Gas Exchange

GAS TRANSPORT IN THE BODY

OXYGEN 

1. 98% BINDS to the hemoglobin found in red blood cells (RBCs).  RBCs carry oxygen to the tissues where oxygen dissociates from the hemoglobin and diffuses into the cells of the tissues. 
2. 2% DISSOLVES in water in the plasma of the capillaries.

CARBON DIOXIDE

CELLULAR RESPIRATION

Cellular respiration includes 3 major steps which occur mainly in the cytoplasm of the cell and within the mitochondria of the cell. 

1. Glycolysis: The breakdown of glucose into pyruvate, ATP, H2O, and heat.
2. Krebs Cycle: Produces NADH from pyruvate.
3. Oxidative Phosphorylation: Produces ATP from NADH, oxygen, and H+. The oxygen plays the role of electron receptor in an electron transport chain to produce ATP.

The net formula for cellular respiration is:

Glucose + 6 Oxygen → 6 Carbon Dioxide + 6 Water + 38 ATP

OXYGEN SATURATION

OXYGEN DISSOCIATION CURVE

BOHR EFFECT

The Bohr effect describes the delivery of oxygen to the muscles and tissues where metabolism is occurring and carbon dioxide is being produced. 

The Bohr effect enables the body to adapt to changing conditions and makes it possible to supply extra oxygen to tissues that need it the most.  

How does hemoglobin know when to take or give up oxygen?

First let's review pH: it is a measure of acidity (proton (H⁺) concentration). 

The lower the pH, the higher the  [H⁺], and the more acidic. 

The higher the pH, the lower the [H⁺], and therefore the less acidic (more basic/more alkaline). 

Oxygen is an electron hog and it pulls shared electrons close to itself. 

Hydrogen, which only has a single positive proton to pull back so sometimes leaves an electron behind, thus hydrogen is now just a single proton without an electron [-] to balance it, so it has a positive charge, H⁺. This makes the overall concentration more ACIDIC.

AFFINITY = likes something more 

BOHR EFFECT - hemoglobin binds oxygen more tightly at high pH than it does at low pH. 

 As pH rises, hemoglobin loses hydrogen ions and this causes a subtle change in its structure that enhances its ability to bind oxygen. 

When pH falls, the reverse happens: hemoglobin picks up hydrogen ions and its affinity for oxygen decreases.  

FACTORS AFFECTING BOHR EFFECT

• Higher Temperature (Higher temperatures in the tissues decreases affinity)
• O2 Partial Pressure (As altitude increases or exercise intensity increases, partial pressure of oxygen (PaO2) decreases as a result. In response to this lowered oxygen pressure)
  

• Blood pH (more acidic)
• Pressure of CO2 unloads oxygen (Increasing CO2 shifts the curve to the right, Hyperventilation and hypocapnia shifts the curve to the left)
• Concentration of BPG/DPG (Increased 2,3-BPG/DPG (eg. in response to hypoxia or erythropoietin) shifts the curve to the right)

Left Shift: higher O2 affinity (holds on to oxygen)

Neutral: Homeostasis 

Right Shift: lower O2 affinity (gives up oxygen)

BOHR EFFECT & EXERCISE

When you workout or exercise you are going to see and feel the following things

1. The decrease in pH (from the muscle cells getting more acidic- build LACTATE)
2. An increase in muscle temperature (from muscle contraction- doing work)
3. An increase in the partial pressure of carbon dioxide (from the working muscles- byproduct of making ATP)
4. An increase of a byproduct molecule from glycolysis known as 2,3-BPG.

During Exercise

Working muscles NEED more oxygen and therefore, during exercise increasing muscle blood flow will allow more oxygen to get to the mitochondria. 

Exercising muscle cells release H+, CO2, and lactate into blood capillaries, and there is also a higher temperature in working muscle than in inactive tissues. 

Blood entering capillaries of exercising muscles is acutely exposed to these changes, which causes a rapid decrease in Hb-O2 affinity. 

Temperature increases from 37°C at rest to 41°C during exercise and increases unloading of O2 from HGB considerably 

Trained individuals have a higher Bohr effect at low SO2 probably due to elevated 2,3-DPG which might cause an even greater increase in the arterio-to-venous O2 difference.

Physical training can increase total HGB, which enhances O2-carrying capacity!

Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' "to make") is the process which produces red blood cells (erythrocytes), erythropoiesis occurs in the bone marrow.