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Gas Exchange Medley
(Chemoreceptors/The Bohr Effect)

by Greg Crowther


A lot of physiology involves uncovering and understanding relationships between variables (e.g., when this goes up, that goes down). Here is a two-part song covering two such sets of relationships: those governing feedback control of ventilation, and those governing hemoglobin's affinity for oxygen. Depending on your learning goals, you could focus only on the chemoreceptor part, or only on the hemoglobin affinity part, or both.


[Part 1: chemoreceptor control of ventilation]

Breathing rate and metabolic rate need to match up great,
But when they could match better,
Chemicals serve as warning bells for the sentinels
Of the chemoreceptors.

That information is poured
Into the medulla, just above the spinal cord.

Ventilation's up (up!)
When O2 goes on down (down!).
Ventilation's up (up!)
When pH goes on down (down!).
Ventilation's up (up!)
When CO2 goes up (up!).
To get you back to setpoint,
Negative feedback comes around.

[Part 2: the Bohr effect]

Hemoglobin is cooperative, binding oxygen
In a sigmoid fashion,
Showing me its affinity -- that's the property
Of the strength of attraction.

Binding strength will rise and fall.
So said the data of Christian Bohr et al.

Affinity goes up (up!)
When temperature goes down (down!).
Affinity goes up (up!)
When CO2 goes down (down!).
Affinity goes up (up!)
When pH goes on up (up!),
So protons going up
Means affinity goes down.

Other Files

MP3 (demo; with Santa and His Elves)

sheet music (with melody play-back)

Lesson Plan

Songs like this one can be used during class meetings and/or in homework assignments. Either way, the song will be most impactful if students DO something with it, as opposed to just listening.

An initial, simple follow-up activity could be to answer the study questions below. A more extensive interaction with the song might entail (A) learning to sing it, using an audio file and/or sheet music as a guide, and/or (B) designing kinesthetic movements ("dance moves") to embody it. The latter activity could begin with students identifying the most important or most challenging content of the song, and deciding how to illustrate that particular content.

Study Questions

(1) Where in the body are these chemoreceptors located?

(2) At sea level, is ventilation rate more sensitive to changes in PCO2 or changes in PO2?

(3) What does it mean to say that hemoglobin binds oxygen "in a sigmoid fashion"?

(4) When temperature increases and PCO2 increases, does the hemoglobin-oxygen curve shift to the left or to the right?

(5) How does the Bohr effect improve oxygen delivery to exercising muscles?

(Answers may be found on the answers page.)