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B2W2 > Respiratory Tract Histology and Defence Mechanisms > Flashcards

Respiratory Tract Histology and Defence Mechanisms Flashcards

- Describe the respiratory epithelium as found in the trachea and bronchus. - Describe the change in epithelial pattern in the alveoli and relate this to gas exchange. - Describe the micro-anatomy of the wall of the respiratory tract and relate this to function. - Outline the nature of the secretions of the lung.

1
Q

Describe the epithelial lining of the trachea.

A

Girthy ;)

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2
Q

What purpose and features of the nose and oropharnyx make it a useful component of the respiratory system?

A
  • Filters large particles
  • Warms & Humidifies air, prevents epithelium from drying out.
  • Mucosal layer lined with different types of epithelial cells.
  • Respiratory epithelium-based in aqueous viscous & sticky mucus to trap particles.
  • Ciliated epithelium have a coordinated beat-mucocilary escalatory push material towards naso & oropharynx.
  • Irritant particles stimulate irritant receptors and provoke sneezing & couging to remove material.
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3
Q

Describe the histological features of the conducting airways, from the nasal passages to the small bronchi.

A

Pseudostratified with 3 cell types:

  • Ciliated epithelial cells - mucosillary escalatory.
  • Goblet cells (secretory, non-ciliated).
  • Basal cells (act as stem cells, may contribute to structure).
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4
Q

Describe the epithelial histology of the bronchioles.

A
  • Epithelium changes to simple ciliated cuboidal
  • Club (Clara) cells replacing goblet cells.
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5
Q

Briefly describe the componenents of the mucocillary escalator.

A
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6
Q

Which parasympathetic nerve can increase mucus secretion?

A

The vagus nerve (CN X)

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7
Q

What is CN II?

A

The Optic Nerve

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8
Q

Describe the features of the tract wall in different respiratory conducting zones.

A

Trachea & Primary Bronchi: Held open by C-shaped cartilage anterolaterally, smooth muscle (Trachealis) posteriorly.

Trachea: (generally 16-20) rings of cartilage.

Bronchi: cartilage plates, smooth muscle, blood vessels of systemic circulation (bronchial arteries).

Bronchioles: smooth muscle helical bands

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9
Q

Describe the epithelial lining of the trachea

A
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10
Q

Describe the histology of the olfactory epithelium.

A
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11
Q

Describe the histology of the bronchus.

A
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12
Q

Describe the histology of the terminal bronchioles.

A
  • They have no cartilage, glands.

Epithelial in initial portion is ciliated columnar, but then becomes cuboid with cilia.

  • Final portion un-ciliated.
  • Smooth muscle.
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13
Q

Outline the histological nature of the respiratory bronchioles.

A
  • They have a low simple cuboidal epithelium and a thin coat of interlaced smooth muscle and elastic fibres.
  • It has thin evaginations in its wall: 1st respiratory alveoli, where gaseous exchange can take place.
  • Primary alveoli, thin-walled spaces with minimal diffusion distance to pulmonary capillaries.
  • This is where gas exchange occurs.
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14
Q

Give some factual information about Type I pneumocytes.

A
  • 95% of alveolar surface.
  • Highly flattened.

Simple squamous epithelium.

Form occluding junctions with one another.

(Barrier to extracellular fluid into alveolus).

  • Type I cells forms thin diffusion barrier - fused with pulmonary capillary endothelium - the blood-gas interface.
  • Neighbouring alveoli interconnected by Pores of Kohn.
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15
Q

Give some factual information about Type II pneumocytes.

A
  • less numerous; only about 5% of alveolar surface
  • Cuboidal
  • Capable of rapid cell division
  • Dispersed among type I pneumocytes and form occluding junctions with them
  • Produce surfactant - reduces surface tension, prevents alveoli from collapse.
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16
Q

Histologically distinguish between Type I and Type II pneumocytes.

A
17
Q
A
18
Q

Describe the spatial arrangements of Type I and Type II pneumocytes in the alveolar membrane.

A
19
Q

Give some properties of the Type II pneumocyte alveolar cells.

A
  • Type II cells are thicker & produce a fluid layer that lines alveoli.
  • Fluid contains pulmonary surfactant in lamellar bodies.
  • Reduces the surface tension within alveoli
  • Interstitium contains reticular and elastic fibres, allowing for elasticity.
  • Lymphoid cells.

Lamellar Bodies: Secretory organelles found in type II alveolar cells and kertainocytes in the skin.

20
Q

Give an overview of the defence mechanisms in the respiratory tract.

