Download Topic D.4 Heart - Cougar science rocks!

U: Structure of Cardiac muscle cells allows
propagation of stimuli through the heart wall
Comparison to skeletal muscle:
Similarities: striated, long fibers
Differences:
• Shorter & wider
• Y-shaped cells
• one nucleus per cell
• Intercalated discs = junction between cells
• Under INvoluntary control
Cardiac cells contract as if one large cell
• Y-shaped cells and Intercalated discs allow
physical connection
• Gap junctions allow electrical connection –
(channels of connected cytoplasm between cells)
• Both allow rapid movement of ions & a wave of
depolarization to pass easily from cell to cell
• Both allow synchronization of muscle contraction
• Network of cells contract as if it was 1 large cell
Identify…
• Cardiac muscle fibers
• Orange & blue
• Mitochondria
• Red
• One sarcomere
• Between narrow dark blue lines
• Intercalated disc
• Wavy dark blue line
U: Signals from the sinoatrial node that cause
contraction cannot pass directly from atria to ventricles
Cardiac cycle = one complete heart beat
Systole = contraction of heart
Diastole = relaxation of heart/filling of blood
Cardiac Cycle animation
The Pacemaker
SA node = sinoatrial node = “pacemaker”
oCollection of cells that spontaneously initiate action
potentials without stimulation by other nerves
oGap junctions allow electric charges to flow freely
between cells, so spreads rapidly across atrium
SA node AV node  AV Bundle  Purkinje fibers
(NOTE: AV bundle a.k.a. Bundle of His)
SA node  AV node AV bundle  Purkinje fibers
Pressure changes inside heart
U: There is a delay between the arrival and passing on of
a stimulus at the atrioventricular node.
Delay of ~0.12 s
Features of AV node that cause delay:
• Smaller fibers
• Fewer Na+ channels
• Fewer gap junctions
• More non-conductive connective tissue
U: This delay allows time for atrial systole before
the atrioventricular valves close
• Delay allows time for atria to empty blood into ventricles before ventricles contract.
• Once ventricles contract, AV valves snap shut.
• If no delay, AV valves would close too early & not enough blood would go into
ventricles!
U: Conducting fibres ensure coordinated
contraction of the entire ventricle wall
Once through AV bundle, signal conducted rapidly
to coordinate contraction of ventricles
Contraction of ventricles begins at the apex.
Features of Purkinje fibers allowing fast
signal:
• Fewer myofibrils
• Bigger diameter
• More Na+ channels
• Lots of mitochondria and glycogen stores
Signal conduction through heart animation
NOS: Developments in scientific research followed improvements in
apparatus or instrumentation: invention of stethoscope led to improved
knowledge of the workings of the heart.
Stethoscope = tool for listening to heart &
lungs, and to check blood pressure
Invented by Rene Laennec, 1816
History of stethoscope
First tool allowing for non-invasive investigation
of internal anatomy (e.g. abnormal heartbeats)
Why was there a need? Before stethoscopes,
doctors placed ear directly on chest…
• If patient obese, can’t hear heartbeat
• Bathing was not social norm… gross!
• Female patients… ‘nuf said
Evolution of the stethoscope!
New Visual Stethoscope
records heart sounds for 10 seconds
U:Normal heart sounds are caused by AV valves and semilunar valves
closing, causing changes in blood flow
Normal heart beat = 2 sounds
LUB = closing of AV valves
DUB = closing of semilunar valves
Skill: Measurement & interpretation of heart rate under different conditions
Variables that can influence heart rate:
Types of exercise
Intensity of exercise
Recovery from exercise
Relaxation
Body position
Breathing and breath holding
Exposure to a cold stimulus
Facial immersion in water
Ways to take a pulse
DBQ p688 Cold Exposure & Heart Rate
Answers:
1. 89 BEATS MIN-1
2. 83 - 89 /89 × 100% = 6.7% DECLINE
3. decline is small/data is variable; experiment limited: face or total exposure might have
a more profound reduction/greater time of exposure might have an effect; data is
inconclusive
APP: Use of artificial pacemakers to regulate heart rate.
Purpose: maintain rhythm of heart beat
How it maintains rhythm:
• Constantly
• Only when heartbeat is missed
Why needed?
• SA node not working
• Block in signal pathway
How it works?
• Ventricle stimulated with low voltage pulse
• Atria and ventricles stimulated
ARTIFICIAL PACEMAKER
SKILL: Mapping of cardiac cycle to a normal electrocardiogram (ECG) trace
P wave = atrial systole (contract)
QRS wave = ventricular systole
(contract)
T wave = ventricular diastole (relax)
Analysis of EKGs:
 Lengths of intervals between waves
 Height of R wave
 Overall pattern compared before/after
exercise or different positions of body
APP: Use of defibrillation to treat life-threatening cardiac
conditions.
Ventricle fibrillation = twitching of
ventricles due to rapid and chaotic
contraction of individual muscle cells
Consequence: heart can’t pump any
blood, cardiac arrest
Defibrillator = device that discharges
electrical current to restore normal heart
rhythm
Note: Can begin with ventricle tachycardia
(“v-tach”) = fast heart rhythm
APP: Causes & consequences of hypertension &
thrombosis
Atherosclerosis = hardening of
arteries caused by formation of plaques
(atheromas) on inside
Plaque = debris (fat, cholesterol)
Clot = thrombosis = RBCs caught up in
the plaque
Can lead to hypertension (high BP)
Consequences of thrombosis:
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Blockage of blood flow
Myocardial infarction (heart attack)
Consequences of hypertension:
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Narrow & stiff arteries
Aneurysm = bulging of weak artery (can burst and
cause internal bleeding)
Stroke due to blood vessels in brain narrowing,
clotting, rupturing, leaking
Kidney failure due to damage to arteries leading to
kidney & damage to glomerulus
Risk factors for thrombosis and hypertension
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GENETICS
AGING
POST-MENOPAUSE (DROP IN ESTROGEN) – ESTROGEN MAY KEEP BLOOD VESSELS FLEXIBLE
MALES (LOW ESTROGEN)
SMOKING (RAISES BP)
HIGH-SALT DIET
ALCOHOL
STRESS
HIGH-SATURATED FAT AND CHOLESTEROL DIET
HEIGHT
SKILL: Interpretation of systolic & diastolic blood pressure measurements
Blood pressure = arterial pressure
Ventricular systole/ventricular diastole
Normal = 120/80 mm Hg
High = 140/90 (only one has to be high)
Pre-eclampsia = high bp during pregnancy
SKILL: Analysis of epidemiological data relating to the incidence of
coronary heart disease
Epidemiology = study of spread of
disease through a population
CHD = coronary heart disease
= damage to heart as result of
reduced blood supply to heart tissue
• Often caused by narrowing & hardening of
coronary artery
• Groups that may differ in CHD risk: ethnic,
gender, age, physical activity, genetics,
medical history
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ROGER VL, GO, AS, LLOYD-JONES DM, ET AL. HEART DISEASE AND STROKE STATISTICS—2012
UPDATE: A REPORT FROM THE AMERICAN HEART ASSOCIATION. CIRCULATION.2012:E2-E220.
HOW TO TAKE BLOOD PRESSURE
EPIDEMIOLOGY OF CHD
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NATIONAL HEALTH AND NUTRITION EXAMINATION SURVEY: 2009–2012.