Anatomy Flashcards
Where does the sternum lie?
Anteriorly in the midline of the thoraic cage
3 parts the sternum is composed of
The Manubrium
The body
the xiphoid process
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’).
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
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.
How many ribs form the anterior, lateral, and posterior walls of the thoraic cage
12
What are the anterior parts of the ribs made of?
costal cartilage
Where do the ribs articulate with their costal cartilage?
at costochondral joints.
● The costal cartilages of ribs 1 - 7 articulate directly with the sternum at sternocostal joints – they are ‘true’ ribs.
● The costal cartilages of ribs 8 - 10 unite and join the seventh costal cartilage –they are ‘false’ ribs.
What forms the costal margin, which is palpable?
The costal cartilages of ribs 7-10
Ribs 11 and 12
are short and do not articulate with the sternum – they are
‘floating’ ribs
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.
Typical ribs
look similar and share common anatomical features
Ribs 3 - 9 are typical ribs. They have a head, neck, tubercle, and body (shaft).
Atypical ribs
look different to typical ribs and / or lack some of the features of typical 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.
The 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.
What forms the superior thoracic aperture?
The manubrium, the first ribs and the first thoracic vertebra form the boundary of the superior thoracic aperture
What is the role of the superior thoracic aperture
The ‘passageway’ through which structures pass between the neck and the thorax
Dermatome
an area of skin innervated by a single spinal nerve.
Each pair of thoracic spinal nerves supplies a ‘strip’ around the chest wall
Axillary tail
The part of the breast where Breast tissue extends towards the anterior axilla (armpit)
Contents of the breast
● 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
What branches is the breast primarily supllied by?
● internal thoracic artery (which arises from the subclavian artery)
● axillary artery
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 does blood return?
Venous blood returns to the axillary and internal thoracic veins.
Somatic nerves and sympathetic fibres
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.
There are 5 groups of lymph nodes in the axilla:
central
pectoral
humeral
subscapular
apical
Role of the nodes
● 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.
Intercostal muscles lie in the intercostal spaces between the ribs. Within each intercostal space, there are three layers of muscles:
● the external intercostal is most superficial
● the internal intercostal lies deep to the external intercostal
● the innermost intercostal lies deep to the internal intercostal.
Functions of intercostal muscles
Collectively they move the ribs and alter the dimensions of the thoracic cavity with inspiration (breathing in) and expiration (breathing out).
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.
Pectoralis minor
is a smaller muscle that lies deep to pectoralis major. It attaches to the scapula (shoulder blade) and ribs 3-5.
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.
Role of these muscles
The prime function of these muscles is to move the upper limb (pectoralis major adducts the humerus; pectoralis minor and serratus anterior protract the scapula).
However, they can also function as accessory muscles of breathing because they attach to the ribs and hence can move the ribs if the humerus and scapula are fixed.
In patients, use of these muscles is a sign of respiratory distress.
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.
External intercostal is most superficial. Its fibres are orientated antero-inferiorly (down and inwards)
● Contraction of external intercostal muscles 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.
Internal intercostal lies deep to the external intercostal. Its fibres run perpendicular to those of the external intercostal, running in a postero-inferior direction (back and below)
● 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.
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.
The endothoracic fascia lies deep to the innermost intercostal and superficial to the parietal pleura, which surrounds the lung.
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
Location of the intercostal neurovascular bundle
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.
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
intercostal veins
Anterior intercostal veins drain into the internal thoracic vein
Posterior intercostal veins drain into the azygos system of veins
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.
Function of the two layers of membranes- 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
The two layers of pleura are continuous with each othe
What lies between the parietal and visceral pleura
A very thin pleural cavity (or space)
Role of pleura and pleural fluid
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.
The parts of the parietal pleura are named according to the structures they lie adjacent to.
● 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.
The costodiaphragmatic recess
is a ‘gutter’ around the periphery of the diaphragm, where the costal pleura becomes continuous with the diaphragmatic pleura.
smaller costomediastinal
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.
The two pleural layers are innervated by different nerves
hence we perceive painful sensations from the parietal and visceral pleura differently
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.
The visceral pleura is innervated by autonomic sensory nerves
Sensation from visceral afferents usually does not reach our conscious perception.
What is the most superior part of the lung?
Apex which projects into the root of the neck, above the clavicle.
The base of the lung ‘sits’ on the diaphragm.
Each lung is formed of lobes- the right lung has 3 lobes
a superior (upper), middle, and inferior (lower) lobe.
The left lung has 2 lobes
a superior and inferior lobe.
An anterior extension of the superior lobe – the lingula (Latin for ‘small tongue’) – extends over the heart.
Function of fissures
Seperate the lobes. Both lungs have an oblique fissure.
Role of oblique fissure In the left lung,
it separates the superior and inferior lobes.
Role of oblique fissure In the right lung,
it separates the superior and middle lobes from the inferior lobe
Role of HORIZONTAL fissure in RIGHT lung
It separates the superior lobe from the middle lobe.
The lungs are described in terms of surfaces
● Costal surface - adjacent to the ribs
● Mediastinal surface - adjacent to the heart
● Diaphragmatic surface - the inferior surface of the lung
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.
