Question

Where is the respiratory membrane located?

Answer 1

Hint: Respiration is the process of movement of oxygen inside the body from the outside environment and $CO_2$ comes out from inside the body. Respiration is of two types cellular and physiological in animals, cellular respiration takes place in individual cells of an organism, while physiological respiration is the diffusion and transport of metabolites between the organism and therefore the external environment.

Complete answer:
The respiratory system is divided into two divisions: A.conducting division and B. respiratory division. The conducting division is from the external nostril to the lungs.

Air passage in conducting division:

External nostril---> vestibule----> Nasal chamber-----> internal nares----> nasopharynx-----> pharynx----> glottis-----> larynx-----> trachea------> bronchial tree------> respiratory tree

Bronchial tree and respiratory tree:

When trachea enters into the thoracic cavity, it divides into two branches called primary bronchi at the level of the fifth thoracic vertebra.Branches of primary bronchi Upto terminal bronchioles make a bronchial tree.

Terminal bronchioles divide to form respiratory bronchioles and branches of respiratory bronchioles make the respiratory tree.

In the bronchial tree cardiac rings are present, while these are absent in the respiratory tree.

Gaseous exchange occurs in the respiratory tree while it is absent in the bronchial tree.

Exchange zone is the site of actual diffusion of $O_2$ and $CO_2$ between blood and atmospheric air.

The conducting zone transports the atmospheric air of the alveoli, clears it from foreign particles, humidifies and also brings the air to body temperature.

A pair of lungs are present in the thoracic cavity. In human beings the right lung is made up of 3 lobes and the left lung is made up of 2 lobes.

Each lobe is further divided into several lobules by the septaby septa of connective tissue. Each lobule is further divided into several air-sacs and in the end, each air sacsacs is lastly divided into 3 or 4 alveoli,which is also termed thetermed as the unit of lungs.

Approx 300 million alveoli are present in both lungs. Inner alveolar surface area of both lungs is approx 100 m².

Wall of alveoli consists of two layers, the outer layer is composed of yellow fibrous connective tissue, the inner layer is composed of simple squamous epithelium. Squamous cells of alveoli are called pneumocytes. Most of these pneumocytes help in Gaseous exchange, whereas few pneumocytes secrete lecithin which acts as surfactant which prevents alveoli from remaining collapse by reducing its surface tension.

The alveoli wall is made up of connective tissue and it is richly supplied with blood capillaries. These blood capillaries come from the pulmonary artery.

Respiratory membrane:

It's thickness is about 0.2 mm.
It is made up of alveolar epithelium + epithelial basement membrane+thin interstitial space + capillary basement membrane+capillary endothelial membrane.

So the respiratory membrane is located inside the lungs at the site of terminal alveolus.

Note:
The respiratory membrane in human beings is about 0.6 micrometers thick and is made up of the alveolar squamous cell, the capillary endothelial cell, and two fused basement membranes (formed by the alveolar and capillary cells). The main function of the respiratory system is to provide oxygen to the body and eliminate waste product which is $CO_2$ out of the body and also helps in maintaining acid-base balance. The bonding of $O_2$ to hemoglobin within the RBCs causes their color to vary from purple to red.