Cardiac Muscle Flashcards
Define CV disease and outline common types
Disease affecting the heart or blood vessels
CV disease- flow of blood to the heart is reduced/ stopped putting increased strain on heart–> angina–> heart attach (blood supply suddenly stopped- myocardial infarction)–> heart failure (unable to pump blood efficiently) and irreversible cell death of cardiac muscle
Stroke/ TIA (transient ischaemic attack)- blood floe to brain blocked- FAST
Diseases of arteries, arterioles or capillaries e.g. peripheral arterial disease, aortic disease (e.g. aortic aneurism)
Hypertrophic cardiomyopathy- congenital disease- thickening heart walls
Why is the heart called a dual circuit peristaltic pump?
Dual circuit= pipes of R and L contiguous (common border/ touching)
Peristaltic= operates in squeezing motion
What types of images can be achieved with an MRI
- Short axis- mis-ventricular section
- Long axis- oblique sagittal (through midline) plane
- Sinai magnetic resonance imaging- photos taken in quick succession to form video
Explain what structures can be seen from MRI
- Dominated by muscular wall of the left ventricle
- within left ventricle 2 black dots - papillary muscles
- Connected to the chordae tendineae and to the mitral valves
- Assist opening and closing of the mitral valve (left atrium to ventricle) in cardiac contraction
- White areas= blood so MRI distinguishes between fluid and solid masses (myocardium)
- Surrounding the 2nd white are= thinner myocardium of the right ventricle
Define terms inotropy and chronotropy
Inotropy- increased force of contraction
Chronotropy- increased frequency of contraction
Outline structure cardiac tissue
- Mononucleated
- Branched and connected via intercalated discs
- Fibres organised to max. electrical propagation through heart
- Fibres more vertical in inside and more transverse on outside
- Helical arrangement causes wringing motion of heart
How are cardiac cells adapted for synchronous electrical activity
- intercalated dics- desmosomes holding scaffolding of heart together and low resistance gap junctions improving electrical conductivity of heart
Explain what type of twitches are utilised in cardiac muscle
- synchronous, single twitches
- Electrical impulse form SAN- AVN, Purkinje fibres and other adaptations maximising and ensure simultaneous contraction
- Twitch contractions- due to a single electrical event the cell decreases In length
- Duration of twitch contraction similar to vesicular contraction
- These twitches summate in heart at a single point in time causing an increase in function i.e. causing contraction of heart
Explain how the action potential is propagated into the myocyte
- Cardiac AP propagated along the sarcolemma into the T- tubules
Explain differences in the twitches in cardiac and skeletal muscle and what causes this
- Cardiac muscle- depolarisation caused by single twitch,
- Further twitches prevented by plateau of action potential before full repolarisation
- Skeletal muscle- we gave a summation of twitches, more frequent so they fuse forming smooth tetanus
Explain how membrane potential changes in cardiac and skeletal muscle tissue? Why?
- Cardiac tissue: depolarisation (Na), then there is a platau (Ca), then repolarisation occurs (K)
- The plateau is due to an influx of Ca ions
- Due to opening of L- type Ca channels (long type Ca channels), which open more slowly than the Na channels
- Therefore there is a plateau as Ca enters cell
- Therefore cardiac action potentials are much longer than in muscle
Explain how Ca handling regulates cardiac contraction
- Some Ca channels on surface of cardiac tissue
- Open in response to an action potential
- Accounts for only 10-25% contraction
- Or Ca- induced Ca release
- T tubules are associated with structures called a diad- consist of L type Ca channels, ryanodine receptors and the terminal cisternae of the sarcoplasmic reticulum
- Action potential causes opening of L-type Ca channels causing Ca to flow into the cell down its concentration gradient
- The extracellular Ca binds to ryanodine receptors in induces endings of sarcoplasmic reticulum to release more Ca
- ATPase pumps more Ca into SR (75-90%) or expelled from cell via Na- Ca exchange (10-25%)
Outline differences in Ca handling between skeletal and cardiac muscle
- Skeletal muscle: Triads- 1 t-tubule has terminal cisternae on either side aka terminal cisternae- t-tubule- terminal cisternae
- More SR
- T-tubules: less lacier
- VS Cardiac- Diad- t-tubule associated with 1 terminal cisternae
- Less SR
- More lacier t-tubules
Explain how the Ca transient is key to many drug actions and give an example of a positive and negative inotrope
- Positive inotrope- increases force of contraction
- caffeine- acts on Ca release channels of sarcoplasmic reticulum
- more Ca release allows for more actin- myosin cross bridges to for so greater strength of contraction
- Negative inotrope- decreases force of contraction
- L-type Ca blockers- Verapamil
- Insufficiency of coronary flow caused by stenosis on coronary artery (narrowing of blood vessel): muscle contracting while producing too mush lactate (anaerobic respiration)–> angina (heart pain)
- Beneficial in angina (chest pain) as reduces energy demand reducing ischaemia and therefore chest pain
- Also blood pressure drug
How does digitalis work
- positive inotrope- like caffeine allows for more free cytosolic Ca being released from SR so more force
- Relieves symptoms of congestive heart failure
- Yet small therapeutic window as safe dose close to lethal dose
