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 closely correlate,
But when they could match better,
Chemicals serve as warning bells for receptor cells
Known as chemoreceptors.

That information is poured
Into the medulla, just above the spinal cord.
(Hey!)

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.
(Hey!)

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.

• karaoke

• MP3 (demo)

• music video

• sheet music (with melody play-back)

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) illustrating it with pictures, bodily poses, and/or bodily movements. 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.

(1) The song opens with the line, "Breathing rate and metabolic rate closely correlate." What does this mean?

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

(3) If you aren't breathing enough to keep up with your body's metabolism, what will happen to the levels of CO₂ and H+ in your blood? (That is, will they get higher or lower?)

(4) The end of the first part of the song mentions setpoint and negative feedback. How does this specific example fit the general pattern of homeostasis via negative feedback? What is/are the regulated variable(s) here?

(5) At sea level, is ventilation rate more sensitive to changes in P_CO2 or changes in P_O2?

(6) What is meant by the line that hemoglobin binds oxygen "in a sigmoid fashion"?

(7) When temperature increases and P_CO2 increases, does the hemoglobin-oxygen curve shift to the left or to the right?

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