Cell Biology of the Respiratory Tract Flashcards
What is the main purpose of the specialised cell biology of the respiratory tract?
To protect the respiratory system, maximise airflow and minimise damage eg from. microbes, pollen, pollution
Describe the airway epithelium
A relatively delicate surface layer that runs continuously from nasal passages to terminal bronchioles. Needs to protect itself from many pollutants. Is highly metabolically active in order to maintain the beating cilia.
Describe and explain the function of goblet cells
They secrete specific high MW glycoproteins (mucins) onto the airway surface, along with submucosal glands. The mucin granules contained in the cells moves to the apical surface where they fuse with the membrane and are exocytosed. The dehydrated granules repidly take on water and expand to over 100x their size. ATP is a main inducer of mucin secretion - secretagogue.
Describe and explain the function of submucosal glands
They are found in larger airways and reduce markedly as the airways get smaller. Most of the structure is below the surface, the glandular opening secretes mucins onto airway surface. Each secretous acini has multiple secretory cells. Mucins secreted onto collecitng duct via cilia.
Explain the organisation of the serous vs mucous acinini positioning in the submucosal glands
Serous acini are distal to mucous acini because the watery secretions from serous acini wash the mucous secretions into the collecting duct. Serous cells secrete antibacterial molecules such as lysozyme and lactoferrin. Glands secrete water and salt, making the final mucus an aqueous electrolyte solution with high MW proteins for gel-like properties which allow trapping of particles.
Describe the structure and function of ciliated cells.
They make up the majority of the surface epithelia in healthy human airways. About 200 cilia per cell and many mitochondria to maintain the 9-17 beats per sec. The axoneme is anchored into the cell body and has microtubules that run the length of the cilium. The microtubules slide over eachother and the anchoring makes them bend back and forward. Beat is highly regulated, shows metachronicity.
How do the cilia move mucus?
Each field of cilia moves a portion of mucus on the power stroke, disengages, moves back, and moves the second portion of mucus. This results in the mucus moving as a whole.
Describe the structure and function of the airway smooth muscle
It controls the patency of the airways and is most prominent in larger airways, reducing in mass as airways get smaller. The airways are always slightly constricted (have tone) - this allows fast contstriction in the case of accidently inhaled objects needing to be blocked. Also, when we need extra air in fight or flight, they relax.
Describe the tracheobronchial circulation
It is a part of the systemic circulation, and forms a vast network of vessels just below the airway epithelium. Has low % of CO but high blood perfusion, this is because there are many bronchial arteries that come off the aorta. Blood returns from the tracheal circ via systemic veins and from bronchial circ to both sides of heart via bronchial and pulmonary viens.
What are the functions of the tracheobronchial circulation having high tissue perfusion?
Gas exchange between airway tissues and blood
Warming and humidification of inspired air
Clear inflammatory mediators from the tissue
Clear inhaled drugs
Supplies airway tissue and lumen with inflammatory cells
Supplies airway tissue and lumen with proteinaceous plasma via plasma exudation
Explain the innervation of the airways
Sensory pathways in the vagus nerve from airway to brainstem. Parasympathetic cholinergic pathway in vagus nerve sets basal tone and also involved in constriction (brainstem). Nitrous oxide pathway from spinal cord leads to relaxation, as does adrenaline from adrenal gland. Also a sensory pathway via DRG.
Explain how the nervous pathways function together in the airways
Sensory pathways detect inhalation of a foreign object which then stimulates a cholinergic reflex in order to constrict the airways so that the object doesn’t travel down far enough to make it impossible to cough up. Cholinergic nerve activity induces mucus secretion, probably to make expulsion easier. When the object is expelled, adrenaline form adrenal gland induces relaxation. In animals it’s sympathetic nerve activity, in humans the neuronal relaxation is stimulated by NO from NO-synthase containing nerves.
Explain the function of regulatory inflammatory cells and mediators in the airways (humoral control)
They also regulate the function of the airways and contribute to homeostasis. Structural cells like epithelium, endothelium, smooth muscle, produce airway function regulating mediators. Epi -> NO to regulate ciliary beat. Inflammatory cells monitor airways and lungs. Macrophages ingest inhaled particles, neutrophils for serious infections, and lymphocytes and eosinophils for nematode infections. Cells produce multiple mediators with multiple roles. Cytokines and GFs may lead to structural remodelling observed in respiratory diseases.
