RESPIRATORY SYSTEM This resource is licensed under the Creative Commons Attribution Non-Commercial & No Derivative Works LicenseCreative Commons Attribution Non-Commercial & No Derivative Works License

Objectives Students should be able to : 1.Describe the structure of the conducting and exchange parts of the respiratory system and relate this to function. 2.Compare the microscopic structure of the walls of trachea, bronchi and bronchioles. 3.Examine the structure of the alveolar wall.

SLIDE 62 Trachea (rat) At low magnification identify the principal features. 1.0 mm ? ? ? ? ? ? ?

SLIDE 62 Trachea (rat) At low magnification identify the principal features. 1.0 mm Cartilage of trachea Oesophagus Muscle (skeletal) Line across lumen is a fold in the section Dorsal Ventral Thyroid Lumen of trachea

SLIDE 62 Trachea (rat) Tracheal wall What type of cartilage is present? 1.0 mm

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm What type of cartilage is present? Hyaline. cartilage lumen

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm cartilage lumen Why is there a need for cartilage?

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm cartilage lumen Why is there a need for cartilage? Gives support during inspiration and expiration (radially and longitudinally). Its rigidity prevents collapse of the trachea.

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm cartilage lumen Give two reasons why the cartilage rings are incomplete.

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm cartilage lumen Give two reasons why the cartilage rings are incomplete. Radial expansion of the trachea is possible. Bolus of food can pass down the oesophagus.

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm Find the trachealis muscle at the dorsal aspect of the trachea.

SLIDE 62 Trachea (rat) Tracheal wall What lies immediately dorsal to this? 250 µm

SLIDE 62 Trachea (rat) Tracheal wall What lies immediately dorsal to this? The oesophagus. 250 µm trachealis muscle oesophagus lumen of oesophagus

SLIDE 62 Trachea (rat) Trachealis muscle Classify the type of muscle present. 50 µm

SLIDE 62 Trachea (rat) Trachealis muscle Classify the type of muscle present. Smooth muscle. 50 µm smooth muscle spindle shaped cells with single, central nucleus

SLIDE 62 Trachea (rat) Tracheal wall 1.0 mm Examine the epithelium lining the trachea.

SLIDE 62 Trachea (rat) Epithelial lining What type of epithelium is it? 25 µm

SLIDE 62 Trachea (rat) Epithelial lining 25 µm What type of epithelium is it? Pseudostratified, ciliated, columnar epithelium. mucous on surface cilia pseudostratified epithelium

SLIDE 151 Trachea epithelial lining Pseudostratified, ciliated, columnar epithelium from cat trachea. 25 µm

SLIDE 62 Trachea (rat) Tracheal wall Are there any glands in the submucosa? 50 µm

SLIDE 62 Trachea (rat) Tracheal wall 50 µm Are there any glands in the submucosa? Yes. lumen epithelium submucosal glands

SLIDE 62 Trachea (rat) Tracheal wall 50 µm What is their function? lumen epithelium submucosal glands

SLIDE 62 Trachea (rat) Tracheal wall 50 µm What is their function? They are mucoserous glands; secreting mucous. lumen epithelium submucosal glands

SLIDE 63 Trachea (cat) Stained for elastic fibres Observe the transversely sectioned elastic fibres. Where are they located? 50 µm

SLIDE 63 Trachea (cat) Stained for elastic fibres 50 µm Observe the transversely sectioned elastic fibres. Where are they located? Just below the epithelium. Why are the fibres longitudinally arranged, and why are they so abundant? epithelium pseudostratified columnar, ciliated. band of black stained elastic fibres in lamina propria.

SLIDE 63 Trachea (cat) Stained for elastic fibres 50 µm Observe the transversely sectioned elastic fibres. Where are they located? Just below the epithelium. Why are the fibres longitudinally arranged, and why are they so abundant? Part of the elastic continuum of the lung. Add to the elastic recoil of the lungs after inspiration and expiration. epithelium pseudostratified columnar, ciliated. band of black stained elastic fibres in lamina propria.

SLIDE 63 Trachea (cat) Stained for elastic fibres Note the presence of lymphocytes. How are they distributed? 25 µm

SLIDE 63 Trachea (cat) Stained for elastic fibres 25 µm Note the presence of lymphocytes. How are they distributed? Mostly sub epithelial, but some can be seen amongst the epithelial layer. L : lymphocytes L L

Dog Lung deflated (adult). Left lung in situ. Dog. Cr cr - Cranial lobe, pars cranialis Cr ca - Cranial lobe, pars caudalis Ca - Caudal lobe Cr cr Cr ca Ca

Dog Lung inflated (adult). Left lung inflated in situ.

