Histology                                                                                                                     Stanley Shostak
BioSc 1450                                                                                                                  Spring 05
 

Lecture 11. Respiratory System

Mechanical respiration: process by which oxygen is absorbed from the atmosphere into the blood vascular system and carbon dioxide is excreted into the atmosphere ? occurs in respiratory system

conducting system: single tube divides repeated to form airways of ever decreasing diameter

transport of inspired and expired gases btwn atmosphere and circulatory system

interface: passive exchange of gases btwn atmosphere and blood

alveoli: blind-ended sacs; sites of gas exchange; constitute bulk of lung tissue; thin-walled structures enveloped by rich network of capillaries = pulmonary capillaries

Upper Respiratory Tract

filtering, humidifying and adjusting temperature of inspired air; lined by pseudostratified columnar epithelium with numerous goblet cells (respiratory epithelium), supported by loose collagenous layer = lamina propria (with numerous glands)
 

MALT = mucosa-associated lymphoid tissue

DM-ALT = diffuse mucosa-associated lymphatic tissue
BALT = bronchiolar-associated lymphatic tissue
(also GALT = gut-associated lymphatic tissue)
respiratory mucous membrane or respiratory mucosa: = lamina propria + respiratory epithelium
submucosa: supporting layer separates mucosa from underlying structures nasal cavity: receptors for sense of smell; divided by nasal septum; bones projecting into nasal cavity and paranasal sinuses = turbinate system; increased surface area > filter particulate matter; thin-walled veins in lamina propria comprise heat-exchange system and serous glands in lamina propria provide humidifier  
nasal mucosa: pseudostratified columnar cilated epithelium; numerous goblet cells suppored by richly vascular lamina propria containing serous and mucous glands; mucosa similar to that of nasal cavity

nasal vestibule: entrance each cavity; lined by skin with short, coarse vibrissae; mucosa similar to that of nasal cavity
 

 paranasal sinuses: act as resonance chambers for speech (also reduce bony mass of facial skeleton); mucosa similar to that of nasal cavity   nasopharynx: connected via auditory (Eustachian) tubes to middle ear cavities; mucosa similar to that of nasal cavity   pharynx: separates upper and lower respiratory tracts Lower Respiratory Tract: gradual transition respiratory epithelium: 'mucocillary escalator' from tall, pseudostratified columnar, ciliated, to simple, cuboidal, non-ciliated; goblet cells numerous in trachea, decrease in number and absent in terminal bronchioles; K (Kulchitsky) cells neuroendocrine system: serotonin, bombesin & calcitonin
Clara (bronchiolar epithelial cells: nonciliated);
particulate matter trapped in surface mucus secreted by goblet cells and mucous glands in lamina propria; coordinated wave-like beating of cilia propels mucus upward lamina propria: fibroelastic tissue; lymphoid aggregations of variable size; (M-A LT) mucosa-associated lymphoid tissue; production of IgA class antibodies secreted onto mucosal surface smooth muscle: sympathetic activity causes smooth muscle relaxation and thus dilation of airways; parasympathetic activity causes constriction, reducing "dead space."

submucosal layer: contains serous and mucous glands above level of tertiary bronchi

cartilage: larynx, trachea and bronchi; outside submucosa; absent below level tertiary bronchi

adventitia: CT merges with surrounding

serosa: CT and pleural mesothelium of lungs

 Respiratory tree purely conducting portion of tract
  larynx

vocal cords: protect lower respiratory tract against entry of foreign bodies; lined by stratified squamous epithelium

trachea:

trachealis muscle: bands of smooth muscle join free ends of cartilagenous rings posteriorly;

in consequence of irritation from tobacco smoke: epithelium commonly undergoes morphological change (metaplasia) to a stratified squamous form with loss of ciliary action

 left and right bronchi (-us: sing.) = primary bronchi cartilage in plates; submucosa with fewer sero-mucous glands; smooth muscle layer separates submucosa from lamina propria; lamina propria with lg quantity elastin superficially; respiratory epithelium fewer goblet cells; secondary or lobar bronchi

tertiary bronchi or segmental: respiratory epithelium is tall columnar with little pseudostratification and few goblet cells; lamina propria thin, elastic, surrounded by spiraling smooth muscle; serous mucous glands sparse; no cartilagenous plates; submucosa merges with adventitia; small aggregates lymphocytes = diffuse mucosa-associated lymphoid tissue (MALT)

bronchioles: respiratory epithelium simple, columnar and ciliated; few goblet cells; prominant smooth muscle spiral

mast cells: antigen-antibody complexes on surface trigger release of histamine causing smooth muscle constriction and vasodilation leading to mucosal swelling; partly responsible for asthma; less than 1 mm in diameter terminal bronchioles: no goblet cells   respiratory and conducting respiratory bronchioles: noncillary bronchiolar (Clara) cells become predominant type (secretory cell; function unknown); may synthesize components of surfactant

alveolar ducts: long winding; smooth muscle along wall associated with collagen and elastic fibers ringing;

alveolar sacs give rise to several alveoli
 

 purely respiratory alveoli: lined by flattened epithelium; surrounded pulmonary capillaries; wall or alveolar septum consists of flattened alveolar surface epithelium + blood vessels (capillaries: 7 to 10 micro m in diameter) + supporting tissue of delicate collagen (reticulum) and elastin; alveolar pores = small openings about > 8 micro m in diameter; permit equalization of pressure between alveoli, provide collateral air circulation;
surface epithelium: Type I pneumocytes (= alveolar lining cells): thin, large; rarely seen due to attenuation; nuclei small, dense, flattened; part gaseous diffusion barrier; basement membrane may fuse with that of capillary

Type II pneumocyte (= surfactant cell): typically at branching point of interalveolar septum; vesicular nuclei with nucleolus; eosinophilic cytoplasm contains phospholipid (palmitoyl phosphatidylcholine) vesicles in form of lamellar bodies; discharge into alveolar air space contributes to surfactant layer; represent 60%; rounded; occupy about 5% surface area; lg, rounded nuclei with prominent nucleolus and vacuolated cytoplasm; secrete surface-active material called surfactant; reduces surface tension thereby preventing alvolar collapse; capable of cell division in response to damage to alveolar lining

tubular myelin: phospholipid, carbohydrate and protein-containing secretory products

alveolar macrophages or dust cells: in wall or on surface; derived from monocytes; some from cell division

  Dual Blood Supply of Lungs Pulmonary pulmonary artery: enter root or hilus (hila)

arterial vessels

thin-walled; large caliber; histologically elastic arteries rather than muscular; elastic expansion maintains relatively constant presssure throughout cardiac cycle; pulmonary veins extremely thin-walled; wide caliber; bronchial system (to upper tree and plura); small part drains to right side of heart via azygous venous system


last revised: 02-01-05