Tag: zoology

Alveoli are small pouches or sacs. Large number of alveoli occur inside each lung. The whole surface area of an alveolus functions as a respiratory surface. Due to large number of  alveoli in each lung, a very large area of respiratory surface becomes available (about $80{ m }^{ 2 }$) for exchange of gases. Thus, alveoli are designed to maximize the exchange of gases.

Trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of 5th thoracic vertebra into a right and left primary bronchi. Each bronchi undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles. The tracheae, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings. Each terminal bronchiole gives rise to a number of very thin, irregular walled and vascularised bag-like structures called alveoli. The branching network of bronchi, bronchioles and alveoli comprise the lungs. Thus trachea and bronchi are present outside the lungs and alveoli are tiny bags of lungs.

Hiccups occur due to hasty eating or wrong posture during the meal which allows the food particles to enter the windpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacent to the food pipe. But inside the throat, air and food share a common passage. During the act of swallowing a flap-like valve closes the passage of the windpipe and guides the food into the food pipe. If by chance,food particles enter the windpipe, hiccups can be experienced.

A.Bronchus - a passage of airway in the respiratory system that conducts air into the lungs.

B.Alveoli - any of the many tiny air sacs of the lungs which allow for rapid gaseous exchange.

C.Bronchioles - any of the minute branches into which a bronchus divides.

D.Hilum - a part of an organ where structures such as blood vessels and nerves enter the body.

So, the correct option is ‘Bronchioles’

Breathing involves expansion and contraction off lungs to adjust the partial pressure of relative gases for exchange. The process of inhalation occurs due to an increase in the lung volume (diaphragm contraction and chest wall expansion) which results in a decrease in lung pressure in comparison to the atmosphere. Thus, air rushes in the airway. The process of exhalation occurs due to an elastic recoil of the lung tissue which causes a decrease in volume, resulting in increased pressure in comparison to the atmosphere. Thus, air rushes out of the airway. 

A bronchus, also known as a main or primary bronchus, is a passage of airway in the respiratory tract that conducts air into the lungs. There is a right bronchus and a left bronchus and these bronchi branch into smaller secondary and tertiary bronchi which branch into smaller tubes, known as bronchioles. No gas exchange takes place in the bronchi. The trachea (windpipe) divides into two main or primary bronchi, the left and the right, at the level of the sternal angle and of the fifth thoracic vertebra or up to two vertebrae higher or lower, depending on breathing, at the anatomical point the carina of trachea. An alveolus is an anatomical structure that has the form of a hollow cavity. Thus, option B is correct.

The vertebral column, also known as the backbone or spine, is a bony skeletal structure found in vertebrates. Skull is present in head. The rib cage is formed by the vertebral column, ribs, and sternum and encloses the heart and lungs. In humans, the rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the pectoral girdle (shoulder girdle).