73 - Respiratory Histology Flashcards
Effect of tubinate bones
Increase surface area of nasopharynx
Location of epiglottis
Where larynx and oesophagus diverge
Structure immediately below epiglottis
Larynx
Function of the larynx
Phonation
Cells lining airways 1 2 3 4
1) Pseudostratified epithelium. 2) Ciliated cells. 3) Secretory cells (goblet cells, specialised glands) 4) Sensory cells to initiate coughing to expel irritants
Cells in this slide
1) Ciliated columnar cells (30%) 2) Goblet cells (30%) 3) Basal (stem) cells (30%) 4) Serous cells (3%) 5) Brush cells with microvili (3%) 6) Small granule cells (3%)
Function of ciliated columnar cells
Move mucus. Move mucus upwards through the airways into the oesophagus. Mucociliary elevator.
Function of basal (stem) cells
In the base of the epithelium, renew the epithelium
Function of brush cells
Not clear. Maybe sensory
Function of serous cells
Unknown
Function of small endocrine cells
Endocrine
Aetiology of smoker’s cough
Smoking kills airway cilia, which can no longer operate mucociliary elevator. Coughing is only way to clear airways.
Trachea dimensions
12cm long, 2cm diameter
Trachea structure
10 - 12 rings of hyaline cartilage. C-shaped cartilage, opening backwards, bounded by smooth muscle.
Layers of trachea
Mucosa, submucosa, adventitia
Why does the trachea need to be stiff?
To resist the negative pressure that can arise in the conducting airways
Function of trachea smooth muscle
Can alter the diameter of the trachea
C= C-shaped cartilage M = Mucosa S = Submucosa A = Adventitia
Parts of the tracheal mucosa
Respiratory epithelium and lamina propria
Which part of the trachea are the cartilage rings considered to be?
Adventitia?
What does the trachea split into?
Two primary, extrapulmonary bronchi in the thorax
What do primary bronchi split into?
Each split into five branches (three right, two left)
Number of branches of the airways
~23
Structure of a bronchus 1 2 3 4 5
1) Initially like trachea, but with thinner walls 2) Cartilage ring becomes cartilage plates in intrapulmonary bronchi. 3) Smooth muscle is at boundary between the lamina propria and submucosa. 4) Glands present 5) Lymphoid nodules present
C = Cartilage plate reinforcing wall G = Glands S = Smooth muscle (G and S arranged circumferentially, parts of the submucosa)
Difference between bronchi and bronchioles
Bronchioles have lost cartilage
DIameter of bronchioles
About 1mm in diameter
Branches of respiratory system that are bronchioles
10th - 15th dichotomous branch
Cells lining bronchioles
Respiratory epithelium,
What keeps bronchioles open?
Radial connective tissue
Can bronchioles dilate and constrict?
Yes. Have smooth muscle
Do ciliated cells or goblet cells extend further down airways?
Ciliated cells (need ciliated cells to be able to sweep out mucus secreted by goblet cells, so goblet cells can’t be where there are no ciliated cells)
Clara cells 1 2 3 4 5
1) Columnar to cuboidal cells with short microvili 2) Secrete surfactant 3) Granules contain a glycoprotein 4) Might also neutralise toxins 5) More common in deeper bronchioles
Function of surfactant
Breaks surface tension of fluid lining airways, which would otherwise collapse airways.
Why are premature babies put into humidicribs?
Because they don’t produce surfactant yet, so need to keep their airways form collapsing
Final part of conducting system
Terminal bronchioles
Aspects of terminal bronchioles 1 2 3 4
1) No goblet cells 2) Clara cells 3) Cuboidal epithelium with some cilia 4) One or two layers of smooth muscle
What do terminal bronchioles give rise to
Respiratory bronchioles
Difference between terminal bronchioles and respiratory bronchioles
Terminal bronchioles don’t exchange gasses. Respiratory bronchioles have bronchiAlveolioles
What do respiratory bronchioles give rise to?
Alveolar ducts (chains of linked alveoli)
How do respiratory bronchioles appear on a hist slide?
Have occasional outpockets (alveoli)
Number of alveoli in most lungs
~300 million
Gas exchange surface in normal, adult lungs
140m^2 exchange surface
Structure of an alveolus 1 2 3 4
1) Around 200 uM across 2) Lined with mainly simple squamous epithelium 3) Wall contains many pulmonary (respiratory) capillaries) 4) Individual alveoli connected by pores
What keeps alveoli from collapsing?
Interalveolar septa.
Interalveolar septa
Between alveoli. Contain reticular fibres and elastin fibres Pores allow air to equilibrate Elastin fibres prevent alveolar collapse
Illustration of how thin pulmonary epithelium is
Thin enough to see RBCs through walls
Type I pneumocyte role
Form simple squamous epithelium in alveoli
Type I pneumocytes
Provide majority of surface area of bronchi (95%) Tight junctions prevent ECF leakage Basal lamina is prominent
Type II pneumocytes
More numerous than type I, but only 5% of surface area. Cuboidal calls Short microvilli and lamellar bodies Lamellar bodies contain surfactant, which is secreted
Lamellar bodies
In type II pneumocytes Contain, secrete surfactant
Relative frequency of type I and II pneumocytes
TII are more common, but only make up 5% of surface area, whereas TI make up 95% of surface area
How are pneumocytes replaced?
Type II pneumocytes can divide, give rise to TI and TII
Blood-gas barrier role
Exchange of air takes place across the TI pneumocyte wall, and the endothelium of the capillary
Blood-gas barrier structure 1 2 3 4 5 5 6 7
1) Mucus and surfactant on alveolar side 2) Type I pneumocyte 3) Basal lamina of T1 pneumocyte 4) Connective tissue 5) Basal lamina of epithelial cell 6) Endothelial cell 7) Plasma
Aspect of thinnest blood-gas barriers
Fused basal laminae, no connective tissue between T1 and endothelial cells
Intra-alveolar macrophages
Phagocytose any debris that enter alveoli
Why do alveoli need alveolar macrophages to remove debris?
No cilia to remove debris
What happens to alveolar macrophages towards then end of their lives?
When full, migrate up the airways until they are carried off by ciliated cells. Some end up in alveolar septa.
Name for outer surface of pleura
Mesothelium
Pleura lining lung
Visceral pleura
Pleura lining thoracic cavity
Parietal pleura
Cell structure of pleura
Squamous epithelium Supported by basal lamina and fibrous connective tissue
Visceral pleura structure 1 2 3
1) Connective tissue contains blood vessels and lymphatics. 2) Some lymphatics drain to pleural space 3) Microvilli on surface of mesothelial epithelium trap hyaluronic acid (for lubrication)
How do the lungs drain fluid?
Some lymphatics drain to the pleural space (open on the surface of the visceral pleura)
Pathological consequences of some lymph draining to pleural space.
Metastasising cancers can travel thorough lymph vessels to the pleural space.
