Session 2 - The lungs and the mediastina Flashcards
Describe the surface structure of the lungs
○ An apex ○ Three surfaces: a costal surface, a diaphragmatic surface and a mediastinal surface ○ Three borders § Anterior, inferior, posterior ○ A base ○ Lobes § Two (left lung) or three (right lung) § Created by one or two fissures
What is the oblique fissure in the right lung?
• Separates the right upper and middle lobes from the lower lobe of the right lung
What is the oblique fissure in the left lung?
Separates the upper and lower lobes
What is the horizontal fissure in the right lung?
• Separates the right upper and middle lobes
What extends into the fissures of the lungs?
The visceral pleura
What do the lungs receive nervous supply from?
• The vagi and sympathetic trunk via the pulmonary plexuses, situated in the hilum
What enters the lung through the hilum
- Pulmonary arteries and veins
- Bronchial arteries and veins
- Nerves
- Lymphatics
What is the hilum of the lung?
A wedge shaped area on the mediastinal surface of each lung through which structures forming the roots of the lung pass to enter or exit
What do the roots of the lung consist of?
- Bronchi
- Pulmonary arteries
- Superior and inferior pulmonary veins
- Pulmonary plexus of nerves
- Lymphatics
What is the mediastinum?
• The central compartment of the thoracic cavity
What is the mediastinum covered by?
• Mediastinal plueura
Where does the mediastinum extend to and from?
- Superior thoracic arpeture to the diaphragm
* Sternum and costal cartilages anteriorly to the bodies of the thoracic vertebrae posteriorly
What two sections is the mediastinum divided into?
• Superior and inferior parts
Where does the superior mediastinum extend to and from?
• Superior thoracic aperture to the transverse thoracic plane
What is the transverse thoracic plane?
• Horizontal plane that includes the sternal angle anteriorly and passes approximately through the junction of T4 and T5 posteriorly
Where does the inferior mediastinum extend to and from?
• Transverse thoracic plane to the diaphragm
• Further subdivided by the pericardium
○ Anterior
○ Middle
Posterior
Give one structure which lies in more than one compartment of the mediastinum
Oesophagus
Where do the pulmonary arteries carry mixed venous blood?
• From the right ventricle for gas exchange at the alveoli
What does the main pulmonary artery divide into?
The right and left pulmonary arteries
What structure do the pulmonary arteries divide with?
The bronchial tree
What do the pulmonary arteries supply?
• The alveoli only
Are there any anastamoses between bronchial and pulmonary arteries?
Yes, at pre capillary and capillary level
How does the path of the pulmonary veins differ from that of the pulmonary arteries?
- Do not follow divisions of bronchi
* Tend to run into intersegmental septa
How many pulmonary veins leave each hilum?
• Two
What is the name of the two lymphatic plexi that drain the lungs?
• Subpleural lymphatic plexus
Deep bronchopulmonary lymphatic plexus
What is the diaphragm?
A dome shaped muscle which divides the thoracic cavity from the abdominal cavity.
Why is the large size of the diaphragm clinically important, as pertaining to the position of other organs?
- Means kidneys, liver, spleen, parts of the stomach and upper kidneys lie in the abdominal cavity and are covered by the ribs
- Lower chest injuries significant
Outline the structure of the diaphragm
• A peripheral muscular part and a central tendon
What is the peripheral muscular part of the diaphragm made up of?
- The crura tendons which arise from L1-L3
* Arcuate ligaments, which are thickening of the fascia
What are the three parts of the diaphragm?
- Vertebral arising from the crura and acruate ligaments
- Costal part arising from inner aspects of 7-12 costal cartilage
Sternal part arising from deep surface of xiphissternum
What happens if you have cervical spinal damage from C2 downwards
• Severs link to phrenic nerve (C3, C4, C5), so lose function of the diaphgragm
What is the phrenic nerve sensory for?
- Both surfaces of diaphragm
- Medialstinal part of the pleura
- Diaphragmatic part of the parietal pleura
What are the three parts of the thoracic cavity?
• Two lateral pulmonary cavities and one central compartment - the mediastinum
What compartments is the mediastinum divided up into?
- Superior
- Middle
- Posterior
Inferior
What is the purpose of the parietal pleura?
• Secretes fluid, which sticks it to the visceral pleura
This means everything moves at once
What proportion of chest expansion is done by the diaphragm?
70%
What proportion of chest expansion is governed by the chest wall?
30%
What does inspiration involve?
• Elevation of external intercostal muscles
What does inspiration result in?
- Increase in transverse diameter of thoracic cavity
- In the A=P diameter of thoracic cavity
- Increase in vertical dimension
What occurs in expiration?
• In quiet respiration it simply relaxes elastic of chest wall and lungs
In forced expiration, internal and innermost intercostal muscle and abdominal muscle are used
What muscles are used in quiet inhalation?
- Diaphragm
* External intercostals
What muscles does forced inhalation involve? (6)
• Diaphragm • External Intercostals • Scalene • Pectoralis Minor • Sternocleidomastoid Serratus Anterior
What muscles does forced exhalation involve?
- Internal intercostals
- Innermost intercostals
- Abdominal muscles
