Question

What tube is used by both the digestive and respiratory systems ?
A. Oesophagus
B. Larynx
C. Pharynx
D. None of these

Answer 1

Hint: Food pipe also called oesophagus is the part of the alimentary canal which directs the food towards the stomach. Larynx also called a sound box is a cartilaginous box present in the trachea that is the windpipe.

Complete Answer:
- The human alimentary canal is the passage for food where the ingestion, digestion, assimilation, absorption and egestion of food takes place. These various activities take place through various enzymes.
- The human alimentary canal begins at buccal cavity and ends at rectum whereas the human respiratory system begins at an external one pair of nostrils located above the lips and ends at alveoli or the respiratory tree.
- Between the two systems discussed above, there is a common passage called a pharynx. It allows both food and the air to pass through it. It is made up of compound epithelium.
- Compound epithelium is the multi-layered epithelium present in the buccal cavity, salivary duct, pancreatic duct, pharynx and the dry surface of skin. Its main functions are protection against chemical and mechanical stresses.
- The food in the buccal cavity or the oral cavity passes into the pharynx before reaching the oesophagus. The opening of the oesophagus is the gullet. Similarly the opening of the windpipe is the glottis.
- When air passes through the respiratory system, it first enters through the external nostrils or nares present above the lips and then nasal passage and then internal nostrils leading to pharynx.
- The air from the pharynx enters the trachea or the windpipe through glottis. The glottis is covered by epiglottis which is the cartilaginous flap so as to prevent food from entering into the windpipe.
- Therefore the food from the pharynx reaches the oesophagus and then the entire digestive tract whereas the air from the pharynx reaches the trachea and then the respiratory tract entering lungs.
- The beginning of the pharynx is the base of the skull, it is a short muscular cone – shaped passageway. Connective tissue and thick fibres of muscles attach the pharynx to the base of the skull and other surrounding structures.

The correct option is C.

Note: Two types of muscles are present in the pharynx such as circular and the longitudinal muscles. During swallowing, the longitudinal muscles lift the walls of the pharynx. To push the food from the pharynx to the oesophagus constrictions need to be formed which are done by circular muscles, they also prevent air from being swallowed.