Outermost layer consisting of connective tissue.; collagen; vasovasorum (network of small blood vessels that serve large vessels); nerve fibers, lymphatics.
- collagen (connective tissue)
pressure gradient is produced by what?
contraction of heart
opposition to flow
- friction between blood vessel and walls og blood vessels
sources of resistance
- blood vessel length
- blood vessel radius
TPR (total peripheral resistance)
the sum of all resistance - due to resistance offered bu arterials
TPR can affect what?
- mean arterial pressure
- stop blood flow to certain peripheral locations and concentrate on more core organs
which variables are physiologically regulated
- delta P
The force (or tension)stretching vessel wallopen is proportional tovessel’s diameter (orradius) * BPLESS tension on walls ofvery small vessels…thusif P < CCP (closing critical pressure), (small) vessel collapses
elastic artery are also called what?
- b/c they bring blood to the major regions of the body
sequence of arteries
- elastic artery
- muscular artery
- also called distributing arteries
- has less elastic and proportionally more muscle in their walls
- they are what lead blood to arterioles
function of arteries
- low resistance pipes
- pressure reservoir (esp elastic artery)
Pressure Reservoir Function of Elastic Arteries
• During systole, strokevolume of blood isejected, stretchingcompliant walls of elasticarteries
• When systole ends,stretched arterial wallsrecoil, continuing to driveblood into arteriolesduring diastole
– NOTE ARTERIALPRESSURE does NOT go tozero during diastole!
– Note VENTRICULARpressure DOES go toalmost zero during diastole!
blood pressure = ?
force / unite exerted by blood on wall of blood vessel
what is normal blood pressure
pulse pressure = ?
systolic - diastolic pressure
what is mean arterial pressure
the driving force that pushes blood around the entire systemic circuit
MAP is for which system?
MPAP is for which system
mean arterial pressure (MAP) = ?
diastolic pressure + 1/3 pulse pressure
two major roles of arterioles
– Determine relative blood flows to tissues(blood flow distribution)
– Major factor in determining MAP (due to effect on Total Peripheral Resistance)
THREE MECHANISMS regulate arteriolar radius
– Local Control
– Neural (reflex)Control
– Hormonal Control
Local (“intrinsic”) Control of Arteriolar Radius
1) Active Hyperemia: Blood flow adjusted tomeet tissue’s needs
2) Flow Autoregulation
Active Hyperemia: Blood flow adjusted tomeet tissue’s needs
Following stimuli increase blood flow(by increasing radii of arterioles, metarterioles andprecapillary sphincters):
– Decreased O2
– Increased CO2
– Increased [H+] / decreased pH
– Metabolites, including K+, ↑ osmolarity
This mechanism is not important in MAPregulation.
– Decreased blood pressure in organ => arteriolardilation in organ to restore blood flow
– Several factors mediate – including decreased O2and increased metabolites
This mechanism is not important in MAPregulation
Reflex (Neural) Control of Arteriolar Radius
• Sympathetic nervous regulation
Sympathetic nervous regulation of arteriolar radius
what can increase TPR (total peripheral resistance)
mass vassel constriction, which can also boost your MAP
alpha 1 receptors
blood vessel will restrict
beta 2 receptors
do not really respond to NE but they do to EPI
- they open up and relax smooth muscle
Hormonal Control of Arteriolar Radius
Hormonal Control of Arteriolar Radius: Epinephrine
Vasoconstrictorfor vessels withα1-adrenergicreceptors;vasodilator forvessels with β2-adrenergicreceptors
in flight/flight mode, which mechanism over powers which?
the extrinsic (hormonal and neural) take over the local controls
thin tunica intima
Types of Capillaries
Capillary Beds consist of?
- True capillaries
branches off the arterial and connects the arterial with its oxygenated blood with the venule with the deoxygenated blood will go - the capillaries branch off the metarteriole - also has surrounding smooth muscle where is first branches off the arterial - this muscle likewise can squeeze shut to divert blood away from capillaries- the distal region where it lacks smooth muscle is called the thoroughfare channel which connects to the venule
branch from the metarterioles and at the entrance of each is a precapillary sphincter which is the ultimate control of whether or not blood enters the capillaries and thus a tissue - under local control (if it needs blood the sphincter will open. it closes when it does not need nutrients or are not burdened with wastes. closing allows the blood to flow directly into the venule)
Capillary Blood Pressure
• 35 – 40 mm HG at beginningof capillary bed
• 15 – 20 mm Hg at end
how do lipid soluble molecules and ions/ polar molecules diffuse through the capillaries?
- lipid soluble: diffuse through endothelial cell membrane
- ions/ polar molecules may diffuse through intercellular cleft
movement of water across capillary walls down a pressure gradient - this is important in fluid balance
where does mediated transport play a role in the capillaries?
when in the brain
Failure of lymphatic system leads to what?
Weakness / loss elasticity in venous walls
- Veins widen and stretch
– Valves don’t close => backflow of blood
standing for too long can cause what?
veins are considered blood reservoir due to what?
high compliance of venous walls which can accommodate large volumes of blood with realtively little increase in pressure
what is a major determinant of cardiac output?
venous pressure which determine venous return
Determinants of Venous Return
• Total Blood Volume is one determinant of pressure(and thus venous return)
• Compliance, normally high, can be decreased tostiffen venous walls
• Valves and large lumens also crucial to venous return
Two other functional adaptations ensure venous return
– Skeletal Muscle Pump
– Respiratory Pump
Skeletal Muscle Pump
• Compression of veinsby skeletal musclecontraction raiseslocal venouspressure; thenvalves preventbackflow
• Blood forcedtowards heart
• Heart (and lungs) are inthoracic cavity
• Pressure in thoracic cavity is subatmospheric (negative)