Transcript Heart Physiology - Northwest ISD Moodle

Heart Physiology
Chapter 11
Microscopic Anatomy
 Cardiac muscle fibers (cells)
 Striated, short, and branched
 One nucleus
 Plasma membrane of adjacent cardiac cells
interlock at intercalated discs
 Large mitochondria account for 25% of the
volume and give the cells high resistance to
fatigue
 Only operates on aerobic respiration
 Contracts by the sliding filament mechanism
 Self-excitable and can initiate their own
depolarization
 Spontaneous and rhythmic stimulation
 The heart contracts as a unit or not at all
because all cells are tied together at
intercalated discs
Physiology of The Heart
 Cardiac muscle cells have
the ability to contract
intrinsically (within) or with
autonomic NS
 Contractions occur in a
regular continuous rhythm
 Heart needs a control
system to be an efficient
pump
 Main conduction system is
the intrinsic conduction
system
 Specialized noncontractile cardiac cells
that initiate and distribute
impulses throughout the
heart so that it contracts
Intrinsic Conduction System
 Sinoatrial node (SA)
 Located in the right atrial wall
 Pacemaker (sets the pace for HR)
 Atrioventricular (AV) node
 Located between atria and ventricles
 Atrioventricular bundle (Bundle of His)
 Located in the septum
 Right and left bundle branches
 Located in the septum
 Purkinje fibers
 Spread in the ventricle walls
Intrinsic Conduction System
1. Sinoatrial (SA) node starts each
heartbeat and sets the pace –
pacemaker
2. Impulse spreads through the atria
to the AV node (causing the atria
to contract)
3. Impulse pauses for a 0.1 sec to
allow atria to finish contracting
4. Then the impulse goes through
the AV bundle (bundle of His) and
splits into the right and left bundle
branches
5. The impulse ends in the Purkinje
fibers causing the ventricles to
contract
Nervous System Conduction System
 Basic heart rate is set by intrinsic
conduction system
 Autonomic nervous system can
modify the heart rate
 Sympathetic activation
increases the heartbeat
 Parasympathetic activation
slows the heartbeat
Conduction System Imbalances
 Arrhythmias
 Irregular heart rhythms due to defects in the intrinsic conduction
system
 Fibrillation
 A condition of rapid and irregular contractions
 Defibrillation is accomplished by electrically shocking the heart
which interrupts the chaotic twitching
• Heart block
• Damage to the AV node, totally or partially releasing the ventricles
from the control of the sinoatrial (SA) node
Electrocardiography (ECG or EKG)
 Electrical currents generated and transmitted through the
heart spread throughout the body and can be detected with
an electrocardiograph
 A graphic record of heart activity is called an
electrocardiogram (ECG or EKG)
 Recording electrodes are positioned at various sites on the
body surface
 12 leads are typically used
Electrocardiography (ECG or EKG)
 Typical ECG has 3 waves
 P wave
 Atrial depolarization
before they contract
 QRS complex
 Depolarization of
ventricles and
contraction of
ventricles
 T wave
 Ventricle repolarization
Electrocardiography (ECG or EKG)
 P-R interval
 From the atrial excitation
to the beginning of
ventricular excitement
 S-T segment
 Action potentials of the
ventricular cells are in their
plateau phases
 Q-T interval
 From the beginning of
ventricular depolarization
through ventricular
repolarization
Electrocardiography (ECG or EKG)
 In a healthy heart the
size, duration and timing
of the waves tend to be
consistent
 Changes in the pattern or
timing may reveal a
diseased or damaged
heart or problems with
the heart’s conduction
system
 Example: an enlarged R
wave hints of enlarged
ventricles
Electrocardiography (ECG or EKG)
Heart Sounds
 http://www.viddler.com/explore/humananatomy/videos/7/
 Two sounds (lub-dup) can be heard when listening to the
thorax with a stethoscope
 Associated with the closing of the valves
 First sound (lub) occurs when the AV valves close
 Second sound (dup) occurs when the SL valves close
Heart Sounds
 Heart murmurs
 Abnormal heart sounds
 Blood flows silently as long as the flow is smooth
 If it strikes obstructions, its flow generates heart murmurs that
can be heard with a stethoscope
The Cardiac Cycle
 Cardiac cycle
 All events associated with the blood flow through the heart
during one complete heartbeat
 Diastole
 Relaxation period (atria and ventricles)
 Systole
 Contraction period (atria and ventricles)
The Cardiac Cycle
1. Ventricular filling: mid-to-late diastole (AV valves open)
2. Ventricular systole (SL valves open)
3. Early diastole (AV valves open)
Heart Rate
•
•
•
•
Heart rate can be affected by age, gender, exercise and
body temperature
Resting heart rate is fastest in the fetus
• 140-160 beats/min
Average heart rate for females
• 72-80 beats/min
Average heart rate for males
• 64-72 beats/min
Heart Rate
•
Tachycardia
•
•
•
Abnormally fast heart rate more than 100 beats/min
Results from elevated body temperature, stress, certain drugs,
or heart disease
Bradycardia
•
•
Heart rate slower than 60 beats/min
Results from low body temperature, certain drugs or
parasympathetic activation
The Vascular System
 Arteries
 Taking blood away from the heart to the tissues
 Capillaries
 Gas and nutrient exchange
 Walls of capillaries are only one cell layer thick to
allow for exchanges between blood and tissue
 Veins
 Taking blood back to (visit) the heart
 Skeletal muscle “milks” blood in veins toward the
heart
Pulse
 Pressure wave of
blood
 Monitored at
“pressure points”
where pulse is
easily palpated
Blood Pressure
 Pressure the blood exerts against the inner blood
vessels walls
 Because the heart contracts and relaxes, the rhythmic
flow of blood causes the pressure to rise and fall each
beat.
 Systolic – pressure at the peak of ventricular contraction
 Diastolic – pressure when ventricles relax
Variations in Blood Pressure
 Human normal blood pressure range is variable
 Pressure in blood vessels decreases as the
distance away from the heart increases
 Normal
 140–110 mm Hg systolic
 80–75 mm Hg diastolic
 Hypotension
 Low systolic (below 110 mm HG)
 Often associated with illness
 Hypertension
 High systolic (above 140 mm HG)
 Can be dangerous if it is chronic
Measuring Arterial Blood Pressure
Figure 11.18