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THE BLOOD VESSELS
(vascular system)
CONTENT
1) Overview of Vascular System
2) Arterial Pressures and Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the Vascular System
6) Special Circulations
H2OGlucoseLipidsAmino acidsVitaminesMineralsO2
Blood vessel
External Environment
Permeability of Blood Vessels ?
Tissue cells
permeable to
H2OGlucoseLipidsAmino acidsVitaminesMineralsO2,
ArteriesVeins
Capillaries
veins54%
capillaries 5%
arteries 11%12%
18%Distribution of Blood
(at rest)Distribution of Blood
(at rest)
1) Simplest pathway
Circulatory pathwaysCirculatory pathways
artery
100 mmHg0
vein capillary
2) Portal systemLiver intestines
coronary
4) Arterial anastomoses
3) Arteriovenous anastomosis
skin
Skeletal muscles
Skin
Brain
Liver-Intestine
Coronary
The blood flows along pressure gradient.
100 mmHg
40
40
40
40
40
20
20
20
20
20
0
Can blood vessel volume change quickly ?
Can blood vessel volume change quickly ?
Skeletal muscles
Skin
Brain
Liver-Intestine
Coronary
hemorrhagehemorrhage afterbefore
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
100 mmHg
Total BVV Individual BVV Total BVV Individual BVV
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
98 mmHg
20%
Functions of blood vessels? Functions of blood vessels?
#1: help maintain blood pressure #1: help maintain blood pressure
before Vascular ShockVascular Shock after
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
Total BVV Total BVV
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
100 mmHg 50 mmHg
before Exercise Exercise after
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
Total BVV Individual BVV Total BVV Individual BVV
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
100 mmHg 100 mmHg
before Dinner Dinner after
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
Total BVV Individual BVV Total BVV Individual BVV
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
100 mmHg 100 mmHg
before Hypothermia Hypothermia after
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
Total BVV Individual BVV Total BVV Individual BVV
Skin
Liver-Intestine
Skeletal muscles
Coronary
Brain
100 mmHg 100 mmHg
Functions of blood vessels? Functions of blood vessels? #2: help redistribute blood #2: help redistribute blood
autonomic nerves
muscle
hormonesautoregulation
precapillary sphincters
1) Overview Of Vascular
System
2) Arterial Pressures
and Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the
Vascular System
6) Special Circulations
100 mmHg
40
40
40
40
40
0
20
20
20
20
20
Is the blood flow
continuous or intermittent ?
both
systole
120 mm Hg40 mm Hg
Intermittent flow continuous flow
heart aorta
earlydiastole
100 mm Hg40 mm Hg
heart aorta
75 mm Hg 40 mm Hgend ofdiastole(refilled)
heart aorta
systole
120 mm Hg40 mm Hg
heart aorta
Function of large arteries?
Function of large arteries?
change intermittent flow into continuous flow
change intermittent flow into continuous flow
hose
systole
120 mm Hg
75 mm Hg
40 mm Hg
40 mm Hgend ofdiastole(refilled)
heart
heart
aorta
aorta
systolic pressure (Ps)
diastolic Pressure (Pd)
pulse pressure (Pp)
Predict the change in Ps and Pp in atherosclerosisPredict the change in Ps and Pp in atherosclerosis
- is the average pressure over the cardiac cycle
- MAP = Pd + 1/3 (Ps – Pd)
Mean arterial pressure (MAP)
systolic pressure (Ps)
diastolic Pressure (Pd)
110 mmHg
80 mmHg
- MAP = 80 + 1/3 (110 – 80) = 90 (mmHg)
The pressure pulse disappears in capillaries.The pressure pulse disappears in capillaries.
