Respiratory Physiology Lec5 PDF

Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 Lung Physiology Page|1  Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 By the end of lecture 5; you will be able to:...

Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 Lung Physiology Page|1  Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 By the end of lecture 5; you will be able to: ▪ Role of HB in O2 transport ▪ O2-HB dissociation curve ▪ Bohr and Haldane effect ▪ Types of lung ventilation and lung zones Role of Hemoglobin in Oxygen Transport Normally, about 97 per cent of the oxygen transported from the lungs to the tissues is carried in chemical combination with hemoglobin in the red blood cells. The remaining 3 per cent is transported in the dissolved state in the water of the plasma and blood cells. Thus, under normal conditions, oxygen is carried to the tissues almost entirely by hemoglobin. Reversible Combination of Oxygen with Hemoglobin The oxygen molecule combines loosely and reversibly with the heme portion of hemoglobin. When Po2 is high, as in the pulmonary capillaries, oxygen binds with the hemoglobin, but when Po2 is low, as in the tissue capillaries, oxygen is released from the hemoglobin Page|2  Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 Oxygen-Hemoglobin Dissociation Curve. The oxygen-hemoglobin dissociation curve, which demonstrates a progressive increase in the percentage of hemoglobin bound with oxygen as blood Po2 increases, which is called the per cent saturation of hemoglobin. Because the blood leaving the lungs and entering the systemic arteries usually has a Po2 of about 95 mm Hg, the dissociation curve that the usual oxygen saturation of systemic arterial blood averages 97 per cent. Conversely, in normal venous blood returning from the peripheral tissues, the Po2 is about 40 mm Hg, and the saturation of hemoglobin averages 75 per cent. Notice that the curve is sigmoidal or S-shaped, owing to the cooperativity among the four O2-binding sites on the Hb molecule The PO2 at which the Hb is half saturated is known as the P50 Factors That Shift the Oxygen- Hemoglobin Dissociation Curve Number of factors can displace the dissociation curve in one direction or the other that when the blood becomes slightly acidic, with the pH decreasing from the normal value of 7.4 to 7.2, the oxygen-hemoglobin dissociation curve shifts, on average, about 15 per cent to the right. Conversely, an increase in pH from the normal 7.4 to 7.6 shifts the curve a similar amount to the left. In addition to pH changes, several other factors are known to shift the curve. Three of these, all of which shift the curve to the right, are (1) increased carbon dioxide concentration, (2) increased blood temperature, and (3) increased 2,3-biphosphoglycerate (BPG), a metabolically important phosphate compound present in the blood in different concentrations under different metabolic conditions. Page|3  Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 Bohr effect physicist Niels Bohr, observed that: “respiratory acidosis shifts the Hb-O2 dissociation curve to the right “This decrease in O2 affinity has come to be known as the Bohr effect. Haldane effect The Haldane effect is a property of hemoglobin first described by John Scott Haldane, within which oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of carbon dioxide. Page|4  Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 P 2 04 g. of the bloo that enters the le atriu passe through al eolar apillaries P 40 2 g. pon lea ing the lung 2 not e pose to lung air. of the bloo has passe fro the aorta through the shunt o bron hial ir ula on fall in Po2 g o bines in the pul onary eins ith the o ygenate bloo enous fro the al eolar apillaries a i ture y ZA Page|5 Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 (Incidentally, the high Po2 at the apex probably accounts for the preference of adult tuberculosis for this region because it provides a more favorable environment for this organism.) The minimal contribution to overall O 2 uptake made by the apex can be mainly attributed to the very low blood flow there. The difference in CO2 output between apex and base is much less because this can be shown to be more closely related to ventilation. As a result, the respiratory exchange ratio (CO2 output/O2 uptake) is higher at the apex than at the base. On exercise, when the distribution of blood flow becomes more uniform, the apex assumes a larger share of the O2 uptake. Page|6 Respiratory Physiology.LEC5 Dr.Zainab Ali Altufailie \2024 Page|7