Chapter 10 - Vascular Physiology Flashcards
Components of the Circulatory System
the heart, blood vessels, blood
Affects of the Circulatory system
a) endocrine system: hormones such as epinephrine increase HR
b) nervous system: role in increasing/decreasing HR
c) kidneys: filter blood, regulate water levels and BP
Blood Flow Characteristics
-constantly reconditioned
-composition remains relatively constant
Reconditioning Organ Role
-receive more blood than needed for metabolic needs
-adjust extra blood to maintain homeostasis
Reconditioning Organs
digestive organs, kidneys, skin
Adjusting Blood Flow
-blood flow to organs is adjusted according to metabolic needs
-ie. the ANS controls: exercise means blood flow is increased to skeletal muscles whereas during relaxation blood flow is increased to GI organs
Which organ can’t tolerate a disrupted blood supply?
the brain must have constant blood supply to maintain functions
Distribution of Cardiac Output at REST
-almost half (41%) is directed to reconditioning organs (digestive system and kidneys)
-13% to brain
-15% to skeletal muscles which don’t need lots of blood at rest
Cardiac Output
-equal to the stroke volume x heart rate
-ie. 70 x 70 = 5L/min at rest
What does blood flow depend on?
pressure and resistance in the vascular system
Blood Flow Definition
-the volume of blood passing through a vessel per unit of time
Blood Flow Equation
F (flow) = ΔP (pressure)/R (resistance)
Pressure Gradient (ΔP)
-the pressure difference between the beginning and end of a vessel
Gradient of Blood Flow
-blood flows from an area of high pressure to areas of low pressure
Resistance (R)
-the measure of opposition/friction of blood flow through a vessel
Resistance depends on…
a) blood viscosity: how thick the blood is
b) vessel length: how long the tube is
c) vessel radius: how wide/narrow the vessel is
Pressure/Flow Relationship
-a directly proportional relationship
-if you increase pressure you increase flow
Remember when calculating Flow…
-ΔP is the difference in the pressure between the beginning and end of a vessel
-ie. 50mmHg - 10mmHg = 40mmHg
What changes in blood vessels?
-Blood vessel length does NOT change
-blood vessel diameter does change
Changing vessel diameter
via smooth muscle cells in the vessel walls arranged in a circular pattern that are initiated by the ANS to control vasoconstriction/dilation
Blood Viscosity
-the friction between molecules of a flowing fluid
-increase friction, increase viscosity
-determined by the number of RBCs
Vessel length vs. resistance
the longer the vessel the greater the resistance (length is constant)
Vessel radius vs. resistance
-radius is the major variable
-smaller the vessel the greater the resistance
-resistance (R) is proportional to 1/r⁴ (radius)
-ie. doubling radius decreased R by 16x and increases flow by 16x
-small changes on radius (r) give big changes in resistance (R)
Where is resistance highest?
Arterioles
Pressure (P)
-the force exerted
-measured in mmHg
Flow (F)
-the volume moved
-measured in mL/min
Resistance (R)
-how difficult it is for blood to flow between any to points at a given pressure difference
Equation that relates PFR
F = ΔP/R or ΔP = F x R
Grouping Vessels
-vessels are defined by their anatomy not their oxygen content
Veins
-bring blood to heart
-formed when venules merge
-ie. vena cava (brings blood from extremities to heart) or pulmonary vein (brings blood from the lungs back to the heart)
Arteries
-take blood away from the heart
-ie. aorta (brings blood from heart to rest of body) or pulmonary artery (brings blood from heart to lungs)
What variables does the body control?
-controls flow and resistance which together control pressure
Arterioles
-smaller branches of arteries
Capillaries
-smaller branches of arterioles
-where exchanges are made with surrounding cells
Venules
-formed when capillaries rejoin
-return blood to the heart
Systemic Circulation
-provides blood supply to organs and tissues
-between heart and organ systems
Pulmonary Circulation
-provides blood supply to lungs to be reconditioned
-between heart and lungs
Artery Functions
1) passageway for blood from heart to organs
2) act as a pressure reservoir to provide the driving force when the heart is relaxing
Artery Resistance
-arteries have a large radius and therefore offer little resistance to blood flow
Arterial Connective Tissue
contains collagen and elastin
Collagen Fibres
-provide tensile strength
-tough
-stretch resistant
-prevent overstretching
Elastin Fibres
-provide elasticity to arterial walls
-stretchy
-recoil - returns to original size
Arteries as Pressure Reservoir: Contracting and emptying (systole)
-stretch to act as a minor storage reservoir
-inflated balloon
-blood can’t go to tissues
Arteries as Pressure Reservoir: Relaxing and filling (diastole)
-recoil to squeeze blood out
-deflated balloon
-blood reaches the tissues
Is the reservoir a muscular property?
