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CARDIOVASCULAR

SYSTEM

•

Consists of the heart, blood vessels and blood
...


ANATOMY OF HEART

A
...


MEDIASTINUM
– Is a region that extends from the sternum to the vertebral
column in the back
...

- About 2/3 of the heart’s mass lies to the left of body’s
midline

• Heart is about the size of a clenched fist
...
Formed by left ventricle
...
Formed by the atrium – mainly left atrium

HEART BORDERS;
i) ANTERIOR SURFACE – deep to sternum and ribs
ii) INFERIOR SURFACE – part of the heart between apex
and right border and rests on the diaphragm
iii) RIGHT BORDER – faces the right lung and extends from
the inferior surface to the base
iv) LEFT BORDER – called the pulmonary border, faces the
left lung and extends from the base to the apex
...

• Chest compression alone (minus
artificial respiration) is equally
effective compared to the
traditional CPR (i
...
chest
compression plus mouth-tomouth respiration)
...
g
...
Mesothelium is a simple squamous epithelial layer)
1
...
Inner visceral pericardium (visceral pericardium =
epicardium) – fused to the surface of the heart

Pericardium

PERICARDIAL CAVITY
- This is the potential space between the serous parietal
and visceral pericardium
...


*PERICARDITIS is the inflammation of the pericardium
Acute pericarditis – sudden onset, 1 week duration, linked to
viral infection
...
g
...
Build up
in pericardial fluid that can compress the heart (cardiac
tamponade)

LAYERS OF HEART WALL
The heart wall has 3 LAYERS;

i) EPICARDIUM - outermost layer, consists of
mesothelium and connective tissue
(visceral pericardium)
ii) MYOCARDIUM - middle and thickest layer, composed of
myocardium (~ 95% of heart)
iii) ENDOCARDIUM- innermost layer and consists of
smooth endothelium and its underlying connective
tissue

LAYERS OF HEART WALL

LAYERS OF THE HEART WALL

Arrangement of myocardium in the heart

• Cardiac muscle fibers swirl diagonally around the heart in
bundles

• Myocardium: striated, branched, have intercalated
discs, involuntary control
...
Continuous with endothelium
lining of blood vessels
...

Clinical presentation
Signs and Symptoms: fever, heart murmur, fatigue,
irregular to rapid heart rate etc
...
e
...


CHAMBERS OF THE HEART
- The heart has 2 upper chambers (atria - right and left)
and 2 lower chambers (ventricles - right and left)
...

i) AURICLES are small pouches on the anterior surface
of each atrium that slightly increases the capacity of the
atrium
...
Superior vena cava (drains blood from body regions above
below the heart)
2
...
Coronary sinus (drains blood from the heart venous
system)
- Blood passes from R/Atrium
R/Ventricle through tricuspid valve
(right atrio-ventricular valve)
...

- “RAT on the Right” (Right atrio-ventricular, Tricuspid)
- The septum separating the right and left atria has an oval depression
called the fossa ovalis - the remnant of the foramen ovale

RIGHT VENTRICLE
- Forms most of anterior surface of heart
- Blood passes from R/ ventricle
pulmonary
trunk via pulmonary semilunar valve
...

- Bicuspid valve: 2 cusps, “LAMB on the left”
;Left Atrio-ventricular Mitral or Bicuspid

LEFT VENTRICLE
~ 10 - 15mm thickness
- Forms the apex of the heart
- Blood passes from L/ Ventricle
Aorta
(ascending) through the aortic semilunar valves
* ductus arteriosus (ligamentum arteriosum)
* Trabecular carneae
* Chordae tendinae
* Coronary artery – branch of ascending artery

MYOCARDIAL THICKNESS & FUNCTION
- Thickness of myocardium of the four chambers varies
according to the function of each chamber
...

- Ventricle walls are thicker because they pump blood to a
greater distance
...

• RIGHT VENTRICLE walls are thinner (~ 4 -5 mm) ; lumen
crescent shaped
- they pump blood to the lungs, which is close to the heart
- offers little resistance to blood flow (i
...
low pressure
circulation) (small distance to travel, small area = lungs, low
pressure)
• LEFT VENTRICLE walls are thicker (~10 -15mm) ; lumen ~
circular
- they pump blood through the rest of the body (EXCEPT
lungs) (long distance to travel, large area, high pressure)
- offers high resistance to blood flow (i
...
high pressure
circulation)

Lumen and thickness of ventricles

Fibrous skeleton of he heart
• Contains dense connective tissue
• Consists of four dense CT rings surrounding valves of
the heart, fuses with one another and merges with
the inter-ventricular septum
Function:
1
...
Prevents overstretching of valves when blood passes
through them
3
...
Electrical insulator between atria and ventricles

FIBROUS SKELETON OF THE HEART

Atrioventricular valves
• When AV valves are open, their rounded edges of the
cusps project into the ventricles
• At ventricular filling, ventricles are relaxed, chordae
tendineae are slack, and blood moves from the atria into
ventricles down their pressure gradient
...

