (functions as other respiratory tract mucous membranes).

E) The bronchi and smaller subdivisions.

1)  The bronchial tree of the conducting zone.

a)  Primary bronchi.

1)  Right and left.  Right is wider, shorter, more vertical.

b) Secondary, tertiary, etc., bronchi.

c)  Bronchioles.

d) Terminal bronchioles.

2)  Differences between the smaller bronchi and the trachea.

a)  Cartilage: eventually disappears.

b) Epithelium: loses ability to make mucus, hence lacks air-filtering ability.

c)  Smooth muscle appears: regulates amount of air entering lungs by constricting and                                dilating bronchioles.

3)  The respiratory zone.

a)  Includes respiratory bronchioles, alveolar ducts, and alveoli (alveoli are mostly                                     grouped in alveolar sacs at the end of the alveolar duct).

1)  Alveoli are the air sacs, surrounded by capillaries (pulmonary capillary networks),                     where the gas diffusion occurs.

a)  Respiratory membrane (Type I cells) is the air-blood barrier (allows gas                                     diffusion but not blood cell diffusion) in the alveoli.

b)  Type II cells (surfactant cells) are also a part of the alveoli.  They secrete                                    surfactant which reduces surface tension of the lung fluids which in turn                               keeps the alveoli from sticking together and collapsing during expiration.

c)  Alveolar pores between the alveoli allow equalization of air pressure in the                                  lungs and alternate air routes.

d)  Alveolar macrophages roam freely within the alveoli and remove dust particles.


F) Lungs and pleural cavities.


     Note that the lungs are the collective arrangement of the respiratory         zone items and connective tissue.

1)  Lungs.

a)  Located in thoracic cavity; anterior, lateral, and posterior surfaces lie in contact with ribs (the costal surface).

b) Apex - superior aspect.  Base - posterior aspect resting on diaphram.  Hilus - medial aspect indention allowing bronchi, lymph and blood vessels, and nerves to enter lungs.  Together, these structures in the hilus form the lung root.

c)  Left and right lung differ in shape and size due to location of heart.  The left is smaller and has the cardiac notch.

d) Lobes - sections in each lung divided by fissures.

1)  Left lung has 2 lobes; upper and lower.

2)  Right lung has 3 lobes; upper, lower, middle.

3)  The lobes are served by secondary bronchi.

4)  Each lobe divided into bronchiopulmonary segments; these segments receive air from tertiary bronchi.

5)  Bronchiopulmonary segments are further divided into lobules; served by large bronchioles.

e)  Stroma - a framework of connective tissue that supports the lungs.

f)  The lungs have their own blood and nervous supply.


2)  The pleura.

a)  The pleura is a serous membrane with 2 layers (parietal and visceral layers) inside of the thoracic cavity surrounding the lungs.

1)  The parietal pleura lines internal surface of thoracic cavity.

2)  The visceral pleura covers lung external surface.

3)  Pleural cavity is a fluid-filled (pleural fluid) space between parietal and visceral layers.

4)  The fluid reduces friction during breathing and keeps layers together.

 a)  Keeping the layers together results in the lungs expanding/recoiling with the thoracic cavity.

 b) The pleura also compartmentalize the organs - keeps them from interfering with each other.

IV.     Ventilation (breathing).

·      is composed of inspiration (inhale air into lungs) and expiration (exhale air from lungs).

A)        Inspiration.

1)  The volume of the thoracic cavity is increased, resulting in an air pressure decrease, which        then results in air coming into the lungs.

passive         a) The diaphram contracts and moves inferiorly (flattens), increasing vertical dimension of a

& forced       thoracic cavity.

inspiration     b) The intercostal muscles contract and raise ribs, increasing lateral and anterior-posterior                                  dimensions of thoracic cavity.

forced           c) Other muscles may contract to forcibly expand thoracic volume; scalenes,                       

inspiration           sternocleidomastoid, pectoral, etc.


B)        Expiration.

1)  Generally a passive process caused by relaxation of the inspiratory muscles (results in a decreased volume in the thoracic cavity).

2)  Forced expiration - an active process produced by contraction of abdominal wall muscles            (e.g., obliques, transverse abdominis).

a)  Increased intra abdominal pressure, forcing diaphram superiorly (thus decreasing thoracic cavity volume).

b)  Depresses rib cage which decreases thoracic cavity volume.


C)        Control of ventilation.

1)  Generally controlled automatically by nervous system (various brain centers, especially in the brain stem, control the basic rate of 12-15 breaths per minute).

2)  Chemoreceptors (small organs or tissue that sense the chemical composition of the blood send messages to the brain about the levels of O2 and CO2 in the blood.  If there is a lot of CO2 the ventilation rate will increase (as during exercise), if there is a lot of O2 the rate will          decrease.

3)  Higher order nervous system control (i.e., voluntary) can also control breathing rate.


V.      Diseases of the respiratory system.

A) Understand the meaning of the following terms.

1)  Chronic obstructive pulmonary disease.

a)  Emphysema (obstructive)

b) Bronchitis (obstructive)

c)  Dyspnea

2)  Lung cancer.