Thorax Flashcards
The Sternum
- Flat bone (for protection) in the anterior aspect of thorax
- Makes up the thoracic wall & protects the internal thoracic visera (lungs, heart, oesophagus)
- Fractures are usually comminuted due to blunt force - breaks into several pieces
- Fragments arent usually displaced due to attachment to pectoralis muscles
- High mortality rate if damaged, due to further heart or lung injuries (important to do indepth investigations)
- Bone marrow aspiration is not taken from the sternum anymore - too likely to puncture viscera & misjudge sternum depth (anatomical variation). Now from hip & ultrasound guided
- Sternal angle - used as an anatomical landmark to palpate other structures within the thorax
Typical Ribs
- consists of a head, neck & body
- head - articular facets x 2
- neck - tubercle that articulates with numerically corresonding vertabrae, no bony prominences
- body/shaft - flat and curved, internal surface has costal groove for neurovascular supply (protecting them from damage)
Atypical Ribs
- 1,2,10,11,12 have features that aren’t common to all ribs
Rib 1
- shorter and wider than other ribs
- only has one facet (no thoracic vertabre above it)
- superior surface marked by two groves for subclavian vessels
Rib 2
- thinner and longer than rib 1 with two articular facets (normal)
- roughened area on upper surface - serratus anterior originates
Rib 10
- only one facet
Ribs 11&12
- no neck
- only one facet
Rib Classification - Relationship to Sternum
- Typical & Atypical ribs are classified based on structure
Classification based on relationship to sternum:
- true ribs - 1-7 (connect with sternum)
- false ribs - 8-12
- Floating ribs - (don’t have an anterior attachment)
Posterior Rib Articulations
- All twelve ribs articulate posteriorly with vertabrae
- each rib forms two joints
Costotransverse - between the tubercle of rib & transverse costal facet of corresponding vertabrae
Costovertebral - between the head of rib, superior costal facet of corresponding vertabre & the inferior costal facet of the vertabrae above
Anterior Rib Articulations
- Ribs 1-7 attach independently to the sternum
- Rib 8-10 attach to the costal carttilages superior to them
- Ribs 11-12 don’t have any anterior attachement - end in the abdominal musculature (‘floating ribs’)
Clinical Relevance - Rib Fractures
- Most common in the middle ribs - crushing or direct trauma
- Common complication - soft tissue injury from broken fragments (most at risk: lungs, spleen or diaphragm)
Flail Chest
- 2+ fractures in 2+ ribs means the area is no longer in control of thoracic muscles
- Flail chest - paradoxical movement during inflation/deflation impaires full expansion of the ribcage, effects oxygen content of the blood
- Treated by fixing the affected ribs to prevent their paradoxical movement
Characteristics of Thoracic Spine
- spinous processes - increased protection to spinal chord, preventing an object such as a knife entering the spinal canal
Vertabral Facets
Typical
T2-T9 - demi-facets
Atypical
T1 - superior facet is not a demi-facet, only vertabrae to articulate with 1st rib
T10 - single pair of whole facets articulate with 10th rib, located across both the vertabral body and pedicle
T11 & T12 - single pair of entire costal facets, located on the pedicles
Joints of Spine
Present Throughout Vertabral Column
- between vertebral bodies - adjacent vertebral bodies joined by intervertevral discs, made of fibrocartilage (cartilaginous joint - symphysis)
- between vertebral arches - formed by articulation of superior and inferior articular processes form adjacent vertabrae (synovial joint)
Unique to Thoracic Spine
- costovertebral joints
- costotransverse joints
Ligaments of Thoracic Spine
Present Throughout Vertebral Column
- anterior & posterior longitudinal ligaments - long, run length of vetebral column, covering the vertebral bodies & intervertebral discs
- ligament flavum - connects laminae of adjacent vertebrae
- Interspinous ligament - connects spinous processes of adjacent vertabrae
- supraspinous ligament - connects tios if adjacent spinous processes
Unique to Thoracic Spine
- radiate ligament of head of rib - fans outwards from the head of the rib to bodies of the two vertabrae and intervertabral disc
- costotransverse ligamanet - connects the neck of rib & transverse process
- lateral costotransverse ligament - extends from the transverse process to tubercle of rib
- superior costotransverse ligament - passes from upper border of the neck of the rib to transverse process of the vertabra superior to it
Clinical Relevance - Thoracic Kyphosis
- kyphosis - excessive curvature of the thoraci spine, back appears “hunched”
- early development - poor posture, abnormally wedge-shaped vertabrae (Scheurmann’s Kyphosis), fusing of vertabrae during development
- later development - osteoporosis (bone mass is lost) in older people, leaves spine less able to support weight of the body
The Diaphragm
- Double-domed musculotendinous sheet
- Separates the thoracic cavity from the abdominal cavity
- Undergoes contraction and relaxation, altering the volume of the thoracic cavity & lungs - producing inpsiration & expiration
- Fills the inferior thoracic aperture
- Primary muscle of respiration
- Inspriation - contracts & flattens to increase vertical diameter of thoraic cavity, produces lung expansion and air is drawn in
- Expiration - diaphragm passively relaxes & returns to dome shape, reduces volume of thoracic cavity
Diaphragm Attachments
Three peripheral attachments:
- lumbar vertebrae & articulate ligaments
- costal cartilages of ribs 7-10 (attach directly to 11-12)
- Xiphoid process of sternum
Parts that arise from the vertabre - right & left crura:
- right crus - from L1-L3 and their intervertebral discs. some fibres surround the oesophageal opening, acting as a sphincter to prevent reflux of gastric contents into the oesophagus
- left crus - from L1-L2 and their intevertebral discs
Muscle fibres come together to make a central tendon - ascends to fuse with inferior surface of fibrous pericardium. Either side of pericardium, diaphragm ascends to form left & right domes.
