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
100%
Lungs
Flow = DP/R
= MAP/resistance of system’s arterioles ………
………= 93
93 mmHg/Resistance in “systemic circuit”
Right side of heartLeft side of heart
Digestive
system
(Hepatic portal
system)
Liver
Kidneys
Skin
Brain
21%
6%
20%
9%
13%
Heart
muscle
3%
Skeletal
muscle
15%
Bone
Other
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, per
minute ? __%__ x 5 liters/min CO = ______ liters per min
Flow liter/minute = P/ Resistance
Flow liter/minute = 93mmHg/ Resistance Units
Resistance Units = Liters/min/93mmHg
5%
8%
In general, lower flow = increase resistance when pressure is constant
Fig. 10-1, p. 262
Systolic pressure
120
110
Mean pressure
100
Pressure (mm Hg)
90
80
Diastolic
pressure
70
60
50
40
30
20
10
0
Left
ventricle
Large
arteries
Arterioles Capillaries
Venules and veins
Fig. 10-8, p. 269
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
Smooth
muscle cells
(a) Scanning electron micrograph of an arteriole showing how
the smooth muscle cells run circularly around the vessel wall
Fig. 10-9a, p. 270
(b) Normal arteriolar tone due to smooth muscle
contraction activity with no outside factors
Fig. 10-9b, p. 270
Cross section
of arteriole at
normal arteriole
tone in a human
in homeostasis
MAP = 93mmHg
CO = 5 liter
TPR = 18.6 r.u.’s
(c) Vasoconstriction (increased contraction of circular
smooth muscle in the arteriolar wall, which leads to
increased resistance and decreased flow through the vessel)
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 additional
vasoconstriction:
Major causes of additional
vasoconstriction:
Extrinsic
A. 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
Intrinsic
Myogenic Mechanisms – stretch induced contraction
Fig. 10-9c, p. 270
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
(d) Vasodilation (decreased contraction of circular smooth
muscle in the arteriolar wall, which leads to decreased
resistance and increased flow through the vessel)
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)
Arteriolar radius
Fig. 10-11, p. 275
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
Red blood cell
Capillary
Fig. 10-12, p. 276
Capillaries
• Under resting conditions many capillaries are not open
• Capillaries surrounded by precapillary
sphincters
– 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
Blood flow rate
(liters/min)
5
3000
Blood flow is
slow through
capillary beds
as they have
large total
area
Total crosssectional area
(cm2)
4.0
Anatomical
distribution
200
Velocity of flow
(mm/sec)
0.3
Veins
Aorta Arteries
Arterioles Venules
Capillaries
Venae
cavae
Fig. 10-13, p. 276
Interstitial fluid
Endothelial cell
Water-filled pore
allows water movement
Plasma
Lipid-soluble
substances
pass through
the
endothelial
cells
Plasma
proteins
typical
O2, CO2
Plasma proteins
generally cannot
cross the capillary
wall
Plasma
membrane
Cytoplasm
Exchangeable
proteins
Na+, K+, glucose,
amino acids
Small
water-soluble
substances pass
through the pores
(b) Transport across a typical capillary wall
Exchangeable
proteins are
moved across
by vesicular
transport
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 “nonpenetrating”
(3) Create constant osmotic pressure that favors
movement of H2O from ISF into capillary
Capillary Exchange
= plasma protein
Reabsorption of fluid into capillary
Osmotic Pressure (fluid into capillary) constant
Overall
Filtration
venous end
from
capillary
Arterial end of capillary
Blood Pressure (fluid out of capillary) decreasing arterial to venous
Arterial End: Filtration of fluid out of capillary
Inward pressure =26
( πP + PIF)
25 + 1
Capillary Exchange
Overall
capillary = 11
out – 9 in
= 2 out to
interstitial fluid
Outward pressure =37
(PC + π IF)
37 + 0
All values are given in mm Hg.
Inward pressure = 26
( πP + PIF)
25 + 1
Outward pressure = 17
(PC + π IF)
17 + 0
Capillary Exchange
Out
Transition
point
0
26
Inward pressure
( πP + PIF)
17
Outward pressure
(PC + π IF)
Fluid movement
Capillary pressure (mm Hg)
37
In
Capillary length
End
Beginning
KEY
= Ultrafiltration
= Reabsorption
Fig. 10-18, p. 280
2 mmHg outward pressure
during capillary exchange forms
Lymph.
Lymph is a fluid which once
formed fills LYMPHATIC
CIRCULATION
Lymphatic Vessels collect lymph formed by net capillary
filtration of fluid into interstitial space
• 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
To venous
system
Arteriole
Tissue
cells
Interstitial
fluid
Plasma
filtered
Venule
Lymph
collected
Blood capillary
Initial
lymphatic
(a) Relationship between initial lymphatics and blood capillaries
Fig. 10-19a, p. 281
Fluid pressure on the outside of the vesselpushes the endothelial cell's free
edge inward, permitting entrance ofinterstitial fluid(now lymph).
Plasma
Filtered
From
Capillary
into
Interstitial
fluid
Becomes
Lymph
Overlapping
endothelial cells
Fluid pressure on the inside of the vessel
forces the overlapping edges together so
that lymph cannot escape.
(b) Arrangement of endothelial cells in an initial lymphatic
Systemic
circulation
Lymph node
Fig. 10-19b, p. 281
Pulmonary
circulation
Initial
lymphatics
Lymph vessel
Blood
capillaries
Valve
Arteries
Veins
Heart
Lymph
node
Initial
lymphatics
(a) Relationship of lymphatic system to circulatory system
Blood
capillaries
Fig. 10-20a, p. 282
Lymph
20 L /day
7200 L /day
3 L /day
17 L /day
Blood
(b) Comparison of blood flow and lymph flow per day
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