Flashcards in Lecture 19 - Local Regulatory Mechanisms Deck (54)
What is the term for vessels that control blood FLOW? What are the 4 vessels?
3. Pre-Capillary Sphincters
4. Venous RESISTANCE
What structure in a vessel controls/determines the total peripheral resistance, arterial & venous tone, and blood FLOW throughout the body?
Vascular Smooth Muscle
Resistance and thus FLOW, is constant from organ to organ, the same mechanism is employed for every organ. True or False?
- resistance varies from organ to organ, and multiple mechanisms are responsible
1. Neural & Hromonal - GLOBAL
What is the term for the intrinsic property of an organ to maintain constant blood flow, regardless of changes to arterial or percussion pressure? Does this change with gravity?
- constant flow despite any changes in Gravity
What is the equation for flow?
Flow = change in Pressure / Resistance
Following an abrupt increase in arterial pressure, what happens to blood flow? Does this change stay constant? How is flow changed?
1. Initial INCREASE in flow followed by a gradual decline to baseline
- decrease in flow due to an INCREASE in resistance due to AUTOREGULATIOn
What happens to flow as arterial pressure increases and thus arterial RESISTANCE? Why does this occur?
FLOW STAYS CONSTANT!!
- due to AUTOREGULATION
When does auto regulation fail?
- very HIGH or very LOW pressures
What are the two primary mechanisms of auto regulation ?1
1. Myogenic Hypothesis
2. Metabolic Hypothesis
What is the Myogenic Hypothesis? What changes occur to resistance and flow upon an INCREASE or DECREASE in PRESSURE?
1. smooth muscle contracts in response to stretch (relaxes when stretch is reduced)
2. Increase in pressure = initial stretch of the vessel wall which causes smooth muscle to CONTRACT (vasoconstrictor)
= increase in resistance, reduction in flow
3. DECREASE in pressure = reduction in stretch
- smooth muscle RELAXES (vasodilation)
-decrease resistance, increase in FLOW
What is the metabolic hypothesis of Autoregulation? What occurs when pressure is increased and decreased?
1. Metabolic activity makes substances for VASODILATION ( adenosine, K+, H+)
2. When pressure increases: brief increase in FLOW so metabolites are removed and resistance vessels CONSTRICT
- increase in resistance, decrease in flow
3. Pressure DECREASES: less blood flow so metabolites ACCUMULATE and cause vasodilation!!
- dilation decreases resistance and INCREASES flow
What substances cause metabolic vasodilation? What determines their concentration in the body?
Adenosine, K+, H+
- BLOOD FLOW determines the concentration in the microvascular beds
Since auto regulation varies from organ to organ, which areas have:
1. Strong Autoregulation
1. Strong: heart, brain, kidney, skeletal muscle
2. Weak: Splanchnic
3. Little: skin, lungs
What happens to the diameter of an arteriole when transmural pressure INCREASES & flow is held constant?
What is this an example of? Is this endothelium dependent?
1. Diameter DECREASES (constricts)
2. example of AUTOREGULATION
3. NOT DEPENDENT ON ENDOTHELIUM!!!
When the pressure gradient (flow) through an arteriole is INCREASED (transmural pressure held constant), how does the diameter change? Is this Endothelium Dependent?
1. diameter is INCREASED (dilates)
2. YES dependent on endothelium; no dilation when the endothelium is removed
What is released in response to shear stress due to the increase in flow through a vessel? What changes occur to the FLOW? When does this occur, typically? (example)
EDRF (endothelium derived release factor) & NO
- increase in blood flow directly releases endothelial mediated vasodilators to increase flow EVEN MORE
- occurs during EXERCISE!
Are the following vasodilators or a vasoconstrictors?
Where is metabolic regulation most important? When is a SITUATION that metabolic activity is stimulated?
1. Skeletal muscle, Cardiac, Brain
2. Decrease in oxygen delivery to a tissue can stimulate the formation of METABOLITES that are vasodilators
What is ACTIVE hyperemia? What factors are responsible for this type of response? (3)
1. Increased blood flow caused by enhanced tissue activity
2. K+, inorganic Phosphate, and interstitial Osmolarity
What is Reactive/PASSIVE hyperemia? What kind of debt increases flow?
1. Transient increase of blood flow that follows a brief arterial occlusion
2. METABOLIC debt increases blood flow
What occurs to the blood flow following an occlusion? What type of hyperemia is this? If the occlusion is longer in duration, how does the response change?
1. Blood flow INCREASES following the period of occlusion
2. REACTIVE Hyperemia
3. Longer occlusion duration = GREATER RESPONSE (intuitive) - want to increase flow!
What can occur to small vessels & thus FLOW with an increase in tissue pressure?
Mechanical tissue pressure can COMPRESS small vessels and alter flow
What are 3 possible causes of Mechanical (Tissue) Pressure?
1. Muscle Contraction (heart, skeletal)
2. Alveolar Pressure (lungs)
3. Tumors (venous obstruction)
What are the 2 main factors affecting Total Peripheral Resistance?
1. Arteriolar Radius
2. Blood viscosity
What are the 3 types of extrinsic control of Arteriolar Radius? Intrinsic control?
1. baroreceptor Reflex
2. Hormonal effects (angiotensin, epinephrine)
3. Sympathetic Activity
1. Metabolic changes
(02, CO2, metabolites)
3. Myogenic response
Regulation of blood flow is primarily determined by what resistance vessel, specifically?
- these have little affect on capillary hydrostatic pressure because of the significant resistance they provide
Mechanical effects like compression via skeletal muscle has a larger affect on veins or arteries? Why?
1. larger affect on VEINS
2. Lower pressure than arteries/ AUTOREGULATION of arteries
What is the mechanism of E-C couple in vascular smooth muscle? (5 steps)
1. increased intracellular calcium binds calmodulin
2. activates myosin light chain kinase (MLCK).
3. MLCK phosphorylates the regulatory light chains of the myosin heads. (MLC)
4. Phosphorylated myosin heads are able to cross bridge-cycle
5. Myosin light chain phosphatase removes the phosphate groups from the myosin heads = relaxation
(and leaving the muscle in latch-state).
Auto regulation regulates pressure. True or False?
Regulates FLOW due to result in changes in pressure (standing up/gravity)