Page 204 - 84 human physiolofy part-1

Chapter 11

therefore tend to take shallow breaths and breathe more frequently.

Determination of Lung Compliance Two major things determine lung compliance. The first is
the elasticity of the lung tissue. Any thickening of lung tissues due to disease will decrease lung
compliance. The second is surface tensions at air water interfaces in the alveoli. The surface of the
alveoli cells is moist. The attractive force, between the water cells on the alveoli, is called surface
tension. Thus, energy is required not only to expand the tissues of the lung but also to overcome the
surface tension of the water that lines the alveoli.

To overcome the forces of surface tension, certain alveoli cells secret a protein and lipid complex
called ""Surfactant””.

Respiratory System: Upper and Lower Respiratory Tracts

For the sake of convenience, we will divide the respiratory system in to the upper and lower
respiratory tracts:

Upper Respiratory Tract

The upper respiratory tract consists of the nose and the pharynx. Its primary function is to receive
the air from the external environment and filter, warm, and humidify it before it reaches the delicate
lungs where gas exchange will occur.

Air enters through the nostrils of the nose and is partially filtered by the nose hairs, then flows into
the nasal cavity. The nasal cavity is lined with epithelial tissue, containing blood vessels, which help
warm the air; and secrete mucous, which further filters the air. The endothelial lining of the nasal
cavity also contains tiny hairlike projections, called cilia. The cilia serve to transport dust and other
foreign particles, trapped in mucous, to the back of the nasal cavity and to the pharynx. There the
mucus is either coughed out, or swallowed and digested by powerful stomach acids. After passing
through the nasal cavity, the air flows down the pharynx to the larynx.

Lower Respiratory Tract

The lower respiratory tract starts with the larynx, and includes the trachea, the two bronchi that
branch from the trachea, and the lungs themselves. This is where gas exchange actually takes place.

Larynx

The larynx (plural larynges), colloquially known as the voice box, is an organ in our neck involved
in protection of the trachea and sound production. The larynx houses the vocal cords, and is situated
just below where the tract of the pharynx splits into the trachea and the esophagus. The larynx contains
two important structures: the epiglottis and the vocal cords.

The epiglottis is a flap of cartilage located at the opening to the larynx. During swallowing, the
larynx (at the epiglottis and at the glottis) closes to prevent swallowed material from entering the lungs;

204 | Human Physiology