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
Permeability of Blood Vessels ?
External
Environment
H 2O
Glucose
Lipids
Amino acids
Vitamines
Minerals
O2
Blood vessel
Tissue cells
Arteries
Veins
permeable to
Capillaries
H 2O
Glucose
Lipids
Amino acids
Vitamines
Minerals
O2,
18%
12%
veins
54%
Distribution of Blood
(at rest)
arteries
11%
capillaries
5%
Circulatory pathways
4) Arterial anastomoses
coronary
100
0
vein
capillary
mmHg
artery
1) Simplest pathway
Liver
intestines
2) Portal system
skin
3) Arteriovenous anastomosis
20
20
40
Brain
40
Coronary
100
0
mmHg
Skeletal muscles
20
40
20
Liver-Intestine
20
Skin
40
40
The blood flows
along pressure
gradient.
Brain
Coronary
Skeletal muscles
Liver-Intestine
Skin
Can blood vessel
volume change
quickly ?
hemorrhage
before
after
20%
Brain
Brain
Coronary
Coronary
100
98
mmHg
mmHg
#1: Functions
help maintain
of blood
bloodvessels?
pressure
Skeletal muscles
Liver-Intestine
Skeletal muscles
Liver-Intestine
Skin
Skin
 Total BVV
 Individual BVV
before
Vascular Shock
after
Brain
Brain
Coronary
Coronary
100
Skeletal muscles
Liver-Intestine
Skin
50
mmHg
Skeletal muscles
Liver-Intestine
Skin
 Total BVV
mmHg
Exercise
before
Brain
Brain
Coronary
Coronary
100
Liver-Intestine
100
mmHg
Skeletal muscles
Skin
after
Skeletal muscles
Liver-Intestine
Skin
 Total BVV
 Individual BVV
mmHg
Dinner
before
Brain
Brain
Coronary
Coronary
100
Skeletal muscles
Liver-Intestine
Skin
after
100
mmHg
Skeletal muscles
Liver-Intestine
Skin
 Total BVV
 Individual BVV
mmHg
Hypothermia
before
after
Brain
Brain
Coronary
Coronary
100
100
mmHg
#2:
Functions
help redistribute
of blood vessels?
blood
Skeletal muscles
Skeletal muscles
Liver-Intestine
Skin
Liver-Intestine
Skin
 Total BVV
 Individual BVV
mmHg
muscle
autonomic nerves
hormones
autoregulation
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
20
40
20
40
Is the blood flow
100 mmHg
continuous or
intermittent ?
0
both
20
40
20
40
20
40
Intermittent flow
120 mm Hg
systole
heart
end of
diastole
(refilled)
heart
40 mm Hg
aorta
change intermittent
flow into
Function
of large arteries?
continuous
flow
75 mm Hg
40 mm Hg
heart
aorta
120 mm Hg
systole
40 mm Hg
aorta
100 mm Hg
early
diastole
continuous flow
heart
aorta
40 mm Hg
hose
120 mm Hg
systole
heart
aorta
75 mm Hg
end of
diastole
(refilled)
heart
40 mm Hg
40 mm Hg
aorta
Predict the change in Ps and Pp in atherosclerosis
systolic
pressure
(Ps)
diastolic
Pressure
(Pd)
pulse pressure
(Pp)
- is the average pressure over the cardiac cycle
- MAP = Pd + 1/3 (Ps – Pd)
- MAP = 80 + 1/3 (110 – 80) = 90 (mmHg)
systolic
pressure
(Ps)
110 mmHg
80 mmHgdiastolic
Pressure
(Pd)
Mean arterial pressure (MAP)
The pressure pulse disappears in capillaries.
Pulse
Points
Measure 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
F
 P = P1 - P2
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
heart
Total vascular bed
40 mm Hg
Factors on Peripheral Resistance
1) blood viscosity ()
- A measure of thickness of the blood
RBCs
-   resistance
- stable (short-term)
Plasma lipids
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
2x
  r4
16x F =
8L
Poiseuile’s law
2x
  r4
16x F =
8L
Poiseuile’s law
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
Capillary Wall
Permeable to:
O2, CO2
ions
H2O
glucose
amino acids
fatty acids
vitamins
hormones
Impermeable to:
proteins
blood cells
Routes of the cross-wall movement
1) intercellular cleft
Basement
membrane
2) fenestration
more important
in specific regions like
liver, bone marrow, and
lymphoid organs
3) endothelial cells
driving force for the movement?
Mechanisms of Capillary Exchange
1) simple diffusion:
Particles move along their own concentration gradient.
regulated by:
- concentration gradient
- permeability of capillary
walls
O2
CO2
Mechanisms of Capillary Exchange
1) simple diffusion
2) filtration/reabsorption (difficult stuff!)
Filtration
-- fluid movement from
plasma to interstitium
(outward)
Reabsorption
-- fluid movement from
interstitium back to
plasma (inward)
determined by:
- hydrostatic pressures
- colloid osmotic pressures
filtration
reabsorption
capillary hydrostatic pressure (BP)
- favor filtration
- decreases from arterial end to venous end
Capillary
BP
Interstitial fluid hydrostatic pressure
- favor filtration in loose connective tissues
- favor reabsorption in encapsulated organs (brain, kidneys)
Interstitial
hydrostatic
pressure
Capillary
BP
Plasma colloid osmotic (oncotic) pressure (p)
- favor reabsorption
What does colloid mean ?
