In this lab, you'll explore respiratory physiology. First you'll learn about spirometry and the clinically useful lung volumes and capacities. Then you'll do an activity that demonstrates the role of

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Activity 2 : R egula tio n o f B re ath in g

Although oxygen levels are important, interestingly , oxygen is not the primary regulator of breathing

rate. Instead the primary regulator of ventilation is carbon dioxide and the carbon dioxide-generated

hydrogen ion concentration in the extracellular fluid of the brain. If breathing rate slows or if you hold

your breath, carbon dioxide will begin to build up in your body . This increase in plasma carbon

dioxide, carbon dioxide combines with water to form carbonic acid, which then dissociates into

bicarbonate and hydrogen ions as the reversible reaction below shifts to the right due to Le

Chatelier's principle:

CO + H O H CO HCO + H

The resulting increase in hydrogen ion concentration (lower pH, more acidic) strongly stimulates the

central chemoreceptors in the brain and the peripheral chemoreceptors in the carotid body and aortic

arch. These chemoreceptors increase their firing rate to the respiratory centers in the medulla

obligation and pons of the brain stem. The brain stem will then send the command via motor

neurons to your respiratory muscles (the diaphragm and intercostals) to cause the respiratory

muscles to contract faster or strong to rate or depth of breathing, respectively . This increase in depth

and rate of breathing will flush out the built up carbon dioxide and shift the reaction in the opposite

direction to return the blood pH to normal.

If you hyperventilate (breath too fast or too deeply, you'll flush carbon dioxide out faster than than the

tissues can produce it. In this case the equation above would begin to shift to the left, and your blood

would become more basic. To counteract this, the negative feedback mechanism would lead to a

decrease in ventilation, which would conserve carbon dioxide in the body to return the blood pH back

to normal.

While oxygen levels can influence breathing rate, they only do so if the partial pressure of oxygen

falls very low (<60 mmHg), which typically does not happen.

For this experiment you will examine the ef fects of eupnea (normal breathing) and hyperventilation

(faster and/or deeper breathing than normal) on the length of time that you can hold your breath

(apnea ). Before you begin the experiment, make sure you write down your hypothesis!

Part 1 : G en era tin g a H yp o th esis

Before you do the experiment, record your hypothesis on the worksheet:

Do you think you'll be able to hold your breath longer after eupnea or after hyperventilation?

Why?

P art 2 :  E upn ea f o llo w ed b y B re ath -H old in g

2 2 2 3 3- + 7/15/2020 Activity 2: Regulation of Breathing : Sum20 PYSO 001 #50663 HUMAN PHYSIOLOGY-Online

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1. While seated and relaxed, breathe normally for 2-3 minutes.

2. Have a stop watch ready (your phone or a clock with a second hand is fine) and press start as

soon as you take a breath in. Hold your breath as long as possible without swallowing or

exhaling. Record how long you were able to hold their breath on the worksheet.

3. Wait at least 3-5 minutes and then repeat two more times. Record your results and the

worksheet and calculate the average .

 P art 2 :  H yp erv en tila tio n f o llo w ed b y B re ath -H old in g

CAUTION: Hyperventilation can cause you to faint, so if you begin to feel dizzy or faint,

please stop the activity! As an added precaution, you should be seated in a location without

sharp corners or edges nearby .

1. After waiting 3-5 minutes, you will now hyperventilate by taking deepest breaths possible at your

normal rate (approximately 12/min) for 1 minute and then take a breath in.

2. Again, have a stop watch ready and beginning recording the length of time you can breath. Again

you should should hold your breath as long as possible without swallowing or exhaling. Record

how long you were able to hold your breath on the worksheet .

3. Wait at least 3-5 minutes and then repeat two more times. Record your results on the

worksheet and calculate an average . Then answer the related questions on the worksheet .