The blood pressure during heart contraction is 80. The velocity of blood flow is lowest in the aorta arteries. The sinoatrial node in humans delays transmission in the cardiac conduction system after the pacemaker has fired. In negative pressure breathing, inhalation results from forcing air from the throat down into the lungs contracting the diaphragm relaxing the muscles of the rib cage using muscles of the lungs to expand the alveoli contracting the abdominal muscles 32. Compared to the interstitial fluid that bathes active muscle cells, blood reaching these cells in arteries has a high Po 2 . high Pco 2 .
Gas exchange takes place across moist membranes.
The gases move across the exchange membranes by diffusion. The total exchange surface area is relatively large. The lining of the alveoli is only one cell thick. The concentration of CO 2 is higher in the air than in the alveolar capillaries. Select the formula below that correctly represents the behavior of CO 2 in the blood.