Vascular Physiology Flashcards
Non-conditioning organs
heart, skeletal muscles
The vascular tree consists of…
arteries- carry blood from heart to tissues
arterioles- smaller branches of arteries
capillaries- smaller branches of arterioles that perform all exchanges with surrounding cells
venules- formed when capillaries rejoin and return blood to heart
veins- formed when venules merge and return blood to heart
Blood vessel walls are composed of alternating layers of ..
connective tissue (elastic and collagen fibers), smooth muscle and epithelial cells
Outermost layer of blood vessel
tunica externa/adventitia
Middle layer of blood vessel
tunica media
Innermost layer of blood vessel
tunica intima
What does blood flow depend on?
pressure in vascular system and resistance developed in vascular system
flow rate of blood
the volume of blood passing through a blood vessel per unit of time
pressure gradient
pressure difference between the beginning and end of a vessel (H–>L)
resistance
measure of opposition to blood flow through a vessel
what causes resistance
friction between moving fluid/blood against the stationary vessel wall
resistance to blood flow is dependent on 3 factors..
- blood viscosity (fluid dependent)
- vessel length (vessel dependent)
- vessel radius (vessel dependent)
Blood viscosity
friction between the molecules of a flowing fluid
Blood viscosity is determined by..
number of RBCs
relationship between #RBCS, friction, viscosity, resistance and blood flow
more RBCS= more friction= more viscous= greater resistance= less blood flow
less RBCs= less friction= less viscous= less resistance= more blood flow
Is blood viscosity important to controlling resistance?
No, relatively constant
relationship between vessel length, SA, resistance, blood flow
longer vessel= greater SA= more resistance= less blood flow
shorter vessel= less SA= less resistance= more blood flow
Is vessel length important to controlling resistance?
No- not a variable factor (cannot control it)
relationship between vessel radius, resistance and blood flow
bigger radius= less resistance= more blood flow
smaller radius= more resistance= less blood flow
Is vessel radius important to controlling resistance?
YES- it is a major determinant of resistance to flow, major variable
arteries 2 functions
- serve as ‘rapid-transit passageways’ for blood from the heart to the organs
- act as a ‘pressure reservoir’ to provide a driving force for blood when heart is relaxing
collagen fibers
provide tensile strength, temporarily expand without damage
elastin fibres
provide elasticity to arterial walls
systolic pressure
maximum (peak) pressure is exerted in the arteries when blood is ejected into them during cardiac systole
heart contract –> increase blood to arteries
averages 120mmHg
diastolic pressure
minimum (less) pressure in arteries when blood is draining off into vessels downstream during diastole
averages 80mmHg
Pulse pressure
pressure difference between systolic and diastolic pressure
40mmHg
Mean Arterial Pressure (MAP)
average pressure driving blood forward into the tissues throughout the cardiac cycle
=diastolic pressure + 1/3 pulse pressure = 93mmHg
=cardiac output x total peripheral resistance
2 criteria about MAP
1) must be high enough to ensure sufficient driving pressure
2) must not be SO high, it creates hard work for the heart, causing a rupture in the small blood vessels in the brain (capillaries cannot withstand high pressure because they are not elastic and are instead narrow and single celled)
Muscular arteries
- arteries deliver blood to specific organs
- contains a thick, smooth muscle layer in tunica media (very active in vasoconstriction and vasodilation)
-can play major role in blood pressure regulation
Arterioles
- major resistance vessels
- highly muscular
- exist within organs
The radius of arterioles supplying individual organs can be adjusted independently to…
- distribute CO among systemic organs, depending on the body’s momentary needs
- help regulate arterial blood pressure
Arteriole wall contains..
- very little elastic connective tissue
- have a thick layer of smooth muscles (richly supplied by sympathetic nerve fibers)
vasoconstriction
narrowing of a vessel
vasodilation
enlargement in circumference and radius of the vessel
relationship between vasoconstriction, resistance and blood flow
vasoconstriction= contraction circular smooth muscle in arteriolar wall= increased resistance= decreased blood flow
What is vasoconstriction caused by
- increased myogenic activity
- increased oxygen
- decreased carbon dioxide and other metabolites
-increased endothelin - increased sympathetic stimulation
- vasopressin, angiotensin II, cold
relationship between vasodilation, resistance and blood flow
vasodilation= decreased contraction of circular smooth muscle in the arteriolar wall= decreased resistance= increased blood flow
What is vasodilation caused by
- decreased myogenic activity
- decreased oxygen
- increased carbon dioxide and other metabolites
- increased nitric oxide
- decreased sympathetic stimulation
- histamine release, heat
vascular tone
arteriolar smooth muscle displays a state of partial contraction
2 factors are responsible for vascular tone
1) myogenic (self-induced) activity of smooth muscle
2) sympathetic fibres continually release norepinephrine
fraction of total CO delivered to each systemic organ depends on..
