Download Heart Part 2 Powerpoint

Heart pt 2: Function
Cardiac Cycle
• The heart goes through the cardiac
cycle to contract and pump blood
through the body efficiently
• The cycle is deemed to start when
the sinoatrial node (SA node)
initiates an action potential
• The SA node is the pacemaker of
the heart and is influenced by the
sympathetic and parasympathetic
nervous systems
SA node to AV node
• The SA node stimulates the
atria to contract, filling the
ventricles
• The SA node also stimulates
the AV node which then
stimulates the ventricles
– This delay allows the ventricles
to fully fill up before initiating
ventricular contraction
• If the SA node fails the AV
node can take over but the
ventricles don’t fill all the way
Completion of Contraction
• Once the AV node has delayed
the signal for a moment it
transmits it to the AV bundles,
which go through the septum
of the heart
• At the base of the ventricles the
AV bundles become the bundle
branches that innervate the
ventricles
• Ventricles contract, closing AV
valves and forcing blood out the
aorta and pulmonary trunk
Ventricular Pressure
• When the ventricles
contract, they squeeze
blood at a high pressure
into the major arteries
• The pressure in the major
arteries is approximately
equivalent to the pressure
in the heart
– 120/80 means peak pressure
of 120 when the left ventricle
squeezes, 80 when it relaxes
– These are also called systole
and diastole
Systole and Diastole
• Systole is the maximum blood
pressure caused by a chamber’s
squeezing
• Atrial systole is followed by
ventricular systole
• When the ventricles are refilling it
is known as diastole (minimum
blood pressure)
• 120/80 is average healthy blood
pressure
• Varies somewhat by age, size, etc.
Measuring Blood Pressure
• The theory behind measuring blood pressure works on
two principles:
1. The pressure in the major arteries is approximately
equivalent to the left ventricle
2. When the external squeezing pressure on an artery is
greater than its blood pressure, the blood flow stops
•
•
When the arm cuff cuts off blood pressure entirely,
this is systolic pressure
When the arm cuff allows all blood to flow again, this
is diastolic pressure
–
In between these two points, blood only squirts through
at diastole but not systole which makes a distinctive
sound
Measuring Blood Pressure
Systemic Blood Pressure
Blood Volume and Pressure
• The more blood is in the blood
vessels, the harder the heart
has to work to pump it
– High blood pressure can result
from excess of water (usually
from eating too much salt)
– Low blood pressure can result
from not enough salt, blood loss,
or dehydration
• Excess high blood pressure
(hypertension) can eventually
overwork the heart
Electrocardiogram
• The electrocardiogram (EKG or ECG) is the famous
“beep beep” in the hospital
• Measures the electrical activity of the heart
– First small wave (P wave) corresponds to SA node
depolarizing
– Large wave (QRS complex) corresponds to AV node and
ventricles depolarizing
– Second small wave (T wave) is repolarization of ventricles
• If the SA node fails, the p wave disappears and the
AV node becomes the pacemaker (junctional rhythm)
– Time for an artificial pacemaker!
EKG Breakdown
EKG Readings
Cardiac Output
• The total volume of blood that is
pumped by each ventricle per
minute is the cardiac output (CO)
– Fun fact: the CO of the left and
right ventricles should be the
same! Think about it!
• Affected by stroke volume
(amount of blood pumped per
beat) and heart rate
– These are affected by the overall
health, activity, and autonomic
nervous systems
See you Friday!
• Friday: blood vessels
• Next week: Exam!
– Monday: Review day
– Wednesday: Exam #3
– Friday: Good Friday holiday