CVR anatomy 🫁💓 Flashcards
Triangles of the Neck
2 major triangles: Anterior triangle + Posterior triangle
Used to help to locate things in the neck
Describe the Cervical Vertebrae
7 cervical vertebrae – uniquely adapted for the neck:
Smaller than other vertebrae
Transverse foramina transmit and protect the vertebral arteries > brain
Good range of movement of the C-spine
What is the vertebral foramen?
Vertebral foramen is triangle-shaped and relatively large compared to the size of the vertebra – allows ‘extra room’ for the cervical spinal cord
Describe the hyoid bone
Small, U-shaped bone
Right at the top of the neck, inferior to the mandible
Attachment point for muscles of the floor of the mouth, some muscles of the tongue and muscles of the neck
Describe the larynx
The larynx is composed of several small cartilages
Connected by small joints and membranes /ligaments
Two are palpable in the anterior midline of the neck (thyroid and cricoid)
Vital for protecting the airway and for modified in humans for speech
Thyroid cartilage- Larger in men
What is the clinical relevance of the C-spine?
Dislocations are more common in the cervical spine than in the thoracic or lumbar spine.
Fractures and dislocations of the C-spine can cause spinal cord injury or death
Describe fractures of the hyoid bone and larynx
Fractures of the hyoid bone – very rare – it is well protected and mobile. Most commonly occur secondary to strangulation, RTAs and other trauma.
Fractures of the larynx – rare. Blunt trauma (RTA, sports injuries, assault inc. strangulation)
Major vessels in the neck
Common carotid, internal carotid and external carotid arteries
Vertebral arteries
Internal jugular vein
Major nerves in the neck
Phrenic nerves
Cranial nerves:
-Glossopharyngeal (CN IX)
-Vagus (CN X)
-Accessory (CN XI)
-Hypoglossal (CN XII)
Where do the common carotid arteries arise from?
The arch of the aorta:
RCC from the brachiocephalic trunk
LCC directly from the arch
WHat happens after the carotid arteries enter the neck?
Bifurcate into internal and external branches
Internal > enters the skull > brain; no branches in the neck
External > supplies many structures in the neck and head
Where do vertebral arteries arise from?
Vertebral arteries arise from the subclavian arteries > brain
Describe the internal jugular vein
Drain blood from the dural venous sinuses in the cranium
Descend in the neck with the carotid artery and vagus nerve
Unite with the subclavian vein to form the brachiocephalic vein
Clinical relevance of carotid arteries
Easy to access central pulse
Commonly affected by atheroma – if plaques break away, they travel to the arteries of the brain, causing stroke or TIA
Atheroma can be surgically removed from the carotid arteries
What is the clinical relevance of the internal jugular vein?
Common site for inserting a central line in patients who are unwell or having major surgery and need lots of fluid and drugs
Describe the phrenic nerves
Somatic nerves
Formed by fibres from spinal cord levels C3, 4 and 5
Left and right nerves supply ipsilateral diaphragm (and the pericardium)
Run anterior to the root and hilum of the lung
Describe the cranial nerves
Attached to the brain or the brainstem
12 pairs (there is a left and a right)
Supply head and neck structures
Contain different combinations of somatic motor, somatic sensory, special sensory and parasympathetic fibres.
CNs IX, X, XI and XII are found in the neck
Describe the CN IX - Glossopharyngeal nerve
Contains:
Somatic sensory fibres > sensation in the pharynx and posterior 1/3 of the tongue
Special sense fibres > taste posterior 1/3 of the tongue
Vital for swallowing
Describe the CN X - Vagus nerve
Contains:
Somatic motor fibres > muscles of the pharynx and larynx (left and right recurrent laryngeal nerves)
Somatic sensory fibres > larynx
Parasympathetic fibres > thoracic and abdominal viscera
Visceral sensory fibres > internal monitoring and physiological reflexes
Vital for swallowing and speech
Describe the CN XI – Accessory nerve
Contains:
Somatic motor fibres only > sternocleidomastoid and trapezius
Describe the CN XII – Hypoglossal nerve
Contains:
Somatic motor fibres only > muscles of the tongue
Important for normal swallowing and speech
Clinical relevance of the nerves in the neck
Penetrating injuries of the neck > direct injury to these nerves
Injuries to the brain or brainstem > dysfunction of the nerves
What happens when there is a phrenic nerve injury?
