Blood as a Fluid Blood Composi.on •  Whole blood consists of formed elements and plasma
•  Formed elements: Red blood cells (RBCs) (99.9%)
• White blood cells (WBCs) or leukocytes
Platelets
•  Plasma consists of: Water (92%)
Plasma proteins (7%)
Other solutes (1%)
Cons.tuents of Blood Red Blood Cells •  In adult males 1 µl of whole blood contains 4.5-6.3 billion RBCs
•  Shape: Biconcave disk-thin central region and thick outer margin.
•  Composition: Only organelles related to transport of respiratory gases
Hemoglobin (Hb) accounts for 95% of the cell’s intracellular proteins
Shape a)  At rest the red blood cell is a biconcave disk. b)  b) In flow, the blood cell looks more like a dimpled fluid droplet White Blood Cells •  In adults 1 µl of whole blood contains 6-9 thousand WBCs
•  Shape: Divided to granulocytes and agranulocytes
•  Composition: They do have a nucleus
They contain vesicles and lysosomes
•  Function: Defend the body against invasion by pathogens
Remove toxins, waste, abnormal or damaged cells
Platelets •  In adults 1 µl of whole blood contains 150-500 thousand platelets
•  Shape: Flattened disks, round when viewed from above
•  Composition: They do not have a nucleus
They carry enzymes and other substances important for
the process of blood clotting
•  Function: Transport chemicals for initiation and control of clotting
Form temporary platelet plug in the walls of injured blood
vessels
Actively contract when the clot has been formed
Plasma •  Composition: Contains significant quantities of dissolved
proteins Albumins (60%)
• Also major contributors to the osmotic pressure of plasma
Globulins (35%): Antibodies and transport proteins
Physical Proper.es Blood Circula.on Change in Viscosity with Size •  Blood is not a homogeneous fluid; it is a suspension. •  Viscosity is not a well-­‐defined material property. •  It is defined as an observed resistance to flow. •  Viscosity of blood will depend upon the confining geometry. •  Viscosity decreases with decreasing vessel diameter. •  It is easier to move blood through a narrow vessel! [the Fahraeus-­‐Lindqvist effect] Viscosity and Flow Velocity MaRhew ScoR, PhD Thesis – Applied Mathema.cs, Univ. of Waterloo, 2005 Shear Thinning •  Accumula.on of blood cells along the axis leads to a favorable decrease in the suspension viscosity. •  The final flow anomaly we wish to highlight is the decrease in blood viscosity with increased shear rate, a characteris.c called shear-­‐thinning Blood in Microfluidic Channels •  Can use microfluidic proper.es to extracts plasma/white-­‐red cells Reynolds Numbers Blood in Microfluidic Channels •  Can use microfluidic proper.es to extracts plasma/white-­‐red cells Blood Flow Proper.es •  Blood is a non-Newtonian fluid
•  Blood viscosity depends on shear rate
•  Low shear rate=> Rouleaux formations (clumps) and sedimentation
•  High shear rate=> the stacks break down=> newtonian behavior