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D.4 The Heart
Understanding:
- Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
- Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
- There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
- This delay allows time for atrial systole before the atrioventricular valves close
- Conducting fibres ensure coordinated contraction of the entire ventricle wall
- Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flor
Applications:
Use of artificial pacemakers to regulate the heart rate
Use of defibrillation to treat life-threatening cardiac conditions
Causes and consequences of hypertension and thrombosis
Nature of science:
Developments in scientific research followed improvements in apparatus or instrumentation: the invention of the stethoscope led to improved
knowledge of the workings of the heart
Skills:
Measurement and interpretation of the heart rate under different conditions
Interpretation of systolic and diastolic blood pressure measurements
Mapping of the cardiac cycle to a normal ECG trace
Analysis of epidemiological data relating to the incidence of coronary heart disease
Review Topic 6
Aorta
Pulmonary vein
Pulmonary artery
Vena cava
Left atrium
Right atrium
Left ventricle
Right ventricle
Semi lunar valves
Atrioventricular valves
Septum
Review Topic 6
Semi lunar valves
(Arteries)
Atrioventricular valves
(Atria/Ventricles)
Right
Left
Pressure changes
- Aorta (black)
- Left atrium (Blue)
- Left ventricle (red)
Systole and Diastole of
ventricles and atria
Heart Sounds
Valves opening and closing
(Aortic valve = semilunar
valve)
Aorta
Pressure decreasing during
atrial and ventricular
diastole.
Semi lunar valve is closed
Blood has left the ventricle
and the heart relaxes
Aorta
Atrial systole begins followed by
ventricular systole
Immediately the semi lunar valve
opens
Pressure increases rapidly as
blood enters the Aorta
Pressure reaches a maximum
point
At the end of ventricular systole
the semilunar valve closes and
pressure in Aorta decreases
Atrium and Ventricle
Pressure is low during
atrial and ventricular
diastole
Heart is relaxed
Atrioventricular valve is
open
Blood starts to fill atrium
and moves into ventrcle
Atrium and Ventricle
Pressure increases in
both atrium and
ventricle as blood fills
Atrium contracts to push
blood into ventricle
Atrioventricular valve
closes and pressure in
atrium decreases
Atrium and Ventricle
Rapid increase in pressure
in ventricle as it contracts
As the pressure rises, the
semilunar valve opens
Pressure has reached a
maximum and blood is
pumped out of ventricle
and into aorta
Atrium and Ventricle
Semilunar valve closes and
pressure in ventricle
decreases rapidly
Blood slowly fills atrium
Atrioventricular valve opens
and blood continues to fill
the atrium and now the
ventricle
Atrium contracts and the
cycle starts again
Defibrillator
No/reduced bloody supply to the heart = cardiac
arrest
Heart tissues deprived of oxygen
Causes ventricular fibrillation = twitching of muscle
cells in ventricles
Defibrillators detect if this is happening
Then used to restore rhythm to the heart
Paddles must be placed diagonally across the heart
Applications:
Use of defibrillation to treat life-threatening cardiac conditions
Heart Beat
Caused by valves snapping shut
Atrioventricular valves closing = lub
Semilunar valves closing = dub
Stethoscopes invented in 19th century
Doctors used to place ears on patients chest before
Difficulty with female or obese patients
Now a lot easier and non invasive
Understanding:
- Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flor
Nature of science:
Developments in scientific research followed improvements in apparatus or instrumentation: the invention of the stethoscope led to improved
knowledge of the workings of the heart
ECG machine
ELECTROCARDIOGRAM
Use the ECG machine to measure your heart rate
under the following different conditions
•
•
•
•
•
•
Exercise
Relaxation
Lying down
Holding your breathe
Fast breathing
Facial immersion in water (OPTIONAL!!)
Skills:
Measurement and interpretation of the heart rate under different conditions
Blood Pressure
Measuring blood pressure
Pressure on artery walls by circulating blood
Higher number = ventricular systole pressure
Lower number = ventricular diastole pressure
Many different blood pressure machines
Take your blood pressure!
Skills:
Interpretation of systolic and diastolic blood pressure measurements
Review Topic 6
The heart is myogenic
Sinoatrial node initiates
and sets pace for heart
beat
Atrial systole
Ventricular systole
Diastole
SA node
Uniquely structured
cardiac cells
Initiate action potential
without stimulation by
other nerves
Contractions spread
rapidly across atrium
Understanding:
- Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
Cardiac Muscle
Cardiac muscle is unique
Striated appearance
Understanding:
- Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
Cardiac Muscle
Y shaped cells
Joined end to end in complex network of
interconnected cells
Gap junctions called intercalated discs
Provide channels of connected
cytoplasm between cells
Allows rapid movement of ions
Very fast wave of depolarization
Understanding:
- Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
Cardiac Cycle
Signals pass from SA node to
atrioventricular node.
Passes down to Bundle of His
Moves down left and right
bundle branches to the apex of
the heart
Down to the Purkinje fibres
Causes the ventricles to contract
at apex
Understanding:
- Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
Purkinje Fibres
Able to conduct signal at
high speed
- Large diameter of cells
- Many Na+ channels
- Many mitochondria
Understanding:
- Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
- Conducting fibres ensure coordinated contraction of the entire ventricle wall
Cardiac Cycle
Delay needed between nodes
Ensures staggering of
contractions
Atria empty first before
ventricles contract
AV node has many features
delaying the contractions of the
ventricles
Understanding:
- There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
- This delay allows time for atrial systole before the atrioventricular valves close
AV node
o Smaller cell diameter
o Reduced number of Na+ channels
o Fewer gap junctions between cells
Slower conduction overall compared to SA node
Understanding:
- There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
- This delay allows time for atrial systole before the atrioventricular valves close
ECG machine
ELECTROCARDIOGRAM
Use the ECG machine detect the electrical signals in
your heart
P wave: Atrial systole
QRS complex: Ventricular systole
T wave: Ventricular diastole
Doctors use this to see if your heart pattern is normal
Able to detect fibrillations
Skills:
Mapping of the cardiac cycle to a normal ECG trace
Hypertension and thrombosis
Revisit atherosclerosis – what is it?
Then answer the following questions
- What is thrombosis?
- What is hypertension?
- What causes each of these?
- What are the consequences?
- How do the factors on the right affect
thrombosis and/or hypertension?
Applications:
Causes and consequences of hypertension and thrombosis
Height
Genetics
Age
Gender
Smoking
Diet
Exercise