DIMS Lectures Thoracic Anatomy PDF
Thoracic Anatomy
The thorax plays a crucial role in respiration, circulation, and protection of vital organs. It consists of the thoracic wall, pleural cavities, lungs, heart, great vessels, esophagus, and neurovascular structures.
1. Thoracic Skeleton and Joints
The bony thorax provides protection to the heart and lungs while allowing movement for breathing.
1.1 Bones of the Thorax
Sternum: Composed of the manubrium, body, and xiphoid process.
Manubrium articulates with clavicles and first ribs.
Sternal angle (Angle of Louis) is a key landmark at the 2nd rib and the level of the T4-T5 intervertebral disc.
Xiphoid process is the inferior part, important in CPR as a landmark for chest compressions.
Ribs:
True ribs (1-7): Attach directly to the sternum via costal cartilages.
False ribs (8-10): Attach indirectly to the sternum.
Floating ribs (11-12): No anterior attachment, prone to fractures.
Thoracic Vertebrae (T1-T12): Provide articulation points for the ribs.
1.2 Joints of the Thorax
Costovertebral Joints: Between ribs and vertebrae.
Sternocostal Joints: Between ribs and sternum.
Costochondral Joints: Between ribs and costal cartilage.
Clinical Relevance:
Rib fractures commonly occur in trauma and can cause pneumothorax if the lung is punctured.
Flail chest occurs when multiple adjacent ribs are fractured, causing paradoxical chest wall movement.
2. Thoracic Muscles and Their Function
Thoracic muscles assist in breathing and upper limb movement.
2.1 Respiratory Muscles
Primary Muscles of Respiration:
Diaphragm: The main muscle of inspiration, innervated by the phrenic nerve (C3-C5).
Intercostal Muscles:
External intercostals: Elevate ribs during inspiration.
Internal intercostals: Depress ribs during expiration.
Innermost intercostals: Assist in forced expiration.
Accessory Muscles of Respiration:
Sternocleidomastoid, scalene muscles (used in labored breathing).
Abdominal muscles (aid in forced expiration).
2.2 Clinical Relevance
Diaphragmatic Paralysis: Can occur due to phrenic nerve injury, leading to respiratory distress.
Intercostal Muscle Spasms: Cause rib pain (costochondritis), often mistaken for cardiac pain.
Paradoxical Breathing: Seen in diaphragmatic dysfunction, where the abdomen moves opposite to normal breathing.
3. Pleura and Pleural Cavities
The pleura is a double-layered membrane that surrounds the lungs.
Parietal Pleura: Lines the thoracic cavity.
Visceral Pleura: Covers the lungs.
Pleural Cavity: The potential space between the layers containing lubricating fluid.
3.1 Clinical Relevance
Pneumothorax: Air enters the pleural cavity, causing lung collapse.
Pleural Effusion: Fluid accumulation, diagnosed via thoracocentesis.
Pleuritis (Pleurisy): Inflammation of the pleura causing sharp chest pain with breathing.
4. Lungs and Their Functional Anatomy
The lungs are the primary organs of respiration, divided into lobes, segments, and airways.
4.1 Lung Lobes and Fissures
Right Lung:
Three lobes: Upper, middle, lower.
Two fissures: Oblique and horizontal.
Left Lung:
Two lobes: Upper and lower.
One fissure: Oblique.
Cardiac notch (indentation for the heart).
4.2 Clinical Relevance
Aspiration Pneumonia: More common in the right lung due to the more vertical right main bronchus.
Lung Cancer: Common in smokers, can involve the bronchi or peripheral lung tissue.
Pulmonary Embolism: Blockage of the pulmonary artery by a blood clot, leading to sudden shortness of breath and chest pain.
5. Heart and Great Vessels
The heart is located in the mediastinum, surrounded by the pericardium.
5.1 Heart Chambers and Valves
Right Atrium: Receives deoxygenated blood from the vena cava.
Right Ventricle: Pumps blood to the lungs via the pulmonary artery.
Left Atrium: Receives oxygenated blood from the lungs.
Left Ventricle: Pumps blood into the aorta for systemic circulation.
Valves:
Atrioventricular (AV) Valves: Tricuspid (right), Mitral (left).
Semilunar Valves: Pulmonary, Aortic.
5.2 Clinical Relevance
Pericarditis: Inflammation of the pericardium causing chest pain relieved by leaning forward.
Myocardial Infarction (Heart Attack): Blockage of coronary arteries, leading to ischemia and chest pain.
Aortic Aneurysm: Weakening of the aortic wall, which can rupture and be life-threatening..
Clinical Points
Pneumothorax: Can be spontaneous, traumatic, or tension-type, with tension pneumothorax requiring emergency needle decompression at the 2nd intercostal space, midclavicular line.
Pleural Effusion: Accumulation of fluid in the pleural cavity, requiring thoracocentesis for analysis.
Hemothorax: Blood in the pleural space due to trauma or vessel rupture, managed by chest tube insertion.
Pulmonary Embolism: Sudden blockage of the pulmonary artery, leading to acute hypoxia, tachycardia, and pleuritic chest pain.
Pericardial Tamponade: Fluid accumulation in the pericardial sac compressing the heart, presenting with Beck’s triad (hypotension, muffled heart sounds, distended neck veins), requiring pericardiocentesis.
Myocardial Infarction (Heart Attack): Severe chest pain radiating to the left arm or jaw, requiring immediate ECG, troponin testing, and PCI intervention.
Case Example:
1.A 40-year-old male is brought to the emergency room following a high-speed motor vehicle accident. He complains of severe right-sided chest pain and difficulty breathing. Examination reveals tachypnea, absent breath sounds on the right side, and tracheal deviation to the left.
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