73 - Respiratory Histology Flashcards by Jack Cuthbertson

Effect of tubinate bones

Increase surface area of nasopharynx

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Location of epiglottis

Where larynx and oesophagus diverge

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Structure immediately below epiglottis

Larynx

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Function of the larynx

Phonation

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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

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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%)

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Function of ciliated columnar cells

Move mucus. Move mucus upwards through the airways into the oesophagus. Mucociliary elevator.

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Function of basal (stem) cells

In the base of the epithelium, renew the epithelium

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Function of brush cells

Not clear. Maybe sensory

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Function of serous cells

Unknown

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Function of small endocrine cells

Endocrine

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Aetiology of smoker’s cough

Smoking kills airway cilia, which can no longer operate mucociliary elevator. Coughing is only way to clear airways.

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Trachea dimensions

12cm long, 2cm diameter

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Trachea structure

10 - 12 rings of hyaline cartilage. C-shaped cartilage, opening backwards, bounded by smooth muscle.

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Layers of trachea

Mucosa, submucosa, adventitia

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Why does the trachea need to be stiff?

To resist the negative pressure that can arise in the conducting airways

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Function of trachea smooth muscle

Can alter the diameter of the trachea

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C= C-shaped cartilage M = Mucosa S = Submucosa A = Adventitia

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Parts of the tracheal mucosa

Respiratory epithelium and lamina propria

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Which part of the trachea are the cartilage rings considered to be?

Adventitia?

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What does the trachea split into?

Two primary, extrapulmonary bronchi in the thorax

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What do primary bronchi split into?

Each split into five branches (three right, two left)

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Number of branches of the airways

~23

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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

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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.