Respiratory system Li Jinxin, associate professor No Department of Histology and Embryology

Objectives Objectives 1.Components of the conducting and respiratory portions of the respiratory system. 2.Wall structure of the trachea. 3.The general structure of the lung.The key distinguishing features and the various segments of the bronchial tree. 4.Structure of the alveolar wall and components of the gasblood barrier. 5.The two sets of pulmonary blood vessels.

Respiratory system Components nose pharynx larynx trachea bronchi lung Conducting portions Respiratory portions

1. Trachea and main bronchi T hree layers: Mucosa Submucosa Adventitia

1.1 Mucosa epithelium: pseudostratified ciliated columnar epithelium ciliated cell goblet cell brush cell small granule cell basal cell lamina propria: CT

1.2 Submucosa LCT tracheal gland: mixed 1.3 Adventitia LCT cartilage ring

2. Lung paired organ, located in thoracic cavity 2.1 General structure capsule: visceral layer of pleura, mesothelium parenchyma: all branches of bronchi and alveoli interstitia: CT, BV, LV, N

Lung

bronchial tree intrapulmonary bronchus ( lobar bronchi and small bronchi) → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar duct → alveolar sac → alveoli Conducting portion, respiratory portion

pulmonary lobule one bronchioles and its all branches and all alveoli. cone or pyramidal-shaped: apex pointed toward the hilum and basalfaced the surface. more CT between them.

2.2 Conducting portion From lobar bronchi to small bronchi Regulation of simplification: (gradually) mucosa: epithelium: become thinner goblet cell ↓ lamina propria: thinner, SM ↑ submucosa: gland ↓ adventitia: cartilage→decreasing

2.2.2 bronchiole: D < 1mm ---continuous to change goblet cell, Gland, cartilage ↓ or disappear smooth muscle ↑, mucosa plica ↑

---goblet cell, gland, cartilage disappear ---Wall: A layer of SM: form a whole layer of circumferential simple columnar epi.: two types of cells terminal bronchiole: D < 0.5 mm

i. ciliated cell ii. secreting cell: Clara cell

2.3 respiratory portion respiratory bronchiole alveolar duct alveolar sac Pulmonary alveoli

2.3.1 respiratory bronchiole ---similar to terminal bronchioles: The walls of respiratory bronchioles are populated with alveoli. simple cuboidal epi. → simple squamous epi. less smooth muscles.

2.3.2 alveolar duct The wall of alveolar duct are hard to see in histological section as a result of the numerous opening of the alveoli and alveolar sacs. simple cuboidal epithelium or squamous epithelium form knobs between adjacent alveoli. Alveolar duct Knob-liked structure

2.3.3 alveolar sac ---many alveoli open to it ---no proper wall, no knob-liked structure alveolar sac

2.3.4 alveoli ---polygonal, with opening the alveolar sac. 0.2mm in diameter total number: million total area: 70-80m 2 ---wall: epithelium and basal lamina alveolar septum: CT with BV, EF

alveolar epithelium ---type I alveolar cell: LM: flattened, 0.2µm, with round nucleus EM: plasmalemmal vesicles Function: constitute the blood-air barrier

---type II alveolar cell: LM: scattered, 5-8/per alveoles. cuboidal or round, with round nucleus, pale- stained, foamy cytoplasm.

EM: microvilli, mitochondria, lysosome, RER, Golgi secreting granules: lamellar body contains: phospholipid, glycosaminoglycan and protein lamellar body

Function: i. secreting surfactant ii. differentiated into type I alveolar cell

alveolar septum The interalveolar septum contains alveolar capillaries,elastic fibres,fibroblast, and macrophages. pulmonary macrophages: belong to the mononuclear phagocyte system. dust cell: macrophage which phagocytose carbon or duct particles.

alveolar pore ---balance the air-pressure between alveoli ---lober pneumonia- bacteria or inflammatory spread through the pore

Blood-air barrier The structure through which the gaseous exchange takes place. components: a layer of liquid type I alveolar cell and basement membrane connective tissue capillary endothelial cell and basement membrane

Questions 1.Describe the structure and function of the trachea. 2. Describe the structure and function of two types of alveolar epithelial cells. 3.Name the components of the blood-air barrier.