- at rest, right is slightly higher than left - presence of the liver
Pathways Through Diaphragm
Caval Hiatus (T8)
- inferior vena cava
- terminal branches of right phrenic nerve
Oesophagel Hiatus (T10)
- oesophagus
- right & left vagus nerves
- oesophageal branches of left gastric artery/vein
Aortic Hiatus (T12)
- Aorta
- Thoracic duct
- Azygous vein
Tip for remembering vertebral levels: vena cava = 8 letters (T8), oesophagus = 10 letters (T10), aortic hiatus = 12 letters (T12)
Diaphragm Innervation & Vasculature
- Halves recieve motor function from phrenic nerve - left half (hemidiaphragm) innervated by left phrenic nerve, visa versa
- Each phrenic nerve is formed in the neck of the cervical plexus - contains fibres from spinal roots C3-C5
- Majority of the arterial supply is from the phrenic arteries which arise from the abdominal aorta
- Remaining supply is from the superior phrenic, pericardicophernic & musculophrenic arteries
- Draining vessesl follow the arteries
Clinical Relevance - Paralysis of Diaphragm
This is due to interruption of nervous supply. Can occur in cervical spinal cord, brain stem or most commonly phrenic nerve:
- mechanical trauma: ligation or damage during surgery
- compression: tumour in chest cavity
- Myopathies: such as myasthenia gravis
- Neuropathies: such as diabetic neuropathy
Produces a paradoxical movement - affected side moves upwards during inspiration & downwards in expiration
Unilateral diaphragmatic paralysis is usually asymptomatic - incidental finding on an x-ray
Both sides - poor exercise intolerance, orthopnoea & fatigue. Lung function tests will show restrictive deficit
Managment is two-fold:
- underlying cause must be identified & treated
- symptomatic relief - non invasive ventilation such as a CPAP (Continuous Positive Airway Pressure) machine
External Intercostal Muscles
- 11 pairs of external intercostal muscles
- Run inferoanteriorly from the rib above to the rib below
- Continious with the oblique of the abdomen.
Attachments
Originate: lower border of rib
Insert: superior border of rib below
Function
Elevates ribs to increase the thoracic volume
Elevates ribs during forced inspiration (deep breath)
Innervation
Intercostal nerves (T1-T11)
Internal Intercostal Muscles
- Lie deep to external intercostals
- Run from the rib above to the rib below but in an oppsoite direction (inferoposteriorly)
- Continous with the internal oblique muscle of the abdominal wall
Attachments
Originates: lateral edge of costal groove
Inserts: superior surface of rib below
Functions
- Interosseous part reduces thoracic volume by depressing ribcage
- Interchondral part elevates ribs
- Elevates ribs during forced expiration (coughing)
Innervation
Intercostal nerves (T1-T11)
Innermost Intercostal Muscles
- Deepest of intercostal muscles
- Similar structure to internal intercostals
- Seperated from internal intercostals by the intercostal neurovascular bundle
- Found in the most lateral portion of intercostal spaces
Attachments
Originates: medial edge of costal groove
Inserts: superior surface of rib below
Functions
- Interosseous part reduces thoracic volume by depressing the ribcage
- Interchondral part elevates ribs
Innervation
Intercostal nerves (T1-T11)
Transverus Thoracis
- Continious with transversus abdominis inferiorly
Attachments
Originates: posterior surface of inferior sternum
Attaches: interal surface of costal cartilages 2-6
Function
Weakly depresses ribs
Innervation
Intercostal nerves (T2-T6)
Subcostals
- Found in inferior portion of thoracic wall
- Comprise of thin slips of muscle, which run from the internal surface of one rib, to the second & third ribs below
- Direction of the fibres parallels that of the innermost inercostal
Attachments
Originates: inferior surface of the lower ribs, near the angle of the rib
Attach: superior border of the rib 2 or 3 below
Actions
Share the action of the internal intercostals
Innervation
Intercostal nerves
Clinical Relevance - Rib Bruising
- Heavy bruising on the ribs is a sign of a rib puncture
- Could mean fluid on the lungs
- Patient would appear breathless & in pain
- Fluid on the lungs would cause for a chest drain (above the ribs to avoid neurovascular damage)
- Sometimes, chest drains have radio-opaque lines for them to be visible on an x-ray - to check positioning & make adjustments
Surface Anatomy
- Angle of Louis/Sternal Angle (formed by the articulation between the manubrium and sternum body) is palpable & an important clinical landmark
- Important for counting ribs & locating respiratory findings horizontally
- Distinct bony ridge down from the sternal notch
Rib Movements
Pump Handle Movement
- elevation of ribs
- upper part of thoracic cage
- increases antero-posterior diameter of thoracic cavity
Bucket Handle Movement
- elevation of ribs
- lower part of thoracic cage
- increases lateral diameter of thoracic cavity
Allows the intercostal muscles to draw the ribs upwards & outwards
Clinical Relevance - Intercostal Nerve Blocks
- Local anaesthetic to alleviate pain in emergency situations
- Intercostal nerves lie inferior to the ribs in the costal groove (nerve block location)
- Advisable for severe pain from rib fractures & post-operative pain management
Clinical Relevance - Chest Drains
- Intercostal chest drain - flexible plastic tube inserted into the plural cavity
- Used to drain fluids or air that has leaked into the pleural space (pneumothorax)
- Cyanosis - bluing of skin is a sign of low blood oxygen
- Shortness of breath & cynosis are more obvious in someone with compromised lung function already e.g COPD
- pneumothorax can be determined by a large gap between the thoracic wall & lung on an x-ray
Triangle of Saftey
- Area of axilla considered safe for the insertion of needles, catheters & drains
- Most commonly taken from the 2nd or 5th intercostal space, nearest to the midaxillary line as possible
With arm abducted, triangle is formed:
- lateral border of pectoralis major (anterior axillary line)
