Topic 6: Physiological role of the blood, definitions and changes in blood volumes Flashcards
What should be mentioned in this topic?
- Physiological Role of Blood
- Hematocrit
- Sedimentation Rate
- pH of the Blood
- Determination of Blood Volume
- Changes of Blood Volume
- Factors affecting Blood Volume
Physiological Role of Blood:
- Important buffer
- takes part in defence
- Important in homeostasis (coagulation) = Reacts after vessel injuries.
- Maintains homeostasis–> Isovolemia, Isotonia, Isoionia, Isohydria
Hematocrit
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.
Sedimentation Rate
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.
pH of the Blood
- 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
Calculation of Blood Volume:
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
Blood transports:
The primary function of blood is transportation. It is the main transport medium of:
- Gases
- Nutrients
- Metabolites
- Information
- Heat
Blood as buffer:
As a buffer there are two types found in the blood:
- Bicarbonate – 53%
- Non bicarbonate – 47%
What does blood consist of?
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.
Stages of normovolaemia:
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
Stages of hypovolaemia
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
Stages of hypervolaemia:
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)
What are the factors affecting blood volume?
- 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