I.                 Introduction

A.     Upper conducting portion

§  Extrapulmonary nasal cavity, nasopharynx, larynx, tracheas, bronchi, and intrapulmonary bronchi, bronchioles, terminal bronchioles

§  Function: provide conduit for air to travel to and from lungs

§  Function: to condition inspired air

§  Cartilage (hyaline) and collagen fibers, smooth muscle provide rigid structural support, flexibility, extgensiliblity to ensure an uninterrupted supply of air

§  Cartilage in periphery of lamina propria in C-shaped rings, irregular rings, and small plaques:  support walls and prevent collapse of lumen

§  Rich in elastic fibers that are oriented longitudinally.

§  Bundles of smooth muscle found from trachea down to alveolar ducts, contraction of muscle reduces diameter of conducting tubes and restricts airflow

§  Passages lined with ciliated pseudostratified columnar epithelium = respiratory epithelium

does not mediate gas exchange

function: cleanse, moisten, warm air before enters lungs

§  Lamina propria contains serous and mucous glands, also rich superficial vascular network

§  Goblet cells producing rich mucous secretion are abundant in upper portions

§  Number of goblet cells, ciliated epithelium, and cartilage decrease as conducting tubes proceed into respiratory portion

§  Smooth muscle and elastic fibers progressively increase

B.     Respiratory epitheilum

§  Ciliated pseudostratified columnar epithelium à simple columnar à simple squamous (alveoli)

§  Rich goblet cell population tapers off in smaller bronchi and absent from terminal bronchioles

§  Ciliated cells continue beyond goblet cells, preventing accumulation of mucous

§  Cilia move fluid and mucus toward oral cavity where its is swallowed or expectorated

§  5 cell types:

§

Ciliated columnar cells	Most abundant Each cell has 300 cilia on apical surface Many apical mitochondria provide energy for beating
Mucous goblet cells	Contain polysaccharide-rich mucous droplets
Brush cells	Have many microvilli on apical surface Afferent nerve endings on basal surfaces Considered to be sensory receptors
Basal (short) cells	Small round cells that lie on basal lamina but do not extend to lumnal surface Belived to be generative cells and give rise to other cell types by mitosis
Small granule cells	Resemble basal cell Contain numerous dense granules Constitute part of diffuse neuroendocrine system

C.    Respiratory Portion

§  Consists of alveolar ducts, sacs, pore

§  Exchange of gases occurs between alvelolar and capillary lumen across sqamous epithelium of alveolar pneumocyte and capillary endothelium

	Conducting							Respiratory
	nasal	larynx	trachea	Large Bronchi	Small Bronchi	Large bronchioles	Small Bronchioles	Alveoli
Epithelium	Pseudo/ Columnar	Pseudo/ Columnar	Pseudo/ Columnar	Pseudo/ Columnar	Pseudo/ Columnar	Pseudo/ Columnar	Pseudo/ Columnar	Simple/ Sqamous
Cilia	many	many	many	many	many	many	many	None
Goblet	many	many	many	some	little	little	none	None
Glands	many	many	Some	some	little	none	none	None
Cartilage	little	little	many	some	little	none	none	None
Muscle	none	none	Little	little	little	some	little	None
Elastic	none	little	Little	some	some	some	some	Many

II.               Nasal cavity

§  As air enters into vestibule of nose, large specialized hairs (VIBRISSAE) remove large dust particles

§  Inside nasal cavity or fossa a layer of mucus traps particulate material

§  Nasal epithelium are ciliated pseudostratified columnar

§  Scattered mucus secreting goblet cells

§  Microvillion on luminal surface

§  Lamina propria:

Many mucus and serous gland

Variable numbers of immune cell (lymphocytes, plasma cells, macrophages)

Extensive network of blood vessels plays major role in warming inspired air

Also Smooth muscle

§  Bony lateral projections from nasal septum, CONCHAE, create narrow, ribbon like passages and incrase SA of epithilium and increase conditioning of air

§  Epithelium covering superior conchae is a specialized olfactory epithelium

§  Within lamina propria of conchae are large venous plexuses known as SWELL BODIES, become engorged with blood every 20-30 minutes and cause decrease in air flow, decreasing desccation of respiratory epithelium

§  Allergic reactions and inflammation can cause abnormal engorgement of swell bodes and  restrict airflow

III.              Larynx

§  Tube that connects pharnx to trachea

§  Laryngeal cartilages found within lamina propria, most of cartilages are hyaline, some smaller ones are elastic

§  Epiglottis projects from rim of larynx extending into pharynx.

