Anatomy
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Thorax
You are preparing an anatomy teaching session on the diaphragm. The thoracic duct passes through the diaphragm together with which of the following structures:
Answer:
The aortic opening in the diaphragm is at vertebral level T12 and transmits the aorta, the thoracic duct and the azygos vein.The diaphragm is a musculotendinous structure that separates the thoracic cavity from the abdominal cavity.
Table: Anatomical Overview of the Diaphragm
| Structure | Diaphragm |
|---|---|
| Primary function | Respiration – contraction of diaphragm flattens diaphragm increasing vertical dimension of thorax (inspiration), relaxation of diaphragm elevates diaphragm decreasing vertical dimension of thorax (expiration) |
| Secondary functions | Assists in straining movements by increasing intra-abdominal pressure, acts as functional sphincter on oesophagus preventing acid reflux |
| Peripheral attachments | Xiphoid process of sternum, costal cartilages ribs 7 – 10, ends of ribs 11 and 12, arcuate ligaments and lumbar vertebrae |
| Central attachment | Fuses with fibrous pericardium superiorly |
| Surface markings | Anterior attachment: vertebral level T8/T9, Posterior attachment: vertebral level T12, Right dome: 5th rib, Left dome: 5th intercostal space, Central tendon: xiphoid process |
| Openings | Oesophageal opening at T10 (oesophagus, vagus nerve), aortic opening at T12 (aorta, thoracic duct and azygos vein), caval opening at T8 (inferior vena cava and right phrenic nerve) |
| Innervation | Phrenic nerve (C3 – C5) |
Function
The diaphragm performs an important function in respiration; contraction of the domes of the diaphragm in inspiration flattens the diaphragm, increasing the vertical dimension of the thorax and vice versa in expiration, with relaxation and elevation of the diaphragm reducing the vertical dimension of the thorax.
The diaphragm is also involved in non-respiratory functions; helping to expel vomit, faeces, and urine from the body by increasing intra-abdominal pressure, and preventing acid reflux by exerting pressure on the oesophagus as it passes through the oesophageal opening.
Attachments
The diaphragm is attached peripherally to:
- the xiphoid process of the sternum and the costal cartilages of ribs 7 - 10 (the costal margin) anteriorly
- the ends of ribs 11 and 12 laterally
- the arcuate ligaments and vertebrae posteriorly.
From these peripheral attachments, muscle fibres converge to form the central tendon which fuses with the fibrous pericardium superiorly.
Diaphragm. (Image by OpenStax [CC BY 4.0 , via Wikimedia Commons)
Diaphragmatic openings
Structures travelling between the thorax and abdomen must pass through the diaphragm via three main openings.
The oesophageal opening at vertebral level T10 transmits:
- the oesophagus
- the anterior and posterior vagal trunks
- oesophageal branches of the left gastric vessels
- a few lymphatics.
The aortic opening at vertebral level T12 transmits:
- the aorta
- the thoracic duct
- the azygos vein and sometimes the hemiazygos vein.
The caval opening at vertebral level T8 transmits:
- the inferior vena cava
- the right phrenic nerve.
Surface markings
In the medial sagittal plane, the diaphragm slopes inferiorly from its anterior attachment to the xiphoid at approximately vertebral level T8/T9 to its posterior attachment to the median arcuate ligament at approximately vertebral level T12.
At rest the right dome of the diaphragm lies slightly higher than the left; this is thought to be due to the position of the liver. In normal expiration, the normal upper limits of the superior margins are the fifth rib for the right dome, the fifth intercostal space for the left dome and the xiphoid process for the central tendon.
Innervation
The entire motor supply of the diaphragm is from the right and left phrenic nerves (C3 - C5) which penetrate the diaphragm and innervate it from its abdominal surface.
Paralysis of the Diaphragm
Diaphragmatic paralysis is due to an interruption in its nervous supply. This can occur in the phrenic nerve, cervical spinal cord, or the brainstem. It is most often due to a lesion of the phrenic nerve:
- Mechanical trauma: ligation or damage to the nerve during surgery.
- Compression: due to a tumour within the chest cavity.
- Myopathies: such as myasthenia gravis.
- Neuropathies: such diabetic neuropathy.
Paralysis of the diaphragm produces a paradoxical movement. The affected side of the diaphragm moves upwards during inspiration (as it is pushed superiorly by the abdominal viscera that are being actively compressed by the other half), and downwards during expiration.
A unilateral diaphragmatic paralysis is usually asymptomatic and is most often an incidental finding on x-ray. If both sides are paralysed, the patient may experience poor exercise tolerance, orthopnoea and fatigue. Lung function tests will show a restrictive deficit.
Management of diaphragmatic paralysis is two-fold. Firstly, the underlying cause must be identified and treated. The second part of treatment deals with symptomatic relief. This is usually via non-invasive ventilation, such as a CPAP (continuous positive airway pressure) machine.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