SLIDE 67 Lung (adult) Examining the lung at low magnification. What covers its surface? Left lung in situ. Dog. Cr cr - Cranial lobe, pars cranialis Cr ca - Cranial lobe, pars caudalis Ca - Caudal lobe Cr cr Cr ca Ca Left lung inflated in situ. 1 mm

SLIDE 67 Lung (adult) 1 mm Examining the lung at low magnification. What covers its surface? Visceral pleura. outer surface of lung covered by visceral pleura B : blood vessels small bronchus B B

SLIDE 67 Lung (adult) Visceral pleura. Surrounds the lungs. 100 µm surface mesothelium connective tissue layer with elastic fibres

Scanning electron micrograph of adult sheep lung Shows cut surface of the lung. 50 µm B : cut bronchioles alveoli B B

Lung How can you distinguish between a bronchus and a bronchiole?

Lung How can you distinguish between a bronchus and a bronchiole? Bronchus Bronchiole Lining cells pseudostratified ciliated columnar epithelium ciliated columnar epithelium

Lung How can you distinguish between a bronchus and a bronchiole? Bronchus Bronchiole Lining cells Cartilage pseudostratified ciliated columnar epithelium ciliated columnar epithelium plates of cartilagecartilage absent

Lung How can you distinguish between a bronchus and a bronchiole? Bronchus Bronchiole Lining cells Cartilage present absent Mucosal glands pseudostratified ciliated columnar epithelium ciliated columnar epithelium plates of cartilagecartilage absent

Incised Lung Lobe. Dog. 2 larger airways have been opened to show branching of the bronchial tree. V-shaped dark areas are post-mortem artefacts – blood has pooled in dependent areas.

SLIDE 68 Lung (adult) Bronchus Low magnification view of bronchus. Plates of cartilage can be identified. 1.0 mm Incised Lung Lobe. Dog. 2 larger airways have been opened to show branching of the bronchial tree. V-shaped dark areas are post-mortem artefacts – blood has pooled in dependent areas.

SLIDE 68 Lung (adult) Bronchus Low magnification view of bronchus. Plates of cartilage can be identified. 1.0 mm cartilage cut edge of section lumen

SLIDE 68 Lung (adult) Bronchus Identify : plates of cartilage lining epithelium smooth muscle glands 250 µm C

SLIDE 68 Lung (adult) Bronchus Identify : plates of cartilage lining epithelium smooth muscle glands 250 µm C C : cartilage M : smooth muscle epithelium lumen G : glands M G

SLIDE 68 Lung (adult) Bronchus 25 µm Typical respiratory tract epithelium lines the bronchus. Pseudostratified, ciliated, columnar with goblet cells. Further down as the bronchus gets smaller the epithelial lining also reduces in height.

SLIDE 68 Lung (adult) Bronchus 25 µm Typical respiratory tract epithelium lines the bronchus. Pseudostratified, ciliated, columnar with goblet cells. Further down as the bronchus gets smaller the epithelial lining also reduces in height. cilia RB : blood cells in capillary G : goblet cells mucous on surface RB G G

SLIDE 68 Lung (adult) Another bronchus from slide mm

SLIDE 68 Lung (adult) Identify : epithelium blood vessels cartilage smooth muscle glands Smooth muscle runs in a spiral around the bronchus. 100 µm

SLIDE 68 Lung (adult) Identify : epithelium blood vessels cartilage smooth muscle glands Smooth muscle runs in a spiral around the bronchus. 100 µm epithelium cartilage glands muscle blood vessel

SLIDE 67 Lung (adult) At low magnification identify : bronchus bronchiole large blood vessels 1.0 mm

SLIDE 67 Lung (adult) At low magnification identify : bronchus bronchiole large blood vessels 1.0 mm blood vessels bronchus bronchiole

SLIDE 67 Lung (adult) Bronchus and blood vessels 0.5 mm BR : bronchus BV : blood vessel BR BV

SLIDE 67 Lung (adult) Although there is little evidence of cartilage in this structure, some glands can be seen suggesting that this is a small bronchus. 250 µm glands

SLIDE 67 Lung (adult) Bronchiole Why is cartilage absent from the wall of a bronchiole? 250 µm

SLIDE 67 Lung (adult) Bronchiole 250 µm Why is cartilage absent from the wall of a bronchiole? To allow a change in diameter. They must be flexible in a way that minimises ‘dead space’ but does not cause too great a resistance to air flow. epithelium M : muscle M

