structure of airways

Question 1

• What are trachea held open by?
• What property does cartilage provide the airway with?
• What is the name of the point at which the bronchi enter the lungs at?

Answer 1

Trachea held open by C-shaped cartilage rings (C-shaped - transport of substrate down oesophagus, with minimum resistance).

Mechanical stability 

Hilium

Question 2

• Describe type I and type II alveolar cells and give their function

Answer 2

Type I - Very thin delicate barrier, large and flat in shape. facilitates GE

Type II - Replicate to replace type I; secrete surfactant (reduces surface tension), antiproteases; Xenobiotic metabolism

Question 3

• Explain the distribution of type I and type II alveolar cells in the alveolar region

Answer 3

Type I - Cover ~95% of alveolar surface; lesser in number than type II, but are much larger.

Type II - Greater numbers than type I, but only cover ~5% of surface.

Question 4

• what is the basic function of the respiratory airways and what are these functions facilitated by?

Answer 4

Conduit to conduct O2 to the alveoli and conduct CO2 out of the lung - Gas Exchange

- Facilitated by

    Mechanical stability (Cartilage) 

    Control of calibre (Smooth muscle) 

    Protection and cleansing

Question 5

• What are each of the lateral walls of the nasal cavity called?

Answer 5

Superior, middle and inferior nasal conchae

Question 6

• What is the purpose of conchae?

Answer 6

Highly vascular - contribute to warming and humidification of intra-nasally-inhaled air

Nasal hairs filter out large particles

Question 7

• What do the conchae, meatuses and paranasal sinuses produce?
• What assists in the removal of mucous and debris from the nasal cavity?
• What is the pharynx a path for?

Answer 7

Mucous → Trap debris

Cilia

Common passageway for food, liquids and air.

Question 8

• What is embedded within the smooth muscle ring?

- What does contraction of this smooth muscle lead to?

Answer 8

Inferior portion of submucosal gland

Contraction of smooth muscle stimulates secretion into epithelial lining
Also closes airway to prevent something going down airways

Question 9

• Describe the structure of the airway wall

Answer 9

Smooth muscle at the outside of airway-> basement membrane-> epithelium -> mucociliary

Submucosal gland partially embedded within the contractile smooth muscle ring;

goblet cells within the epithelium contribute to the production of mucous, lies superficially above the ciliated epithelial layer

Mucociliary transport to release the pollutants

blood vessels between basolateral membrane and smooth muscle

Question 10

List the categories of airway cell types

Answer 10

Life Can Seem Crazy, Not Very Interesting

• Lining cells
  Ciliated, intermediate, brush, basal

- Contractile cells
    Smooth muscle (airway, vasculature)

• Secretory cells
  Goblet (epithelium), mucous, serous (glands)
• Connective tissue
  Fibroblast, interstitial cell (elastin, collagen, cartilage)
• Neuroendocrine
  Nerves, ganglia, neuroendocrine cells, neuroepithelial bodies
• Vascular cells
  Endothelial, pericyte, plasma cell (+ smooth muscle)
• Immune cells
  Mast cell, DC, lymphocyte, eosinophil, macrophage, neutrophil

Question 11

• What do mucin granules contain and how is this substance hydrated?

Answer 11

Mucin granules contain mucin in goblet cells
highly condensed forms of mucin requires hydration
hydrated through water absorption in trachea
Expansion of mucin generates expansive mucous

Question 12

• What are the functional units of the airway’s submucosal glands, what is their function and what are their different types?

Answer 12

Functional unit - Acini (secrete mucous extracellularly into the collecting duct traversing to ciliated duct, the cilia waft the mucous out of gland)

Serous acini - secrete anti-bacterial enzymes (serous cells produce more dilute mucous). more watery to help wash out viscous substance

Mucous acini - secrete mucous

Glands also release water and salts

Question 13

• What is the arrangement of ciliary structures?

