Respiratory system pdf - د. رند عبد اللطيف

The Respiratory System د.رند عبد اللطيف

Lecture 1

The Respiratory System

Is the complex of organs and tissues which are necessary to exchange

blood carbon dioxide (CO

) with air oxygen (O

). It consists typically of

pharynx, larynx, bronchi, lungs and diaphragm.

1. Conducting portion (upper respiratory tract): formed of a series of transport

passages by which air pass from the atmosphere to the lung. It consist of (nasal

cavity, nasopharynx, larynx, trachea, bronchi, bronchioles & terminal

bronchioles).

2. Respiratory portion (lower respiratory system): which is responsible for

gaseous exchange consist of (respiratory bronchioles, alveolar ducts & alveoli).

The alveoli are specialized sac like structures forming the greater part of the

lung & they are the main sites for exchange of O2 & CO2 between the air &

the blood.

The Respiratory System د.رند عبد اللطيف

Lecture 1

The conducting portion of the respiratory system has many functions:

1. It is a system of channels through which air will reach the lungs and to

ensure adequate & continuous supply of air to both lungs a combination of

cartilages, elastic fibers, collagen fibers & smooth muscle fibers provides the

conducting part with rigid structural support and with the necessary flexibility

and extendibility.

2. While passing through the conducting part the air will be cleaned (by

removal of foreign particles), moistened & warmed, to carry out these

functions, the mucosa of the conducting part is lined with a specialized

epithelium called respiratory epithelium.

3. In addition the proximal part of the respiratory tract has a specialized

structures that are involved in the perception of smell & flavor (Olfactory

mucosa) & the production of sound (Larynx).

Cartilages in the respiratory system:

Cartilages are mainly hyaline in type, they have various forms ranging from

small plaques in the bronchi to irregular rings & in the trachea C-shaped

cartilages. The cartilages generally produce support to the wall of the

conducting part to prevent collapse of the lumen during expiration & to ensure

continuous air entry to the lungs.

Elasic fibers in the respiratory system:

found in both conducting and respiratory parts to provide these areas with

flexibility and to allow them to return to their original shape after

inspiration.The concentration of elastic fibers is inversely proportionate to the

diameter of the conducting tubule (ie. the smallest bronchioles have the highest

amount of elastic fibers in their lamina propria).

The Respiratory System د.رند عبد اللطيف

Lecture 1

Smooth muscles in the respiratory system:

bundles of smooth muscles encircle the tube from the trachea to the alveolar

ducts. Contraction of those smooth muscles reduces the diameter of the

conducting tubules to regulate the air flow during inspiration and expiration.

The conducting part of the respiratory system gradually undergoes transition

into the respiratory part. The ciliated epithelium, goblet cells & cartilages

will gradually decrease in the wall of the system while the content of smooth

muscles & elastic fibers gradually increase.

Respiratory Epithelium:

Most of the conducting portion of the respiratory system is lined with

pseudostratified ciliated columnar epithelium that contains large number of

mucous secreting cells called goblet cells. As the bronchi subdivide into

bronchioles some structural changes occure are:



pseudostratified epithelium will change to simple columnar epithelium

which is further reduced to simple cuboidal epithelium in the terminal

bronchioles.

The Respiratory System د.رند عبد اللطيف

Lecture 1



goblet cells gradually decrease in number in the smaller bronchi & are

completely absent from the epithelium in the terminal bronchioles.



ciliated cells still present in the terminal bronchioles without the goblet

cells in order to prevent accumulation of mucous in the respiratory

portion of the system because the cilia help to move this mucous upward

toward the mouth where it is either swallowed or expectorated.

Typical respiratory epithelium: consists of five cell types:

1. Ciliated columnar cells: most numerous type of cells, each cell has about

300 cilia in its apical surface, sometimes defective functioning of the cilia

is present leading to immotile cilia syndrome (due to deficiency of the

protein Dynein) this will lead to increased incidence of respiratory

infections. Ciliated columnar cells become shorter with successive

branching of the bronchial tree until they become cuboidal in the most

peripheral branches.

2. Mucous secreting goblet cells: the second most numerous type of cells,

they are scattered in between the ciliated columnar cells, their cytoplasm is

filled with mucous droplets and their number gradually decrease until they

are absent in the terminal bronchioles, they increase in some chronic

respiratory diseases.

3. Basal cells: small rounded cells lie on the basement membrane, they are

not in contact with the lumen, and they form stem cells from which other

cell types develop.

4. Brush cells: columnar cells with many microvilli on their apical surface,

they have afferent nerve endings on their basal surface & are considered to

be sensory receptors.

