Topic 6: Physiological role of the blood, definitions and changes in blood volumes

Question 1

What should be mentioned in this topic?

Answer 1

• Physiological Role of Blood
• Hematocrit
• Sedimentation Rate
• pH of the Blood
• Determination of Blood Volume
• Changes of Blood Volume
• Factors affecting Blood Volume

Question 2

Physiological Role of Blood:

Answer 2

The primary function of blood is transportation. It is the main transport medium of:
- Gases
- Nutrients
- Metabolites
- Information
- Heat
Blood is an important buffer and takes part in defence and reacts after vessel injuries. It is also important in homeostasis.
As a buffer there are two types found in the blood:
- Bicarbonate – 53%
- Non bicarbonate – 47% Homeostasis
- Isovolemia, Isotonia, Isoionia, Isohydria

Blood is a liquid connective tissue consisting of 90% water. It consists of blood plasma and suspended cellular elements. It can be separated into a liquid phase and corpuscular elements.
Plasma contains fibrinogen – Collected from anticoagulated blood Serum does not contain fibrinogen – Collected from normal blood

Question 3

Hematocrit

Answer 3

It shows the proportion of corpuscular elements relative to the whole volume. It is an important diagnostic parameter.
Average value is around 40% or 0.4.

Question 4

Sedimentation Rate

Answer 4

The determination of the sedimentation rate is done using anticoagulated blood put in a standard size tube. The thickness of the plasma layer formed on the top of the tube is measured in certain time periods.

Question 5

pH of the Blood

Answer 5

• Blood pH is 7.35-7.45
• Extremely stable
• Can withstand fluctuations for short periods 7.1-7.6
• pH arterial > pH venous due to transport of CO2

Question 6

Determination of Blood Volume:

Answer 6

Ideal substance for measurement should not cross capillary wall. This substance does not exist, hence extrapolation is required.
To measure plasma space, Evans Blue or 125-I/131-I are used
To measure blood cell volume, labelled red blood cells are used

Question 7

Calculation of Blood Volume:

Answer 7

Calculation of Blood Volume (V) on the basis of plasma volume (Vp) or blood cell volume (Vrbc) In case of Ht value being known:

• V=Vp/(1-0.9xHt)
• V=Vrbc/0.9xHt

Question 8

Changes of blood volume:

Answer 8

Normocythaemic normovolaemia
Polycythaemic normovolaemia
Olygocythaemic normovolaemia
Normocythaemic hypovolaemia (Oligaemia)
Polycythaemic hypovolaemia
Olygocythaemic hypovolaemia
Normocythaemic hypervolaemia
Polycythaemic hypervolaemia
Olygocythaemic hypervolaemia