Basic anatomy of mediastinum and respiratory system :

Dr.sarah ali abed

M.B.Ch.B.,F.I.C.M.S(Path)

Department of anatomy /faculty of pharmacy

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Mediastinum :is a movable partition that extends superiorly to the thoracic inlet and the root of theneck and inferiorly to the diaphragm. It extends anteriorly to the sternum and posteriorly to the vertebral column. It is divided into two part :

I. Superior mediastinum : (a) Thymus, (b) large veins, (c) large arteries, (d) trachea,(e) esophagus and thoracic duct, and (f) sympathetic trunks.

II. inferior mediastinum : (a) Thymus, (b) heart within the pericardium with thephrenic nerves on each side, (c) esophagus and thoracic duct, (d) descending aorta, and (e) sympathetic trunks. which is subdivided into anterior ,,middle and posterior mediastinum  all relative to the pericardium . anterior mediastinum being in front of the pericardium, the middle mediastinum contains the pericardium and its contents, and the posterior mediastinum being behind the pericardium .

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Respiratory tract :It is divided into upper respiratory tract which includes (nose , Para nasal sinuses ,nasopharynx , larynx) and lower respiratory tract( trachea ,major bronchi ,lung).

Nose : The nose consists of the external nose and the nasal cavity.

The External nose has two elliptical orifices called the nostrils,which are separated from each other by the nasal septum . The lateral margin the ala nasi is rounded and mobile. is made up above by the nasal bones , the frontal processes of the maxillae, and the nasal part of the frontal bone. Below is formed of plates of hyaline cartilage .Blood Supply of the External Nose is supplied by branches of the ophthalmic , the maxillary arteries and facial artery.Nerve Supply of the External Nosebranches of the ophthalmic nerve (CN V /trigeminal nerve) and branch of the maxillary nerve (CN V /trigeminal nerve ) .

nasal cavity : extends from the nostrils in front to the posterior nasal apertures or choanae behind, where the nose opens into the nasopharynx. The nasal vestibule is the area of the nasal cavity lying just inside the nostril.The nasal cavity is divided into right and left halves by the nasal septum .

Walls of the Nasal Cavity:

Each half of the nasal cavity has a floor, a roof, a lateral wall,and a medial or septal wall.

Floor:Formed by the palatine bone and the maxillary bone Roof:is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones, in themiddle by the cribriform plate of the ethmoid, posteriorly by the downward sloping body of the sphenoid

Lateral Wall:

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The lateral wall has three projections of bone called the superior, middle, and inferior nasal conchae.The space below each concha is called a meatus.

Medial Wall:The medial wall is formed by the nasal septum.

Blood Supply to the Nasal CavityThe arterial supply to the nasal cavity is from branches of the maxillary artery, one of the terminal branches of the external carotid artery. The submucous venous plexus is drained by veins that accompany the arteries.

Lymph Drainage of the Nasal Cavity

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The lymph vessels draining the vestibule end in the submandibularnodes. The remainder of the nasal cavity is drained by vessels that pass to the upper deep cervical nodes.

Nerve Supply of the Nasal CavityThe olfactory nerves from the olfactory mucous membrane ascend through the cribriform plate of the ethmoid bone to the olfactory bulbs The nerves of ordinary sensation are branches of the ophthalmic division (V1)and the maxillary division (V2) of the trigeminal nerve.

Functions of the nasal cavity:1. Conduction of air.2. Air conditioning, by warming and humidifaction.3. Filtration of air by mucus.

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The Paranasal Sinuses:

The paranasal sinuses are cavities found in the interior of the maxilla, frontal, sphenoid, and ethmoid bones they communicate with the nasal cavity through relatively small apertures

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The pharynx: is funnel shaped, its upper, wider end lying under the skull and its lower, narrow end becoming continuous with the esophagus.it is divided into three parts :

Nasopharynx : The upper portion of the pharynx, extends from the base of the skull to the upper surface of the soft palate.  The adenoids, also known as the pharyngeal tonsils, are lymphoid tissue structures located in the posterior wall of the nasopharynx. Waldeyer's tonsillar ring is an annular arrangement of lymphoid tissue in both the nasopharynx and oropharynx.

Oropharynx:lies behind the oral cavity, extending from the uvula to the level of the hyoid bone.

The laryngopharynx,also known as hypopharynx: is the caudal part of the pharynx; it is the part of the throat that connects to the esophagus. It lies inferior to the epiglottis and extends to the location where this common pathway diverges into the respiratory (larynx) and digestive (esophagus) pathway.

