host defence in the lung : non immune mechanisms Flashcards
what are the functions of the lung
- respiration
- non respiratory functions
describe respiration
ventilation and gas exchange :
oxygen, carbon dioxide , pH, warming and humidifying
what are the non respiratory functions of the lung
- 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
how much air do we inhale in a day
more than 10,000 litres
this means the lung is exposed to a large number of airborne pathogens which contains pathogens and particulates
why are respiratory infections so comparatively rare
because of mechanisms of host defence
3 types of host defences
intrinsic
innate defence
adaptive immunity
what is intrinsic host defences
they are always present
physical and chemical
eg apoptosis, autophagy, RNA silencing, antiviral proteins
what is innate defence
induced by infection
( interferon, cytokines, macrophages, NK cells)
define adaptive immunity
a type of immunity that develops when a person’s immune system responds to a foreign substance or microorganism, such as after an infection or vaccination
where are host defences mechanisms
throughout the respiratory tract and involves the epithelium
what is epithelium
a tissue compose 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 respiratory epithelium
serves to moisten and protect the airways
also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator
how to classify epithelium
on the basis of:
- number of layers -simple or stratified
- cell shape - squamous, cuboidal, columnar
describe epithelium in nasal cavity and superior portion of pharynx
a respiratory mucosa, with mucous cells and the mucus escalator lines it
describe epithelium in inferior portions of pharynx
stratified squamous
protects epithelium from abrasion and chemical attack
describe epithelium in the conducting portion of the lower respiratory tract
a typical respiratory mucosa lines it
describe epithelium in the finer bronchioles
it becomes cuboidal
describe epithelium on gas exchange surfaces
consists of a delicate simple squamous epithelium
here the distance between the air and the blood in adjacent capillaries is less than 1 um
do airway epithelium in different regions have the same cell types
no they contain multiple cell types that express multiple cell-specific genges
what are chemical epithelial barriers
molecules secreted from the epithelium cells that play a role in host defence
give 5 examples of chemical epithelial barriers
- antiproteinases
- anti-fungal peptides
- anti-microbial peptides
- antiviral proteins
- opsins
does the alveolar epithelium have a host defence function
yes
even though it is specialised for gas exchange it is also involved in host defence
what are the physical barriers in the respiratory tract
- mucus
- products of the submucosal glands
what is airway mucus
a viscoelastic gel containing water, carbohydrates, proteins and lipids
what secretes airway mucus
mucous cells - the goblet cells of the airway surface epithelium and the submucosal glands
what does mucus do
protects the epithelium from foreign material and fluid loss
has antiseptic peptides and works passively to prevent bacterial adhesion. The viscous nature of mucous traps bacteria,, which can then be actively cleared by the mucociliary escalator
how is mucus transported from the lower respiratory tract into the pharynx
by air flow and mucociliary clearance
describe the mucociliary escalator
mucus clearance occurs via the mucociliary escalator
bronchial cilia cells form the escalator
cilia beat in directional waves to move the mucus up the airways
allows the gradual removal of pathogens from the respiratory system
what makes the epithelial strong
it is held together by tight junctions, making it robust enough to impede deeper pathogen access
what is a cough
an expulsive reflex that protects the lungs and respiratory passages from foreign bodies
3 causes of cough
- irritants - smokes, fumes, dusts etc
- diseased conditions eg COPD, tumours
- infections eg ifluenza
what are the 2 ways coughing is initiated
voluntarily or reflexively
what are the cough pathways as a defensive reflex
afferent and efferent pathwats
what does the afferent limb include
receptors within the sensory distribution of the trigeminal, glossopharyngeal, superior laryngeal and vagus nerves
what does the efferent limb include
the recurrent laryngeal nerve and spinal nerves
what is a sneeze
the involuntary expulsion of air containing irritants from nose
2 causes of sneezing
- irritation of nasal mucosa
- excess fluid in airway
sensory pathway of a sneeze
receptor - nerve endings in nose
sensory neurone
integration centre - sneezing centre in brain stem
motor neurone
effectors - eyes, nose, lungs, diaphragm, chest muscles and parts of the mouth
why does airway epithelium exhibit a level of functional plasticity
following an insult/injury the airway epithelium can effect a complete repair
this is good
what hapens when complete repair goes wrong
you get pulmonary disease
what is a cause of many obstructive lung diseases
abnormal epithelial responses to injury/insult
what causes mucus plugs/ inflammation
mucus and inflammatory cells blocking the airways
can be fatal