- later border of lattisimus dorsi & teres major (posterior axillary line)
- Horizontal line drawn from nipple (5th intercostal space)
Safest to insert catheter close to the superior border of the rib below the intercostal space to ensure the neurovascular bundle doesn’t get damaged (costal groove on upper rib)
Superior Mediastinum
Borders
Anterior - manubrium
Posterior - T1-T4
Superior - thoracic inlet & first rib
Inferior - sternal/Angle of Louis
Contents - BATS & TENT:
Brachiochepalic vein
Arch of Aorta Branches
Thymus (children, adults dissolve in adipose - T-cells in lymphocytes degenerate as no longer needed)
Superior vena cava
&
Thoracic duct (lymphatic)
OEsophagus
Nerves (vagus, phrenic, reccurent lar)
Trachea
Posterior Mediastinum
A subdivision of the inferior mediastinum
Borders
Lateral - medistinal pleura (part of parietal pleural membrane)
Anterior - pericardium
Posterior - T5-T12 vertebrae
Roof - imaginary line extending between sternal angle and T4 vertabrae
Floor - diaphragm
Contents - DATES:
Descending thoracic aorta
Azygos system of veins
Thoracic duct
OEsophagus
Sympathetic trunks
Anterior Mediastinum
A subdivision of the inferior Mediastinum
Borders:
Lateral - mediastinal pleura (part of the parietal pleural membrane)
Anterior - body of sternum & transversus thoracis muscles
Posterior - pericardium
Roof - continuous with the syperior mediastinum at the level of the sternal angle
Floor - diaphragm
Contents:
- no major structures - loose tissue (including sternopericardial ligaments)
- In infants & chilresn, thymus extends inferiorly into anterior mediastinum
Middle Mediastinum
A subdivision of the inferior mediastinum
Borders:
Anterior - anterior margin of pericardium
Posterior - posterior border of pericardium
Laterally - mediastinal pleura of lungs
Superior - imaginary line extending between sternal angle & T4 vertabrae
Inferiorly - superior surface of the diaphragm
Contents:
Organs:
- Heart & pericardium (protective sheath)
- Tracheal Bifurcation & left/right bronchi
Vessels:
- ascending aorta (arises from aortic orifice)
- pulmonary trunk (gives rise to left & right pulmonary arteries)
- superior vena cava (returns deoxygenated blood from upper half of body)
Nerves:
- cardiac plexus - sympathetic: T1-T4 of spinal chord, parasympathetic: vagus nerve
- phrenic nerves (left & right) - motor innervation to diaphragm
Mediastinum
- Central compartment of thoracic cavity located between the two pleural sacs
- Contains most of thoracic organs
- Acts as a conduit for structures transversing the thorax on the way into abdomen
- Divided into superior & inferior parts - divided by an imaginary line between the sternum angle to the T4 vertabrae
- Inferior mediastinum can be subdivided inot the anterior, middle & posterior mediastinum
Lungs
- Located in the thorax, either side of the mediastinum
- Function is to oxygenate blood - main organ of respiration
Medial surfaces lie close to otger mediastinal structures:
Left Lung
- heart
- arch of aorta
- thoracic aorta
- oesophagus
Right Lung
- oesophagus
- heart
- inferior vena cava
- superior vena cava
- azygous vein
Lung Structure
Roughly cone-shaped & consists of:
- Apex - blunt superior end of lung above 1st rib and into floor of neck
- Base - inferior surface of lung, sits on diaphragm
- Lobes (two or three) seperated by fissures within lung
- Sufaces (three) - correspond to area of the thorax they face: costal, mediastinal & diaphragmatic
- Borders (three) - the edges of lungs, named the anterior, inferior & posterior borders
Lobes
- Left lung has three lobes - superior middle & inferior
The lobes are split by two fissures:
- oblique - runs from the inferior border in a superoposterior direction, until the posterior lung border
- horizontal - runs horizontally from sternum at 4th rib level, to meet the oblique fissure
- Left lung has two lobes which are seperated by a similar oblique fissure
Lung Surfaces & Borders
Surfaces
Mediastinal surface - lateral aspect of middle mediastinum (lung hilum located on this surface
Diaphragmatic surface - base of lung rests on the dome of the diaphragm, has a concave shape (concavity is deeper in the right lung due to the higher position of the right dome, overlying the liver)
Costal surface - smooth & convex, faces the internal surface of chest wall
Borders
Anterior border - convergence of the mediastinal & costal surfaces. Marked by a deep notch on the left lung called the cardiac notch (created by heart apex)
Inferior border - seperates the base of the lung from the costal & mediastinal surfaces
Posterior border - smooth & rounded (unlike other two which are sharp), formed by the costal & mediastinal surfaces meeting posteriorly
Root & Hilum
Lung root - collection of structures that suspends the lung from mediastinum. Each root contains:
- bronchus
- pulmonary artery
- two pulmonary veins
- bronchial vessels (arteries - support lung tissue supply, veins provide venous drainage)
- pulmonary plexus of nerves
- lymphatic vessels
All these structures enter/exit lung via the hilum - wedged shape area on it’s mediastinal surface
- can differentiate the lungs by the hilum (RBS - Right, Bronchus, Superior)
- bronchi have the same cartilaginous rings as the trachea so they are easy to spot against veins/arteries
Structure of the Pleura
- Two pleurae in the body - one associated with each lung
- Consist of a serous membrane - layer of simple squamous cells supported by connective tissue
- Simple squamous epithelial layer is known as the mesothelium
Each pleura can be divided into two:
- visceral - covers the lungs
- parietal - covers the internal surface of the thoracic cavity
The two parts are continous with each other at the hilum & there is a space between the two called the pleural cavity.
Thymus
- Thymus gland is located in the anterior & superior mediastinum
- On rare occasions, it may give rise to tumors (benign & malignant)
- Main fuction of thymus is the production of T lymphocytes
- T-cells are produced in the bone marrow then sent for maturation in the thymus.
