Vascular pt 1 Flashcards
Tunica media consists of?
- Smooth muscle
- External elastic lamina
Tunica intima consists of ?
- Endothelium
- Subendothelial layer of loose CT
- Internal elastic membrane
Tunica externa (adventitia) contains?
- Loose CT with collagen and elastin
- Contains vasa vasorum & nervi vascularis (autonomics) in larger arteries and veins
Large (elastic) artery contains?
– Eg. aorta, subclavian, common carotid
- Tunica intima
- Internal elastic membrane
- Tunica media
- Tunica adventitia
Medium (Muscular) contains ?
– Eg. ulnar, coronary a.
- Tunica intima
- internal elastic membrane
- Tunica media – more SM, less elastic
- Tunica adventitia (thick layer of collagen, with less elastin)
List Small arteries and arterioles functions and characteristics?
Both maintain an endothelium surrounded by basement membrane
arterioles are the primary site of smooth muscle control over blood pressure and flow regulation
capillaries contain?
- Endothelium
- Basement membrane
- Pericytes (primitive smooth muscle cells)
Venules and veins contain?
-Small elastic fibers
-smooth muscle and CT
Pressures are low so walls are thin
Medium Veins contain?
• T. media
• T. adventitia (externa)
veins up to 10 mm diameter, many with valves, especially lower limb
Large Veins contain?
-eg. SVC, IVC portal vein, over 10 mm diameter
- T. media: few smooth muscle layers
* T. adventitia: thick with CT (collagen & elastin) plus longitudinal smooth muscle
Blood distribution in the circulatory system
• Veins 64% • Arterial side 20% – Arteries 13% – Arterioles and capillaries 7% • Heart/pulmonary 16% Where the blood is depends on Blood Flow and Vascular Resistance
Q (flow) is the Cardiac Output, how is this determined?
– Determined by stroke volume and heart rate: Q = SV ∙ HR
– Regulated by neural and hormonal systems
R (resistance) is the Total Peripheral (Vascular) Resistance is regulated by?
Regulated by metabolic and neurohumoral mechanisms
ΔP (pressure gradient) is the Blood Pressure, how is this determined.
– derived from the interactions of the cardiac output (flow) and resistance.
– ΔP is estimated by various measures of blood pressure: systolic/diastolic, mean arterial pressure (MAP), pulse pressure, etc.
TOTAL PERIPHERAL (VASCULAR) RESISTANCE
R = ΔP/Q
• Pressure gradient is ΔP = (P aorta – P vena cava)
– Since P vena cava is negligibly small, it can be eliminated so that ΔP = P aorta
VELOCITY is similar to FLOW, but is a very different measure.
- Flow is the amount of blood that passes a given point in a period of time (volume/sec)
- Velocity is the rate of linear displacement of fluid (cm/sec).
For a given cardiac output (Q), velocity varies inversely with diameter of blood vessel
- The more dilated the blood vessel, the slower the blood flow.
- Fluid slows at it enters wider vessels and accelerates as it enters smaller vessels.
Highest velocity of blood flow is in __
Lowest Velocity is in __
- Highest velocity of blood flow is in the aorta
* Lowest velocity in capillaries.
explain Laminar streaming
- Fluid particles travel in concentric layers (lamina): from slowest near walls to fastest in the center, creating a velocity gradient
- Velocity gradient is generated by viscosity
what is viscosity?
- Viscosity is the inner friction in the fluid: it is generated by the interaction between molecules and particles in the blood and resists any relative motion among them
- Increase in viscosity (η) reduces flow Q ~1/η
Velocity gradient is created by blood viscosity and friction from walls, what does a higher viscosity do to the velocity gradient?
- Higher viscosity increases the velocity gradient .
- A greater velocity gradient increases shear stress which alter vascular properties
- Excess rbc synthesis in response to hypoxia (polycythemia) increase viscosity, impairing blood flow
in capillaries rbc’s travel in single file and adhere less to the vessel wall. what does this do for viscosity?
there is less viscosity; in fact there is a water space between cells and the capillary wall (Fåhræus‐Lindquist effect).
according to Bernoulli’s principle:
Constricting a blood vessel?
Expanding a blood vessel?
- increases blood velocity and shear stress
* decreases blood velocity by increasing lateral (transmural) pressure
explain Shear Stress
• Excess velocity of laminar flow produces shear stress (viscous drag) on endothelial cells
• Temporary shear stress can be compensated by autoregulation that vasodilates the vessel and slows the flow
• Shear stress (τ)
– increases with viscosity, flow and velocity
– decreases with radius
what are the problems with prolonged shear stress
- Excess shear stress associated with occlusion can alter gene expression via cytoskeletal signaling
- can lead to inflammation, remodeling, atherosclerosis involving the extracellular matrix (ECM), smooth muscle and endothelium.
Turbulence develops under the conditions of:
high velocity (V), large vessel diameter (D), high fluid density (ρ) and low viscosity (η). – Combined into the Reynold’s number which determines the threshold of turbulence.
Turbulence can occur in __
Turbulence produces sounds called __
narrow, atherosclerotic vessels (high velocity), aortic arch (large diameter), bifurcations, eg aorta
called bruits (blood vessels) and murmurs (heart)
Turbulence produces greater levels of transmural pressures that increase the chance of endothelial injury & subsequent plaque formation. this manifests as?
an Aortic aneurism: involves rupture of endothelium and infusion of blood into the tunica media creating a false lumen
• Because it separates the aortic wall layers, it is called a “dissecting aortic aneurism”
Differences in resistances affect blood flow in the vascular system how?