• Ventricular contraction, pressure in ventricles increases,
pushing the cusps of AV valves upwards until their edges
meet and close the opening
...
Prevents the cusps from prolapsing into the
atria in response to the high ventricular pressure
...

• Each cusp attaches to arterial wall by its convex outer
margin
• They allow ejection of blood into the large arteries and
prevent backflow of blood into ventricles
• Free margin of the cusps project into lumen of arteries
...
When ventricles relax , blood starts to
flow back into the heart
...
Atria contraction blood is
ejected into ventricles but small amount flows backward
into these vessels
...
e
...

• Insufficiency (incompetence) – valve fails to close
completely e
...
mitral insufficiency due to mitral valve
prolapse (MVP)
• Mitral valve prolapse (MVP) – one or both cusps of valve
protrudes into left atrium during ventricular contraction
...
Most common valvular disorder
...
Strep bacteria
provokes immune response (antibodies produced)
...
*damage mitral and
aortic valves

SYSTEMIC & PULMONARY

CIRCULATION

- Two circuits in series (i
...
output from one circulation
feeds onto the other circulation – cycle repeating
itself)
SYSTEMIC CIRCULATION
- Left side of heart is the pump for the systemic
circulation
- It pumps oxygenated blood to the vessels of the body
(systemic circulation)
PULMONARY CIRCULATION
- Right side of heart is the pump for pulmonary
circulation
- It pumps deoxygenated blood to the lungs for
oxygenation

SYSTEMIC & PULMONARY

CIRCULATION

CORONARY CIRCULATION
• Heart is too thick to rely on diffusion alone from
blood in the heart chambers, therefore it has it’s own
circulation – coronary circulation
...

• When heart muscle relaxes, the high pressure of
blood in aorta pushes blood through the coronary
arteries, into capillaries and then into coronary veins
...

- It delivers oxygenated blood and removes
deoxygenated blood from the myocardium
...

- The principal arteries, branching from ascending
aorta & carrying oxygenated blood, are right & left
coronary arteries
...
– 1
...
circumflex
artery) – supplies both ventricles and left atrium
- Right coronary artery (2 brs
...
posterior Interventricular artery and 2
...

• The main tributaries (veins) carry blood into the
coronary sinus include:
1
...
Middle cardiac vein – drains both ventricles
3
...
Anterior cardiac veins – drains veins and opens
directly

CORONARY CIRCULATION (VENOUS)
• Great cardiac vein – drains both ventricles, left
atrium (supplied by left coronary artery)
• Middle cardiac vein – drains both ventricles and
atriums (supplied by post
...
of
right coronary artery)
• Small cardiac vein – drains right atrium, right
ventricle
• Ant
...

• They provide collateral circulation in the myocardium
(i
...
alternate routes for blood flow when the main route
becomes blocked)
• Myocardium has many anastomosis that connect
branches of a given coronary artery or between
branches of different coronary arteries
...


CORONARY CIRCULATION (ARTERIAL)

Clinical - reperfusion
• Blockage of coronary artery deprives the myocardium of
its oxygen supply
...

• Damage due to formation of oxygen free radicals,
(unstable highly reactive molecules) that can cause cellular
damage and death
...
g
...
Other antioxidants – Vit E, C, betacarotene, zinc, selenium

Clinical – myocardial ischemia, infarction
• Myocardial ischemia - reduced blood flow to
myocardium (causes hypoxia)
...

Severe pain that accompanies myocardial ischemia
...


