THE RESPIRATORY SYSTEM

VENTILATING PORTION: - diaphragm, intercostal muscles, elastic tissue in lungs- means by which air is moved in and out of lungs continuously

CONDUCTING PORTION:- nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles- warm/cool, humidify, filter & conduct incoming air to respiratory passageways- lined with respiratory epithelium

RESPIRATORY PORTION:-respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli-site of exchange of O2 and CO2

between blood and alveoli

3 DIVISIONS OF RESPIRATORY SYSTEM

Nasal cavity

Nasopharynx

Oropharynx

Larynx

Trachea

Br

B

RBADA

Lung

Diaphragm

NASAL CAVITY & PARANASAL AIR SINUSES

- Respiratory area is lined with pseudostratified ciliated columnar epithelium with goblet cells and is highly vascularized- Olfactory area (roof of nasal cavity and superior concha) is lined with olfactory epithelium – specialized bipolar (sensory) neurons with sustentacular (supporting) cells and basal cells (stem cells)

SAGITTAL VIEW CORONAL VIEW

O

R

CELLS OF RESPIRATORY EPITHELIUM

•Ciliated cells – most abundant, tall with basal nuclei, lots of mitochondria to provide ATP for ciliary beating of mucus and its’ trapped particulate matter.•Goblet cells - ~30% of cells, have narrow basal stem containing nucleus and most organelles and apical theca containing mucinogen which becomes hydrated to form mucus. •Basal cells – ~30% of cells, lie on basal lamina, do not reach apical surface. Undifferentiated stem cells that will give rise to other cell types.•Brush cells - ~3% of cells, narrow columnar cells with tall microvilli. Thought to have sensory receptors on basal surfaces and act as sensory receptors.•DNES cells -~3% of cells – have numerous small granules in their basal cytoplasm whose contents act on other cells of the respiratory epithelium

Ciliated cells

Basal body beneath cilia

Gobletcell

Brushcell

RESPIRATORY EPITHELIUM

Microvilli

Basal cellSmall granule cell (DNES, Enteroendocrine)

RESPIRATORY EPITHELIUM

Plasma cells

Basement membrane

Basal cell

Lymphocyte

Cilia withbasal bodies

Ciliated cell

Goblet cell

OLFACTORY EPITHELIUM

•Olfactory cells – bipolar neurones, apical dendrite ends in olfactory vesicle from which non-motile cilia with receptors for odiferous substances arise. When a threshold level of receptors are occupied an action potential is generated and transmitted to the olfactory bulb via axon which passes through cribiform plate to synapse in olfactory bulb.•Sustentacular cells – tall columnar cells with microvilli. Provide physical support, nourishment and electrical insulation for olfactory cells. •Basal cells – stem cells to replace olfactory and sustentacular cells.•Bowman’s glands – provide serous fluid to refresh olfactory cilia.

Basal cell

Olfactory cell

Sustentacular cell

Bowman’s gland

Dendrite

Olfactory vesicle

Olfactory cilia

Olfactory epithelium, 68a (H&E)

OLFACTORY EPITHELIUM

Olfactory cell

Sustentacular cell

Basal cell

THE PHARYNX

The NASOPHARYNX serves only as an air passageway. It is lined with pseudostratified ciliated columnar epithelium

The OROPHARYNX and LARYNGOPHARYNX serve as passageways for both air and food. They are lined with stratified squamous epithelium (for protection).

The muscular wall of the entire pharynx consists of skeletal muscle

THE LARYNX

Vestibularfold

Vocalfold

Cricoidcartilage

All cartilages hyaline exceptepiglottis (elastic).Vocal ligaments are elasticligaments.

Laryngealventricle

Larynx, 69b (H&E)

THE LARYNX

Skeletal(arytenoid)

muscles

Stratified squamous non-keratinizedepithelium of vocal fold

Pseudostratified ciliated columnarepithelium of vestibular fold and ventricle

Vocalligament

Mixedglands

CONDUCTING & RESPIRATORY PORTIONS OF THE RESPIRATORY TREE

THETRACHEA

•Mucosa lined with respiratory epithelium which continuously propels mucus and debris towards the larynx •Seromucous glands in submucosa help produce mucus ‘sheets’•16-20 C-shaped rings of hyaline cartilage prevent the trachea from collapsing. Closed posteriorly by trachealis (smooth) muscle - allows oesophagus to expand anteriorly when swallowing.

