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– Oxygen 20.93% x PB @ sea level = 159 mm Hg

– Nitrogen 79.04% x PB = 600.7 mm Hg

– Carbon dioxide 0.03% x PB = 0.2 mm Hg

Tracheal air becomes diluted w/ water vapor– 760 – 47 = 713 mm Hg– 713 x .2093 = 149 mm Hg PO2

Alveolar air is mixed with CO2 leaving blood– Oxygen concentration = 14.7% (x 713 = 104 mm Hg PO2)

respiratory

Partial Pressure

Alveolar Air Percentages and Partial Pressures differ from Ambient Air and Tracheal Air1. 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

respiratory

Gas Transport

External respirationOxygen 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 respirationCarbon dioxide produced in cells moves from higher pressure to lower pressure into blood.

respiratory

Oxygen Transport in the Blood

Dissolved in plasma– amount is proportional to partial pressure– O2 is poorly soluble in plasma

average .3 ml O2 / 100 ml blood

Combined with hemoglobin– each hemoglobin molecule combines with 4 O2

– average 20 ml O2 / 100 ml blood

respiratory

respiratory

Oxygen Capacity of Hemoglobin

Men average grams of hemoglobin = 15/100 ml

Women average grams of hemoglobin = 14/100 ml

Amount of O2 per gram of hemoglobin = 1.34 ml

Maximal amount of O2 that combine 100 ml blood =– 20.1 ml O2 for men– 18.8 ml O2 for womenif 100% saturated.

respiratory

Oxygen Capacity of Hemoglobin

Percent saturation (%SO2) is proportion of hemoglobin bound with oxygen.

Even with sufficient atmospheric oxygen, adequate pulmonary ventilation, & optimum diffusing capacity, Hb not become 100% saturated.

SO2 arterial blood at rest = 98%

Hemoglobin carries 19.7 ml O2 (.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 PO2 in cell fluids at

rest averages 40 mm Hg. Dissolved oxygen in arterial

blood readily diffuses into cells.

This causes Hb to release its oxygen.

At 40 mm Hg, Hb holds about 75% of total capacity for oxygen (15 mL O2).

Arteriovenous-oxygen difference at rest = 5 mL O2

respiratory

Hb Saturation Differences in Arteries and Veins

Arteriovenous O2 difference Reveals the amount of oxygen extracted by

the tissues

Arterial O2 Venous O2 A-V O2 diff

Rest 20 ml/ 100 ml blood 15 ml/ 100 ml blood 5 ml/ 100 ml blood

Exercise 20 ml/ 100 ml blood 5 or 4 ml/ 100 ml blood

15-16 ml/ 100 ml blood

respiratory

Oxygen Capacity of Hemoglobin

During exercise, tissue PO2 decreases to about 20 mm Hg.

Hemoglobin retains about 25% or 5 mL O2 (.25 x 20.1).

A-v O2 difference = 20.1 – 5 = 15 mL/100.

During exhaustive exercise, tissue PO2 about 3 mm Hg, Hb releases all.

respiratory

Blood Conditions Influencing O2 Saturation of Hemoglobin

Temperature pH PCO2

PO2

2,3-diphosphoglycerate (also called 2,3-DPG or BPG)

respiratory

Resting Conditions

Temperature = 37 degrees Celsius pH = 7.4 Arterial PO2 = 100 mm Hg

Mixed venous PO2 = 40 mm Hg

respiratory

Changes with Exercise

Temperature rises pH drops PO2 at the tissues decreases

PCO2 rises No change in 2,3-DPG