EPHE 160: Cardiovascular System: Blood Flow

How do you calculate Blood Flow?

Flow = (Pressure Gradient) / (Resistance)

Increase in Resistance causes what to flow?

flow decreases

decrease in resistance to flow causes what to flow rate?

flow rate increases

What relation foes flow have to resistance?

inversley proportionate

What factors influence resistance?

• viscosity of the fluid

• length of the vessel

• radius of the vessel

Viscosity of Blood

thickness of blood

proportional to resistance

Length of Vessel

resistance is proportional to the length of the vessel

Radius of Arterioles

main determining factor of Resistance

resistance proportional to vessel radius

• vasoconstriction → increased resistance → increased blood flow

• vasodilation → decreased resistance → decreased blood flow

How is Blood Pressure affected in Vasculature?

1. Volume of blood in the vessel

2. how easily walls cans be stretched(compliance)

Arteriolar Tone

sustained partial constriction of vascular smooth muscle in arteriolar

(think about how this parallels muscle tone)

How are Arterioles controlled?

Arterioles are controlled both intrisically and extrinscally

What are the two methods of intrisic control of blood flow by local regulation

Reactive Hyperemia and Active Hyperemia

both cause low [O2] and high [CO2]

Active Hyperemia

reaction to increase in metabolic rate (exercise, inflammation, digestion)

• bodys mechanism to match blood flow to new base metabolic rate

Pathway for regulating Active Hypermia

incr metabolic rate → inc o2 consumption, inc co2 production = high co2 low o2 → vasodilation in arterioles → dec resistance = incr blood flow → incr o2 delivery + in co2 removal = inc [o2] dec [co2] → negative feedback inhibits vasodilation of arterioles

Reactive Hyperemia

reaction to decrease in blood flow (ischemia/hypoxia)

• body’s mechanism to restore homeostatic levels

Pathway for Reactive Hypermia

low [o2] high [co2] → vasodilation in arterioles = dec resistance = incr blood flow → inc o2 delivery + co2 removal = incr [o2] dec [co2] → negative feedback inhibits vasodilation

Reynauds Disease

a form of reactive hyperemia

when exposed to cold → vasospasm of arteries → limits blood supply → mech causing vasodilation causes pain+discomfort

Capillaries(facts)

25,000miles of capillaries

thin walled tube one layer thick and attached to basement membrane

cells separated by intercellular clefts

capillaries are very easily damaged bc they are only one cell thick

Microcirculation

capillary network that is the site of nutrient and gas exchange

being one cell thick, capillaries max