cardiovascular physiology

Lecture Outline
• Cardiovascular System Function
• Functional Anatomy of the Heart
• Properties of Myocardium
• Cardiac Cycle
• Cardiac Output
• Blood Pressure

Cardiovascular system
is the system of heart and blood
vessels that circulate blood throughout
the body.

Functions of cardiovascular
system
• Circulates OXYGEN and removes Carbon
Dioxide.
• Provides cells with NUTRIENTS.
• Removes the waste products of
metabolism to the excretory organs for
disposal.
• Transports HORMONES to target cells
and organs.
• Helps regulate body temperature.

Cardiovascular System
• Functional components of the
cardiovascular system:
1. Heart
2. Blood Vessels
3. Blood

What Are the Parts of the Circulatory
System?
• Two pathways come from the heart:
• The pulmonary circulation is a short loop
from the heart to the lungs, where blood is
oxygenatedand.
• The systemic circulation carries blood
from the heart to all the other parts of the
body.

Pulmonary circulation
• In pulmonary circulation:
• The pulmonary artery is
a big artery that comes
from the heart. It brings
blood from the heart to
the lungs. At the lungs,
the blood picks up
oxygen and drops off
carbon dioxide. The
blood then returns to the
heart through the
pulmonary veins.

Systemic circulation
The left side of the heart
pumps blood to the rest of the
tissues of the body through the
systemic circulation: Blood
pumped from left ventricle
passes through a series of
blood vessels, arterial system
and reaches the tissues.
Exchange of various
substances between blood and
the tissues occurs at the
capillaries. After exchange of
materials, blood enters the
venous system and returns to
right atrium of the heart. From
right atrium, blood enters the
right ventricle.

HEART
• The heart is a muscular organ about
the size of a closed fist that functions
as a body’s circulatory pump.

Functional anatomy of the heart
The heart is located in
the center of the thoracic
cavity. It sits directly
above the muscles of the
diaphragm, which
separates the thorax from
the abdomen, and lies
beneath the sternum
between the two lungs.

The heart is enclosed
and anchored in place
by a double-walled
fibrous sac referred to
as the pericardium.
The membranes of
the pericardium produce
a small amount
of pericardial fluid
that minimizes friction
produced by the movement
of the heart when it beats.
FUNCTIONAL ANATOMY OF THE HEART

Functional Anatomy of the Heart
CARDIAC MUSCLE
• Characteristics:
– Striated
– Short branched cells
– Uninucleate
– Intercalated discs

CHAMBERS
Human heart
has 4 chambers
– 2 Atria
– 2 Ventricles
Chambers
are separated
by septum…
Due to separate
chambers,
heart functions as double pump

VALVES
Two sets of valves in the heart maintain the
one-way flow of blood as it passes through
the heart chambers:
• Atrioventricular (AV) valves
• Semilunar valves

VALVES
Each of these valves consists of
thin flaps of flexible but tough
fibrous tissue whose movements
are passive.
The atrioventricular (AV)
valves are found between the
atria and the ventricles.
The right AV valve is a tricuspid
valve and has three cusps or
leaflets. The left AV valve (also
referred to as the mitral valve) is
a bicuspid valve because it has
two cusps.

VALVES
The semilunar valves
separate the ventricles from
their associated arteries.
The pulmonary valve is found
between the right ventricle and
the pulmonary artery and the
aortic valve is found between
the left ventricle and the aorta.
These valves prevent
backward flow of blood from
the pulmonary artery or the
aorta into their preceding
ventricles when the ventricles
relax. The semilunar valves
also have three cusps.

The wall of the heart
The wall of the heart has three layers:
• Epicardium
• Endocardium
• Myocardium
The outermost layer, the epicardium, is the thin membrane
on the external surface of the heart. The innermost layer,
the endocardium, consists of a thin delicate layer of cells
lining the chambers of the heart and the valve leaflets.
The endocardium is continuous with the endothelium ,
which lines the blood vessels.
The middle layer is the myocardium, which is the
muscular layer of the heart. This is the thickest
layer, although the thickness varies from one
chamber to the next. Thickness of the myocardium
is related to the amount of work that a given
chamber must perform when pumping blood.

