invaginations of first pharyngeal arch / stomodeum

mesenchyme of paraxial and lateral plates

neural crest

ectodermal epithelium in roof of nasal cavity

communicates via axons to olfactory bulbs of brain

oro-nasal membrane separating oral cavity from nasal cavity (nasal sacs) ruptures

(choana connects nasal cavity and nasal pharynx in adult)

small anterior bud from FOREGUT

median laryngotracheal groove

foregut bordered on each side by "gills" (pharyngeal arches / branchial arches)

endodermal cells lining the groove become epithelium and glands of larynx, trachea, bronchi, pulmonary epithelium

bud elongates and branches into 2 at the carina / tracheal bifurcation

mainstem bronchi formed

branching forms dichotomously (2 at a time)

number of branches depends on species

mesenchyme that goes w tubes forms vessels, nerves, muscle of lungs

pseudoglandular (1st trimester)

canalicular (2nd trimester)

terminal sac (late 2nd and 3rd trimester)

alveolar period (continues into neonatal and later)

major conductive elements of lungs formed

no respiration possible

bronchial and bronchiolar become larger

lungs get vascularised

respiration becomes possible (chances of survivial slim)

terminal bronchioles, air sacs and capillaries develop

sacs lined w type 2 pneumocytes that produce surfactant

counteracts surface tension and facilitates expansion of terminal sacs (reduces amount of pressure needed for in/exspiration)

prevents collapse (atalectasis)

regulates rate and size of alveolar expansion

95% of alveoli develop and mature after birth

through mouth and nose by pressure at birth

capillary and lymphatic drainage

trachea

bronchi

bronchioles

terminal bronchioles

respiratory bronchioles

alveolar ducts

terminal alveoli

entrance: oral nasal cavity and trachea

egress: vascular bed

everything is pushed in one direction or the other

superficial

one exception: nasal cavity

Vestibular

Respiratory

Olfactory

vestibules: 1st 1.5 cm following nares

lined w keratinized stratified squamous epithelium

hairs and sebaceous glands also present for filtering

supported by normal dermal tissue

epithelium is pseudostratified columnar and ciliated AKA respiratory epithelium, goblet cells present

conchae

lamina propria: mucous and serous glands in submucosa; veins form thin walled cavernous sinusoids

tissues on superior concha and dorsal nasal septum

olfactory epithelium

goblet cells not present

Bowman's glands (seromucous) moisturize epithelium

olfactory cells

sustentacular cells

basal cells

 basal cells differentiate into olfactory and sustentacular

filtration by seromucinous secretions and ciliated epithelial cells

temperature regulation and humidity control by vascular submucosa

50% of conductive airway resistance

bony protrusions that increase surface area of nasal cavity and create turbulence

in Respiratory portion of nasal cavity

lymphoid aggregates (tonsils) serve as defensive function

hyperplasia of tonsils can inhibit air flow

entrapment of bacteria can cause deep respiratory issues

stratified squamous epithelium

protective covering at interface of digestive and respiratory tracts

complex cartilage

fibrovascular stroma

respiratory epithelium (ciliated ps columnar)

basal cells

goblet cells

brush cells

endocrine cells

Clara cells (produce surfactant)

serous cells

neural endopeptidases degrade vasoactive and smooth muscle contractile neuropeptides

metabolize arachidonic acid pathway products to make eicosanoids with vascular and smooth muscle contraction activity

seromucinous secretions of goblet cells and submucosal glands

minimally deformable, incomplete C shaped hyaline cartilage rings

free dorsal ends: connected by bands of smooth (trachealis) muscle and connective tissue fiber

cartilages linked by longitudinal collagenous and elastic connective tissue fibers (annular ligaments)

main bronchi

lobar bronchi

segmental bronchi

similar to trachea histologically

differences:

surrounded by a layer of smooth muscle between the cartilage and epithelium

increased submucosal glands

discontinuous hyaline cartilage rings only allow minimal deformity

connective tissue more pronounced, separates bronchi from pulmonary parenchyma

80%

any narrowing of bronchial diameter can have profound effects on airflow

think anaphylaxis

mix of ciliated and non ciliated cuboidal

most cell types in other conductive portion parts still present (goblet, clara, submucosal...)

thicker smooth muscle layer

lack of cartilage!

2-6

species dependent

peribronchiolar connective tissue attaches to intra-alveolar septa arranged radially from the bronchiole

inspiration: brionchiolar diameter increases as alveoli expand (tethered alveolar septae are stretched)

expiration: tethering force and bronchiolar lumen diameter decreases (small bronchioles may completely collapse)

serous secretions trap particulate matter

secretions moved toward conductive bronchioles

caused by normal collapse of bronchioles in expiration

alveolar grouping

acini: gas exchange unit for a single terminal bronchiole

lobules: groups of acini served by common proximal conductive airways, demarcated by CT septa

terminally differentiated flattened cells

60% of cells, 95% of alveolar surface

tight junctions and desmosomes between epithelial cells

susceptible to injury (large surface area, minimal enzymes)

progenitor cells of Type 1

remaining 40% of epithelium

cuboidal or irregular shape

produce surfactant

make components of CT matrix

metabolize arachidonic acid pathway products

express MHC II molecules for antigen presentation

tracheal epithelium and type 2 pneumocytes

they make eicosanoids with vascular and smooth muscle contraction activity

produce matrix

contribute to mechanical properties of the pulmonary parenchyma

LARGEST capillary bed in the BODY!

initial permeability barrier b/w bloodstream and pulmonary interstitium

key role in solute and gas transport, inflammatory cell adhesion, metabolism of pro inflammatory cytokines/ vasoactives

type 2

they become type 1

 2-5 micrometer thick sheet separating air space from vascular system

(air)

pneumocytes

basement membrane

interstitial tissue (matrix, fibroblasts, capillaries)

basement membrane

endothelial cells

(blood)

primary defense mode of alveoli

70% of cells in lavage from normal lung

migrate freely over the alveolar epithelium

migrate to bronchioles or CT septa

Type 1 pneumocytes transfer to interstitial space

can eb phagocytosed by interstitial macrophages or drain to peribronchial lymphoid nodules via local lymphatics (entrapped in dendritic cells)

mesothelial cells and connective tissue membrane

continuous with lobar and interlobar septa

mesothelial cells: phagocytic activity, maintain lubrication of plerual cavity

well developed interlobar septa

thick pelura

few resp bronchioles

sheep, cattle, pigs

no secondary interlobar septatio,

thin pleura,

well developed resp bronchioles

dog, cat, primates

incomplete lobulation,

thick pleura

poorly developed resp bronchioles

horse, man