Cardian innervation:

Pacemaker regulation:
Once the pacemaker cells reach threshold, the
magnitude and duration of the AP is always the same.
In order to change the frequency, the time between APs
must vary.
The interval can only be changed in two ways.
The rate of depolarization can be changed
The amount of depolarization required to reach threshold can be
Vascular physiology:
Peripheral Circulatory System
Systemic vessels
Pulmonary vessels
Transport blood through most all body parts
from left ventricle and back to right atrium
Transport blood from right ventricle through
lungs and back to left atrium
Blood vessels and heart regulated to ensure
blood pressure is high enough for blood flow
to meet metabolic needs of tissues
Blood Vessel Structure
Elastic, muscular, arterioles
Blood flows from arterioles to capillaries
 Most of exchange between blood and interstitial
spaces occurs across the walls
 Blood flows from capillaries to venous system
Venules, small veins, medium or large veins
Capillary wall consists
mostly of endothelial
Types classified by
Do not have fenestrae
Have pores
Large diameter with large
Capillary Network:
Blood flows from
arterioles through
metarterioles, then
through capillary
Venules drain network
Smooth muscle in
arterioles, metarterioles,
precapillary sphincters
regulates blood flow
Structure of Arteries and Veins
Three layers except for
capillaries and venules
Tunica intima (interna)
Tunica media
Tunica adventitia (externa)
Merges with connective
tissue surrounding blood
Structure of Arteries
Elastic or conducting arteries
Muscular or medium arteries
Largest diameters, pressure high and fluctuates
Smooth muscle allows vessels to regulate blood
supply by constricting or dilating
Transport blood from small arteries to capillaries
Structure of Veins
Venules and small veins
Medium and large veins
Tubes of endothelium on delicate basement
Allow blood to flow toward heart but not in
opposite direction
Atriovenous anastomoses
Allow blood to flow from arterioles to small
veins without passing through capillaries
Blood Vessel Comparison:
Muscular contractions aid venous return:
Pulmonary Circulation
Moves blood to and from the lungs
Pulmonary trunk
Pulmonary arteries
Arises from right ventricle
Branches of pulmonary trunk which project to
Pulmonary veins
Exit each lung and enter left atrium
Systemic Circulation: Arteries
From which all arteries are derived either directly or
 Parts
Ascending, descending, thoracic, abdominal
Coronary arteries
Supply the heart
Systemic Circulation: Veins
Return blood from body to right atrium
Major veins
Coronary sinus (heart)
 Superior vena cava (head, neck, thorax, upper
 Inferior vena cava (abdomen, pelvis, lower limbs)
Types of veins
Superficial, deep, sinuses
Dynamics of Blood Circulation
Interrelationships between
 Flow
 Resistance
 Control mechanisms that regulate blood pressure
 Blood flow through vessels
Laminar and Turbulent Flow
Laminar flow
Outermost layer
moving slowest and
center moving fastest
Turbulent flow
Rate of flow exceeds
critical velocity
Fluid passes a
constriction, sharp turn,
rough surface
Aging of the Arteries
General term for
degeneration changes in
arteries making them
less elastic
Deposition of plaque
on walls
Blood Pressure
Measure of force exerted by blood against the
Blood moves through vessels because of blood
Measured by listening for Korotkoff sounds
produced by turbulent flow in arteries as
pressure released from blood pressure cuff
Blood Pressure Measurement
Blood Flow, Poiseuille’s Law
and Viscosity
Blood flow
Amount of blood moving
through a vessel in a given
time period
Directly proportional to
pressure differences,
inversely proportional to
Poiseuille’s Law
Flow decreases when
resistance increases
Flow resistance
decreases when vessel
diameter increases
Measure of resistance
of liquid to flow
As viscosity increases,
pressure required to
flow increases
Critical Closing Pressure,
Laplace’s Law and Compliance
Critical closing pressure
Pressure at which a blood
vessel collapses and blood
flow stops
Laplace’s Law
Force acting on blood