Weakness or paralysis of ipsilateral diaphragm
What happens when there is an injury to the Glossopharyngeal nerve?
Dysfunctional swallowing as sensation to the pharynx lost > may result in aspiration of fluid and food into the respiratory tract
What is the clinical relevance of injury to the vagus nerve
Dysfunctional swallowing and speech (hoarseness of the voice
What is the clinical relevance of the accessory nerve?
weakness or paralysis of the ipsilateral SCM and trapezius
What is the clinical relevance of injury to the hypoglossal nerves?
Weakness or paralysis of the ipsilateral tongue
Describe the pharynx
Muscular tube
Part of the respiratory and GI systems
Three parts > nasopharynx, oropharynx, laryngopharynx
Formed by constrictor muscles
Swallowed fluid and food prevented from entering the larynx by the epiglottis > diverted into the oesophagus instead
Outline the main parts of the larynx
Cartilaginous skeleton
Extrinsic muscles
Intrinsic muscles
Describe the intrinsic muscles of the larynx
Move the individual cartilages and the vocal cords
Innervated by the vagus nerve (most via the recurrent laryngeal branch)
Describe the cartilaginous skeleton of the larynx
Cartilaginous skeleton - paired and unpaired cartilages – some are palpable
Connected by small joints, ligaments and muscles
Describe the extrinsic muscles of the larynx
Move the larynx as a whole ‘unit’ with speech and swallowing
Suprahyoid and infrahyoid muscles
Vocal ligaments within the thyroid cartilage
Describe the thyroid gland
Produces thyroid hormone
Two lobes lie either side of the larynx
Lobes connected across the midline by the isthmus
Supplied by branches of the external carotid and the subclavian arteries
Recurrent laryngeal nerves lie close by – can be injured by removal of the thyroid
Describe the sternum
The sternum lies anteriorly in the midline of the thoracic cage. It is composed of three parts.
Manubrium
body
Xiphoid process
Describe the manubrium
The manubrium is the superior part of the sternum:
● the superior border has a notch in it – the suprasternal (jugular) notch.
● laterally, it articulates with the clavicle (collarbone) at the sternoclavicular joint, and with the first rib.
● inferiorly, it articulates with the body of the sternum at the manubriosternal joint, also known as the sternal angle (or the ‘angle of Louis’).
Describe the body of the sternum
The body is inferior to the manubrium:
● it articulates with ribs 2 – 7.
● the second rib articulates with the sternum at the sternal angle (i.e. with the inferior part of the manubrium and the superior part of the body).
● inferiorly, it articulates with the xiphoid process.
Describe the xiphoid process
The xiphoid process (or xiphisternum) is inferior to the body:
● it is small and variable in shape.
● the seventh rib articulates with the inferior part of the body of the sternum and the superior part of the xiphoid process.
What are the ribs and where do they articulate with the sternum?
- The anterior parts of the ribs are composed of costal cartilage.
- The ribs articulate with their costal cartilages at costochondral joints..
- The ribs articulate posteriorly with the thoracic vertebrae at costovertebral joints.
- Adjacent ribs are connected to each other by intercostal muscles, which lie in the intercostal spaces.
What are floating ribs?
Ribs 11 and 12 don’t have costal cartilages and therefore don’t articulate with the sternum
What are false ribs?
Ribs 8-10
Their costal cartilages don’t individually articulate with the sternum but rather they join together and connect to the 7th costal cartilage which does articulate with the sternum
What are the true ribs?
The costal cartilages of ribs 1 - 7 articulate directly with the sternum at sternocostal joints – they are ‘true’ ribs.
What is the costal margin?
- The costal cartilages of ribs 7 - 10 form it
Palpable
What are typical ribs?
Look similar
* Ribs 3 - 9 are typical ribs. They have a head, neck, tubercle, and body (shaft).
What are atypical ribs?
Look different from other ribs
Ribs 1 - 2 and 10 - 12 are atypical, for various reasons. For example, ribs 1, 11 and 12 are much shorter than typical ribs.
