1. Airways   2. Lungs   3. Blood supply   4. Muscles

1. Airways

Two parts: Upper system – nose, nasal cavity, pharynx, larynx 
                     Lower system – trachea, bronchi, lungs

Upper system
Nose – Air enters, is humidified and warmed.  Hairs (cilia) and mucous clear debris.
Nasal cavity – Inside the nose; direct air to lungs. Has olfactory cells for sense of smell.
Pharynx – The “throat”. Passage of food and air. Muscles control swallowing.                                       Divided into: nasopharynx, oropharynx, laryngopharynx.                                          Includes adenoids and tonsils.
Larynx – The “voice box”. About 2 inches long in adults.  Houses vocal chords.                                  Made of 9 pieces of cartilage, including epiglottis which keeps food from entering the lungs.

Lower system
Trachea – The “windpipe”. About 5 inches long in adults. Branches into 2 main bronchi.
Bronchi – Conducts air into lungs. Divided into Right and Left main bronchus, which are       
                      further divided into smaller bronchi and then bronchioles.
Lungs – Main respiratory organ.  Place of O2 and CO2 exchange.

2. Lungs

Lie on either side of mediastinum in thoracic cavity.
Surrounded by chest wall and 24 ribs.
Made of spongy tissue.
Apex is the top part that lies about 1 inch above the clavicle.
Base is the bottom part that lies on the diaphragm.


a) Lobes   b) Pleura   c) Bronchial Tree   d) Alveoli

a) Lobes

Right lung is larger and has 3 lobes – superior, middle, inferior.
Left lung is smaller with 2 lobes due to the position of the heart.
Lobes are separated by fissures.

b) Pleura

Pleural membrane – membrane that encloses each lung.
Parietal pleura – membrane lining the chest wall.
Visceral pleura – membrane lining the lungs inside the chest.
Pleural cavity – space between the pleurae.
Pleural fluid – thin film of fluid that acts as a lubricant allowing lungs to move during breathing.

c) Bronchial Tree

Resembles an upside-down tree made of rings of cartilage, except in smaller bronchioles.
Right primary bronchus and Left primary bronchus divide from the trachea.                                                                                       Carina – ring of cartilage at the trachea where it divides (triggers cough).
The right bronchus is shorter, wider and straighter, so aspiration is more likely to occur there.
The primary bronchi divide into smaller bronchi -> bronchioles -> terminal bronchioles (smallest).
The bronchial tree consists of smooth muscle, mucous membrane, cilia and goblet cells
Goblet cells secrete mucous that trap substances and cilia sweep the mucous out of lungs

d) Alveoli

Alveolus – a small sac that resembles a grape attached to an alveolar duct at the terminal bronchiole.
Alveoli – small clusters within the sac that are the sites of gas exchange.  There are about 300 million alveoli in adults (0.3mm in diameter) with a surface area of a tennis court.
Surfactant – a lipoprotein that lowers the surface tension in alveoli and prevents them from collapsing (they have a natural tendency to collapse).  Reduces the amount of pressure needed to inflate the alveoli.
A thin basement membrane connects alveoli and capillaries where gas exchange occurs.
Atelectasis – collapsed, airless alveoli.


3. Blood Supply

Lungs receive blood via pulmonary and bronchial arteries.

Pulmonary arteries bring deoxygenated blood from the right ventricle thru a pulmonary trunk that divide into right and left pulmonary artery.

Arteries branch into arterioles and then capillaries at the alveoli level where the blood gives up CO2 and picks up O2.  Oxygenated blood returns via 4 pulmonary veins to left atrium.

Bronchial arteries from the aorta bring oxygenated blood to the bronchi, bronchioles and tissues. They do not extend to the alveoli.  Oxygenated blood returns via bronchial and pulmonary veins to the systemic circulation and some to left atrium of heart.

4. Muscles

Diaphragm – the main muscle involved in respiration.  Flat, dome shaped.
Inspiration – diaphragm contracts and moves down to allow air to enter.
Expiration – diaphragm relaxes passively and air moves out.
Intercostal muscles between ribs, abdominal and sternocleidomastoid muscles are some of the other muscles that support breathing.
Intercostal muscles lie between the ribs and assist in chest expansion during inspiration.

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