Heart Flashcards
Structure of the heart
4 chambers
- Striated actin and myosin
- Small sized cells
- Branching interconnections between cells
- Single central nucleus
- intercalated discs – interlocking membranes of adjacent myocytes to allow simultaneous contraction and prevent separation during stress of contraction.
- Between each cardiac muscle is a gap junctions allow AP to pass between adjacent muscles to depolarise
Function-syncytium
muscular pump
auto-rhythmic beating involuntary and continuously
2 independent interconnecting network of
each syncytium contracts as unit
(The Atria contract as one unit & the ventricles)
one muscle cells stimulated the whole syncitium to contracts
syncitia are electrically insulated to prevent simultaneous contraction
- SA node pacemaker frequency of contractions
- SA node responds to Autonomic nervous system control altering HR and force of contraction
Cardiac muscle
short in length
branched
conected by intercalated disc which allow simultaneous contraction
intercalated disc holds myocytes together, allow electrical contraction
gap junctions alllow AP to pass between adjacent muscle fibres
striated actin and myosin-internal ultrastructure of highly organized contractile myofilaments.
arrhythmic muscle fibers interlock
heart beats continually
Contract from apex upwards forcing blood into arteries through pulmonary and aortic valves.
located in the myocardium layer of the walls of the atria and ventricles
The SAnode
pacemaker
conduction system
contractile
resting membrane potential of -90mV
AP in adjacent fibres passes via agap junction and opens the sodium ian channels
rapid influx of sodium fibres
depolarisation
action potential
last longer than AP skeletal muscles resulting in a plateau
sodium is pumped out
calcium ions slowly enter cell balancing loss of sodium ions
balancing the membrane potential at 0mV
potassium ions remain in cells
therefore repolaristation cant occue
slow calcium ion channels close
potassium ion channel open potassium leave cells
resting potential restored -90mmV
repolorised
Refractory period
time between two contraction
longer than skeletal muscle
longer than the contraction itself
fibres are in relaxation before ext contraction can occur allowing maxium pumping action of cardiac muscle
Coordination
effective pump requires coordinated contraction
chambers of heart need to contract in sequence
Sino-atrial node is a pace makever
responsible for auto-rythmity
inherat rate of 100 AP per minures
vagus nerve conducts impulses from parasymphatic and sympathetic nervous system
slowed to 75 APs per minute
SA node sets HR by depolarization of the atria
inter-nodal pathway between the SA node and the AV node
Conduction
FROM AP TO PURKENJE
each AP causes contraction of atria
atria are electricallly insulated from ventricle
AP reached AV node and enter AV bundle of HIS
AV node delays impulse for few 1/100th of a second
allows atria contraction to fill ventricle
AP passes along septum into purkinje fibres
conduction of purkinje fibres is 6x faster than ventricular muscle fibres
Conducting system
network of spezialised tissue that stimulae contraction
modified cardiac myocytes
contract with no innervation
Clinical application
SA node disease pr damage allows AV node to take over at 40-60bpm
both AV and SA nodes suprresed ventrivles will beat at 20-30bpm
insufficient blood to brain requires pacemaker
ECG
Recording of electrical activity within heart
i.e. the initiation of every heart beat
electrical activity is detected by electrodes placed on the skin
Atrial fibrillation
irregular and often abnormally fast heart rate
caffeine
increase HR by increasing rate of despolirisation of SA node
nicotine
increase HR by stimulating the activity of neurones the innervate the heart by sympathetic neurotransmission.
Cardiac Output
Cardiac output-(mil/min) =HR (bpm) x stroke volume (ml)
Stroke Volume
Stroke volume is the amount of blood ejected from the ventricle in each pump affected by end-diastole volume (preload) and end diastole volume (afterload). This is influence by the size of the cardiac muscle, contractility duration of contraction (determined by HR) these factor are affected by age, gender, and lifestyle.
Heart rate
Heart rate is controlled by the autonomic nervous system through activation of the Parasympathetic and sympathetic system. Sympathetic system accelerates heart rate through the release of hormones, the parasympathetic nervous system by the vagus nerve to counteract the effects of the sympathetic nervous system
Blood pressure
Cardiac output (SV x HR) x Total Peripheral resistance
BP during aerobic exercise
steep initial rise, linear relationship with intensity and time
BP after exercse
Cardiac output decreases before vasodilation occurs resuling in low peripheral resistance so low BP
structure and pathway
Right Atrium: receives blood from systemic circulation via the superior and inferior venae cavae.
Superior vena cava returns blood to the right atrium from the head, neck, upper limbs and chest.
Inferior vena cava returns blood from the rest of the trunk, the viscera and lower limbs.
Right Ventricle: receives blood from the right atria via the right AV (tricuspid) valve. Blood leaves the right ventricle via the pulmonary semilunar valve and enters into the pulmonary trunk and on to the right and left pulmonary artery. Blood from here will them travel to the lungs.
Left Atrium: receives oxygenated blood returning from the lungs via the pulmonary veins. The left AV bicuspid or mitral valve is found at the entrance from the left atrium to the left ventricle.
Left Ventricle: is much larger than the right ventricle. Thick muscular walls designed to push blood into the systemic circulation.
Blood leaves the left ventricle through the aortic valve and goes into the ascending aorta. Blood then flows through the aortic arch and into the descending aorta