Describe the thoracic vertebrae
Twelve thoracic vertebrae (T1 - T12) lie posteriorly in the midline of the thoracic cage. The spinous processes of the thoracic vertebrae are palpable in the midline of the back. The thoracic vertebrae articulate with the posterior parts of the ribs at costovertebral joints. Typically the head of the rib articulates with the vertebral body and the tubercle of the rib articulates with the transverse process of the vertebra.
Describe the superior thoracic aperture
The manubrium, the first ribs and the first thoracic vertebra form the boundary of the superior thoracic aperture – the ‘passageway’ through which structures pass between the neck and the thorax.
How to locate the site of pain or injury in the chest?
● The ribs provide one coordinate (e.g. is the patient’s pain at the level of rib 2 or rib 8?). The second rib lies at the level of the sternal angle. From here we can count ribs and intercostal spaces.
● A series of imaginary vertical lines provide a second coordinate.
Vertical lines on the chest
● Midsternal line
● Midclavicular line
● Anterior axillary line
● Mid-axillary line
● Posterior axillary line
● Scapular line
● Midvertebral line
Describe the nervous system of the skin of the thoracic wall
The skin of the thoracic wall is innervated by spinal nerves T1 – T12 . Sensation from the skin of the thoracic wall (touch, pain, temperature) reaches our conscious perception via somatic sensory fibres in the spinal nerves
What is a dermatome?
A dermatome is an area of skin innervated by a single spinal nerve. Each pair of thoracic spinal nerves supplies a ‘strip’ of skin around the chest wall.
What are somatic motor fibres and what do they do?
Somatic motor fibres in spinal nerves T1 -12 innervate the skeletal muscles of the thoracic wall and sympathetic fibres innervate sweat glands and the smooth muscle of blood vessels and hair follicles in the skin (arrector pili).
Describe the breast?
The breasts (mammary glands) are superficial to the muscles of the chest wall. In females, the breasts are well developed but in males, they are rudimentary. The female breast grows during puberty and pregnancy. Breast tissue extends towards the anterior axilla (armpit) – this part of the breast is the axillary tail.
What is the breast made up of?
● Fat - variable amounts.
● Glandular / secretory tissue arranged in lobules.
● Ducts which converge on the nipple. The areola is the region of pigmented skin that surrounds the nipple.
● Connective tissue and ligaments.
● Blood vessels and lymphatics.
Describe the vascular supply of the breast
The breast is primarily supplied by branches from the:
● internal thoracic artery (which arises from the subclavian artery)
● axillary artery.
Venous blood returns to the axillary and internal thoracic veins.
Describe the internal thoracic artery
The internal thoracic artery courses deep to the lateral edge of the sternum. It gives rise to anterior intercostal arteries that supply the breast and the intercostal spaces .
How is the breast tissue innervated?
The breast is supplied with somatic nerves and sympathetic fibres via the intercostal nerves. Somatic sensory fibres innervate the skin of the breast. Sympathetic fibres innervate smooth muscle in the blood vessel walls and nipple.
What are the three type of intercostal muscles and where are they?
Intercostal muscles lie in the intercostal spaces between the ribs. Within each intercostal space, there are three layers of muscles:
* External intercostal is most superficial.
* Internal intercostal lies deep to the external intercostal.
* Innermost intercostal lies deep to the internal intercostal.
Describe the lymphatic drainage of the breast
Most lymph from the breast drains to lymph nodes in the axilla. However, because axillary nodes communicate with other groups of lymph nodes in the thorax, the patterns of lymph drainage are complex.
There are five groups of lymph nodes in the axilla: central, pectoral, humeral, subscapular, and apical.
● They drain the breast, upper limb, chest wall, scapular region, and the abdominal wall.
● The apical nodes (in the apex of the axilla) receive lymph from all other lymph nodes in the axilla. Because they drain most of the lymph from the breast, the axillary lymph nodes are often involved in the spread of breast cancer.
Describe the 5 groups of lymph nodes in the breast
There are five groups of lymph nodes in the axilla: central, pectoral, humeral, subscapular, and apical.
● They drain the breast, upper limb, chest wall, scapular region, and the abdominal wall.
Describe the apical nodes
The apical nodes (in the apex of the axilla) receive lymph from all other lymph nodes in the axilla. Because they drain most of the lymph from the breast, the axillary lymph nodes are often involved in the spread of breast cancer.