Properties of myocardium
• Different cells within the heart are
specialized for different functional roles. In
general, these specializations are for
1.automaticity
2.excitability
3. conduction
4. contraction

Automaticity
• The specialized (pacemaker) cells of heart
spontaneously depolarize to threshold and
generate action potential. They are located in
• Sinoatrial (SA) node
This cells have the highest intrinsic rhythm (rate), making
them the pacemaker in the normal heart. Their intrinsic
rate is 60- 100beats/min.
• Atrioventricular (AV) node
Its cells have the second highest intrinsic rhythm (40-
60beats/min). Often, these cells become the pacemaker
if SA node cells are damaged.
• Purkinje fibers
They exhibit spontaneous depolarization with a rate of – 35
beats/min.

Myocardial Physiology
Autorhythmic Cells (Pacemaker Cells)
• Characteristics of
Pacemaker Cells
– Smaller than
contractile cells
– Don’t contain many
myofibrils
– No organized
sarcomere structure
• do not contribute to
the contractile force
of the heart
normal contractile
myocardial cell
conduction myofibers
SA node cell
AV node cells

Automaticity
Autorhythmic Cells (Pacemaker Cells)
•Characteristics of Pacemaker Cells: They
have unstable membrane potential
•“bottoms out” at -60mV
•“drifts upward” to -40mV, forming
a pacemaker potential
•The upward “drift” allows the membrane
to reach threshold potential (-40mV) by
itself
•This is due to:
1.Leakage Na+ causes slow depolarization
2.Ca2+ voltage-gated channels opening as
membrane approaches threshold (Ca2+
goes in)
At threshold additional Ca2+ voltage-gated
channels open causing more rapid
depolarization
3. Slow K+ voltage-gated channels open
causing an efflux of K+ (K+ goes out) and
Ca2+ in K+out
Ca2+ in
Na+in

The RMP in different cell types

Excitability
Contractile Cells
• Special aspects
– Intercalated discs
•Highly convoluted and
interdigitated junctions
–Joint adjacent cells with
»Desmosomes & fascia adherens
–Allow for synticial activity
»With gap junctions
–More mitochondria than skeletal
muscle
–Less sarcoplasmic reticulum
•Ca2+ also influxes from ECF reducing
storage need
–Larger t-tubules
•Internally branching
–Myocardial contractions are
graded!

EXCITABILITY
Phases of action potential of contractile
cells

Excitability
Action potential of contractile cells
• Phase 0
(depolarization)begins when
the membrane potential
reaches threshold (–40 mV).
Similar to nerve and skeletal
muscle, mediated by the
opening of voltage-gated, fast
Na+ channels
• Phase 1 (initial
repolarization) Slight
repolarization mediated by a
transient potassium current.
Sodium channels are in the
inactivated state.

Excitability
• Phase 2 (plateau)
Depolarization opens voltage-gated Ca2+ channels
and voltage-gated K+ channels
• Phase 3 (repolarization)
At this point, the Ca++ channels close and K+
channels open. The resulting efflux of K+ ions
causes the repolarization phase of the action
potential.
• Phase 4 Resting membrane potential

Excitability
• As in neurons, cardiac muscle
cells undergo an absolute or
effective refractory period in
which, at the peak of the action
potential, the voltage-gated fast
Na+ channels become inactivated
and incapable of opening
regardless of further stimulation.
As a result, the absolute refractory
period lasts almost as long as the
duration of the associated
contraction — about 250 msec.
The physiological significance of
this phenomenon is that it
prevents the development of
tetanus or spasm of the
ventricular myocardium.
The effective refractory period is followed by
a relative refractory period that lasts for the
remaining 50 msec of the ventricular action
potential. During this period, action
potentials may be generated; however, the
myocardium is more difficult than normal to
excite.

