Host Defence In The Lung 2 Flashcards
Function of the lungs
Respiration
Non-respiratory function
Respiration
Ventilation and gas exchange: O2, CO2, pH, warming and humidifying
Non- respiratory function
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.
Airborne pathogens
The lung is exposed to a large number of airborne pathogens as the result of the daily inhalation of >10,000 litres of air.
This contains both pathogens and particulates
Why are respiratory infections so comparatively rare?
because of mechanisms of host defence
Host defence mostly involves barriers
Host defences
Intrinsic: Always present: Physical and chemical. Apoptosis, autophagy, RNA silencing, antiviral proteins
Innate defence: Induced by infection (Interferon, cytokines, macrophages, NK cells
Adaptive immunity: Tailored to a pathogen (T cell, B cells)
Host defence functions throughout the respiratory tract (and involves the 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.
The airway epithelium is different in distinct regions – reflecting functions –
Slide 18
The airway epithelium in distinct regions contain multiple cell types and these express multiple cell specific genes
Slide 19 and 20
Multiple molecules secreted from the epithelium play a role in host defence.
These are chemical epithelial barriers:
antiproteinases
anti-fungal peptides
anti-microbial peptides
Antiviral proteins
Opsins
Produced by most (all?) epithelial cells
The alveolar epithelium is specialised for gas exchange but also has a host defence function
Host defence in the respiratory tract relies on more than epithelial cell products - physical barriers (mucus) and products of the submucosal glands are important
Mucus
Airway mucus is a viscoelastic gel containing water, carbohydrates, proteins, and lipids.
It is the secretory product of the mucous cells (the goblet cells of the airway surface epithelium and the submucosal glands).
Mucus protects the epithelium from foreign material and from fluid loss
Mucus is transported from the lower respiratory tract into the pharynx by air flow and mucociliary clearance.
Mucus clearance occurs via the escalator
Cilia beat in directional waves to move the mucus up the airways
Coughing and sneezing
are significant non-immune defence mechanisms
What is a cough
Cough is an expulsive reflex that protects the lungs and respiratory passages from foreign bodies
Causes of cough
-irritants- smokes, fumes, dust
-Diseased conditions like COPD, tumours etc
-infections (influenza)
What causes a cough?
Initiated either voluntarily or by reflex
As a defensive reflex it has both affront and efferent pathways
What is a sneeze?
Sneeze is defined as the involuntary explosion of air containing irritants from nose
Cause of sneeze
-Irritant of nasal mucosa
-excess fluid in airway
Following an insult/injury the airway epithelium can in (many cases) effect a complete repair
This is because it exhibits a level of functional plasticity
Plasticity exists in multiple cells
This is beneficial
When the process goes wrong we get pulmonary disease
Abnormal epithelial responses to injury/insult underpin many obstructive lung diseases
Mucus plugs/inflammation is associated with severe disease
Mucus and inflammatory cells blocking the airways. Hence the term obstructive lung disease is sometimes used
Mucus plugs can completely obstruct the airways and can be fatal
Summary
The respiratory tract is made of a number of distinct epithelial compartments containing unique cells
Many of these epithelial cells directly contribute to the non-immune host defence functions of the lung
They provide a physical and chemical barrier to prevent infection
They exhibit a remarkable ability to repair
Aberrant repair and re-organisation underpins many lung diseases