Clinical – myocardial ischemia, infarction
• Myocardial infarction – death in myocardium because
of prolonged interrupted blood supply
• Dead myocardial cells is replaced by scar tissue –
some loss in myocardial muscle strength
• Infarction in certain areas of the myocardium can
disrupt the conduction system of the heart causing
sudden death by triggering ventricular fibrillation
...
g
...


myocardium
• Diameter ~ 14 microns,
• 1 – 2 centrally located nucleus
• Branched, striated – same alternate light (actin filaments)
and dark (myosin filaments) bands, zones and z discs as
skeletal muscle fiber
• Myocardial cells connect with neighboring myocardial cells
via intercalated discs – irregular transverse thickening of
sarcolemma
...
Gap junctions allow atria and
ventricles to contract as a single coordinated unit
(functional syncytium)

myocardium

myocardium
• Has more mitochondria (25% cytosol space) than skeletal
muscle fibers (2% cytosol space)
• Transverse tubules are wider but less abundant than
skeletal muscle fiber; one transverse tubule per
sarcomere is located at z disc
...

- The heart is not activated all at one instant - but by a
wave of excitation that spreads through the myocardium
in a coordinated manner
...

- If the normal pattern of spread of electrical activation
is upset then the heart will not be an effective pump

PROPERTIES OF HEART MUSCLE
Let us review properties that allows the heart to be an
effective pump in the body
...
EXCITABILITY
2
...
AUTOMATICITY
4
...
EXCITABILITY
- There are 2 types of action potential in the cardiac
muscle cells;
i) SLOW RESPONSE – (E
...
Sinoatrial node and
atrioventricular node)
ii) FAST RESPONSE - (E
...
Atria, ventricles and
fast parts of the specialized conduction system)

Slow action potential

Fast action potential

PROPERTIES OF HEART MUSCLE
2
...

- Electrical activation spreads throughout myocardium
from cell to cell
...

- As one cell depolarizes, current spreads to adjacent
cells

PROPERTIES OF HEART MUSCLE
3
...
e
...

- Rate of depolarization rate:
SA node – 60 -100 times per minute
AV node – 40 – 60 times per minute
Purkinje fibres – 15 – 40 times per minute

PROPERTIES OF HEART MUSCLE
4
...

CELL TYPES OF THE CONDUCTION SYSTEM
- made of autorhythmic cells (~1% of all cardiac cells)
- Autorhythmic cells are self-excitable;
i
...
have an in built ability to repeatedly depolarize to
threshold spontaneously (pacemaker potential)
...


Action potential from an sinoatrial node

CONDUCTION AND PACEMAKER OF THE HEART
TWO FUNCTIONS OF THE CONDUCTION SYSTEM;
1
...
Forms CONDUCTION SYSTEM – route for
conduction of action potentials throughout the heart
muscle
...

- It includes; sinoatrial node, atrioventricular node,
AV bundle (Bundle of His), Bundle branches and
purkinje fibers
...
The
cells are continuous with atrial myocardial cells
2) INTERNODAL TRACTS
- the cells that form these tracts offer preferred paths
for activation spread between the SA node and AV node
“PREFERRED ROUTES OF ACTIVATION” means the
cells in these tracts are connected and aligned in such a
way to favor rapid conduction
...


SEQUENCE OF ACTIVATION OF THE HEART
4) ATRIOVENTRICULAR NODE, (AV NODE)
- Auto-rhythmic cells located in the septum between
the two atria
...
05 m/s)
SIGNIFICANCE: This delay between atrium and
ventricular systole (contraction) gives the atria time
to fill-up the ventricle before they contract
...


FIBROUS SKELETON OF THE HEART

SEQUENCE OF ACTIVATION OF THE HEART
6) BUNDLE BRANCHES
- The bundle of His splits into left and right bundle
branches
...

7) PURKINJE FIBERS
- The bundle branches splits into purkinje fibers
- Purkinje fibers sends braches over endocardial surface
• Conduction velocity in bundle branches and purkinje
fibers is rapid (~2 - 4m/s)
8) VENTRICULAR MYOCARDIUM
- The activation spreads muscle-to-muscle through gap
junctions
- It travels from endocardium to epidocardium

Clinical – artificial pacemaker
• SA node (~100 – 75 AP/ min) damaged/ diseased,
slower AV node (~65 -40 AP/ min) become the
pacemaker
...
Firing rate
too slow to maintain normal blood flow to the brain
...
Implant
beneath skin just inferior to clavicle
...


Clinical – artificial pacemaker

Action potential and contraction of heart
contractile fibers
• An action potential in contractile fibers has 3 phases:
1
...
Plateau
3
...
e
...
Depolarization
- Contractile fibers have a resting membrane potential
of -90mV
...

- Voltage-gated fast Na+ channels opens and causes a
rapid inflow of Nat ions, therefore rapid depolarization
...


Action potential and contraction of
heart contractile fibers

2
...

