Question

Figure 16.9 Which of the following statements about the human respiratory system is false? a. When we breathe in, air travels from the pharynx to the trachea b. The bronchioles branch into bronchi. C. Alveolar ducts connect to alveolar sacs. d. Gas exchange between the lungs and blood takes place in the alveolus.

Short answer

The false statement about the human respiratory system is B. The bronchioles branch into bronchi. In fact, bronchi branch into bronchioles.

Step-by-step solution

Understanding the Respiratory System

The human respiratory system is a series of organs that takes in oxygen and expels carbon dioxide. The primary organs of the respiratory system are lungs, which carry out this exchange of gases as we breathe. When we breathe in, air enters the body through the nose or mouth, goes down the trachea into bronchus and then into the lungs. Within the lungs are millions of tiny air sacs called alveoli where the exchange of gases takes place.

Analyzing Each Statement

Statement A says that air travels from the pharynx to the trachea when we breathe in, which is true. Air enters the body through the nose or mouth, passes through the pharynx (throat) and then into the trachea (windpipe).\nStatement B says that bronchioles branch into bronchi. In fact, the trachea splits into two bronchi (singular: bronchus), one for each lung, and these further branch into smaller bronchioles. So, statement B is false. \nStatement C says alveolar ducts connect to alveolar sacs, which is true. The alveolar ducts are small passages that connect the respiratory bronchioles to alveolar sacs, each of which contains a collection of alveoli (small mucosal pouches where gas exchange occurs).\nStatement D says that gas exchange between the lungs and blood takes place in the alveolus, which is also true. The walls of the alveoli are extremely thin (allowing for the quick exchange of gases), and surrounded by a network of capillaries. Here, oxygen passes into the blood being pumped by the heart around the body, and carbon dioxide in the blood passes into the alveoli ready to be exhaled.

Identifying False Statement

Based on the above analysis, we concluded that statement B is false because bronchi branch into bronchioles, not the other way around.

Key concepts

Gas Exchange

Gas exchange is a crucial process in the human respiratory system. It involves the transfer of oxygen from the air we breathe into the blood, and the removal of carbon dioxide from the blood to be exhaled. This occurs in the alveoli, tiny air sacs within the lungs. The walls of the alveoli and the surrounding capillaries are incredibly thin, allowing for efficient gas exchange.
Oxygen, which is vital for cellular respiration, diffuses from the alveoli into the bloodstream where red blood cells transport it throughout the body. Conversely, the waste product carbon dioxide diffuses from the blood into the alveoli to be expelled from the body.

• Gas exchange is essential for cellular metabolism and energy production.
• It maintains the balance of oxygen and carbon dioxide in the bloodstream.

The whole process is driven by differences in pressure; oxygen and carbon dioxide move from areas of higher to lower concentrations.

Bronchioles

Bronchioles are tiny branches of airways that stem from the bronchi within the lungs. They play a key role in air passage as they carry inhaled air from the bronchi to the alveoli where gas exchange occurs. Unlike the larger bronchi, bronchioles are smaller and lack cartilaginous support, offering flexibility and elasticity.
The bronchioles further divide into even finer tubes known as terminal bronchioles and finally into respiratory bronchioles that connect directly with alveolar ducts.

• They ensure that inhaled air reaches all parts of the lungs.
• Muscle layers surrounding bronchioles can constrict or relax to regulate airflow.

This regulation of airflow is crucial during activities such as exercise or in response to irritants.

Alveoli

Alveoli are tiny balloon-like structures at the end of the respiratory tract where gas exchange occurs. They are clustered like grapes and are surrounded by a network of capillaries.
This design maximizes the surface area available for gas exchange. The walls of the alveoli are one-cell thick, creating a very short diffusion path for gases.

• A typical adult lung contains about 300 million alveoli, providing ample surface area for gas exchange.
• Alveoli are coated in a substance called surfactant that prevents their collapse.

During inhalation, air fills the alveoli, allowing oxygen to pass into the blood, and during exhalation, carbon dioxide is expelled from the alveoli.

Pharynx and Trachea

The pharynx and trachea are vital components of the respiratory tract. When you breathe in air through your nose or mouth, it first passes through the pharynx. The pharynx is a muscular tube that serves as a pathway for both air and food. It connects the nasal and oral cavities to the larynx and esophagus.
From the pharynx, air moves into the trachea, also known as the windpipe. The trachea is a rigid tube supported by C-shaped cartilaginous rings, providing structural support and keeping the air passage open.

• The trachea bifurcates into two bronchi, each leading to a lung.
• It is lined with cilia and mucus to filter out dust and pathogens.

Understanding the role of the pharynx and trachea highlights the importance of these structures in directing airflow to the lungs.