Transcript Reading Part 3: The Cardiovascular System

Unit 4—Maintenance of the
Human Body
Dr. Achilly
Part 2: The Cardiovascular System

Concepts: Chapter 21-22
The Cardiovascular System
Consists of blood, heart & blood vessels.
 Heart is the pump that circulates blood
throughout the body.
 Blood carries nutrients to cells & wastes
away from them. It’s made of:

55% plasma—water, proteins, other solutes
 45% formed elements—platelets, white &
red blood cells

The Cardiovascular System—heart
structure




Heart is located in
mediastinum (btwn
sternum & vert. col).
~2/3 of heart is to the
left of midline.
Like a cone lying on its
side with apex pointing
anteriorly, inferiorly & to
left.
Base points posteriorly,
superiorly & to the right.
The Cardiovascular System—heart
structure

Heart is surrounded by
pericardium.
 Has 2 layers with
pericardial fluid
inbtwn.
 Prevents
overstretching of
heart, protects,
anchors & reduces
friction while heart
contracts.
The Cardiovascular System—heart
structure

Heart consists of 3 layers:
Epicardium—outermost thin, slippery layer
(continuous with inner pericardial layer)
 Myocardium—muscular layer which is
responsible for the pumping
 Endocardium—thin inner layer which gives
smooth lining to the heart chambers

The Cardiovascular System—heart
structure

Heart has 4 chambers:
2 superior atria (sing.—atrium) with small
pouch extensions called auricles that allow
each atrium to hold more blood.
 2 inferior ventricles

The Cardiovascular System—heart
structure
The Cardiovascular System—heart
structure

Right atrium

Receives deoxygenated blood from 3 veins
Sup. vena cava
 Inf. vena cava
 Coronary sinus

Wall of atrium has muscular ridges called
pectinate muscles
 Has fossa ovalis (remnant of foramen ovalis
in fetal heart)

The Cardiovascular System—heart
structure

Blood passes to right ventricle thru an
atrioventricular (AV) valve (aka tricuspid
valve)
The Cardiovascular System—heart
structure

Right ventricle
 Inside contains muscular
ridges & the chordae
tendonae which anchor
the flaps of the tricuspid
valves.
 Blood leaves right
ventricle thru pulmonary
valve & goes into the
pulmonary trunk which
splits into the right & left
pulmonary arteries.
The Cardiovascular System—heart
structure

Left atrium
Receives oxygenated blood from lungs via
pulmonary veins.
 Similar structure to right atrium
 Blood passes to left ventricle thru the left
atrioventricular valve (aka bicuspid or mitral)

The Cardiovascular System—heart
structure

Left ventricle
Forms apex of heart
 Similar structure to right ventricle, but the
myocardium is much thicker here.
 Blood leaves left vent. thru aortic valve into
the ascending aorta.
 Some blood goes to supply the heart tissue
via the coronary arteries.
 Rest of blood goes into arch of aorta &
descending aorta to supply the body.

The Cardiovascular System—heart
structure

Valves
When the atria contract, blood is forced thru
the AV valves and into the ventricles.
 When the ventricles contract, the cusps of
the AV valves are forced upward & the
tension from the chordea tendonae keeps
them from being forced open the wrong
way.

The Cardiovascular System—heart
structure
The aortic & pulmonary valves are made
of 3 crescent moon shaped cusps (so
they are aka semilunar valves).
 The cusps are forced open when the
ventricles contract.
 When the vent. relaxes, blood starts to
flow backwards, but fills the valve cusps
& they close tightly.

The Cardiovascular System—circuits

After birth, the heart pumps blood into 2
circuits:
Systemic—serves most of the body
 Pulmonary—goes back & forth btwn lungs &
heart


The output of one becomes the input of
the other.
The Cardiovascular System—circuits
Left side of heart receives oxygen-rich
blood from lungs.
 Left ventricle ejects blood into aorta.
 From here it enters progressively smaller
arteries thru out the body, then into
smaller arterioles, finally into capillaries.

The Cardiovascular System—circuits

Nutrient & gas exchange occurs across
the thin capillary walls.

