How the Respiratory System Works

We normally think of respiration as the movement of air into and out of the lungs. This action should not to be confused with cellular level respiration that occurs inside of cells to produce ATP, although both are needed along with proper functioning of the cardiovascular system for you to stay alive. Any disruption of these results in a loss of homeostasis and death of the organism. The Respiratory System is involved in more than gas exchange. Functions include:

1. Pulmonary ventilation - oxygen/carbon dioxide exchange.
2. Vocalization in general and speech in particular.
3. Supports olfaction by bringing air to the olfactory receptors.
4. Control of pH by eliminating carbon dioxide.
5. Assist with blood pressure regulation through angiotensin II
6. Changes in pressure in the thoracic cavity assist venous blood return and movement of lymph.

Lumen Learning has several pages devoted to this system

Another good link to the human respiratory system is at the Online Biology Book

Typically the respiratory system is divided into an upper and lower system. The upper system is often referred to as the conducting zone because it is the path by which air gets into and out of the lungs. The lower half is referred to as the Exchange Zone because oxygen and carbon dioxide are exchanged here.

Upper Respiratory System

External nose - flexible cartilage
Nasal cavity
           a. From nares to choanae

           b.  Vestibule: just inside nares
c. Hard palate: floor of nasal cavity
           d.  Nasal septum: partition dividing cavity. Anterior cartilage; posterior vomer and perpendicular plate of ethmoid

           e.  Choanae: bony ridges on lateral walls with meatuses between. Openings to paranasal sinuses and to nasolacrimal duct

            Functions - 1. incoming air is warmed, moistened and filtered – nasal conchae - superior middle inferior
                                           a.  ciliated epithelium

                                           b.  mucous glands
2. olfactory stimuli are received
3. large hollow resonating chambers are provided for speech sounds – sinuses- frontal, maxillary, sphenoid, ethmoid
Pharynx –(throat) shared by the respiratory and the digestive systems

                        1. nasopharynx – to posterior edge of soft palate
a. Openings of Eustachian (auditory) tubes
                                          b. Uvula is posterior extension of the soft palate.

                        2. oropharynx – soft palate to hyoid bone
                        3. laryngopharynx – hyoid bone – esophagus

          Functions - 1. passageway for air and food
                              2. provide a resonating chamber for speech sounds
3. Tonsils – lymphoid organs –pharyngeal (adenoids when inflamed) and two lateral palatine tonsils

Larynx - voice box

Functions 1. connects pharynx with the trachea
                  2. contains 9 cartilage's - epiglottis - prevents entry of food or liquid into the respiratory tract – Box shapedThyroid cartilage →ridge →Adam’s Apple

             3. sound production - vocal cords vibrate when air passes through the glottis – vocal cords = fibroelastic bands – length changes at puberty, larynx in male enlarges more = deeper voice

Trachea - windpipe

        Functions 1. provides a tough flexible tube for passage of air
a. composed of 16-20 "C" shaped cartilage
b. opened part allows for expansion
c. lined with pseudostratified ciliated epithelium

  Carina - cartilage at bifurcation. Membrane of carina especially sensitive to irritation and inhaled objects initiate the cough reflex

Lungs - gross anatomy

Pleural Cavity – each lung has it’s own cavity separated by mediastinum
       1.  Parietal pleura – inner surface of thoracic cavity, diaphragm, & mediastinum

       2.  Visceral pleura – outer surfaces of lungs & between the lobes in the fissures
Paired organs - - lobes separated by deep fissures
Apex - superior point of lung
Base - rests on the diaphragm

       Hilus - on medial surface where bronchi and blood vessels enter the lung. All the structures in hilus called root of the lung.

             Right lung - 3 lobes – superior, middle, inferior
             Left lung -  2 lobes, - superior, inferior, cardiac notch

Bronchi - bronchial tree

             Structure         1. Right and left primary bronchi
2. secondary bronchi - enter each lobe of that lung
                                     3. tertiary bronchi - 9-10 divisions

                                     4. bronchioles - can vary in diameter – smooth muscle
5. terminal bronchioles - provide passageway to the respiratory bronchioles
6. alveolar ductsalveolar sacsalveoli - the exchange surface of the lungs

Surfactant - oily secreation that coats the alveolar epithelium
            1. reduces surface tension within the alveolus prevents the collapse of aveolar walls

Respiratory Membrane - gas exchange area

          Structure  1. surfactant --> alveolar epithelium ( simple squamous ) -->fused basement membrane -->endothelium of the capillary ( simple squamous

Function -  place where large quantities of air and large quantities of blood come in close contact for rapid exchange of gases to occur -diffusion – of gases – area of high concentration to area of low concentration