Objective 64: Transport of Carbon Dioxide and Oxygen

Discuss how oxygen and carbon dioxide are transported......

Oxygen transport

Basic hemoglobin saturation curve. It is moved to the right in higher acidity (more dissolved carbon dioxide) and to the left in lower acidity (less dissolved carbon dioxide)

About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the Hgb. About 1.5% is physically dissolved in the other blood liquids and not connected to Hgb. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity of between 1.36 and 1.37 ml O₂ per gram Hemoglobin, which increases the total blood oxygen capacity seventyfold, compared to if oxygen solely was carried by its solubility of 0.03 mL O₂ per liter blood per mmHg partial pressure of oxygen (approximately 100 mmHg in arteries).  With the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries, where the oxygen is consumed; afterwards, venules, and veins carry deoxygenated blood back to the heart.  Under normal conditions in adult humans at rest; hemoglobin in blood leaving the lungs is about 98–99% saturated with oxygen, achieving an oxygen delivery of between 950 - 1150 mL/min to the body. In a healthy adult at rest, oxygen consumption is approximately 200 - 250 mL/min, and deoxygenated blood returning to the lungs is still approximately 75% (70 to 78%) saturated. Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions. Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia. Sustained hypoxia (oxygenation of less than 90%), is dangerous to health, and severe hypoxia (saturations of less than 30%) may be rapidly fatal.  A fetus, receiving oxygen via the placenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), and, so, fetuses produce another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) in order to function under these conditions.

Carbon dioxide transport:
When blood flows through capillaries, carbon dioxide diffuses from the tissues into the blood. Some carbon dioxide is dissolved in the blood. A part of CO₂ reacts with hemoglobin and other proteins to form carbamino compounds. The remaining carbon dioxide is converted to bicarbonate and hydrogen ions through the action of RBC carbonic anhydrase. Most carbon dioxide is transported through the blood in the form of bicarbonate ions. Carbon dioxide (CO₂), the main cellular waste product is carried in blood mainly dissolved in plasma, in equilibrium with bicarbonate (HCO₃^-) and carbonic acid (H₂CO₃). 86–90% of CO₂ in the body is converted into carbonic acid, which can quickly turn into bicarbonate, the chemical equilibrium being important in the pH buffering of plasma. Blood pH is kept in a narrow range (pH between 7.35 and 7.45).

Transport of hydrogen ions:
Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin binds most of the hydrogen ions as it has a much greater affinity for more hydrogen than does oxyhemoglobin.

http://en.wikipedia.org/wiki/Blood

    Ok, so there's alot of information covered above!  We've been buzzing around this subject since back in BIO-100 when we talked about carrier proteins and Mrs. Gess did the football player tucking the ball into a safe hold in  order to get it up the field.  In this case, the football player is hemoglobin and oxygen is the ball.  The only difference is that hemoglobin is like a multi-handed player because it can actually carry up to four oxygen's at a time! 
     We touched further on this subject when we were discussing the physical components of blood and the fact that respiratory gases are included in those physical components, and that they also play a part in the overall pH of the blood.  Over seventy percent of the carbon dioxide in the blood travels as bicabonate ion and is quickly transported to the lungs. 

Nurse's Note: Oxygen saturation, also known as your O2 sat, is considered one of your basic vital signs in a hospital setting.  Your O2 sat is measured by the use of a handheld machine called a pulse-oximeter.  This device clips onto either a finger, toe, or earlobe and determines the amount of oxygen available to your tissues in just a few seconds. Nail polish should be removed prior to taking the reading if a fingertip is the desired testing site as it can misconstrue the reading.  An O2 sat below 95% is considered an emergency or crisis situation that requires immediate attention and is often referred to as Hypoxia.