NO! it is an elastic property
Pulse
the pulsating feeling provided when arteries stretch and recoil as blood is pumped through them
Blood Pressure
-the force exerted by blood against a vessel
-fluid moves from an area of high to low pressure
-supplies tissues
Dependants of BP
BP depends on: a) volume of blood b) compliance of vessel walls
Compliance
-equal to Δvolume/Δpressure
-the higher the compliance the easier it can be stretched
Are arteries or veins more compliant?
Veins
Systolic Pressure
-peak pressure exerted by ejected blood against vessel walls during systole
~ 120 mmHg
Diastolic Pressure
-minimum pressure in arteries when blood is draining off into vessels
~ 80 mmHg
Sphygmomanometer
-used to indirectly measure BP
Korotkoff Sounds
-heard when determining BP
-sounds associated with valve closure
Pulse pressure
-difference between systolic and diastolic pressure
-ie. BP is 120/80 so pulse pressure is 120mmHg-80mmHg=40mmHg
-the pulse that is felt through skin is due to pulse pressure
Mean Arterial Pressure
-the average pressure driving blood forward into tissuess
MAP formula
-MAP = diastolic pressure + ⅓ pulse pressure
-ie. At 120/80: 80mmHg + ⅓40mmHg = 93mmHg
-ΔP=MAP
Arteriole Properties
-where most of the resistance to blood flow occurs in the body
-exist within organs
Vasoconstriction
-narrowing of a vessel via muscle cells
-increased resistance and decreased flow
-a muscular property of vessels involving the contraction of smooth muscle cells
Vasodilation
-widening of diameter of a vessel
-leads to decreased resistance and increased flow
-a muscular property of vessels involving the relaxation of smooth muscle cells
Causes of Vasoconstriction
-increased myogenic activity
-increased oxygen
-decreased carbon dioxide
-increased endothelin
-increased sympathetic stimulation
-increased sympathetic stimulation
-cold temperatures
Vasodilation Causes
-decreased myogenic activity
-decreased oxygen
-increased CO2
-increased nitric oxide
-decreased sympathetic stimulation
-histamine release
-hot temperatures
Where does vasoconstriction not occur?
in the brain
Myogenic Activity
-a property of muscles
-they respond to stretch with constriction
Endothelin
-released from endothelium cells
Nitric Oxide
-from endothelial cells
-chemicals
-acts on muscles causing them to relax
Histamine
-released during an allergic reaction
Vascular Tone
-the activity of smooth muscle cells
-smooth muscle displays a state of partial constriction
Factors Responsible for Vascular Tone
-myogenic activity of smooth muscle
-sympathetic fibres continually releasing norepinephrine
Blood Flow Changes to Organs
-Branching vessels can have branches constrict to direct blood flow to specific areas
Increasing Flow to a Tissue
-increase pressure
-vasodilate to decrease resistance
Distribution of Cardiac Output During Moderate Exercise
-increase in blood flow to: skeletal muscle, skin, heart
-decrease in blood flow to: GI organs, kidneys, bone
-no change: brain
Intrinsic Factors to adjust organ blood flow
-occur within the organ
-local environment around the arteriole
Extrinsic factors to adjust organ blood flow
-occur outside the organ
-nerve inputs
-hormones
Local Chemical Influences on Arteriolar Radius
-local metabolic changes (ie. O2 and CO2)
-histamine release
Local Physical Influences on Arteriolar Radius
-local heat/cold application
-chemical response to stress
-myogenic response to stretch (contraction)
Active Hyperemia
-increase in metabolic activity to increase local blood flow
Local Chemical Factors that Produce Relaxation of Arteriolar Smooth Muscle
-decreased oxygen
-increases CO2
-increased lactic acid (pH)
-increased potassium (action potentials)
-increased osmolarity
-adenosine release
-prostaglandin release
Endothelial Cells
-a vasoactive mediator
-release chemical mediators that regulate vasoconstriction/dilation
-release chemical messengers in response to environmental changes
-participate in material exchange
-determine capillary permeability by contracting to vary pore size
Nitric Oxide
-a vasoactive mediator
-cause relaxation of arteriolar smooth muscle
-controls blood flow through tissues
-maintains MAP
Extrinsic Control (arteriole extrinsic factors)
-accomplished by sympathetic nerve influence and some hormones
Total Peripheral Resistance (TPR)
-the force required to maintain blood flow throughout venous system
-when entire circulation is considered
-MAP=COxTPR
Norepinephrine
-a neurotransmitter that attaches to alpha and beta receptor sites to influence smooth muscle
-influence TPR
-an extrinsic sympathetic control mechanism
Local Controls on TPR
-override sympathetic vasoconstriction to direct blood to necessary areas
-an extrinsic sympathetic control mechanism
Do arterioles have parasympathetic innervation?
