Dr Dalia El Marakby 1 RESPIRATORY SYSTEM • The respiratory system consists of 2 lungs + many tubes. • The respiratory system is divided into: I- Conducting portion. II- Respiratory portion. I- Conducting Portion : It has two functions: 1- Conduction of air: 2- Conditioning of inspired air: - provided with cartilage + collagen fibers to: * Prevent collapse. * Ensure continuous supply of air. - provided with elastic fibers + smooth muscles for: flexibility and extensibility Clean, moist & warm by: - The pseudostratified columnar ciliated with goblet cells. -The vascular network, serous & mucous glands in the C.T. under epithelium • It includes nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles. II - Respiratory Portion: • Functions: It is the site of gas exchange between blood and inspired air. • It includes respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.
2 I. CONDUCTING PORTION NASAL CAVITIES • The nasal cavity consists of the external vestibule and the internal nasal fossae. 1- The Vestibule 2- The Nasal Fossae * Is the anterior dilated portion of the nasal cavity. * They are two chambers separated by bony nasal septum. * Lined with hairy keratinized stratified squamous epithelium , the epithelium has thick short hairs (vibrissae) that filter out large particles from the inspired air. *Deeper epithelium changed to non-keratinized stratified squamous. * Extending From the lateral wall of each nasal fossa 3 bony shelf-like projections ( superior, middle and inferior conchae ). * The middle and inferior conchae are covered with respiratory epithelium . * The superior conchae are covered with olfactory epithelium. * The lamina propria of the conchae: loose C.T. contains large venous plexuses (swell bodies) , mucous & serous glands . * Function: improve the conditioning of the inspired air by increasing the surface area of respiratory mucosa (epithelium & underlying C.T.). N.B . - Allergic reactions and inflammation can cause abnormal congestion of swell bodies of both nasal fossae, limiting air flow. - Epistaxis: Hemorrhage from the nose, arising in the cavity or in sinuses leading into it. The epithelium that lines most of the conducting portion is pseudostratified columnar ciliated with goblet cells (Respiratory Epithelium). Epithelial cell types: Five cell types are recognized.
3 1- Ciliated columnar cells: 2- Mucous goblet cells: 3- Brush cells: 4- Basal cells: 5-Small granule cells: The most abundant cells. The next most numerous. * Columnar ciliated cells (300 motile cilia/cell). *The apical cytoplasm contains basal bodies of cilia & many mitochondria which supply energy for ciliary beating. *Their apical portions are filled with mucin granules . * Columnar cells with abundant apical microvilli . *They have basal afferent nerve . * Small, rounded cells on the basal lamina but do not reach the lumen. *They have numerous basal dense granules. *They push mucus with bacteria & dust in one direction outwards *They secrete mucus that covers the epithelium and traps bacteria & dust particles. *They act as sensory receptors. *They are stem cells that replace other cell types. *They are neuroendocrine cells belonging to APUD . *Secrete hormones like serotonin and catecholamines that control diameter of airways & blood vessels and regulate mucous and serous secretions . • N.B. In smokers , there is accumulation of mucus in the small airways. This is occurring either due to reversed ratio between ciliated cells and goblet cells or paralysis of the cilia. Olfactory Area • It covers the roof & superior conchae of the nasal cavities. • It is lined by olfactory mucosa = olfactory epithelium + lamina propria of C.T . A- Olfactory epithelium: • It is the neuroepithelium responsible for smell sensation. • It is a modified pseudostratified columnar ciliated epithelium but with no goblet cells . • It is much thicker than respiratory epithelium . Formed of 3 types of cells
