THE BLOOD VESSELS

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THE BLOOD VESSELS
Blood Vessels
(vascular system)
Are they simple pipelines?
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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

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 Permeability of Blood Vessels ?
External Environment
H2O Glucose Lipids Amino acids Vitamines Minerals
O2
Tissue cells
Blood vessel
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Is blood vessel wall permeable everywhere?
Arteries
Veins
Capillaries
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Distribution of Blood (at rest)
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Circulatory pathways
1) Simplest pathway
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40
20
Brain
40
20
Coronary
The blood flows along pressure gradient.
100 mmHg
0
Skeletal muscles
40
20
Liver-Intestine
40
20
Skin
40
20
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Can blood vessel volume change quickly ?
Brain
Coronary
Skeletal muscles
Liver-Intestine
Skin
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hemorrhage
after
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Functions of blood vessels?

1 help maintain blood pressure

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Vascular Shock
before
after
Brain
Coronary
100 mmHg
50 mmHg
Skeletal muscles
Liver-Intestine
Skin
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Exercise
before
after
Brain
Coronary
100 mmHg
100 mmHg
Skeletal muscles
Liver-Intestine
Skin
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Dinner
before
after
Brain
Coronary
100 mmHg
100 mmHg
Skeletal muscles
Liver-Intestine
Skin
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Hypothermia
before
after
Brain
Coronary
100 mmHg
100 mmHg
Functions of blood vessels?

2 help redistribute blood

Skeletal muscles
Liver-Intestine
Skin
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How to change blood vessel volume ?
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How to change blood vessel volume ?
precapillary sphincters
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Anatomy of blood vessels are studied in the lab.
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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

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40
20
40
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Is the blood flow continuous or
intermittent ?
100 mmHg
0
40
20
40
20
40
20
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Intermittent flow
continuous flow
120 mm Hg
40 mm Hg
systole
heart
aorta
Function of large arteries?

change intermittent flow into
continuous flow
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hose
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Predict the change in Ps and Pp in atherosclerosis
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• - is the average pressure over the cardiac cycle
• MAP Pd 1/3 (Ps Pd)

Mean arterial pressure
(MAP)
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The pressure pulse disappears in capillaries.
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Pulse Points
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Measure arterial pressures using sphygmomanometer
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BLOOD FLOW   Definition volume of blood moving
through a blood vessel in a given time (ml/min)
? P
F
R
P2
P1
F
? P P1 - P2
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Peripheral Resistance - opposition to blood
flow due to friction between the blood and the
blood vessel wall and among components of the
blood
120 mm Hg
40 mm Hg
heart
Total vascular bed
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Factors on Peripheral Resistance 1) blood
viscosity (?)
2) blood vessel length - ? length ?
?resistance - stable
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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
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Arterial Blood Flow is primarily controlled by
changing arterial diameters.
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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

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Capillary Blood Flow
is gated by precapillary sphincters - blood
shunt - open alternatively
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Capillary Wall
Permeable to O2, CO2 ions H2O
glucose amino acids fatty acids
vitamins hormones
Impermeable to proteins blood cells
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Routes of the cross-wall movement
Basement membrane
driving force for the movement?
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Mechanisms of Capillary Exchange 1) simple
diffusion
Particles move along their own concentration
gradient.
regulated by - concentration gradient -
permeability of capillary walls
O2
CO2
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Mechanisms of Capillary Exchange 1) simple
diffusion
2) filtration/reabsorption (difficult stuff!)
filtration
determined by - hydrostatic pressures -
colloid osmotic pressures
reabsorption
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capillary hydrostatic pressure (BP) - favor
filtration - decreases from arterial end to
venous end  
Capillary BP
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• Interstitial fluid hydrostatic pressure
• - favor filtration in loose connective tissues
• - favor reabsorption in encapsulated organs
  (brain, kidneys) 

Capillary BP
Interstitial hydrostatic pressure
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Plasma colloid osmotic (oncotic) pressure
(?p) - favor reabsorption  
What does colloid mean ?
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Plasma colloid osmotic pressure - is generated
by large molecules like proteins that are
impermeable to capillary wall.
Plasma colloid osmotic pressure
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Review of Osmosis and Osmotic Pressure
A
B
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A
B
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Osmosis
A
B
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Balance between hydrostatic pressure and osmotic
pressure is reached.
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Principle-1 differential membrane
permeability
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Principle-1 differential membrane
permeability
A
B
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Principle-1 differential membrane
permeability
A
B
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Principle-2 determined by the number of
particles
A
B
osmotic pressure
100 H2O
lt 100 H2O
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Question 1 Can electrolytes generate
osmotic pressure across capillary wall?
A
B
capillary wall
plasma proteins
Interstitial fluid
plasma
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Question 2 Can blood cells generate
osmotic pressure across capillary wall?
A
B
capillary wall
plasma proteins
Interstitial fluid
plasma
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Question 3 Does plasma osmotic pressure
favor filtration or reabsorption?
A
B
capillary wall
plasma proteins
Interstitial fluid
plasma
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salts proteins
interstitial fluid
Water Concentration 90
salts proteins
Blood
Water Concentration 70
cell
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4) Interstitial oncotic pressure - favor
filtration, - generated by proteins leaked out
of capillary . 
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What is the difference between diffusion and
filtration/reabsorption ?
plasma
interstitium
Filtration
diffusion
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Mechanisms of Capillary Exchange 1) simple
diffusion
2) filtration/reabsorption (difficult stuff!)
3) transcytosis
transcytosis
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transcytosis
Large molecules such as peptide hormones and
other proteins, have to be transported across
endothelial cells via endocytosis/exocytosis.
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BLOOD VESSELS

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

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• VEINS
• thinner walls but larger lumens,
• able to constrict,
• act as blood reservoirs,

contain 60 of bodys blood, thus, called
capacitance vessels.

