The Lungs - Research Paper Example

The lungs are composed of a substance which is light, porous, have a spongy texture and are highly elastic. The surface has many polyhedral areas. The lungs are heavier in a male than in a female; the left lung is smaller than the right one in order to accommodate the heart. The lungs can be examined in terms of an apex, a base, three borders (anterior and inferior) and two surfaces (Costal and mediastinal). Each lung is conical in shape and is divided into lobes by interlobular fissures. The left lung is divided into the left superior or upper lobe and the left inferior or lower lobe.

The right lung is divided into the right superior lobe, the right middle lobe and the right inferior lobe. Each lobe is further divided into pyramidal bronchopulmonary segments: ten in the right and eight in the left one. The root of each lung or the hilum connects the lung to the heart and the trachea. According to Gray (1918), “the bronchus, the pulmonary artery, the pulmonary veins, the bronchial arteries and veins, the pulmonary plexuses of nerves, lymphatic vessels, bronchial lymph glands, and areolar tissue enter and leave the lungs through the root”.

The trachea, or windpipe, reaches the thorax and is divided into the right and left bronchi. In the lungs the bronchi divide into large ventral and small dorsal branches. The bronchi are divided into smaller bronchi and bronchioles. Each bronchiole further splits into two or more respiratory bronchioles connected to alveolar ducts which, in turn, are connected to a cluster of small alveoli or air sacs. The pulmonary artery, the pulmonary veins, and the pulmonary capillaries supply deoxygenated blood to the lungs and remove oxygenated blood.

The bronchial arteries and the bronchial vein supply oxygenated blood for the nutrition of the lung itself. All these arteries and veins enter and leave the lung through the hilum, as do the lymphatic vessels of the lungs. Pulmonary nodes, bronchopulmonary nodes and tracheobroncheal nodes are present. The lungs are supplied with nerves from the anterior and posterior pulmonary plexuses which have small ganglia on them. (Gray, 1918). The function of the lungs is to provide a continuous gas exchange between the inhaled air and the blood in pulmonary circulation.

Oxygen is supplied and carbon dioxide is eliminated by exhalation. The exchange of gases takes place through simple diffusion: oxygen diffuses from the alveoli into the blood and CO2 diffuses from the blood into the alveoli. This diffusion requires a concentration, or pressure, gradient. The concentration of oxygen in the alveoli is kept higher than in the blood and the concentration of CO2 in the alveoli is kept lower than in the blood by the breathing of fresh air into the lungs. This breathing mechanism is generated by the respiratory muscles: the exterior intercostals located between the ribs, and the diaphragm which is a sheet separating the thorax from the abdomen.

During inspiration the intercostals and the diaphragm contract, the dimension of the thoracic cavity increases, air pressure in the lungs decreases and becomes slightly negative as compared to atmospheric pressure. This causes the air to move from the atmosphere into the lungs. During exhalation the muscles relax, lung volume decreases, pressure in the lungs increases and air is exhaled. The surface tension on the walls of the alveoli caused by water molecules is reduced by the pulmonary surfactant produced by the lungs.

The exchange