- Most T-cells get eradicated when they have a high chance of being self-reactive and causing cell death
- The remaining T-cells that mature emigrate to provide vital functions in the immune system
- This means in adults, the thymus degenerates & dissolves into adipose tissue as mature cells have left
- In adults, the lymph nodes take a greater importance of T-Cell maturation
Clinical Relevance - Pleurisy
- Painful condition where visceral and parietal pleura become inflamed
- Can be caused by influenza, tuberculosis, pneumonia or autoimmune disease
- Symptoms include shortness of breath, chest pain during breathing & dry cough
- Patients may find temporay relief in holding their breath - phenomenon as the pleura are no longer frictionless against each other
Clinical Relevance - Accompaniments to Pleurisy
Pleural Effusion
- fluid builds up in the small space between the two layers of tissue
- a large amount of fluid may result in a pain lessening as pleura no longer rub together
- capacity to breath normally is flawed, as respiring surfaces are drowned
Atelectasis
- large amount of fluid creating pressure
- compresses lung(s) to the point that it partially/completely collapses
- difficulty breathing, may cause coughing
Empyema
- extra fluid can become infected
- results in accumulation of pus
- often accompanied by a fever
Bronchial Tree - Trachea
- Beginning of bronchial tree, arises at the lower border of cricoid cartilage in the neck as a contiuation of the larynx
- Held open by c-shaped cartilaginous rings - free ends supported by trachealis muscle
- Lined with cilliated pseudostratified epithelium with goblet cells that produce mucus - sweeping movement forms the muociliary escalator (to trap inhaled particles/pathogens & move them up and out to be swallowed & destroyed)
- Burification happens at the level of sternal angle (T4) - carina runs between two bronchi openings
- Carina is the most sensitive area of trachea for cough reflex (can be seen on bronchoscopy)
- Sensory innervation - recurrent laryngeal nerve
- Blood supply - inferior thyroid artery
- Venous drainage - brachiocephalic, azygos & accessory hemiazygos veins
Bronchial Tree - Bronchi
- At sternal angle, trachea bifurcates into right & left bronchi (primary)
- Make up roots of lungs
- Right main bronchus - wider, shorter & descends more vertically
- Clinically, higher incidence of foreign body inhalation - reason why recovery position is on left side (less chance)
- Primary (main) bronchi branch into secondary (lobar) bronchi that supply a lobe of the lung - 3 in right, 2 in left
- Secondary (lobar) bronchi burificate into several tertiary (bronchopulmonary) bronchi that each supplies a bronchopulmonary segment (subdivisions of lobes, functional units)
- Innervated - pulmonary branches of vagus nerve
- Blood supply - bronchial arteries
- Venous drainage - bronchial veins
Brachial Tree - Bronchioles
- Segmental bronchi undergo further branching to form bronchioles
- No cartilage or mucus-secreting goblet cells - surfactant lipoprotein that prevents the walls sticking together during expiration
- Conducting bronchioles - transport air but lack glands, not involved in gas exchange
- Terminal bronchioles - end of conducting bronchioles
- Respiratiory bronchioles - further branches, distinguishable by the presence of alveoli extending from their lumens
- Alveoli - air-filled pockets with thin walls, site of gas exchange, large SA
Clinical Relevance - Asthma
- Inflammatory disorder of airways - hypersensitivity, reversible outflow obstruction & bronchiospasm
- Remodelling of small airways caused by smooth muscle thickness around the bronchioles, damaged epithelium & thickened basement membrane
- “Asthma attack” - trigger (allergens, exercise) causes sudden inflammation & contraction of these muscles (bronchospasm)
- Narrows airways, causing difficulty in breathing and wheezing
Clinical Relevance - Pneumothorax
- Collapsed lung (partially or fully) - caused by air in pleural space, usually by a tear on outside of lung or outside of body (accident or surgery)
- Presents as a sharp pain on one side of chest, gets worse as you breath in & breathlessness
- May cause medistinal shift - movement of organs/tissues to one side of chest cavity
- Negative air-flow - air keeps entering but not leaving
- May be treated by a chest drain/aspiration (emergency) so air can escape & lung can re-inflate
- Continuous pneumothorax may need a surgery including pleurodisis - lung stuck to inside of chest wall so it cannot collaspe again
Clinical Relevance - Types of Pneumothorax
- Primary spontaneous - happens on an otherwise healthy person (usually on young adults with weakness in tissue due to growth), small tear on outer lung tissue
- Secondary spontaneous - develops in a person with an existing condition such as COPD, TB, CF or cancer as it weakens edges of the lung, making it more likely to tear
- Small pneumothorax may present no symptoms, not complete collapse
- Tension-pneumothorax, compresses lung & heart, medical emergency - needs to be treated by aspiration (inserting a small needle & sucking the air through a syringe)
Great Vessels
- Function is to carry blood to & from the heart as it pumps
- Largely located within the middle mediastinum
The great vessels are:
- aorta
- pulmonary arteries
- pulmonary veins
- superior vena cava
- inferior vena cava
Aorta
- Largest artery in body
- Carries oxygenated blood away from the heart, to the rest of the body
- Pumped by the left side of the heart
- Arises from aortic orifice at base of left ventricle - inflow via aortic valve
- Ascending aorta lies within the pericardium, covered by visceral layer - origin of coronary arteries
- Major arteries to head & neck (brachiochepalic trunk, left common carotid artery, left subclavian artery) arise from the arch of the aorta
- After the arch of the aorta, aorta then becomes the descending branch which continues through diaphragm, into abdomen
Clinical Relevance - Disorders of Aorta
Aortic Dissection
- tear in the inner wall
- creates two channels for the blood - usual lumen & into the wall (blood becomes stationary)
- blood in the wall can constrict the aortic lumen, reducing blood flow to the rest of the body
- can also cause further weakness & dilation of the wall, potentially leading to an aortic aneurysm
Aortic Aneurysm
- dilation (expansion) of an artery, greater than 50% of normal diameter
- due to an underlying weakness of the walls (e.g Marfan’s syndrome), or a pathological process (e.g aortic dissection)
- main concern is rupture of the aorta, will lead to death if not treated
Pulmonary Arteries
- Recieve doxygenated blood from right ventricle & deliver it to the lungs for gas exchange (carrys deoxygenated blood to the heart)
- Begins as the pulmonary trunk - thick & short vessel, seperated from the right ventricle by the pulmonary valve
