The O2 carrying capacity of blood is most affected by?
Ans. A. Hemoglobin. (Ref. Ganong 23rd/Chapter 32; Figure 32-24).# The resistance to blood flow is determined not only by the radius of the blood vessels (vascular hindrance) but also by the viscosity of the blood. Plasma is about 1.8 times as viscous as water, whereas whole blood is 3 to 4 times as viscous as water. Thus, viscosity depends for the most part on the hematocrit, that is, the percentage of the volume of blood occupied by red blood cells. The effect of viscosity in vivo deviates from that predicted by the Poiseuille- Hagen formula (R=8hL/pr4).# In large vessels, increases in hematocrit cause appreciable increases in viscosity. In severe polycythemia, the increase in resistance does increase the work of the heart. Conversely, in marked anemia, peripheral resistance is decreased, in part because of the decline in viscosity.# Of course, the decrease in hemoglobin decreases the O2-carrying ability of the blood. but the improved blood flow due to the decrease in viscosity partially compensates for this.# Ordinarily, arterial blood has a pH of about 7.41, and as the blood acquires carbon dioxide in the tissue capillaries, the pH falls to a venous value of about 7.37. In other words, a pH change of 0.04 unit takes place. In heavy exercise or other conditions of high metabolic activity, or when blood flow through the tissues is sluggish, the decrease in pH in the tissue blood (and in the tissues themselves) can be as much as 0.50, about 12 times.# Each hemoglobin (Hb) molecule has four subunits.# Each subunit has a mheme mojety with an iron in the ferrous state (Fe2+), and two a and two b polypeptide chains.# O2 capacity: maximal amount of O2 that can bind to Hb# O2 content*: Total O2 in blood (bound + dissolved)= (O2 capacity X % saturation) + dissolved O2= (1.39 x Sat) + 0.003 Po2100# Conetent reflects O2 bound to Hb (the amount of O2 that is dissolved is trivial compared to bound).# Partial pressure reflects dissolved O2,Shift to right (| P50)Shift to left (|P50)# Facilitates unloading# Facilitates loading# | temperature,| Pco2 |pH,| 2,3-DPG# |temperature, |Pco2, | pH, |2,3-DPG# Exeercising muscle is hot, acidic and hypercarbic# CO poisoning
Hemoglobin
pH
pCO2
RBC count
Respiratory System