Describe the pectoralis major
Pectoralis major is the most superficial muscle of the anterior chest wall. It attaches to the upper humerus, the clavicle and the upper six ribs.
Describe the pectoralis minor
● Pectoralis minor is a smaller muscle that lies deep to pectoralis major. It attaches to the scapula (shoulder blade) and ribs 3-5.
Describe the serratus anterior
Is a superficial muscle that sweeps around the lateral aspect of the thoracic cage. It attaches to the scapula and the upper eight ribs.
What does use of the upper limb muscles as accessory muscles of breathing signify?
Respiratory distress
Describe rib fractures
Rib fractures result from blunt trauma to the chest wall (falls, traffic accidents, assault). They are painful and the pain is typically worse on inspiration. If there is concern about multiple rib fractures or a pneumothorax a chest X-ray or CT scan may be required to assess the extent of the injury. Isolated rib fractures are treated conservatively (i.e. left to heal on their own) but patients need adequate pain relief. Multiple rib fractures are more serious (and complex to manage), as they can lead to dysfunctional movements of the chest wall and inadequate ventilation.
Describe shingles
Patients with shingles present with a red, painful, and itchy rash, typically over the chest or abdomen on one side of the body only. The rash typically appears in a strip-like distribution, as it affects dermatomes. Shingles affects people who have previously had chickenpox. After an infection with chickenpox, the virus lays dormant in the dorsal root ganglion. When reactivated, it causes a rash and pain in the dermatome associated with the affected spinal nerve.
Describe breast cancer
Because most lymph from the breast drains to the axillary lymph nodes, breast malignancy typically metastasizes (spreads) to these nodes first. A malignant axillary node may be palpable as a lump in the armpit and noticed before a mass in the breast itself. If a breast mass is confirmed as malignant, the axillary lymph nodes are biopsied to assess if malignancy has metastasized to them. If so, they are removed as part of a patient’s treatment. Because the axillary nodes drain lymph from the upper limb, their removal can lead to fluid accumulation and swelling in the affected upper limb, a condition called lymphoedema.
What is found in the intercostal spaces?
- three layers of intercostal muscles and their associated membranes
- an intercostal neurovascular bundle, comprising an intercostal nerve, an intercostal artery, and an intercostal vein.
What are the intercostal muscles?
The muscles in the intercostal spaces attach to the rib above and rib below. There are three layers of muscles in the intercostal spaces. Their fibres run in different directions to each other and hence act on the ribs in different ways.
Describe the external intercostal muscles
External intercostal is most superficial. Its fibres are orientated antero-inferiorly.
* Contraction pulls the ribs superiorly, hence is it most active in inspiration.
* In the anterior part of the intercostal space, the muscle becomes membranous and forms the external intercostal membrane.
Describe the internal intercostal muscles
Internal intercostal lies deep to the external intercostal. Its fibres run perpendicular to those of the external intercostal, running in a postero-inferior direction.
* Contraction pulls the ribs inferiorly, hence is it most active in expiration.
* The internal intercostal becomes membranous in the posterior part of the intercostal space and forms the internal intercostal membrane.
Describe the innermost intercostal muscles
The innermost intercostal lies in the posterior part of the intercostal space deep to the internal intercostal. Its fibres are orientated in the same direction as those of the internal intercostal.
Where is the endothoracic fascia?
fascia lies deep to the innermost intercostal and superficial to the parietal pleura, which surrounds the lung
Describe the intercostal neurovascular bundle
The neurovascular bundle in each intercostal space lies in the plane between the internal and innermost intercostal muscle. It supplies the intercostal muscles, the overlying skin, and the underlying parietal pleura
Where is the intercostal neurovascular bundle found and what is the clinical relevance of this?
The neurovascular bundle for each intercostal space lies along the inferior border of the rib superior to the space. It lies in a shallow costal groove on the deep surface of the rib. In medical procedures that involve piercing the intercostal space (such as placing a chest drain), the incision is made in the middle to lower part of the intercostal space, to avoid the intercostal vessels and nerve. Smaller collateral branches run in the same tissue plane, but in the lower part of the intercostal space
Describe the intercostal arteries
- Anterior and posterior intercostal arteries supply the anterior and posterior parts of the intercostal space, respectively.
