Respiratory System: Organs

• Nose• Nasal Cavity• Pharynx• Larynx• Trachea• Bronchi & their

divisions• Lungs

Respiratory systemIs divided into:I-I-Conducting portion (transports, filters, moistens and warms the inspired air): Is formed of nasal cavity, nasopharynx, larynx, trachea, primary bronchi, secondary bronchi (lobar), tertiary bronchi (segmental), bronchioles, and terminal bronchioles.

II-II-Respiratory portion ( has alveoli- the sites of gas exchange): Is formed of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.

Parts of respiratory systemParts of respiratory system

Nasal cavityNasal cavity

1-Anterior portion1-Anterior portion: or vestibule, is lined with skin (sweat &sebaceous glands) and vibrissae.

2-Posterior portion2-Posterior portion: is lined with respiratory mucosa (except olfactory area) Is formed of: respiratory epithelium and vascular lamina propria rich in seromucous glands, lymphoid nodules, mast cells and plasma cells. It has three conchae (superior, middle and inferior)

Nasal Mucosa

Olfactory region of the nasal cavityOlfactory region of the nasal cavity

It covers the roof of the nasal cavity, superior aspect of the nasal septum and the superior concha.It is formed of olfactory mucosa (olfactory epithelium and lamina propria).

Olfactory epithelium comprises three types of cells:

1-Olfactory cells.

2-Sustentacular cells.

3-Basal cells.

Olfactory mucosaOlfactory mucosa

Olfactory mucosaOlfactory mucosa

Para-nasal sinuses & nasal septum

Paranasal sinusesParanasal sinuses

They are mucoperiosteum-lined spaces in ethmoid, sphenoid, frontal and maxillary bones. They communicate with the nasal cavity and have same lining.

PharynxPharynx

Is subdivided into: a-Nasopharynx (lined with respiratory mucosa and has pharyngeal tonsil) b-Oral pharynx (lined with non-keratinized stratified squamous epthelium) c-Laryngeal pharynx (lined with respiratory mucosa)

LarynxLarynx

Is located between pharynx and trachea(4 cm in length and 4cm in diameter). It is responsible for phonation and prevent the entry of solids into the respiratory system during swallowing. It is reinforced by hyaline cartilagehyaline cartilage (thyroid, cricoid and arytenoids) and elastic cartilageelastic cartilage (epiglottis, corniculate and cuneiform)

Larynx has 2 pairs of shelf-like folds:

A-superiorly vestibular folds.

B-Inferiorly vocal folds

Epiglottis

The epiglottisThe epiglottis

• It is leaf like structure. It covers the upper end of larynx to prevent the entrance of food to respiratory passage.

• It is formed of elastic cartilage that surrounded with respiratory epithelium EEXCEPTEEXCEPT its superior (anterior or dorsal) surface and the upper part of the (inferior or ventral) posterior surface that are covered with non-keratinized st. sq. epith.

Vestibular folds &Vocal cordsVestibular folds &Vocal cords*Vestibular folds are immovable. They

are surrounded with respiratory epith.The lamina propria composed of loose C.T, houses seromucous glands, adipose cells and lymphoid elements.

*Vocal cords: are formed of dense regular elastic C.T, vocal ligament, skeletal (intrinsic) muscle and covered with non-keratinized st. sq. epith.

Trachea

Trachea• It is formed of:• 1.Mucosa,1.Mucosa, composed of:* Lining epith.Lining epith.• a-Respiratory epith(col.ciliated)• b-Basal cells.• c-Brush cells.• d-Serous cells.• e-DNES (defuse neuro-endocrine cells).• Lamina propria: fibroelastic C.T.contains

lymphoid elements, mucous, serous glands and elastic lamina.

2.Submucosa: 2.Submucosa: is composed of dense irregular fibero-elastic C.T. containing mucous and seromucous glands. It contains lymphoid elements and bl. Vessels.3.Adventitia3.Adventitia:is composed of fibero-elastic C.T.and C-rings of hyaline cartilage.

Bronchial treeBronchial tree• It begins at the bifurcation of the trachea.

• It is composed of:

1.Extrapulmonary or 1ry bronchi.

2.Intrapulmonary (2ry &3ry) bronchi.

3.Bronchioles.

4.Terminal bronchioles.

5.Respiratory bronchioles.

General Characters of Bronchial Tree

Progressive decrease in: Size (diameter) Amount of cartilage. Number of glands and goblet cells The height of epithelial cells.