SLIDE 67 Lung (adult) Respiratory Bronchiole Respiratory bronchioles are lined by a cuboidal epithelium. Alveolar ducts open into alveoli. 100 µm blood vessel alveoli

SLIDE 67 Lung (adult) Respiratory duct/sac The lips of the alveoli contain smooth muscle. Respiratory bronchiole → alveolar ducts → alveolar sacs → alveoli. 100 µm

SLIDE 67 Lung (adult) Respiratory duct/sac The lips of the alveoli contain smooth muscle. Respiratory bronchiole → alveolar ducts → alveolar sacs → alveoli. 100 µm A AS AD A : alveoli AS alveolar sacs AD alveolar ducts A

Transmission electron micrograph of adult lung Section through the alveoli of the lung. alveolar type I (flattened, squamous like cells) are the main lining cell of the alveolus. alveolar type II cells form about 10%. Numerous capillaries lined with endothelial cells and blood cells within. 2.5 µm

Transmission electron micrograph of adult lung Section through the alveoli of the lung. alveolar type I (flattened, squamous like cells) are the main lining cell of the alveolus. alveolar type II cells form about 10%. Numerous capillaries lined with endothelial cells and blood cells within. 2.5 µm RB : erythrocytes A : alveolar spaces A A RB

Transmission electron micrograph of adult lung Briefly describe the blood gas barrier in the alveolus. 1.0 µm

Transmission electron micrograph of adult lung 1.0 µm Briefly describe the blood gas barrier in the alveolus. The walls of the alveoli and the walls of the capillaries are only one cell thick. They share a basal lamina so minimising the blood gas barrier. RB : red blood cell A : alveolar cell E : endothelial cell N : nucleus of endothelial cell A RB E N BL : basal lamina BL

SLIDE 70 Lung (marsupial mouse) Injected lung for alveolar phagocytes. 25 µm

SLIDE 70 Lung (marsupial mouse) Injected lung for alveolar phagocytes. 25 µm alveoli phagocytes

SLIDE 70 Lung (marsupial mouse) alveolar phagocytes What do they look like? 25 µm

SLIDE 70 Lung (marsupial mouse) alveolar phagocytes What do they look like? 25 µm Wandering irregular shaped cells. On this slide with prominent dark inclusions. What is their function? P : phagocytes P P

SLIDE 70 Lung (marsupial mouse) alveolar phagocytes What do they look like? 25 µm Wandering irregular shaped cells. On this slide with prominent dark inclusions. What is their function? The lung’s defence mechanism to protect the inner surfaces. P : phagocytes P P

SLIDE 71 Lung In this slide the blood vessels have been injected with a red dye. 1 cm

SLIDE 71 Lung injected for blood vessels Note the arrangement of the capillaries supplying the alveoli. What happens to these capillaries during inspiration and expiration? 100 µm

SLIDE 71 Lung injected for blood vessels 100 µm Note the arrangement of the capillaries supplying the alveoli. What happens to these capillaries during inspiration and expiration? During inspiration the lungs expand and the resulting traction to the capillaries increases the blood flow through the capillary bed. Blood is drawn from the pulmonary artery. During expiration resistance to the blood flow increases.

SLIDE 72 Lung stained for elastic tissues Examine this section stained for elastic tissue. At low magnification. 1 cm

SLIDE 72 Lung stained for elastic tissues Note the distribution of these fibres throughout the section especially in relation to the alveolar ducts and alveoli. 100 µm elastic fibres surrounding alveoli elastic fibres and smooth muscle cells below the cuboidal lining of the alveolar ducts

SLIDE 72 Lung stained for elastic tissues Why are there so many elastic fibres in the lung? 50 µm

SLIDE 72 Lung stained for elastic tissues Why are there so many elastic fibres in the lung? The lung is stretched during inspiration. The elastic fibres enable the elastic recoil during expiration. 50 µm elastic fibres

SLIDE 72 Lung stained for elastic tissues 50 µm elastic fibres Why does their distribution differ in different parts of the respiratory tract?

SLIDE 72 Lung stained for elastic tissues 50 µm elastic fibres Why does their distribution differ in different parts of the respiratory tract? There are more fibres in the parts that expand the most, the respiratory ducts and the alveoli.

Lectures. Dr C. Lawson. First Year Histology Respiratory. J.Bredl Gross Anatomy Correlates. S.Frean Histology Slides and Stains. Tanya Hopcroft. This version