Circulation Flashcards
function of circulation
transport
- nutrients and O2 to tissues
- waste and CO2 away from tissues
- hormones from one area of body to another
- heat throughout the body
guiding principles of circulation
circulation primarily influenced by tissue needs
cardiac output is a response to vascular inflow
arterial pressure generally controlled independently of local tissue flow or CO
key factors influencing circulation
blood flow
pressure
resistance
control mechanisms mediating these characteristics
characteristics of arteries
transport blood under high pressure
strong vascular walls
characteristics of arterioles
act as control conduits
strong musclar walls that vasoconstrict/dilate
innervated by SNS only
characteristics of capillaries
exchange site for nutrients, wastes
directed by local tissues, rather than SNS, to determine dilation/constriction
characteristics of veins
serve as a blood reservoir (64% of total blood volume)
contain muscle - can constrict/dilate
function of sphincters in capillaries
open or close in response to need for blood
blood flow definition
the volume of blood flowing through a vessel, an organ, or the entire circulation in a given period
blood pressure definitiion
the force per unit area exerted on a vessel wall by the contained blood
resistance definition
opposition to flow; amount of friction blood meets when passing through the vessels
what are the 2 factors that affect blood flow?
pressure gradient
vascular resistance
Ohm’s Law for blood flow
blood flow = change in pressure between 2 ends of vessel / resistance
2 descriptions of blood flow
laminar
-linear, parallel flow
turbulent
conductance
- units
- what is it?
ml/sec/mmHg
measure of blood flow through a vessel for a given pressure difference
reciprocal of resistance
small change in vessel diameter causes enormous change in conductance
Poiseuille’s Law
- related to what type of blood flow
- what plays the greatest role in determining rate of blood flow
related to laminar flow
diameter
2/3 of resistance to flow is _____ resistance
arteriole
arteriole walls can change diameter up to _____
fourfold
viscosity relationship to blood flow
inverse
what is hematocrit?
-typical value
% of blood that consists of cells
40
how can hematocrit increase?
living at altitude
theory of circulatory function
needs of tissue tightly controls blood flow; small tissue-specific vessels dilate or constrict locally to control flow in addition to change in cardiac output
-cardiac output primarily controlled by sum of all local tissue flows
in general, arterial pressure is controlled independently of local blood flow or cardiac output
MAP
- what is it?
- equation
pressure that propels blood to tissues
DBP + 1/3 (SBP-DBP)
mean pressure at
- venae cavae
- capillaries
- pulmonary circulation
vena cavae -0 mmHg capillaries -17 mmHg pulmonary circulation -16 mmHg
effects of pressure on blood flow
increases force on blood flowing through vessels
distends vessel
-increases blood flow
do veins or arteries have more distensibility
veins
compliance definition
capacitance
total quantity of blood than can be stored in a given portion of the circulation for each mmHg pressure rise
compliance equation
distensibility x volume
gravitational effect on venous pressure
- quiet stance
- movement - “venous pump”
quiet stance
-90 mmHg if you are standing still
movement
-15 mmHg
two phases of local blood control
acute
-fast adjustment of arterioles, metarterioles, and precapillary sphincters
long-term
-adjustment over days/weeks/months to control blood flow to tissue
vasodilator theory of blood flow regulation
vasodilator substance released from local tissue
examples
-adenosine, CO2, adenosine phosphate compounds
-histamine
-potassium ions
-H+
oxygen lack theory (nutrient lack theory)
sphincters don’t have enough oxygen to remain closed
precapillary sphincters
metarteriole sphincters
other “lack of substances” may facilitate vasodilation
dilating “upstream” arteries
larger arteries “upstream” from local tissue control response to effects of “downstream regulation”
drag on “upstream” endothelium of vessel walls by rapid increased flow allows release of substance that can vasodilate the “upstream” vessels
-EDRF made primarily of nitric oxide
-reduces the resistance to blood flow in upstream arteries
reactive hyperemia
what happens when you restrict blood flow for a period of time
active hyperemia
what you get then you exercise
actively using tissues
autoregulation of BF
after increase in BF to a tissue due to increase in arterial pressure, BF returns to near normal levels
