Theme 1: Lecture 1 - The Lungs and Pleura Flashcards
What are the cavities that the thoracic cavity is divided into?
Left pleural cavity - contains left lung
Right pleural cavity - contains right lung
Mediastinum - space between the 2 pleural cavities, contains trachea, heart, oesophagus, blood vessels and nerves
From which germ layer does the lung bud develop?
Endoderm
Pericardioperitoneal canal
The space between the parietal and visceral pleura that develops into the pleural cavity
How do the lungs and pleura develop?
- The respiratory system begins to develop at 4-6 weeks from the endoderm layer
- Endodermal out pouches form lung buds and bronchial buds
- Rapid division of the airways occurs
- Hence the lungs push their way out into the primitive thoracic cavity. As they do they take the lining (visceral pleura) with them.
Visceral pleura
- Closely adheres to the lungs including the fissures
- Creates a smooth and slippery surface
- Connects to the parietal pleura at the hilum (root of lung)
Parietal pleura
Lines the internal aspect of the thoracic wall
What are the parts that the parietal pleura are divided into?
- Costal (internal rib cage - outer edge)
- Mediastinal (lateral wall of mediastinum - inner edge)
- Diaphragmatic (superior diaphragm -bottom edge)
- Cervical (cervical region - top edge)
Pleural cavity
-Space between the two layers of pleura
-Contains a thin layer of serous fluid
-Surface tension of the serous fluid holds lungs against thoracic wall
Lungs expand as thoracic cavity expands
Pneumothorax
Air in the pleural cavity causing lung to collapse due to loss of surface tension between pleural layers
Haemothorax
Blood in the pleural cavity, can cause surface tension between the pleural layers to be lost
Pleural cavity recesses
- Areas where the visceral and parietal pleura aren’t touching
- These recesses can be occupied by the lung but only during forced inspiration
- They aren’t symmetrical because of the heart
Costomediastinal recess
Found on the left hand side due to the heart sitting over to the left creating the cardiac notch
Costodiaphragmatic recess
Area behind the dome of the diaphragm that the parietal pleural enters into, but no lung tissue enters into
What is the parietal pleura innervation?
Cervical - 1st intercostal nerve
Costal - intercostal nerves
Mediastinal - phrenic nerve
Diaphragmatic - lower intercostals and phrenic nerves
What is the visceral pleura innervation?
Autonomic (sympathetic and parasympathetic) from pulmonary plexus
Features of the left lung
- 2 lobes
- Oblique fissure
- Impression for the heart (the cardiac notch)
- Lingua
Features of the right lung
- 3 lobes
- Horizontal and oblique fissues
What are the lobes of the left lung?
Superior and inferior
What are the lobes of the right lung?
Superior, middle and inferior
What are the surfaces of the lung?
Costal, mediastinal and diaphragmatic
What are the borders of the lung?
Anterior (thinner), posterior (thicker) and inferior
Hilum/Root of lungs
The area where everything that needs to travel to and from the lung passes into and out of the lung, it’s also the place where the viscera and parietal pleura meet
Pulmonary ligament
Formed from parietal pleura and hangs inferiorly from the hilum of the lung. It allows the hilum to move up and down with lung movement
What is the organisation of vessels in the hilum?
-Bronchi most posterior
-Arteries most superior
-Veins most inferior
(generally)
Which arteries supply the lung and visceral pleura?
Bronchial arteries
Where do the left bronchial arteries come from?
Branch from the descending aorta
Where do the right bronchial arteries come from?
Branch from the intercostal arteries (the intercostal arteries have branched from the descending aorta and travelled in the intercostal groove)
Where do the bronchial veins terminate?
The azygos system of veins
What is the innervation of the lungs?
It comes from the ANS like all viscera
Sympathetic from the sympathetic trunk:
- Bronchial musculature dilates
- Pulmonary vasculature constricts
Parasympathetic from vagus:
- Bronchial musculature constricts
- Pulmonary vasculature dilates
Through where does lymph drain?
Lymph drains towards the hilum via Bronchopulmonary (Hilar) nodes then Tracheobronchial nodes and then Paratracheal nodes
Trachea
- Flexible tube, distal to larynx
- Runs from C6 to T4/5
- Anteriorly has C-shaped cartilage rings
- Posteriorly has trachealis muscle
- Bifurcates at level of sternal angle
- Lined by mucus membrane and cilia
Carina
The piece of cartilage that separates the two main bronchi where the trachea bifurcates
Primary bronchi
- One for each lung
- Passing through lung at hilum
- Right main bronchus is wider, shorter and runs more vertically
- Contains cartilage
Secondary (lobar) bronchi
Supply one lung each, therefore there’s 3 in the right and 2 in the left
Tertiary bronchi
Each supplies a bronchopulmonary segment
Bronchopulmonary segments
There’s usually 10 in the right and 8-10 in the left
Each segment is:
- Supplied by a single tertiary bronchus
- Receives a single branch of the pulmonary artery
- Separated by connective tissue
- Surgically resectable (removable in isolation)
Bronchioles
- 20-25 generations of conducting bronchioles
- No cartilage in walls
- Terminal bronchioles gives rise to several generations of respiratory bronchioles
- Respiratory bronchioles characterized by by out pockets of alveoli
Alveoli
Alveolar ducts are elongated airways lined by alveoli which leads to common places called alveolar sacs. Each alveolus is surrounded by capillaries
What are the alveoli cell types?
- Type 1 pneumocytes (95%)
- Type 2 pneumocytes (5%), these secrete pulmonary surfactant
What is the purpose of pulmonary surfactant?
There is a thin film of fluid present in the alveoli, this could cause the alveoli to collapse due to the surface tension from that fluid. The pulmonary surfactant prevents the surface tension from collapsing the alveoli.
