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Biology LibreTexts

Respiratory System

Exploring the Respiratory System

Structure of the Mammalian Respiratory System: Models and Displays

Identify the following structures on the human torso model and on the model of a human head (longitudinal section):

  • pharynx, epiglottis, glottis, trachea, bronchi, bronchioles
  • How many lobes does the left lung have? How many lobes does the right lung have?

Model alveoli - Observe a model of alveoli from a mammal lung. This model is a magnified view of a small section of the lung Note the networks of capillaries that surround each alveolus. Part of the model shows a cutaway view into a cluster of alveoli.

  • Identify alveolar ducts and alveolar sacs.

Model lung - Observe the model lung composed of balloons in a bell jar. Each balloon represents one lung. The plastic sheet covering the bottom of the jar represents the diaphragm. Observe how the model diaphragm can be used to inflate the model lungs.

Dried sheep lung - Be careful with this specimen; it is fragile. Why is the lung so light?

Model respiratory tree - Observe the model respiratory tree and note the branching pattern of the bronchi and bronchioles. Identify primary, secondary, and tertiary bronchi.

Volumes

The procedures for the rest of this laboratory exercise (below) might be easiest to do if you work with one or two lab partners. Each group of students (lab partners) should do the procedures or measurements one time and share the data.

A spirometer will be used to measure the various lung capacities described below. The spirometer can only measure air that you exhale. Do not inhale air from the spirometer tube.

The tidal volume (TV) is the amount of air that moves into and out of the lungs during normal breathing. This is approximately 500 ml for many people. Use the spirometer apparatus to measure your tidal volume. This can be done by measuring the amount of air exhaled during normal breathing. Repeat this procedure five times and calculate an average.

Expiratory reserve volume (ERV) is the amount that can be expired beyond that which is expired during normal quiet breathing. This is approximately 1000 to 1200 ml for many people. Measure your expiratory reserve volume by exhaling a normal breath. Then, after the breath is exhaled, use the spirometer to measure how much additional air can be exhaled.

Vital capacity is total amount of exchangeable air that your respiratory system can hold. Measure your vital capacity by inhaling until your lungs are as full as possible and then measuring the amount of air that can be exhaled. Be sure to exhale as much as possible.

Inspiratory reserve volume (IRV) is the amount that can be inspired beyond the tidal volume. It is approximately 2100 to 3200 ml. This may be difficult to measure but can be determined by subtraction.

\[\textrm{Vital capacity = ERV + TV + IRV}\]

The equation above can be rearranged to produce:

\[\mathrm{IRV = Vital\: capacity - ERV - TV}\]

Inspiratory capacity = TV + IRV

Breathing Rate

Measure your breathing rate while resting (breaths per minute).

Minute volume is the amount of air exchanged in one minute. This is equal to the tidal volume (TV calculated above) multiplied by the breathing rate (breaths per minute). Calculate your minute volume and record it on the data sheet.

Exercise

Run up and down one flight of stairs three times.

Immediately after finishing, measure your breathing rate (breaths per minute) and also calculate your mean Tidal Volume based on 5 samples taken immediately after exercise. Multiply these two values to calculate your minute volume after exercise.

How does the minute volume after exercise compare to that before exercise (calculated above)?

Oxygen and Carbon Dioxide

During cellular respiration, energy stored in glucose and other organic molecules is used to produce ATP. The reactions that break down these organic compounds release CO2 and consume O2.

\[\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \textrm{36-38 ATP}}\]

Oxygen is needed by cells because it serves as the final electron acceptor in the electron transport chain in the mitochondria. Carbon dioxide is produced as the glucose molecule is disassembled during the process.

An important function of the respiratory system is to deliver oxygen to the body's cells and to remove carbon dioxide. As a result, the oxygen concentration in air that is exhaled should be less than that in air that is inhaled. The concentration of carbon dioxide should be greater in air that is exhaled than it is in air that is inhaled.

pH of Water with Dissolved CO2

Background Information

Our breath contains a higher proportion of carbon dioxide than the air because it is produced by our cells and eliminated by the respiratory system.