A
  • Warming & humidification of air.
  • Muco-ciliary escalator

Secreted factors for non-specific defence:

  • A number of factors produced by epithelial cells & other cells or derived from plasma.
  • Anti-proteases e.g. a1-antirypsin - inhibits proteases released from bacteria/neutrophils.
  • Lysozyme - has antifungal and bacteriocidal properties.
  • Antimicrobial proteins: Lactoferrin, Peroxidases & Neutrophil-derived Defensins & Cathelicidins.
21
Q

What principal immunglobulin exists within respiratory tract?

A

IgA.

22
Q

Give an example of immune defence mechanisms:

A
  • Leucocytes: neutrophils & lymphocytes present in alveoli.
  • Neutrophils kill bacteria
  • Alveolar macrophages migrate throughout the respiratory tract - phagocytose any particles that get this far.
  • Macrophages act as antigen presenting cells & products presented to T & B lymphocytes.
  • Macrophages secrete Interleukens (ILs), Tumour Necrosis Factor (TNF) & chemokines.
  • ILs & TNF activate immune system.
  • Chemokines attract white cells to site of inflammation.
  • Mast cells secrete heparin, histamine, 5-HT & hydrolytic enzymes involved in allergy & anaphylaxis (IgE).
23
Q

How do Natural Killer (NK) cells confer immunity?

A
  • Present in lungs & lymphoid organs.
  • Contains granules with hydrolytic enzymes.
  • 1st line of defence against viruses.
  • Secrete interferons & TNFs.
  • T & B lymphocytes migrate to lymph nodes, tonsils & adenoids.
  • Diffuse batches of bronchus-associated lymphoid tissue (BALT) in lamina propria.
  • Antigens presented to T-lymphocytes by antigen-presenting cells-cascade of cytokines released & a variety of antibodies produced (Immunoglobulins).
  • Most important are dendritic cells.
  • Specialised mononuclear phagocytes.
  • Act as antigen presenting cells.
24
Q

Give some background info about the cough reflex

A
  • Caused by irritation of respiratory tract by gases, smoke & dust.
  • Receptors throughout the airways between epithelial cells.
  • Rapidly adapting afferent myelinated fibres in vagus.
  • In trachea, leads to cough. Lower airway leads to hyperpnoea.
  • Also causes reflex bronchia & laryngeal constrictions.
  • Characterised by deep inspiration followed by forced expiration with closed glottis.
  • Results in expulsion of irritants from respiratory tract.
25
Q

Explain some stuff about the sneezing reflex.

A
  • Caused by irritation of nasal mucous membrane due to dust particles, debris and excess fluid accumulation.
  • Characterised by deep inspiration followed by forced expiration with open glottis.
  • Results in expulsion of irritant from airways.
  • Irritation of nasal mucous membrane, olfactory receptors and trigeminal nerve endings in nasal mucosa.
  • Afferents from trigeminal and olfactory nerves pass to sneezing centre in medulla.
  • Efferent fibres pass from medulla via trigeminal, facial, glossopharyngeal, vagus and intercostal nerves.
  • Results in activation of pharyngeal, tracheal & respiratory muscles.
26
Q

Briefly describe the process and benefits of the swallowing reflex.

A
  • Initiated by stimuli to dorsum of tongue, soft palate & epiglottis.
  • During swallowing, respiration is inhibited - deglutition.
  • Prevents inhalation of food.
27
Q

Give some facts about the stretch receptors and why they are relevant for respiration.

A
  • Located in the smooth muscle of bronchial walls
  • Slowly adapting
  • Afferents ascend via vagus
  • Stimulation results in inspiration being shorter and shallower
  • These receptors responsible for Hering-Breuer inspiratory reflex.
  • Lung inflation inhibits inspiratory muscle activity.
  • Deflation reflex-augments inspiratory muscle activity.
  • Normal breathing weak reflex, more active during excersise when tidal volume > 1L.
  • In neonates, protects against over-inflation.
28
Q

Explain the significance of the Juxtapulmonary (J) receptors:

A
  • Located on alveolar & bronchial walls close to capillaries.
  • Afferent unmyelinated C-fibers or myelinated nerves in vagus.

Activation causes:

  • Apnoea (cessation of breathing) or rapid shallow breathing
  • HR & BP fall
  • Laryngeal constriction & relaxation of the skeletal muscles.

J receptors activated by:

  • Increased alveolar wall fluid
  • Pulmonary congestion and oedema
  • Microembolisms
  • Inflammatory mediators such as histamine

(Above associated with lung disease).

29
Q
A

B2W2 (3 decks)

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