The Respiratory System د.رند عبد اللطيف

Lecture 1

5. Neuroendocrine cells: small rounded cells with dark nuclei & cytoplasm

filled with endocrine granules that regulate the interaction between mucous

and serous secretory functions of the system.

In smokers the proportion of ciliated cells to goblet cells is altered so greater

number of goblet cells are found to aid in clearing the increased amount of

particulates & gaseous pollutants in their respiratory epithelium, while the

reduction in ciliated cells caused by excessive intake of CO resulting in

decreased movement of the mucous layer leading to congestion of the

smoker’s airways.

 Nasal Cavity:

The Nasal cavity is divided into three structurally and functionally different

parts.

1. Vestibule: is the most anterior dilated part of the nasal cavity forming the

first ~1.5 cm of the conductive portion following the nostrils which are lined

with a keratinized stratified squamous epithelium, numerous sebaceous glands

& thick short hairs, within the vestibule the epithelium loses its keratinization

and undergoes gradual transition into typical respiratory epithelium.

2. Respiratory region: at the transition from the vestibule to the respiratory

region of the nasal cavity the epithelium becomes first non keratinized

stratified squamous and then pseudostratified ciliated columnar with goblet

cells (respiratory epithelium). The surface of the lateral parts of the nasal

cavity is thrown into folds by bony projections called conchae. These folds

increase the surface area of the nasal cavity and they create a turbulence in the

stream of the passing air, both functions will facilitate the conditioning

(warming, moistening and filtration) of the air. The lamina propria contains

mucous and serous glands which supplement the secretions of the goblet cells

The Respiratory System د.رند عبد اللطيف

Lecture 1

with a large venous plexuses known as swell bodies, they are important for

conditioning of air thus abnormal enlargement of swell bodies with blood

occurs in allergic reaction & inflammation so they restrict air flow to the air

passages.

3. Olfactory region formed by tissues on the superior concha and the nasal

septum of the nasal cavity, it is lined with a special type of epithelium called

Olfactory mucosa.

Olfactory mucosa:

Is a special type of mucosa, located in the roof of the nasal cavity & extend for

a short distance down the septum and lateral wall it is responsible for the

sensation of smell & the more sophisticated epithelium aspect of taste. The

Olfactory mucosa has a pseudostratified columnar epithelium that is composed

of three types of cells which are:

1. Basal cells: are small cone shape cells rest on the basement membrane not

in contact with the lumen their nuclei are close to the basement membrane,

these cells are regarded as the stem cells from which new olfactory cells can

develop.

The Respiratory System د.رند عبد اللطيف

Lecture 1

2. Sustentacular cells (supporting cells): are tall cells their nuclei are

closest to the lumen & they have a narrow base in contact with the basement

membrane & microvilli on their free surface, they give mechanical &

metabolic support to the basal & olfactory cells.

3. Olfactory receptor cells: are bipolar neurons found in between the basal

& sustentacular cells they have a central bulge contain the nucleus & from the

cell extend 2 processes:

a) Dendritic process: extend to the surface epithelium where its tip

expand into a club-shaped prominence called Olfactory vesicle which

bears cilia that protrude into the nasal cavity these cilia are sensitive

to odorous substances.

b) Proximal process: very narrow & pass between the basal &

sustentacular cells to penetrate the basement membrane & join the

other proximal processes of other cells to form what is called fila

olfactoria which will then form a synaptic connection with the

olfactory bulb to form the first cranial nerve (Olfactory nerve).

Beneath the epithelium of the olfactory mucosa the connective tissue of the

lamina propria contain small serous glands called Bowman's glands their

secretion may act as a solvent for the odorous substances, this connective

tissue is highly vascular and contain the fila olfactoria.

The Respiratory System د.رند عبد اللطيف

Lecture 1



Pharynx:

The pharynx connects the nasal cavity with the larynx. Depending on the

extent of abrasive forces on the epithelium, the pharynx is either lined with

respiratory epithelium (nasopharynx) or with a stratified squamous epithelium

(oropharynx) which also covers the surfaces of the oral cavity and the

oesophagus.Lymphocytes frequently accumulate beneath the epithelium of the

pharynx.Accumulations of lymphoid tissues surrounding the openings of the

digestive and respiratory passages form the

tonsils



Larynx:

The larynx connects the pharynx and trachea. The vocal folds of the larynx

control airflow and allow the production of sound. The vocal folds are lined by

stratified squamous epithelium and contain the muscle (striated, skeletal) and

ligaments needed to control the tension of the vocal folds.