VETERINARY PHYSIOLOGY –I (VPB -111) Blood – Part 1 (VCI Syllabus) – VCI Physiology Syllabus – Introduction to Blood; Properties of blood as a body fluid
Introduction to Blood
- Blood is a fluid connective tissue.
- Blood consists of cells and other cell-like formed elements suspended in a fluid called plasma.
- Main function of blood is to carry oxygen, carbon dioxide, nutrient molecules and waste.
- Blood volume is the typical values given as a percentage of body weight are 7–9%.
Functions of blood
- Transportation
- Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs
- Transport nutrients from GI tract to liver and other cells
- Transport hormones from endocrine glands to target cells
- Transport waste products from cells to excretory organs
- Regulation
- Maintains homeostasis
- Regulates pH / acid base balance
- Regulates body temperature and water balance
- Regulates osmotic pressure
- Protection
- Provides immunity
Properties of Blood
- Hematocrit
- Blood color
- Blood volume
- Blood pH
- Specific gravity
- Viscosity
1.Hematocrit (Hct)
- Hct is international recognized abbreviation for Hematocrit
- Proportion of cells to plasma;
- Clinically useful measure of pathological conditions
- Technically – When a column of blood is centrifuged, the components are separated according to their relative specific gravity.
- The cellular components occupy the lower portion and, taken together, are known as the Hct. Plasma occupies the top portion and is the liquid component of blood.
- Note down that PCV and Hematocrit are different measure and hematocrit produces real picture of blood vascular physiology for example, if an animal lost large amount of blood due to hemorrhage than PVC might be normal (because it is relative to whole blood volume and whole blood volume remain same) but hematocrit would be greatly reduced
2.Blood Color
- The red color of blood is imparted by the hemoglobin contained within the erythrocytes.
- Gradations of color from bright red to bluish‐purple are seen, depending on the degree of saturation of hemoglobin with oxygen. The greater the saturation, the brighter the red color.
- Plasma is yellow to colorless, depending on the quantity and species examined. The color is due to bilirubin, a degradation product of hemoglobin. In cats, dogs, sheep, and goats, it is colorless / very slight yellow. It is a darker yellow in the cow & even darker in the horse, which has a relatively high bilirubin concentration
3.Blood Volume
- Blood volume (BV) is a function of lean body weight and is generally 8–10% of body weight.
- BV cannot be measured directly because exsanguination (removal of blood) results in the loss of only about 50% of the blood; the remainder is trapped in capillaries, venous sinuses, and other vessels.
- Erythrocyte volume and plasma volume (PV) can be measured by various techniques.
- If one or the other is measured, and the Hct is known, the BV can be calculated.
- For example, if the PV is 600 mL and the Hct is 40%, the PV represents 60% of the BV. BV is then determined by the following relationship:
4.Blood pH
- The normal pH of the blood is 7.4.
- The venous blood is slightly towards acidic side because of the increased content of CO2, whereas the arterial blood is slightly more towards alkaline side.
- The plasma is more alkaline than the corpuscles.
The blood pH range:
- Dog : 7.32- 7.68
- Cattle : 7.35 – 7.50
- Horse : 7.35 – 7.43
- Fowl : 7.56.
Difference between pH of vein and artery is 0.4 points
- pH represents conc. of hydrogen ions in solution,
- When the pH is 7.4, the [H+] is 0.00000040 g‐atoms of H+ in 1 L of solution, or 40 nEq (nanoequivalents).
- When the [H+] doubles (80 nEq) or halves (20 nEq), the pH changes by 0.3 units as follows: (fig given)
5.Specific gravity
- Specific gravity is the ratio of weight of a given volume of a fluid to the weight of the same volume of distilled water measured at 25°C.
- Plasma protein concentration is largely responsible for the specific gravity of the plasma. The cellular elements called the corpuscles have higher specific gravity than the plasma.
- The copper sulphate drop falling method is commonly used for the assessment of specific gravity of blood and plasma. Various factors influence the specific gravity of the blood.
Specific gravity is decreased in the following conditions
- Pregnancy: Increase in plasma volume causes hemodilution.
- Anaemia.
- Renal diseases: Loss of albumin, oedema etc.
- Hemodilution: Hypersecretion or prolonged treatment with glucocorticoids.
- Starvation and malnutrition: Decrease in plasma protein.
- Intravenous fluid transfusions.
Specific gravity is increased in the following conditions
- Polycythemia: High altitude, polycythemia vera, newborns etc.
- Severe dehydration: Excessive fluid loss such as in vomiting, diarrhoea.
- Hemoconcentration: Loss of plasma as in burns.
6.Viscosity of blood
- It is normally about five times greater than water
- Viscosity is influenced by concentration of RBCs and plasma proteins.
- Among plasma proteins, the viscosity is mainly contributed by the gamma globulins which provide the resistance to blood flow and helps the normal pumping activity of the heart.
- Viscosity of blood is determined using viscosimeter.
- An increase in the viscosity of blood is seen in conditions like polycythemia, congestive heart failure, jaundice, vomiting, diarrhoea etc, whereas a decrease in the viscosity is commonly noticed in anemia, oedema etc.