The lungs are described in terms of borders.
● Anterior border - sharp and tapered
● Posterior border – thick and rounded
● Inferior border - sharp and tapered
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.
The hilum of the lung
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.
● At the hilum of the right lung, the main bronchus lies anterior to the pulmonary artery
● At the hilum of the left lung, the main bronchus lies inferior to the pulmonary artery
At both the right and left hila, the two pulmonary veins are usually the most anterior and inferior vessels
The trachea bifurcates into the left and right main bronchi at the level of the sternal angle (T4/T5)
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.
The bronchial tree
is the branching system of tubes that conduct air into and out of the lungs.
Each main bronchus divides into lobar bronchi;
three in the right lung and two in the left lung (i.e. one lobar bronchus for each lobe).
Each lobar bronchus divides to give rise to segmental bronchi.
There are ten segmental bronchi in each lung
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.
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
The walls of the trachea and bronchi contain smooth muscle and cartilage, but the walls of bronchioles only contain smooth muscle.
Contraction and relaxation of the smooth muscle is under autonomic control.
The pulmonary arteries carry deoxygenated blood to the lungs
Bronchial arteries from the descending aorta also supply the lungs
The pulmonary veins return oxygenated blood to the heart from the lungs.
Bronchial veins return blood to the azygos system of veins
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.
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.
somatic sensory fibres carried in the intercostal nerves innervate the parietal pleura
Lymph from the lungs ultimately drains into the venous system via…
the thoracic duct or right lymphatic duct.
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.
Surface Anatomy of the Lungs and Pleura
The apex of each lung projects into the lower neck, just superior to the medial end of the clavicle.
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)
The parietal pleura extends to the:
• 8th rib anteriorly (midclavicular line)
• 10th rib laterally (midaxillary line)
• 12th rib posteriorly (at the vertebral column)
Fissures of the left and right 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.
What is the diaphragm?
a broad, thin, domed sheet of skeletal muscle.
Role of The Diaphragm
● 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)
Attachments and Movements of The Diaphragm
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 tendon
The central part of the diaphragm is not muscular, but fibrous
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.
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.
Breathing mechanics:
● 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.
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
The pleurae and pleural fluid are integral to 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
Role of surface tension
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 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
ventilation may become dysfunctional.
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.
In expiration:
● The diaphragm and external intercostal muscles relax, and the internal intercostals contract, 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.
Muscles Involved in Breathing
● In normal, quiet breathing…
inspiration is active and is mainly driven by movement
of the diaphragm, but expiration is passive.
Muscles Involved in Breathing
● In vigorous breathing (e.g. exercise)
the intercostal muscles become important.
Active expiration uses the internal intercostal muscles
Muscles Involved in Breathing
● 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.
Mediastinum
part of the thoracic cavity that lies between the lungs
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.
The mediastinum contains
● 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
the mediastinum is divided into a superior and inferior compartment
The ‘line’ between these compartments runs from the sternal angle anteriorly to the T4/T5 junction posteriorly
The inferior mediastinum is further divided into
anterior, middle, and posterior compartments
Anterior
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.
Middle
The middle mediastinum contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta
Posterior
The posterior mediastinum lies between the posterior aspect of the pericardial sac and the vertebrae
The main contents of the superior mediastinum are the:
● 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
The aorta leaves the left ventricle and carries oxygenated blood to the systemic circulation.
There are three ‘parts’ in the thorax:
The ascending aorta
The arch
The descending (thoraic) aorta
The ascending aorta
is the short, first part.
It gives rise to the coronary arteries, which supply the myocardium
Found in the middle mediastinum
The arch
The arch of the aorta curves posteriorly.
It lies in the superior mediastinum.
The descending (thoracic) aorta
descends through the posterior mediastinum
and into the abdomen posterior to the diaphragm.
The arch of the aorta in the superior mediastinum gives rise to three major branches that supply the upper body
● First, the brachiocephalic trunk. It bifurcates into the right common carotid artery which supplies the right side of the head and neck, including the brain, and the right subclavian artery which supplies the right upper limb
● Second, the left common carotid artery, which supplies the left side of the head, neck, and brain
● Third, the left subclavian artery, which supplies the left upper limb
The arch of the aorta contains the aortic bodies where chemoreceptors are located.
These receptors constantly monitor arterial oxygen and carbon dioxide.
This visceral sensory information travels back to the CNS along the path of the vagus nerve and results in reflex responses that regulate ventilation
Ligamentum arteriosum
The ligamentum arteriosum is a fibrous, cord-like connection between the pulmonary trunk and the arch of the aorta
It is the remnant of the ductus arteriosus, a foetal circulatory shunt. In the foetus, gas exchange occurs at the placenta, not in the lungs
The ductus arteriosus
The ductus arteriosus diverts most of the blood entering the pulmonary trunk directly to the aortic arch (only a small amount of blood circulates through the foetal lungs; enough for them to develop).
When a baby starts to use their lungs at birth, the ductus arteriosus closes, and blood in the pulmonary trunk enters the lungs.
