Respiratory SystemCHAPTER 18.4 PAGE 490

Overview of the respiratory system

Main function of the system

To provide the efficient exchange of respiratory gases – absorption of oxygen and removal of carbon dioxide

Remove and destroy foreign matter that enters the system

General features of the system 2 lungs in the thoracic cavity connected to the exterior by a series of

tubes.

Gases in the lungs are exposed to continuous blood flow via the pulmonary artery and associated capillaries

The surfaces of the lungs and the other surfaces that they come into contact with, which include the interior surface of the thoracic cavity, the heart and oesophagus, are all covered by the pleural membranes. The space between the membranes is filled with fluid that reduces friction. In the same way that moisture causes the two layers of a plastic bag to adhere, the lungs are attached to the chest wall by this vacuum effect. If air is allowed into this space the lung detaches from the chest wall and a pneumo-thorax results.

Along with the functional tissues listed later, the lungs are composed of elastic connective tissues that gives the lungs their characteristic ‘spring back into shape’ ability.

Anatomy and physiology of the respiratory system

Air enters via the nose, nostrils or nares – the hair and mucus act as filters to remove dust and other particles. The capillaries beds of the nasal cavity also warm and humidify the air.

Olfactory sensors high in the nasal cavity are sensitive to smells and convey that information via the olfactory nerve to the brain.

The anterior floor of the nasal cavity is formed by the hard palate (bone) and the posterior section is formed by the soft palate (soft tissue).

The nasal cavity and buccal (mouth) cavity both open into the pharynx – back of the throat.

Also found here are the uvula, tonsils, adenoids and the Eustachian tubes

Anatomy and physiology of the respiratory system

Two major vessels lead off from the pharynx – the trachea (windpipe) is anterior to the oesophagus (food tube)

The larynx (voice box) is at the superior (anterior) end of the trachea. The opening of the larynx is called the glottis. There is an upwardly directed hard flap of cartilage known as the epiglottis that prevents food from entering the trachea at this point. It automatically closes as you swallow.

Air passing through the larynx can be made to vibrate the vocal chords – flaps of skin that can have variable tension to change pitch.

Vocal chords

Trachea and bronchi

Trachea and bronchi

The trachea splits into the left and right bronchus

Within the lung, each bronchus divides into bronchioles which ultimately give rise to alveolar ducts and then to a cluster of alveoli (pl).

The trachea, bronchi and major branches contain incomplete cartilaginous rings that are controlled by smooth muscle to vary the diameter of the airway.

The internal surfaces are lined with ciliated epithelial cells (hair like projections) and goblet cells that produce mucus.

The combination of the mucus trapping dust and foreign particles and the beating cilia moves the trapped matter towards the pharynx for removal.

Cilia and goblet cells

Alveoli

Each alveolus (s) is the individual air sac where gas exchange occurs. The alveolar walls are very thin with flattened cells and a capillary network to which allow for the rapid exchange of carbon dioxide and oxygen.

Certain cells in the wall of the alveolus secrete ‘surfactant’ a natural detergent that reduces surface tension and allows the lungs to inflate.

Phagocytic cells destroy and remove foreign particles and bacteria.

General alveolar structure

Gas exchange in the alveolus

Diagram of gas exchange