Respiratory system : brief and easy handout

Respiratory system

•          It consists of paired lungs and a series of air passages that lead to and form the lungs.

Function

•          Air conduction

•          Air filtration

•          Gas exchange

•          In addition, air passing through the larynx produce speech

•          The olfactory mucosa of nasal cavities carries sense of smell

The air passages of respiratory system consists of a conducting portion and a respiratory portion

Extrapulmonary region

•          Nasal cavities

•          Pharynx

•          Larynx

•          Trachea

•          Bronchi

The intrapulmonary region

•          Intrapulmonary bronchi

•          Bronchioles

•          Terminal bronchioles 

•          Respiratory bronchioles

•          Alveolar duct

•          Alveoli

Olfactory epithelium

The olfactory chemoreceptors are located in the olfactory epithelium, a specialized area of the mucous membrane in the superior conchae, located in the roof of the nasal cavity.

It is a pseodostratified ciliated columnar epithelium composed of three types of cells

•          Supporting cell

•          Olfactory cell

•          Basal cell

Lamina propria  is richly vascularized and possesses Bowman’s glands which produce a watery mucus

The respiratory epithelium

•      Most of the conducting portion is lined with ciliated pseudostratified columnar epithelium that contain rich population of goblet cells and is known as respiratory epithelium

Typical respiratory epithelium consists of 5 cell types

Ciliated cells:  Tall columnar cells with cilia that project into the mucus covering the surface of epithelium

Goblet cells : That synthesize and secrete mucus

Brush cells: Bear short, blunt microvilli

 Small granule cells: That resemble basal cells but contain secretory granules

 Basal cells : Stem cells from which the other cell types arise

Trachea

is a short, flexible, air tube about 2.5 cm in diameter and about 10 cm long 

The wall of the trachea consists of four definable layers

Mucosa: Composed of a ciliated pseusostratified epithelium and an elastin, fiber-rich lamina propria

Submucosa : Contains denser conn. tissue than the lamina propria

Cartilaginous layer : Composed the C shaped hyaline cartilages. Fibroelastic tissue & smooth muscle , the trachealis muscle , bridge the gap between the free ends of the C shaped cartilages at the posterior border of the trachea 

Adventitia: Composed of conn. Tissue that binds the trachea to adjacent structures

Bronchus

Bronchus are two type extra pulmonary bronchus and intra pulmonary bronchus

a bronchus is lined by  the respiratory epithelium with goblet cells and columnar ciliated cells.

 lamina propria (connective tissue ) contains serous glands and smooth muscle (SM).

Extra pulmonary Bronchus is surrounded by a continuous plate of cartilage but intra pulmonary bronchus is surrounded by discontinuous cartilaginous plates

Outer most part of bronchus is covered by adventitia a collagen fibres rich connective tissue

Terminal bronchiole

Difference between bronchus and bronchioles are : bronchus is surrounded by cartilage and bronchiole is not surrounded by cartilage

•      The smallest conducting bronchioles are referred to as terminal bronchioles

•      They are lined with the simple cuboidal epi. Interspersed with clara cells

•      No cartilage plates

•      No glands

•      No goblet cell

•      Well developed and continuous  smooth muscle cells layer are  surrounded the thin lamina propria of terminal bronchiole

•      Outer most part is surrounded by the adventitia 

Respiratory bronchioles

The difference between terminal and respiratory bronchiole are :

Terminal bronchiole contain continuous layer of smooth muscles cells and respiratory bronchiole contain discontinuous smooth muscle cells layer

•      It is lined by simple cudoidal epithelium consisting of some ciliated cells and clara cells

•      Clara cells have three functions:

1. They produce one components of surfactant
2. They act as a reserve cells
3. They detoxify the noxious substances 

•      Alveolar outpocketing are found in the wall of respi. bronchioles

•      A thin, incomplete layer of smooth muscle surrounded the epithelium

•      Each res. Bronchioles gives rise to an alveolar ducts into which open numerous alveoli.

Alveoli

•      They are the site of gas exchange

•      Each alveoli consists of a pocket, open at one side and surrounded by a rich network of pulmonary capillaries

•      the wall between adjacent alveoli is called the alveolar septum. It is formed by two layers of alveolar epithelium with their basement membranes and capillaries. The alveolar septa contain small openings  called alvealar pores  which allow equalisation of pressure between  alveali  and provide a collateral air circulation 

Alveoli:

its epithelium is composed of type I & II alveolar cells & occasional brush cells

Type I alveolar cells/ type I pneumocytes are extremely thin squamous cells that line most (95%) of surface of the alveoli. But number of type II alveolar cells are more than the type I alveolar cells

They are not capable of cell division

•         Type II pneumocytes or septal cells are secretory cells

•         These are cuboidal cells

•         The number of the cell is  more than the type I pneumocytes

•         They retain capacity for cell division & can differentiate into type I pneumocyte

•         They secrete surfactant

Surfactant: A surface-active material which reduces surface tension within the alveoli , preventing  alveolar collapse during expiration
 

•         Secretion of surfactant by a type II cell. Surfactant is a protein-lipid complex synthesized in the rough endoplasmic reticulum and Golgi complex and stored in the lamellar bodies. It is continuously secreted by means of exocytosis (arrows)