CELLS & TISSUES

RESPIRATORY TRACT

by

Dr. SAAD EL-SHAFEY

A- Conducting portion:

It is the portion for conduction and conditioning of air.

It cosistes of nasal cavities, nasal sinuses , nasopharynx ,

Larynx, Trachea, Bronchi, Bronchioles & Terminal bronchioles.

B- Respiratory portion:

It is the portion where gases exchange takes place.

It consists of Respiratory bronchioles, Alveolar ducts & Alveoli.

RESPIRATORY SYSTEM

Nasal Cavities

1- The vestibule:

It is the most anterior and dilated portion of the nasal cavity.

It is lined by skin rich in thick hairs.

The hairs filter out the large particles from the inspired air.

II- The Nasal fossae:

It is the posterior part.

It is divided into two chambers separated by osseous nasal septum.

Each fossa could be divided into two areas:

A. Respiratory area: (middle part of nasal cavity).

B. Olfactory area: (roof of nasal cavity) .

A. The respiratory area

It is lined by mucous membrane consisting of:

1. Epithelium: pseudo-stratified columnar ciliated with goblet cells.

2. Corium:

Dense fibro-elastic connective tissue, infiltrated by:

a. Lymphocytes, macrophages and plasma

cells.

b. Serous and mucous glands.

c. Large venous plexuses (swell bodies).

B. The olfactory area Site:

It is the roof of the nasal cavity.

Structure: It is lined by olfactory mucosa which consists of:

1- Olfactory epithelium:It is a thick neuroepithelium; formed of:

1- Supporting cells:

Shape: High columnar with thin base.

Nuclei: Oval & pale.

Cytoplasm: contains yellow pigment.

Free border: is covered with microvilli.

2- Sensory (olfactory) cells:

Site: between the basal parts of the supporting cells.

Shape: Bipolar nerve cells (fusiform).

Axons: Pass to the corium to form the olfactory nerve.

Dendrites:

▪ Extend towards the surface where they end in

olfactory

vesicles from which olfactory cilia arise.

▪ The olfactory cilia are long, non motile and lie flat on

the

epithelial surface.

3- Stem (Basal) Cells:

They are pyramidal in shape.

They are present in the deepest zone of the epithelium.

They act as reserve cells to regenerate the columnar cells.

2- Corium

It is a dense fibro-elastic tissue.

It contains tubulo-alveolar glands (Bowman's glands).

The Bowman's glands secrete a serous fluid which passes to the

surface where it acts as a solvent for the odorous gases.

NASO-PHARYNX

The mucous membrane of the nasopharynx consists of:

I. Epithelium: Pscudo-stratified columnar ciliated

with goblet cells.

2. Corium: Contains Mucous glands & Pharyngeal

tonsil (adenoids).

THE LARYNX

It is an irregular tube connecting the pharynx with the trachea.

The mucous membrane consists of:

I- Epithelium:

▪ pseudo-stratified columnar ciliated with goblet cells.

2-Corium (Lamina propria):

▪ It contains a number of laryngeal cartilages.

▪ The larger cartilages (thyroid, cricoid and most the arytenoids)

are

hyaline cartilage.

▪ The smaller cartilages (epiglottis, cuneiform, corniculate and

tips of

the arytenoids) are elastic cartilage.

▪ The cartilages are present between the extrinsic and intrinsic

muscles of the larynx.

Epiglottis:

It projects from the rim of the larynx and extends into the pharynx.

Structure:

I- A central elastic cartilage.

2- Covering epithelium:

The lingual surface is lined by stratified squamous non

keratinized.

The remaining laryngeal surface is lined by pseudo-stratified

columnar ciliated epithelium.

A- Mucosa:

It is folded posteriorly to allow expansion of the oesophagus.

1- Epithelium:

▪ Pseudo-stratified columnar ciliated with goblet cells.

▪ The cells of epithelium are:

a. Ciliated columnar cells: cilia beat towards the larynx.

b. Goblet cells: secrete mucous.

c. Basal cells: act as mother cells.

d. Serous cells: secrete serous fluid .

e. Neuro-endocrine (K): secretes serotinin & calcitonin.

f. Migrating cells: Lymphocytes & mast cell.

TRACHEA

2- Corium (Lamina Propria):

Loose connective tissue infiltrated with lymphocytes.

It is rich in elastic fibres which condenses to form elastic

membrane between the corium and submucosa.

B- Submucosa:

It is loose connective tissue contains tracheal glands.

These glands are mixed Tubulo-alveolar (mucous & serous)

glands.

C- Fibro-Cartilagenous coat:

Dense connective tissue contains 16-20 C-shaped rings of

hyaline cartilage.

The cartilage rings are arranged above each other.

They are connected together by fibro-elastic membrane.

The gaps between their free edges (facing the oesophagus)

contain smooth muscle fibres.

BRONCHIA- Extra-pulmonary bronchi: same structure as trachea.

B- lntra-pulmonary bronchi:

1- Mucosa: It is highly folded & is formed of:

a. Epithelium: the same as trachea but has few goblet cells.

b. Corium: loose connective tissue rich in elastic fibres.

c. No elastic membrane.

2- Muscle Layer: It is a complete layer of spirally arranged smooth muscle.

3- Adventitia: Loose connective tissue rich in elastic fibres & contains :

a. Hyaline cartilaginous plates

b. Mucous and serous tubulo-alveolar glands.

c. Lymphatic nodules.

TracheaIntrapulmonary Bronchus

Lumen:Wider.Narrower.

Mucosa:Folded only posteriorly.

Folded all around the circumference.