§  Lingual surface of epiglottis covered by stratified sqamous epithelium that transistions to ciliated pseudostratified columnar epithelium on laryngeal side.

§  Mucous and serous gland are also present in lamina propria.

§  Below epiglottis, mucosa form two pairs of fold that extend into lumen of larynx.

§  Upper pair are FALSE or VESTIBULAR VOCAL CHORDS and are covered by ciliated pseudostratified columnar epithelium beneath which are numerous serous glands.

§  Lower flolds are TRUE VOCAL CHORDS: large bundles of elastic fibers composing vocal ligaments lie within. Parallel to ligaments are bundles of skeletal muscle, the VOCALIS muscle, stratified sqamous epithelium.

IV.             Trachea

§  Thin walled tube approx. 10 cm long entending from larynx to point at which it divides into two main bronchi

§  Tube is lined with typical respiratory epithelium

§  In lamina propria, 16-20 C- shaped rings of hyaline cartilage that keep tube open.

§  Fibroeleastic cartilage and bundle of smooth muscle (trachealis muscle) bridge two ends of cartilage

§  Contraction of this muscle narrows lumen and is used in cough reflex

V.               Bronchial tree

§  Trachea divides into two PRIMARY BONCHI

§  After entering lungs, primary bronchi give rise to LOBAR BRONCHI which supply a PULMONARY LOBE

§  There are 3 lobar bronchi in right lung and two in left

§  Lobar bronchi divide repeatedly givig rise to smaller bronchi whose termini are the BRONCHIOLES

§  Each bronchiole enters a  PULMONARY LOBULE where it branches to form 5-7 TERMINAL BROCHIOLES

§  Primary bronchi histologically resemble trachea, however, as one proceed toward respiratory portion the epithelium and lamina propria become simplified

A.     Bronchi

§  as diameter decreases, cartilage rings replaced with isolated plates or island of hyaline cartilage

§  lamina propria have bundles of smooth muscle which become more prominent near respiratory zone

§  lamina propria lso contains many elasti fibers, abundant mucous and serous glands and many lymphocytes along with lymphatic nodules

B.     Bronchiles

§  Intralobar airways with diameter of 5 mm or less

§  Mucosa contains no glands or cartilage

§  Inlarger bronchioles, epithelium is ciliated peudostratified columnar, which decrease in height  to become ciliated simple columnar or cuboidal epithelium in terminal bronchioles

§  Within terminal bronchioles epithelium contains CLARA cells

§  Cells have no cilia but contain secretory granules and secrete glycosaminoglycans protect epithelium

§  Lamina propria contains mainly smooth muscle and elastic fibers

C.    Respiratory Brochioles

§  Each terminal bronchiole divides into 2+ respiratory bronchioles

§  This is where conducting portion transitions into respiratory portion

§  Mucosa of respiratory bronchioles resembles that of terminal bronchioles except walls are interrupted by numberous saccular ALVEOLI where gas exchange occurs.

§  Art rim of alveolar openings ciliated cuboidal epithelium becomes continuous with sqamous alveolar lining cells

D.    Alveolar Ducts

§  As number of alvelolar openings increases to point that bronchial wall disappears the tube is called alveolar ducts.

§  Sqamous alveolar cells line alveolar duct and alveoli

§  Lamina propria around rim of alveoli and network of smooth muscle cesll that appear as knows between adjacent alveoli

§  Smooth muscle disappears at distal ens of alveolar ducts.

§  Alveolar ducts open into atria which communicate with alveolar sacs.

§  Complex networks of elastic and reticular fibers encirlce atria, alveolar sacs, and alveoli

E.     Alveoli

§   Sac like structures about 200 mM in diameter

§  300 million with surface area of 140 m² form spongy structure of lungs

§  within these structures, oxygen and carbond dioxide are exchanged between air and blood

§  structures of alveolar wall are specialized  to serve ths function

§  each alveoli walllies between two neighbouring alveoli and is call:

INTERALVEOLAR SEPTUM.

