Histology of the respiratory tract Flashcards
What does the respiratory system consist of?
The lungs, the site of gas exchange, a system of conducting passage connected by the pharynx.
What does the upper respiratory tract consist of and what are the main functions of this?
Nasal cavity
Paranasal sinuses
Nasopharynx
Functions:
Filtration, moistening and warming on inhaled air
Smell
What does the lower respiratory tract consist of?
Larynx - sphincter, phonation Trachea Primary bronchi - lungs Secondary bronchi - lobes of lungs Tertiary bronchi - bronchopulmonary segments Bronchioles Alveolar duct Alveolar sacs (where gas exchange takes place)
What does respiratory epithelium line?
What type of epithelium is it?
What does it contain?
Trachea, bronchi and larger bronchioles.
Pseudostratified columnar, ciliated epithelium with goblet cells.
Contains - tall columnar ciliated cells, goblet cells, neuroendocrine cells, basal cells
What is the function of the respiratory epithelium?
Mucus from goblet cells (G) and submucosal glands traps dust
Coordinated beating of cilia propels the mucus towards the pharynx (muso-cillary escalator). This moves it away from there lungs and do the pharynx and disposed of through the digestive tract.
Serous secretion from submucosal glands humidifies inspired air (these glands are the in trachea). Mucus cells are also present in these glands.
How many micrometres is cilia?
How are they arranged?
Motile structures, 7-10 micrometres long
Core of 20 microtubules arranged as 9 doublets around a central pair (9+2)
Microtubules grow out from a basal body: structurally identical to a centriole and acts as a template.
Give details on trachea
- C shaped rings of cartilage to prevent collapse during inspiration and expiration (right of cartilage is over half the diameter)
- Contraction of trachealis muscle (connecting the free ends) reduces diameter, raising intrathroacic pressure. This muscle is smooth muscle. This allows some ability to modulate diameter of trachea. Longitudinal strands of smooth muscle also.
- Tall respiratory epithelium (E)
- Rests on a highly cellular and vascular lamina proper (LP), rich in elastin. LP is connective tissue.
- Submucosa (SM) contains mucoserous glands, located mainly between the cartilage rings
How many bronchi are there?
Explain the layers and structure of the bronchi
One goes into each lung.
Respiratory epithelium less tall; fewer goblet cells
Discontinuous smooth muscle layer separating lamina propria and submucosa
Plates of cartilage rather than C - shaped rings. Stops the bronchus from being displaced.
Give info on the structure of the tertiary bronchus?
- epithelium type
- smooth muscle
- glands
- cartilage
Respiratory epithelium tall columnar = little pseudostratification; fewer goblet cells. Still has cilia.
Complete layer of smooth muscle below lamina propria
parasympathetic NS = contraction, opposed by sympathetic NS
Few mucoserous glands
Irregular plates of cartilage
Bronchi have cartilage (primary, secondary and tertiary). Bronchioles do not have any cartilage.
How large is a bronchiole?
Does it have cartilage?
Does it have submucosal glands?
Any other info
Airways <1mm diameter
Lack cartilage
Discrete bundles of smooth muscle (M) - implicated in asthma
No submucosal glands (no mucus produced)
Respiratory epithelium columnar gradually changed to cuboidal ciliated cells; a few goblet cels in larger bronchioles only
Smooth muscle cells here respond to allergic reaction e.g. asthmatic attack. Smooth muscle cells are released by antihistamine in inhalers.
Primary response generates the respond.
Where do terminal bronchioles terminate?
Do they have a gas exchange role?
What type of cells are they?
What are goblet cells replaced by here?
What happens if there is a lack of chloride ions in surfactant?
Respiratory bronchioles
No
Cuboidal ciliated cells (squamous, no stratification)
Clara cells (secrete components of surfactant to reduce surface tension)
Increases the surface tension
Explain respiratory bronchioles and alveolar ducts
RB - first tubules involved in gas exchange, have single alveoli in walls, terminate in alveolar duct
AD- passageway make entirely of alveoli, supported by spring-like spiral of smooth muscle, collagen, elastin, terminate in alveolar sacs
What are the two prominent cells in alveoli?
What are alveoli lined by?
Lining cells and surfactant secretion cells.
Extremely flattened type 1 pneumocytes and more rounded type 2 pneumocytes which secrete surfactant
Give details on type 2 pneumocytes
- coat the surface of the cells with surfactant
- contain lamellar bodies in phospholipids and cholesterol
- phospholipids released by exocytosis and combine with secreted surfactant proteins to form a tubular, lipoprotein lattice
- overcomes surface tension, allowing the alveolar walls to separate
What does the alveolar wall contain?
How far is the diffusion distance?
What do endothelial cells share here?
An extensive capillary plexus
0.2um
A common basal lamina with the type 1 pneumocytes.