Respiratory System

BIO 408

Histology

Dr. D. L. Daley

Overview: Respiratory System

n Composed of the lungs and airways leading to the external environment

n Breathing or ventilation - movement of air into & out of the lungs

n External respiration - exchange of O₂ in the inspired air for CO₂ in the blood

n Transport of gases - conveyance of O₂ and CO₂ to and from the cells

n Internal respiration - exchange of CO₂ and O₂ in the vicinity of the cells of the body

Nasal Cavity

n Divided into left and right halves by cartilaginous and bony nasal septum

n Each nasal cavity is bounded laterally by a bony wall and a cartilaginous ala (wing) of the nose

n Communication to the outside is via nares or nostrils and via choana with the nasopharynx

n Projecting from the bony lateral wall are three thin, scroll-like bony shelves, situated one above the other

n Superior, middle and inferior nasal conchae

Anterior Nasal Cavity

n Dilated portion of the nasal cavity - vestibule

n Lined with skin that has short stiff hairs called vibrissae - keeps out dust

n Dermis contains numerous sebaceous glands and sweat glands

n Dermis is anchored by numerous collagen bundles to the perchondria of the hyaline cartilage segments that form the supporting skeleton of the ala

Posterior Nasal Cavity

n Lined with pseudostratified ciliated columnar epithelium

n Goblet cell population is very high in the deeper regions of the nasal cavity

Nasal Cavity: Olfactory Region

n Roof of the nasal cavity, the superior aspect of the nasal septum and the superior nasal concha are covered with olfactory epithelium (60 mm thick)

n Appears yellow in the living person

n Composed of three cell types

n Olfactory, sustentacular and basal cells

Olfactory Cells

n Bipolar neurons whose apical aspect, the distal terminus of a slender dendrite, is modified to form a bulb. the olfactory vesicle

n This projects above the surface of surrounding sustentacular cells

n Scanning EM reveals 6 to 8 long nonmotile olfactory cilia extended from the olfactory vesicle and lie on the free surface of the epithelium

Sustentacular & Basal Cells

n Sustentacular cells - 50-60 mm tall columnar cells

n Have granules with yellow pigment

n These cells probably provide physical support, nourishment and electrical insulation for the olfactory cells

n Basal cells - short pyramid-shaped cells - apical aspect does not reach the the epithelial surface

n Capable of replacing olfactory and sustentacular cells

Paranasal Sinuses

n The ethmoid, sphenoid, frontal and maxilla bones of the skull have large mucoperiosteum-lined spaces called paranasal sinuses - these connect with the nasal cavities

n Epithelium is ciliated columnar and the cilia normally sweep the mucous layer toward the nasal cavity

Pharynx

n The pharynx begins at the choana and extends to the opening of the larynx

n Three regions

n Superior nasopharynx

n Middle oral pharynx

n Inferior laryngeal pharynx

n Nasopharynx is lined with a respiratory epithelium

n The oral and laryngeal regions are lined with stratified squamous epithelium

Larynx

n The larynx is positioned between the pharynx and the trachea

n Responsible for phonation and prevents entry of solids or liquids into the trachea

n The wall of the trachea is reinforced by several hyaline cartilages (unpaired thyroid and cricoid cartilages) & the inferior aspect of the paired arytenoids and the elastic cartilages (unpaired epiglottis, the paired corniculate and cuneiform cartilages) and the superior aspect of the arytenoids

Larynx

n Cartilages of the larynx are held together by ligaments and their movements are controlled by intrinsic and extrinsic muscles

n Lumen of the larynx has two pairs of shelf-like folds, superior positioned vestibular folds and inferiorly placed vocal cords (free edge (vocal fold) reinforced with dense regular connective tissue (vocal ligament)

n During phonation the vocal folds are strongly adducted, forming a narrow slit between them

n Lined with pseudostratified ciliated columnar epithelium

Trachea

n 12 cm long & 2 cm wide tube - begins at the cricoid cartilage and ends when it bifurcates into the primary bronchi

n Wall is reinforced by 10 to 12 horseshoe shaped hyaline cartilage rings (c rings)

n The open end of the rings faces posteriorly and are connected to each other by smooth muscle (trachealis muscle)

n Contraction of the trachealis muscle decreases the diameter of the trachea - speeds up air flow - during coughing to remove foreign matter from the passage way

Tracheal Mucosa

n Composed of pseudostratified ciliated columnar epithelium and a subepithelial connective tissue (lamina propria) and a relatively thick bundle of elastic fibers separating the mucosa from the submucosa

n Six cell types

n Goblet cells, ciliated columnar cells, basal cells, brush cells, serous cells and DNES (diffuse neuroendocrine system) cells - all of these cells touch the basement membrane