Pulse Points
Measure arterial pressures using sphygmomanometerMeasure arterial pressures using sphygmomanometer
BLOOD FLOW Definition: volume of blood moving through a blood vessel in a given time (ml/min)
F = P
R
P1 P2
P = P1 - P2F
Peripheral Resistance
- opposition to blood flow due to friction between the blood and the blood vessel wall and among components of the blood
heart
120 mm Hg40 mm Hg
Total vascular bed
Factors on Peripheral Resistance
1) blood viscosity ()
- A measure of thickness of the blood
RBCs Plasma lipids
- resistance
- stable (short-term)
Factors on Peripheral Resistance
1) blood viscosity ()
2) blood vessel length
- length resistance
- stable
Factors on Peripheral Resistance
1) blood viscosity () - stable (short-term)
2) blood vessel length
- stable
3) blood vessel radius
- radius resistance
- change quickly under physiological control
Poiseuile’s law
r4
8LF =
2x
16x
Poiseuile’s law
r4
8LF =
2x
16x
1) Overview Of Vascular
System
2) Arterial Pressures
and Flow
3) Capillary Blood Flow
and Exchange
4) Venous Blood Flow
5) Regulation of the
Vascular System
6) Special Circulations
Capillary Blood Flow
is gated by precapillary sphincters
- blood shunt
- open alternatively
Permeable to:
O2, CO2
ions H2O
glucose amino acids fatty acids vitamins hormones Impermeable to:
proteins
blood cells
Capillary Wall
Routes of the cross-wall movement
1) intercellular cleft
2) fenestration
more important in specific regions like liver, bone marrow, and
lymphoid organs
3) endothelial cells
driving force for the movement?
Basementmembrane
Mechanisms of Capillary Exchange
1) simple diffusion:
regulated by:
- concentration gradient
- permeability of capillary
walls
Particles move along their own concentration gradient.
O2O2
CO2CO2
Mechanisms of Capillary Exchange
1) simple diffusion
2) filtration/reabsorption (difficult stuff!)
filtrationfiltration
reabsorptionreabsorption
-- fluid movement from plasma to interstitium (outward)
Filtration
Reabsorption
-- fluid movement from interstitium back to plasma (inward)
determined by: - hydrostatic pressures- colloid osmotic pressures
CapillaryBPCapillaryBP
capillary hydrostatic pressure (BP)
- favor filtration
- decreases from arterial end to venous end
CapillaryBPCapillaryBP
Interstitial hydrostatic pressure
Interstitial hydrostatic pressure
Interstitial fluid hydrostatic pressure
- favor filtration in loose connective tissues
- favor reabsorption in encapsulated organs (brain, kidneys)
Plasma colloid osmotic (oncotic) pressure (p)
- favor reabsorption
Capillary BPCapillary BPInterstitial hydrostatic pressure
Interstitial hydrostatic pressure
Plasma colloid osmotic pressurePlasma colloid osmotic pressure
What does colloid mean ?
solution colloid suspension
particle size < 1 nm 1-100 nm > 100 nm
stand still
Aftercentrifugation
Whole blood
Plasma
NaCl
Whole bloodPlasmaNaCl
Plasma colloid osmotic pressurePlasma colloid osmotic pressure
Plasma colloid osmotic pressure
- is generated by large molecules like proteins that are impermeable to capillary wall.
Plasma protein
gm/dL p (mmHg)
Albumin 4.5 21.8
globulins 2.5 6.0
fibrinogen 0.3 0.2
Total 7.3 28.0
How do plasma proteins generate
colloid osmotic pressure ?
Review of Osmosis and Osmotic Pressure
A B
100% H2O 100% H2O
A B
100% H2O < 100% H2O
100% H2O < 100% H2O
A B
Osmosis
100% H2O < 100% H2O
A B
hydrostatic pressure
osmotic pressure
Balance between hydrostatic pressure and osmotic pressure is reached.
100% H2O < 100% H2O
A B
osmotic pressure
Principle-1
differential membrane permeability
A B
Principle-1
differential membrane permeability
% H2O % H2O
% H2O % H2O
A B
Principle-1
differential membrane permeability
100% H2O < 100% H2O
A B
osmotic pressure
Principle-2
determined by the number of particles
100% H2O < 100% H2O
A Bcapillary wall
plasmaproteins
plasmaInterstitialfluid
Question 1 Can electrolytes generate osmotic pressure across capillary wall?
100% H2O < 100% H2O
A Bcapillary wall
plasmaproteins
plasmaInterstitialfluid
Question 2 Can blood cells generate osmotic pressure across capillary wall?
