Thorax Notes.pdf

THORACIC ANATOMY : https://youtu.be/wfVAPi1UcZo?si=xMSxvB2_LxdecnUK Sternum is found in the anterior midline (manubrium, body, xiphoid process) Jugular / Suprasternal Notch - found superiorly on the manubrium and articulates with the medial end of each clavicle Manubriosternal...

THORACIC ANATOMY : https://youtu.be/wfVAPi1UcZo?si=xMSxvB2_LxdecnUK Sternum is found in the anterior midline (manubrium, body, xiphoid process) Jugular / Suprasternal Notch - found superiorly on the manubrium and articulates with the medial end of each clavicle Manubriosternal Joint / Sternal Angle, Angle of Louis - joint between body and manubrium. - It is at interior most projection and easily palpated - Where the 2nd rib is located Xiphisternal Joint - body and xiphoid process joint Clavicle joins the manubrium at Sternoclavicular Joint Sternocostal (sternochondral) Joints - where the Costal cartilages (connects joints and bones of the ribs) join the sternum body Superior Thoracic Aperture (inlet) - T1, 1st Rib, 1st Costal Cartilage, and Manubrium Inferior Thoracic Aperture - 12th Rib, T12 Vertebra, and Cartilaginous Ends of Ribs 7-10 (costal margin) Ribs 1-7 = True Ribs Ribs 8-10 = False Ribs [connected to the Costal Cartilage of Rib 7 through interchondral joints] Ribs 11-12 = Floating Ribs [12th rib only has a single articular surface] Head of the Rib articulates with the vertebral body The Tubercle of the Rib articulates with the vertebral transverse process Costotransverse Joint - joint between the transverse process and tubercle of the rib Costovertebral Joint - joint between the vertebral body and head of the rib Costal Groove - exists the intercostal VAN (vein, artery, and nerve) Cervical ribs - rare condition, but most of the times, cause no problem at all - 1 of 200 people - Found in the c7 and can either be unilateral (one side of the body) or bilateral (body sides) - Asymptomatic but can compress structures that lead to thoracic outlet syndrome, compressing the brachial plexus which causes pain/numbness in arm or hand. INTERCOSTAL SPACE ANATOMY : https://youtu.be/AFO0MxrV8h0?si=sBvxzT2RnVocE7Pb Space between the ribs = intercostal space Intercostals / Intercostal Muscles = muscles that run between the ribs External Intercostal Muscles = most external - Fibers run in a diagonal direction from rib to the rib below - Elevates the rib cage and expanding the thoracic cavity which helps inhalation Internal Intercostals = deeper layer, fibers running the opposite direction, depressing the rib cage, decreasing the thoracic cavity, exhalation Innermost Intercostal Muscle = deepest layer. same fiber orientation with the inner so they function the same way Intercostal Vein = runs along the ribs, meeting the internal thoracic vein Intercostal Artery = runs along the ribs and branches from the internal thoracic artery Intercostal Nerve = spinal nerve branch below the artery  1. Subcostalis Muscles : tend to exist in the lower ribs and attach to the internal surface of one rib and skip again to at least 2-3 ribs below. Assists exhalation, depresses the ribs. 2. Transversus Thoracis : sits along the internal surface of costal cartilages 2-6 and inferoposterior surface of the body of sternum and xiphoid process. Depress the ribs and assists with exhalation THORACIC CAVITY : https://youtu.be/AqEA61efyYs?si=x34dN_gFVSbsFfMs Pleural Fluid : small amount of fluid, helping reduce the friction of the visceral and parietal pleura, as the lungs expand and contract during breathing. Hilum : little indentations where structures enter and exit  Visceral Pleura is largely sensitive to pain while the Parietal Pleura, consisting of the Somatic Innervation, which gives out the sharp amount of pain felt during trauma in the area Cervical Pleura : close to the neck, superior thoracic aperture, innervated by the intercostal nerves. Covered by the Suprapleural Membrane for protection. Parietal Pleura (Intercostal Pleura) : Intercostal Nerves Diaphragmatic Pleura, Mediastinal Pleura : Phrenic Nerve Pleural Recess : double fold form of space the lungs don’t fill Pulmonary Ligament : double fold, extending inferiorly below the hilum and root of the lung Costodiaphragmatic / Costophrenic Recess : the posterolateral fringe of the pleural space, a potential space around the lung inside the pleural cavity. - Too much pleural fluid : Pleural Effusion Costomediastinal Recess : the potential space in the pleural cavity between the costal pleura and mediastinal pleura at approximately the level of the fifth intercostal space on the left hand side. Phrenic Nerves : cervical area (c3-c5) to diaphragm. Provide sensory information Thorax Anatomy Notes (from book, using chatgpt hehe) Muscles of the Thorax: Pectoralis Minor Muscle: Located beneath the pectoralis major, plays a role in stabilizing the scapula. Pectoralis Major Muscle: Large, superficial chest muscle responsible for movement of the shoulder joint. Anterior Serratus Muscle: Attaches to the ribs and helps in the movement of the scapula, particularly during breathing. External Abdominal Oblique Muscle: Helps with trunk rotation and lateral flexion. Rectus Abdominis Muscle: Commonly known as the "abs," it helps with flexing the lumbar spine. Rectus Sheath: Encloses the rectus abdominis muscles. Sternothyroid, Sternohyoid, Sternocleidomastoid Muscles: ○ Sternocleidomastoid: Major neck muscle involved in head rotation and flexion. ○ Sternohyoid and Sternothyroid: Muscles that assist in depressing the hyoid bone and larynx. Platysma Muscle: Thin muscle that extends from the chest to the jaw, involved in facial expressions. Bones and Ligaments: Clavicle (Collarbone): ○ Superior and Inferior Views: Superior View: Smooth, subcutaneous surface. Inferior View: Contains grooves for muscle attachments. ○ Attachments: Acromioclavicular Ligament: Stabilizes the shoulder. Costoclavicular Ligament: Anchors the clavicle to the first rib. Trapezoid Ligament: Part of the coracoclavicular ligament that connects the clavicle to the scapula. Conoid Ligament: Another part of the coracoclavicular ligament. Ribs: ○ True Ribs (1-7): Attach directly to the sternum. ○ False Ribs (8-10): Attach indirectly via costal cartilage. ○ Floating Ribs (11-12): Have no anterior attachment. Sternum: ○ Manubrium: The upper part of the sternum. ○ Body of Sternum: Main portion of the sternum where ribs attach. ○ Xiphoid Process: The small, cartilaginous lower part of the sternum. Vertebrae:  ○ Thoracic Vertebrae: Specifically T4-T5, significant for their association with the tracheal bifurcation. Trachea and Bronchi: Trachea: Windpipe that allows air passage to the lungs. ○ Bifurcation: At the level of T4-T5, the trachea splits into the right and left main bronchi. Right Main Bronchus: Wider, shorter, and more vertical than the left bronchus; directs air into the right lung. Left Main Bronchus: Longer and more horizontal, leads to the left lung. Tracheobronchial Nodes: Lymph nodes located near the trachea and bronchi, involved in the drainage of lymph from the lungs. Heart and Major Blood Vessels: Superior Vena Cava (SVC): Large vein carrying deoxygenated blood from the upper body into the heart. Inferior Pulmonary Vein: Carries oxygenated blood from the lungs back to the left atrium of the heart. Pulmonary Trunk: The major vessel arising from the right ventricle, splits into the right and left pulmonary arteries. ○ Right Pulmonary Artery: Carries deoxygenated blood to the right lung. ○ Left Pulmonary Artery: Carries deoxygenated blood to the left lung. Ascending Aorta: The first section of the aorta, extending upwards from the heart. Descending Aorta: Continuation of the aorta that arches downward, supplying blood to the thorax and abdomen. Left Atrium: Chamber of the heart that receives oxygenated blood from the lungs. Right Atrium: Chamber that receives deoxygenated blood from the body. Left Ventricle: Pumps oxygenated blood to the body via the aorta. Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary arteries. Pericardial Sinus: A cavity within the pericardium, surrounding the heart. Other Key Structures: Esophagus: Muscular tube that connects the throat (pharynx) to the stomach. Mediastinum: Central compartment of the thoracic cavity containing the heart, trachea, esophagus, and major vessels. Manubriosternal Junction: Joint between the manubrium and the body of the sternum (also called the "sternal angle").  Intervertebral Disc (T4-5): Located between thoracic vertebrae T4 and T5, relevant to the bifurcation of the trachea. Lungs and Pleura: Lungs: ○ Right Lung: Divided into three lobes: upper, middle, and lower. Horizontal and Oblique Fissures: Separate the lobes. ○ Left Lung: Divided into two lobes: upper and lower. Oblique Fissure: Separates the two lobes. Cardiac Notch: A concave space on the surface of the left lung to accommodate the heart. Bronchial Tree: ○ Segmental (Tertiary) Bronchi: Supply air to bronchopulmonary segments. ○ Bronchioles: Smaller airways leading to the alveoli where gas exchange occurs. Pleura: ○ Visceral Pleura: Covers the surface of the lungs. ○ Parietal Pleura: Lines the inside of the chest wall and diaphragm. ○ Pleural Cavity: The space between the visceral and parietal pleura, containing a small amount of fluid for lubrication. Diaphragm and Thoracic Inlet: Diaphragm: ○ Primary Muscle of Respiration: Contracts to allow air into the lungs. ○ Innervation: Supplied by the Phrenic Nerve (C3-C5). ○ Openings: Aortic Hiatus: Allows passage of the aorta. Esophageal Hiatus: Allows the esophagus to pass into the abdomen. Caval Opening: Passage for the inferior vena cava. Thoracic Inlet: ○ Superior Thoracic Aperture: The upper boundary of the thoracic cavity, allowing passage of structures like the trachea, esophagus, and blood vessels between the neck and thorax. Nerves of the Thorax: Phrenic Nerve: Innervates the diaphragm and controls breathing.  Vagus Nerve: Provides parasympathetic innervation to the heart, lungs, and digestive tract. ○ Recurrent Laryngeal Nerve: A branch of the vagus nerve, loops under the aortic arch on the left side and under the subclavian artery on the right side. Sympathetic Chain: Runs parallel to the vertebral column and provides sympathetic innervation to thoracic organs. Intercostal Nerves: Supply the muscles between the ribs and the skin overlying the thorax. Circulation within the Thorax: Coronary Circulation: ○ Right Coronary Artery: Supplies blood to the right atrium, right ventricle, and portions of the conduction system. ○ Left Coronary Artery: Left Anterior Descending Artery: Supplies the front of the heart. Circumflex Artery: Wraps around the heart, supplying the left atrium and part of the left ventricle. Venous Drainage: ○ Azygos Vein: Drains the thoracic wall and empties into the superior vena cava. ○ Hemiazygos and Accessory Hemiazygos Veins: Drain the left side of the thorax. Lymphatic System of the Thorax: Thoracic Duct: ○ Main Lymphatic Vessel: Drains lymph from the lower body, left thorax, left arm, and left side of the head and neck. ○ Drains into the Left Subclavian Vein. Right Lymphatic Duct: Drains the right side of the thorax, right arm, and right side of the head and neck. Lymph Nodes: ○ Mediastinal Nodes: Located within the mediastinum. ○ Pulmonary and Bronchial Nodes: Filter lymph from the lungs. Clinical Landmarks and Relevance: Sternal Angle (Angle of Louis): ○ Located at the junction of the manubrium and the body of the sternum. ○ Clinical Importance:  Marks the level of the second rib and helps in counting ribs for clinical examination. Lies at the level of the T4-T5 intervertebral disc, corresponding to the bifurcation of the trachea (carina). Serves as a landmark for the beginning of the aortic arch. Thoracic Outlet Syndrome (TOS): ○ A condition where there is compression of the nerves or blood vessels (typically the subclavian artery or brachial plexus) in the thoracic outlet, which can lead to pain, numbness, or weakness in the upper limbs. ○ Structures potentially involved include the first rib, clavicle, and scalene muscles. Respiratory Mechanics: Breathing Movements: ○ Inspiration: Diaphragm contraction is the main driver of quiet inspiration, increasing thoracic cavity volume. External intercostal muscles also elevate the ribs, expanding the thoracic cavity. ○ Expiration: Passive expiration involves the relaxation of the diaphragm and elastic recoil of the lungs. Active expiration (during exercise or forced breathing) involves internal intercostal muscles and abdominal muscles. Changes in Thoracic Pressure: ○ During inspiration, intrapleural pressure becomes more negative, drawing air into the lungs. ○ Pneumothorax: Occurs when air enters the pleural cavity, disrupting negative pressure and causing lung collapse. Mediastinal Divisions: Superior Mediastinum: ○ Contains major vessels (e.g., aortic arch, brachiocephalic veins), the trachea, esophagus, and thymus. Inferior Mediastinum: ○ Anterior Mediastinum: Contains fat, connective tissue, and remnants of the thymus. ○ Middle Mediastinum: Contains the heart, pericardium, and major vessels like the ascending aorta and pulmonary arteries.  ○ Posterior Mediastinum: Contains the descending aorta, esophagus, thoracic duct, and azygos vein. Coronary Circulation Variants: Dominance of the Coronary Artery: ○ Most people have right coronary artery dominance (meaning the right coronary artery supplies the posterior descending artery). ○ Some have left coronary artery dominance or a co-dominant circulation. ○ This anatomical variance can affect how heart disease (like myocardial infarctions) impacts different regions of the heart. Esophageal Relations: Esophageal Constrictions: ○ There are three natural constrictions of the esophagus that are clinically relevant: 1. Cervical constriction: Caused by the cricopharyngeal muscle at the pharynx-esophagus junction. 2. Thoracic (broncho-aortic) constriction: Where the esophagus is compressed by the aortic arch and left main bronchus. 3. Diaphragmatic constriction: Where the esophagus passes through the esophageal hiatus of the diaphragm. ○ These constrictions are important for the passage of food and can be sites where swallowed objects become lodged. Cardiac Conduction System: Sinoatrial (SA) Node: Known as the "pacemaker" of the heart, located in the right atrium. Atrioventricular (AV) Node: Conducts electrical impulses from the atria to the ventricles. Bundle of His and Purkinje Fibers: Distribute the electrical signal throughout the ventricles to stimulate contraction. Clinical Relevance: ○ Abnormalities in the conduction system can lead to arrhythmias such as atrial fibrillation or ventricular fibrillation. Thoracic Pathologies: Pleural Effusion: ○ Accumulation of fluid in the pleural cavity. ○ Can be caused by conditions like heart failure, pneumonia, or cancer. Pericarditis: ○ Inflammation of the pericardium, the sac surrounding the heart. ○ Can cause pericardial effusion, leading to cardiac tamponade (compression of the heart due to fluid buildup). Aortic Dissection: ○ A serious condition where the inner layer of the aorta tears, allowing blood to flow between the layers of the aortic wall. ○ Can lead to rupture and life-threatening complications. Surgical Access to the Thorax: Thoracotomy: ○ A surgical procedure where an incision is made into the pleural space of the chest to gain access to thoracic organs. ○ Commonly used for lung resections, heart surgery, or esophageal surgery. Sternotomy: ○ A vertical incision through the sternum, often used in open-heart surgery to provide access to the heart and mediastinum. Embryological Development of the Thorax: Septation of the Heart: ○ The heart develops from a simple tube into a four-chambered organ through a process called septation. ○ Missteps in this process can result in congenital defects such as atrial septal defect (ASD) or ventricular septal defect (VSD). Development of the Diaphragm: ○ Arises from four embryonic components: the septum transversum, pleuroperitoneal folds, body wall, and dorsal mesentery of the esophagus. ○ Failure of these structures to fuse can lead to a congenital diaphragmatic hernia.