Transcript How the heart works - Appoquinimink High School

How the heart works
Electrical Conduction System
• The heart is
composed primarily of
muscle tissue. A
network of nerve
fibers coordinates the
contraction and
relaxation of the
cardiac muscle tissue
to obtain an efficient,
wave-like pumping
action of the heart.
The sinus node (1) is located high in the heart's right upper
chamber (right atrium) and it sends out an electrical impulse
- about 60 times a minute when you are at rest.
The impulse quickly spreads throughout the muscular atrial
wall (2). This causes the atrium to contract, pushing the
blood from the upper chambers into the lower chambers.
The impulse then travels to
the lower chambers via the
AV node (3). This is a cordlike structure that is usually
the only electrical
connection between the
heart's upper and lower
chambers. The AV node
delays the conduction of
the impulse so the lower
chambers have time to fill
with blood.
The impulse then
travels very quickly
throughout the lower
chambers. This
causes the muscular
walls of the lower
chambers (ventricles)
(4) to contract pushing
the blood out of the
right side of the heart
to the lungs and the
left side of the heart to
the body.
http://www.medmovie.com/mmdata
base/MediaPlayer.aspx?ClientID=1
3&TopicID=868
Systole
• The contraction of the
cardiac muscle tissue in the
ventricles is called systole.
When the ventricles
contract, they force the
blood from their chambers
into the arteries leaving the
heart. The left ventricle
empties into the aorta and
the right ventricle into the
pulmonary artery. The
increased pressure due to
the contraction of the
ventricles is called systolic
pressure.
Diastole
• The relaxation of the
cardiac muscle tissue in
the ventricles is called
diastole. When the
ventricles relax, they
make room to accept the
blood from the atria. The
decreased pressure due
to the relaxation of the
ventricles is called
diastolic pressure.
P = Atria Contracting
QRS = Ventricles Contracting
T = Ventricles relaxing
http://www.usccardiology.org/patienteduc
ation-generalcardiology.html
http://www.usccardiology.org/patienteduc
ation-generalcardiologyheartelectricalsystem.html
How is the cardiac cycle
controlled?
Medulla oblongata and the heart…
• The hearts control center is in the medulla
oblongata
• It is a part of the parasympathetic and
sympathetic nervous systems
• Parasympathetic fibers attach to the SA
and AV nodes in the heart and innervate
the these areas
• SA node controls the heart rate
Parasympathetic nerves and the
heart…
• Carry continuous impulses to the SA and
AV nodes, changing heart rate
– An increase in impulses slows heart rate
– A decrease in impulses increases heart rate
• Acetycholine is the “break” of the
parasympathetic nerves, decreasing the
heart rate
• When absent, heart rate increases
Sympathetic nerves and the
heart…
• Also attach to the SA and AV nodes, as
well as other areas of the heart
• Secrete norepherine in response to
impulses, which increases heart rate and
force of heart muscle (myocardial)
contractions
Medulla oblongata and the heart…
• Baroreceptors or pressure receptors
sense changes in pressure of the heart..
• This message gets sent to the medulla
oblongata, and it then regulates the heart
pressure
– High pressure gets reduced, low pressure
gets increased
Other factors that affect heart rate
• Impulses from the cerebellum- specifically the
hypothalamus
– Fight or flight response
• Fainting (decrease heart rate)
• Anxiety attack (increased heart rate)
• Temperature
– Rising temp = rise in heart rate
– Lower temp = decrease in heart rate
• Ions
– Too much potassium (K+) hyperkalemia
• Decrease rate and contractions = arrhythmia
– Too much calcium (Ca+2) hypercalcemia
• Increases heart action, prolonged contractions
How is the cardiac cycle
measured?
EKG
• An electrocardiogram (EKG) diagnostic
test is often performed to evaluate a
patient's electrical heart activity. It
provides cardiologists with a blueprint
of the propagation of the electrical
signal within different regions of the
heart.
ECG Strip
• The ECG strip shows the electrical activity
of the heart. Electrical signs cause the
heart to contract or pump. Each signal
begins in the atria. The signal then
immediately moves down the ventricles.
The heart muscle relaxes for an instant
before the next electrical signal begins.