Myocardial Physiology
Contractile Cells
• Skeletal Action Potential vs Contractile
Myocardial Action Potential

Conduction
Intrinsic Conduction System
• Consists of
“pacemaker”
cells and
conduction
pathways
– Coordinate the
contraction of the
atria and
ventricles

Contractility
• Initiation
– Action potential via pacemaker
cells to conduction fibers
• Excitation-Contraction Coupling
1. AP spreads along sarcolemma
• T-tubules contain voltage gated L-
type Ca2+ channels which open upon
depolarization
• Ca2+ entrance into myocardial cell
and opens RyR (ryanodine receptors)
Ca2+ release channels
2. Ca2+ (Ca2+ from SR and ECF) binds
to troponin to initiate myosin head
attachment to actin
• Contraction

Contractility
• Relaxation
– Ca2+ is transported back
into the SR and
– Ca2+ is transported out of
the cell by a facilitated
Na+/Ca2+ exchanger (NCX)
– As ICF Ca2+ levels drop,
interactions between
myosin/actin are stopped
– Sarcomere lengthens

Electrocardiography
• is the recording of the electrical activity
of the heart.
• It is based on recording of
electric potentials generated by heart on
different body parts (mostly on body
surface)
Electrocardiogram is graphic record
of the electrocardiography

Elements of ECG
1.Waves
2.Segments
3.Intervals

Elements of ECG
• Waves are parts of ECG, which are
located above or below the isoline.
• Segments are parts of ECG, which are
located on the isoline.
• Intervals include waves and segments.

Waves of ECG
• P wave represents atrial depolarization
• QRS complex represents ventricular
depolarization
• T wave represents ventricular
repolarization
• U wave represents repolarization of the
papillary muscles or Purkinje fibers.

Blood Vessels
Over 80,000 miles of blood vessels transport your blood throughout your body.
There are 3 types of blood vessels.
• Arteries: Blood vessels
that carry blood away
from the heart to other
parts of the body.
• Veins: Blood vessels
that carry blood from
the body back to the
heart.
• Capillaries: Tiny tubes
that carry blood from
the arteries to the
body’s cells, and then
back to the veins.

Arteries:
carries blood Away from heart
– Large
– Thick-walled, Muscular
– Elastic
– Oxygenated blood
 Exception Pulmonary Artery
– Carried under great pressure
– Steady pulsating
Arterioles: smaller vessels, enter tissue

Capillaries
– Smallest vessel
– Microscopic
– Wall one cell thin
– Nutrients and
gases diffuse here

Veins:
Carries blood to heart
– Carries blood that contains
waste and CO2
• Exception pulmonary vein
– Blood not under much
pressure
– Valves to prevent much
gravity pull
Venules: larger than capillaries

Blood Components
Blood is made up of plasma and
formed elements
 Plasma: It transports blood solids,
nutrients, hormones, and other
materials.
 Formed elements:
–Erythrocytes (Red blood cells)
–Leukocytes (White blood cells)
–Platelets (thrombocytes)

Red blood cells
1. Made up about 99%
of the blood’s cellular
component
2. Small, disk-like shape
3. No nucleus
4. Cannot reproduce
5. Last 4 months then
rupture
6. Produced by red bone
marrow
7. Contain hemoglobin
8. Carry oxygen

Hemoglobin
• Hemoglobin is a
complex protein
made up of four
protein strands, plus
iron-rich heme
groups.
• Each hemoglobin
molecule can carry
four oxygen atoms.
The presence of
oxygen turns
hemoglobin bright
red.

White blood cells
• Nucleus present
• Types of leukocytes:
• most are neutrophils
that engulf
microorganisms
• Basophils
• Eosinophils
• Lymphocytes
Active in immune system.
Help fight disease and infection by
attacking germs that enter the body.

Platelets
• Platelets are cell
fragments used in
blood clotting.
• Platelets are derived
from egakaryocites.
Help blood form a clot at the
site of a wound. A clot seals a
cut and prevents excessive
blood loss.

