Transcript Cardiovascular system: Blood vessels, blood flow, blood

Cardiovascular system: Blood
vessels, blood flow, blood pressure
Outline
• 1- Physical laws governing blood flow and blood
pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes
Vascular system possesses different mechanisms for promoting continuous flow of
blood to the capillaries:
Elastic recoil
smooth m. regulation of diameter
valves
Muscular arteries
Substances causing contraction in vascular smooth muscle
Chemical
Physiologic role
Source
Type
NE (a )
Baroreceptor reflex
Sympathetic neurons
Neural
Endothelin
Paracrine
Vascular endothelium
Local
Serotonin
Platelet aggregation, smooth
muscle contraction
Neurons, digestive
tract, platelets
Local, neural
Substance P
Pain, increased capillary
permeability
Neurons, digestive
tract
Local, neural
Vasopressin
Increase blood pressure during
hemorrhage
Posterior pituitary
Hormonal
Plasma hormone
Hormonal
endothelium
local
Angiotensin II Increase blood pressure
Prostacyclin
Minimize blood loss from
damaged vessels before
coagulation
Substances that mediate vascular smooth muscle relaxation
Chemical
Physiologic role
Source
Type
Nitric oxide
Paracrine mediator
Endothelium
Local
Atrial natriuretic
peptide
Reduce blood pressure
Atrial myocardium,
brain
Hormonal
Vasoactive intestinal
peptide
Digestive secretion, relax
smooth muscle
Neurons
Neural, hormonal
Histamine
Increase blood flow
Mast cells
Local, systemic
Epinephrine (b2)
Enhance local blood flow
to skeletal muscle, heart,
liver
Adrenal medulla
Hormonal
Acetylcholine
(muscarinic)
Erection of clitoris, penis
Parasympathetic
neurons
neural
Bradykinin
Increase blood flow via
nitric oxide
Multiple tissues
Local
Adenosine
Enhance blood flow to
match metabolism
Hypoxic cells
local
Even though there are many mechanisms for altering the radius of the vascular
system, pressure still drops as blood moves further away from the heart. Why?
Resistance = tendency of the vascular system to oppose flow; Flow1=
R
• Influenced by: length of the tube (L), radius of the tube (r), and viscosity of the blood (h)
Poiseuille’s Law
R = Lh/r
4
• In a normal human, length of the system is fixed, so blood viscosity (5x that of water) and
radius of the blood vessels have the largest effects on resistance
Factors promoting total peripheral resistance
(TPR)
• Total peripheral
resistance = TPR
-- combined resistance of
all vessels
-- vasodilation 
resistance decreases
-- vasoconstriction 
resistance increases
Physical laws governing blood flow and blood
pressure
• Flow of blood through out
body = pressure gradient
within vessels X
resistance to flow
- Pressure gradient: aortic
pressure – central venous
pressure
- Resistance:
-- vessel radius
-- vessel length
-- blood viscosity
All four tubes have the same driving pressure. Which tube has the greatest
flow? The least flow? Why?
Biggest has
least friction
from blood
against vessel
walls!
