Structure of Cardiac muscle cells allows propagation of stimuli through the heart wall Comparison to skeletal muscle Similarities striated long fibers Differences Shorter amp wider Yshaped cells ID: 785092
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Slide1
The Heart
Option D.4
Slide2U:
Structure of Cardiac muscle cells allows propagation of stimuli through the heart wall
Comparison to skeletal muscle:
Similarities
: striated, long fibersDifferences: Shorter & widerY-shaped cellsone nucleus per cellIntercalated discs = junction between cellsUnder INvoluntary control
Slide3Cardiac cells contract as if one large cell
Y-shaped cells
and
Intercalated discs
allow physical connectionGap 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 cellBoth allow synchronization of muscle contractionNetwork of cells contract as if it was 1 large cell
Slide4Identify…
Cardiac muscle fibers
Orange
&
blueMitochondriaRedOne sarcomereBetween narrow dark blue linesIntercalated discWavy dark blue line
Slide5U: S
ignals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
Cardiac cycle
= one complete heart beat
Systole = contraction of heartDiastole = relaxation of heart/filling of blood
Slide6Cardiac Cycle animation
Slide7The Pacemaker
SA node
= sinoatrial node = “pacemaker”
Collection of cells that spontaneously initiate action potentials without stimulation by other nerves
Gap junctions allow electric charges to flow freely between cells, so spreads rapidly across atriumSA node AV node AV Bundle Purkinje fibers
(NOTE
: AV bundle a.k.a. Bundle of
His)
Slide8SA node
AV node AV bundle Purkinje fibers
Slide9Pressure changes inside heart
Slide10U: 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 fibersFewer Na+ channelsFewer gap junctionsMore non-conductive connective tissue
Slide11U: 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!
Slide12U: 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 myofibrilsBigger diameterMore Na+ channelsLots of mitochondria and glycogen storesSignal conduction through heart animation
Slide13NOS
:
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 pressureInvented by Rene Laennec, 1816History of stethoscopeFirst 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 heartbeatBathing was not social norm… gross!
Female patients… ‘
nuf
said
Slide14Evolution of the stethoscope!
Slide15N
ew Visual Stethoscope
records heart sounds for 10 seconds
Slide16U:
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 valvesDUB = closing of semilunar valves
Slide17Skill:
Measurement & interpretation of heart rate under different conditions
Variables that can influence heart rate:
Types of exercise
Intensity of exerciseRecovery from exerciseRelaxationBody position Breathing and breath holdingExposure to a cold stimulusFacial immersion in water
Slide18W
ays to take a pulse
Slide19DBQ
p688
Cold Exposure & Heart Rate
Answers:
89 beats min-1 83 - 89 /89 × 100% = 6.7% declinedecline 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
Slide20APP:
Use of artificial pacemakers to regulate heart rate.
Purpose
: maintain rhythm of heart beat
How it maintains rhythm:ConstantlyOnly when heartbeat is missed Why needed?SA node not workingBlock in signal pathwayHow it works? Ventricle stimulated with low voltage pulseAtria and ventricles stimulated
Slide21Artificial pacemaker
Slide22SKILL:
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 wavesHeight of R wave
Overall pattern compared before/after exercise or different positions of body
Slide23Slide24APP:
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 arrestDefibrillator = device that discharges electrical current to restore normal heart rhythmNote: Can begin with ventricle tachycardia (“v-tach”) = fast heart rhythm
Slide25Slide26APP:
Causes & consequences of hypertension & thrombosis
Atherosclerosis
= hardening of arteries caused by formation of plaques (
atheromas) on insidePlaque = debris (fat, cholesterol)Clot = thrombosis = RBCs caught up in the plaqueCan lead to hypertension (high BP)
Consequences of thrombosis:
Blockage of blood flow
Myocardial infarction (heart attack)
Consequences of hypertension:
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
Slide27Risk factors for thrombosis and hypertension
Genetics
Aging
Post-menopause (drop in estrogen) – estrogen may keep blood vessels flexible
Males (low estrogen)Smoking (raises BP)High-salt dietAlcoholStressHigh-saturated fat and cholesterol dietheight
Slide28SKILL:
Interpretation of systolic & diastolic blood pressure measurements
Blood pressure
= arterial pressure
Ventricular systole/ventricular diastoleNormal = 120/80 mm HgHigh = 140/90 (only one has to be high)Pre-eclampsia = high bp during pregnancy
Slide29Slide30SKILL:
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 tissueOften caused by narrowing & hardening of coronary arteryGroups that may differ in CHD risk: ethnic, gender, age, physical activity, genetics, medical historyRoger 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.
Slide31How to take Blood pressure
Slide32Epidemiology of CHD
National Health and Nutrition Examination Survey: 2009–2012.