-no
-the ANS doesn’t always work in opposition
Cardiovascular Control Centre
-in medulla
-integrating center for BP regulation
Epinephrine and Norepinephrine
-hormones that influence arteriolar radius
-result from sympathetic stimulation of the adrenal medulla
Vasopressin and Angiotensin II (extrinsic control)
-hormones that influence arteriolar radius
-important in controlling fluid balance
-vasoconstrictor effect
A1 Recptors
-receive norepi and epi
-located on all arteriolar smooth muscle except in the brain
-result in vasoconstriction
B2 Receptors
-receive epi
-located on arteriolar smooth muscle in heart and skeletal muscles
-result in vasodilation
Summary: What affects TPR?
-blood viscosity (# of RBCs)
-Arteriolar Radius: Influenced by Local/Intrinsic (hot and cold temps, stress response, myogenic response, histamine release, metabolic changes) and Extrinsic (sympathetic activity, hormones) Factors
Capillaries
-single layer of endothelial cells
-as wide as a single RBC
-the smallest blood vessels
-thin walled to allow diffusion of gases between blood and tissue cells
-extensively branched
Blood Flow Through Capillaries
-relatively slow
-provides adequate exchange time
Easing Diffusion
-RBCs packed together combined with the tin walls of capillaries reduce diffusion distance
-increased surface allows more diffusion sites
Pores
-narrow, water filled gaps that lie at junctions between cells
-size of the pores varies from organ to organ
Do capillaries have a pulse?
-no, blood just flows through them
Capillary Wall Permeability
-selectively permeable
-made of a lipid bilayer
Water Soluble Substances
-Na+, K+, Amino Acids, H20
-follow a concentration gradient
-pass through the pores
Lipid Soluble Substances
-readily pass through endothelial cells by dissolving in lipid bilayer barrier
-oxygen and carbon dioxide
Proteins
-pass by vesicular transport (endocytosis and exocytosis)
-plasma proteins don’t pass because the capillary wall is a barrier to them
Continuous Capillary
-skin, muscle, brain (BBB)
-common kind have tight junctions
-smaller gaps
Fenestrated Capillary
-more permeable
-intestines, hormone producing tissues, kidneys
Sinusoidal Capillary
-have an incomplete basement membrane
-liver, bone marrow, lymphoid tissues
-big gaps
-can be quite leaky
Active Hyperemia
-when arterioles dilate because of surrounding cell activity
Passive Exchanges
-no ATP energy is spent
Passive Diffusion
-diffusion down concentration gradients of materials between blood and interstitial fluid
-plasma proteins cannot pass
Bulk Flow (SLIDE 89 DIAGRAM)
-the movement of fluid from blood to interstitial fluid and back again
-moves by pores
-functions to distribute ECF (fluid volume), not metabolic exchange
-balance of hydrostatic and colloid osmotic pressure
-keeps blood flow constant
-controls BP in the long term
Ultrafiltration
-fluid movement from plasma to interstitial fluid
-usually at the arteriole end
-needs to be higher than reabsorption
Reabsorbtion
-fluid movement from interstitial fluid to plasma
-usually on the venule end
-needs to be lower than ultrafiltration
Extracellular Fluid Composition
-made of plasma, blood, interstitial fluid
Starling Forces
-control the net flow of fluid
-influences bulk flow
Hydrostatic (Capillary Blood) Pressure
-the force of fluid on the inside of the capillary tube
-moves from the direction of inward to outward from the centre towards the walls
-net pressure decreases along the length of capillary (it varies)
Plasma-colloid Osmotic Pressure
-pressure draws fluid towards plasma proteins
-mostly created by plasma proteins
-doesn’t vary from one end to the other like hydrostatic pressure
What is bulk flow dependent on?