- Sharea a common layer of pericardium with the asscending aorta
- At T5-T6, pulmonary trunk splits into right & left pulmonary arteries
- Left (shorter & thinner) - supplies blood to left lung, bifurcating into two branches to supply each lobe
- Right (thicker & longer) - supplies blood to right lung, also bifurcates into two branches
Pulmonary Veins
- Receive oxygenated blood from lungs, delivers it to left side of the heart to be pumped back around body
- Four pulmonary veins - one superior & one inferior for each of the lungs
- They enter the pericardium & drain into the superior left atrium, on the posterior surface
- Oblique pericardial sinus can be found within the pericardium , between left & right veins
- Superior pulmonary veins return blood from upper lobes of lung & inferior return blood from lower lobes
Superior Vena Cava
- Superior vena cava recieves deoxygenated blood from the upper body (superior to diaphragm, excluding lungs & heart), delivering it to the right atrium
- Formed by merging of the brachiocephalic veins, travelling inferiorly through the thoracic region
- Drains into the superior portion of the right atrium, at level of 3rd rib
- Located in the right side of the superior mediastinum before entering the middle mediastinum to lie beside ascending aorta
Inferior Vena Cava
- Recieves deoxygenated blood from lower body (all structures inferior to diaphragm), delivering it back to heart
- Initally formed in pelvis by the common iliac veins joining together
- Travels through abdomen, collecting blood from the hepatic, lumbar, gonodal, renal & phrenic veins
- Passes through diaphragm, entering pericardium at T8
- Drains into inferior portion of right atrium
Aortic Sinuses
- Small openings found within the aorta behind the left/right flaps of the aortic valve
- Widenings are between the wall of the aorta & each of the three cusps of the aortic valvew
- When the heart is relaxed, back-flow fills these valve pockets, allowing blood to enter the coronary arteries
There are 3 aortic sinuses (x1 anterior, x2 posterior):
- left posterior - gives rise to left coronary artery (LCA)
- anterior - gives rise to right coronary artery (RCA)
- right posterior - usually no vessels arise, non-coronary sinus
Coronary Arteries
- Coronary - encircle the heart like a crown
- Supply oxygenated blood to heart muscles
- Left (LCA) & Right (RCA) arteries arise from left & right posterior sinuses
LCA splits into:
- diagonal branch (LAD) -anterior
- circumflex branch (LCA) - anterior
- marginal branch (LMA) - posterior
RCA splits into:
- marginal branch (RMA) - anterior
- posterior descending branch (PIv) -posterior
- Sinoatrial branch - anterior
Cardiac Veins
- Coronary sinus - main vein of the heart (posterior side, in coronary sulcus between left atrium & ventrice)
- Sinus drains into the right atrium - between the right AV orifice & inferior vena orifice
5 main tributaries that run into the sinus:
- Great cardiac vein - main tributary (anterior - accompanies LCA diagonal branch )
- Small cardiac vein - (anterior - accompanies RCA marginal branch)
- Middle cardiac vein - (posterior - accompanies RCA posterior descending branch)
- Left marginal vein - (posterior - accompanies LCA marginal branch)
- Left posterior ventricular vein - (posterior - runs between middle & left marginal vein)
Distribution of Coronary Arteries
- LCA, circumflex branch - supplies left atrium & ventricle
- LCA, diagonal branch - supplies left & right ventricle and interventricular septum
- LCA, marginal branch - supplies left ventricle
- RCA, PIv & sinoatrial branch - supplies right atrium & ventricle
- RCA, marginal branch - supplies right ventricle & apex
Clinical Relevance - Coronary Artery Disease
- AKA coronary heart disease (CHD)
- Leading cause of death UK & worldwide
- Reduction of blood flow to the myocardium
- Result in reduce blood flow to the heart as a result of a blockage/narrowing of the artery
- May be due to atherosclerosis, thrombosis, high blood pressure, diabetes or smoking - all lead to reduced blood flow (either via physical obstruction/changes in vessel wall)
- Angina pectrois - transient pain as a result of lack of O2 supply to heart, felt across the chest but quickly resolved when resting
- Excercise is a trigger for angina - as coronary arteries fill during the diastolic period (period is shortened - less time for blood to overcome a blockage to supply heart)
- If left untreated, angina can progress to myocardial infarction - necrosis (tissue death)
- Myocardial infarction means a section of the heart is unable to beat (depending on what artery is occluded)
- ECG leads can locate the atery that has been occluded if the MI change appears on the graph
Clinical Relevance - CHD Diagnosis & Treatment
- A blockage in a coronary artery can be rapidly identified by performing a coronary angiogram
- Coronary angiogram - insertion of a catheter into the aorta via femoral artery, contrast dye injected to show up on X-ray images
- Immeadiate treatment: coronary angioplasty - inflation of a balloon within the affected artery
- Ballon pushes aside the atherosclerotic plaque & restores blood flow to myocardium
- Artery may then be supported by the addition of an interavascular stent to maintain volume
Overview of the Vasculature (Coronary) of the Heart
Structure of Pericardium
- fibroserous, fluid-filled sack that surrounds the heart body & roots of the great vessels
- Two main layers: fibrous & serous pericardium
Fibrous - continious with the central tendon of the diaphragm, made of tough connective tissue & is relatively non-distendible
Rigid structure prevents rapid overfilling of the heart
Serous - enclosed within fibrous, split into the outer parietial (lines the internal surface of fibrous pericardium) & inner visceral layer (forms the outer layer of the heart - epicardium)
Inbetween the two layers is the pericardial cavity which contains small amount of lubricating serous fluid - minimises friction generated by the heart as it contracts
Order of layers can be remebered by:
Fart - fibrous layer of pericardium
Police - parietial layer of the serous pericardium
Smell - serous fluid
Villains - visceral layer of the serous pericardium
Functions of the Pericardium
- Fixes the heart to mediastinum & limits motion - attached to the diaphragm, sternum & outer layer of the great vessels (tunica adventitia)
- Prevents overfilling of heart - fibrous layer prevents size increasing too rapidly, placing a physical limit on potential size
- Lubrication - serous fluid reduces friction of the heart as it moves within the thoracic cavity
- Protection from Infection - fibrous pericardium serves as a physical barrier between the heart’s muscular body & adjacent organs (e.g lungs) that are prone to infection
