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

• Important buffer
• takes part in defence
• Important in homeostasis (coagulation) = Reacts after vessel injuries.
• Maintains homeostasis–> Isovolemia, Isotonia, Isoionia, Isohydria

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 with stand fluctuations for short periods 7.1-7.6
• pH arterial > pH venous due to transport of CO2

Question 6

Calculation of Blood Volume:

Answer 6

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 7

Blood transports:

Answer 7

The primary function of blood is transportation. It is the main transport medium of:

• Gases
• Nutrients
• Metabolites
• Information
• Heat

Question 8

Blood as buffer:

Answer 8

As a buffer there are two types found in the blood:

• Bicarbonate – 53%
• Non bicarbonate – 47%

Question 9

What does blood consist of?

Answer 9

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.

Question 10

Stages of normovolaemia:

Answer 10

1: Normocythaemic normovolaemia – healthy stage
2: Polycythaemic normovolaemia
– haemoconcentration
– viscosity increases
– increased load on heart (turbulence)
3: Olygocythaemic normovolaemia
– haemodilution
– blood gets diluted with concurrent normal volume

Question 11

Stages of hypovolaemia

Answer 11

1: Normocythaemic hypovolaemia (Oligaemia) – blood cells and plasma loss together
– blood loss
– plasma replaced quickly, cells return slowly

2: Polycythaemic hypovolaemia – anhydraemia: lack of water, thirst – end up with haemoconcentration
3: Olygocythaemic hypovolaemia

Question 12

Stages of hypervolaemia:

Answer 12

1: Normocythaemic hypervolaemia – plethora
– excess transfusion
– permanent, exhausting physical work

2: Polycythaemic hypervolaemia

3: Olygocythaemic hypervolaemia – hydraemia
– intake of excess water
– infusion (followed by haemodilution)

Question 13

What are the factors affecting blood volume?

Answer 13

• amount of body fat
• position of the body
• muscle work
• climate
• nutrition
• lack of oxygen
• sympathetic activity
• pregnancy
• blood loss
• age
• changes in the total water supply