CH.6 Oxygen and Carbon Dioxide Transport Flashcards
Oxygen Transport
–the transport of oxygen between the lungs and the cells of the body is a function of the blood and the heart
2 Methods Oxygen is carried in the Blood
–As dissolved oxygen in the blood plasma
–chemically bound to the hemoglobin that is encased in the erythrocytes or red blood cells
Oxygen dissolved in the blood plasma
–as oxygen diffuses from the alveoli into the pulmonary capillary blood, it dissolves in the plasma of the blood
–the quantity of oxygen that dissolves in the plasma is a function of Henry’s Law
–At normal body temperature about 0.003mL of oxygen will dissolve in 100mL of blood every 1 MM HG of P02
Henry’s Law
–the amount of gas that dissolves in a liquid (in this case, plasma) at a given temperature is proportional to the partial pressure of the gas
Oxygen bound to hemoglobin
–Most of O2 that diffuses into the pulmonary capillary blood rapidly moves into the RBCs and chemically attaches to the Hemoglobin (HB)
–Each RBC contains approximately 280 million HB molecules, which are highly specialized to transport oxygen and carbon dioxide
Oxygen Attached to HB for Transport
–the four polypeptide chains of HB are coiled together into a ball-like structure, the shape of which determines its affinity for O2
–when fully saturated, 4 O2 molecules bind to the iron ion of HB, 1 for each protein chain. With complete O2 binding, all electrons become paired, and HB is converted to its Oxygenated state
—Oxyhemoglobin {HBO2}
Hemoglobin Saturation
–Saturation is a measure of the proportion of available HB that is carrying O2
–Saturation is computed as the ratio of HBO2 (content) to the total HB (capacity)
–HB Arterial O2 saturation (SAO2) us usually expressed as percentage
Hemoglobin Saturation Formula
–SaO2= (HBO2 / Total HB) * 100
Red Blood Cells Formula
–HB: reduced hemoglobin (uncombined or deoxygenated hemoglobin)
–O2: oxygen
–HbO2: oxyhemoglobin ( combined or oxygenated hemoglobin)
–HB+O2= HbO2
Oxygen Bound to Hemoglobin
–there are 4 Heme/Iron groups in each HB molecule, a total of 4 oxygen molecules can combine with each HB molecule
–when 4 oxygen molecule are bound to 1 HB molecule, the HB is 100% saturated
–3 molecules of oxygen saturated= 75%
Oxygen bound to Hemoglobin
–oxygen bound to hemoglobin: Oxyhemoglobin
–HB not bound with oxygen: reduced hemoglobin or deoxyhemoglobin
–the amount of oxygen bound to HB is directly related to the partial pressure of oxygen
Hemoglobin
–Adult Male: average 14 to 16G per 100mL of blood
–Adult Female: averages 12 to 15 G/DL
–Infant: averages 14 to 20 G/DL
–Hb constitutes about 33% of RBC weight
–under normal conditions, each G/DL is capable of carrying 1.34 of oxygen
Oxyhemoglobin Dissociation Curve: Left Side of the graph
–a nomogram that illustrates the Percentage of Hemoglobin that is chemically bound to oxygen at each oxygen pressure (bottom portion of the graph)
–the curve is S-Shaped with a steep slope between 10 and 60 MM HG and a flat portion between 60 and 100 MM HG
Oxyhemoglobin Dissociation Curve: right side of the graph
–precise oxygen content carried by hemoglobin at each oxygen pressure
Oxyhemoglobin Dissociation Curve: clinical significance of the flat portion of the curve
–the PaO2 can fall from 100 to 60 mm Hg and the Hb will still be 90% saturated with oxygen
Clinical Connections: Pulse Oximeter
–pulse oximeters indirectly monitor the patient’s arterial oxyhemoglobin saturation
–the pulse oximeter measures oxygen saturation by reflecting light off the hemoglobin
–the color change of hemoglobin is directly related to its oxygen saturation
PaO2 SaO2 Relationship
–most pulse oximeter measurements below 70% are considered inaccurate and unreliable
Oxygen Dissociation Curve: Factors that Shift the Curve
–Ph
–Temperature
–2,3 Biphosphoglycerate (2,3-BPG)
–Carbon Monoxide
Other Factors that Affect the Curve
–among the most important of these in clinical practice are blood Ph, body temperature, and erythrocyte concentration
–in healthy individuals, the complex interaction of these factors results in maximal loading of HB (high affinity) with O2 in the lungs and appropriate unloading of O2 (low affinity) in the tissues
–these abnormal changes can increase or decrease the HB affinity for O2 and interfere with O2 transport
Ph (Bohr effect)
–the impact of changes in blood pH on HB’s affinity for O2 is called the Bohr effect
–the Bohr effect alters the position of the HBO2 dissociation curve. A low pH (acidity) shifts the curve to the right, whereas a high pH (alkalinity) shifts it to the left
Body Temperature
–A decrease in body temperature shifts the curve to the left, increasing HB’s affinity for O2
–As body temperature increases, the curve shifts to the right, and the affinity of HB for O2 decreases
Organic Phosphates: Biphosphoglycerate
found in abundance in the RBCs where it forms a loose chemical bond with globin chains of deoxygenated HB
Fetal Hb
–chemically different than an adult
–it has a greater affinity for oxygen and shifts the curve to the left
Carbon Monoxide
–CO has about 210 times the affinity of oxygen for HB
–Co can tie up a large amount of HB and prevent O2 molecules from bonding to oxygen is unable to unload easily in the tissue
oxygen Consumption
–the amount of oxygen extracted by the peripheral tissues during the period of 1 minute
Factors that Increase VO2
–exercise
–seizures
–shivering
–hyperthermia
Factors that Decrease the VO2
–skeletal muscle relaxation (drugs)
–peripheral shunting (sepsis, trauma)
–certain poisons ( cyanide prevents cellular metabolism)
–hypothermia
Oxygen Extraction Ratio
–the amount of oxygen extracted by the peripheral tissues divided by the amount of oxygen delivered to the peripheral cells
