Host defence in the lung 2 Flashcards
What are the respiratory functions of the lung?
Respiration:
Ventilation and gas exchange: O2, CO2, pH, warming and humidifying
What are the non-respiratory functions of the lung?
Non-respiratory functions:
- Synthesis, activation and inactivation of vasoactive substances, hormones, neuropeptides
- Lung defence: complement activation, leucocyte recruitment, host defence proteins, cytokines and growth factors
- Speech, vomiting, defecation.
What is the lung exposed to daily?
Large numbers of airborne pathogens
- Containing both pathogens and particles
E.g. Covid-19
What does our host defence mainly involve?
Barriers
What is an intrinsic host defence?
It is always present: physical and chemical
Apoptosis, autophagy, RNA silencing, antiviral proteins
What is an innate host defence?
Induced by infection (Interferon, cytokines, macrophages, NK cells)
What is an adaptive immunity defence?
Tailored to a pathogen (T cell, B cells)
- Can involve memory cells
What is the epithelium?
Epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body. Many glands are also formed from epithelial tissue. It lies on top of connective tissue, and the two layers are separated by a basement membrane.
What is a respiratory epithelium?
Respiratory epithelium serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.
What is the epithelium like in the nasal area (head)?
- Respiratory mucosa, with mucous cells and the mucus escalator, lines the nasal cavity and the superior portion of the pharynx
- Cells are attached to basement membrane so pseudostratified
What is the epithelium like in the inferior pharynx area?
- A stratified squamous epithelium lines the inferior portions of the pharynx, protecting the epithelium from abrasion and chemical attack
What is the epithelium like in the lower respiratory tract area?
A typical mucosa lines the conducting portion of the lower respiratory tract (trachea)
What is the epithelium like in the bronchi?
In the finer bronchioles, the epithelium becomes cuboidal
What is the epithelium like in the gas exchange surfaces (alveoli)?
Consist of delicate simple squamous epithelium
What are some examples of multiple cell types in the airway epithelium?
- Basal cell
- Ciliated cell
- Fibroblast
- Goblet cell
etc…
These express multiple cell specific genes to protect the alveoli as they all contribute to the cell lining
What are chemical epithelial barriers?
Multiple molecules separated from the epithelium:
- Antiproteinases (pathogens use protease to invade epithelium so these block this)
- Anti-fungal peptides
- Anti-microbial peptides (proteins impact specifically bacterial pathogens)
- Antiviral proteins
- Opsins
What is the host defence for alveolar epithelium?
- Alveolar type 2 cells: Alveolar type II cells secrete a lipoprotein material called surfactant, whose primary function is to reduce the surface tension in the alveoli.
- Physical barriers (mucus)
- Submucosal glands
What is mucus?
- It is a viscoelastic gel containing water, carbohydrates, proteins and lipids
- It is the secretory product of the mucous cells (goblet cells of the airway surface epithelium and the submucosal glands)
What is mucus protecting?
The epithelium from foreign material and from fluid loss (stops/reduces the evaporation across epithelium)
How is mucus transported?
From the lower respiratory tract into the pharynx by air flow and mucociliary clearance
What is the mucus escalator?
- This is how mucus is cleared
- Cilia beat in directional waves to move mucus up the airways
- coughing and sneezing are significant non-immune defence mechanisms
What is a cough?
- an expulsive reflex that protects the lungs and respiratory passages from foreign bodies
What are the causes of a cough?
- Irritants (Smokes, fumes, dusts etc…)
- Diseased conditions (COPD, tumours etc…)
- Infections (influenza)
How is a cough initiated?
- Can be voluntarily or reflexively
- As a defensive reflex it has both afferent and efferent pathways
What are the afferent and efferent pathways of a cough?
Afferent limb: Includes receptors within the sensory distribution of some nerves e.g. vagus
Efferent limb: Includes the laryngeal nerve and spinal nerves
What is a sneeze?
- Involuntary expulsion of air containing irritants from the nose
What are the causes of a sneeze?
- Irritation of a nasal mucosa
- Excess fluid in airway
What is the pathway of a sneeze?
- Receptor: nerve endings in nose
- Sensory neuron: to the integration centre (sneezing centre in the brain stem)
- Motor neuron: to the effectors (eyes, nose, lungs, diaphragm, chest muscles, parts of the mouth)
How does the epithelium repair after an injury?
- Because it exhibits a level of functional plasticity (change its’ function)
- There is cell migration (cell movement)
- Then cell proliferation (growth of cells)
- Then re-differentiation (return to original form)
- Then re-generation (increase no. of cells)
What happens when epithelium repair goes wrong?
Pulmonary disease
- We can also get abnormal epithelial responses to injury/insult underpin many obstructive lung diseases
An example of goblet cell metaplasia in the airway of a heavy smoker
What is obstructive lung disease?
- Mucus and inflammatory cells blocking the airways
- Can be fatal
