DSA: Circulation and Hemodynamics Flashcards
Site of highest resistance and largest drop in pressure across
Arterioles
when activated, elicits contraction of smooth muscle and vasoconstriction and increased resistance to flow
alpha-1 adrenergic receptors
when stimulated elicits relaxation of smooth muscle and vasodilation
Beta-2 adrenergic receptors
Site of exchange of products, a single layer of endothelial cells surrounded by basal lamina
capillaries
contains unstressed volume of blood and largest % of blood at any given time
venules and veins
contains stressed volume of blood
arteries
What does velocity in circulation is greater at the ends mean?
That while velocity is low in the capillaries, it is higher in the arteries and veins especially in the vena cava
Relationship between flow and pressure difference and resistance
Flow is proportional with the pressure difference and inversely proportional to the resistance
What is the major mechanism to changing flow
Changing the resistance of a vessel at the arteriolar level
When does turbulent flow occur
Turbulent flow occurs when laminar flow is disrupted and takes more energy to drive turbulent flow forward, while laminar flow is more efficient
What do bruits indicate?
Stenosis. Bruits can be heard when turbulent flow occurs in an artery or other vascular channel.
Laminar flow
Means streamlines which means that velocity is greatest at the center and the least towards vessel walls
What predicts whether flow will be turbulent or laminar?
Reynolds number - influenced by changes in viscosity or velocity of blood flow
What happens when a vessel is partially occluded
Blood velocity will increase at this site
Describe shear in blood vessels
shear stress occurs because velocity is not the same along the vessel wall as it is in the center, it is greatest along the vessel wall and lowest at the center
compliance of blood vessels
- represents distensibility of a vessel and inverse of elasticity
- compliance is greatest in veins compared to arteries
What happens when the compliance of veins is decreased (i.e. vasoconstriction)?
there will be a redistribution of blood from the unstressed volume to the stressed volume
unstressed volume
- volume of blood in veins
- volume of blood that produces no pressure
stressed volume
- volume of blood in arteries
- volume that produces pressure by stretching the elastic fibers in the blood vessel walls
Starling Equation
Jv = Kf [(Pc-Pi) – (πc – πi)]
Changes in Starling Forces
increase in filtration can be caused by increases in Pc or decreases in πc
Increases in Pc
Venous constriction leads to increases venous pressure, heart failure and ECF volume expansion (edema)
Decrease πc
reduced plasma concentration leads to severe liver failure, protein malnutrition, loss of protein in urine
What is active hyperemia?
When the blood flow to an organ is proportional to its metabolic activity
What is reactive hyperemia?
An increase in blood flow in response to a period of decreased blood flow (i.e. ischemia-reperfusion)
Myogenic response
increased in arterial pressure, the arterioles are stretched and vascular smooth muscle contracts in response to increasing resistance and maintain flow
Shear stress when vascular smooth muscle is stress
Lead to greater pressure
Metabolic control
oxygen delivery is matched to oxygen consumption
What is the response when oxygen consumption is increases in metabolic control?
Vasodilatory metabolites are released to dilate vascular smooth muscle and increase blood flow
Histamine and Bradykinin
released in response to trauma and causes dilation of arterioles and constriction of venules, lead to local edema
Serotonin
release in response to damage, leads to vascular spasm and is a vasoconstrictor
Prostacyclin / Pg-E
causes dilation
Thromboxane A2 / Pg-F
causes constriction
NO
vasodilator and relaxes vascular SM
Angiotension II and vasopressin
constrictors that increase TPR
