Anatomy
Thorax
Regarding the lung roots, which of the following statements is CORRECT:
Answer:
Each lung root contains a pulmonary artery, two pulmonary veins, a main bronchus, bronchial vessels, nerves and lymphatics. Generally the pulmonary artery is superior in the lung root, the pulmonary veins are inferior and the bronchi are somewhat posterior in position. The vagus nerves pass posterior to the lung roots while the phrenic nerves pass anterior to them.Lung
Anatomy / Thorax / Pleura and Lungs
Last Updated: 30th March 2020
The lungs lie on either side of the mediastinum, each surrounded by a pleural cavity. They are suspended from the mediastinum by the root of the lung, a short tubular collection of structures.
Lung roots
The root is lined by a layer of mediastinal pleura that reflects onto the surface of the lungs as visceral pleura. The region outlined by this pleural reflection on the medial surface of the lung is the hilum, where structures enter and leave.
The hila are located at the level of the 3rd - 4th costal cartilage anteriorly, and the T5 - T7 vertebrae posteriorly.
Each lung root contains:
- a pulmonary artery
- two pulmonary veins
- a main bronchus
- bronchial vessels,
- nerves and
- lymphatics.
Generally the pulmonary artery is superior in the lung root, the pulmonary veins are inferior and the bronchi are somewhat posterior in position.
In the mediastinum, the vagus nerves pass immediately posteriorly to the lung roots, while the phrenic nerves pass immediately anterior to them.
On the right side, the lobar bronchus to the superior lobe branches from the main bronchus in the root, whereas on the left, it branches within the lung itself.
![Modified by FRCEM Success. Original by Gray, Henry, 1825-1861; Carter, H. V. (Henry Vandyke), 1831-1897; Pick, T. Pickering (Thomas Pickering), 1841-1919 [No restrictions], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2017/02/Root-of-lung.jpg)
Root of the Lung. (Image modified by FRCEM Success. Original by Gray, Henry, 1825-1861; Carter, H. V. (Henry Vandyke), 1831-1897; Pick, T. Pickering (Thomas Pickering), 1841-1919 [No restrictions], via Wikimedia Commons)
Relations
The medial surface of the right lung lies adjacent to:
- the heart
- the inferior vena cava
- the superior vena cava
- the azygos vein
- the oesophagus
The medial surface of the left lung lies adjacent to:
- the heart
- the aortic arch
- the thoracic aorta
- the oesophagus.
The right and left subclavian arteries and veins arch over and are related to the superior lobe of the right and left lung as they pass over the dome of the cervical pleura and into the axilla.
![Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/02/Lung.png)
Relations of the Lungs. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Blood supply
The right and left pulmonary arteries originate from the pulmonary trunk (at the vertebral level T4/T5) and carry deoxygenated blood to the lungs.
On each side a superior and inferior pulmonary vein carries oxygenated blood from the lungs back to the heart.
The bronchi (down to the terminal bronchioles), lung roots, visceral pleura and supporting lung tissues receive their nutrient blood supply from the bronchial arteries, which arise from the descending aorta.
Lymphatics
The parenchyma of the lungs as well as the visceral pleura are drained by a vast plexus of tiny lymph vessels which drain lymph from these areas towards the hilum of the lung. All lobes of the lungs first drain into the intrapulmonary nodes, located around the bifurcations of the branching lobar bronchi, then onto the bronchopulmonary nodes, located at the hilum of the lungs. From here, they drain first into the inferior and then the superior tracheobronchial nodes, located inferior and superior to the tracheal bifurcation respectively. Then they drain onto the paratracheal nodes, running superiorly on either side of the trachea, and finally into the right and left bronchomediastinal lymph trunks, located medially to the superior portion of the azygos vein and anterior to the vertebral bodies of the spinal column.
Knowledge of the lymphatics of the lung is very important in both the staging and treatment of lung cancer. As lung cancer spreads and metastasises from its primary tumor, it often does so via the lymphatic system and usually proceeds in a sequential order. Hypothetically, the sentinel lymph node is the first lymph node or group of lymph nodes draining a cancer, and is also the first place where cancer cells are most likely to spread. With other pathologies of the lung, the bronchopulmonary nodes are those which most frequently become enlarged. On radiography of the chest, this may be indicated as a classical hilar lymphadenopathy which may be caused by inflammation, cancer or carcinoma or infection such as tuberculosis.
Innervation
The nerve supply to the lungs is from the anterior and posterior pulmonary plexus (networks of nerves derived from the sympathetic trunk and vagus nerve).
The parasympathetic nerve supply, carried by the vagus nerve, stimulates secretion from the bronchial glands, contraction of bronchial smooth muscle, and vasodilation of the pulmonary vessels. The vagus nerve also carries afferent fibres of pain, cough reflex and stretch of the lung (during inspiration).
The sympathetic nerve supply stimulates relaxation of bronchial smooth muscle, and vasoconstriction of the pulmonary vessels.
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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 |
