Resp 5 - airways structure and function Flashcards
How do the airways divide into smaller airways?
Dichotomous branching
Describe the arrangement of cartilage rings in the airways.
They are slightly offset - gives them greater tensile strength to hold the airways open
Where are submucosal glands found and what are their functions?
The lower part of the submucosal glands are embedded in the smooth muscle
They secrete mucus
When smooth muscle cell contracts it squeezes the gland - they work in tandem
Describe the secretion of mucus by goblet cells.
Mucin granules accumulate at the cell surface, fuse with it.
A little pore forms allowing water to move in.
This causes rapid expansion of the (initially) very concentrated mucin - the pore opens more and the mucus pops out
Describe the structure of submucosal gland.
Submucosal glands have functional units (acini)
The acini are either SEROUS or MUCOUS
The serous acini are found peripheral to the mucous acini
Serous acini produce WATERY secretions (containing antibacterials like lysozyme and ions)
Mucous acini produce MUCOUS
The serous secretions wash over the mucous secretions into the collecting duct
Describe the structure of a cilium.
They have specifically arranged microtubules with 9 pairs of microtubules around the outside and 2 individual microtubules on the inside (9+2 formation)
There are apical hooks that interact with the mucus
There are roughly 200 cilia per cell
What is the pattern of beating of cilia?
Metachronal rhythm
State some of the regulatory and inflammatory mediators produced by airway epithelial cells.
NO, CO, Prostaglandins, cytokines, chemokines
In which cells of the airway do you find a high concentration of Nitric Oxide Synthase?
Epithelial cells so a lot of NO gets produced in epithelial cells
Could be used to control beating of cilia
What inflammatory mediators can be produced by smooth muscle cells?
NO, Prostaglandins, cytokines, chemokines
In response to cytokines (ie. inflammation) NOS can be upregulated
Chemokines lead to the recruitment of inflammatory cells
How does blood return to the heart from the tracheal circulation?
Systemic veins
How does blood return to the heart from the bronchial circulation?
Pulmonary veins AND systemic veins
What is the function of the tracheo-bronchial circulation?
Provides perfusion to the lung tissue
Also involved in WARMING and HUMIDIFYING inspired air
Massive input and output
Explain the process of plasma exudation in the airways.
Plasma exudation usually takes place at the POST-CAPILLARY VENULES (tissues bathed in plasma)
Post-capillary venules have endothelial cells that will contract - when they do so, they pull away a bit from each other - plasma can leak out
Histamines, PAF and other mediators can activate the sensory nerves supplying these cells and cause plasma exudation.
What effect does platelet activating factor (PAF) have on exudation?
Causes contraction of the endothelial cells leading to exudation
What are the most important motor pathways in the airways?
Cholinergic
Describe the organisation of airways
first layer is ciliated cells + goblet cells
then smooth muscle surrounding this with submucosal glands embedded
then cartilage
In what disease is plasma exudation exaggerated?
Asthma
Describe the cholinergic reflex.
It is used to make bronchoconstriction. Sensory nerves detects signal to constrict, this goes to brainstem then parasympathetic (cholinergic) motor pathway activated (both vagus nerves), gets to parasympathetic ganglion and this will cause constriction. –> contracts smooth muscle cells (in response to acetylcholine)
What causes bronchodilation in humans?
Unlike other animals, humans do not have sympathetic pathway which will dilate the airways. Humans rely on adrenaline from the adrenal gland. It relaxes the airway.
We also have a neuronal pathway but it is not sympathetic, it releases NO.
Adrenaline and NO work together.
State three respiratory diseases that involve a loss of respiratory control.
Asthma
COPD
Cystic Fibrosis
-> abnormalities in airway obstruction and inflammation
What are the characteristics of asthma?
Increased airway responsiveness to a variety of stimuli
Airway obstruction varies and is REVERSIBLE
Dyspnea, wheezing, cough
Airway inflammation leads to remodelling
Describe the histological features of asthma.
Thickening of basement membrane Mucus plug Epithelial fragility Prominent blood vessels Infiltration of eosinophils
What cells are abundant in a mucus plug formed by asthma?
Eosinophils
How does asthma set up a central cholinergic reflex?
Epithelial fragility –> exposes sensory nerves –> can respond mediators produced by inflammatory cells –> sets up cholinergic reflex –> causes smooth muscle contraction and shutting down of airways + mucus secretion
This repeats itself
—-> hypertrophy of smooth muscle and the glands + increase in number of goblet cells
Chemical mediators are released by these cells
What are the consequences of asthma to the structure of the airways?
epithelial fragility, goblet cell hyperplasia, enlarged submucosal mucus glands, angiogenesis, increased matrix deposition in the airway wall, increased airway smooth muscle mass, wall thickening
