Anatomy of The Thoracic Cavity & Its Contents PDF

Preview

Summary

Anatomy of The Thoracic Cavity & Its Contents...

Description

23/10/2020

Anatomy of The Thoracic Cavity & Its Contents Radiograph of The Thoracic Cavity 

The big medial white bulge is the heart sitting on top of the diaphragm (second horizontal bulge)

Gross Anatomy of The Bony Thorax • Its skeleton is constructed from the following:  Midline Bony Structures o Manubrium of Sternum o Body of Sternum o Xiphoid Process o Vertebral Column 

Bilateral bony assemblies: o Ribs o Costal Cartilages

Boundaries of The Thorax in Gross Terms   

Superior: Thoracic inlet Lateral: Rib cage Inferior: Diaphragm



It contains o A pair of Lungs o Great Vessels – aorta and vena cava o The Heart o Trachea o Oesophagus o Mediastinum (space) 1

Soft Tissues of The Thorax • Pleura (2 layers) • Lungs • Diaphragm • Intercostal Muscles • Great Vessels • Nerves • Viscera

Gross Anatomy of Tissues Layers of The Thoracic Wall 

  

The chest wall has 10 layers of tissues (superficial to deep): o Skin o Superficial Fascia (tethers the skin to the rest of the body) o Pectoral Fascia o Pectoralis Major o Clavipectoral Fascia (separates Pectoralis major from Pectoralis minor) o Pectoralis Minor o External Intercostal Muscle o Internal Intercostal Muscle & Ribs o Innermost intercostal Muscle o Endothoracic Fascia The muscular layers vary according to the region of the chest wall Some muscles cover only limited territories For example, they may include muscles like o Pectoralis major or not o Latissimus Dorsi or not o Serratus Anterior or not, etc

Gross Anatomy of Tissues Layers of The Thoracic Cavity (Under the endothoracic fascia) • Pleura consist of simple squamous epithelium supported by loose connective tissue (contains blood vessels nerves and lymphatic vessels) •

•

•

•

Parietal Pleura – Thin layer of membrane. It is simple squamous epithelium. (behind the endothoracic fascia) that lines the internal surface of the thorax body wall. Visceral Pleura – Thin layer of membrane, It is also simple squamous epithelium. It lines the outer surfaces of all visceral organs of the thorax. o The function of the pleura is to allow optimal expansion and contraction of the lungs during breathing. Pleural Cavity: o A fluid-filled space between the parietal and visceral pleura. o The pleural fluid acts as a lubricant, allowing the parietal and visceral pleura to glide over each other friction free. o This fluid is produced by the pleural layers themselves. o If the fluid dries up e.g. through infection, the rubbing of the membranes would give very sharp pain. o The pleura space is classified as a potential space. o It is a sealed vacuum between both membranes. If air were to enter the pleural cavity, the lung would collapse due to air pressure. This is called pneumothorax Thoracic (Pulmonary) ligament: Double fold of visceral and parietal pleura.

Gross Anatomy of The Thoracic Cavity • The thoracic cavity is conceptually divided into 3 separate anatomical compartments • The fibrous pericardium forms the boundaries of the three compartments • The 3 compartments, from left to right are as follows: 

Left Pulmonary Cavity o The anatomical space to the left of the mediastinum o Occupied by the left lung and various blood vessels



The Mediastinum o Occupies the centre of the thoracic cavity o Its boundaries are created by the fibrous pericardium o It contains the heart which sits on the superior surface of the diaphragm



Right Pulmonary Cavity o The anatomical space to the right of the mediastinum o Occupied by the right lung and various blood vessels

 

Note: with all CT scans you are looking from the feet (bottom) up to the head (top) So as a result

Right side of patient Left side of patient

Tissue Layers of Pulmonary Cavities   



Left and Right pulmonary cavities are designed similarly They are thus, treated as having common tissue layers Sequentially, they present as follows: From outside-to-inside o Endothoracic Fascia o Parietal Pleura o Pleural Cavity: Filled with Pleural Fluid which reduces friction between the movement of the parietal pleura and the visceral pleura. o Visceral Pleura o Outer Surface of lung o Parenchyma (tissue) of the lung  Alveoli Heart lies slightly to the left side

MEDIASTINUM   

Mediastinum: the central anatomical compartment of the chest It lies posterior to the sternum but anterior to the vertebral column Its boundaries are defined by outlines of the fibrous pericardium

The main contents of the mediastinum are as follows:   

Fibrous pericardium: connective tissue sac of the Heart Membranous linings of the heart Heart



Great vessels connected to the heart (aorta and vena cava)

Tissue Layers of The Mediastinum  In sequence, they present as follows:



From outside-to-inside o Fibrous Pericardium o Parietal Layers of Serous Pericardium o Pericardial Cavity: Filled with serous fluid which reduces friction when the parietal and visceral layers move over each other o Visceral Layer of Serous Pericardium (Also known as Epicardium). This forms the outer layer of the heart. o Myocardium: muscular component of the heart  It is of variable thickness, depending on chambers of the heart o Endocardium (lines the inside of heart muscles – lines the cardiac chambers

The Pericardial Sac:  It is a double walled sac containing the heart & great vessels  Made up of Fibrous pericardium, and a thin, internal layer known as the serous pericardium (Fibrous layer of serous pericardium & Visceral layer of serous pericardium)  It is in-expansible – therefore it limits the capacity of the heart – limits the volume of blood that can be in the heart

ANATOMICAL LOCATION OF THE HEART (THE THORACIC CAGE)  

 

 



It is located within the thoracic cavity more specifically in the mediastinum surrounded by the fibrous pericardium Encased within the pericardial sac o Fibrous pericardium o Serous pericardium  Parietal pericardium (Pleural Cavity filled with serous fluid)  Visceral pericardium It sits in relation to the following structures: It is above o The Diaphragm o Rests on the superior surface of the diaphragm, above its central tendon It is below o The sternal angle of Louis It is behind: o the sternum with a slight shift to the left o the thymus gland It is in front of: o The trachea o oesophagus o Descending Aorta o Vertebral column

Division of the Mediastinum



The sternal angle is this angle formed between the manubrium of the sternum and the body of the sternum. o It's important because we know that this level marks the level of the intervertebral discs which lies between thoracic vertebra T4 and T5.



