Ch. Eight: Vascular Physiology Flashcards
1
Q
Flow Rate
A
- blood through a vessel is directly proportional to the pressure gradient and inversely proportional to vascular resistance
- can be adjusted according to metabolic needs
- brain can least tolerate disrupted supply
2
Q
Reconditioning Organs
A
- receive more blood than needed for metabolic needs
ex. kidneys, digestive organs and skin - adjust extra blood to achieve homeostasis
3
Q
Resistance Depends on 3 Things
A
- blood viscosity: remains the same
- vessel length: does not change
- vessel radius: smaller the radius= less blood flow and more resistance
4
Q
Fluid Properties
A
- friction between molecules of flowing fluid
- greater the friction, greater the viscosity
- blood viscosity determined by number of RBC’s
5
Q
Vessel Properties
A
- longer the vessel, greater the resistance but remains constant in the body
- vessel radius is the major variable; smaller the vessel, greater the resistance
R is proportional to 1/r^4
6
Q
Relationship of Resistance and Flow
A
- doubling radius= decreases resistance x16 and increases flow by x16
7
Q
Arteries
A
- serve as rapid-transit passageways for blood from the heart to organs
- due to large radius, arteries offer little resistance to blood flow - act as pressure reservoir to provide driving force for blood when heart is relaxing
- arterial connective tissue contains collagen and elastin fibres
8
Q
Blood Pressure
A
- force exerted by blood against a vessel wall
- depends on volume of blood contained within vessel and compliance of vessel walls
9
Q
Pressure Reservoir
A
- expand and contract as blood is ejected by heart
- allows blood flow to be continuous
- compliance= V/P
- higher the compliance of a structure, the more easily it can be stretched
- elastic recoil (not as compliant as veins)
10
Q
Systolic and Diastolic Pressure
A
- peak pressure exerted by ejected blood (~120mm Hg)
- minimum pressure in arteries when blood is draining off into vessels downstream (~80mm Hg)
- mean pressure: 93mm Hg
11
Q
Measuring Blood Pressure
A
- measured indirectly by using sphygomomanometer
- Korotkoff sounds: heard when determining blood pressure and are distinct from heart sounds associated with valve closure
12
Q
Pulse Pressure
A
- pressure difference between systolic and diastolic pressure
ex. bp is 120/80, pulse pressure is 40 mm Hg - pulse that can be felt in artery lying close to surface of skin is due to pulse pressure
13
Q
Mean Arterial Pressure
A
- average pressure driving blood forward into tissues throughout cardiac cycle
- formula for approximating mean arterial pressure: map= diastolic+ 1/3 pulse pressure
ex. 120/80, mean pressure= 80+1/3(40)= 93mm Hg - spend more time in diastolic
14
Q
Muscular Arteries
A
- deliver blood to specific organs (mesenteric and renal artery)
- proportionally thick muscular media (smooth muscle); very active in vasoconstriction
- can play a large role in the regulation of blood pressure
ex. mesenteric artery caries 25% of the CO, so alterations in its diameter would have a large effect
15
Q
Muscular Arteries: Radius Adjustment
A
radius supplying individual organs can be adjusted independently to:
- distribute cardiac output among systemic organs, depending on body’s momentary needs
- if they contract, blood flow is diverted away from their tissues
- if they dilate, then blood flow to the tissue increases - help regulate arterial blood pressure
16
Q
Arterioles
A
- major resistance vessels
- radius supplying individual organs can be adjusted independently to:
1. distribute cardiac output among systemic organs depending on body’s momentary needs
2. help regulate arterial blood pressure - mechanisms involved in adjusting arteriolar resistance: vasoconstriction and vasodilation
17
Q
Vasoconstriction (Arterioles) Caused By…
A
- increase in: myogenic activity, oxygen, endothelin, and sympathetic stimulation (except in brain) and NE, alpha receptors
- decrease in carbon dioxide and other metabolites
- vasopression; anglotensin II
- cold
18
Q
Vasodilation Caused By…
A
- decrease in myogenic activity, oxygen, and sympathetic stimulation
- increase in carbon dioxide and nitric acid (causes relaxation)
- histamine release
- heat
19
Q
Pressures Throughout Systemic Circulation
A
- arterioles have high resistance
- capillaries then are non-pulsatile
20
Q
Vascular Tone
A
- smooth muscle displays a state of partial constriction
- 2 factors: myogenic activity of smooth muscle and sympathetic fibres continually release NE
21
Q
Arterioles
A
- only blood supply to brain remains constant; myogenic activity
- changes within other organs; alter radius to vessels to adjust blood flow to organ
22
Q
Arterioles Local Effect
A
- local chemical influences on radius: local metabolic changes and histamine release