- Caused by opening of voltage-gated slow Ca2+ channels in
sarcolemma
...
The inflow of Ca2+
causes more inflow of Ca2+ by opening of the sarcoplasmic
reticulum membrane
...

- Voltage-gated K+ channels also located in sarcolemma
...

The inward Ca2+ current and the small K+ current
balances out and produces the plateau phase that
lasts 0
...
At this phase the membrane potential is
close to 0 mV

Action potential and contraction of
heart contractile fibers
3
...
This brings about the repolarization phase
...


Action potential and contraction of
heart contractile fibers

Action potential and contraction of
heart contractile fibers
• Refractory period is the time interval during which
2nd contraction can not be triggered
...

i
...
another contraction can not occur until relaxation
from previous contraction has completed
...


ATP production in cardiac muscle
• ATP is mainly sourced from aerobic cellular respiration
from its many mitochondria
...

i
...
(resting)
fatty acids (60%) ,
glucose (35%),
others – lactic acid, creatine phosphate, amino
acids, ketone bodies (~ 5%)
...

- ECG is a combined record of action potentials produced by
all heart muscles during each heart beat
...

- Electrocardiograph amplifies heart’s electrical signals
...


ELECTROCARDIOGRAM

Limb leads –
I, from the right arm (-) toward the left arm (+)
II, from the right arm toward the left leg
III, from the left arm toward the left leg
(taken together, these three form the classic
"Einthoven's triangle")
aVR, augmented lead toward the right (arm)
aVL, augmented lead toward the left (arm)
aVF, augmented lead toward the foot
(note: aVR is approximately opposite of I and should
essentially mirror the shape of I vertically)
Arms (RA, LA) anywhere from the upper arm to the wrists
Legs (RL, LL) anywhere from the thigh to the ankles
(positions of limb leads or their distances from heart are not
critical, as long as they are more than 10 cm [4 inches] from
the heart)

AVR

AVF

Chest leads:
V1 to the right of the sternum, next to it, in the space between
ribs 4 and 5
V2 as V1 but to the left of the sternum
V3 halfway between V2 and V4 (see next one)
V4 below the middle of the clavicle, between ribs 5 and 6
V5 left of V4, halfway between V4 and V6 (see next one)
V6 on same horizontal line with V4 and V5, below middle of
armpit]

ELECTROCARDIOGRAM
- Each limb and chest electrode shows different
electrical activity because of its different position
relative to the heart
Uses: By comparing these recordings with one another
and with normal records we can show:
1
...
Heart enlargement
3
...
Causes of chest pain

ELECTROCARDIOGRAM

ELECTROCARDIOGRAM
• Typical record shows recognizable waves with each
heartbeat
...

- Relatively longer than QRS complex – shows a relatively
slow event
...

- Shorter than P wave means mean rapid spread due to
purkinje fiber
...
Conduction time from beginning of
atrial excitation to beginning of ventricular
excitation
...
Represents time when ventricular fibers
depolarized during plateau phase of action potential
• Elevated(above baseline) S-T segment in acute MI
• Depressed (below baseline) S-T segment when oxygen
supply to muscle is depressed

ELECTROCARDIOGRAM
• Q-T interval begins from start of QRS complex to
end of T wave
...

• Q-T interval lengthens at myocardial ischemia,
myocardial damage, conduction abnormalities
...

i
...
(Resting) sufficient O2 reaches muscles
...

NB: Electrical activity can be recorded at a distant from
the heart because the body tissues act as conductors
...

- When heart rate is 75 beats per minute, a cardiac cycle
lasts 0
...

- Cardiac cycle (~ 0
...
Atrial systole – lasts about ~ 0
...
e atrial systole
2
...
3 sec
(includes isovolumetric contraction, ventricular ejection)
3
...
4 sec
(includes diastole, isovolumetric relaxation, ventricular
filling)

HEART SOUNDS

 PRODUCED by blood turbulence created as valves closes
- 4 types of heart sounds (S1, S2, S3 and S4)
 NORMAL HEART SOUNDS; - S1 and S2

i
...
1) S1 – “LUBB” sound
- louder and longer
- produced by blood turbulence from closure of AV
valves after ventricular systole
...

HEART RATE, (HR) – is the number of heart beats per
minute
...