- The anterior intercostal arteries are branches of the internal thoracic artery (a branch of the subclavian artery).
- The posterior intercostal arteries are branches from the descending aorta in the posterior thorax.
Describe the intercostal veins
- Anterior intercostal veins drain into the internal thoracic vein and posterior intercostal veins drain into the azygos system of veins
Describe the intercostal nerves
The intercostal nerves are somatic and contain motor and sensory fibres. They innervate the intercostal muscles, the skin of the chest wall and the parietal pleura. Intercostal nerves also carry sympathetic fibres.
Describe the pleura and pleural cavities
Two layers of membranes - the pleurae - cover the lungs and the structures passing into and out of the lungs (the pulmonary blood vessels and the main bronchi).
- The parietal pleura lines the inside of the thorax.
- The visceral pleura covers the surface of the lungs and extends into the fissures.
A very thin pleural cavity (or space) lies between the parietal and visceral pleura.
What are the differences between the pleura
The parietal pleura is visible with the naked eye, but the visceral pleura is not. The two layers of pleura are continuous with each other. The pleural cells produce a small amount of pleural fluid, which fills the pleural cavity. The pleura and pleural fluid are integral to the mechanics of breathing.
What are the different parts of the parietal pleura?
- The cervical pleura covers the apex of the lung.
- The costal pleura lies adjacent to the ribs.
- The mediastinal pleura lies adjacent to the heart.
- The diaphragmatic pleura lies adjacent to the diaphragm.
What are the recesses in the thorax
The costodiaphragmatic recess is a ‘gutter’ around the periphery of the diaphragm, where the costal pleura becomes continuous with the diaphragmatic pleura. A smaller costomediastinal recess lies at the junction of the costal and mediastinal pleura. These are potential spaces that the lungs expand into during deep inspiration
What innervates the parietal pleura
The parietal pleura is innervated by the intercostal nerves that innervate the overlying skin of the chest wall. Somatic sensory fibres in these nerves carry sensation to our consciousness. Injury to the parietal pleura (e.g. tearing by a fractured rib) is typically very painful.
What innervates the visceral pleura?
- The visceral pleura is innervated by autonomic sensory nerves (visceral afferents). Sensation from visceral afferents usually does not reach our conscious perception.
Describe the lobes of the lung
● The right lung has three lobes – a superior (upper), middle, and inferior (lower) lobe.
● The left lung has two lobes – a superior and inferior lobe. An anterior extension of the superior lobe – the lingula (Latin for ‘small tongue’) – extends over the heart.
Describe the fissures that separate the lobes
- Both lungs have an oblique fissure. In the left lung, it separates the superior and inferior lobes. In the right lung, it separates the superior and middle lobes from the inferior lobe.
- The right lung has a horizontal fissure. It separates the superior lobe from the middle lobe.
Surfaces of the lung
- Costal surface - adjacent to the ribs.
- Mediastinal surface - adjacent to the heart.
- Diaphragmatic surface - the inferior surface of the lung
Borders of the lung
- Anterior border - sharp and tapered.
- Posterior border – thick and rounded.
- Inferior border - sharp and tapered.
Describe the indentations on the lungs
The surfaces of the lungs bear indentations (impressions) created by adjacent structures. Rib markings are seen on the costal surfaces of both lungs. Indentations created by the left ventricle and the descending aorta are seen on the mediastinal surface of the left lung and indentations made by the superior vena cava and azygos vein are seen on the mediastinal surface of the right lung.
What is the root of the lung?
The root of each lung lies between the heart and the lung and comprises the pulmonary artery, pulmonary veins, and main bronchus. Pleura encloses the root of the lung like a sleeve.
What is the hilum of the lung?
The hilum of the lung (plural = hila) is the region on the mediastinal surface of the lung where the pulmonary artery, pulmonary veins and main bronchus enter and exit the lung. The positions of the pulmonary artery and main bronchus relative to each other at the hilum is slightly different between the right and left lungs.
What is the position of the pulmonary arteries in relation to the main bronchi on each side?
- At the hilum of the right lung, the pulmonary artery lies anterior to the main bronchus.
- At the hilum of the left lung, the pulmonary artery lies superior to the main bronchus.
Where are the pulmonary veins?