Outline
• 1- Physical laws governing blood flow and blood
pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes
Vasculature
Structure of vasculature changes in response to different needs
Arteries and blood pressure
• Arterial walls are able to
expand and recoil
because of the pressure
of elastic fibers in the
arterial wall
• Systolic pressure:
maximum pressure
occurring during systole,
ventricles contracting
• Diastolic pressure:
pressure during diastole,
ventricles filling
Even with a decrease in overall pressure, the pressure in the vessels is not
constant. The pressure in the vessels mirrors the pressures generated in the
heart – systolic and diastolic pressures. Systolic = ventricles contracting
Diastolic = ventricles filling
Normal
blood
pressure =
120/80
High blood
pressure =
140/90
Figure 14.8
Outline
• 1- Physical laws governing blood flow and blood
pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes
Capillaries
• Allow exchange of gases,
nutrients and wastes between
blood and tissues
• Overall large surface area and
low blood flow
• Two main types:
- continuous capillaries:
narrow space between cells 
permeable to small or lipid
soluble molecules
- fenestrated capillaries:
large pores between cells
large molecules can pass
Local control of blood flow in capillaries
• Presence of precapillary
sphincters on the arteriole
and beginning of
capillaries
• Metarteriole: no sphincter
 continuous blood flow
 controls the amount of
blood going to
neighboring vessels
Movement of materials across capillary walls
• Small molecules and lipid
soluble molecules move
by diffusion through the
cell membrane
• Larger molecules,
charged molecules must
pass through membrane
channels, exocytosis or in
between 2 cells
• Water movement is
controlled by the capillary
hydrostatic and osmotic
pressures
Outline
• 1- Physical laws governing blood flow and blood
pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes
Veins
•
Veins are blood volume reservoir
•
Due to thinness of vessel wall  less resistance to stretch = more compliance
Factors influencing venous return
• 1- Skeletal muscle pump
and valves

• 2- Respiratory pump
• 3- Blood volume
• 4- Venomotor tone
Outline
• 1- Physical laws governing blood flow and blood
pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes
Mean arterial pressure and its
regulation
• Regulation of blood flow in arteries
- Intrinsic control
- Extrinsic control
-- Neural control
-- Hormonal control
* Control of blood vessel radius
* Control of blood volume
Mean arterial pressure and its
regulation
• Regulation of blood flow in arteries
- Intrinsic control
- Extrinsic control
-- Neural control
-- Hormonal control
* Control of blood vessel radius
* Control of blood volume
Regulation of blood flow in arteries
• It is important to adjust blood flow to
organ needs  Flow of blood to particular
organ can be regulated by varying
resistance to flow (or blood vessel
diameter)
• Vasoconstriction of blood vessel smooth
muscle is controlled both by the ANS and
at the local level.
• Four factors control arterial flow at the
organ level:
- change in metabolic activity
- changes in blood flow
- stretch of arterial smooth muscle
- local chemical messengers
Intrinsic control of local arterial blood flow
• Change in metabolic
activity
– Usually linked to CO2 and
O2 levels (↑ CO2 
vasodilation ↑ blood flow)
intrinsic control
• Changes in blood flow
- decreased blood flow 
increased metabolic wastes 
vasodilation
• Stretch of arterial wall =
myogenic response
- Stretch of arterial wall due to
increased pressure  reflex
constriction
• Locally secreted
chemicals can promote
vasoconstriction or most
commonly vasodilation
- inflammatory chemicals,
(nitric oxide, CO2)
Mean arterial pressure and its
regulation
• Regulation of blood flow in arteries
- Intrinsic control
- Extrinsic control
-- Neural control
-- Hormonal control
* Control of blood vessel radius
* Control of blood volume
Extrinsic control of blood pressure
• Two ways to control BP:
- Neural control
- Hormonal control
** Use negative feedback
Neural control of BP - 1
• Baroreceptors: carotid
and aortic sinuses
sense the blood
pressure in the aortic
arch and internal
carotid  send signal
to the vasomotor
center in the medulla
oblongata
• Other information are
sent from the
hypothalamus, cortex
• 
Neural control of BP - 2
• The vasomotor center
integrates all these information
• The vasomotor sends decision
to the ANS center:
- Both parasympathetic and
sympathetic innervate the S/A
node  can accelerate or slow
down the heart rate
- The sympathetic NS
innervates the myocardium
and the smooth muscle of the
arteries and veins  promotes
vasoconstriction
Hormonal control of BP
• Hormones can control blood
vessel radius and blood
volume, stroke volume and
heart rate
• On a normal basis, blood
vessel radius and blood
volume are the main factors
• If there is a critical loss of
pressure, then the effects on
HR and SV will be noticeable
(due to epinephrine kicking in)
• Control of blood vessel radius
- Epinephrine
- Angiotensin II
- Vasopressin (?)
• Control of blood volume
- Anti-diuretic hormone
(vasopressin)
- Aldosterone
• Control of heart rate and stroke
volume
- Epinephrine
Control of blood volume
• Anti-diuretic hormone =
ADH
-
-
Secreted by the posterior
pituitary in response to ↑blood
osmolarity (often due to
dehydration)
Promote water reabsorption by
the kidney tubules  H2O
moves back into the blood 
less urine formed
Control of blood volume
• Aldosterone:
-
-
Secretion by the adrenal cortex
triggered by angiotensin II
Promotes sodium reabsorption
by the kidney tubules (Na+
moves back into the blood)
H2O follows by osmosis
Whereas ADH promotes H2O
reabsorption only (in response
to dehydration), aldosterone
promotes reabsorption of both
H2O and salt (in response to ↓
BP)