O2 is unloaded, CO2 is picked up
The Cardiovascular System—circuits
Usually blood passes thru one capillary
bed & then enters a systemic venule.
 Venules carry nutrient & oxygen poor
blood away from tissues.
 They merge into larger systemic veins &
then into the superior or inferior vena
cava to the right atrium.

The Cardiovascular System—circuits
Right side of heart is pump for
pulmonary circuit.
 Blood ejected from right ventricle flows to
pulmonary trunk which branches into
pulmonary arteries (only arteries that
carry deoxygenated blood).
 Pulmonary arteries branch to right & left
lung.

The Cardiovascular System—circuits
Oxygen-rich blood returns to left side of
heart via pulmonary vein (only vein that
carries oxygenated blood).
 The trip to the systemic circuit repeats.

The Cardiovascular System—circuits
Part of the systemic circuit includes
coronary circulation.
 Blood does not diffuse thru the chambers
to the heart tissue, so it needs its own
supply.
 Coronary arteries branch from the
ascending aorta & encircle the heart.

The Cardiovascular System—tissue





Myo fibers that make up myocardium are
similar to those that are in skeletal myo.
They are a bit shorter & more branched.
Usually mononucleated, but may have more
than one nuclei in a cell.
The ends of the cells connect to each other
thru intercalated discs. Helps to hold the cells
together.
Channels in the disc allow cells to
communicate & for nerve impulses to spread
quickly from cell to cell.
The Cardiovascular System—
conduction
Cardiac myo fibers are autorhythmic—
they generate action potentials that
trigger heart contractions.
 Heart will beat even when removed from
body with all of its nerves cut.
 These autorhythmic fibers act as a
pacemaker & they form a conduction
system that allows contraction to
progress thru heart.

The Cardiovascular System—
conduction
1.
2.
Excitation begins in sinoartrial (SA)
node located in wall of R atrium. The
impulse from SA node spreads thru
both atria via gaps in the intercalated
discs. Both atria contract (aka atrial
systole).
Nerve impulse reaches atrioventricular
(AV) node located in septum btwn 2
atria.
The Cardiovascular System—
conduction
3.
4.
5.
Nerve impulse enters AV bundle
(bundle of His)
Impulse travels thru both right & left
bundle branches which are located in
the interventricular septum.
Impulse travels thru Purkinje fibers to
apex of heart & upward. Both
ventricles contract (aka ventricular
systole).
The Cardiovascular System—
conduction
conduction animation
The Cardiovascular System—
conduction

Nerve impulses from
CNS & hormones
modify timing &
strength of each
heartbeat, but they
don’t establish the
fundamental rhythm.
The Cardiovascular System—
electrocardiogram
As nerve impulses travel thru heart, they
generate electrical currents (action
potentials) that can be detected on body
surface.
 Electrocardiogram (ECG or EKG) can
record these signals.
 Electrodes are placed on limbs & chest.
Each records slightly different activity.

The Cardiovascular System—
electrocardiogram

Helps to determine:




if conduction
pathway is normal.
If heart is enlarged.
If heart regions are
damaged.
Cause of chest
pain.
The Cardiovascular System—
electrocardiogram

P wave


QRS complex


Represents atrial depolarization as the
impulse spreads from SA node & thru both
atria.
Rapid ventricular depolarization
T wave

Ventricular repolarization, just as ventricles
are starting to relax (diastole).
The Cardiovascular System—
electrocardiogram

Size of waves can indicate
abnormalities.
Larger P wave = enlarged atrium
 Larger Q wave may = myocardial infarction
 Larger R wave = enlarged ventricles
 Flat T wave = heart myo not getting enough
oxygen (from blockage of coronary artery)
 Larger T wave = high blood K+

The Cardiovascular System—
electrocardiogram

Times between waves are called
segments or intervals.

P-Q interval represents time required for the
impulse to travel thru atria, AV node & rest
of conduction fibers. If there is scarring or
damage to heart tissue, that “trip” will take
longer. P-Q interval lengthens.
The Cardiovascular System—
electrocardiogram
The Cardiovascular System—
electrocardiogram
S-T segment represents ventricular systole.
It can be elevated during acute MI or
depressed when heart myo is not getting
enough oxygen.
 Q-T interval represents beginning of vent.
depolarization to the end of repolarization.
May be lengthened by myo damage,
decreased blood flow or conduction
abnormalities.

