In Investigation One, students explored the nervous system. Students counted eye blinks to study the effects of autonomic nervous control of the eyelids. Students also engaged in memory tests to learn how the brain controls thought and memory. Finally, students examined the role of the sensory nervous system by exploring reaction time. In Investigation Two, students modeled a joint to investigate how skeletal muscle and bone interact to cause movement. Investigation Three continues students’ introduction to the human body by providing an opportunity for them to explore the respiratory system.

The respiratory system is responsible for obtaining oxygen for the body and removing carbon dioxide, a waste gas, from the body. The respiratory system also provides the mechanisms for speech. The respiratory system consists of the nose, pharynx, larynx, trachea, and lungs.

The nose is the entry point for oxygen-containing air and the exit point for carbon dioxide. The nose is the lung’s first defense against disease-causing airborne particles, such as bacteria and viruses. The nose is lined with tiny hairs to catch particles such as dust. The nose is also lined with special mucosal cells that produce mucus to trap particles not trapped by the hairs. It should therefore not be surprising that one of the COVID19 diagnostic tests involves swabbing the inside of a patient’s nostril with a Q-Tip. 

The mucosal cells also warm and humidify the air as it enters the body. This is important because for the lungs to exchange gases and work properly, the surface of the alveoli must be kept moist. Dry air irritates the respiratory tract. Since cold air holds less moisture than warm air, our bodies must add a great deal of water to inhaled air, up to liters a day. The moistness of the air in the lung can be easily demonstrated by exhaling with an open mouth on a mirror or other shiny surface.

Air enters the nose and passes through the pharynx, which is the common area shared by the trachea and esophagus. This intersection point allows a person to inhale air by mouth if necessary. However, this is also the area where food material or other swallowed objects may cross from the digestive system into the respiratory system and cause choking. Naturally, talking and gasping for air while eating and swallowing should be avoided.

Air moves from the pharynx into the larynx. The larynx is also called the voice box because it is the location of the vocal cords. Vocal cords making varying loudness of sound are shown here. The vocal cords are actually a valve that opens and closes very rapidly to form sound by controlling the passage of air from the lungs. The vocal cords remain open during regular breathing activity, narrowing only when a person talks. Try feeling your throat with your fingers while you speak to detect the vibrations of your own vocal cords. Notice the change in vibrations when you make a very low versus a very pitched note.

Larynx to Lung

Air passes from the larynx into the trachea or windpipe. The trachea is the main air passage leading into the lungs. The air passages branch into two bronchi (single bronchus) or bronchial tubes. Each bronchus connects the trachea to a lung. The bronchus leads to a series of smaller bronchioles, which in turn serve even smaller bronchioles. At the end of the smallest bronchiole is an air sac, called an alveolus (plural alveoli).

Gas Exchange in the Alveoli

The alveolus is surrounded by a network of tiny blood vessels called capillaries. The capillaries bring de-oxygenated blood to the lungs where the carbon dioxide is transferred to the alveolus for exhalation and oxygen is transferred to the blood for transport to the remainder of the tissues in the body.

The alveoli are also surrounded by elastic support tissue. This elastic tissue stretches when the diaphragm contracts, expanding the alveoli and drawing air into the lungs. This process is called inhalation. When the diaphragm relaxes, the elastic tissue relaxes and forces the carbon dioxide-laden air back out of the lungs. This process is called exhalation. Respiration is primarily under the control of the autonomic nervous system. However, a person has the ability to also voluntarily control his or her breathing. This allows a person to speak, or to protect his or her lungs from inhaling a dangerous substance such as an airborne chemical or water.

The body adjusts the breathing, or respiratory, rate in response to the needs of the rest of the body’s tissues. The respiratory rate increases during exercise to meet the muscle’s demands for oxygen. When the body is at rest, the respiratory rate slows in response to a lower need for oxygen. When a person exercises, the brain responds to decreased oxygen levels in the blood by increasing the rate of breathing. This corresponds to an increase in the rate of blood passage through the capillaries around the alveoli. In Investigation Three, students will explore the respiratory system by measuring respiratory rate at rest and during exercise. Students will also explore lung function through the use of a model, and explore lung capacity by calculating the amount of air they can exhale after taking a deep breath.

Finally, no discussion of the human respiratory system would be complete without including a warning of the dangers of tobacco smoking. From what we have just discussed about the respiratory system, it is clear that any chemicals or particles that we inhale go deep into our lungs and then may even be transported into the blood. The graphic here can be clicked to launch a full-sized copy in a new window. The graphic contains information about the contents of tobacco smoke. As noted, there are more than 7,000 chemical compounds in tobacco smoke, at least 70 of which are confirmed to cause cancer.

COVID19: Affect on the Respiratory System

During the recent COVID19 virus pandemic, students have likely become more than familiar with the concept that disease-causing pathogens can easily gain access to our bodies through our respiratory system. Thus the need for masks. Pathogens like the coronavirus COVID19, which likely originated in China, can also gain access to our bodies through exposed mucosal tissue like the membranes around the eyes.

One of the most deadly effects of COVID19 is that it interferes with the normal exchange of gases in the alveoli. This leads to low blood oxygen levels that can damage other organs. In addition, the body responds to COVID19 infection in the lung by causing various secretion to fill the alveoli with fluid, which further impairs breathing and blood oxygenation. The best way to avoid the dangers of COVID19 infection is to be vaccinated. That way, even if you do come in contact with the virus, you will be unlikely to become sick from it. The cartoon below provides some simple advice to stay healthy. These steps work not only for COVID19 but many other respiratory pathogens as well.