Physiology Lecture 59
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow
• Control
– Acute control
• Vasodilation/vasoconstriction of
arterioles, metarterioles, and
precapillary sphincters
• Very rapid
– Long-term control
• Increase/decrease in size and number of
blood vessels
• Slow
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Figure: Diagram of a tissue
unit area for explanation of
acute local feedback control
of blood flow, showing a
metarteriole passing through
the tissue and a sidearm
capillary with its precapillary
sphincter for controlling
capillary blood flow.
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Effect of Tissue Metabolism
– Increased metabolism increases blood flow
• Oxygen Availability
– Decreased 02 availability increases flow
• Acute increase in arterial pressure
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Figure: Effect of increasing
rate of metabolism on tissue
blood flow
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Figure: Effect of decreasing
arterial oxygen saturation on
blood flow through an
isolated dog leg
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Effect of different
levels of arterial
pressure on blood
flow through muscle.
Solid red curve shows
effect if arterial
pressure raised over
a period of a few
minutes. Dashed
green curve shows
arterial pressure is
raised extremely
slowly (many weeks)
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Effect of Tissue Metabolism
• Oxygen Availability
• Acute increase in arterial pressure
– Immediate rise in blood flow. But, within
less than a minute, blood flow returns
almost to the normal level, even though
the arterial pressure is elevated
(autoregulation of blood flow)
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Effect of Tissue Metabolism
• Oxygen Availability
• Acute increase in arterial pressure
– Autoregulation of blood flow
• The metabolic theory
– High arterial pressure causing excess flow
provides too much O2 and nutrients. These
constricts blood vessels and flow returns
nearly to normal despite raised pressure
• The myogenic theory
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Effect of Tissue Metabolism
• Oxygen Availability
• Acute increase in arterial pressure
– Autoregulation of blood flow
• The metabolic theory
• The myogenic theory
– High arterial pressure stretches vessel wall,
causing reactive vascular constriction that
reduces blood flow nearly back to normal
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Special Consideration
– Kidneys
• Tubuloglomerular feedback
– Feedback signals from macula densa cause
constriction of afferent arterioles. Reducing
renal blood flow and glomerular filtration rate
back to or near to normal
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• Special Consideration
– Brain
• In addition to tissue O2; CO2 and H+
concentrations are very Important
– Dilates cerebral vessels
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
Relationship between
arterial Pco2 and cerebral
blood flow
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Acute Control
• EDRF
– Endothelium-Derived Relaxing Factor
• Mainly Nitric Oxide (NO)
– Increases Blood Flow in upstream arteries
– Released from endothelial cells lining the
arterioles and small arteries
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Long Term Control
• Change in "Tissue Vascularity"
– Occurs during
–Growth
–Scar tissue
–Cancerous tissue
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Long Term Control
• Change in "Tissue Vascularity"
– Growth Factors (Angiogenic Factors)
• Vascular Endothelial Growth Factor (VEGF)
• Fibroblast growth factor
• Angiogenin
Certain substances have opposite effect
on small blood vessels, ex: Some steroid
hormones
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood
Flow
• Collateral
Circulation
Fig: Translumbar
aortography in acute
occlusion of the infrarenal
aorta. The intercostal
arteries (arrows) serve as
major collaterals
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Local Blood Flow: Long Term Control
• Collateral Circulation
– When an artery or a vein is blocked, a new
vascular channel usually develops around
the blockage and allows at least partial blood
supply
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Norepinephrine (NE) and Epinephrine (E)
– Angiotensin II
– Vasopressin
– Endothelin
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Norepinephrine (NE) and Epinephrine (E)
• NE powerful vasoconstrictor hormone
• E is less powerful, in some tissues even
causes mild vasodilation
– E vasodilates coronary arteries during
increased heart activity
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Norepinephrine (NE) and Epinephrine (E)
• Sympathetic stimulation
– To nerve endings in individual tissues
release NE, which excites the heart and
contracts veins and arterioles
– To adrenal medullae secrete both NE and E
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Angiotensin II
• Powerful vasoconstrictor
– Constrict powerfully the small arterioles
• Increase total peripheral resistance,
– Increases the arterial pressure (Regulates
BP)
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Vasopressin
• a.k.a. Antidiuretic hormone (ADH)
• More powerful than angiotensin II as a
vasoconstrictor
• Formed in nerve cells in hypothalamus
of the brain
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasoconstrictor Agents
– Endothelin
• Powerful Vasoconstrictor in Damaged
Blood Vessels
– Usual stimulus for release is damage to the
endothelium
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasodilator Agents
– Bradykinin
– Histamine
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasodilator Agents
– Bradykinin
• Causes both powerful arteriolar dilation
and increased capillary permeability
• Powerful vasodilator
– Once formed persists for only few minutes
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasodilator Agents
– Bradykinin
• Plays special role in
– Inflammation
– Regulate blood flow in
» Skin
» Salivary glands
» Gastrointestinal glands
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasodilator Agents
– Histamine
• Released in essentially every tissue of
the body
– Damaged tissue
– Inflammation
– Allergic reaction
• Powerful vasodilator increase greatly
capillary permeability
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Vasodilator Agents
– Histamine
• Most of the histamine is derived from
mast cells in the damaged tissues and
from basophils in the blood.
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Ions and Other Chemical Factors
– Ca++
– K+
– Mg++
– H+
– Anions
– CO2
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Ions and Other Chemical Factors
– Ca++
• Increase causes vasoconstriction
– K+
• Increase causes vasodilation
– Inhibit smooth muscle contraction.
– Mg++
• Increase causes vasodilation
– inhibit smooth muscle contraction.
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Ions and Other Chemical Factors
– H+
• Increase (decrease in pH) causes
dilation of the arterioles.
– Anions
• Acetate and citrate
– cause mild degrees of vasodilation
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Humoral Control of the Circulation
• Ions and Other Chemical Factors
– CO2
• Increase causes moderate vasodilation
in most tissues, but marked vasodilation
in the brain
• CO2 in blood, acting on brain vasomotor
center, has an extremely powerful
indirect effect, transmitted through the
sympathetic nervous vasoconstrictor
system, to cause widespread
vasoconstriction throughout the body
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Nervous Regulation of Circulation
• Blood flow control is mainly local
• Nervous control of circulation has more
global functions
– Redistributing blood flow to different areas
of body
– Increasing/decreasing heart pumping
– Very rapid control of systemic arterial
pressure
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Nervous Regulation of Circulation
• Nervous system controls almost entirely
through autonomic nervous system
(ANS)
– Sympathetic
• More Important for circulation control
– Parasympathetic
• Regulates heart function
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Anatomy of sympathetic nervous control of
the circulation. Also shown by the red
dashed line is a vagus nerve that carries
parasympathetic signals to the heart.
Tanveer Raza MD MS MBBS
razajju2@yahoo.com
Thank You