- Blood flow through individual organs depends on the resistance of organ’s vessels
- Blood flow through the entire system depends on the TPR
generalize how TPR and MAP are caclulated
Organ vascular systems are arranged in parallel and the sum of the individual resistances determine not just local pressures, but also the resistance and pressure of the entire system.
Blood flow through individual organs is determined mostly by regulation of
arteriolar resistance
Generalize central control of vascular system
-mostly vasoconstrictive
Autonomic neurons and endocrines regulate total vascular system maintain overall blood pressure and flow
Generalize local control ( autoregulation )
mostly vasodilatory
- maintaining constant blood flow to an organ with a steady metabolic rate in the face of changing blood pressure
- adjusting blood flow to an organ according to local changes in its metabolic activity
explain ANS regulation of organ blood blow (i.e. arteriolar resistance)
Mainly sympathetic nervous system (NE & EPI)
- Alternating increased or decreased sympathetic activity produces constriction and dilation respectively via alpha‐1 receptors
explain alpha 1 receptors
most common vascular adrenergic receptors; found in all arterioles .
– binding with norepinephrine or epinephrine leads to vasoconstriction via IP3
Explain β2 receptors
found in arterioles of skeletal and cardiac muscle (non‐innervated; hormonal only)
– binding of mostly epinephrine leads to vasodilation via cAMP
During sympathetic response (eg. exercise) blood is directed to?
skeletal muscle and heart (β2 vasodilation) and away from the internal organs (α1 vasoconstriction)
– However, most vasodilation in continuing muscle activity is due to build up of metabolites
Mechanisms for autoregulation include:
Metabolic
Myogenic
Endothelial
Explain Active Hyperemia
the increase in organ blood flow (hyperemia) associated with increased activity of an organ or tissue.
• consumes O2 , generating local hypoxia, this vasodilates arterioles by inducing formation of vasodilator metabolites.
• Increased blood flow washes out metabolites and vessels constrict back to normal
Metabolic vasodilators are specific to organs and include:
- Adenosine (Ado) inhibits contraction via cAMP in coronary and possibly muscle arterioles
- K+ & PO4 dilate skeletal muscle vasculature
- CO2, H+ dilate cerebral vasculature
Major vasodilator in most blood vessels
Nitric oxide (NO)
how is NO synthesized?
Synthesized from arginine via nitric oxide synthase, NOS.
How is NO released?
• NO is released from endothelial cell & enters smooth muscles cells
• Released from endothelium by:
– Shear forces of blood flow (flow mediated vasodilation)
– Chemical means: ACh, ATP, hypoxia, histamine, bradykinin
what does NO generate?
- NO generates cGMP which inhibits Ca++ actions on myosin light chain kinase, leading to its relaxation
- NO also regulates proliferation of SM cells
Prostaglandins (prostacyclin), PG does what?
uses cAMP to inhibit Ca++ mediated smooth muscle contraction
how is endothelin ET-1 released?
Released in response to vasoconstrictors
NO and PG are counterbalanced by ?
• NO and PG counterbalanced by ET‐1 which contracts smooth muscle (vasoconstriction)
What is ET function?
• ET both constricts and induces proliferation of smooth muscle cells
ET-1 and NO roll in hypertesion?
• In hypertension, ET‐1 is up regulated, while NO is down regulated. Endothelial cells hypertrophy and smooth muscles proliferate
Smooth muscle cells secrete ?
collagen, elastin and proteoglycan
Even though blood pressure derives from direct interaction of CO and R, it can also be affected by?
renal regulation of fluid volume and salt concentration
Parasympathetic vasodilation is localized to a few structures:
eg. cerebral and genital vessels
Blood flow (Q) is related to
blood pressure (ΔP) and vascular resistance (R) Q = ΔP/R
Define Total peripheral resistance
TPR = ΔP/Q = P aorta/CO
P (aorta) is estimated by the Mean Arterial Pressure
TPR = MAP/CO
Explain how resistance is inversely proportional to 4th power of vessel radius
– small decreases in arteriolar radius (vasoconstriction) causes significant increases in resistance, reducing flow or increasing pressure differences.
– Tube with twice the radius yields 16 times the flow.
Velocity is a function of
flow and cross‐sectional area
what does local control (autoregulation) use to optimizes blood flow and O2 delivery ?
uses metabolites, myogenic and endothelial mechanisms
Alpha & beta receptors both bind NE & EPI, but
produce opposite responses
α1 receptors: Vasoconstriction via IP3
β2 receptors: Vasodilation via cAMP
During exercise blood is shunted away from the GI tract to the skeletal muscles and the heart by ?
epinephrine
Autoregulation maintains constant blood flow to the organ/tissue by constricting or dilating arterioles via ?
metabolites, NO, or myogenic actions
Without autoregulation, blood flow would
increase with rise in perfusion pressure
- If pressure drops __
* If pressure increases__
blood vessels dilate to maintain flow
blood vessels constrict to reduce blood flow
Pressure enhances smooth muscle contraction by activating cell pathways that increase
both Ca++ influx and Ca++ binding to myosin light chains
___ minimize arterial pressure build up in legs and feet during standing
Myogenic responses
Smooth muscle contains?
- elastic & reticular fibers
- proteoglycans between SM cells
what does collagen do in arteries
limits expansion
what does elastin do in arteries ?
creates recoil pressure during diastole