Answer 13

9+2 microtubule arrangement

Question 14

• Briefly explain the process of beating cilia and describe the rhythm at which they beat

Answer 14

Cilia efficiently move mucous

Metachronal rhythm

Backwards cilia sequentially move through alternating forward and backward movements

Question 15

• List all the airway epithelium functions

Answer 15

1. Secretion of mucin, water and electrolytes (Components of mucous + plasma, mediators)
   
   2. Movement of mucous by cilia - Mucociliary clearance
   3. Physical barrier against inhaled insult
   4. Production of regulatory and inflammatory mediators:

Question 16

• List the inflammatory mediators

Answer 16

NO secreted by nitric oxide synthase (NOS)

CO by haem oxygenase (HO); enzyme catalyses the degradation of haem to produce biliverdin, Fe2+ (ferrous iron) and CO. Products activate vasodilatory pathways

Arachidonic acid metabolites (COX, prostaglandins)

Chemokine (IL-8)

Cytokines (GM-CSF)

Proteases

Question 17

outline the function of smooth muscle in epithelium airways (secretion)

Answer 17

• Secretion - Smooth muscle cells produce small amounts of secretions eg chemokines, cytokines and mediators. chemokines lead to recruitment of inflammatory cells; smooth muscle subsequently gets involved in the inflammatory process
  
  1. In response to cytokines however, NOS is up-regulated (inc no. of receptors on its surface) ; enhancing secretion of NO, accentuating its effect on cilia and inflammation
  2. COX enzymes produce more prostaglandins;

Question 18

outline the function of smooth muscle in epithelium airways (tone and structure)

Answer 18

• Tone (airway calibre)Level of relaxed or contracted the airway is
  contracts when needed eg if food goes down the wrong way
• StructureInflammation and smooth muscle hypertrophy occurs through proliferation of smooth muscle cells, in addition to hyperplasia.

Question 19

• What % of cardiac output does this system represent and what volume of blood flow goes to airway mucosa?

Answer 19

1-5%

Blood flow to airway mucosa = 100-150 mL/min/100g tissue

The tracheo-bronchial systemic circulation blood flow is AMONG THE HIGHEST to any tissue

Question 20

• How does blood return from tracheal circulation?

- How does blood return from bronchial circulation to both sides of the heart?

Answer 20

Systemic veins

Via bronchial and pulmonary veins

Question 21

• List all the functions of tracheo-bronchial circulation

Answer 21

• Direct gaseous exchange between systemic circulation in the tissue of sub-epithelial micro-vasculature.
  
  • Contributes to warming and humidification of inspired air
  • Clearance of inflammatory mediators and inhaled drugs (Benefit is dependent on the mechanism of delivery of drug)
  • Supplies airway tissue and lumen with inflammatory cells; in addition to proteinaceous plasma (mechanism of plasma exudation)

Question 22

• Outline the parasympathetic ‘motor’ pathway for airway control

Answer 22

Innervation via vagus nerve through corticospinal tract, motor pathway

Secretion of ACh NT via cholinergic synapse of postganglionic fibre and gland

This stimulates the bronchostriction and contraction of smooth muscles within trachea + stimulates submucosal glands to secrete mucous

Question 23

• Outline the sympathetic and nitric oxide (NO) pathway for airway control

Answer 23

Sympathetic - Adrenergic reflex causes bronchodilation, smooth muscle relaxes, dilating the airways

Adrenaline is secreted by adrenal gland, and directly relaxes the airways

NO - NO is a NT of neuronal pathway that dilates and opens airways

Question 24

• List the regulatory and inflammatory mediators for the control of airway function

Answer 24

Histamine 
arachidonic metabolites (prostaglandins and leukotrienes)
cytokines
chemokines
proteinases (e.g. neutrophil elastase).

Question 25

• Name 3 respiratory diseases associated with loss of airway control

Answer 25

Asthma, COPD and cystic fibrosis - all common conditions