100% H2O < 100% H2O
A Bcapillary wall
plasmaproteins
plasmaInterstitialfluid
Question 3 Does plasma osmotic pressure favor filtration or reabsorption?
salts
proteinsWater Concentration = 70%
Water Concentration = 90%
interstitial fluid
Blood
salts
proteins
cell
Capillary BPCapillary BPInterstitial hydrostatic pressure
Interstitial hydrostatic pressure
Plasma colloid osmotic pressurePlasma colloid osmotic pressure
Interstitial oncotic pressureInterstitial oncotic pressure
4) Interstitial oncotic pressure
- favor filtration,- generated by proteins leaked out of capillary .
SUMMARY
What is the difference between diffusion and filtration/reabsorption ?
plasma
Filtration
interstitium
diffusion
Mechanisms of Capillary Exchange
1) simple diffusion
2) filtration/reabsorption (difficult stuff!)
3) transcytosis
transcytosistranscytosis
Large molecules such as peptide hormones and other proteins, have to be transported across endothelial cells via endocytosis/exocytosis.
transcytosis
1) Overview Of Vascular System
2) Arterial Pressures And Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the Vascular System
6) Special Circulations
BLOOD VESSELS
VEINS
- thinner walls but larger lumens, - able to constrict,- act as blood reservoirs,
contain ~60% of body’s blood, thus, called capacitance vessels.
- travel in parallel with arteries,- located more superficially.
- Venous valves prevent backflow of venous blood.
- assisted by respiration and skeletal muscle contraction.
Characteristics of Venous Blood Flow
Incompetent venous valves cause hemorrhoids & varicose veins.Incompetent venous valves cause hemorrhoids & varicose veins.
1) Overview Of Vascular System
2) Arterial Pressures And Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the Vascular System
6) Special Circulations
BLOOD VESSELS
Maintaining Blood Pressure
100 mmHg
40
40
40
40
40
0
20
20
20
20
20
The regulated targets:
1) The heart
2) Blood vessel wall
3) Precapillary sphincters
Essential !
Mechanisms of Vascular Control
1) Neural Control
2) Hormonal Control
3) Autoregulation (Local Control)
a. Control by sympathetic nervous system
- innervates arteries and arterioles in almost all organs,
- releases norepinephrine (NE) as neurotransmitter,
- causes vasoconstriction (except in the heart and brain).
b. Control by parasympathetic nervous system
- innervates some arteries and arterioles,
- releases acetylcholine (Ach) as neurotransmitter,
- causes dilation of arteries and arterioles.
Neural Reflexes
1) Baroreceptor-Initiated Reflexes
2) Chemoreceptor-Initiated Reflexes
1) Baroreceptor-Initiated Reflexes The reflexes sense variation of MAP, and try to bring MAP back to normal immediately.
When MAP increases
Stretch of baroreceptors to a greater extend
Cardiovascular centers
Autonomic nerves
heart rate and cardiac contractility, and peripheral vasodilatation
Drop of MAP
When MAP drops
Stretch of baroreceptors to a lesser extend
Cardiovascular centers
Autonomic nerves
Increase in heart rate and cardiac contractility, and peripheral vasoconstriction
Elevation of MAP
chemoreceptor
2) Chemoreceptor-Initiated Reflexes - The reflexes sense variation of O2, CO2, and pH of the blood, and try to bring them back to normal immediately.
- The reflexes serve the primary purpose of regulating respiration, with side effects on blood vessels.
Hormonal Control of Blood Vessels 1) Epinephrine and Norepinephrine
2) Angiotensin II
3) Vasopressin = antidiuretic hormone (ADH)
4) Atrial Natriuretic peptide
Hormonal Control of Blood Vessels 1) Epinephrine and Norepinephrine
- secreted from adrenal gland,
- cause peripheral vasoconstriction via alpha adrenergic receptors.
(Note: low dose epinephrine can cause vasodilation in a few organs via beta-2 adrenergic receptors)
2) Angiotensin II
- is converted from blood borne angiotensinogen under the regulation of renin which is produced in kidney.
- is released from posterior pituitary when blood volume decreases or osmolarity increases,
- causes vasoconstriction via V1 receptor.
3) Vasopressin (antidiuretic hormone)
Vasopressin
posterior pituitary
anterior pituitary
- is released from atria when blood volume increases,
- caused vasodilation and natriuresis/diuresis.