Clinical Relevance - Cardiac Tamponade & Pericarditis
Cardiac Tamponade
- relatively inextensible fibrous pericardium can cause problems when there is an accumulation of fluid (pericardial effusion) within the pericardial cavity
- rigid pericardium can’t expand, subjecting heart to increased pressure
- chambers can become compressed, comprimising cardiac output
Pericarditis
- inflammation of the pericardium
- causes can include bacterial infection & myocardial infraction
- main symptom is chest pain
- can cause acute cardiac tamponade due to an accumulation of fluid in the pericardial cavity
- sometimes pain can be felt in the shoulder as the phrenic nerve C3-C5 (somatic innervation of the pericardium) originates in the neck - reffered pain
Surfaces & Borders of the Heart
- Heart is like a fallen pyramid - apex points in anterior-inferior direction
Heart has 5 surfaces, formed by different internal divisions:
- anterior (sternocostal) - right ventricle
- posterior (base) - left atrium
- inferior (diaphragmatic) - left & right ventricles
- right pulmonary - right atrium
- left pulmonary - left ventricle
Separating the surfaces of the heart are 4 borders:
- right border - right atrium
- inferior border - left & right ventricle
- left border - left ventricle (& some left atrium)
- superior border - right & left atrium & great vessels
Sulci of the Heart
- The heart is a hollow structure - on infterior, it is divided into four chambers
- Divisions create grooves on the surface of the heart - sulci
- Coronary sulcus - runs transversely around heart, represnts wall dividing atria from ventricles (contains important vasculature)
- Anterior & posterior interventricular (descending) sulci - run vertically on respective sides, representing the wall sperating the ventricles
Pericardial Sinuses
- Passageways formed uniquely by the way the pericardium folds around the great vessels
- Oblique pericardial sinus - blind-end passageway (cul de sac) located on the posterior surface of heart
- Transverse pericardial sinus - found superiorly on heart, can be used in coronary bypass grafting
Clinical Relevance - Transverse Pericardial Sinus
Location:
- posterior to asscending aorta & pulmonary trunk
- anterior to superior vena cava
- superior to left atrium
Seperates the arterial vessels (aorta, pulmonary trunk) & venous vessels (superior vena cava, pulmonary veins) of the heart
Can be used to identify & ligate (tie off) the arteries of the heart during coronary artery bypass grafting
Right Atrium
- Recieves dexoygenated blood from the vena cavae & coronary veins
- Pumps the blood through the right atrioventricular orifice (gaurded by tricuspid valve) & into right ventricle
- Forms the right border of the heart - right auricle (right atrial appendage) is a muscular pouch that acts to increase capacity of the atrium
Interior surface can be split into two parts seperated by a muscular ridge, crista terminalis:
Sinus venarium - posterior to crista terminalis. Recieves blood from the vena cava, has smooth walls
Atrium proper - anterior to crista terminalis, includes the right auricle. Has rough, muscular walls formed by pectinate muscles
Coronary sinus recieves blood from coronary veins & opens into the right atrium between inferior vena cava orifice & right atrioventricular orifice
Interatrial Septum
- Solid muscular wall that seperates the right & left atria
- Septal wall in right atrium is marked by a small oval-shaped depression, fossa ovalis
- Fossa ovalis is a remnant of the foramen ovale in the foetal heart - allows shunting of blood right to left to bypass the lungs
- Fossa ovalis closes once the newborn takes it’s first breath
Clinical Relevance - Atrial Septal Defect
- Abnormal opening in the interatrial septum, persistent after birth
- Most common site is the foramen ovale - known as the patent foramen ovale
- In adults, left atrial pressure is greater than right so blood is shunted over left to right
- Large defects can cause ventricular overload, leading to pulmonary hypertension, right ventricular hypertrophy & heart failure
- Definitive treatment is closure by surgery or transcatheter closure
Left Atrium
- Recieves blood from the four pulmonary veins
- Pumps blood through the left atrioventricular orifice (gaurded by mitral valve) into left ventricle
- Left atrium forms posterior (base) border of the heart
- Left auricle extends from the superior aspect of the chamber, overlapping the root of the pulmonary trunk
Interior surface can be split into two parts:
Inflow portion - recieves blood from the pulmonary veins (derived by them also). Internal surface is smooth.
Outflow portion - located anteriorly, includes left auricle. Lined by pectinate muscles & is dervived from the embryonic atrium
Right Ventricle
- Recieves deoxygenated blood from the right atrium
- Pumps blood through the pulmonary orifice (gaurded by pulmonary valve), into pulmonary artery
- Triangular in shape & forms the majority of the heart’s anterior border
Can be divided into two portions, split by a muscular ridge - supraventricular crest:
Inflow Portion
Covered by a series of irregular muscular elevations, trabeculae carnae - give the ventricle a ‘sponge-like’ apperance & can be grouped into three main types:
- ridges - attached along entrie length from one side to form ridges along interior surface of ventricle
- bridges - attaches to ventricle at both ends but free in the middle. Example: moderator band, spans across ventricle & has an important conductive function
- pillars (papillary muscles) - anchored by their base. Apices attached to fibrous chords (chordae tendineae), which attach to the three cusps of the tricuspid valve. By contracting, the palpillary muscles pull on the chords to prevent prolapse of valve leaflets during ventricular systole
Outflow Portion (conus arteriosus)
Leads to the pulmonary artery & is located in the superior aspect of the ventricle. Dervived from the embryonic bulbus cordis. Visibly different from the rest of right ventricle - smooth walls & no traveculae carnae
Interventricular Septum
- Separates the two ventricles
- Composed of a superior membranous part & an inferior muscular part
- Muscular part forms the majority of the septum & is the same thickeness as the left ventricular wall
- Membranous part is thinner & part of the fibrous skeleton of the heart
Left Ventricle
- Recieves oxygenated blood from left atrium
- Pumps blood through aortic orifice (gaurded by the aortic valve) into aorta
- Forms the apex of heart as well as left & diaphragmatic borders
Can be divided into an inflow & outflow portion:
Inflow - walls are lined by trabeculae carnae. There are two papillary muscles present which attach to the cusps of the mitral valve
Outflow - known as the aortic vestibule. Smooth-walled with no trabeculae carnae, derivative of the embryonic bulbus cordis