- local physical influences on radius: local application of heat or cold, chemical response to shear stress, and myogenic response to stretch
23
Q
Cardiac Output at Rest and During Moderate Exercise
A
- increase in skeletal muscle (15%-64%) and skin (9%-14%), and heart
- decrease digestive tract, bone, and kidneys
24
Q
Intrinsic and Extrinsic Factors in Vaso-const./dilation
A
- local environment; oxygen, carbon dioxide, sympathetic stimulation
- neuronal inputs
25
Active Hyperemia
- increase in metabolic activity increase local blood flow
- increase in metabolic activity and decrease in oxygen
- increase in metabolites in organ interstitial fluid
- causes dilation and increase blood flow
26
Local chemical factors the produce relaxation
- decreased O2
- increases CO2, acid, K+, osmolarity
- Adenosine release
- prostaglandin release
27
Local Vasoactive Mediators: Endothelial Cells
- release chemical mediators that play key role in locally regulating arteriolar caliber
- release locally acting chemical messenger in response to chemical changes in their environment
- among best studied local vasoactive mediators is nitric oxide
28
Extrinsic Control
- accomplished primarily by sympathetic nerve influence
- cause constriction
- some by hormones
29
Extrinsic Sympathetic Control of Radius
- influence of total peripheral resistance
- NE influence on smooth muscle
- local controls overriding sympathetic vasoconstriction
- NO parasympathetic innervation
30
Total Peripheral Resistance (TPR)
Mean Arterial Pressure= Cardiac output x TPR
(delta) P= F x R
* sympathetic nervous system influences TPR
31
How does SNS control TPR
- cardiovascular control centre: medulla of brain stem, and integrating centre for blood pressure regulation
- hormone that influence radius:
- SNS stimulation of adrenal medulla (NE and E)
- vasopression (control fluid balance)
32
Capillaries
- smallest blood vessels
- thin-walled, small-radius, extensively brached
- sites of exchange between blood and surrounding tissue cells
- max surface area and min. diffusion distance
- velocity of blood flow through is relatively slow (non-pulsatile)
- provides adequate exchange time
33
2 Types of Passive Exchanges
- diffusion:
| - bulk flow:
34
3 Types of Capillaries
1. Continuous:
- skin, muscle; have tight junctions
2. Fenestrated:
- more permeable; intestines, hormone producing tissues, kidneys
3. Sinusoidal:
- incomplete basement membrane; liver, bone marrow, lymphoid tissues
35
Capillaries (substances that pass)
- narrow, water-filled gaps (pores) lie at junctions between cells; permits passage of water-soluble substances, and size of pores varies from organ to organ
- lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer barrier
- proteins by vesicular transport; not plasma proteins
36
Capillary Bed
- many capillaries are not open
- capillaries surrounded by precapillary sphincters
- contraction of sphincters reduces blood flowing into capillaries in an organ; relaxation of sphincters has opposite effect
- metarteriole; runs between an arteriole and a venule
37
Passive DIffusion
- down concentration gradients of material between blood and interstitial fluid
- except plasma proteins
38
Bulk Flow
- movement of fluid from blood to interstitial fluid and back again:
- via water-filled pores, ultrafiltration (out of capillaries), and reabsorption
- functions to distribute ECF not metabolite exchange
39
Bulk Flow (influence of Starling Forces)
- capillary blood (hydrostatic) pressure= hydrostatic pressure
- plasma-colloid osmotic pressure
- interstitial fluid hydrostatic pressure
- interstitial fluid-colloid osmotic pressure
40
Bulk Flow (dependent on difference between)
- net hydrostatic pressure:
is the force exerted by the fluid pressing against a wall = capillary blood pressure
- net colloid osmotic pressure
41
Bulk Flow (Hydrostatic Pressure)
- forces fluid out (filtration):
| - especially on the arterial end where pressure is higher
42
Colloid Osmotic Pressure
- force that opposes the hydrostatic pressure
- created by large nondiffusible molecules (plasma proteins)
- does not vary from one end of the capillaries to the other; unlike hydrostatic force
43
Net flitration and Net Reabsorption Along the Vessel Length
- outward pressure is higher= ultrafiltration
- inward pressure (colloid osmotic) remains constant
- outward pressure (hydrostatic) decreases along the vessel= reabsorption
* lack of plasma proteins= swelling
44
Role of Bulk Flow
- important in regulating the distribution of ECF between the plasma and the interstitial fluid
- keeps plasma volume constant; ensure that the circulatory system functions effectively
- fluid exchange (not for solute exchange)
- if BP falls, fluid moves into plasma
- if BP rises (high blood pressure), fluid moves into interstitial space (edema)
45
Lymphatic System
- extensive network of one-way vessels