𝑪𝑶 = 𝑺𝑽 𝒙
𝒎𝑳
𝒎𝑳
=
𝒎𝑳
𝒃𝒆𝒂𝒕𝒔

𝑯𝑹

𝒙

𝒃𝒆𝒂𝒕𝒔
𝒎𝒊𝒏

CARDIAC OUTPUT, STROKE VOLUME, HEART RATE
- Therefore for a resting adult;
- SV ~ 70mL/beat
- HR ~ 75 beats/ min

- Therefore the CO of resting adult of 5
...
e
...


Cardiac reserve
• Cardiac reserve – difference between a person’s
maximum cardiac output (CO) and CO at rest
...
e
...
e
...


FACTORS REGULATING STROKE VOLUME


3 main factors regulating SV are;
1) PRELOAD - It is the stretch on the heart
before it contracts
...

3) AFTERLOAD - It is the pressure that must be
exceeded before the ejection of blood from the
ventricle can begin
...


END-DIASTOLIC VOLUME
 DESCRIBE THE FACTORS THAT DETERMINE
End-diastolic volume, (EDV)
...


Contractility
• Is the contraction at any given preload
...

E
...
sympathetic stimulation, hormones such as
epinephrine and norepinephrine, drug digitalis
- General mechanism: Increase Ca2+ in interstitial fluid so
increase force of contraction
...
g
...

 NORMAL HR - 60 – 100 bpm
 BRADYCARDIA - (slow HR) < 60 bpm

 TACHYCARDIA – (rapid HR) > 100 bpm

REGULATION OF HEART RATE
SIGNIFICANCE OF A CHANGING HEART RATE
- It is important in short-term control of cardiac output
and blood pressure
...


1
...
SA node, 2
...
e
...

- Also will discuss a bit on the histology of blood vessels
and anatomy of the primary routes of arterial and venous
blood

BRIEF OVERVIEW OF BLOOD VESSELS
 Blood vessels form a closed system of tubes that carry
blood away from the heart
transport it to tissues
of the body then return
it to the heart
...


BLOOD VESSEL STRUCTURE

ARTERIES

STRUCTURE;
– Are thick walled with extensive elastic tissue and smooth
muscle
- The walls of artery consists of;
i) TUNICA INTERNA
ii) TUNICA MEDIA – which maintains the elastic &
contractility
iii) TUNICA EXTERNA

ARTERIES

ARTERIES
CHARACTERISTIC;
Blood are under high pressure
...

2) CONTRACTILITY – due to the smooth muscle in tunica
media
...

FUNCTION:
- Carries oxygenated blood away from the heart to the
tissues
...
e
...
e
...

- Contains smooth muscles and endothelial cells
...

FUNCTION – They permit the exchange of nutrients,
water, gases and metabolic wastes between the blood
and tissue cells through interstitial fluid
...
CONTINUOUS CAPILLARY
2
...
FENESTRATED CAPILLARY

CONTINUOUS CAPILLARY
They have a complete basal lamina
...

- They undergo exchange continuously
...

- They allow small and medium-sized proteins such as albumin to
enter and leave the blood stream
- Some spaces are large enough for blood cells to pass through
...


FENESTRATED CAPILLARIES
-They allow capillary exchange but at a rapid rate
...


CAPILLARY EXCHANGE
- Blood flow at capillary bed is regulated by a sphincter
muscle on the arteriole side
...


VENULES
STRUCTURE: - Are small vessels formed when
capillaries unite
...

- Its lumen is larger compared to artery
- They have valves
...

SIGNIFICANCE;
- For a person standing up, the pressure pushing blood
up in the veins in the legs is barely enough to
overcome gravity
...


VEINS

Respiratory pump
• Breathing (= Respiratory pump):
• At inspiration the pressure inside the chest gets lower
(becomes more negative) and also lower than abdominal
pressure
...

• At expiration, the reverse happens so pressure in the
chest becomes higher than abdomen
...
The backflow of blood also
does not occur because of the valves in the veins which
prevents them
...
Hence an arterial pulse propagated down
the artery, causes a local expansion (bulging/ swelling)
that pushes against the adjacent veins
...

artery
vein

VEINS
FUNCTION:
i) Returns blood to the heart
ii) Blood reservoirs (capacitance vessels)
NOTE: BLOOD VOLUME DISTRIBUTION
- Systemic veins and venules ~ 60 %
- Systemic capillaries ~ 5 %
- Systemic arteries and arterioles ~ 15 %
- Heart ~ 8 %
- Pulmonary vessels ~ 12 %

Blood vessels in the circulation

ANASTOMOSES
- Are the union of the branches of 2 or more arteries
supplying the same region

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