Respiratory System Histology Flashcards
What are the structures of the upper respiratory tract?
Nasal cavity
Paranasal sinuses
Oral cavity
Pharynx
What are the functions of the upper respiratory tract?
Filtration via nasal hairs
Humidify and warm inhaled air to prevent damage to epithelium
Smell
Where does the lower respiratory tract start?
Larynx
What is the function of the larynx?
Phonation
Sphincter stops things entering respiratory tract
List the arrangement of the lower respiratory tract from the trachea to the alveolar sacs.
Trachea
Primary bronchi
Secondary bronchi
Tertiary bronchi
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
What is the alternative name for secondary bronchi and why?
Lobar bronchi
One per lung lobe
What is the alternative name for tertiary bronchi and why?
Segmental bronchi
Reflects bronchopulmonary segmentation
Describe typical respiratory epithelium.
Pseudostratified, columnar, ciliated epithelium with goblet cells
What is the length of cilia often the same as?
Diameter of nucleus
What cells are found in the trachea/bronchi?
Tall columnar ciliated cells
Goblet cells
Neuroendocrine/Kulchitsky cells
Basal cells
What do Kulchitsky cells do?
Secrete serotonin, bombesin and calcitonin which affect the smooth muscle beneath the epithelium
What is the function of the goblet cells and submucosal glands of respiratory epithelium?
Produce mucus to trap dust, bacteria and viruses
What is the ‘muco-ciliary escalator’?
Coordinated beating of cilia propels mucus from as low as bronchioles to the pharynx
What is the function of the serous secretions of the submucosal glands for the respiratory epithelium?
Humidifies inspired air to prevent dehydration and damage
How long are cilia?
7-10um
Describe the structure of a cilium.
20 microtubules arranged as 9 doublets around a central pair (9+2)
Microtubules growing out from a basal body (similar to centrioles)
What is the function of the C-shaped cartilage rings of the trachea?
Prevent collapse during inspiration and expiration
What joins the free ends of the cartilage of the trachea?
Trachealis muscle
What is the function of trachealis muscle?
Contraction reduces diameter of trachea to raise intrathoracic pressure
What type of muscle is trachealis muscle?
Smooth muscle
Describe the layers of the trachea.
Tall respiratory epithelium
Highly cellular and vascular lamina propria rich in elastin
Submucosa contains mucoserous glands (with ducts) located mainly between ends of cartilaginous rings
How do the layers of the primary bronchi compare to the trachea?
Shorter respiratory epithelium
Fewer goblet cells proportionally
Discontinuous smooth muscle layer separates lamina propria and submucosa
How is the cartilage different in the bronchi compared to the trachea?
Plates rather than C-shaped rings
Describe the layers of tertiary bronchi.
Tall columnar respiratory epithelium with little pseudostratification (mainly simple)
Even fewer goblet cells
Complete layer of smooth muscle below lamina propria
Few mucoserous glands
How do you differentiate between a bronchus and bronchiole?
Bronchi have cartilage whereas bronchioles do not
How wide are the airways of bronchioles?
<1mm
Describe the layers of bronchioles. (4)
Columnar respiratory epithelium gradually changes to cuboidal
Discrete bundles of smooth muscle
No submucosal glands
Goblet cells only present in larger bronchioles
What is the smallest, purely conducting airway?
Terminal bronchioles
Describe terminal bronchioles.
Simple cuboidal ciliated epithelium
Clara cells
Terminate in respiratory bronchioles
What is the function of Clara cells?
Secrete components of surfactant
May also be stem cells
What is surfactant?
Protein and lipid mixture which lowers surface tension of aqueous surfaces
How does cystic fibrosis affect the lungs?
Defective chloride transporter in surfactant secreting cells
Impaired effect of surfactant so hard to breathe
Describe respiratory bronchioles.
Similar to terminal bronchioles but have single alveoli in their walls
Terminate in alveolar ducts
Describe alveolar ducts.
Passageway made up entirely of alveoli
Supported by a spring-like spiral thread of smooth muscle cells, collagen and elastin which recoils during exhalation
Terminate in alveolar sacs/alveoli
What is the function of alveoli?
Site of gas exchange
Describe type 1 pneumocytes.
Squamous cells lining alveoli
Flat and thin for efficient exchange
Describe type 2 pneumocytes.
More rounded and found especially at angles between adjacent septa
Secrete surfactant
Stem cells
How do type 2 pneumocytes produce surfactant?
Contain lamellar bodies rich in phospholipids and cholesterol
Phospholipids released by exocytosis and combine with secreted surfactant proteins
Tubular lipoprotein lattice coats cell surfaces
Which phospholipid is especially rich in lamellar bodies of type 2 pneumocytes?
Dipalmitoyl phosphatidylcholine
How is the alveolar wall adapted for gas exchange?
Extensive capillary plexus
Endothelial cells share a common basal lamina with type 1 pneumocytes to create a thin diffusion barrier (as little as 0.2um)
What is the function of alveolar macrophages?
Remove inhaled particulate matter from alveoli
What happens to dust-laden alveolar macrophages?
Crawl back to ciliated part of tract to join muco-ciliary escalator
OR
Travel to lymph nodes via lymphatics present at bronchiole level
What are alveolar pores?
Small openings in alveolar wall, 8-10um dia.
What are the functions of alveolar pores?
Allow equilibration of pressure between adjacent alveoli
Provide an alternative route for air circulation in case of blockages
What is the function of alveolar elastin?
Support alveolar walls (especially condensed around openings of alveoli)
With collagen and smooth muscle form a 3D spiral network to support the lung parenchyma as a whole - important for passive recoil
What happens to alveolar elastin in emphysema and what does this cause?
Destruction of elastin contributes to breakdown of alveolar walls
Inefficient recoil leading to shortness of breath
What is the anatomical dead space and its average value?
Volume of purely conducting airways, ~150ml (third of an average breath)
What is the physiological dead space?
Volume of alveoli contributing little to gas exchange due to damage or poor blood supply
Describe the pulmonary arteries. (4)
Supply deoxygenated blood
Bifurcate along with adjacent bronchi
Elastic in character up to bronchioles then changes to muscular
Relatively thin-walled (lower pressures)
How does pulmonary systolic pressure compare to systemic systolic pressure?
5 times lower
Describe bronchial arteries.
Muscular arteries
Supply oxygenated blood to bronchi, bronchioles and pleura
When do the pulmonary and bronchial arteries anastomose?
At levels of respiratory bronchioles
Are there valves in the pulmonary veins?
No
How does blood from the bronchial arteries return to the heart?
Via alveolar capillaries (after anastomosing) draining into pulmonary veins to left heart
Small proportion via azygos and hemiazygos veins into right heart
Describe the lymphatic system of the lungs.
Absent from alveoli - fluid diffuses from interstitium to small lymphatics around respiratory bronchioles
Drain into larger lymphatics which follow airways back to hilum, passing through the hilar lymph nodes
