Tissues, Organs and Systems

Question 1

From inside to out, what are the layers of the trachea?

Answer 1

• Lumen
• Mucous membrane made of pseudostratified ciliated columnar epithelium
• Submucosa, containing seromucous glands
• Hyaline cartilage ring (horse shoe shape)
• Adventitia

Question 2

What is the structure of the mucosa in trachea?

Answer 2

• Epithelial layer is several layers deep
• Surface covered in cilia (moves debris, dust, bacteria etc. towards mouth)
• Lamina propria is very thin
• No muscularis mucosa layer

Question 3

What is the structure of the submucosa of the trachea?

Answer 3

• The connective tissue layer contains mainly collagen and elastin fibres and many fibroblasts
• Contains seromucous glands that produce watery mucus that thickens during infections

Question 4

What are the features of the cartilage in the trachea?

Answer 4

• C-shaped hyaline cartilage ring
• Made of two distinct layer:
  
  • perichondrium layer (contains fibroblasts that lay down collagen fibres)
  • chondrogenic (contains chondroblasts which form cartilage)

The cells present can interconvert from chondroblasts to chondrocytes and so can make both hyaline and elastic cartilage

Question 5

What do secretions are produced from the epithelium and and submucosal glands of the trachea and bronchi?

Answer 5

• Mucins and water (makes sticky mucus)
• Serum proteins (lubricate the surface)
• Lysozymes (destroy bacteria)
• Anti-proteases (inactivate bacterial enzymes)

Question 6

What makes up the mucociliary escalator?

Answer 6

The ‘cilia wave’ and mucous moves materials to oral cavity where it can be swallowed- making the mucociliary escalator

Question 7

What does cilia contribute to the mucociliary escalator?

Answer 7

• Tracheal mucosa contains approximately 250 cilia/cell

- Cilia beat at 12Hz beneath a moveable, viscoelastic mucus blanket

Question 8

What does trachea look like in histology?

Answer 8

• Unusually thick basement membrane

- Lamina propria rich in immune cells and contains layers of elastic

Question 9

What differences in structure are there between primary and secondary/tertiary bronchi?

Answer 9

• ## Histology similar to primary bronchi but cartilage is only present as cresents and not full C-shapes

Question 10

What features are present in secondary and tertiary bronchi?

Answer 10

• Epithelium made of pseudostratified ciliated columnar cells
• Bound by smooth muscle
• Supported by seromucous glands in the submucosa
• Airway kept open by crescent shaped hyaline cartilage.
• No layer of outer smooth muscle

Question 11

How are alveolus connected to capillaries?

Answer 11

• Capillaries are lined with flattened specialised epithelial cells (called endothelium)
• These cells are attached to fused basal lamina with even thinner specialised cells of the air sac

Question 12

How are alveoli adapted for their function?

Answer 12

• Folds in basal lamina allow for expansion of the air sacs when air is drawn into the lungs
• At junctions, small amounts of collagen are present and surrounded by layers of elastin fibres in the mucosa to allow recoil
• The connective tissue ‘muscle’ layers in the mucosa are created by the collagen and elastin fibres