•10cm long, 2.5cm diam. flexible tube, divides at carina (T4) into right and left primary bronchi

Trachea, 70a (H&E)

THE TRACHEA

Cartilage

Seromucous glands

Trachealis muscle

Respiratory epithelium

Thyroid

Hyalinecartilage

Trachea, 70a (H&E)

Respiratory epithelium Mixed seromucous glands

Mucus acinusSerous demilune

BRONCHI

•Primary bronchi run obliquely in the mediastinum, enter lung where they subdivide into secondary and tertiary bronchi •Mucosa and submucosa similar to trachea. Inc. smooth muscle & elastic fibers in lamina propria. Mixed glands in submucosa.•Plates of hyaline cartilage encircle bronchus and prevent collapse.

Lung, 72a (H&E) – bronchi and bronchioles

Bronchi

LUNG

WALL OF A BRONCHUS

Hyalinecartilage

Respiratory epithelium

Lumen

Blood vessels and glands

Alveoli (surrounded by fine elastic fibers)

Bronchus (cartilage & smooth muscle in wall)

Bronchiole ( no cartilage, just smooth muscle in wall)

Terminal bronchiole

Respiratory bronchiole(alveoli off walls)

Alveolar duct

Alveolar capillary network

CELLS LINING BRONCHIOLES

Ciliatedcell

Basalcell

Claracell

Clara (bronchiolar) cells – columnar cells with domed apices and short blunt microvilli. Apical cytoplasm filled with secretory granules containing surfactant-like material that reduces surface tension and faciliates patency of bronchioles. Cells also degrade inhaled toxins.

BRONCHIOLE

As tubes become smaller, resp. epithelium becomes lower with fewer goblet and ciliated cells. Terminal bronchioles are lined with simple cuboidal epithelium. Proportion of smooth muscle increases allowing for constriction (para.) and dilation (symp.) of airways.

Lumen

Smooth muscle

Claracells

BRONCHIOLAR EPITHELIUM

ClaraCil

Brush Clara

SEM TEM

Cil Cil

Terminal bronchiole

Alveolar duct

Alveoli

Respiratory bronchioles

RESPIRATORY BRONCHIOLES

Respiratory bronchioles – first structures in respiratory zone, alveoli arise from their walls, terminate in alveolar ductsAlveolar ducts – linear arrangements of alveoli, lined with type I cells, isolated regions of smooth muscle cells in lamina propria between adjacent alveoli, lead to alveolar sacs

Type I

Type II

Resp. bronchiole

Alveolar duct

Smooth muscle

Atrium or alveolar sac

RESPIRATORY REGION OF THE LUNG

ALVEOLI

Type II cells

Capillary

Dust cell (macrophage)

Type I cell

Capillary

Alveolus(airspace)

~ 250 million alveoli in lungs provide 140m2 of surface area for gaseous exchange

Interalveolar septumSurfactant

CELLS OF ALVEOLAR WALLS•Type I cells (squamous alveolar cells) - highly attenuated, cover 97% of surface area of alveolus, organelles grouped around nucleus so most cytoplasm virtually free of organelles. Joined to other type I and type II cells by tight junctions to prevent leakage of fluid into air space. Basement membrane fuses with that of endothelial cell to minimise thickness of respiratory membrane.

•Type II cells (septal cells) – account for 60% of alveolar cells but only 3% of surface area. Cytoplasm filled with lamellar bodies which contain surfactant that lowers alveolar surface tension. They divide to form new Type II and type I cells.

•Alveolar macrophages (dust cells) – derived from monocytes, found in alveolar septa, migrate between type I cells to enter lumen of alveolus, phagocytose dust and bacteria and migrate to bronchioles where ciliary action carries them to the pharynx to be swallowed. Over 2 million dust cells are cleared per hr.

ALVEOLI & INTERALVEOLAR SEPTUM

Alveolar pores connect adjacent alveoli – allow for equalization of pressure and alternate routes for blocked passages

Type II cell Type I cell

Endothelial cell

Capillary

Dust cell

Alveolar poresAlveoli

Respiratorymembrane

THE BLOOD-AIR BARRIER

•Surfactant

•Type I cell

•Basement membrane

•Endothelial cell

Barrier is extremely thin(15 times thinner than apiece of paper) to facilitate gaseous exchange

Redblood

cell

Endothelium

Type I cell

Fusedbasal

laminae

Alveolus

Interfacebetweencapillary

and alveolus

ALVEOLI & INTERALVEOLAR SEPTUM

Netter 201

Bronchial artery

CIRCULATIONWITHIN THE

LUNGS

Pulmonary artery(next to air passages)

Pulmonary veins(in septum)