The respiratory system
The respiratory system consists of the nose, the pharynx, the larynx, thejrachea, the bronchi and the two lungs.
THE NOSE: (Fig. 16)
It consists of a bony part and a cartilaginous part. The nasal septum divides it into right and left halves. It opens anteriorly on the face by the anterior nares, and posteriorly into the nasopharynx by the posterior nares. Its lateral wall contains bony projections covered by mucous membrane called co.ochae…They are 3. in number, superior, middle, and inferior conchae.
The nasal cavity is lined by the nasal mucosa, whose upper part is concerned with the sensation of smell, while its
The paranasal sinuses are air filled extensions of the nasal cavity into the surrounding cranial bones. They are lined by mucous membrane. The secreted mucus passes to the nasal cavity through meatuses in its lateral walls.
The pharynx is a muscular tube that extends from the base of the skull above to the sixth cervical vertebra below. It lies behind the nasal cavity, the mouth cavity and the larynx. Its wall is composed of a muscle layer lined from the inside by mucous membrane. It is divided into 3 parts:
a) The nasopharynx: is the highest part which lies behind
the7 nose. It communicates anteriorly with the nose
through the posterior nares and on each side with the
middle ear through the openings of the right and left
auditory tubes (Eustchian tubes). Its roof contains the
pharyngeal tonsils which is a collection of lymphoid
b) The oropharynx: which lies behind the oral cavity. It
communicatesanteriorly with the oral cavity. It is
common to both the alimentary and respiratory systems.
On its lateral walls lie the palatine tonsils.
cy The laryngopharynx: which lies behind the larynx. It communicates anteriorly with the inlet of the larynx.
The Larynx: (Fig. 17)
It is an air passage and it is also the organ of voice production. It connects the laryn go pharynx above with the
trachea below. It extends in the midline of the neck lying opposite the third, fourth, fifth, and sixth cervical vertebrae.
It is formed of a number of cartilages, which are connected together by ligaments, membranes, and muscles. It is lined by mucous membrane. The most important of its cartilages are the thyroid cartilage, the cricoid cartilage and the epiglottis. The epiglottis closes the inlet of the larynx during deglutition. It contains the two vocal cords which bound the glottis which is the narrowest part of the cavity of the larynx.
THE TRACHEA: (Fig. 17)
The trachea is a cartilaginous and membranous tube which conveys air into and out of the lungs. It begins at the lower end of the larynx at the level of the 6th cervical vertebra and terminates at the lower border of 4th throacic vertebra where it divides into the two main bronchi.
It is composed of about 20 cartilaginous C-shaped rings connected together with membranes. The) are incomplete posteriorly, where it is related to the oesophagus, being replaced by involuntary musc’e^ controlling its diameter.
The trachea is lined by mucous membrane provider with cilia which sweep the secretions to the outside.
THE TWO MAIN BRONCHI: (Fig. 17)
At the level of the lower border of the fourth thoracis vertebra, the trachea divides into the right and left ma;i bronchi which are similar to the trachea in their structure.
a) The right main bronchus: it is shorter, wider, and more ertical than the left main bronchus.
b)The left main bronchus: it is longer, narrower, and more
oblique than the right main bronchus.
The LUNGS: (Fig. 18)
The lungs are the essential organs of respiration. They are normally light, soft, spong\ and elastic. During early life they are pink but during late life they are dark and mottled due to the entrapped carbon particles in the phagocytes.
Each lung has the shape of half a cone so that it has an apex, a base. 2 surfaces, and 3 borders.
The apex is directed upwards and lies above the Is1 rib.
The base is concave, directed downwards and lies on the diaphragm.
The lateral surface is com ex and is related to the chest wall.
The medial surface is concave, related to the heart, and contains the hilum of the lung.
The hilum is the region where the corresponding bronchus, pulmonary artery, pulmonary veins, lymphatics, and nerves enter or leave the lung. These structures collectively form the root of the lung.
The lower border separates the base from the 2 surfaces, it is semilunar in shape.
The anterior border is sharper and shorter than the posterior border.
The posterior border is longer and thicker than the anterior border.