4 1- Olfactory neurons 2- Sustentacular (supporting) cells 3- Basal cells * Bipolar nerve cells . * Tall columnar cells with wide cylindrical apexes& narrow bases. * Small pyramidal cells . *The level of their nuclei is between those of supporting and basal cells. *Their dendrites end in olfactory swelling (olfactory vesicle) with multiple basal bodies, from which arise cilia. * Cilia are few , very long, non-motile. They increase surface area for odorous substance. * Axons of the cells pass to the lamina propria where they form the olfactory nerve fibers. * Apical microvilli submerged in a fluid layer. *Cytoplasm contains apical yellow lipofuscin granules which gives olfactory mucosa its yellow color * Junctional complexes bind supporting cells to olfactory cells. * They have basophilic cytoplasm (free ribosomes) and round nuclei. * They are stem cells for both sensory and supporting cells. Diagram of olfactory epithelium. A . shows details of area squared in B . Olfactory cilia Microvilli Junctional complex Axon Sustentacular cell Basal cell Dendrite Olfactory receptor cell B A
5 B- Lamina propria: • It is a dense C.T that contains: a- Olfactory nerve bundles . b- Bowman’s glands that secrete serous fluid that passes through ducts to the surface. This fluid act as medium around the olfactory cilia where the odorous substances dissolve. N.B. Olfactory neurons are the only neurons that can highly regenerate due to high capacity of stem cells. Differences between Respiratory & Olfactory Mucosa: Olfactory Mucosa Respiratory Mucosa 1. E pithelial thickness Thicker Thinner 2. Goblet cells Absent Present 3. Cilia olfactory cells have few long non motile cilia Has numerous true cilia 4 . Basement membrane Thin Thick 5. Bowman ’ s glands Present Absent 6. Pigment . Present in sustentacular cells Absent PARANASAL SINUSES • They are paired closed cavities in the frontal, maxillary, ethmoid and sphenoid bones of skull. • They are lined with thinner respiratory epithelium with few goblet cells . N.B. Sinusitis is an inflammation of the sinuses. It may be acute or chronic. NASOPHARYNX • It is the first part of the pharynx. • It is lined with respiratory epithelium + lamina propria contains mucous glands , pharyngeal tonsils & openings of the 2 Eustachian tubes.
6 LARYNX • It connects the pharynx with the trachea.is lined with : 1- Respiratory epithelium except the true vocal cords and lingual surface of epiglottis which are covered with stratified squamous epithelium. 2- Lamina propria contains laryngeal cartilages. Laryngeal cartilages Large cartilages Thyroid, cricoid, and most of the arytenoids hyaline cartilages Calcify with age Small cartilages Epiglottis, cuneiform, corniculate and the tip of the arytenoids elastic cartilages. Don ’ t calcify Vocal Cords • The vocal cords include two pairs of folds that extend in the lumen of larynx. False vocal cords (vestibular folds) True vocal cords The upper pair The lower pair 1-lining Respiratory epithelium. Non keratinized stratified squamous epithelium. 2- function Prevent food & fluid from entering larynx. Production of voice Functions: 1-Production of voice by the true vocal cords. 2-Prevent food and fluid from entering the respiratory passages by epiglottis & false vocal cords. 3-Maintain open air way by the laryngeal cartilages. TRACHEA • It is about 12 cm long. • It extends from the larynx to the bifurcation into 2 primary bronchi. • Its wall is formed of 4 layers:
7 1-Mucosa: a) Epithelium: Respiratory epithelium (pseudostratified columnar ciliated with goblet cells) b) Lamina propria: loose C.T with elastic fibers . c) Elastic membrane: condensation of elastic fibers . 2- Submucosa: Loose C.T containing lymphoid nodules and mucous & serous glands. 3-Fibrocartilaginous coat: *Dense C.T contains 20 C- shaped (incomplete) rings of hyaline cartilage (keep the trachea always open). *The gaps between the free ends of the rings face the esophagus posteriorly and are bridged by fibroelastic ligament (prevents overdistension) and by smooth trachealis muscle bundles (constrict the lumen and increase the force of air flow during coughing and forced expiration). 4- Adventitia: loose C.T. Muco Epithelium Pseudo.str. colu. Cil with goblet. Lamina propria Elastic membrane Submucosa Tracheal glands Lymphatic nodule Fibro cartilagenous layer
