CTB6: Cell biology of the respiratory tract Flashcards
How many L of air do we inhale a day under normal circumstances?
12000L
Why is it important that the respiratory tract has adaptations to maximise airflow whilst minimising damage?
The air contains microbial and non-microbial particles as well as noxious gases
What are goblet cells are responsible for secreting?
mucin, onto the airway surface. The goblet cells can secrete mucus globules almost as large as the size of the cell itself
What is mucin?
high molecular weight glycoproteins
How does secretion of mucin occur?
occurs by exocytosis and is a highly regulated, rapid process
What induces the secretion of mucin?
ATP
Where are submucosal glands normally found?
predominantly found in the larger airways and reduce greatly in number by the time the smaller airways are reached, the distal airways contain no submucosal glands
What do submucosal glands contain?
Secretory acini - Mucous acini - Serous acini Collecting duct Ciliated duct
What do serous acini secrete?
Watery, serous secretions (lysozyme and lactoferrin) which have been hypothesised to wash the mucous acini’s thicker, mucous secretions (mucins) into the collecting duct
What is secreted in order to make an aqueous electrolyte solution of mucins and other high molecular weight proteins?
Na+ and Cl-, along with water, secreted by the glands
What give the mucus viscoelastic, gel-like properties which allows it to entrap particles and be swept away by cilia?
Other high molecular weight proteins
What two characteristics of ciliated cells allow them to maintain the ciliary beat?
Numerous cilia on their apical surface and mitochondria to provide sufficient ATP to maintain the ciliary beat
How frequently do cilia beat?
~7-9/s
How are cilia arranged?
axoneme
What is the axoneme made up of?
- 9+2 arrangement of microtubules
- Linking dynein arms
- Nexin links to prevent microtubules moving with respect to one another
What allows the ciliary to beat?
microtubules slide over one another
What can the ciliary beat be described as?
Metachronicity
What does metachronicity mean?
This describes a sequential movement of fields of cilia, not a synchronised movement
Describe how cilia move
A field of cilia first undergo a power stroke which moves the viscoelastic gel forward, then disengages with the mucus using a recovery stroke which is at 90˚ to the power stroke. The second field of cilia performs a power stroke whilst the first field undergoes recovery.
What does airway smooth muscle control?
The patency of the airways
Where is there greatest and least mass of airway smooth muscle?
It is found in greater mass in the larger airways and in smaller mass in the distal airways.
What is tone (passive partial contraction) thought to be important for?
to prevent large accidentally inhaled objects from penetrating too far into the airways
What happens to the airways smooth muscle to increase airflow?
It relaxes
What is tracheobronchial circulation made up of?
Vast network of blood vessels found under the airway epithelium
How much does blood flow to the airway mucosa make up of cardiac output?
Just 1-5%, but there is approx. 100-150ml of blood per minute per 100g of tissue which is higher than almost any other tissue
How is high output of blood to airway mucosa facilitated?
- Bronchial arteries arising from many sites on aorta, intercostal arteries and other
- Blood returns from tracheal circulation via systemic veins
- Blood returns from bronchial circulation to both sides of the heart via bronchial and pulmonary veins
What facilitates airway homeostasis?
This vascular plexus highly perfuses the airways includes:
- aiding gas exchange
- warms and humidifies the inhaled air
- clears inflammatory mediators and inhaled drugs
- supplies the airway tissue with inflammatory cells and proteinaceous plasma
What influences influences smooth muscle contraction, mucus secretion, and vascular tone?
nervous control
Under normal circumstances, what maintains minimal smooth muscle tone and airway patency?
parasympathetic (cholinergic) outflow
What does accidental inhalation of a large object activate and lead to?
sensory nerves which sets up a cholinergic reflex to constrict the airways and induce mucus secretion to aid in expulsion of the foreign object.
What induces relaxation of the airways?
Non-neuronal adrenaline from the adrenal medulla induces relaxation
In humans and other animals, what causes neuronally-induced relaxation?
Humans: Nitric Oxide released from Nitric Oxide Synthase containing nerves (NOS nerves)
Other animals: sympathetic outflow has been shown to induce relaxation.
How do immune cells protect the airways?
pulmonary macrophages ingest inhaled pathogens, neutrophils combat infections and eosinophils and lymphocytes fight nematode infections.
Mast cells produce histamines, prostaglandins and leukotrienes.
What do histamines do to
a) airway smooth muscle
b) vascular smooth muscle
c) mucus secretion
d) plasma exudation
e) nervous system control
Histamines contract airway smooth muscle, relax vascular smooth muscle, induce mucus secretion and plasma exudation, and alter nervous control.
What can cytokines and growth factors do to the respiratory tract?
Cytokines and growth factors can also remodel the respiratory tract in respiratory diseases
