Structure and Function of the Airways 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
Describe the secretion of mucus by goblet cells.
Mucin granules accumulate at the cell surface
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 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
What inflammatory mediators can be produced by smooth muscle cells?
NO, Prostaglandins, Cytokines, Chemokines
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
Explain the process of plasma exudation in the airways.
Plasma exudation usually takes place at the POST-CAPILLARY VENULES
Post-capillary venules have endothelial cells have sensory innervation (have some motor function as well).
Histamines, PAF and other mediators can activate these sensory nerves 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 cholinergic reflex.
Something can go into the airways and trigger a signal via an afferent pathway to the brain.
This will cause a CHOLINERGIC reflex —> BRONCHOCONSTRICTION
What causes bronchodilation in humans?
Bronchodilation is caused by:
Release of ADRENALINE from the adrenal medulla (part of sympathetic response)
Release of NITRIC OXIDE from the neuronal pathway (NOTE: in this case NO is a neurotransmitter)
What does the cholinergic reflex cause?
Constriction of smooth muscle
Secretion of mucus
State three respiratory diseases that involve a loss of respiratory control.
Asthma
COPD
Cystic Fibrosis
What are the characteristics of asthma?
Increased airway responsiveness to a variety of stimuli —> leads to reversible airway obstruction
Describe the histological features of asthma.
Mucus plug formation (with a lot of eosinophils within it) Epithelial fragility Thickening of the basement membrane Congested/vasodilated blood vessels Infiltration by eosinophils
What cells are abundant in a mucus plug formed by asthma?
Eosinophils
How does asthma set up a central cholinergic reflex?
Epithelial fragility means that there are exposed sensory fibres.
Sensory fibres are stimulated by inflammatory mediators resulting in messages being sent to the brain and setting up a cholinergic reflex.
The cholinergic reflex results in BRONCHOCONSTRICTION and SECRETION OF MUCUS
What are the consequences of asthma to the structure of the airways?
Smooth Muscle Hypertrophy
Increase in number of goblet cells