Plasma colloid
osmotic pressure
Interstitial
hydrostatic
pressure
Capillary BP
solution
particle size
colloid
suspension
< 1 nm
1-100 nm
> 100 nm
NaCl
Plasma
Whole blood
Whole
stand blood
still
Plasma
After
NaCl
centrifugation
Plasma colloid osmotic pressure
How do plasma proteins generate
- is generated by large molecules like proteins that
colloid osmotic
pressure
are impermeable
to capillary
wall. ?
gm/dL
p (mmHg)
Albumin
4.5
21.8
globulins
2.5
6.0
Plasma
protein
fibrinogen
0.3
0.2
Total
7.3
28.0
Plasma colloid
osmotic pressure
Review of Osmosis and Osmotic Pressure
A
100% H2O
B
100% H2O
A
B
100% H2O
< 100% H2O
Osmosis
A
B
100% H2O
< 100% H2O
Balance between hydrostatic pressure and
osmotic pressure is reached.
A
B
hydrostatic
pressure
osmotic pressure
100% H2O
< 100% H2O
Principle-1
differential membrane permeability
A
B
osmotic pressure
100% H2O
< 100% H2O
Principle-1
differential membrane permeability
A
% H2 O
B
% H 2O
Principle-1
differential membrane permeability
A
% H2 O
B
% H 2O
Principle-2
determined by the number of particles
A
B
osmotic pressure
100% H2O
< 100% H2O
Question 1
Can electrolytes generate osmotic pressure
across capillary wall?
A
B
capillary wall
Interstitial
fluid
100% H2O
plasma
< 100% H2O
plasma
proteins
Question 2
Can blood cells generate osmotic pressure
across capillary wall?
A
B
capillary wall
Interstitial
fluid
100% H2O
plasma
< 100% H2O
plasma
proteins
Question 3
Does plasma osmotic pressure favor
filtration or reabsorption?
A
B
capillary wall
Interstitial
fluid
100% H2O
plasma
< 100% H2O
plasma
proteins
salts
interstitial fluid
proteins
Water Concentration = 90%
salts
Blood
Water Concentration = 70%
proteins
cell
4) Interstitial oncotic pressure
- favor filtration,
- generated by proteins leaked out of capillary .
Interstitial
oncotic pressure
Interstitial
hydrostatic
pressure
Plasma colloid
osmotic pressure
Capillary BP
SUMMARY
What is the difference between
diffusion and filtration/reabsorption ?
plasma
interstitium
diffusion
Filtration
Mechanisms of Capillary Exchange
1) simple diffusion
2) filtration/reabsorption (difficult stuff!)
3) transcytosis
transcytosis
transcytosis
Large molecules such as peptide hormones and other
proteins, have to be transported across endothelial cells
via endocytosis/exocytosis.
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
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.
Characteristics of Venous Blood Flow
- Venous valves prevent
backflow of venous blood.
- assisted by respiration
and skeletal muscle
contraction.
Incompetent venous valves cause
hemorrhoids & varicose veins.
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
Maintaining Blood Pressure
20
40
20
40
Essential !
100 mmHg
0
The regulated targets:
20
40
1) The heart
20
40
20
40
2) Blood vessel wall
3) Precapillary sphincters
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
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
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.
3) Vasopressin (antidiuretic hormone)
- is released from
posterior pituitary
when blood volume
decreases or
osmolarity increases,
- causes
vasoconstriction via V1
receptor.
anterior pituitary
posterior pituitary
Vasopressin
4) Atrial Natriuretic peptide (factor)
- is released from atria when blood
volume increases,
- caused vasodilation and
natriuresis/diuresis.
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
- 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
SUMMARY
Mechanisms of Vascular Control
1) Neural Control
2) Hormonal Control
3) Autoregulation (Local Control)
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
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
(CO2, pH, adenosine, and K+),
- proportional to local neuronal activities.
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,
endocardium
• pressure gradient
from endocardium to
epicardium,
• decreased blood flow
in systole,
• highly efficient uptake
of oxygen (70/100).
epicardium
LV
RV
Features of Coronary Circulation
• rich in arterial
anastomosis to secure
blood supply.
endocardium
epicardium
LV
RV
Features of Coronary Circulation (continued)
• regulated primarily by local metabolic products such
as adenosine, K+, H+, and CO2.
ATP
ADP
AMP
adenosine
adenosine
Coronary
arterioles
Blockade of coronary artery causes myocardial
infarction, or heart attack.
endocardium
epicardium
LV
RV
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.
O2
Constriction of
pulmonary vasculature
Dilation of
systemic vasculature
Ventilation-Perfusion Ratio
Bronchial vasculature
Distribution
from bronchial
arteries
Function:
Provide oxygenated
blood to bronchial
tree.
Cutaneous Circulation
Skin
warm
hot
SSkin vessels under
emotional control
Head
Neck
Shoulders
upper chest
SKELETAL MUSCLE
CIRCULATION
• low flow at rest,
• Local factors dominate
during exercise.
Blood Distribution at Rest
Blood Distribution during Exercise
Regulation during Exercise
1. The neural control
2. Control by local factors
The neural control
1) from motor cortex
2) from
proprioceptors
- initiates the following
changes:
 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.
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