Clinical Relevance - Tetralogy of Fallot
Cyanotic congenital heart disease made up of four abnormalities:
- overrriding aorta - lies over the VSD, resulting in deoxygenated blood passing into aorta
- pulmonary valve stenosis - increases the force needed to pump blood through it, resulting in right ventricular hypertrophy
- right ventricular hypertrophy - pressure eventually becomes higher in right ventricle than left so blood gets shunted right to left
- ventricular septal defect - shunted blood passes through the VSD
The condition is usually treated surgically within the first few months of life/soon after birth in severe cases
Endocardium
- Innermost layer of the cardiac wall
- Lines the cavities & valves of the heart
- Composed of losse connective tissue & simple squamous epithelia
- Similar to the endothelium that lines inside of blood vessels
- It also regulates contractions & aids cardiac embryological development
Clinical Relevance - Endocarditis
- Inflammation of the endocardium
- Most commonly occurs on the valves of the heart
- Main form is infective endocarditis - caused by a pathogen
- Bacteria colonise in the heart valve & cause vegetations (small lumps) to develop
- Resulting inflammation can cause permenant damage to the valve, creating a murmur
- Damage valves are more likely to be colonised again in the future - re-infection
Subdenocardial Layer
- Lies between & joins the endocardium and myocardium
- Consists of a layer of loose fibrous tissue, containing vessels & nerves of the heart’s conducting system
- Purkinje fibres are located in this layer
- As the layer houses the conducting system, damage can result in arrhythmias
Myocardium
- Composed of cardiac muscle
- Is an involuntary striated muscle
- Responsible for contractions of the heart
Clinical Relevance - Myocarditis
- Inflammation of the heart muscle
- Often due to viruses e.g adenovirus & coxasckie B
- Symptoms depend on severity of inflammation but include chest pain, shortness of breath & tachycardia
- Common sequelae is damage to the cardiac muscle of myocardium - can result in arrhythmias & heart failure
Clinical Relevance - Myocardial Infarction
- Myocardial infarction = heart attack caused by a blockage in a coronary artery
- Myocardium looses oxygen supply & undergoes ischaemic change
Two main tyoes of myocardial infarctions:
- NSTEMI (non S-T elevated) - coronary artery is only partially blocked. Ischaemic damage to partial thickness of myocardium
- STEMI (S-T elevated) - coronary artery is completely blocked. Ischaemic damage to the full thickness of myocardium
- Most common cause is an atheroma (lipid collection in artery walls)
- Risk factors include obesity, high BP, smoking & diabetes
Clinical Relevance - Angina
- Refers to chest pain which arises as a result of temporary myocardial ischemia
- Coronary arteries are narrowed but not completely blocked
- Majority as a result of atherosclerosis
- Reduced blood flow cause intermittent ischemia when oxygen demand exceeds supply
Two types of angina:
- stable angina - can be predicted with chest pain developing after exercise or under stress
- unstable angina - does not require exertion to set off symtoms
- Both conditions can be treated with a GTN spray
- Unstable angina is the more serious of the two - more likely to progress to a myocardial infarction
Subepicardial Layer
- Lies between & joins the myocardium to epicardium
Epicardium
- Outermost layer of the heart
- Formed by visceral layer of the pericardium
- Composed of connective tissue & fat
- Connective tissue secretes a small amount of lubricating fluid into the pericardial cavity
- Lined on outer surface by simple squamous epithelial cells
Cardiac Conduction System
A collection of nodes & specialised conduction cells that initate & co-ordinate contraction of heart muscles. It includes:
- Sinoatrial node
- Atrioventricular node
- Atrioventricular bundle (bundle of his)
- Purkinjie fibres
Heart Conduction Overview
Sequence of electrical events during one full contraction of the heart muscle:
- Excitation singal (an action potential) is created by the SA node
- Wave of excitation spreads across the atria, causing them to contract
- Upon reach the AV node, signal is delayed
- Singal is then conducted into the bundle of his, down the interventricular septum
- Bundle of his & perkinjie fibres spread the wave impluses along the ventricles, causing them to contract
Sinoatrial (SA) Node
- Collection of specialised cells (pacemaker cells)
- Located in the upper wall of right atrium, at the junction where superior vena cava enters
- Pacemaker cells spontaneously generate electrical impulses
- Wave of excitation created by the SA node spreads via gap junctions across both atria causing contraction - atrial systole, blood moves into ventricles
The rate of impulses created by the SA node is influenced by the autonomic nervous system:
- Sympathetic - increases firing rate of SA node, increases heart rate
- Parasympathetic - decreases firing rate of SA node, decreases heart rate
Atrioventricular (AV) Node
- After impulses spread across the atria, they converge at the AV node
- Located within hte atrioventricular septum, near opening of the coronary sinus
- AV node acts to delay the impulses by 120ms, to ensure the atria have enough time to fully eject blood into ventricles before ventricular systole
- Wave of excitation then passes from the AV node to AV bundle
AV Bundle
- AKA bundle of His
- Continuation of the AV node, transmitts electrical impules to the perkinjie fibres of the ventricles
It descends down the membranous part of the interventricular septum, before dividing into two main bundles:
- Right bundle branch - conducts impulse to the perkinjie fibres of right ventricle
- Left bundle branch - conducts impulse to the perkinjie fibres of left ventricle
Perkinjie Fibres
- Sub-endocardial plexus of conduction cells - network of specialised cells
- Abundant with glycogen & have extensive gap junctions
- Located in the subendocardial surface of the ventricular walls
- Able to rapidly transmit cardiac action potentials from AV bundle to myocardium of ventricles
- Rapid conduction allows co-ordinated ventricular contraction (ventricular systole) - blood is moved from right & left ventricles to pulmonary artery & aorta respectively
Clinical Relevance - Artificial Pacemaker
- Small electrical device commonly fitted to monitor & correct heart rate/rhythm
- Inserted into chest under left clavicle, with wires connected to the heart via venous system
- Most common indication for a pacemaker is bradycardia
- Pacemaker monitors heart rate & only fires if rate becomes too slow
- Can also be used to treat some tachycardias, certain types of heart block & other rhythm abnormalities
Valves of the Heart
- Structures which ensure blood flows only in one direction
