Cardio 6 Flashcards
Describe the circulatory system.
-closed circuit
-blood returning to heart equals blood pumped by LV into aorta
-flow of blood around circuit depends on:
>number & strength of heart contractions
>total volume of blood
>characteristics of vessels
What are the 2 circulations in series in the cardiovascular system?
- Pulmonary circulation
- Systemic circulation
Describe pulmonary circulation.
-portion of CVS that carries deoxygenated blood away from heart, to the lungs, & returns oxygenated blood back to the heart
Describe systemic circulation.
-part of CVS that carries oxygenated blood away from the heart to the body & returns deoxygenated blood back to the heart
Describe the circulation 3 divisions.
- Distribution system
-ventricles, arteries, arterioles - Perfusion/exchange system
-capillaries - Collecting system
-venules, veins, atria
Describe arteries.
aorta is the largest artery in systemic circulation
-receive blood from heart
-strong vascular walls
-blood flows at high velocity
-elastic tissue
-smooth muscle
-CT
-transport blood under high pressure to tissues
>carry stressed volume
-deliver oxygen & other nutrients to organs
What are the two types of arteries?
- Elastic (high compliance)
-more elastin (increased distensibility)
-more capable to hold lg volume of blood
EX: aorta & carotid artery - Muscular (high resistance)
-more smooth muscle
-more capable to vasoconstriction & dilation
EX: femoral & mesenteric arteries
Describe compliance.
volume of blood the vessel can hold at a pressure
[C = V/P]
C = compliance (mL/mmHg)
V = volume (mL)
P = pressure (mmHg)
Describe vascular resistance.
-resistance that must be overcome to push blood through the circulatory system & create flow
Describe arterioles.
-last smallest branch of arterial system
-act as control conduits (blood released into capillaries)
-strong muscular walls = allow vasoconstriction/vasodilation
>innervated by sympathetic adrenergic nerve fibers
>alter blood flow in response
site of highest resistance to blood flow
Describe alpha 1 & 2 receptors.
-expressed in arterioles of most visceral organs
-alpha 1 = predominant & couple to Gq
-alpha 2 = couple to Gi
>present in nerve terminal to inhibit NE release (feedback)
-norepinephrine = primary endogenous agonist
>released from postganglionic neurons
-found in vascular smooth muscle
-causes vasoconstriction
smooth muscle contraction
Describe beta 2 adrenergic receptors.
-expressed in arterioles of coronaries, skeletal muscle, & liver
-GPCR = Gs
-epi is primary endogenous agonist
>released from adrenal gland
-found in vascular smooth muscle
-cause vasodilation
smooth muscle relaxation
Describe the tonic control of arteriolar diameter.
-arterioles = site of highest resistance & site where resistance can be changed by sympathetic activity
>by circulating cathecolamines & other vasoactive substances
Describe capillaries.
-exchange fluid, nutrients, electrolytes, hormones, & other substances between the blood & interstitial fluid
-thin walled
-single layer of endothelial cells surrounded by basal lamina
-lipid soluble substances cross capillary wall by dissolving in & diffusing across endothelial membrane
-water soluble (ex. Ions) cross capillary wall through:
1. Water filled clefts (spaces) between endothelial cells
2. Large pores in walls (ex. Fenestrated)
not all capillaries perfumed w blood always = depends on metabolic needs
Describe venules.
-collect blood from capillaries & coalesce into larger veins
-thin walled
-endothelial layer
-elastic
-smooth muscle
-CT
Describe veins.
-function as conduits to transport blood from the venules back to heart
-low pressure
-thin wall
-carry unstressed volume
-muscular (contract/expand)
-major controllable reservoir for extra blood
valves = prevent backflow of blood
Describe compliance VS capacitance.
-compliance or capacitance of veins higher than arteries
-capacitance = related w distensibilty
-higher compliance = more volume can hold at a pressure
-veins hold large volumes at low pressure
-arteries have low compliance bc hold less blood at higher pressure
What happens if there is a change in compliance/capacitance of veins?
-redistribution of blood between veins & arteries
-veins constrict = decrease in volume the veins can hold
-blood shifted from veins to arteries
-smooth muscle in walls of veins (arterioles) is innervated by sympathetic nerve fibers
-A1 adrenergic activation = contraction of veins & reduce capacitance & unstressed volume
Describe the velocity of blood flow.
-rate of displacement of blood per unit of time
vary in diameter & cross section area
[V = Q/A]
V = velocity of blood flow (cm/sec)
Q = flow (mL/sec)
A = cross sectional area (cm^3)
Describe the relationship between cross sectional area & velocity of flow.
-cross section area of veins are larger than arteries
>explains lg blood storage capacity of venous system
-as systemic arteries branch to form small arteries, arterioles & capillaries = the total cross sectional area of vessels increase
>forward velocity of blood flow decreases
-blood is collected into venules & veins = total cross sectional area is reduced
>velocity of blood flow increases
Describe the total cross sectional area & velocity.
-velocity of blood varies inversely with total cross sectional area of blood vessels
-TOTAL = all capillaries/arteries/veins together
-CROSS SECTIONAL AREA = area of circle
although capillaries have a smaller diameter, they are more numerous
>flow of blood slows down when there’s a bigger cross sectional area
What is blood flow through a blood vessel determined by?
- Pressure difference between 2 ends of vessel (inlet/outlet)
>driving force for blood flow - Resistance of vessel to blood flow
>impediment to flow
[Q = deltaP/R]
Q = flow (mL/min)
deltaP = pressure difference (mmHg)
R = resistance (mmHg/mL/min)
What is the direction of blood flow determines by?
-the direction of pressure gradient
-high to low pressure
Describe vascular resistance.
-resistance that must be overcome to push blood through circulatory system (creates flow)
-amount of blood flowing through circulation = inversely proportional to resistance
>increasing resistance = decreases flow
(EX: arteriolar vasoconstriction)
vice versa
What is the major mechanism for changing blood flow in the cardiovascular system?
-changing the resistance of blood vessels
-particularly arterioles
What are the 3 factors that interfere with resistance to blood flow?
- Viscosity of blood
- Length of blood vessel
- Radius of blood vessel
relationship between resistance, blood vessel diameter (radius), & blood viscosity = poiseuille equation
Describe the poiseuille equation.
[R = 8 ηl/πr4]
R = resistance to flow is directly proportional to viscosity (n) of the blood
L = resistance to flow is directly proportional to length
R^4 = resistance is inversely proportional to the fourth power of the radius
What does the total resistance of blood vessels depend on?
whether the vessels are arranged in series or in parallel
1. Series
-blood flow sequentially from one vessel to the next
-ex: pulmonary circulation
2. Parallel
-total blood flow distributed simultaneously among vessels
-ex: organs of systemic circulation
-if only in series = lose pressure, O2, & nutrients & any damage would interrupt whole circulation
Describe series VS parallel arrangement of blood vessels.
less resistance of blood flow in parallel rather than in series
-if resistance of one vessel in a parallel increases = total resistance increases
-resistance of systemic circulation = systemic vascular resistance or total peripheral resistance (TPR)
-flow = pressure/resistance
-cardiac output = blood pressure (MAP)/TPR
