Diaphragm, mechanism of breathing and surface anatomy

Question 1

what is the diaphragm

Answer 1

Musculotendinous dome that separates the thoracic cavity from the abdominal cavity
Pale blue position centrally which represents the tendinous part
Muscular fibres peripherally

Question 2

what are the anterior attachments of the diaphragm

Answer 2

Anteriorly attachment to the xiphisternum and costal cartilages of ribs

Question 3

why is the right hemidiaphragm higher than the left

Answer 3

due to the position of the liver

Question 4

wha lies between the two crura

Answer 4

Median arcuate ligament which attaches to L1

Question 5

what are crura and where are they

Answer 5

Posteriorly two crura which are musculotendinous slips arise from the diaphragm.

Question 6

where is the right crus

Answer 6

attach to bodies and intervertebral disks of L1-L3

Question 7

where is the left crus

Answer 7

attach to bodies and

intervertebral disks of L1-2

Question 8

Lateral accurate ligament

Answer 8

attaches to rib 12

Question 9

Caval opening

Answer 9

at level of T8

allows the passage of the IVC and the right phrenic nerve

Question 10

Aortic Hiatus

Answer 10

at the level of T12

allows the passage of the descending aorta, the thoracic duct and the azygous

Question 11

Oesophageal opening

Answer 11

at the level of T10

allows the passage of the oesophagus and the posterior and anterior vagal trunks

Question 12

The IVC

Answer 12

pierces the tendinous part of the diaphragm. As the diaphragm moves it helps ‘push’ blood to return to the heart.

Question 13

The oesophagus

Answer 13

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’)

Question 14

the aorta

Answer 14

lies behind the diaphragm with the right and left crus either side (the thoracic duct is also visible passing through at T12 )

Question 15

The phrenic nerves

Answer 15

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

Question 16

Right phrenic nerve

Answer 16

passes through the diaphragm with the IVC

Question 17

The left phrenic nerve

Answer 17

pierces the diaphragm but does not pass through it

Question 18

Peripherally the diaphragm has sensory innervation from the

Answer 18

intercostal and subcostal nerves

Question 19

the internal thoracic arteries

Answer 19

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.

Question 20

Two inferior phrenic arteries

Answer 20

are direct branches of the abdominal aorta and supply the diaphragm inferiorly

Question 21

The thoracic aorta

Answer 21

gives off superior phrenic arteries

Question 22

The internal thoracic arteries

Answer 22

give off a pericardiophrenic artery which supplies the diaphragm.
They also give off
musculophrenic arteries

Question 23

Referred pain

Answer 23

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

Question 24

During expiration the diaphragm

Answer 24

is raised therefore reducing the volume of the thoracic cavity

Question 25

During inspiration the diaphragm

Answer 25

flattens. This increases the volume in the thoracic cavity

Question 26

Boyle’s law states

Answer 26

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

Question 27

Damage to the phrenic

Answer 27

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

Question 28

external intercostal muscles

Answer 28

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)

Question 29

What muscles are involved in quiet respiration?

Answer 29

inspiration: Diaphragm – main muscle of respiration. Descends and flattens External intercostal muscles – elevate ribs expiration: Relaxation of diaphragm and external intercostals provide elastic recoil.

Question 30

What muscles are involved in forced respiration?

Answer 30

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

Question 31

Accessory muscles of respiration

Answer 31

Trapezius, scalenus anterior and sternocleidomastoid

Question 32

Visceral pleura

Answer 32

lines the lungs

Question 33

Parietal pleura

Answer 33

lines the rib cage

Question 34

Role of the pleura

Answer 34

1) Reduce friction to allow movement of lungs 2) Intrapleural pressure - negative relative to atmospheric pressure to prevent collapse of lungs

Question 35

the costodiaphragmatic

Answer 35

recess (also called the costophrenic recess) two layers of parietal pleura oppose each other creating a potential space

Question 36

Horizontal fissure

Answer 36

starting at the costal cartilage of rib 4 anteriorly and ending by meeting the oblique fissure.

Question 37

Oblique fissures

Answer 37

can be drawn from T4 vertebrae posteriorly to rib 6 anteriorly

Question 38

Pneumothorax definition and risk factors

Answer 38

``` 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

Question 39

Haemothorax

Answer 39

blood between the visceral and parietal layers of pleura

Question 40

Chylothorax

Answer 40

chyle (lymph) between the visceral and parietal layers of pleura

Question 41

what is a tension pneumothorax

Answer 41

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

Question 42

how do you decompress a tension pneumothorax

Answer 42

Insert a cannula on the side of the pneumothorax, 2nd intercostal space midclavicular line.

Question 43

chest drain

Answer 43

``` • Large pneumothorax • Tension pneumothorax • Haemothorax – often traumatic • Large pleural effusion Aims to enable removal of fluid/air from intrapleural space. ```

Question 44

what makes up the safe triangle

Answer 44

- base of the axilla - lateral edge of lat dorsi - lateral edge of pec major - 5th intercostal space

Question 45

why is the safe triangle not exactly safe

Answer 45

* False passage * Damage to long thoracic nerve * Haemothorax due to damage to intercostal arteries • Liver/spleen injury