- number and calibre of the arterioles supplying that organ/area
- extent of vascularization of organ/area
- differences in the resistance offered by the arterioles supplying organ
Active hyperemia
increased metabolic activity of organ= decreased oxygen, increased metabolites in organ interstitial fluid= arteriolar dilation in organ= increased blood flow to organ
endothelial cells
- release chemical mediators that play a vital role in locally regulating arteriolar calibre
- release locally acting chemical messengers in response to chemical changes in their environment
- among best studied local vasoactive mediators is NO and endothelin
Factors affecting arteriolar radius and therefore total peripheral resistance
local(intrinsic) control and extrinsic control
Local (intrinsic) control
local changes acting on arteriolar smooth muscle in the vicinity
Examples/types of local controls
- heat,cold application
- response to shear stress
- myogenic responses to stretch
- histamine release (involved with injuries and allergic responses)
- local metabolic changes in oxygen and other metabolites
Extrinsic control
important in regulation of blood pressure
Examples/types of extrinsic controls
- vasopressin (hormone important in fluid balance, exerts vasoconstrictor effect)
- angiotensin II (hormone important in fluid balance, exerts vasoconstrictor effect)
- epinephrine and norepinephrine (hormones that generally reinforce sympathetic nervous system)
- sympathetic activity (exerts generalized vasoconstrictor effect)
capillaries
- maximized surface area and minimized diffusion distance (capillaries lie close to cells)
- slow velocity through capillaries allows adequate time for the exchange of materials
how water-soluble substances, lipid-soluble and proteins pass through capillary wall
- water soluble: through water-filled gaps that lie at junctions between cells
- lipid-soluble: dissolving in a lipid bilayer barrier
- proteins: vesicular transport
lymphatic system
- extensive network of one-way vessels
- provides accessory route by which fluid can be returned from interstitial spaces to the blood
functions of lymphatic system
- return of excess filtered fluid
- defense against disease- lymph nodes have phagocytes that destroy bacteria filtered from interstitial fluid
- transport of absorbed fat
- return of filtered protein
Oedema
swelling of tissues, occurs when too much interstitial fluid accumulates
causes of oedema
- reduced concentration of plasma proteins e.g. kidney disease, liver disease, loss of proteins from burned skin
- increased permeability of capillary wall e.g. allergic reaction
- increased venous pressure (esp in pregnancy)
- blockage of lymph vessels e.g. filariasis and elephantiasis
Veins large ___ offers little resistance to blood flow
Veins large radius offers little resistance to blood flow
Veins also serve as …
blood reservoir- ability to store large amounts of blood
Veins:
- walls are ___ than arteries
- ___ smooth muscle, ___ elasticity, __collagen than elastin
- ___ resistance
- ___ cross-sectional area due to ___ in numbers than arteries
Veins:
- walls are thinner than arteries
- little smooth muscle, little elasticity, more collagen than elastin
- low resistance
- less cross-sectional area due to less in numbers than arteries
Venous return
driving pressure from cardiac contraction
Sympathetic stimulation causes ___, which ___ venous return
Sympathetic stimulation causes vasoconstriction, which elevates venous return
primary determinants of blood pressure
cardiac output, total peripheral resistance
Cardiac output (CO)
heart rate (HR:beats per minute) x Stroke volume (SV: blood volume ejected with each beat)
OR
CO= HR x SV
baroreceptors
special nerve cells or receptors that sense blood pressure, by the way that the walls of the blood vessels stretch. That information is sent from the baroreceptors to the brain to help keep blood pressure balanced
The baroreceptors send signals to the brain and the signals are interpreted as a rise in blood pressure
Baroreceptors and MAP
- number of action potential increases when MAP increases
- number of action potential decreases when MAP decreases
ANS on heart function
Parasympathetic
- vagus nerves that release acetylcholine to atria never ventricles
Sympathetic
- thoracic spinal nerves/bloodstream that release norepinephrine and epinephrine to both atria and ventricles
less sympathetic input= ___ blood vessels
more sympathetic input = ___ blood vessels
less sympathetic input= dilated blood vessels
more sympathetic input = constricted blood vessels
Circulatory shock(s) occurs when..
blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained
4 main types of circulatory shock (s)
- hypovolemic (“low volume”) shock
- cardiogenic (“heart produced”) shock
- vasogenic (“vessel produced”) shock
- neurogenic (“nerve produced”) shock
Hypovolemic shock
1) severe hemorrhage or excessive vomiting, diarrhea, urinary losses, etc.
2) loss of fluids derived from plasma
3) loss of blood volume
4) decrease cardiac output
5) decreased MAP –> circulatory shock
Cardiogenic shock
1) weakened heart
2) decreased cardiac output
3) decreased MAP –> circulatory shock
Vasogenic shock
1) (a) septic shock or (b) anaphylactic shock
2 (a) vasodilator substances released from bacteria, (b) histamine released in severe allergic reaction
3) widespread vasodilation
4) decreased peripheral resistance
5) decreased MAP –> circulatory shock
Neurogenic shock
1) decreased sympathetic nerve activity
2) loss of vascular tone
3) widespread vasodilation
4) decreased peripheral resistance
5) decreased MAP –> circulatory shock