- Composed of connective tissue & endocardium (inner layer of the heart)
There are four valves of the heart, divided into two categories:
- Atrioventricular valves - tricuspid & mitral (bicuspid) valve. Loacted btween the atria & corresponding ventricle
- Semilunar valves - pulmonary & aortic valve. Located betwwen ventricles & their corresponding artery, regulate flow of blood leaving the heart
Atrioventricular Valves
- Located between atria & ventricles
- They close during the start of ventricular contraction (systole), producing the first heart sound
Tricuspid valve
- located between right atrium & right ventricle - right AV orifice
- consists of three cusps - anterior, septal & posterior
- base of each cusp anchored to a fibrous ring that surrounds the orifice
Mitral Valve
- located between the left atrium & left ventricle - left AV orifice
- AKA bicuspid valve as it has two cusps - anterior & posterior
- bases of each cusp is secured to a fibrous ring surrounding the orifice
- Both valves are supported by the attachment. of chordae tendinae (fibrous chords) that attach to the free edges of the cusps
- Chordinae tendinae are attached to papillary muscles, located on interior surface of the ventricles
- Papillary muscles contract during ventricular systole to prevent proplase of valve leaflets into atria
- 5 papillary muscles in total - 3 in right ventricle to support tricuspid valve & 2 in the left ventricle to act on mitral valve
Semilunar Valves
- Located between ventricles & outflow vessels
- Close at the start of ventricular relaxation (diastole), producing second heart sounds
Two semilunar valves:
Pulmonary
- located between the right ventricle & pulmonary trunk -pulmonary orifice
- valve consists of three cusps - left, right & anterior
Aortic
- located between the right ventricle & pulmonary trunk - aortic orifice
- valve consits of three cusps - right, left & posterior
- Left & right aortic sinuses mark the origin of the left & right coronary arteries
- As blood recoils (ventricular diastole), it fills aortic sinuses & enters coronary arteries to supply the myocardium
- Both valves have simlar structure - sides of each valve leaflet are attached to the walls of the outflow vessel (that is slightly dilated to form a sinus)
- Free superior edge of each leaflet is thickened (lunule) & widest in the midline (nodule)
- At beggining of V-diastole, blood flows back towards the heart, filling the sinuses & pushing the valve cusps together - closes the valve
Clinical Relevance - Aortic Stenosis
- Narowing of the aortic valve, restricting flow of blood leaving the heart
- Three main causes: age-related calcification, congenital defects (most commonly a bicuspid aortic valve which predisposes the valve to calcification later in life) & rheumatic fever
- Classical triad seen is shortness of breath, syncope & angina
- Increasing workload for left ventricle can also result in left ventricular hypertrophy
- Definitive treatment is surgical, can be achieved via a valve replacement or baloon vavuloplasty
Parietal Pleura
- Covers internal surface of thoracic cavity
- Thicker than visceral pleura
Can be subdivided according to the part of the body it is in contact with:
- mediastinal pleura - covers lateral asepct of mediastinam (central compartment)
- cervical pleura - lines the exentesion of the pleural cavity into the neck
- costal pleura - covers the inner aspect of the ribs, costal cartilages & intercostal muscles
- diaphragmatic pleura - covers the thoracic (superior) surface of the diaphragm
Visceral Pleura
- Covers outer surface of the lungs & extends into the interlobar fissures
- Continuous with the parietal pleura at the hilum of each lung
Pleural Cavity
- Potential space between the parietal & visceral pleura
- Contains a small volume of serous fluid, which has two major functions
- Lubricates the surfaces of the pleurae, allowing them to slide over each other
- Serous fluid also produces a surface tension - pulling the parietal & visceral pleura together
- Ensures that when the thorax epands, the lung also expands, filling with air
- If air enters the pleural cavity, the surface tension is lost - pneumothorax
Pleural Recesses
- Anferiorly & posteroinferiorly, the pleural cavity isn’t completely filled by the lungs
- Gives rise to recesses - opposing surfaces of the parietal pleura touch
There are two recesses present in each pleural cavity:
- costodiaphragmatic - located between the costal pleura & diaphragmatic pleura
- costomediastinal - located between the costal & mediastinal pleurae, behind sternum
Recesses are of clinical importance, they provide a location where fluid can collect (e.g in pleural effusion)
Pleural Neurovascular Supply
Parietal Pleura
- sensitive to pain, pressure & temperature
- produces a well localised pain
- innvervated by the phrenic & intercostal muscles
- blood supply derived from the intercostal arteries
Visceral Pleura
- not sensitive to pain, temperature or touch
- sensory fibres only detect stretch
- receives autonomic innervation from the pulmonary plexus (network dervied from the sympathetic trunk & vagus nerve)
- blood supply is via the bronchial arteries (branches of the descending aorta) which also supply the parenchyma of the lungs
Rib Mechanisms
- Upper part of the thoracic cage increases anteroposteriorly - inferior part moved up & outwards (water-pump)
- Lower part increases lateral diameter of thorax - movement of ribs laterally & upward (bucket-handle), fixed at each end but moves away
Cardiac Dominance
- Describes which coronary artery sude provides most of the body supply to ventricles
- Left side dominant - posterior descending ventricular artery arises from a branch of the left coronary artery
- Right side dominant - descending ventricular artery arises from a branch of the right circumflex artery
Clinical Relevance - Heart Mumurs
- Wooshing/swishing noise heard due to turbulent blood in the heart
- Can be congenital (present at birth) or develop later in life
Diastolic murmur - when heart is filling (diastole)
Systolic murmur - when heart is emptying (systole)
Continious murmur - throughout the heartbeat
- Innocent heart murmurs are those that do not require treatment - normal functioning heart, rapid blood flow
- Abornmal heart murmurs are usually due to valve problems - require treatment
Reasons for abnormal heart murmurs:
- holes in the heart - septal defects
- cardiac shunts - abnormal movement of blood in the chambers (usually congenital)
- valve calcification - hardening & narrowing
- endocarditis - infection in lining of heart from bacteria (can completely destroy valves - usually patients have pre-existing valve conditions)
- rheumatic fever
Risk factors include weakened heart muscles (cardiomyopathy), heart valve disease & high BP (hypotension)/high BP in lungs (pulmonary hypertension
