Blood Vessels
• Arteries – rapid distribution, pressure reservoir
• Arterioles – RESISTANCE VESSELS
• Capillaries
• Venules
• Veins
Pulse Pressure
• Pressure difference between systolic and diastolic pressure
• Example
– If blood pressure is 120/80, pulse pressure is 40 mm Hg (120mm Hg –80mm Hg)
• Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure
• Pulse pressure reflects the amount of blood entering aorta and the rapidity that it runs off into the vessels of the peripheral circulation
– Increase systolic
1. Bigger stroke volume into a set of large distribution arteries = : (
2. Same stroke volume into a smaller, less elastic, calcified distribution arteries = : {
– Increased diastolic
1. Harder run off due to smaller or constricted arterial field
– Isometric skeletal muscle contraction = normal
– Calcified, non elastic arteries vessels = not normal
Mean Arterial Pressure
• Average pressure driving blood forward into tissues throughout cardiac cycle
• Formula for approximating mean arterial pressure:
Mean arterial pressure =
diastolic pressure + ⅓ pulse pressure
At 120/80, mean arterial pressure =
80 mm Hg + ⅓ (40 mm Hg) = 93 mm Hg
During Rest, heart spends 2/3 time in disatole
1/3 time in systole, with pressure decreasing towards diastolic pressure
Fig. 10-1, p. 262
21%
100% Lungs
Left side of heartRight side of heart
Digestive system
(Hepatic portal system)
Liver
Kidneys
Skin
Brain
Heart muscle
Skeletal muscle
Bone
Other8%
5%
15%
3%
9%
13%
20%
6%
Flow = DP/R
= MAP/resistance of system’s arterioles ………………= 9393 mmHg/Resistance in “systemic circuit”
What is resting cardiac output ? 5 liters
What % of resting cardiac output goes to regional circuit? __
What is actual liters of blood flow to any regional circuit, perminute ? __%__ x 5 liters/min CO = ______ liters per min
Flow liter/minute = P/ Resistance
Flow liter/minute = 93mmHg/ Resistance Units
Resistance Units = Liters/min/93mmHg
In general, lower flow = increase resistance when pressure is constant
Fig. 10-8, p. 269
Pre
ssu
re (
mm
Hg
)
Systolic pressure
Diastolicpressure
Mean pressure
Leftventricle
Largearteries
Arterioles Capillaries Venules and veins
120
110
100
90
80
70
60
50
40
30
20
10
0
Blood Vessels
• Arteries – rapid distribution, pressure reservoir
• Arterioles – RESISTANCE VESSELS• Capillaries
• Venules
• Veins
Arterioles• Major resistance vessels of vascular tree
– 500,000 arterioles dictate flow to 10 billion capillaries– Typically can alter radius from 0 units to 4 units, thereby altering
resistance and flow by 44 or 256 times
• Regulate the distribution of systemic cardiac output among systemic organ “regional” circulations
– For most regions of systemic circulation local metabolic rate dictates flow requirements
• Increase metabolic rate, increase oxygen requirement, increase blood flow
– For skin, whole body temperature regulation– For kidney, overall fluid and electrolyte balance
• Maintain Mean Arterial Pressure at homeostatic set point– MAP = CO x TsPR
Arterioles • Altering arteriole radius alters arteriolar resistance and thereby flow through downstream capillaries
– Normal, innate, inherent diameter of arteriole exists when no extrinsic factor is altering natural contractile activity of smooth muscle in arterial wall
– Factors that alter smooth muscle contractile activity are numerous
(a) Scanning electron micrograph of an arteriole showing howthe smooth muscle cells run circularly around the vessel wall
Smoothmuscle cells
Fig. 10-9a, p. 270
(b) Normal arteriolar tone due to smooth musclecontraction activity with no outside factors
Fig. 10-9b, p. 270
(c) Vasoconstriction (increased contraction of circularsmooth muscle in the arteriolar wall, which leads toincreased resistance and decreased flow through the vessel)
Fig. 10-9c, p. 270
Cross sectionof arteriole atnormal arterioletone in a humanin homeostasisMAP = 93mmHgCO = 5 literTPR = 18.6 r.u.’s
Major causes of additionalvasoconstriction:
Fig. 10-9c, p. 270
(c) Vasoconstriction: when a person is a normal rest, most systemic arterioles are somewhat vasoconstricted and blood is distributed as in figure 10-1
Major causes of additionalvasoconstriction:
ExtrinsicA. An increase in the normal resting
amount of:1. Norepinephrine from
sympathetic postganglionic efferent neurons or from adrenal medulla
2. Epinephrine from adrenal medulla
3. Arginine Vasopressin (ADH) from posterior pituitary
4. Angiotensin II from Angiotensin I from Renin
IntrinsicMyogenic Mechanisms – stretch
induced contraction
(d) Vasodilation (decreased contraction of circular smoothmuscle in the arteriolar wall, which leads to decreasedresistance and increased flow through the vessel)
Major causes:Local control: O2 and other local chemical changes indicative of increased metabolic rate
ACTIVE HYPEREMIA results from metabolically induced increase in local metabolites (locally active chemical messengers)
Extrinsic control:LESS NE, E, AVP, ANGIO II
IF COMPLETELY REMOVE THESE CIRCULATORY SHOCK OCCURS
Fig. 10-9d, p. 270
Arterioles
• Local vasoactive mediators
– Endothelial cells
•Release chemical mediators that play key role in locally regulating arteriolar caliber
