Diaphragm, Mechanisms of Breathing Flashcards
What are the structures piercing the diaphragm?
Need IVC, oesophagus and aorta to pass through diaphragm.
IVC: T8
- IVC opens through the right side of the central tendon. àIf diaphragm contracts, it pulls on the outer surface of this and therefore pulls on the IVC.
=Pressure gradient created bw the thorax and the abdomen when the diaphragm moves down and at the same time opens up the bounderies of the IVC to allow for increased venous return.
Oesophagus: T10
- Oesophagus occurs to the left of the midline.
=Boundaries of the opening formed by the extension of the right crus
=When the diaphragm contracts, right crus will contract and will pull on the sling it provides around the oesophagus, closing the oesophagus slightly.
==Abdominal contents want to go up through the thorax and regurgitate with increased pressure when breathing it, therefore acts as functional sphincter. If contracting diaphragm, its opening will close off and act as a functional sphincter to prevent regurgitation.
Aorta: T12
- Aorta is furthest out to the periphery, since the periphery is the lowest part of the diaphragm it must be the lowest so occurs at T12.
Describe the diaphragm and where it is situated?
- Muscular sheath that bridges in between the abdominal cavity and thoracic cavity
- Sheath is curved down towards the periphery
- Two domes: right and left
=Very top of the domes sit in the middle of the diaphragm called the central tendon which is aponeurotic (not muscular)
=Muscular fibres attach to the central tendon- therefore when it contracts it pulls on the central tendon to depress the diaphgram. =Heart sits above a lot of the left dome and therefore pushes it slightly down.
=Abdominal viscera below right lobe, pushing it up.
=If you are in supine position, diaphragm will be pushed up further into the thorax by abdo viscera than if you are standing. - Parietal pleura also lines diaphragm and therefore movements of the diaphragm are important in moving lungs around.
What is the median arcuate ligament and lateral arcuate ligament, and describe the differences?
Median arcuate ligament:
- Arches over the descending aorta which sits directly anterior to the vertebral bodies.
- Median arch is directly over the midline and wraps over the aotra as it descends of the thorax into the abdomen.
- Diaphragm muscle attaches via tendinous attachment which arches over the psoas major (more medial) posteriorly.
=Median arcuate ligament also as connective tissue over posterior abdominal wall muscles.
Where is the right phrenic nerve, azygous vein, sympathetic trunk, in relation to the diaphragm?
Right phrenic nerve pierces the central tendon on the right side and left phrenic nerve is just outside the central tendon on the left
Azygous vein:
- Appear on the lateral aspect of the crura.
Sympathetic Trunk:
- Runs lateral to the crura in relation to the medial arcuate ligament.
- Can also see splanchnic nerves coming from the sympathetic trunk and taking nerves to the abdomen
Explain the motor and sensory nerve supply of diaphragm?
Motor and sensory nerve supply of diaphragm:
- Most of it is running in the phrenic nerve
- Takes origin from the ventral horn of the cervical spinal segments C3,4,5 “keeps the diaphragm alive”
- Sensory neurons running back up towards of spinal cord only to central part of diaphragm.
Discuss the mechanisms of breathing, in terms of pressure and volume as well.
- If atmospheric pressure is equal to the pressure in the lungs, then there is no movement of air since no pressure gradient to move along.
- Movement of air into or out of the lungs is passive- moves along pressure gradients created by manipulating thoracic walls and diaphragm.
- Change dimensions of the throacic cavity either through thoracic walls or diaphragm to change pressure gradient.
- Volume and pressure are inversely related.
Inspiration - If we want to breath in, we must decrease pressure in the lungs relative to the atmosphere by increasing lung volume.
- The vertical dimension (height) of the central part of the thoracic cavity increases during inspiration as contraction of the diaphragm causes it to descend, compressing the abdominal viscera
Expiration - Pressure builds up in the lungs relative to the atmosphere by collapsing thoracic cavity and squeezing in on lungs.
- During passive expiration, the diaphragm, intercostal muscles, and other muscles relax, decreasing intrathoracic volume and increasing the intrathoracic pressure. Concurrently, intra-abdominal pressure decreases and abdominal viscera are decompressed. This allows the stretched elastic tissue of the lungs to recoil, expelling most of the air.
- During expiration, the vertical dimension returns to the neutral position as the elastic recoil of the lungs produces sub-atmospheric pressure in the pleural cavities, between the lungs and the thoracic wall. As a result of this and the absence of resistance to the previously compressed viscera, the domes of the diaphragm ascend, diminishing the vertical dimension.
How do expand and collapse our lungs to change the pressure within?
- Lungs are going to move whichever direction the thoracic wall and diaphragm move due to firm attachment provided by the pleura. - Parietal pleura lining the thoracic cavity- reflecting at the hilum of the lungs onto the visceral pleura lining the lungs themselves, creating a pleural cavity between the two with serous fluid generating surface tension.
àThis surface tension allows for the lungs to move with movements of the thoracic wall. - Thus if we want to expand our lungs, can expand thoracic wall or lower diaphragm to pull on the attached parietal pleura which will pull on the visceral pleura due to surface tension- which will, in turn, pull on the lungs.
What happens to diaphragm during inspiration and expiration?
Inspiration:
- Diaphragm lowers, increasing the volume of thoracic cavity (blue)
= Pulls down on the lungs therefore increasing the volume of the lungs therefore decreasing the pressure in lungs, allowing air to move in (inspiration)
Expiration:
- When diaphragm relaxes, lungs will tend to recoil if there is nothing pulling on them.
The rhythmic contractions of the diaphragm is controlled by ……?
Controlled by:
[Respiratory centre of brainstem.]
- Via the phrenic nerve
- Main determinant of quiet breathing
What are the movements of the thoracic cage?
Thoracic cage is narrower at the top than it is lower- means that when you elevate some of the ribs, they will pull on the thoracic cavity in different ways due to their different structure/ orientation.
- The AP dimension of the thorax increases considerably when the intercostal muscles contract.
Pump Handle:
- When you elevate the upper ribs, you elevate the sternum.
=Movement of the ribs (primarily 2nd–6th) at the costovertebral joints around an axis passing through the necks of the ribs causes the anterior ends of the ribs to rise—the pump-handle movement.
- Upper ribs move sternum forwards
=Because the ribs slope inferiorly, their elevation also results in anterior–posterior movement of the sternum, especially its inferior end
Bucket handle:
- If you elevate lower libs, tend to move the ribs outward, increasing the transverse diameter of the thoracic cavity.
- The transverse dimension of the thorax also increases slightly when the intercostal muscles contract, raising the middle (lateral-most parts) of the ribs (especially the lower ones)—the bucket-handle movement.
=The combination of all these movements moves the thoracic cage anteriorly, superiorly, and laterally
=Both movements increasing volume of thoracic cavity and decrease pressure in lungs
What are the accessory respiratory muscles?
- Recruited in addition to the diaphragm. Scalene muscle:
- Attachments to the upper ribs therefore elevate upper ribs
- Good for quick respiratory movements e.g. sniffing
External intercostals: - Expand thoracic cavity.
Internal intercostals : - Collapsing thoracic cavity
- Do the opposite to external intercostals since they run perpendicular
Abdominal muscles: - Good for collapsing the lungs in forced expiration
- Increasing pressure in abdominal cavity via contraction of abdominal muscles allows forced expiration
What are hiccups?
• Quick inspirations • Spasmodic contractions of diaphragm • Irritation of: o Neurons in the phrenic nerve o The diaphragm muscle itself o The respiratory centres in the brainstem