Epithelium:Pseudostratified columnar ciliated with goblet cells.

The same but with fewer goblet cells.

Elastic membrane

s:

Present between the corium and

submucosa.

No elastic membrane but only elastic fibres .

Submucosa:

Present.Absent.

Muscle fibres:Few at the edges of C-shaped rings.

Complete muscle layer .

Cartilage:C-shaped cartilaginous rings.

Irregular cartilaginous plates.

Glands:Present in the submucosa.

Present between the plates.

Lymphatic nodules:

Absent.Present in the adventitia.

BRONCHIOLES

Diameter: less than I mm.

A- Mucosa:1- Epithelium:

a- Simple columnar Ciliated cells.b- Clara cells:

Columnar cells with rounded apex.Secrets serous fluid rich in protein.

No goblet cells no viscous mucus keep them patent.2- Corium:

Loose connective tissue rich in elastic fibres.

B- Muscle layer:Well developed layer.Spirally arranged smooth muscle fibres.

C- Outer connective tissue layer:It is loose C.T. rich in elastic fibres.It has No glands, No Cartilage & No lymphtic nodules.

Intra-pulmonary bronchus

Bronchiole

Epithelium: Pseudo stratified columnar ciliated with few

goblet cells.

Low columnar ciliated with no goblet cells.

Other types of cells:1.Basal cells.2.Brush cells.

3.Serous cells.4.Neuro endocrine cells.

5.Migratory cells.

Clara cells.

Muscular coat:

Present.Well developed.

Cartilaginous plates:

Present.No cartilaginous plates.

Bronchial glands:

Present.No glands.

Lymphatic nodules:

Present in the adventitia.No lymphatic nodules.

TERMINAL BRONCHIOLESThey are the terminal part of the conducting system.

Lining epithelium: ciliated cubical cells alternating with clara cells.

B- RESPIRATORY PORTION

1- Respiratory Bronchiole

Diameter: 0.2 - 0.5 mm

Structure:

It is lined by cubical non ciliated epithelium.

Its wall is interrupted by alveoli which directly open into its lumen so

it is called respiratory bronchiole.

2- Alveolar Duct

Structure:

It is interrupted by numerous openings of alveoli and alveolar sacs.

It is lined by low cubical non ciliated epithelium.

3- Pulmonary Alveoli

Definition:

These are the functional and structural units of the lung.

They appear as minute air spaces which open into the alveolar

ducts and respiratory bronchioles.

Alveolar sac is a group of alveoli having a common space.

Structure:

A. Alveolar epitheliurn.

B. Interalveolar septum.

C. Alveolar pores.

Alveolar Epithelium (Pneumocytes)

1- Type-1 Pneumocytes

Number: 95% .

Structure:

They are flat cells with flat nuclei.

The cell organoids are few & located around the nucleus.

The rest of cytoplasm is thin to facilitate gas exchange.

They have thin basement membranes which fuse with that of the

near capillaries to facilitate gas exchange.

Function:They provide a very thin membrane through which gas exchange takes place.

2- Type-2 Pneumocytes

Number: 5%.

Site: Commonly located at the angles of the interalveolar septa.

Structure:

These are cuboidal cells with rounded central nuclei.

The cytoplasm numerous rER, mitochondria & prominent Golgi.

It also contains electron dense Lamellar bodies which contain

pulmonary surfactant.

Function:1. They can divide and act as mother cells for type-I and type-2.2. They secrete the pulmonary surfactant:

▪ It causes reduction of the surface tension, so facilitating the inflation of the alveoli.

Inter-alveolar septum:Structure:

1. Alveolar epithelium on either sides (described above). 2. Basement membranes of alveolar epithelium & bl. capillary.3. Continuous capillary network (pulmonary capillary bed).4. Supporting network of C.T that is rich in:

a. Elastic & reticular fibers.b. Fibroblasts, macrophages & mast cells.

Blood Air Barrier (membrane)Def.:

It is the wall separating the air in alveoli from the blood in capillaries.

Structure:1.The surfactant.2.The cytoplasm of the alveolar epithelium.3.The fused basal laminae of the alveolar and capillary epithelium. 4.The cytoplasm of the endothelial cells of the capillaries.

Blood air membrane

Alveolar MacrophagesOrigin:

Blood monocytes in the interstitium change into

macrophages migrate to the lumen of the alveoli.

Site:

1. In the interalveolar septum.

2. Over the luminal surface of the lung alveoli.

L/M:

Stain: vital stain with trypan blue.

Nucleus : irregular.

Cytoplasm: vacuolated.

E/M:

The cell membrane is irregular with numerous pseudopodia.The cytoplasm contains many lysosomes.

Types:1- Dust cells:

They phagocytose the dust particles which are inspired with air.

2- Heart failure cells:They phagocytose the extra-vasated RBCs, which escape from the congested capillaries into the alveoli.

Fate:Many of them migrate from the alveoli to the surface of the bronchi carried by the ciliary action to the pharynx swallowed with saliva or expelled in the sputum (coughing).

Alveolar pores The interalveolar septa are interrupted by holes called (pores of kohn). These pores are important for communication between the alveoli in

cases of bronchiolar obstruction.

Pleura The pleura is the serous membrane covering the lung. It consists of two layers, parietal and visceral, that are

continuous in the region of the hilum. Both membranes are composed of mesothelial cells resting on a

fine connective tissue layer that contains collagen and elastic fibers.

The elastic fibers of the visceral pleura are continuous with those of the pulmonary parenchyma.

The parietal and visceral layers define a cavity entirely lined with squamous mesothelial cells.