•Release locally acting chemical messengers in response to chemical changes in their environment
•Among best studied local vasoactive mediators is nitric oxide (NO)
Fig. 10-11, p. 275
Arteriolar radius
Blood Vessels
• Arteries – rapid distribution, pressure reservoir
• Arterioles – resistance vessels
• Capillaries – EXCHANGE VESSELS
• Venules
• Veins
Capillaries• Thin‐walled, small‐radius, extensively branched
• Sites of exchange between blood and surrounding tissue cells
– Maximized surface area and minimized diffusion distance
– Velocity of blood flow through capillaries is relatively slow
• Provides adequate exchange time
– 2 types of passive exchanges: Diffusion, bulk flow
Capillaries • Narrow, water‐filled gaps (pores) lie at junctions between cells
• Permit passage of water‐soluble substances
• Lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer barrier
• Size of pores in capillary walls varies from organ to organ
CapillaryRed blood cell
Fig. 10-12, p. 276
Capillaries• Under resting conditions many capillaries are not open
• Capillaries surrounded by precapillarysphincters
– Contraction of sphincters reduces blood flowing into capillaries in an organ
– Relaxation of sphincters increases blood flow
• Metarteriole
– Runs between an arteriole and a venule
– Bypasses capillaries
Fig. 10-13, p. 276
Velocity of flow(mm/sec)
Anatomicaldistribution
Total cross-sectional area (cm2)
Blood flow rate(liters/min)
Aorta Venaecavae
VeinsVenules
CapillariesArterioles
Arteries
200
0.3
4.0
3000
5
Blood flow is slow through capillary beds as they have
large total area
Na+, K+, glucose,amino acids
Lipid-solublesubstancespass throughtheendothelialcells
Plasma proteinsgenerally cannotcross the capillarywall
Exchangeableproteins aremoved acrossby vesiculartransport
(b) Transport across a typical capillary wall
Water-filled poreallows water movement
Plasma
Smallwater-solublesubstances passthrough the pores
Plasmamembrane
Cytoplasm
Endothelial cellInterstitial fluid
Exchangeableproteins
Plasmaproteins
O2, CO2
typical
Fig. 10-15b, p. 278
Independent exchange of individual solutes down their own concentration gradients across the capillary wall.
Capillary Exchange
• Osmotic Pressure favors fluid movement into capillaries along entire length of capillary
– Due to presence of plasma proteins that(1) Exist in high concentration inside capillary
(2) Cannot “diffuse” to equilibrium, so are “non-penetrating”
(3) Create constant osmotic pressure that favors movement of H2O from ISF into capillary
Osmotic Pressure (fluid into capillary) constant
Blood Pressure (fluid out of capillary) decreasing arterial to venous
Reabsorption of fluid into capillary
Arterial End: Filtration of fluid out of capillary
Arterial end of capillary venous end
= plasma protein
Overall Overall Filtration Filtration
from from capillarycapillary
Capillary ExchangeCapillary Exchange
Inward pressure( πP + PIF)
25 + 1
Outward pressure(PC + π IF)
37 + 0
Inward pressure = 26( πP + PIF)
25 + 1
Outward pressure = 17(PC + π IF)
17 + 0
=26
=37
Overall Overall capillary = 11 capillary = 11
out out –– 9 in9 in= 2 out to = 2 out to
interstitial fluidinterstitial fluid
All values are given in mm Hg.
Capillary ExchangeCapillary Exchange
Fig. 10-18, p. 280
Transitionpoint
Inward pressure( πP + PIF)
Capillary lengthBeginning
Outward pressure(PC + π IF)
In
0
Out
End
37
26
17
Flu
id m
ove
men
t
Cap
illar
y p
ress
ure
(m
m H
g)
KEY
= Ultrafiltration = Reabsorption
Capillary ExchangeCapillary Exchange
2 mmHg outward pressure during capillary exchange forms
Lymph.
Lymph is a fluid which once formed fills LYMPHATIC
CIRCULATION
• 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
• Lymph– 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 intervals direct flow of lymph toward venous outlet in chest
Lymphatic Vessels collect lymph formed by net capillary filtration of fluid into interstitial space
(a) Relationship between initial lymphatics and blood capillaries
To venoussystem
Interstitialfluid
Arteriole
Tissuecells
Venule
Blood capillary
Initiallymphatic
Fig. 10-19a, p. 281
Plasmafiltered
Lymphcollected
Overlappingendothelial cells
(b) Arrangement of endothelial cells in an initial lymphatic
Fluid pressure on the outside of the vesselpushes the endothelial cell's free edge inward, permitting entrance ofinterstitial fluid(now lymph).
Fluid pressure on the inside of the vesselforces the overlapping edges together sothat lymph cannot escape.
BecomesLymph
Fig. 10-19b, p. 281
PlasmaFilteredFrom
Capillaryinto
Interstitialfluid
HeartVeins
Valve
Lymphnode
Bloodcapillaries
Initiallymphatics
Pulmonarycirculation
Lymph node
Lymph vessel
Systemiccirculation
Initiallymphatics
Arteries
(a) Relationship of lymphatic system to circulatory system
Bloodcapillaries
Fig. 10-20a, p. 282
(b) Comparison of blood flow and lymph flow per day
17 L /day
20 L /day 3 L /day
7200 L /day
Lymph
Blood
Fig. 10-20b, p. 282
Lymphatic System
• Functions
– Return of excess filtered fluid
– Defense against disease
• Lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid
– Transport of absorbed fat
– Return of filtered protein
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