8 Bronchi and Bronchioles * The trachea divides into 2 primary or extrapulmonary bronchi which have the same structure as trachea . *Primary bronchi penetrate the hilum of each lung forming intrapulmonary or secondary bronchi that divide giving rise to bronchioles Differences between Extrapulmonary & Intrapulmonary bronchi Extrapulmonary bronchus Intrapulmonary bronchus Lumen Wider & less folded . Narrower & more folded Mucosa: Lining elastic membrane *Lined with pseudostratified columnar ciliated epithelium with many goblet cells. *Separates mucosa from submucosa. *The same epithelium with less goblet cells. *Absent but lamina propria is rich in elastic fibers & lymphatic follicles. Submucosa Present Absent Cartilage C-shaped (incomplete) rings of hyaline cartilage multiple plates of hyaline cartilage in adventitia Smooth muscles Present posteriorly at the ends of C-shaped cartilage. Arranged spirally & encircle the whole lumen Mucoserous glands and lymphatic nodules In the submucosa In the adventitia in between the cartilage plates Differences between Intrapulmonary bronchi &bronchioles Intrapulmonary bronchus Bronchiole Mucosal epithelium: pseudostratified columnar ciliated epithelium with few goblet cells Simple columnar or cuboidal ciliated with Clara cells (no goblet cells) Cilia gradually disappear as the bronchioles become smaller. Musculosa: Less developed spirally arranged smooth muscles. Its contraction → short and less bronchial diameter More developed, circularly arranged smooth muscles. Its contraction controls the flow of air to sites of gas exchange.
9 Adventitia: Cartilage plates Mucoserous glands Lymphatic nodules Present Present Present Absent Absent Absent N.B. Bronchitis is inflammation of the mucous membrane of the bronchi which appears congested with swollen mucous glands. Clara cells: - L.M. Dome shaped, non-ciliated cells. - E.M. basal r-ER and apical s-ER, mitochondria, Golgi & glycoprotein granules. -Functions: 1- Secretion of a surfactant like material which reduces surface tension of bronchioles and maintains their patency (sER& golgi). 2- Protection of bronchiolar epithelium via glycoproteins in their granules (rER & Golgi). 3- Protection against emphysema by inhibiting macrophage- secreted proteases & elastase. 4- Degradation of toxins in the inhaled air (sER). 5- Act as stem cells for other types. N.B. Bronchial Asthma is an allergic condition, in which spasm of bronchiolar smooth muscle causes constriction of bronchioles and difficulty during respiration. II. RESPIRATORY PORTION The wall of this part enables the gas exchange. It includes:
10 Alveolar epithelium if formed of 2 types of cells: type I & II pneumocytes 1.Respiratory bronchioles: 2. Alveolar ducts: 3. Alveolar sacs: 4. Alveoli: *The region of transition between the conducting portion and respiratory portion. Mucosa: * Epithelium: simple cubical ciliated with Clara cells, cilia absent in distal portion. * C.T. corium: rich in elastic fibers Musculosa: thin layer of smooth muscle fibers. Adventitia: loose C.T. *The wall is interrupted with the openings of some alveoli, where gas exchange occurs. * The free terminations of respiratory bronchioles. * Lined Completely by openings of alveoli & alveolar epithelium * Smooth muscles are present at the openings of alveoli. * Group of adjacent alveoli opens into a common central space. * Lined with alveolar epithelium. * No muscle. * The structural and functional units of gas exchange. * Open into alveolar sacs, alveolar ducts & respiratory bronchioles. * Lined with the alveolar epithelium . *Between their walls there are alveolar pores (of Kahn). These pores equalize pressure between alveoli & provide collateral circulation of air when a bronchiole is obstructed.