-net hydrostatic pressure
-net colloid osmotic pressure
Plasma Proteins
-confined to plasma
-made by the liver
Hydrostatic and Colloid Osmotic Pressure of ISF
-so small that they don’t really matter
- ~0-1 mmHg
Net exchange pressure equation
NEP = outward - inward
Distribution of Pressure Along the Capillary
-inward pressure remains constant
-outward pressure decreases along the capillary length
Transition Point
-in the middle of the capillary
-equal pressure
Bulk Flow and BP
-if BP falls, fluid moves into the plasma
-if BP rises, fluid moves into interstitial space resulting in edema
Daily Blood Flow
-7200L/day
-20 L filtered
-17 L reabsorbed
-3 L to lymph vessels
Lymphatic System
-extensive network of one-way vessels
-route where fluid is returned from ISF to blood
Lymph
-ISF that enters a lymphatic vessel
Initial Lymphatics
-small
-blind ended
-terminal lymph vessels
-permeate almost every tissue of the body
Lymph Vessels
-formed from convergence of initial lymphatics
-eventually empty into venous system near where blood enters R atrium
One-way Valves
-spaced at intervals
-direct flow of lymph toward venous outlet in chest
Lymph Entrance
-overlapping endothelial cells
-pressure on the outside of the vessel pushes the free edge inward to allow fluid to enter
Edema
-can be blood or lymphatic vessels
-fluid gathers faster than it can be drained
-causes: reduced conc. of plasma proteins, increased permeability of capillary wall, increased venous pressure, blockage of lymph vessels
Histamine
-allows the gaps to increase and let fluid leave easier
Functions of the Lymphatic System
-return excess filtered fluid
-defence against disease
-transport reabsorbed fat
-return of filtered protein
Phagocytes
-lymph nodes have phagocytes which destroy bacteria filtered from ISF
Vein Size
-quite large
-house about 2/3 of the blood volume at one time
Venous System
-transports blood back to the heart
-where capillaries drain
Veins
-large radius
-little resistance to blood flow
-serve as a blood reservoir
Blood Reservoir
-blood doesn’t settle/remain static in veins
-the blood simply moves more slowly due to vasodilation
Venous Return and Cardiac Output
-increasing venous return will __ cardiac output
-decreasing venous return will __ cardiac output
Vein Composition
-walls are thinner than arteries
-walls appear collapsed in histological slides
-have little smooth muscle
-little elasticity (more collagen than elastin)
-highly distensible (able to expand)
Capacitance Vessels
-act as blood reservoirs
-change blood volume
Factors that Enhance Venous Return
-driving pressure from cardiac contraction
-sympathetically induced vasoconstriction
-skeletal muscle activity
-valves
-respiratory activity
-cardiac suction
Frank-Starling Law
-increased stretch will increase contraction force
How does skeletal muscle activity affect venous return?
-veins pass between skeletal muscles
-when muscles squeeze they reduce the vein radius and create a point of constriction (turkey baster)
-fluid tries to move in both directions, valves ensure there is no back flow
Blood Pressure Regulation
-monitored and regulated by body systems
-ensures adequate blood flow through capillaries
-requires an adequate pressure difference (not too little/too much)
Effects of Increased BP
-eye damage
-atherosclerosis
-kidney damage
-damage to vessels and tissues
Primary Determinants of BP
-cardiac output
-total peripheral resistance
Homeostatic Control System
-regulates BP
-detects changes and adjusts body mechanisms to maintain the ‘set point’
Baroreceptors
-arterial pressure sensors
-measure BP by detecting pressure change
-detect changes in artery stretch due to pressure
-located in carotid sinus and aortic arch
Baroreceptor Reflex
-sends info to the brain which decides on mechanisms of change
-increased BP: increases volume of action potentials
-decreased BP: decreases the volume of action potentials
Medulla
-recieves baroreceptor info
Effect of Parasympathetic NS on Heart Function
-vagus nerves release acetylcholine
-AcH binds to receptors to decrease heart rate
-doesn’t affect TPR
Effect of Parasympathetic Neurotransmitters
-bind to receptors that alter the rate of the SA and AV node
-does not alter contraction strength
Effect of Sympathetic NS on Heart Function
-thoracic spinal nerves release norepinephrine and epinephrine
-the NTs bind to B1 receptors and increase heart rate AND THE FORCE OF CONTRACTION
-regulates arteriolar (TPR) and venular (CO) diameter
Adrenoreceptors
-activate smooth muscle
-sympathetic NS
-more NE = constricted
-less NE = dilated
Parasympathetic Stimulation on MAP
-decreased heart rate
-decreased cardiac output
-decreases blood pressure
Sympathetic Stimulation on MAP (Heart Route)
-increased heart rate
-increased contraction strength (leads to increased stroke volume)
-both will increase cardiac output
-increases blood pressure
Sympathetic Stimulation on MAP (Arteriole Route)
-increased vasoconstriction
-increased TPR
-increases blood pressure
Sympathetic Stimulation on MAP (Vein Route)
-increased vasoconstriction
-increased venous return
-increased stroke volume
-increased cardiac output
-increases blood pressure
Extensive BP Deviation
-baroreceptors set a “set-point” blood pressure that is considered the landmark/normal
-if pressure is changed for an extensive period of time, more than a few days, this will become the new set point
Total Blood Volume
-a long term control of BP
-regulated by restoring water and salt balance