When carbon dioxide dissolves in water it forms carbonic acid, which dissociates to produce hydrogen ions (H+) and bicarbonate ions (HCO3-) as shown by the equation below.

\[\mathrm{CO_2 + H_2O \leftrightarrow H_2CO_3   \leftrightarrow \sideset{ }{_{3}^{-}}{HCO} +\:  H^+}\]

When we bubble our breath in water, the solution becomes acidic; the equation above moves to the right and the increase in hydrogen ions decreases the pH.

This experiment will measure the change in pH associated with the addition of CO2 to water. This has implications for our respiratory system. Elimination of CO2 when we exhale moves the equation toward the left and raises pH of our blood and body fluids. The rate of respiration is determined, in part by pH. Also, most of the CO2 transported by the circulatory system is carried in the form of bicarbonate ions (HCO3-).

Procedure

Set up the pH probe by following the instructions given in the link below.

Obtain a 1 liter beaker and rinse it thoroughly. Add approximately 200 ml of tap water to the beaker.  

Insert the pH probe into the water and let it stabilize for at least 5 minutes while occasionally stirring.

After the 5-minute period, press the "Collect" button on Logger Pro and then use a drinking straw to exhale into the water for 3 minutes.

Record the initial and final pH values.

Rinse the probe with deionized water and return it to its bottle of liquid.

Keep this equipment at your table because it will be used again in this lab.

Gas Concentration in Exhaled Air

Oxygen

Connect an oxygen probe to the probe interface box.

Start Logger Pro if it is not already running.

The percent of oxygen gas in the air is displayed in the lower left part of the computer screen. Wait until the indicator stabilizes, then record the oxygen concentration in the air.

Use a drinking straw and slowly exhale into the probe sample bottle until the bottle is filled with exhaled air.

Use the probe to cap the bottle. When the reading stabilizes, record the percent of oxygen in your exhaled air.

Keep the O2 sensor and sampling bottle at your table because they will be used later in this lab.

Carbon Dioxide

Connect a CO2 probe to the probe interface box.

Start Logger Pro.

The amount of carbon dioxide in the air (parts per million or ppm) is displayed in the lower left part of the computer screen. Wait until the indicator stabilizes, then record the carbon dioxide concentration in the air.

Use a drinking straw and slowly exhale into the probe sample bottle until the bottle is filled with exhaled air.

Use the probe to cap the bottle. Observe the value of the concentration reading. Does it increase? The equipment is not capable of displaying CO2 concentrations higher than 5000 ppm. It is likely that your exhaled breath has a CO2 concentration that is higher than this. In this case, the meter will stop reading at approximately 5000 ppm.

Exercise

Exercise increases the energetic needs of the working muscles. In response, glucose is metabolized at a faster rate in order to provide additional ATP needed for muscle contraction. The respiratory system must supply additional O2 to the muscles and remove additional CO2 produced by the muscle cells. We will measure increased O2 consumption and CO2 production using the procedures that you used earlier in this lab.

Add 200 ml of tap water to a 400 ml beaker.

Connect the pH probe to the probe interface box.

Start Logger Pro.

Insert a pH probe into the water and let it stabilize for at least 1 minute while occasionally stirring.

The equipment (water and pH probe) should be set up and ready to use before you continue.

Bring a gas sampling bottle, cap, and drinking straw with you to a staircase. Your lab partner can hold these items while you run up and down the stairs at least three times.

Immediately after you finish, use the drinking straw to fill the sample bottle with exhaled air and then put the cap on the bottle. The O2 concentration in the sample will be measured later.

After you obtain a sample of exhaled air, return immediately to the lab and begin exhaling bubbles into the water for 3 minutes. Record the initial pH of the water and the pH after 3 minutes.

Remove the pH probe and connect the O2 sensor to the probe interface box. Measure the O2 concentration in the atmosphere and and then measure the O2 concentration in the sample bottle that you filled after exercising. Record these values.

Questions

How did the rate of CO2 production after exercising compare with the rate of production while not exercising? Explain how you know this.

How did the rate of O2 consumption after exercising compare with the rate of consumption when not exercising?