11 N.B. Respiratory Distress Syndrome: Deficiency of pulmonary surfactant is associated with premature labour leading to respiratory distress. Interalveolar walls (septa): These are delicate septa separating adjacent alveoli . *Formed of loose C. T. containing: • have the richest capillary network in the body. • For gas exchange • Elastic fibers • to allow expansion of the lung during inspiration. • Reticular fibers • to support lung tissue and prevent over-expansion that may injure the delicate blood capillaries. • Extravasated leucocytes especially monocytes • monocytes act as alveolar phagocytes. Type I pneumocvtes (squamous alveolar cells): Type II pneumocytes (great alveolar cells): *Percentage 97% 3% *LM: *Flat squamous cells *Flat nuclei. * Little cytoplasm. * Cuboidal cells bulging in air spaces. * Central round nucleus . * Foamy cytoplasm . *EM: *Functions: * Few organelles around the nucleus . * Small pinocytic vesicles (turnover of pulmonary surfactant. - Tight junctions with type I& II . 1-Provide a very thin membrane for gas exchange . 2-Prevent leakage of tissue fluid into the alveolar cavity by tight junction. * Rich in mitochondria, ribosomes, rER and . " secretory cells body “ Golgi developed - well * Membrane bound multilamellar bodies (cytostomes) *Free surface with short microvilli. 1- Secretion of pulmonary surfactant , for both types. tem cells S - 2
12 N.B. Emphysema is abnormal permanent enlargement of the alveoli. It results from the destruction of the inter-alveolar septa by proteases and elastases secreted by lung macrophages (dust cells). It is mainly caused by cigarette smoking that inhibits the protein responsible for destruction of those proteases and elastase. Blood-air barrier: • It represents the structures through which gas exchange occurs. • It comprises four layers: 1 – Film of pulmonary surfactant on the alveolar surface. 2 – Cytoplasm of type I pneumocytes. 3 – Fused basal lamina type I pneumocytes and capillary endothelial cells. 4 – Cytoplasm of endothelial cells of blood capillaries. Alveolar Phagocytes: Dust cells: Heart failure cells: Origin Blood monocytes Site bulging from the interalveolar wall or free inside alveoli. Function Engulf dust Engulf RBCs in congestive heart failure Cytoplasm dust particles brick red color Hemosiderin granules Stain Vital stain e.g. trypan blue Fate a-Migrate into bronchioles to be coughed in the sputum. b-Exit the lung through lymphatic drainage. c-Remain in the interalveolar septa. Components of the interalveolar wall and blood-air barrier. Elastic fibers Blood-air barrier Type I pneumocyte Type II pneumocyte Alveolar macrophage Reticular fibers Blood capillary Endothelium of blood capillary
13 Pleura: • Serous membrane which has 2 layers: visceral pleura: covering the lungs parietal pleura: lining thoracic cavity • Both layers are lined by: flat mesothelial cells + loose C.T. rich in elastic fibers. • The 2 layers are separated by a thin film of fluid to: 1- Lubricate the sliding movement. 2- Reduce friction between the lung surfaces and the thoracic walls during respiratory movements. Fetal lung: • The lung has no function in fetus, so it is collapsed in the intrauterine life. • It is characterized by: 1 – Its lobes and lobules are clear due to presence of thick C.T. septa. 2- The fetal lung is similar to gland (branches of bronchiolar tree are similar to ducts and alveoli are similar to acini ). 3-The alveoli are collapsed and lined by simple cubical epithelium . 4-Its bronchi and bronchioles are folded . 5- The cartilage plates are present around the bronchi, and this differentiates fetal lung from a gland. 6- pulmonary blood vessels are congested . 7- Lung sinks in water & this has a medicolegal importance . Structural Changes in the respiratory airway: 1) Epithelial changes: decrease gradual in thickness. 2) The lamina propria decreases gradual in thickness. 3) Cilia and Goblet Cells: decreases gradual. goblet cells are stopped before cilia as the produced mucus should be cleared by the cilia. 4) Serous & mucous glands decreases gradually. 5) Cartilage changes: decrease gradually then disappear. 6) Smooth Muscle changes: In trachea: Trachealis at the free ends of C-shaped cartilage In intra pulmonary bronchi: spirally arranged. In bronchioles: circularly arranged. In alveolar ducts: at the openings of alveoli. In alveolar sacs: completely absent.