respiratorysystem2

8/14/2019 respiratorysystem2

1/31

Respiratory System

Conductive Structures in the Lung


2/31

Your lungs contain almost 1500 miles of airways and over 300 million alveoli


3/31


4/31

Bronchi

Conductive structures of a size down to ~1mm

main bronchi: a result of the bifurcation of the

lungTheir histological structure correspondslargely to that of the trachea.

divide into lobar bronchi which in turn giverise to segmental bronchi (tertiary) .

segmental bronchi: supply the bronchopulmonarysegments of the lungs


5/31

Bronchial branches

are accompanied bybranches of thepulmonary artery,nerves and lymph

vessels.These structuresusually travel inintersegmental andinterlobar sheets of connective tissue


6/31

bronchi arecharacterized by thepresence of glands

and supportingcartilage. Thecartilage supportingthe bronchi istypically found inseveral small pieces.


7/31

The histological structure of the epithelium andthe underlying connective tissue of the bronchicorresponds largely to that of the trachea and

the main bronchiIn addition, bronchi are surrounded by a layer of smooth muscle, which is located between the

cartilage and epithelium.


8/31

Bronchioles smaller than ~1 mm

are the terminal segmentsof the conductive portion. epithelium change to a

ciliated columnar

epithelium, but most of thecell types found in theepithelium of other parts of the conductive portion arestill present.

Glands and cartilage areabsent. The layer of smooth muscle is relativelythicker than in the bronchi.


9/31


10/31


11/31

Respiratory Structures in the Lung


12/31

respiratory bronchioles result from the division of the bronchioles

are the first structures that belong to the respiratoryportion of the respiratory system

alveoli

Small outpouchings of the walls of the respiratorybronchioles

the site of gas exchange

The number increases as the respiratorybronchioles continue to divide. They terminate in alveolar ducts. The "walls" of

alveolar ducts consists entirely of alveoli.


13/31


14/31

Histological Structure of AlveoliThe wall is formed by athin sheet (~2m) of tissue separating twoneighbouring alveoli.

This sheet is formed byepithelial cells andintervening connectivetissue.

Collagenous (few andfine), reticular and elasticfibers are present.

microscopic view of alveoli


15/31

Between the connective tissue fibers wefind a dense, anastomosing network of pulmonary capillaries whose walls arein direct contact with the epithelial liningof the alveoli.

The basal laminae of the epi- andendothelium may actually fuse.Neighbouring alveoli may be connectedto each other by small alveolar pores


16/31


17/31

The epithelium of the alveoli is formed by twocell types:

Alveolar type I cells Alveolar type II cells


18/31

Alveolar type I cells (small alveolar cells or typeI pneumocytes)

are extremely flattened (the cell may be as thin as

0.05 m) and form the bulk (95%) of the surface of the alveolar walls.

The shape of the cells is very complex, and theymay actually form part of the epithelium on bothfaces of the alveolar wall.


19/31

Alveolar type II cells (large alveolar cells or type II pneumocytes)

are irregularly (sometimes cuboidal) shaped. They form small bulges on the alveolar walls. contain large number of granules called cytosomes

(or multilamellar bodies), which consist of precursors to pulmonary surfactant (the mixture of phospholipids which keep surface tension in thealveoli low).

Their small contribution to alveolar area isexplained by their shape.


20/31


21/31

Cilia are absent from the alveolar epitheliumand cannot help to remove particulate matter

which continuously enters the alveoli with theinspired air.

Alveolar macrophages take care of this job.

They migrate freely over the alveolar epitheliumand ingest particulate matter. Towards the endof their life span, they migrate either towardsthe bronchioles, where they enter the mucuslining the epithelium to be finally dischargedinto the pharynx, or they enter the connectivetissue septa of the lung.


22/31


23/31


24/31

Development of the Lungs

The formation of the lower respiratory passagesbegins in the fourth fetal week.

An outpouching of the foregut gives rise to thelaryngotracheal tube. The lining of this tube willeventually give rise to the epithelia covering thesurfaces of the larynx, trachea, bronchi, bronchiolesand alveoli.

Most of the other tissues of the lower respiratorypassages are derived from splanchnic mesoderm.

The laryngotracheal tube divides distally to form twolung buds.


25/31

Dependent of the state of maturity of the lung,development is divided into three periods:

glandular periodlasts until ~17 th fetal week

bronchi grow and branch

no alveoli present yet canalicular period

Bronchi and bronchioles expand and branch

lung tissue is vascularized

Bronchi and bronchioli begin to form terminal sacs(developing primitive alveoli)

Respiration becomes possible towards the end of thisperiod around the 25th foetal week.


26/31

alveolar period (sometimes also considered a separateperiod of lung development and called terminal sac

period) number of terminal sacs increases during initial period capillary network is developing between the terminal

sacs. The late alveolar period is marked by the development

of mature alveoli from the terminal sacs. The periodbegins shortly before birth, but the first mature alveoliappear only after birth.

Alveolar sacs continue to be formed during earlychildhood (up to year 8) and mature into alveoli.Alveolar maturation and growth continue for another decade, but their numbers do not increase further.


27/31

Miscellaneous

Why Do I Yawn? When you are sleepy or drowsy the lungs do not

take enough oxygen from the air. This causes ashortage of oxygen in our bodies. The brain sensesthis shortage of oxygen and sends a message thatcauses you to take a deep long breath---a YAWN.


28/31

It is possible that yawns are contagious becauseat one time in evolutionary history, the yawnserved to coordinate the social behavior of a groupof animals.

When one member of the group yawned to signal

an event, all the other members of the group alsoyawned.

Yawns may still be contagious these daysbecause of a leftover response (a "vestigial"response) that is not used anymore.

None of this has been proven true and yawns arestill one of the mysteries of the mind.


29/31

New Word: Pandiculation

Pandiculation is the act of stretching andyawning.


30/31

Why Do I Sneeze? Sneezing is like a cough

in the upper breathingpassages. It is the body'sway of removing anirritant from the sensitive

mucous membranes of the nose. Many thingscan irritate the mucousmembranes. Dust, pollen,

pepper or even a coldblast of air are just someof the many things thatmay cause you to

sneeze.


31/31

What Causes Hiccups? Hiccups are the sudden movements

of the diaphragm. It is involuntary ---you have no control over hiccups, asyou well know. There are manycauses of hiccups. The diaphragm

may get irritated, you may haveeaten to fast, or maybe somesubstance in the blood could evenhave brought on the hiccups.

Documents

respiratorysystem2