vessel wall is proportional
to diameter of the vessel
times blood pressure
Vascular compliance
Tendency for blood
vessel volume to
increase as blood
pressure increases
More easily the vessel
wall stretches, the
greater its compliance
Venous system has a
large compliance and
acts as a blood reservoir
Physiology of Systemic
Determined by
Anatomy of circulatory system
 Dynamics of blood flow
 Regulatory mechanisms that control heart and
blood vessels
Blood volume
Most in the veins
 Smaller volumes in arteries and capillaries
Cross-Sectional Area
As diameter of vessels
decreases, the total
cross-sectional area
increases and velocity
of blood flow
Much like a stream that
flows rapidly through a
narrow gorge but flows
slowly through a broad
Pressure and Resistance
Blood pressure averages
100 mm Hg in aorta and
drops to 0 mm Hg in the
right atrium
Greatest drop in
pressure occurs in
arterioles which regulate
blood flow through
No large fluctuations in
capillaries and veins
Pulse Pressure
Difference between
systolic and diastolic
Increases when stroke
volume increases or
vascular compliance
Pulse pressure can be
used to take a pulse to
determine heart rate
and rhythmicity
Capillary Exchange and
Interstitial Fluid Volume
Blood pressure, capillary permeability, and
osmosis affect movement of fluid from
A net movement of fluid occurs from blood
into tissues. Fluid gained by tissues is removed
by lymphatic system.
Fluid Exchange Across
Capillary Walls
Vein Characteristics and
Effect of Gravity on Blood
Vein Characteristics
 Venous return to heart
increases due to
increase in blood
volume, venous tone,
and arteriole dilation
Effect of Gravity
 In a standing position,
hydrostatic pressure
caused by gravity
increases blood
pressure below the
heart and decreases
pressure above the
Control of Blood Flow by
Local control
Nervous System
In most tissues, blood flow is proportional to
metabolic needs of tissues
Responsible for routing blood flow and
maintaining blood pressure
Hormonal Control
Sympathetic action potentials stimulate
epinephrine and norepinephrine
Local Control of Blood Flow
by Tissues
Blood flow can increase 7-8 times as a result of vasodilation of
metarterioles and precapillary sphincters in response to increased
rate of metabolism
Vasodilator substances produced as metabolism increases
Vasomotion is periodic contraction and relaxation of precapillary
Nervous Regulation of
Blood Vessels
Short-Term Regulation of
Blood Pressure
Baroreceptor reflexes
Chemoreceptor reflexes
Change peripheral resistance, heart rate, and stroke
volume in response to changes in blood pressure
Sensory receptors sensitive to oxygen, carbon dioxide,
and pH levels of blood
Central nervous system ischemic response
Results from high carbon dioxide or low pH levels in
medulla and increases peripheral resistance
Baroreceptor Reflex Control
Local mechanisms affect MAP:
General control of MAP:
Long-Term Regulation
of Blood Pressure
Renin-angiotensin-aldosterone mechanism
Vasopressin (ADH) mechanism
Atrial natriuretic mechanism
Fluid shift mechanism
Stress-relaxation response
Vasopressin (ADH) Mechanism
Long Term Mechanisms
Atrial natriuretic
Hormone released from
cardiac muscle cells when
atrial blood pressure
increases, simulating an
increase in urinary
production, causing a
decrease in blood volume
and blood pressure
Fluid shift
Movement of fluid
from interstitial spaces
into capillaries in
response to decrease in
blood pressure to
maintain blood volume
Adjustment of blood
vessel smooth muscle to
respond to change in
blood volume
Effects of pH and Gases
Chemoreceptor Reflex Control
Inadequate blood flow throughout body
Three stages
Compensated: Blood pressure decreases only a moderate
amount and mechanisms able to reestablish normal blood
pressure and flow
Progressive: Compensatory mechanisms inadequate and
positive feedback cycle develops; cycle proceeds to next stage
or medical treatment reestablishes adequate blood flow to
Irreversible: Leads to death, regardless of medical treatment
Fetal circulation:

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