At both the right and left hila, the two pulmonary veins are usually the most anterior and inferior vessels.
Describe the bifurcation of the trachea
The trachea bifurcates into the left and right main bronchi at the level of the sternal angle. Internally, the point of bifurcation is marked by a ridge of cartilage called the carina. The right main bronchus is shorter, wider and descends more vertically than the left main bronchus thus a foreign body entering the trachea is more likely to enter the right main bronchus than the left.
What is the bronchial tree?
branching system of tubes that conduct air into and out of the lungs.
Describe lobar bronchi
Each main (primary) bronchus divides into lobar (secondary) bronchi; three in the right lung and two in the left lung (i.e. one lobar bronchus for each lobe).
Describe the segmental bronchi
Each lobar bronchus divides to give rise to segmental (tertiary) bronchi. There are approximately ten segmental bronchi in each lung.
Describe the bronchopulmonary segments
Each segmental bronchus supplies a functionally independent region of the lung called a bronchopulmonary segment; there are ten segments in each lung. Because they are supplied by their own segmental bronchus and blood vessels, a segment may be resected (surgically removed) without affecting the rest of the lung.
Describe the bronchioles
Segmental bronchi within each bronchopulmonary segment continue to divide into bronchioles. Bronchioles become smaller with each division.
The very smallest bronchioles conduct air to and from the alveoli - the site of gas exchange within the lung.
What controls the contraction and relaxation of the smooth muscle of the conducting airways?
Autonomic nervous system
Arteries of the lungs
The pulmonary arteries carry deoxygenated blood to the lungs. Bronchial arteries from the descending aorta also supply the lungs.
Veins of the lungs
The pulmonary veins return oxygenated blood to the heart from the lungs. Bronchial veins return blood to the azygos system of veins
What type of nerves innervate the lungs?
Autonomic nerves innervate the lungs.
* Parasympathetic fibres stimulate:
* constriction of bronchial smooth muscle (bronchoconstriction)
* secretion from the glands of the bronchial tree.
* Sympathetic fibres:
* stimulate relaxation of bronchial smooth muscle (bronchodilation)
* inhibit secretion from the glands.
What are visceral afferents and what do they do?
Visceral afferents (visceral sensory fibres) accompany the sympathetic and parasympathetic nerves and relay sensory information from the lungs and visceral pleura to the CNS, but these sensations do not usually reach our conscious perception. Remember that somatic sensory fibres carried in the intercostal nerves innervate the parietal pleura.
Where does lymph go in the lungs?
Lymph from the lungs ultimately drains into the venous system via the thoracic duct or right lymphatic duct.
How can we auscultate the lungs?
We can auscultate the lungs by placing a stethoscope over the chest wall. When we listen to healthy lungs, we hear air moving into and out of the lungs with inspiration and expiration. We may hear abnormal sounds, like wheeze or ‘crackles’, or we may not hear any sounds. Pathology can affect just one lobe of a lung, so when we examine the lungs, we must auscultate each lobe separately. To do this, we need to know where each lobe lies relative to the chest wall.
What is the costodiaphragmatic recess?
The surface markings of the inferior borders of the lungs and the inferior extent of the parietal pleura are different as the parietal pleura extends more inferiorly than the inferior border of the lung. The space between them is the costodiaphragmatic recess.
Where is the apex of each of the lungs?
The apex of each lung projects into the lower neck, just superior to the medial end of the clavicle.
Where is the inferior border of the lungs in relation to the ribs?
The inferior border of the lungs lies at the level of the:
* 6th rib anteriorly (midclavicular line)
* 8th rib laterally (midaxillary line)
* 10th rib posteriorly (at the vertebral column).
Where does the parietal pleura extend to?
The parietal pleura extends to the:
* 8th rib anteriorly (midclavicular line)
* 10th rib laterally (midaxillary line)
* 12th rib posteriorly (at the vertebral column).
Where are the fissures of the lungs?
The oblique fissure of both the left and right lungs extends from the 4th rib posteriorly to the 6th costal cartilage anteriorly; the fissure runs deep to the 5th rib.
The horizontal fissure of the right lung extends anteriorly from the 4th costal cartilage and intersects the oblique fissure.
Describe the diaphragm
The diaphragm is a broad, thin, domed sheet of skeletal muscle.