§  An alveolar septum consits of two thin sqamous epithelial layers between which lie capillaries, fibroblast,elastic and reticular fibers and macrophages

§  Capillaries and CT form interstitium, which contains richest network of capillaries whin in body.

§  May contain one or more pores known as PORES OF KOHN- connect neighbouring alveoli and equalize pressure or allow collateral circulation when alveolus is blocked.

§  Alvelolar macrophages canalso pass through these pores.

§  Air in alveoli is separatedfromblood in the capillary by three components called BLOOD-AIR BARRIER: surface and cytoplasm of alveolar cells, fused basal laminae of alvelolar cells, and capillary endothelial cells, and cytoplasm of endothelial cells

§  Reticular fibers within septum act as support for anastomising capillary network.

§  Oxygen from alveolar air diffuses thru layers of alveolar septum whilst carbon dioxide diffuses in opposite direction.

§  Interalvelolar septum consists of 5 main cell types

Capillary endothelial cells	Very thin and non fenestrated
Type I alveolar (sqamou)s pneumocytes	Very attenuated cells making up 97% of alveolar surface All have desmosomes and tight occluding junctions So form as gas permeable barrier of minimal thickness
Type II pneumocytes	Interspersed among type I cells Roughly cuboidal and ;usually found in groups of 2-3 At points where alvelolar walls unite and form angles Resemble secretory cells with well developed golgi network and microvilli on apical       surface Have foamy, vesicular cytoplasm caused by presence of amellar bodies containg lipid, glycosaminoglycans and protein lamellar bodies continuously synthesized and released from apial surface providing alveolar coat of PULMONARY SURFACTANT that lowers alvelolar surface tension.
Interstitial cells	Including fibroblasts and mast cells Fibroblat synthesize collagen, elastic fibers and GAG Collagenand elastic fibers add resilience and elasticity to mechanical properties of lungs
Alveolar macrophages or DUST cell	Derived from monocytes Can be found in interior of septum or on surface of alveolus Often contain large amounts of carbon and dust which they phagocytose from alveolar lumen

VI.             Pulmonary blood vessels

§  Circulating in lungs includes systemic bronchial system  which follows bronchial tree and supplies nutrients to lung tissue up to respiratory bronchioles

§  At this point these vessels anastomose with small branches of pulmonary artery and return blood via pulmonary vein

§  Bronchial arteries branch from aorta and carry blood at systemic pressure

§  Bronchial arteries have smaller lumens and thicker walls than pulmonary arteries, their wall contain a distinct elastic lamina and muscular media

§  Functional circulation in lungs is composed of pulmonary vessels.

§  Pulmonary arteries are low pressure vessels with thin walls

§  Vessels have internal elastic lamina, smooth muscle and elastic fibers

§  Within lung, pulmonary artery braches following the bronchial tree

§  At level of alvelolar duct, braches form capillary network in interalveolar septum

§  Venules originate from capillaries and enter interlobular septum, finally leaving lobule to follow bronchial tree to hilum

VII.           Pulmonary lymphatic vessels

§  Follow bronchi and pulmonary vessels and can occur in interlobular septum

§  All drain into lymphnodes at hilum

§  No lymphatics in terminal portion of bronchial tree or beyond the alveolar ducts.

VIII.          Pleura

§  Serous membrane covering lungs

§  Consists of two layers:  parietal and visceral, which are continuous with hilum

§  Both membranes consists of thin sqamous mesothelium resting on connective tissue layer containing collagen and elastic  fibers.

§  Under normal circumstances spaces between these two layer is filled with layer of fluid that acts as a lubricating agent.

Tags: alveolar ducts, alveoli, and intrapulmonary bronchi, bronchi, Bronchiles, bronchioles, Cartilage, Cilia, Epithelium, Extrapulmonary nasal cavity, Goblet, lamina propria, larynx, lymphnodes, Lymphocytes, nasal cavity, nasopharynx, plasma cells, Pulmonary lymphatic vessels, Respiratory System, sacs, terminal bronchioles, Trachea, tracheas

This entry was posted on Saturday, February 21st, 2009 at 5:07 am and is filed under Histology. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.