Diaphragm, mechanism of breathing and surface anatomy Flashcards
what is the diaphragm
Musculotendinous dome that separates the thoracic cavity from the abdominal cavity
Pale blue position centrally which represents the tendinous part
Muscular fibres peripherally
what are the anterior attachments of the diaphragm
Anteriorly attachment to the xiphisternum and costal cartilages of ribs
why is the right hemidiaphragm higher than the left
due to the position of the liver
wha lies between the two crura
Median arcuate ligament which attaches to L1
what are crura and where are they
Posteriorly two crura which are musculotendinous slips arise from the diaphragm.
where is the right crus
attach to bodies and intervertebral disks of L1-L3
where is the left crus
attach to bodies and
intervertebral disks of L1-2
Lateral accurate ligament
attaches to rib 12
Caval opening
at level of T8
allows the passage of the IVC and the right phrenic nerve
Aortic Hiatus
at the level of T12
allows the passage of the descending aorta, the thoracic duct and the azygous
Oesophageal opening
at the level of T10
allows the passage of the oesophagus and the posterior and anterior vagal trunks
The IVC
pierces the tendinous part of the diaphragm. As the diaphragm moves it helps ‘push’ blood to return to the heart.
The oesophagus
The oesophagus passes through a muscular slip in the diaphragm. (this does not form a true sphincter hence the risk of reflux of gastric acid from the stomach causing ‘heartburn’)
the aorta
lies behind the diaphragm with the right and left crus either side (the thoracic duct is also visible passing through at T12 )
The phrenic nerves
C3,4,5) provide motor and sensory innervation to the central portion of diaphragm (also sensation to fibrous and parietal pericardium and mediastinal pleura)
pass between the venous and arterial planes in the superior mediastinum then descend ANTERIOR to the lung root
Right phrenic nerve
passes through the diaphragm with the IVC
The left phrenic nerve
pierces the diaphragm but does not pass through it
Peripherally the diaphragm has sensory innervation from the
intercostal and subcostal nerves
the internal thoracic arteries
run in the thoracic cavity on either side of the sternum. The internal thoracic arteries are branches of the 2nd part of the subclavian arteries.
Two inferior phrenic arteries
are direct branches of the abdominal aorta and supply the diaphragm inferiorly
The thoracic aorta
gives off superior phrenic arteries
The internal thoracic arteries
give off a pericardiophrenic artery which supplies the diaphragm.
They also give off
musculophrenic arteries
Referred pain
Inflammation of the gallbladder (cholecystitis) may irritate the central tendon of the diaphragm. This area has sensory innervation from the phrenic nerve (C3,4,5) so visceral pain can be referred to the right shoulder which is the dermatome of C4
During expiration the diaphragm
is raised therefore reducing the volume of the thoracic cavity
During inspiration the diaphragm
flattens. This increases the volume in the thoracic cavity
Boyle’s law states
that the pressure exerted by a gas is inversely proportional to the volume it occupies. By increasing volume in the thoracic cavity the pressure is reduced relative to atmospheric pressure so air flows into the lungs
Damage to the phrenic
As the volume of the thoracic cavity increases during inspiration the pressure in the abdominal cavity increases and causes the right hemidiaphragm to elevate.
Damage may occur following cardiac surgery or due to invasion of the phrenic nerve by a lung tumour
therefore the right hemi diaphragm is raised
external intercostal muscles
pass infero-medially in the intercostal space (replaced by aponeurosis anteriorly)
ibres of the external intercostal muscles passing infero-medially. When these fibres contract both the ribs and sternum will be elevated.
raise the ribs and sternum. This increases the antero- posterior diameter if the
thoracic cavity. (the movement of the sternum is referred to as pump handle movement
Contraction of external intercostal muscles raise the ribs and increase the lateral diameter of the thoracic cavity. (the movement of the ribs is likened to the
movement up and down of a bucket handle)
What muscles are involved in quiet respiration?
inspiration:
Diaphragm – main muscle of respiration. Descends and flattens
External intercostal muscles – elevate ribs
expiration:
Relaxation of diaphragm and external intercostals provide elastic recoil.
What muscles are involved in forced respiration?
inspiration:
Diaphragm – can descend up to 10cm
External intercostal muscles
Accessory muscles of respiration i.e.
trapezius, scalenes and sternocleidomastoid help elevate the upper portion of the rib cage
Nasalis – flares the nostrils to increase volume of inspired air
expiration:
Relaxation of diaphragm and external intercostal muscles.
Internal intercostal muscles – contract to help reduce intra-thoracic volume
Muscles of abdominal wall – contraction increases intraabdominal pressure and therefore intrathoracic pressure
Accessory muscles of respiration
Trapezius, scalenus anterior and sternocleidomastoid
Visceral pleura
lines the lungs
Parietal pleura
lines the rib cage
Role of the pleura
1) Reduce friction to
allow movement of lungs
2) Intrapleural pressure - negative relative to atmospheric pressure to prevent collapse of lungs
the costodiaphragmatic
recess (also called the costophrenic recess) two layers of parietal pleura oppose each other creating a potential space
Horizontal fissure
starting at the costal cartilage of rib 4 anteriorly and ending by meeting the oblique fissure.
Oblique fissures
can be drawn from T4 vertebrae posteriorly to rib 6 anteriorly
Pneumothorax definition and risk factors
air in the thorax Between the visceral and parietal layers of pleura causing compression of the lung tissue - tall - male - smoker - underlying lung disease COPD/asthma
Dyspnoea
Pleuritic chest pain
Haemothorax
blood between the visceral and parietal layers of pleura
Chylothorax
chyle (lymph) between the visceral and parietal layers of pleura
what is a tension pneumothorax
MEDICAL EMERGENCY
Air gets trapped between the parietal and visceral pleura however due to a valve like effect air can enter the pleural space but can not leave! There is increasingly positive intrapleural pressure
- Trachea and mediastinum is shifted away from the side of the pneumothorax due to increasingly positive intrapleural pressure
- Due to this increased intrapleural pressure venous return to the heart is impaired and hypotension can develop. This can lead to cardiac arrest
how do you decompress a tension pneumothorax
Insert a cannula on the side of the pneumothorax, 2nd intercostal space midclavicular line.
chest drain
• Large pneumothorax • Tension pneumothorax • Haemothorax – often traumatic • Large pleural effusion Aims to enable removal of fluid/air from intrapleural space.
what makes up the safe triangle
- base of the axilla
- lateral edge of lat dorsi
- lateral edge of pec major
- 5th intercostal space
why is the safe triangle not exactly safe
- False passage
- Damage to long thoracic nerve
- Haemothorax due to damage to intercostal arteries • Liver/spleen injury
