Mechanical and Electrical Properties of the Heart and Cardiomyocyte Biology Flashcards
What types of muscle is the heart composed of?
Atrial, ventricular, and specialised excitatory and conductive fibres. The cells forming these types of muscle fibres are called cardiomyocytes
Describe some properties of different types of cardiomyocytes
Atrial and ventricular cardiomyocytes are connected in parallel, so that they can contract in a synchronised manner. Excitatory and conductive cardiomyocytes show weak contraction but generate and conduct electrical impulses controlling heartbeat.
Describe the structure of a cardiomyocyte
Rectangular shaped segmented cells about 100uM long and 15uM wide. They are joined at their ends by intercalated discs which contain gap junctions that allow ion exchange - important for synchronising contraction. Each cell contains myofibrils of actin and myosin. The cells are organised into sarcomeres.
Describe the action potential of a cardiomyocyte
Phase 0 - Depolarisation: Na channels open and Na floods in. At threshold, about -40mV, there’s an opening of more Na channels, and more flooding in.
Phase 1 - Na channels close at positive charge, and K channels open, allowing K out
Phase 2 - Ca channels open, allowing Ca in and K is still going out, allowing a lag phase. Ca causes contraction which is the lag phase
Phase 3 - Repolarisation - Ca channels close, K still going out.
Phase 4 -Resting potential.
Leaky K channels the whole time
Describe the intrinsic regulation of the heart beart
The signal starts in the SA node in RA, passes down to ventricles via the AV node which delays the signal so that the atria have time to contract and empty before he ventricles contract. The signal is then conducted through the walls of the ventricles so that they contract at the same time.
Describe the path that the wave of excitation takes through the heart
Impulse spreads from SAN through cardiac muscle of atria, causing almost simultaneous contraction. When the impulse reaches the AV node in the middle of the septum it is delayed so that the atria have time to fully empty (0.2s). AV node relays the impulse down the septum along the bundle of His (which splits into left bundle branch and right bundle branch) to the apex where the impulse travels up the walls of the ventricles so that they empty completely. The signal is transmitted along the walls via Purkinje fibres.
Describe extrinsic control of the heart beat
Comes from ANS which modifies and controls the intrinsic heartbeat. Parasympathetic innervation is via the vagus nerve which is dominant at rest. It slows down the intrinsic HR via acetylcholine. Sympathetic NS prepares the body for fight or flight (energy expenditure) via catecholamines (noradr and adr).
What is the cardiac cycle?
The sequence of events that occurs in one heartbeat - simultaneous contraction of the atria, followed by simultaneous contraction of the ventricles a fraction of a second later.
What is phase 1 of the cardiac cycle?
Systole - Ventricular contraction where blood is pumped into the arteries. Blood pressure always increases. AV valves close.
What is phase 2 of the cardiac cycle?
Diastole - Ventricular relaxation, during which the ventricles fill with blood
What are the differences between noradrenaline and adrenaline?
Receptors mainly in the cardiovascular system and it’s produced by the NS mainly, a neurotransmitter mainly
Produced by the NS and adrenal gland, receptors are spread out all over the body and it’s mainly a hormone. ie. it’s released into the bloodstream
How does the cardiovascular system react to hot temperatures?
Skin blood flow increases to about 50-70% of cardiac output (from 5-10%). Reduced blood flow to internal organs. HR goes up to increase blood delivery to skin. Cardiac output increases by about 60-70%. BP effects vary, usually go down abit.
What is the cardiovascular response to the cold plunge after a sauna?
Rapid peripheral vasoconstriction controlled by SNS, also an increase in systolic and diastolic BP, decreased HR and stroke volume
What is the normal adult blood volume? How much is withdrawn in a blood donation? How long does it take to replace the plasma in the blood following blood donation? How long to replace rbcs?
About 5L, and blood donation is about 450-500mL (1pint). 2-3 days. About 5 weeks.
What are the different reactions to the different stages of blood loss?
Stage 1 - 15% (750mL): Everything normal
Stage 2 - 15-30% (750mL - 1.5L): Increased diastolic BP, slight tachycardia, increased respiratory rate, anxiety, delayed capillary refill, less urine to conserve water
Stage 3 - 30-40% (1.5L - 2L): Systolic BP <100, tachycardia, tachypnea (rapid breathing), altered confused, sweating, less urine.
Stage 4 - >40% (over 2L): Systolic BP <70, extreme tachycardia >140 with weak pulse, extreme tachypnea, lethargy, coma, extreme sweating, no capillary refill or urine
How can blood donation help improve health?
Can help metabolic syndrome - a collection of symptoms associated with heart disease, stroke, diabetes. Could be accumulation of iron associated with hypertension and diabetes which oxidises in the blood. 2 blood withdrawals reduce bp and cardiovascular disease, cholesterol levels improves, reducation in viscosity, and iron content.
