Question

Alveoli has
A. Yellow fibrous connective tissue.
B. White fibrous connective tissue.
C. Areolar connective tissue.
D. Adipose connective tissue.

Answer 1

Alveoli are the tiny sac-like structures seen inside the lungs. They are the functional part of the lungs where the exchange or diffusion of respiratory gases takes place. A pair of lungs are seen in human beings and about 300 million alveoli in both the lungs. Alveoli are lined by thin squamous epithelial cells. Alveoli covers a large surface area of the lungs to enable increased area for the exchange of gases.

Complete answer:
The terminal bronchioles give rise to a large number of thin, vascularised, irregular walled, bag-like structures called alveoli which are lined by thin squamous epithelial cells. But beneath the squamous epithelial cells, the alveoli contain yellow fibrous connective tissue for support.
Four types of animal tissues are seen. They are epithelial tissue, connective tissue, muscular tissue, and neural tissue. Squamous epithelium coming under the epithelial tissue is made up of a single thin layer of flattened cells with irregular boundaries. They are found in alveoli and blood vessels.
Connective tissue is classified into loose connective tissue and dense connective tissue. Loose connective tissue has cells and fibers which are arranged loosely in a semi-fluid matrix. They include areolar connective tissue and adipose connective tissue. Areolar connective tissue acts as a support framework for epithelial cells and is seen beneath the skin. Adipose connective tissue is also seen beneath the skin and their function is the storage of fat.
Dense connective tissue includes the yellow fibrous connective tissue and white fibrous connective tissue. White fibrous connective tissue is seen in tendons and sheaths. Yellow fibrous connective tissue is mainly seen in ligaments, respiratory pathways, vocal cords. They contain a large number of yellow elastic fibers which are closely arranged.

The correct answer is option (A) Yellow fibrous connective tissue.

Note: The main tissues seen around the alveoli are the thin squamous epithelium. Yellow fibrous connective tissue is seen only for support. A type 2 alveolar cell called pneumocytes are present in the lungs which produce a lipoprotein called surfactant which reduces the surface tension of the fluid lining the alveoli thus preventing alveolar collapse and sticking of alveolar walls. Lack of surfactant can cause the collapse of alveoli leading to respiratory distress syndrome.