4) Atrial Natriuretic peptide (factor)
Local Control of Blood Flow – Autoregulation
100 mmHg- Autoregulation is the
automatic adjustment of
blood flow to each tissue
in proportion to its
requirements at any given
instant.
- Changes in blood flow through individual organs are controlled intrinsically by modifying the diameter of local arterioles feeding the capillaries.
- two mechanisms: metabolic and myogenic
METABOLIC (chemical) CONTROLS - Declining levels of oxygen and accumulation of metabolic waste products (CO2, low pH, and inflammatory chemicals) cause increased blood flow to the local area by vasodilation of arterioles and relaxation of precapillary sphincters.
Local chemicals involved in autoregulation
hypoxia,
adenosine,
H+, lactic acid,
CO2 ,
K+.
All of the above causes vasodilation.
Myogenic Controls
Smooth muscles in the walls of arterioles respond to STRETCH due to changes in blood pressure and blood low to prevent large fluctuations in local blood flow.
a. Increased stretch causes vasoconstriction.
b. Decreased stretch causes vasodilation.
c. The overall result is constant perfusion.
d. possibly via stretch-regulated Ca channels.
Constant flow
Mechanisms of Vascular Control
1) Neural Control
2) Hormonal Control
3) Autoregulation (Local Control)
SUMMARY
1) Overview Of Vascular System
2) Arterial Pressures And Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the Vascular System
6) Special Circulations
BLOOD VESSELS
Cerebral Circulation
1)
2)
Sources of arterial blood flow to the brain
1)
2)
Drain to jugular vein and vertebral vein
Susceptibility to ischemia
- seconds: loss of consciousness
- minutes: irreversible injury
Regulation
- constant (60 -160 mmHg),
- due to strong autoregulation
- proportional to local neuronal activities.
(CO2, pH, adenosine, and K+),
Coronary Circulation
Can cardiac muscles get nutrients from the blood in heart chambers?
The cardiac muscles get nutrients from coronary circulation.
Anterior view Posterior view
Features of Coronary Circulation
• ~ 225 ml/min (4-5% CO) at resting state,
RV
LVepicardium
endocardium
• decreased blood flow in systole,
• pressure gradient from endocardium to epicardium,
• highly efficient uptake of oxygen (70/100).
Features of Coronary Circulation
• rich in arterial anastomosis to secure blood supply.
RV
LVepicardium
endocardium
Features of Coronary Circulation (continued)
• regulated primarily by local metabolic products such as adenosine, K+, H+, and CO2.
ATPADPAMP
adenosine adenosine
Coronary arterioles
Blockade of coronary artery causes myocardial infarction, or heart attack.
RV
LVepicardium
endocardium
Pulmonary Circulation
Two vascular beds:
1) pulmonary vasculature from pulmonary A
to alveoli
2) bronchial vasculature from aorta
to bronchial tree
Pulmonary Vasculature
- Distribution: to alveoli
- Function :
Characteristics
- low resistance/pressure,
- 500-700 SF,
- affected by gravity.
systemic vasculaturepulmonary vasculatureConstriction of Dilation of
O2
Ventilation-Perfusion Ratio
Bronchial vasculature
Function:
Distribution
Provide oxygenated blood to bronchial tree.
from bronchial arteries
Cutaneous Circulation
Skin
warm hot
SSkin vessels under emotional control
HeadNeckShouldersupper chest
SKELETAL MUSCLE CIRCULATION
• Local factors dominate
during exercise.
• low flow at rest,
Blood Distribution at Rest
Blood Distribution during Exercise
Regulation during Exercise
1. The neural control
2. Control by local factors
1) from motor cortex 2) from proprioceptors
- initiates the following changes:
The neural control
cardiac output,
unstressed volume (venous blood),
venous return.
Venous return is assisted by muscular activity and respiration.
Vasoconstriction in
Skin,
Intestines,
kidneys, and
inactive muscles.
2) Control by local factors
- lactate, K+, and adenosine,
- vasodilation only in the active skeletal muscle,
- The number of perfused capillaries is increased.
1) Overview of Vascular System
2) Arterial Pressures and Flow
3) Capillary Exchange
4) Venous Blood Flow
5) Regulation of the Vascular System
6) Special Circulations
SUMMARY OF BLOOD VESSELS
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