mechanical and electrical properties of the heart - cardiomyocyte biology

Question 1

what is the intrinsic system of the heart?

Answer 1

it’s its own system that maintains regular rhythmic contraction independently from the central nervous system.

Question 2

how many relay station does the electro-chemical circuit system of the heart have? and what are they?

Answer 2

4. sinoatrial (SA) node, atrial-ventricular (AV) node, bundle of HIS, purkinji fibres.

Question 3

what is the natural pace maker of the heart?

Answer 3

SA node.

Question 4

what does the extrinsic system do? and where does It come from?

Answer 4

modifies and control the intrinsic beating established by the heart. it comes from the autonomic nervous system (ANS).

Question 5

what are the two interacting system that the ANS consist of?

Answer 5

parasympathetic and sympathetic.

Question 6

what is the effect exerted by the sympathetic system on the heart? the parasympathetic system on the heart? the relation of these effects?

Answer 6

the sympathetic system accelerates the heart rate by releasing hormones (e.g. epinephrine, norepinephrine…) in fight or flight situations.
the parasympathetic system slows the heart rate by releasing acetylcholine.
the parasympathetic and sympathetic system exert antagonistic effects on the heart.

Question 7

what is the cardiac cycle?

Answer 7

simultaneous contraction of both atria, followed a fraction of a second later by the simultaneous contraction of both ventricles.

Question 8

the heart beat is divided in how many phases? what are they?

Answer 8

the heart beat is divided into 2 main phases. phase 1: systole: ventricular contraction when the blood is pumped into the arteries. phase 2: diastole: ventricular relaxation during which the ventricles fill with blood and the atrioventricular valves get closed.

Question 9

does the heart contract all at once?

Answer 9

no.

Question 10

what are the sequences of events during heart beat?

Answer 10

SA nodes initiate each beat, contraction of RA and LA almost simultaneously, impulse reaches AV node BUT delayed for 0.2s, AV node relays the impulse down the septum along the bundle of HIS, the ventricles contract simultaneously from the bottom upwards. ventricles empty completely.

Question 11

what are the two functions of the heart?

Answer 11

mechanical and electrical

Question 12

what is the normal resting heart rate? what can it reach during exercise?

Answer 12

normal heart rate: 60 to 80 b.p.m

during exercise: for athlete: 200 b.p.m/for others: 150 b.p.m