Anatomy and physiology of the lungs

The lungs sit in the thorax separated from the abdomen by the diaphragm.

The respiratory system has three parts

1. The upper airway (mouth, nose, larynx and pharynx).

2. The lower airways (bronchus and bronchi).

3. The small bronchioles and the alveoli.

The muscles of respiration (diaphragm and intercostal muscles) work to drive air, which contains a mixture of gases including oxygen, into the lungs (inspiration). Gas exchange takes place at the alveoli, where oxygen moves into the body's bloodstream to supply the cells and carbon dioxide is returned to the lungs from the cells and is released out as the muscles relax (expiration). The cycle then begins again.

Air is drawn into the nose. The nasal cavities, are lined with mucous membranes which humidifies and warms the air.

Cilia, tiny hairs on the surface, clean out inhaled dust and pollen. preventing them reaching the lungs.

The inspired air moves into the pharynx and oropharynx.

Expired air passes in the opposite direction from the lungs and out through the nose and mouth.

Air entering through the mouth passes through the oral cavity to the oropharynx, where it meets the nasopharynx.

Air inspired through the mouth is not warmed or cleaned.

The pharynx is a muscular funnel shaped space used for air and food.

The final part of the pharynx is the laryngopharynx. There is a flap, the epiglottis, that is used to stop food entering the lungs.

The larynx (voice box) is a short section of the airway that connects the laryngopharynx and the trachea.

The larynx is made of cartilage containing the vocal cords.  The vocal cords are folds of mucous membrane and vibrate to produce sounds/speech.

The trachea is around 12.7 cm long.  It is supported by cartilage rings.

The lining is mucous membrane with cilia to help clean out any dust particles.

The trachea splits into 2 bronchi (right and left) and allows the air to enter and leave the lungs.

The right and left bronchus divide in 2 and this process continues in both lungs until the terminal bronchi.

The left lung has 2 lobes and the right has 3. 

The terminal bronchi lead into the bronchioles which are only a few millimetres in diameter. 

The bronchioles deliver air to the alveoli.

The alveoli are where the oxygen and carbon dioxide exchange takes place.

The alveoli are tiny sacks with very thin walls only a few cells thick.

They are like small bunches of grapes designed to create a large surface area.

Around the alveoli is a tight network of small arteries and veins.

The oxygen and carbon dioxide move across the alveolar walls from the air sacs to the blood and visa-versa.

The carbon dioxide is expired through all the tubes in the lungs to the nose and mouth and the air with oxygen is inspired all the way into the alveoli.

There are millions of alveoli in both lungs.

The lungs take up most of the thoracic cavity. The heart is surrounded, mainly by the left lung. Thus the left lung has only 2 lobes compared to the three on the right side.

Each lung is covered on the outside by the pleural membrane.

There is another layer of pleural membrane attached to the inside of the chest wall. The two layers allow the lungs to move almost friction free, as they expand and reduce in size with each breath.

The intercostal muscles, which are situated between each of the ribs and some of the muscles in the chest and neck are known as the accessory muscles of breathing. They can become active to increase air flow in and out of the lungs during exercise or activity.

The mechanism of breathing is governed by muscles in the chest, neck and shoulders.

There is a very large muscle between the chest and abdomen called the diaphragm. This is the main muscle used in all breaths. The diaphragm works like a bellows. It contracts and air moves in, and relaxes and air is pushed out.

There are layers of muscles between the ribs which are used for breathing - the intercostal muscles.

There are muscles in the neck and shoulder which are used especially when we are exerting ourselves during heavy exercise.

The lungs never completely empty of air. There is always a residual amount of air to keep open all the tubes and alveoli.

The mechanism of breathing is governed by muscles in the chest, neck and shoulders.

There is a very large muscle between the chest and abdomen called the diaphragm. This is the main muscle used in all breaths. The diaphragm works like a bellows. It contracts and air moves in, and relaxes and air is pushed out.

There are layers of muscles between the ribs which are used for breathing - The intercostal muscles.

There are muscles in the neck and shoulder which are used especially when we are exerting ourselves during heavy exercise.

The lungs never completely empty of air. There is always a residual amount of air to keep open all the tubes and alveoli.