* It separates the thoracic and abdominal cavities from each other.
* Its superior (thoracic) surface is adjacent to the parietal pleura.
* Openings (apertures) in the diaphragm allow the passage of structures between the thorax and abdomen (e.g. the aorta, inferior vena cava, and oesophagus).
* Its function is integral to the mechanics of breathing (ventilation).
Where is the diaphragm attached?
The diaphragm is attached to the xiphoid process, costal margin (and to the tips of the 11th and 12th ribs) and the lumbar vertebrae. The central part of the diaphragm is not muscular, but fibrous - the central tendon.
How does the diaphragm work?
- When the diaphragm contracts during inspiration, the muscle fibres of the right and left domes are pulled towards their peripheral attachments, and the domes flatten. This increases the intrathoracic volume for the lungs to expand.
- During expiration, the diaphragm relaxes and domes superiorly. This decreases the intrathoracic volume and drives expiration of air from the lungs.
What innervates the diaphragm?
The right and left phrenic nerves innervate the right and left sides of the diaphragm, respectively. They are somatic nerves, formed in the neck by fibres from the C3, C4 and C5 spinal nerves, and hence contain motor and sensory fibres.
Mechanics of breathing
The mechanics of breathing (breathing is also called ventilation) are complex. The basic principles are:
* Muscles move the thoracic cage and change the dimensions of the thoracic cavity.
* The dimensions of the thoracic cavity determine intrathoracic volume.
* Changes in intrathoracic volume alter intrathoracic pressure.
* Pressure changes inside the thorax drive inspiration and expiration.
* Different muscles are involved in normal, vigorous, and forced ventilation.
What are the planes that the dimensions of the thoracic cavity change in?
During ventilation, the dimensions of the thoracic cavity change in three planes:
* Vertically - due to the contraction and relaxation of the diaphragm.
* Laterally - due to contraction of the intercostal muscles which move the ribs.
* Antero-posteriorly (AP) – due to movement of the sternum secondary to movement of the ribs.
How does the pleural fluid impact ventilation?
The pleural fluid creates surface tension between the parietal pleura lining the thoracic cavity and the visceral pleura on the surface of the lung. Surface tension keeps the lung and thoracic wall ‘together’, so when the thoracic cavity changes volume, the lung changes volume with it. Surface tension between the two pleural membranes keeps them in contact with each other and prevents the lung from ‘collapsing’ away from the thoracic wall.
What happens when the surface tension broken?
If the surface tension is ‘broken’ (e.g. by a penetrating injury of the chest that punctures the parietal pleura and introduces air into the pleural cavity - pneumothorax) then ventilation may become dysfunctional.
What happens in inspiration?
In inspiration:
* The diaphragm and external intercostal muscles contract, increasing the intrathoracic volume (the external intercostals pull the ribs superiorly and laterally, and the ribs pull the sternum superiorly and anteriorly, increasing the AP and lateral dimensions of the thoracic cavity).
* The lungs expand (increase in volume) with the thoracic wall (due to surface tension).
* The pressure in the lungs decreases below atmospheric pressure and air is drawn into the lungs.
What happens during expiration?
The diaphragm and external intercostal muscles relax, decreasing the intrathoracic volume (the internal intercostals pull the ribs inferiorly, and the ribs pull the sternum inferiorly and posteriorly, decreasing the AP and lateral dimensions of the thoracic cavity).
* The lungs recoil (decrease in volume).
* The pressure in the lungs increases above atmospheric pressure and air is expelled from the lungs.
What are the muscles involved in breathing
- In normal, quiet breathing, inspiration is active and is mainly driven by movement of the diaphragm, but expiration is passive.
- In vigorous breathing (e.g. exercise) the intercostal muscles become important. Active expiration uses the internal intercostal muscles.
- In very vigorous or forced breathing (e.g. in an exacerbation of asthma or COPD, or in strenuous exercise) the accessory muscles of breathing (sternocleidomastoid, pectoralis major and minor, serratus anterior) contribute to movement of the ribs and aid ventilation. The anterior abdominal wall muscles contribute to forced expiration.
Pleuritic chest pain
The pleura can become inflamed or injured (e.g. torn by a fractured rib). Pleuritic chest pain is typically sharp, well localised (i.e. the patient can pinpoint it on the chest wall), and worse on inspiration. The pain is felt from the parietal pleura only.