The sternal angle of louis divides the mediastinum into superior and inferior regions o Superior:  Arc of Aorta  Superior Vena Cava  Vagus and Phrenic Nerve  Thymus  Trachea  Oesophagus  Thoracic duct (lymph duct) Further division of inferior mediastinum o Middle mediastinum – contain pericardial sac with heart o Anterior mediastinum – in front (tucked between heart and sternum) contains:  the thymus  lymph nodes  may contain the portions of a retrosternal thyroid. o Posterior – behind (tucked behind the heart and pericardial cavity) Contains:  thoracic spine  Thoracic aorta  Thoracic duct (lymphatic vessel)  Oesophagus  Sympathetic Trunk (bundles of nerves that extend from the base of the skull to the coccyx)  Azygos system of veins (drain blood from the body walls and mediastinal viscera and empties it into the superior vena cava)



REFLECTIONS OF VISCERAL & PARIETAL PERICARDIUM  Reflection: When the membranes change direction Pericardial Sinuses  The reflections between the visceral and parietal layers of the serous pericardium form two pericardial sinuses: o Transverse pericardial sinus (you can thread a tourniquet through this sinus to reduce blood flow through the great vessels o Oblique pericardial sinus (dead end)

Transverse Pericardial Sinuses  It has the following anatomical relations o Lies anterior to the superior vena cava (SVC) o Lies posterior to the ascending aorta and pulmonary trunk  A tourniquet placed in this sinus is used as a ligature in major surgery of the heart to stop blood flow through these blood vessels without causing damage.  Done with the help of scissors to pull thread through

  



Oblique Pericardial Sinuses No functional applications It is a cul-de-sac formed by reflections of the serous pericardium. It is left over after the heart is remodelled from embryo  child. o It used to line the venous structures of the embryonic heart tube It lies posterior to the heart in the pericardial sac

NB:  

The point where the trachea divides into the bronchi is called the carina The sternal angle of louis is in line with Carina

PULMONARY CAVITIES  There are two pulmonary cavities o Left Pulmonary Cavity o Right Pulmonary Cavity  They are separated by the mediastinum  They are occupied by their respective lungs  The left and right lung have different anatomies,

Gross Anatomy of Lungs 

Each lung has an opening on its medial surface. This is the hilum of the lung



The hilum is the point of entry on each lung for the bronchus, blood vessels, nerves and lymphatics. The lungs are attached to:



o o

The trachea - via the main bronchus Heart - via the pulmonary artery and pulmonary veins.

Hilum of The Lungs Hilum

2 fissure

• Right Lung

• Left Lung

1 fissure

Gross Anatomy of The Lungs 



Lungs are divided by fissures, into lobes o They are the major divisions of the lungs o On the right lung there are 3 lobes and on the left lung there are 2 lobes o So there are two fissures on right lung and one fissure on the left. o The fissure are lined with the visceral pleura Lobes are then divided into Segments called Secondary lobules: o Secondary lobules - a unit of lung supplied by three to five terminal bronchioles and contained by fibrous septa

Broncho-Pulmonary Segments   

  

Functional units of the lungs. The bronchopulmonary segment is a portion of lung supplied by its own bronchus (air supply) and artery (blood supply). Each segment is functionally and anatomically discrete allowing a single segment to be surgically removed without affecting its neighbouring segments. However, before removal you must shut off the artery and bronchus to stop leaking of e.g. blood and air which would cause the lung to collapse. 10 BP Segments in the right lung 8 BP Segments in the left lung

Reflections of Parietal Pleura  

Pleural reflections: When the parietal pleura changes direction The pleura changes name depending on what surface it is lining: o Costal Parietal Pleura: lines the costal surfaces of the thoracic wall – i.e. the ribs o Mediastinal Parietal Pleura: lines the mediastinal surfaces of the lungs and heart o Cervical Pleura: (AKA Cupola) lines the superior thoracic inlet o Diaphragmatic Pleura: lines the diaphragm

Chest Drains  Chest drains involve the introduction of a tube into the pleural cavity.  It is performed due to: o Pleura effusion – When there too much fluid in the pleura cavity. It can squash the lungs so introducing a chest drain can help to remove excess o Pneumothorax: air in the pleura cavity (entered either via piercing injury on the external surface or it has entered due to damage of the lungs) o Perioperative – e.g. after heart surgery Chest drain preparation:  Consent  Aseptic technique – to stop infection Chest drain:  Local anaesthetic is given  Ultrasound is used – for visual guidance  Position: o Usually in the 5th intercostal space o In the safe triangle bordered by latissimus dorsi, pectoralis major and a horizontal line level with the nipple. o Over the rib (not under) to avoid intercostal and nerve and vessels. 1. First aspire some of the fluid or air to make sure you are in the right place 2. Then secure the drain with suture 3. Attach to a drainage system 4. Place dressing over the drain site 5. Repeat an X-ray – to make sure drain is in the right place 6. Give Analgesia (pain relief) as required.

Position of thoracic structures according to vertebral levels

Do the canvas quiz (it is in a video format)...