The Cardiac Cycle:
Events of the cardiac
cycle

• He developed the
modern criteria of
phase analysis of
the cardiac cycle
(1921).
21st APS President (1949-1950)
Carl J. Wiggers
(1883-1963)

• Cardiac cycle refers to all events associated
with blood flow through the heart. A single
cycle of cardiac activity can be divided into
two basic phases:
–Systole – contraction of heart muscle
–Diastole – relaxation of heart muscle
The Cardiac Cycle

The Cardiac Cycle (0,8 sec)
Ventricular Systole (0,33 sec)
• Period of Isovolumic Contraction (0,08 sec)
Phase 1. Asynchronous contraction (0,05 sec)
Phase 2. Isovolumic contraction (0,03 sec)
• Period of Ejection (0,25 sec)
Phase 3. Rapid ejection (0,12 sec)
Phase 4. Reduced ejection (0,13 sec)
Ventricular Diastole (0,47 sec)
• Period of Isovolumic Relaxation (0,12 sec)
Phase 5. Protodiastole (0,04 sec)
Phase 6. Isovolumic relaxation (0,08 sec)
• Period of filling (0,35 sec)
Phase 7. Rapid filling (0,08 sec)
Phase 8. Reduced filling (0,17 sec)
Phase 9. Presystole (0,1 sec)

Phase 1. Asynchronous contraction
• The beginning of this phase
= the end of Presystole (phase 9) = the end of diastole
• The end of this phase
= the beginning of Isovolumic contraction (phase 2)
The beginning of phase
AV valves are open
SL valves are closed
The end of phase
AV valves are closed
During this phase:
•Ventricular contraction
•The ventricular cavity volume
doesn't change
•The ventricular cavity pressure
doesn't change

Phase 2. Isovolumic contraction
= the end of Asynchronous contraction (phase 1)
= the beginning of Rapid ejection phase (phase 3)
During this phase,
Ventricular contraction
The ventricular cavity volume doesn't change
The ventricular cavity pressure increases
The end of phase
AV valves are
closed
SL valves are open

Phase 3. Rapid ejection
= the end of Isovolumic contraction (phase 2)
= the beginning of Reduced ejection (phase 4)
• SL valves are open
The end of phase
AV valves are
closed
SL valves are
openDuring this phase:
Ventricular contraction
2/3rd of stroke volume rapid ejected
The ventricular cavity volume decreases
The pressure inside the ventricles rises
to 120 mmHg

Phase 4. Reduced ejection
= the end of Rapid ejection (phase 3)
= the beginning of Protodiastole (phase 5)
= the end of Systole = the beginning of Diastole
• AV valves are closed
• The end of phase
During this phase:
• Ventricular contraction
• 1/3rd of stroke volume slow ejected
• The ventricular cavity volume decreases

Phase 5. Protodiastole
= the end of Reduced ejection (phase 4)
= the beginning of . Isovolumic relaxation (phase 6)
The end of phase
• SL valves are closed
During this phase:
• The ventricles are relaxing
• The ventricles aren’t filling
• The ventricular cavity volume doesn't change

Phase 6. Isovolumic relaxation
The beginning of this phase
= the end of Protodiastole (phase 5)
• The end of this phase = the beginning
of Rapid filling (phase 7)
The end of phase
• AV valves are open
During this phase,
The ventricles are relaxing
The ventricles aren’t filling
The ventricular cavity volume
doesn't chan
The pressure inside the
ventricles increases
significantly

Phase 7. Rapid filling
= the end of Isovolumic relaxati (phase 6)
= the beginning of Reduced ventricular filling (phase 8)
The beginning of
phase
AV valves are open
SL valves are
closed
The end of phase
AV valves are open
SL valves are
closed
During this phase:
The ventricles are rapid filling
The ventricular cavity volume increases
The pressure inside the ventricles increases
slightly

Phase 8. Reduced filling
The beginning of this phase
= the end of Rapid filling (phase 7)
The end of this phase
= the beginning of Presystole (phase 9)
• The end of phase
During this phase,
The ventricles are slow
filling
The ventricular cavity
volume increases
The pressure inside the
ventricles increases slightly

Phase 9. Presystole
= the end of Reduced filling (phase 8)
= the beginning of ventricular systole (phase 1)
= the beginning of ventricular systole
= the end of ventricular diastole
The end of phase