What is a pneumothorax
A pneumothorax is the presence of air in the pleural cavity. It is usually caused by trauma (e.g. a fractured rib tearing the parietal pleura) but can happen spontaneously (tear in the visceral pleura). If air keeps entering the pleural cavity but cannot escape, a tension pneumothorax develops, in which a rapidly increasing volume of air progressively compresses the lung, heart, great vessels and the opposite lung over to the contralateral side of the thorax. This is rapidly fatal without immediate intervention. Patients with a tension pneumothorax present with severe respiratory distress.
What is a haemothorax?
Haemothorax describes a collection of blood in the pleural cavity and occurs secondary to trauma when blood vessels are torn or cut.
What is a pleural effusion?
Pleural effusion describes the presence of excess fluid in the pleural cavity. It is not a diagnosis - the fluid could be pus from infection, blood, or fluid related to malignancy. A chest drain is used to remove air and / or fluid from the pleural space. The surface anatomy of the heart and lungs must be considered to ensure the tip of the drainage tube does not injure them. An incision is made in the lower part of the chosen intercostal space, to avoid the neurovascular bundle, which lies in the costal groove of the rib superior to the space.
Describe lung cancer and mesothelioma
Lung cancer is one of the most common types of cancer seen in the UK. Lung cancer may be primary (i.e. cancer of the lung tissue or bronchi) or secondary (i.e. cancer from elsewhere that has metastasized to the lungs). Both primary and secondary cancer of the lung is common. Mesothelioma is a malignancy of the pleura.
Describe pulmonary embolism
Pulmonary embolism is a blood clot in the pulmonary circulation. The clot usually forms in the deep veins in one of the legs and is carried in the venous circulation back to the right side of the heart and into the pulmonary trunk. A very large clot lodging in the pulmonary trunk or in one of the pulmonary arteries causes severe respiratory distress and may be rapidly fatal. Smaller clots that occlude smaller pulmonary vessels may cause infarction of the part of the lung they supply.
How do you tell if someone is in respiratory distress?
Patients commonly present with breathlessness or shortness of breath (dyspnoea). The use of the accessory muscles of respiration is a sign of respiratory distress. Patients in respiratory distress will often ‘fix’ their upper limbs steady (e.g. by holding onto the side of the bed or chair), which allows the upper limb muscles that attach to the chest wall (pectoralis major, pectoralis minor and serratus anterior) to move the ribs and aid ventilation.
What happens in paralysis of the diaphragm?
Injury to the phrenic nerve, the C3-5 spinal nerves or the C3-5 spinal cord segments on one side may paralyse the ipsilateral side of the diaphragm, but in a healthy person, this may not cause symptoms. Patients with bilateral paralysis of the diaphragm require ventilatory support.
What is the mediastinum and where is it?
The mediastinum is the part of the thoracic cavity that lies between the lungs. The mediastinum contains all the thoracic viscera apart from the lungs. The mediastinum extends from the:
* superior thoracic aperture superiorly to the diaphragm inferiorly
* sternum anteriorly to the thoracic vertebrae posteriorly
What does the mediastinum contain?
- The heart and pericardium (the fibrous sac around the heart)
- The great vessels that enter and leave the heart
- The veins that drain the chest wall
- The trachea and main bronchi
- The oesophagus
- Nerves (somatic and autonomic)
- Lymphatics
- The thymus gland
Where is the mediastinum divided into superior and inferior?
The ‘line’ between these compartments runs from the sternal angle anteriorly to the T4/T5 junction posteriorly.
Where is the anterior mediastinum?
lies between the posterior aspect of the sternum and the anterior aspect of the pericardial sac. It is a narrow space that contains the thymus gland in children and its remnant in adults.
Where is the middle mediastinum and what does it contain?
Contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta.
Where is the posterior mediastinum?
Lies between the posterior aspect of the pericardial sac and the vertebrae.
Main contents of the superior mediastinum
- arch of the aorta and its three branches
- superior vena cava and its tributaries - the left and right brachiocephalic veins
- trachea
- oesophagus
- phrenic nerves (left and right) and vagus nerves (left and right)
- thoracic duct
- thymus gland
