Hem 04

Blood volume 5 - 6 liters of blood(~ 7 - 8% of total body weight). Volume depends on sex and age. Blood volume decreases due to: Dehydration Blood volume increases in circumstances such as: Sudden addition of blood to the circulation due to contraction of spleen or excessive adrenaline discharge. Pregnancy. Dilution of the blood by tissue fluids during fevers and hyperthyroidism. Increase in the cell number as in cases of polycythemia and leukemia.

Color of the blood Hemoglobin is the principal determinant Oxygenated blood is bright red as O2 impacts a strong red color to the heme group. Deoxygenated blood is a darker shade of red or less redness and more blueness. Blood in carbon monoxide poisoning is bright red, because CO causes the formation of a stable complex called carboxyhemoglobin (COHb). In cyanide poisoning, the body can not utilize oxygen, so the venous blood remains oxygenated, increasing the redness.

Note: Carbon monoxide is produced normally in the body, establishing a low background COHb saturation. Normal COHb levels in an average person are less than 5%, whereas cigarette smokers (two packs/day) may have levels up to 9%. Serious toxicity is often associated with COHb levels above 25%, and the risk of fatality is high with levels over 70%.

Color of the blood (continue) Mechanism of action of carbon monoxide: 1- Binds to hemoglobin (reducing O2 transportation), 2- Binds to myoglobin (decreasing its O2 storage capacity), and 3- Binds to mitochondrial cytochrome oxidase (inhibiting cellular respiration). Skinks in the genus Prasinohaema have green blood.

This condition is caused by an excess buildup of the bile pigment biliverdin.

PH of blood The pH of blood must remain in the range of 7.35 to 7.45. otherwise it begins to damage cells. A pH of 8 or below 7 would be fetal for an individual.

Specific gravity of the blood The specific gravity of blood is the ratio of the weight of blood to the weight of an equal volume of water at 4 ºC. It depends on hematocrit, plasma proteins and water content of the blood. The specific gravity of blood gives

:

1- An idea of the solute and water content of blood. 2- A good index of the hemoglobin content of blood.

Determination of specific gravity 1- Direct method. 2- Indirect methods which comprise: a- Hammar′s Schlog′s method. b- Philips-Vanslyke′s copper sulphate method. The specific gravity of normal blood is 1.060, but may vary from 1.050 to 1.060 and that of plasma 1.026.

Blood density Blood has an average density of approximately 1060 kg/m³, very close to pure water's density of 1000 kg/m3. Viscosity of the blood It is related to the internal friction of the internal molecules of the blood. The friction generated between the fluid and the wall of the vessel. The viscosity of plasma is about 1.8-times the viscosity of water (termed relative viscosity) at 37°C. Whole blood has a relative viscosity of 4.7 in males and 4.4 in females.

Viscosity of the blood (continue) The viscosity of whole blood is strongly influenced by three factors: 1- Hematocrit and chemical composition: At a hematocrit of 40%, the relative viscosity is 4. At a hematocrit of 60%, the relative viscosity is about 8. viscosity is increased in patients with polycythemia, leukemia, diabetes mellitus, more low-density lipoprotein (LDL cholesterol), cyanosis, asphyxia (due to corpuscular swelling), CO2 …… etc. Viscosity is decreased in patients when the count is reduced as in anemia, malaria, vomiting, diarrhea, profuse sweating, moderate exercise, O2 …. etc. Notes: 1- Deoxygenated blood is more viscous than oxygenated blood. 2- If all human haemoglobin was free in the plasma rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function effectvely.

Viscosity of the blood (continue) 2- Temperature: Viscosity increases approximate 2% for each 1°C decrease in temperature. Thus a rise in temperature will facilitate the circulation of the blood. 3- The flow rate of blood also affects viscosity At very low flow states in the microcirculation, as occurs during circulatory shock, the blood viscosity can increase quite significantly. In other words, the greater the viscosity of blood, the greater is the pressure required to force it along blood vessels in a given time and a longer time is required to traverse blood vessel.

Units of viscosity 1- Poise (P, Ps, or Po): Poise is the unit of dynamic viscosity which equal to one dyne-second per square centimeter (dyness/cm2) (N-s/m2). The viscosity of a fluid in which a force of one dyne (10-5 Newton) per square centimeter maintains a velocity of 1 centimeter per second. The poise unit is equivalent to 0.1 Pascal second (Pa-s).

2- Pascal second (Pa-s). The Pascal second is equivalent to 10 poise. The viscosity of plasma is about 0.015 Poise {1.5 centipoises (cP)} and the viscosity of whole blood at a physiological hematocrit of 45 is about 3.2 centipoises (cP), or 3.2x10-3 Pa.s.

Seven-step program for stopping heart disease and stroke by decreasing blood viscosity 1- Not smoking. 2- Eating a healthier diet. 3- Exercising. 4- Reducing stress. 5- Taking low-dose aspirin every day. 6- Donating blood. 7- Drinking 10–12 glasses of water a day.

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