Physical Characteristics Of Blood

Question 1

Describe red blood cells in circulation

Answer 1

Aggregate in still blood but are easily separated as flow increases
Only low pressure is needed to get RBCs into small capillaries ie. 3um diameter
They have an elastic shape- easily deformed and stretch to align with flow

Question 2

What are reticulocytes?

Answer 2

Immature RBCs released from the bone marrow that still have endoplasmic reticulum

Question 3

Flow rate=….?

Answer 3

Pressure difference/resistance to flow
Affected by vascular component- radius and length
And blood component- viscosity

Question 4

Describe steady laminar flow of a Newtonian fluid through a cylindrical, straight rigid tube

Answer 4

Parabolic velocity profile
Poiseulle’s law- Flow rate= dP/L x pi.r^4/8.viscosity
Or
Resistance= viscosity x 8.L/pi.r^4

Question 5

Describe the constituents of blood

Answer 5

55% plasma
45% cells
40-45% RBC- haematocrit
99% of cells are RBC
Plus platelets and WBC

Question 6

What are the factors controlling blood viscosity?

Answer 6

Intrinsic- structure of the blood
-haematocrit
-plasma viscosity
Also, red cell aggregation and deformation- blood is non-Newtonian, increased flow decreases viscosity
Extrinsic- flow conditions
-shear rate is the velocity gradient across the vessel- low in the centre and high at the sides because of the parabolic shape

Question 7

Describe the factors affecting the plasma viscosity

Answer 7

Plasma proteins
-Albumin
-Immunoglobulin
-Fibrinogen- involved in RBC aggregation and clotting
Hyperglobulinaemia- elevated immunoglobulins eg in myeloma, macroglobulinaemia➡️ hyperviscosity syndrome

Question 8

Describe blood viscosity in intermediate sized vessels

Answer 8

Diameter- haematocrit is lower in smaller vessels around 30% in vessels less than 100microm
Apparent viscosity decreases with decreasing diameter between 100-10microm

Question 9

What is ESR?

Answer 9

Erythrocytes sedimentation rate- the amount of RBC aggregation in stationary blood
More sedimentation the worse off the patient

Question 10

What important physiological indicators are there in the blood?

Answer 10

Haematocrit- oxygen carrying capacity and viscosity
ESR
Plasma viscosity
Fibrinogen concentration
Blood content- red cell count and haemoglobin concentration
Cellular characteristics- mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration

Question 11

Describe some blood rheology and circulatory pathology

Answer 11

Hyperviscosity syndrome- immunoglobulins, haematocrit, hyperleukotic leukaemia, abnormal RBCs
Acute phase response- atherosclerotic vascular disease, diabetes, smoking
Increased fibrinogen leads to increased plasma viscosity, increased red cell aggregation and therefore increased ESR

Question 12

Describe cellular mechanical factors affecting deformation and circulation

Answer 12

Cell geometry- size determines the level of deformation required
SA:V determines the ability to adapt shape
Membrane- resistance to deformation determines rigidity
Resistance to disruption determines stability
Cytoplasm- viscosity, cytoplasm, inclusions, organelles

Question 13

Describe how the cellular mechanisms affect WBC and RBCs

Answer 13

WBCs have a spherical shape but a folded membrane, the excess membrane allows sufficient deformation to fit into capillaries- the cytoskeleton (1000x more viscose than RBC) of the dominant resistance factor for WBCs
RBCs have a biconcave shape with excess membrane and its cytoplasm has lower viscosity with no cytoskeleton or organelles- membrane rigidity is the dominant factor for resistance for RBCs

Question 14

How do RBCs and WBCs affect microcirculation?

Answer 14

RBCs capillary entry- msec
WBC- sec
WBCs 1000x slower, 1000x more resistance
RBCs have a steady resistance to flow
WBCs- intermittent flow and affects flow distribution
Can influence flow by adhering to a vessel

Question 15

Describe RBC membrane structure and function

Answer 15

Has external glycolipids and glycoproteins attached on to the outer phospholipid leaflet and integral proteins for recognition and adhesion
Peripheral proteins also attached to integral proteins and also to spectrin tetramers that form the membrane skeleton
No cytoskeleton
Elastic membrane skeleton allows the easy deformation when the RBC is stretched in high flow or to enter capillaries
It controls the cell shape- requires ATP
Provides flexibility, stability
Contributes to homeostasis by regulating the contents and volume

Question 16

Describe how blood cells behave in physiological conditions and pathological conditions

Answer 16

RBCs- don’t adhere normally- will in some disorders
Leucocytes- protective inflammatory, lymphocytes re-circulation
Can be out of control cause vascular occlusion and tissue damage
Platelets- haemostasis vs thrombosis

Question 17

Describe leukocyte a migration

Answer 17

Contact via seletins
Capture via rolling
Stop- integrin activation
Spread over the endothelial cells
Migrate through
Spread under the endothelial cells 
Chemotaxis to infection via chemokines

Question 18

Describe how sickle cell and malaria affects blood rheology

Answer 18

Sickle cell forms a haemoglobin S polymer in deoxygenated conditions
Malaria makes the cytoplasm more viscose and the membrane more rigid
Both make the RBCs more adhesive

Question 19

Describe pathological WBC rheology

Answer 19

Abnormalities- vasculitis- autoantibodies
Smoking
Inflammatory mediators
Uncontrolled adhesion- myocardial infarction, shock, chronic inflammation, graft rejection, vasculitis