Cells of the Tracheal Mucosa

n Goblet cells - 30% of total - produce mucinogen which when hydrate is called mucin

n Narrow base (stem) and a expanded theca containing the secretory granules

n Ciliated columnar cells - 30% of total - tall and slender - have cilia and microvilli on their apical surfaces - move the mucus along

Cells of the Tracheal Mucosa

n Basal cells - short cells - 30% of total - considered to be stem cells

n Brush cells - 3% of total - small granule mucus cells - narrow columnar cells with tall microvilli - function unknown

n Serous cells - 3% of total - columnar cells - dense secretory granules - unknown function

n DNES cells (diffuse neuroendocrine system) - 3% to 4% of total - small granule cells - numerous granule in the basal cytoplasm - release pharmacological agents thought to control the functioning of the other cells

Submucosa and Adventia of the Trachea

n Submucosa - dense irregular connective tissue - many mucous and seromucous glands - ducts open onto the epithelial surface

n Rich blood supply and lymphoid elements

n Adventia - fibroelastic connective tissue

n C rings the most prominent feature

Bronchial Tree

n Begins at the bifurcation of the trachea as right and left primary bronchi (extrapulmonary bronchi)

n The primary bronchi arborize to form a tree-like array of air tubes that decrease in size

n Intrapulmonary - secondary bronchi serve a lobe of the lung

n Each secondary bronchi subdivides into smaller branches called tertiary bronchi

Bronchial Tree

n Each tertiary bronchi arborizes but leads to a bronchopulmonary segments (discrete section of the lung)

n Each lung has 10 bronchopulmonary segments that are completely separate from one another by connective tissue

n All of these tubes have irregular plates of cartilage rather than c rings

Bronchioles

n No hyaline cartilage in their walls - less than 1mm in diameter

n A bronchiole or primary bronchiole supplies air to a pulmonary lobule

n Considered the 10th to 15th generation of dichotomous branching of the bronchial tree

n Clara cells - columnar cells with dome shaped apices with short blunt microvilli

n Produce protective secretion, degrade toxins & can regenerate the epithelium

Terminal Bronchioles

n Each bronchiole subdivides to from several smaller bronchioles - less than 0.5 mm in diameter - the terminus of the conducting portion of the respiratory system

Respiratory Bronchioles

n Similar to terminal bronchioles but heir wall is interrupted by thin-walled pouch-like structures called alveoli

n This is the first place where gas exchange can occur

n As these divide they become narrower in diameter and their population of alveoli increases

n They eventually terminate in an alveolar duct

Alveolar Ducts, Atrium and Alveolar Sacs

n Do not have walls of their own, rather they are merely linear arrangements of alveoli

n Each duct ends in a blind out-pouching composed of two or three clusters of alveoli (cluster know as an alveolar sac)

n These sacs open into a common space called the atrium

n Slender connective tissue between alveoli is called the interalveolar septa (reinforce the duct)

n Fine elastic fibers encircle the alveolar ducts and sacs

Alveolus

n Small outpouching about 200mm in diameter of the respiratory bronchioles, alveolar ducts and alveolar sacs

n The primary unit of gas exchange

n About 300 million - give the lungs its spongy nature

n The total surface area for gas exchange is estimated at 140 m² (size of a average two bedroom apartment)

n Surrounded by capillaries needed for gas exchange with the blood

Alveolus

n Type I Pneumocytes - 95% of the alveolar surface is composed of these squamous epithelial cells

n Very thin cells - only 80nm in width

n Form occluding junctions with one another - no seepage of extracellular fluid into the alveolus

Alveolus

n Type II pneumocytes - 5% of the total surface

n Cuboidal cells that are interspersed among and form occluding junctions with Type I pneumocytes

n Have short apical microvilli

n Show membrane bound lamellar bodies that contain the pulmonary surfactant that these cells secrete

n Surfactant - two phospholipids, dipalmitoyl phosphatidycholine & phosphatidylglycerol & for unique proteins, surfactant proteins A, B, C and D

Alveolar Macrophages

n Also called dust cells

n Migrate between type I pneumocytes and enter the lumen of the alveolus

n Phagocytose duct particles and bacteria

n About 100 million macrophages migrate tot he bronchi and are transported via cilia tot he pharynx to be swallowed or expectorated

Interalveolar Septum

n Region between two adjacent alveoli - lined with alveolar epithelium

n May be very narrow and house only a continuous capillary & its basal lamina or it may be wider with connective tissue elements

Pleural Cavities

n The thoracic cavity is separated into three regions

n Left and right thoracic (pleural) cavities and a centrally located mediastinum (Heart, great vessels, trachea, esophagus, thymus & lymph nodes)

n The lining is a serous membrane, the pleura

n Composed of simple squamous epithelium and a subserous connective tissue

n The visceral pleura covers and adheres to the lung and the remainder of the pleura , the parietal pleura, lines and adheres to the walls of the thoracic cavity