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Gas Exchange. By Adriana Jimenez & Daisy Martinez. Ventilation, or breathing, is the alternate inspiration (inhaling) and expiration (exhalation) of air. Terrestrial vertebrates rely on ventilation to maintain high O2 and low CO2 concentrations at the gas exchange surface.

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Gas Exchange

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Gas Exchange

By Adriana





  • Ventilation, or breathing, is the alternate inspiration (inhaling) and expiration (exhalation) of air.

  • Terrestrial vertebrates rely on ventilation to maintain high O2 and low CO2 concentrations at the gas exchange surface.

42.6 : Breathing Ventilates the Lungs


  • Positive Pressure Breathing: air is forced into the lungs.

How an Amphibian Breathes

How a Mammal Breathes:

  • Lungs pull air into the lungs with the use of muscle action: rib muscles and diaphragm contract.

    • lung volume increases.

  • Negative Pressure Breathing.

How mammals breathe…

  • Visceral Pump: in some species, running causes the visceral organs (like the stomach & liver) to slide back and forth in the body cavity with each stride, this further increases ventilation volume.

  • Tidal volume: the volume of air a mammal inhales and exhales with each breath.

  • Vital capacity: the maximum tidal volume.

  • Residual Volume: the air that remains in the lungs.

Control of Breathing in Humans:

  • Breathing control centers: located in medulla oblongata and the pons; the medulla sets the basic rhythm, while the pons moderates it.

  • Sensors in carotid arteries in the neck and in the walls of the aorta help monitor O2 and CO2 concentrations and blood pH.

  • Low O2 concentration leads to an increased breathing rate to offset the CO2 levels

  • Low pH leads to an increased breathing rate, can lead to hyperventilation

  • The role of partial Pressure gradients

  • Respiratory pigments

    • Respiratory pigments transport gases and help buffer the blood. Respiratory pigments greatly increase the amount of 02 that blood can carry.

42.7: Respiratory Pigments Bind & Transport Genes


  • Partial Pressure is the diffusion of a gas, whether present in air or dissolved in water, depends on differences in a quantity.

  • Atmosphere exerts a total pressure of 760 mm HG.

  • Oxygen and co2 diffuse from where their partial pressures are higher to where they are lower.

The Role ofPartial Pressure Gradients

Loading and unloading of respiratory gases

1. blood arriving at the lungs via the pulmonary arteries has a lower Po2 and a higher P co2 than the air in the alveoli.

2. by the time the blood leaves the lungs in the pulmonary veins, its Po2 has been raised and its Pco2 has been lowered.

After returning to the heart, this blood is pumped through the systematic circuit.

3. in the tissue capillaries, gradients of partial pressure favor the diffusion of o2 out of the blood and co2 into the blood.

Because cellular respiration removes o2 from and adds co2, to the interstitial fluid. (by diffusion, from mitochondria in nearby cells.)

4. after the blood unloads o2 and loads co2 it is returned to the heart and pumped to the lungs again.

Where it exchanges gases with air in the alveoli.

  • The low solubility of o2 in water (&blood) is a problem for animals whom rely on the circulatory system to deliver o2.

  • Respiratory pigments transport most of their o2 bound to certain proteins

    • Circulate with the blood.

    • Greatly increase the amount of oxygen that can be carried in blood.

Respiratory Pigments

A diversity of respiratory pigments have evolved in various animal taxa.

  • Hemoglobin, Respiratory Pigment of almost all vertebrates.

    • Consists of 4 subunits, called a heme group that has an iron atom at its center.

    • Each molecule can carry 4 molecules of O2. Also helps transport CO2 and assists in buffering.

OXYGEN transport

  • Like most pigments, it must bind reversibly, loading O2 in the lungs and unloading it in other parts of the body.

Oxygen Transport

  • Loading and unloading depends on cooperation between the subunits of the hemoglobin molecule.

  • A slight change in O2 Partial Pressures causes hemoglobin to load or unload O2 .

  • When cells in a particular location begin working harder(during exercise) PO2 dips in their vicinity as O2 is consumed in cellular respiration.

Oxygen transport cont…

Dissociation curve

  • Bohr Shift: a drop in pH lowers the affinity of hemoglobin for O2.

  • When carbonic acid forms, an active tissue lowers the pH of its surrounds and induces hemoglobin to release more O2.

(b) pH&Hemoglobin Dissociation

CO2 Transport


  • Campbell, Neil A., and Jane B. Reece. "Chapter 42.6-7." Biology. 7th ed. San Francisco: Pearson, Benjamin Cummings, 2005. 888-90. Print.

  • Egan, Donald F., Robert L. Wilkins, James K. Stoller, and Robert M. Kacmarek. "Carbon Dioxide and Cerebral Blood Flow." Egan's Fundamentals of Respiratory Care. 9th ed. St. Louis, MO: Mosby/Elsevier, 2009. 313-14. Print.

  • Marieb, Elaine Nicpon, Jon Mallatt, Patricia Brady. Wilhelm, and Matt Hutchinson. "Chapter 21 - The Respiratory System." Human Anatomy. 5th ed. San Francisco, CA: Pearson, 2010. 614+. Print

  • Benjamin Cunning, . "Chapter 42 - Circulation and Gas Exchange." Pearson Education, 2005. Web. 11 Mar 2012.

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