(The images are of human models and cat dissections.)
Cells need oxygen in order to obtain energy and the carbon dioxide they produce must be removed since high levels of carbon dioxide are toxic.
There are 4 steps in this process:
a) pulmonary ventilation (breathing): there is an exchange of air between the lungs and the atmosphere
b) external respiration: gases are exchanged between lung spaces and capillaries
c) internal respiration: gases are exchanged between capillaries & tissue cells
d) cellular respiration: cells break down food molecules with oxygen to obtain energy

Obviously, the respiratory system is dependent upon the circulatory system to transport these gases.


The nasal cavity opens to the outside world and the nasal septum splits this cavity. As air enters, 3 bony shelves or conchae (made of the ethmoid & inferior conchae bones) causes the incoming air to swirls through passages. If air went straight to the lungs, dry and cold air would disrupt the homeostasis of the delicate lung tissue. As it swirls, air is warmed and humidified while dust particles and microbes get caught in the mucus. The cilia which line the respiratory tract sweep this mucus into the mouth where it can be removed by spitting or swallowing


From the nasal cavity, air passes to the pharynx where mucus membrane covers skeletal muscle. The pharynx and nasal cavity a resonance chamber for sound and several tonsils are located here.



The larynx connects the pharynx and trachea During swallowing, a flap of cartilage called the epiglottis is raised so that it closes over the opening to the trachea (the glottis) so that food can't enter the trachea. Vocal cords are located in the larynx. As air is forced past them, they vibrate. The larynx controls the pitch of the voice; the muscles of the pharynx control the vowel sounds; and the movements of the mouth, lips, and tongue the make the sounds of the consonants.



The trachea is a tube of cartilage which divides into two primary bronchi as it enters the lungs. The primary bronchi further divide into secondary bronchi (2 to the 2 left lobes of the lung, 3 to the 3 right lobes) which then divide into tertiary bronchi (about 10 per lung) which finally divide into bronchioles. Bronchioles divide further until they become terminal bronchioles (diameter .5 mm). The cartilage decreases and then disappears and smooth muscle replaces it. Where there is no cartilage, muscle constriction may close off the trachea (as in an asthma attack). Epinephrine mists can cause this muscle to relax.



In the lobules of the lungs, elastic connective tissue surrounds a lymphatic vessel, arteriole, venule, and a branch of a terminal bronchiole. From the terminal alveolus branch a number of grape-like sacs known as alveoli.



There are about 150 million alveoli per lung. They are composed of type I cells (very thin cells where most of the gas exchange occurs) and type II cells (which secrete alveolar fluid to keep that alveolus moist and provide the surfactant). Without surfactant, the attraction of water molecules for each other would cause alveoli to collapse. Deoxygenated blood comes from heart through pulmonary arteries and oxygenated returns through pulmonary veins (2 from each lung).


Breathing (Pulmonary Ventilation) is caused by muscle contraction. Inspiration (inhalation) occurs through the contraction of the diaphragm and external intercostals. Contraction flattens the diaphragm, lowering its dome, dropping it 1 cm at rest and 10 cm during exercise. This vertical change is responsible for 75% the air movement and late pregnancy, obesity, and tight clothing may interfere with this movement. When external intercostals contract the sternum is pulled forward and the ribs upwards.
In expiration (exhalation), no muscle contraction involved and it is usually a passive process. Inspiratory muscles relax, decreasing the volume of the thorax; elastic fiber recoil of chest wall & lungs does the same. Labored breathing uses abdominal muscles and internal intercostals. As these muscles contract, the volume of the thorax decreases further.


a) asthma: smooth muscle contraction narrows respiratory passageways; allergins like pollen and dust mites may cause
--may be alleviated through E spray (short term) and anti-inflammatory agents (long term)
--affects 3-6% population

b) emphysema: alveolar degeneration, less surface area for gas exchange; such damage is permanent
--key symptom is decreased forced expiratory volume, extra work to exhale
--cigarette smoke and pollutants cause
--cigarette smoke may decrease the inhibition of proteases which then attack tissue

c) lung cancer
--symptoms usually don't show until tumor masses restrict airflow
--deaths were rare at the turn of the century; have doubled every 15 years since then; each year 22% new cancers detected are lung cancers
--primary cause of cancer death in the U.S. comprising 35% cancer deaths; most patients die within 1 year of diagnosis; 5 year survival rate is 30% for men and 50% for women
--80-90% lung cancer deaths are a direct result of cigarette smoke (no matter what cigarette companies say)
--cancer rates 3.4/100,000 among nonsmokers, 59.3/100,000 for those who smoke 1/2-1 pack a day, 217.3/100,000 for those who smoke 1-2 packs a day
--passive smoke may cause 4000 deaths/year

