Thorax

Thorax or the chest is the region of the body between the neck and the abdomen. The framework of the walls of the thorax is referred as the thoracic cage. Thoracic wall is bounded superiorly by suprapleural membrane , inferiorly by the diaphragm , laterally by the ribs and intercostal space, anteriorly by the sternum and costal cartilage and posteriorly by thoracic vertebrae. Thoracic cavity is divided into median portion, the mediastinum and the laterally placed pleura and lungs. The pleura that lined thoracic wall is referred as parietal pleura and that surround the viscera is the visceral pleura. The space between the parietal pleura and visceral pleura (pleural cavity) is filled with serous fluid. Mediastinum is divided into superior and inferior mediastinum. Inferior mediastinum is further divided into anterior, middle where is the heart situated and posterior mediastinum.
1- Superior mediastinum lies between the first rib and the sternal angle.
2- Inferior mediastinum lies between the sternal angle and diaphragm.
Boundaries of superior mediastinum:
Anterior: manubrium
Posterior: T1-T4
Sides: mediastinum pleura.
Superior: plane of thoracic inlet.
Inferior: plane of sternal angle.
Contents:
Trachea and esophagus
Thoracic duct and lymph nodes
Thymus
Muscles and nerves
Arteries and veins
Boundaries of inferior mediastinum:
Anterior: sternum
Posterior: T5-T12
Sides: mediastinum pleura.
Superior: plane of sternal angle.
Inferior: Diaphragm.
The heart: it is hollow muscular organ. It is pyramidal in shape and located in the thorax between the lungs. It has two atrium, two ventricles , four valves and three surfaces.

Surfaces of the heart:
• Sterno-costal surface or anterior surface is formed by right atrium and right ventricle.
• Diaphragmatic surface is formed by right and left ventricles.
• Base of the heart or the posterior surface is formed by left atrium.
• Apex of the heart is formed by left ventricle and directed downward forward and to the left.
• Heart does not rest on its base; it rests on diaphragmatic surface.
Pericardium: The heart is surrounded by pericardium. The pericardium is a fibro-serous sac encloses the heart and the root of major blood vessels.
Function of pericardium:
Restricted excessive heart movement and lubricated container in which different
parts of the heart can contract.

Heat walls:
• Pericardium: consists of fibrous and serous layers. Serous layer is further divided inoto:
- Parietal pericardium
- Pericardial cavity.
- Visceral pericardium.
• Endocardium:
- Deepest layer of the heart.
- Smooth lining to reduce friction of blood flow.
• Myocardium:
- Middle layer of the heart.
- Location of muscle fibers responsible for pumping.
Heart chambers:
• Atria:
- Small, thin walled chambers.
- Receiving blood from circulation.
- Push blood into adjacent ventricles.
- Right atrium receives blood from superior and inferior vena cava.
- Left atrium receives blood from pulmonary veins.
• Ventricles:
- Makes off most the heart mass.
- The walls of the left ventricle is 3 times thicker than the right ventricle.
- Functions: discharging chambers of the heart.
- Right ventricle Propel blood to pulmonary trunk.
- Left ventricle: aorta.
Note: Right atrium receives blood from superior and inferior vena cava. Whereas, right ventricle receives blood from the right atrium through tricuspid valve.
Left atrium receives blood from four pulmonary veins. Whereas, mitral valve guard the passage of blood between the left atrium and ventricle.

Heart valves:
These are composed of endocardium and connective tissue core. They prevent back flow of the blood through the heart. There are two types of heart valves:
- Atrioventricular.
- Semilunar.
• Heart sounds (lub-dub) is due to valve closing: Lub closing of AV valve and dub closing of semilunar valve.

Blood supply of the heart: By the right and left coronary arteries which arise from ascending aorta above the aortic valve.
Venous drainage: This is through coronary sinus which opens in the right atrium to the left of inferior vena cava.
Nerve supply: By sympathetic and parasympathetic fibers of the autonomic nervous system via the cardiac plexus. The sympathetic supply arises from the cervical and upper thoracic portion. The parasympathetic comes from vagus nerve.
The lungs:
The lung is a Soft spongy and elastic structure in thoracic cavity. It lies on each side of mediastinum. It is a conical in shape. It has apex, base, two borders and two surfaces.
• Apex: projects upward into the neck.
• Base: rests on diaphragm.
• Costal surface.
• Mediastinal surface.
• Hilum: a depression in the mediastinal surface in which bronchi, vessels and nerves enter or leave the lungs.
• Anterior border: thin overlaps the heart. In left lung contains the cardiac notch.
• Posterior border: thick lies besides the vertebral column.
Notes: Right lung: Larger than the left. It is divided by oblique and horizontal fissures into 3 lobes (upper, middle and lower). The root of the right lung contains 2 bronchi posteriorly, pulmonary artery superiorly and two pulmonary veins located inferior and anterior.
Left lung: the oblique fissure divides it into superior and inferior lobes. Cardiac notch is situated in the anterior border. The root of the left lung contains One bronchi lie posterior, Pulmonary artery is superior, two pulmonary veins are inferior and anterior.

Bronchopulmonary segments: it is subdivision of lung. It is pyramidal shaped and Surrounded by C.T. It has segmental bronchus, artery, lymph vessels and autonomic nerves.



Blood supply of the lung: The bronchi, C.T of the lungs and visceral pleura receive blood supply from bronchial arteries a branch of descending aorta. Bronchial veins drain into azygos and hemiazygos veins.

Nerve supply: Via pulmonary plexus which composed of afferent and efferent nerve fibers. The plexus is formed from sympathetic trunk and parasympathetic from vagus nerve.