Phase 9. Presystole
During this phase,
•During ventricular relaxation blood flows from
atria to ventricles. When both atria contracts
almost simultaneously and pupms remaining 25%
of blood flows in respective ventricles (therefore
even when if atrial fails to function it is unlikely to
be noticed unless a person exercises).
•The ventricles are rapid filling
•The ventricular cavity volume increases
•The pressure inside the ventricles increases
slightly

Cardiac Cycle
Blood Volumes & Pressure

Cardiac Output
• Cardiac Output (CO) is the volume pumped by
the left ventricle each minute
– influenced by
• Stroke Volume (SV)
EDV – ESV = SV
135ml – 65ml = 70ml
• Heart Rate (HR) bpm
– CO = SV x HR
(70ml/b x 72bpm = 5040 ml/min
=5.04L/min)

Blood Vessel Structure
• enables specific functions
– Aorta
• absorb pulse pressure
(systolic pressure – diastolic
pressure) and release
energy creating diastolic
pulse
– Large arteries
• conduct and distribute blood
to regional areas
– Arterioles
• Regulate flow to tissues and
regulate MAP (mean arterial
pressure)

– Capillaries
• Allow for exchange
– Venules
• Collect and direct
blood to the veins
– Veins
• Return blood to heart
and act as a blood
reservoir
Blood Vessel Structure

Physical Characteristics of the
Circulation

• Hemodynamics is the description of the
laws which govern blood flow within the
vasculature.
• Ultimately, all blood flow between two
points within the vasculature is actuated
by differences in the pressure of blood
between those two points.

Interrelationships Among
Pressure, Flow, and
Resistance

Blood flow through a vessel is
determined by 2 factors:
• pressure gradient along the vessel
(pressure difference of the blood between
the two ends of the vessel)
• vascular resistance (impediment to blood
flow through the vessel)

The flow through the vessel can be
calculated by the following formula, which is
called Ohm’s law :
Q = (P1 - P2) / R
•in which Q is blood flow,
•(P1 - P2) is the pressure difference
between the two ends of the vessel,
•R is the resistance.

Blood Pressure
– Systolic Pressure
• The pressure that is created when the ventricles
contract
• Usually around 120 mm Hg

Blood Pressure
– Diastolic Pressure
• The pressure that is created by the recoil of the
aorta AND the closure of the aortic semilunar valve
• Usually around 80 mm Hg

Blood Pressure
Pulse Pressure
• Pulse Pressure=Systolic Pressure - Diastolic
Pressure
• The difference between the systolic and diastolic
pressures
– Usually 40 mm Hg (120 mm Hg – 80 mm Hg)
• Only applies to arteries
Mean Arterial Pressure
• We can determine the average pressure within the
arterial system = Mean Arterial Pressure (MAP)
MAP = Diastolic Pressure + 1/3 Pulse
Pressure
MAP = 80 mm Hg + 1/3( 120 mm Hg – 80 mm
Hg)
MAP = 93 mm Hg

QUESTIONS
1. The cardiovascular system. Functions. The pulmonary and systemic circuits.
2. The heart muscle cells. Structure.
3. Properties of the cardiac muscle.
4. Automaticity of the heart. Pasemaker cells.
5. Conductivity of the heart. Conductive system of the heart.
6. Excitability of the heart. Cardiac Action potential . The refractory periods of the cardiac muscle.
7. Contractility of the heart. Mechanism of cardiac muscle cell contraction.
8. The normal electrocardiogram.
9. Elements of ECG.
10. Mechanical events in the heart: cardiac cycle . Steps of the cardiac cycle .
11. Electrical events of cardiac cycle.
12. The origin of the heart sounds.
13. Ventricular volume-pressure loop.
14. Stroke volume. Control of stroke volume. Ejection fraction.
15. Cardiac output (CO). Regulation of CO .
16. Types and characteristics of blood vessels.
17. Relationship between blood flow, pressure and resistance.
18. Pressures in the cardiovascular system. Arterial pressure in the systemic circulation: diastolic,
systolic, pulse and mean arterial pressures.
19. Neural Regulation of Blood Pressure.

cardiovascular physiology

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