A Jedi's Strength Flows from the Force.

GE 345: Week 2

Circulatory System -- Hemodynamics

Physiology/Kinesiology

Updated by Tracey 8 June 02

Blood consists of plasma and cells.

Cells: hematocrit describes percentage of blood composed of cells (men 42, women 38) & varies based on physical activity lefel, elevation where you live, etc. Viscosity (friction) is proportional to hematocrit.
Plasma: part of body's extracellular fluid. Similar to interstitial fluid, but contains 7% protein (vs. 2-3% for interstitial fluid). Proteins have negligible influence on viscosity. 3 major proteins:
- Albumin helps regulate pressure at capillary membranes.
- Globulins transport substances and act as antibodies.
- Fibrinogen is important in blood clotting.

Blood Flow

Quantity of blood passing a point in a given time period (usually ml or l/min). Determined by:

Pressure difference between 2 ends of a vessel. Note: this is the differential and not the absolute pressure in the vessel.
Impediment to flow through the vessel (vascular resistance)

Ohm's Law: Flow = Pressure difference between ends of the vessel / Resistance.

Nervous Resistance: sympathetic response constricts vessels, decreasing flow.

Blood typically flows in streamlines, through a long, smooth vessel, called laminar flow. Extremely high flow rate or obstructions cause turbulence and eddies, which increase friction in the vessel.

Blood Pressure

Force exerted by blood against any unit area of the vessel wall (ex: psi). Usually stated in terms of mm Hg -- the force required to push a column of mercury n mm. Mean arterial pressure: average pressure pushing blood through the systemic system.

MAP = CO x Peripheral Resistance

MAP controlled by: baroreceptors, which are most abundant in carotid sinus & aortic arch; adrenal hormones (norepinephrine, epinephrine); pre-capillary sphincters, which control local blood flow; and the kidney, which secretes renin, stimulating angiotensin release -> vasoconstriction.