Week 8 Flashcards
The diaphragm:
- Change from periphery to central area?
- Motor and sensory supply?
- During inspiration what happens?
- Is muscular at its periphery and tendinous centrally
- Motor and sensory supply from the phrenic nerve (C2,4,5)
- During inspiration the domes descend, causing negative intrathoracic pressure but raising intra-abdominal pressure
Attachments of the diaphragm?
Anterior: To xiphoid process opposite T8/9
Deep surface of ribs and costal cartilages 7-12
(The costodiaphragmatic recess is the narrow, potential space between the periphery of the diaphragm and the ribs)
Posteriorly 5 ligaments (2 crura, 3 arcuate):
- Muscular crura (Left crus from bodies of L1 and 2, right crus from bodies of L1,2 and 3)
- Median arcuate ligment at T12, between the crurua
- Medial arcuate ligament between body and transverse process tip of L1
- Lateral arcuate ligament between tip of L1 transverse process to 12th rib.
Structures passing through the diaphragm
T8: IVC, Right phrenic nerve
T10: Oesophagus, R+L vagus nerves, left gastric vessels
T12: Aorta, thoracic duct, azygos veins
How do the following structures pass through the diaphragm:
- Splanchnic nerves?
- Sympathetic trunk?
- Subcostal vessels and nerves?
- Splanchnic nerves: Through the crura
- Sympathetic trunk: Behind medial arcuate ligament
- Subcostal vessels and nerve: Behind lateral arcuate ligament
Where does the phrenic nerve receive sensory innervation from?
Central tendon, parietal pleura and pericardium
Arteries alongside the phrenic nerve?
Superior and inferior phrenic
What mechanisms are involved in inspiration and exhalation?
Inspiration:
- Increases diameters of the thorax to create a negative pressure (which sucks are into the lungs)
- Diaphragmatic contraction causes the descent of its dome to increase vertical diameter
- Rib elevation pushes the sternum up and forward, and the ribs outward, to increase anterioposterior and lateral diameters
Exhalation (i.e. normal, quiet expiration):
- Muscle relaxation
- Elastic recoil (in lungs and bronchi elastic tissue)
How does contraction of diaphragm assist in quiet inspiration?
- Contraction of the diaphragm
- Contraction flattens the domes of the diaphragm
- Increases the vertical thoracic diameter
- Increases the volume of the thorax
- Decreases intrathoracic pressure
- Air is drawn into the lungs
- Most important inspiratory activity in adult
How does contract of intercostal muscles assist in quiet inspiration?
- Contraction of intercostal muscles
- As the shaft of the rib passes obliquely downwards, contraction of the intercostal muscles to raise the shaft of the rib towards the one above also lifts the sternum and pushes it anteriorly
- Increases the anteroposterior diameter and the thoracic volume
- Decreases intrathoracic pressure
- Air is drawn into the lungs
ALSO
- Raises the ribs 5-10 towards the one above and lifts the CC and pushes the rib laterally
- Lateral splay by ribs with oblique CC only
- Increases the lateral diameter and the thoracic volume
- Decreases intrathoracic pressure
- Air is drawn into the lungs
Describe the “bucket-handle” mechanism that occurs in forced inspiration?
- Occurs in ribs 8-10 that have flat costo-transverse joints that permit gliding
- Once the central tendon of the diaphragm is “anchored” by its attachment to the pericardium, further muscle contraction pulls on the ribs and causes them to evert
- Gives a small, additional increase in the lateral thoracic diameter and therefore the volume
- Even more air is drawn into the lungs by this additional decrease in intrathoracic pressure
Role of accessory muscles of respiration in forced inspiration and expiration?
Add more power of contraction but CANNOT further increase the thoracic diameters
Muscles involved:
- Pectoralis major and minor (inspiration)
- Latissimus dorsi (possibly helps compress ribs in forced expiration, but more superior parts may help raise ribs in forced inspiration)
- Abdominal wall muscles (raise intra-abdominal pressure to push diaphragm up in forced expiration)
- Neck and back muscles (trapezius, sternocleidomastoid, scalene muscles) help to fix the ribs
What is the involvement of intercostal muscles in inspiration and expiration?
External intercostal is more active during inspiration
Internal intercostal is more active during expiration
What is mesothelium?
Simple squamous epithelium that secretes a miniscule amount of serous fluid to lubricate the surfaces of viscera
Parietal pleura is attached firmly to ??
- Thorax wall (costal pleura)
- The fascia at the thoracic inlet (cervical pleura)
- Fibrous pericardium (mediastinal pleura)
- Diaphragm (diaphragmatic pleura)
Pleural cavities surface markings of reflections: Rib, 2cms above clavicle? 2nd CC ? 4th LCC? 6th CC: 8th rib? 10th rib? 12th rib? Midline?
Rise to level of neck of 1st rib, 2cms above clavicle 2nd CC -Lie adjacent in the mid line 4th LCC- notch for heart 6th CC- Deviates laterally 8th rib- Lies in midclavicular line 10th rib- lies in mid axillary line 12th rib- Lies in the mid scapular line Midline - Level with T12 (just below 12th rib)
What are the two pleural recesses?
Costodiaphragmatic recess: Potential space inferiorly around the periphery of the diaphragm
Costomediastinal recess: Anteriorly where pleura wrap around the mediastinum. Larger on left
Recesses= Sites of fluid accumulation
What is the difference between the surface markings of the lungs and the pleura?
Pleura:
8th rib- Lies in midclavicular line
10th rib- lies in mid axillary line
12th rib- Lies in the mid scapular line
Lungs:
6th rib: Lies in midclavicular line
8th rib- lies in mid axillary line
10 th rib- Lies in the mid scapular line and mid line
[i.e. lungs are two spaces higher than pleura]
What are the surface markings of the oblique fissure (R+L lung)?
Spine of T4, down across the 5th rib, follows line of the 6th rib around the thorax
What are the surface markings of the horizontal fissure (R lung only)?
4th CC, horizontally back across 5th rib. Meets oblique fissure in the mid-axillary line
Function of the pleural membrane
Surface tension between the parietal and visceral pleura “pulls” the visceral layer (and lung) with the movements of the thorax wall
Elastic recoil of the lung tissue means that lungs are tending to deflate
The surface tension creates a slight negative pressure that maintains the lung in slight inflation even at the end of expiration
Result of pneumothorax
If air enters the pleural cavity the surface tension and negative tension are lost
–> Lung collapse
If severe, the affected side shows:
- No thoracic movement
- Elevated hemi diaphragm
- Shift of mediastinum to affected side
What is the result of fracture of ribs or sternum during inspiration?
That whole segment would float freely, i.e. a flail segment or flail chest, and on inspiration the segment would be sucked inwards, instead of lifting upwards: paradoxical respiration
Describe the cephalo-caudal and lateral folding of the trilaminar disc?
Starts towards the end of 3rd week
Head and tail folds to meet 2 lateral folds at umbilicus
Creates endodermal tube of pharynx and oesophagus; septum transversum between thorax and abdomen
What is the significance of the intra-embryonic body cavity?
Formed between the somatic and splanchnic mesoderm
Will contribute to the pericardial, pleural and peritoneal cavities.
The cavities are continuous via the pericardio-peritoneal canals until the diaphragm forms.