- provides accessory route by which fluid can be returned from interstitial to the blood
- initial lymphatics:
- small, blind-ended terminal lymph vessels
- permeate almost every tissue of the body
46
Lymph and Lymph Vessels
- interstitial fluid that enters a lymphatic vessel
lymph vessels:
- formed from convergence of initial lymphatics
- eventually empty into venous system near where blood enters right atrium
- one way valves spaced at interval direct flow of lymph toward venous outlet in chest
47
Lymphatic Systems Functions
- return of excess filtered fluid= lymph
- defense against disease; lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid
- transport of absorbed fat
- return of filtered protein
48
Edema
- swelling of tissues: occurs when too much interstitial fluid accumulates
- causes of edema:
- reduced concentration of plasma proteins
- increased permeability of capillary wall
- increased venous pressure
- blockage of lymph vessels
49
Veins
- venous system transports blood back to heart
- capillaries drain into venules
- venules converge to form small veins that exit organs
- smaller veins merge to form larger vessels
- veins have large radius offers little resistance to blood flow and serve as blood reservoir
50
Venous Circulation
- completes circulatory system
| - slowed down, low pressure
51
Vein Anatomy
- walls are thinner than arteries and appear collapsed in histological slides
- little smooth muscle, little elasticity; more collagen than elastin
- veins are highly distensible; capacitance vessels that act as blood reservoirs
52
Factors which Enhance Venous Return
- driving pressure from cardiac contraction (~15mmHg)
- sympathetically induced venous vasoconstriction
- skeletal muscle activity
- effect of venous valves
- respiratory activity
- effect of cardiac suction
53
Regulation of Blood Pressure
- ensure adequate blood flow through capillaries
- requires adequate pressure difference; not too little (lack of supply to brain- fainting) or too much
- blood pressure is monitored and regulated in the body
- primary determinants: cardiac output x total peripheral resistance = mean arterial pressure
54
Pressure, Flow, and Resistance
- P= is the force exerted (MAP)
- F= volume moved and it is measured in L/min (CO; stroke volume)
- R= how difficult it is for blood to flow between two points at any given pressure difference; resistance is the measure of the friction that impedes flow (TPR- arterial pressure)
55
Mechanisms of Blood Pressure
- arterial pressure sensors; baroreceptors (constantly monitors arterial blood pressure)
- carotid sinus baroreceptor
- aortic arch baroreceptor
- baroreceptor reflex
56
Baroreceptors
- number of action potential increases when MAP increases
- number of action potential decreases when MAP decreases
- consider a fall in BP, body responds by increasing CO or TPR through vasocontriction, sympathetic stimulation
57
Sympathetic NS on Blood Vessels
- sympathetic drive regulates arteriolar (TPR) and venular diameter (CO)
- activation of alpha1-adrenoceptors = constriction of arterioles (more SNS)
58
Baroreceptor Reflex
short-term control adjustments:
- occur within seconds
- adjustments made by alterations in cardiac output and TPR
- mediated by autonomic nervous system influences on heart, veins, and arterioles
- rapid response to return blood pressure to normal (set-point)
- if pressure deviated for more than a few days- new set-point
59
Long-term Regulation of Arterial BP
- baroreceptors adapt to long term changes in BP
- Barorecptors cannot set long-term arterial pressure
- Blood Volume is a major determinant:
- via venous side of circulation, influences stroke volume, therefore CO, and renin-angiotensin system
- requires minutes to days
- involves adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst
- blood volume:
via venous side of circulation and influenced stroke volume and CO
- renin-angiotensin system
60
Blood Pressure Abnormalities
Hypertension: blood pressure above 140/90mmHg
- two broad classes: primary and secondary hypertension
hypotensoin: blood pressure below 100/60mmHg
61
Hypertension
- complication of hypertension:
| - congestive heart failure, stroke, heart attack, spontaneous hemorrhage, renal failure, retinal damage
62
Hypotension
- occurs when there is too little blood to fill the vessels and heart is too weak to drive the blood
- orthostatic (postural) hypotension: transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position
63
Circulatory Shock
- occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained
- four main types:
- hypovolemic "low volume" shock
- cardiogenic "heart produced" shock
- vasogenic "vessel produced" shock
- neurogenic "nerve produced" shock
64
Skeletal Muscle Pump
- enhances venous return
- squeeze on veins
- counteracts the effects of gravity
65
Venous Valves
- permit the flow of blood only toward the heart
