# Respiratory Partial Pressure Primary determinant of diffusion and direction Describes the pressure of a particular gas within a mixture Equals the total.

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respiratory Partial Pressure Primary determinant of diffusion and direction Describes the pressure of a particular gas within a mixture Equals the total pressure times the fractional concentration of the particular gas, according to Whose Law?

respiratory Partial Pressure Concentration of gases in ambient air Concentration of gases in ambient air –Oxygen 20.93% x P B @ sea level = 159 mm Hg –Nitrogen 79.04% x P B = 600.7 mm Hg –Carbon dioxide 0.03% x P B = 0.2 mm Hg Tracheal air becomes diluted w/ water vapor Tracheal air becomes diluted w/ water vapor –760 – 47 = 713 mm Hg –713 x.2093 = 149 mm Hg PO 2 Alveolar air is mixed with CO 2 leaving blood Alveolar air is mixed with CO 2 leaving blood –Oxygen concentration = 14.7% (x 713 = 104 mm Hg PO 2 )

respiratory Partial Pressure Alveolar Air Percentages and Partial Pressures differ from Ambient Air and Tracheal Air 1. Humidification reduces pressure of gasses 2. Oxygen is constantly leaving alveoli in capillaries 3. Some residual air is always left in alveolus in each breath to mix with new air.

respiratory

Gas Transport External respiration Oxygen moves from alveoli into blood down concentration gradient (104 mm Hg to 40 mm Hg. Carbon dioxide moves from blood into alveoli down concentration gradient (46 – 40 mm Hg). Internal respiration Carbon dioxide produced in cells moves from higher pressure to lower pressure into blood.

respiratory Oxygen Transport in the Blood Dissolved in plasma Dissolved in plasma –amount is proportional to partial pressure –O 2 is poorly soluble in plasma average.3 ml O 2 / 100 ml blood average.3 ml O 2 / 100 ml blood Combined with hemoglobin Combined with hemoglobin –each hemoglobin molecule combines with 4 O 2 –average 20 ml O 2 / 100 ml blood

respiratory

Oxygen Capacity of Hemoglobin Men average grams of hemoglobin = 15/100 ml Men average grams of hemoglobin = 15/100 ml Women average grams of hemoglobin = 14/100 ml Women average grams of hemoglobin = 14/100 ml Amount of O 2 per gram of hemoglobin = 1.34 ml Amount of O 2 per gram of hemoglobin = 1.34 ml Maximal amount of O 2 that combine 100 ml blood = Maximal amount of O 2 that combine 100 ml blood = –20.1 ml O 2 for men –18.8 ml O 2 for women if 100% saturated.

respiratory Oxygen Capacity of Hemoglobin Percent saturation (%SO 2 ) is proportion of hemoglobin bound with oxygen. Even with sufficient atmospheric oxygen, adequate pulmonary ventilation, & optimum diffusing capacity, Hb not become 100% saturated. SO 2 arterial blood at rest = 98% Hemoglobin carries 19.7 ml O 2 (.98 x 20.1) and.3 ml dissolved in 100 ml blood at 100 mm Hg as in the lungs.

respiratory Oxygen Capacity of Hemoglobin Tissue PO 2 in cell fluids at rest averages 40 mm Hg. Tissue PO 2 in cell fluids at rest averages 40 mm Hg. Dissolved oxygen in arterial blood readily diffuses into cells. Dissolved oxygen in arterial blood readily diffuses into cells. This causes Hb to release its oxygen. This causes Hb to release its oxygen. At 40 mm Hg, Hb holds about 75% of total capacity for oxygen (15 mL O 2 ). At 40 mm Hg, Hb holds about 75% of total capacity for oxygen (15 mL O 2 ). Arteriovenous-oxygen difference at rest = 5 mL O 2

respiratory Hb Saturation Differences in Arteries and Veins Arteriovenous O 2 difference Reveals the amount of oxygen extracted by the tissues Reveals the amount of oxygen extracted by the tissues Arterial O 2 Venous O 2 A-V O 2 diff Rest20 ml/ 100 ml blood15 ml/ 100 ml blood5 ml/ 100 ml blood Exercise20 ml/ 100 ml blood5 or 4 ml/ 100 ml blood15-16 ml/ 100 ml blood

respiratory Oxygen Capacity of Hemoglobin During exercise, tissue PO 2 decreases to about 20 mm Hg. During exercise, tissue PO 2 decreases to about 20 mm Hg. Hemoglobin retains about 25% or 5 mL O 2 (.25 x 20.1). Hemoglobin retains about 25% or 5 mL O 2 (.25 x 20.1). A-v O 2 difference = 20.1 – 5 = 15 mL/100. A-v O 2 difference = 20.1 – 5 = 15 mL/100. During exhaustive exercise, tissue PO 2 about 3 mm Hg, Hb releases all. During exhaustive exercise, tissue PO 2 about 3 mm Hg, Hb releases all.

respiratory Blood Conditions Influencing O 2 Saturation of Hemoglobin Temperature Temperature pH pH PCO 2 PCO 2 PO 2 PO 2 2,3-diphosphoglycerate (also called 2,3-DPG or BPG) 2,3-diphosphoglycerate (also called 2,3-DPG or BPG)

respiratory Resting Conditions Temperature = 37 degrees Celsius Temperature = 37 degrees Celsius pH = 7.4 pH = 7.4 Arterial PO 2 = 100 mm Hg Arterial PO 2 = 100 mm Hg Mixed venous PO 2 = 40 mm Hg Mixed venous PO 2 = 40 mm Hg

respiratory Changes with Exercise Temperature rises Temperature rises pH drops pH drops PO 2 at the tissues decreases PO 2 at the tissues decreases PCO 2 rises PCO 2 rises No change in 2,3-DPG No change in 2,3-DPG

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