• travel in parallel with arteries,
• located more superficially.

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Characteristics of Venous Blood Flow
- Venous valves prevent backflow of venous
blood. - assisted by respiration and skeletal
muscle contraction.
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Incompetent venous valves cause hemorrhoids
varicose veins.
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BLOOD VESSELS

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

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Maintaining Blood Pressure
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40
20
40
20
Essential !
100 mmHg
0

• The regulated targets
• The heart
• Blood vessel wall
• Precapillary sphincters

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20
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• Mechanisms of Vascular Control
• Neural Control
• Hormonal Control
• Autoregulation
• (Local Control)

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• 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).
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b. Control by parasympathetic nervous system
- innervates some arteries and arterioles, -
releases acetylcholine (Ach) as
neurotransmitter, - causes dilation of arteries
and arterioles.
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• Neural Reflexes
• Baroreceptor-Initiated Reflexes
• Chemoreceptor-Initiated Reflexes

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1) Baroreceptor-Initiated Reflexes   The reflexes
sense variation of MAP, and try to bring MAP back
to normal immediately.    
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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
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When MAP drops ? Stretch of baroreceptors to a
lesser extend ? Cardiovascular centers ? Autonomic
nerves ? Increase in heart rate and cardiac
contractility, and peripheral vasoconstriction ? E
levation of MAP
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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.
chemoreceptor
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Hormonal Control of Blood Vessels   1)
Epinephrine and Norepinephrine 2) Angiotensin
II 3) Vasopressin antidiuretic hormone
(ADH) 4) Atrial Natriuretic peptide
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• 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)

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2) Angiotensin II - is converted from blood
borne angiotensinogen under the regulation of
renin which is produced in kidney.
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3) Vasopressin (antidiuretic hormone)

• is released from posterior pituitary when blood
  volume decreases or osmolarity increases,
• - causes vasoconstriction via V1 receptor.
•  

posterior pituitary
anterior pituitary
Vasopressin
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4) Atrial Natriuretic peptide (factor)

• is released from atria when blood volume
  increases,
• - caused vasodilation and natriuresis/diuresis.

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Local Control of Blood Flow Autoregulation
- Autoregulation is the automatic adjustment of
blood flow to each tissue in proportion to its
requirements at any given instant.
100 mmHg
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• - 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

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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.
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Local chemicals involved in autoregulation
hypoxia, adenosine, H, lactic acid, CO2
, K. All of the above causes vasodilation.
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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.
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• Increased stretch causes vasoconstriction.
• b. Decreased stretch causes vasodilation.
• The overall result is constant perfusion.
• possibly via stretch-regulated Ca channels.

Constant flow
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SUMMARY

• Mechanisms of Vascular Control
• Neural Control
• Hormonal Control
• Autoregulation (Local Control)

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BLOOD VESSELS

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

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Cerebral Circulation
 
1)
2)
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Sources of arterial blood flow to the brain
1)
2)
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Drain to jugular vein and vertebral vein
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Susceptibility to ischemia
- seconds loss of consciousness
- minutes irreversible injury
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Regulation
- constant (60 -160 mmHg),
- due to strong autoregulation
(CO2, pH, adenosine, and K),
- proportional to local neuronal activities.
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Coronary Circulation
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Features of Coronary Circulation

• 225 ml/min (4-5 CO) at resting state,

• pressure gradient from endocardium to
  epicardium,

• decreased blood flow in systole,

• highly efficient uptake of oxygen (70/100).

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Features of Coronary Circulation

• rich in arterial anastomosis to secure blood
  supply.

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Features of Coronary Circulation (continued)

• regulated primarily by local metabolic products
  such as adenosine, K, H, and CO2.

Coronary arterioles
ATP ADP AMP adenosine
adenosine
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Pulmonary Circulation
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Two vascular beds 1) pulmonary vasculature
from pulmonary A to alveoli 2) bronchial
vasculature from aorta to bronchial
tree
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• Pulmonary Vasculature
• Distribution to alveoli
• Function

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• Characteristics
• low resistance/pressure,
• 500-700 SF,
• affected by gravity.

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Opposite Responses to Hypoxia
?O2
Constriction of
Dilation of
systemic vasculature
pulmonary vasculature
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Ventilation-Perfusion Ratio
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Bronchial vasculature
Distribution
from bronchial arteries
Function
Provide oxygenated blood to bronchial tree.
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Cutaneous Circulation
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SSkin vessels under emotional control Head Neck
Shoulders upper chest
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SKELETAL MUSCLE CIRCULATION
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• low flow at rest,

• Local factors dominate during exercise.

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Blood Distribution at Rest
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Blood Distribution during Exercise
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• Regulation during Exercise
• The neural control
• Control by local factors

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The neural control

• from motor cortex

2) from proprioceptors
- initiates the following changes
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• ? cardiac output,
• ? unstressed volume (venous blood),
• ? venous return.

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Venous return is assisted by muscular activity
and respiration.
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Vasoconstriction in Skin, Intestines, kidneys,
and inactive muscles.
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• 2) Control by local factors
• lactate, K, and adenosine,
• vasodilation only in the active skeletal muscle,
• The number of perfused capillaries is increased.

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SUMMARY OF BLOOD VESSELS

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