d) Respiratory Distress Syndrome (RDS)--20,000 newborn deaths/year
--deficient surfactant, the surface tension in alveoli is 7-14x the normal amount
--muscular effort is needed to expand the lungs
--premature babies born by Caesarean section have a higher incidence of

e) Sudden Infant Death Syndrome (SIDS)--10,000 babies a year die from (the leading cause of death in infants 1 week to 12 months)
--half display a respiratory illness within 2 weeks of death
--hypotheses for the cause include viruses, hyperthermia, and hypoxia due to sleeping position

f) cystic fibrosis--the most common genetic disease in the U.S.;
--5% Caucasians are carriers; affects 1/1600 births
--a membrane protein can't transport Cl ions; instead of watery secretions the body produces more gooey (a clinical term) secretions
--respiratory cilia can't move causing a higher frequency of infections; may block airways

Sinusitis: swelling of sinus cavity linings or prevents drainage; mucus accumulates, fostering bacterial growth
Bronchitis: involves bronchi but does not extend to alveoli (about 15% population has chronic bronchitis); if spreads to alveoli, becomes pneumoni--bronchitis can be aggravated by smoking, air pollution, coal dust, cotton lint, etc.
Inflammation of the lungs:
--while inflammation is often a normal response, the added fluid and leukocytes can clog airways as in pneumonia and tuberculosis

a) Trachea:
--substances in cigarette smoke inhibit the movement of cilia, decreasing the ability to remove dust and microbes from the respiratory tract
--mucus may accumulate that only coughing can move (since the cilia are no longer performing this function); hence the smoker's cough
--the accumulation of foreign bodies here may trigger the immune inflammatory response
--smoking is the primary cause of chronic bronchitis
--cigarette smoke can trigger asthma attacks
--second hand smoke predisposes children to respiratory problems such as bronchitis during their first year; since the cilia also are responsible for the elimination of microbes, these children are also more vulnerable to pneumonia
b) Lungs

--cigarette smoke can trigger alveolar destruction through 3 means:
--deactivates a protein that inhibits alveolar degeneration
--causes the buildup of mucus and the resultant inflammatory response; action of white blood cells may destroy alveolar cells
--prevents repair of lung tissue
--as alveolar sacs are lost, the lung tissue is represented by more and more air spaces; this is the literal meaning of emphysema; this damage is permanent
--since the alveoli are the sites where gases exchange with the blood, the ability to perform adequate gas transport diminishes; as lungs strain they may even increase in size, creating the "barrel chests" often found in emphysema patients
--forced expiratory volume is less; more effort required to forcefully exhale
--rate is 4-25x higher in smokers

c) Cancer
--substances which are carcinogens can cause mutations in cells which will eventually lead to cancer
--a number of carcinogens are present in cigarette smoke including: aminostilbene, arsenic, benza antracene, benza pyrene, benzene, benzo flouranthene, benzo phenanthrene, cadmium, chrysene, dibenz anthracene, dibenz acridine, dibenz carbazone, N-dibutylnitrosamine, dimethyl chrysene, indenol pyrene, methylchrysene, methylflouranthene, napthylamine, nickel compounds, nitrosodiethylamine, nitrosoanabasine, nitrosonornicotine, nitrosopiperidine, polonium
--smoking presents an increased cancer risk:
--a 25 year old who smokes 2 packs a day has a life expectancy of 8.3 years less than a nonsmoker
--cancer of the larynx, mouth, espohagus, bladder, and pancreas range 2-17x higher in smokers
--radon particles adhere to ash particles and aren't removed by cilia from the respiratory tract as well in smokers; radon related risks are 15x greater in smokers

d) Other
--cigarette smoking is implicated as the major cause of 120,000 deaths of coronary heart disease yearly (including 40,000 deaths due to second hand smoke)
--nicotine causes vasoconstriction that increases blood pressure; increased blood pressure may be one of the factors that damage endothelial linings, leading to atherosclerosis
--mothers who smoke endanger their fetuses:
--higher rates of stillbirth, lower birthweight, higher incidence of disease and death in the first year, lower physical development after 7 years; increases risk of cleft lip & palate
--children who nurse from smoking mothers have increased incidence of gastrointestinal problems