Progressive increase in: Amount of smooth muscle Amount of elastic tissue

Primary bronchiPrimary bronchi are identical in structure to trachea (but smaller).Intrapulmonary bronchiIntrapulmonary bronchi have irregular plates of hyaline cartilage (in lieu of C-ring), which completely surrounds the lumen of intrapulmonary bronchi.

Bronchioles.Bronchioles.• Are less than 1mm in diameter.

• Have no cartilage.

• Have Clara cells.

• Large bronchioles are lined

with simple columnar ciliated

epithelium and few goblet cells

• Small bronchioles are lined with simple cuboidal ciliated epith.without goblet cells.

• Lamina propria has NO glands.

• Are surrounded by helically oriented smooth muscle layers that surrounded by elastic fibers.

Bronchiole

Clara cellsClara cells• Are columnar cells with dome shaped

apices.• Have microvilli.• Have abundant rER.• Are secretory cells,

(glycoprotein and surfactant-like material) • Have abundant sER.• Can degrade toxins in the inhaled air.• Can divide to regenerate the bronchiolar

epith.

Terminal Bronchioles.Terminal Bronchioles.• Are the smallest and most distal region of the

conducting portion (less than o.5mm).• Are lined by Clara cells and partially ciliated

cuboidal cells.• Lamina propria is formed of fibro-elastic C.T.• Have one or two layers of smooth muscle.• Elastic fibers radiate

from the adventitia.• They give rise to

respiratory bronchioles.

Respiratory bronchiolesRespiratory bronchioles

• Have the same structure as terminal bronchioles but,

• They have alveoli through them gas exchange takes place.

• They terminate in an alveolar ducts.

Terminal bronchiole

Alveolar ductsAlveolar ducts

• Do not have walls of their own, but are lined with extremely attenuated squamous alveolar cells.

• They end with two or more small clusters of alveoli (alveolar sac).

• The opening of each alveolus to the alveolar duct is controlled by a single smooth muscle cell, embedded in type III collagen.

• Fine elastic fibers ramify from the alveolar ducts and sacs.

AlveolusAlveolus• Is a small outpouching of respiratory

bronchiole, alveolar ducts and alveolar sacs.• Is the structural and functional unit of

respiratory system.• Contiguous alveoli communicate through an

alveolar pore of Kohn (equilibrate air pressure).• Interalveolar septum is occupied by extensive

continuous blood capillaries and C.T. rich in elastic and type III collagen.

• Opening of alveoli associated with alveolar sacs are devoid of smooth muscle cells, instead there are elastic and reticular fibers.

Lining of the alveoliLining of the alveoli

• A-Type I pneumocytesA-Type I pneumocytes : *Line about 95% of alveolar surface.

*Highly attenuated squamous cells.

*Have thin cytoplasm that contain few mitochondria, few rER and a modest Golgi apparatus.

*Have occluding junctions.

*have well developed basal lamina.

B-Type II pneumocytesB-Type II pneumocytes*occupy 5% of the alveolar surface.*Are cuboidal cells.*Form occluding junctions with type I alveolar cells.*Occupy most of the alveolar septa.*Have basal lamina.*Have apical microvilli.*Have central nuclei.*Have abundant rER, well developed Golgi apparatus and mitochondria.*Have membrane-bound lamellar bodies.*Secrete pulmonary surfactant (phospholipids and proteins) and undergo mitosis.

Type I &Type II pneumocytes

Pneumocyte type IIPneumocyte type II

EM of Pneumocyte II

The surfactantThe surfactant

• Is secreted by exocytosis from type II alveolar cells into the lumen of the alveolus.

• Decrease surface tension of the alveoli thus prevent their collapse.

Blood-Air barrier

Blood-Air Barrier

EM of Blood-Gas Barrier

*Pneumocytes type I and surfactant.

*Fused basal lamina of type I pneumocytes and endothelial cells of the capillary.

*Endothelial cells of the continuous capillaries.

Interalveolar septum

Alveolar macrophages (dust Alveolar macrophages (dust cells)cells)

• Are monocytes in the pulmonary interstitium.

• Migrate between type I alveolar cells, and enter the alveoli.

• Phagocytose dust and bacteria.

• Migrate to bronchi to the pharynx or into lymph vessels.

Lung

PleuraPleuraIs formed of two layers:Parietal and visceral.

It is formed of simple squamous mesothelium. The two layers are separated by serous fluid. The visceral layer has sub-epithelium loose C.T that extends in lung tissue