The Cardiovascular System—
electrocardiogram

No P wave (atrial fibrillation)

ST elevation (acute MI)
The Cardiovascular System—
electrocardiogram

ST depression (not enough O2 to heart myo)
The Cardiovascular System—
electrocardiogram

Some abnormalities may not show
unless heart is stressed.


Some EKG’s are done during exercise
Some abnormalities are unpredictable.

May need 24 hr. monitoring.
The Cardiovascular System—cardiac
cycle

All of the events associated with one
heartbeat.
 Systole & diastole in both atria & ventricles.
The Cardiovascular System—cardiac
cycle

Atrial systole (0.1 sec)
Depolarization of SA node causes atrial
depolarization.
 Atrial systole forces blood that has collected
in the atria thru the open AV valves into the
ventricles.

The Cardiovascular System—cardiac
cycle

Ventricular systole (0.3 sec)
Ventricular depolarization begins with the
contraction of vent. walls. Pressure rises so
blood is forced against AV valves causing
them to shut.
 Pressure rises enough to force blood thru
both SL valves. Called ventricular ejection.
 Total amt of blood ejected = 70 mL

The Cardiovascular System—cardiac
cycle

Relaxation period (0.4 sec)
Both atria & ventricles are relaxed.
 As pressure drops, blood from aorta &
pulmonary trunk flows backwards but is
stopped by cusps of closed SL valves.
 Pressure drops enough so that AV valves
open. Blood that collected in atria during
atrial diastole rushes into ventricles.
 At end of relaxation, P wave appears, atria
contract & cycle starts again.

The Cardiovascular System—cardiac
cycle
Cardiac cycle animation
The Cardiovascular System—cardiac
cycle
During exercise, as the heart beats
faster, the relaxation period shortens, but
the timing for systole doesn’t change
much.
 Athletes have stronger systole & can
pump more blood with each contraction
(increased stroke volume).

The Cardiovascular System—
circulatory routes
Blood vessels are organized into routes
that carry blood to specific organs.
 A part of the cardiac output flows
separately to each part of the body.
 Deoxygenated blood is returned to the
heart in a separate set of veins.

The Cardiovascular System—pulse &
blood pressure

Arteries & arterioles are very elastic.
Blood comes out of the heart from the
left ventricle under great pressure. This
pressure expands arteries and can be
felt as a pulse in several places thru out
the body.
The Cardiovascular System—pulse &
blood pressure
The muscular walls of arterioles allow
them to play a role in maintaining blood
pressure.
 By contracting this muscular layer, less
blood will flow thru that vessel & this
increases the pressure of blood
elsewhere in the body.

Pulse points
The Cardiovascular System—blood
pressure
Blood pressure is a measure of the
pressure in the arteries generated by the
left ventricle during systole & the
remaining pressure in the vessel during
diastole.
 Measured using a sphygmomanometer.
 The top number in the reading
corresponds to systolic pressure & the
bottom to diastolic pressure.

The Cardiovascular System—blood
pressure

Venules & veins do
not have walls that
are as muscular.
 They are distensible
so they can adapt to
changes in blood
pressure & volume.
The Cardiovascular System—blood
pressure
Many veins have valves that form flaplike
cusps.
 Because blood pressure is low in the
veins, blood returning to the heart can
slow & even “back up.”
 Valves help to prevent backflow.
 Myo contraction helps also.

The Cardiovascular System—blood
pressure

Leaky valves can cause
veins to become dilated &
twisted.


Called varicose veins
Caused by:




congenital defects in valves
prolonged standing
pregnancy
aging
Anterior surface of the human heart before coronary artery bypass surgery
Take care of
your heart.
Don’t end up
here 
Cummings, J. E. et al. J Am Coll Cardiol 2004;43:994-1000
Copyright ©2004 American College of Cardiology Foundation. Restrictions may apply.