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Larynx : is an organ that provides a protective sphincter at the inlet of the air passages and is responsible for voiceproduction. It is situated below the tongue and hyoid bone and between the great blood vessels of the neck and lies at the level of the fourth, fifth, and sixth cervical vertebrae .It opens above into the laryngeal part of thepharynx, and below is continuous with the trachea. The larynx is covered in front by the infra hyoid strap muscles and at the sides by the thyroid gland. The framework of the larynx is formed of cartilages that are held together by ligaments and membranes, moved by muscles, and lined by mucous membrane.

Cartilages of larynx :1. Thyroid cartilage (adam apple).2. Cricoid cartilage 3. Epiglottis cartilage4. Arytenoid cartilage 5. Corniculate cartilage6. Cuneiform cartilage

Membranes and Ligaments of the Larynx:7. Thyrohyoid membrane8. median thyrohyoid ligament. 9. Cricotracheal ligament10.Quadrangular membrane

Muscles of the LarynxThe muscles of the larynx may be divided into two groups: extrinsic and intrinsic.

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The vocal fold: is a mobile fold on each side of the larynx and is concerned with voice production. It is formed by mucous membrane covering the vocal ligament and is avascular and white in color. The vocal fold moves with respiration and its white color is easily seen when viewed with a laryngoscope.

Nerve supply :The larynx is innervated by branches of the vagus nerve on each side. Sensory innervation is by the internal branch of the superior laryngeal nerve .Motor innervation is by recurrent laryngeal nerve. Injury to one of the recurrent laryngeal nerves produces hoarseness, if both are damaged the voice may or may not be preserved, but breathing becomes difficult.Function of larynx :

Voice production protect inlet of trachea from aspiration of food by epiglottis .

Trachea : is a mobile cartilaginous and membranous tube .It begins in the neck as a continuation of the larynx at the lower border of the cricoid cartilage at the level of the 6th cervical vertebra. It descends in the midlineof the neck. In the thorax, the trachea ends below at the carina by dividing into right and left principal (main bronchi at the level of the sternal angle (opposite the disc between the 4th and 5th thoracic vertebrae. In adults, the trachea is about 4 1/2 in. (11.25 cm) long and 1 in. (2.5 cm) in diameter .The fibroelastic tube is kept patent by the presence of U-shaped bars (rings) of hyaline cartilage embedded in its wall. The posterior freeends of the cartilage are connected by smooth muscle, the trachealis muscle.

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Blood Supply of the Trachea:

o the inferior thyroid arterieso bronchial arteries

Lymph Drainage of the Trachea:

o the pretracheal and paratracheal lymph nodes.

Nerve Supply of the Trachea:

o The sensory nerve supply is from the vagi. Sympathetic nerves supply the trachealis muscle.

Bronchi :

The trachea bifurcates behind the arch of the aorta into the right and left principal (primary or main) bronchi. The right principal (main) is wider, shorter, and more vertical than the left and is about 1 in. (2.5 cm) long. Before entering the hilum of the right lung, the principal bronchus gives off the superior lobar bronchus. On entering the hilum,it divides into a middle and an inferior lobar bronchus.The left principal

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(main)bronchus is narrower, longer,and more horizontal than the right and is about 2 in.(5 cm) long. It passes to the left below the arch of the aorta and in front of the esophagus. On entering the hilum of the left lung, the principal bronchus divides into a superiorand an inferior lobar bronchus.The bronchi divide giving rise to several million terminal bronchioles that terminate in respiratory bronchioles that divided into aleveolar ducts which enter aleveolar sac.

Lung :

The lungs are the primary organs of respiration in humans. Humans have two lungs, a right lung and a left lung. They are situated within the thoracic cavity of the chest. They are Separated from each other by the heart and great vessels. Each lung has a blunt apex, which projects upward into the neck for about 1 in. (2.5 cm) above the clavicle; a concave base that sits on the diaphragm; a convex costal surface ,which corresponds to the concave chest wall; and a concave mediastinal surface, which is molded to the pericardium and other mediastinal structures . At about the middle of this surface is the hilum, a depression in which the bronchi, vessels, and nerves that form the root enter and leave the lung .The right lung is slightly larger than the left and is divided by the oblique and horizontal fissures into three lobes: the upper, middle, and lower lobes . The

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left lung is divided by a similar oblique fissure into two lobes: the upper and lower lobes . There is no horizontal fissure in the left lung.

PleuraeThe pleurae and lungs lie on either side of the mediastinum within the chest

cavity . Each pleura has two parts: a parietal layer, which lines the thoracic wall, covers the thoracic surface of the diaphragm and the lateral aspect of the mediastinum and extends into the root of the neck , visceral layer, which completely covers the outer surfaces of the lungs and extends into the depths of the inter lobar fissures. Space between two layers called pleural space .

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