Heart

Question 1

Structure of the heart

Answer 1

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

Question 2

Function-syncytium

Answer 2

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

Question 3

Cardiac muscle

Answer 3

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

Question 4

The SAnode

Answer 4

pacemaker

conduction system

Question 5

contractile

Answer 5

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

Question 6

action potential

Answer 6

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

Question 7

Refractory period

Answer 7

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

Question 8

Coordination

Answer 8

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

Question 9

Conduction

FROM AP TO PURKENJE

Answer 9

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

Question 10

Conducting system

Answer 10

network of spezialised tissue that stimulae contraction
modified cardiac myocytes
contract with no innervation

Question 11

Clinical application

Answer 11

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

Question 12

ECG

Answer 12

Recording of electrical activity within heart
i.e. the initiation of every heart beat

electrical activity is detected by electrodes placed on the skin

Question 13

Atrial fibrillation

Answer 13

irregular and often abnormally fast heart rate

Question 14

caffeine

Answer 14

increase HR by increasing rate of despolirisation of SA node

Question 15

nicotine

Answer 15

increase HR by stimulating the activity of neurones the innervate the heart by sympathetic neurotransmission.

Question 16

Cardiac Output

Answer 16

Cardiac output-(mil/min) =HR (bpm) x stroke volume (ml)

Question 17

Stroke Volume

Answer 17

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.

Question 18

Heart rate

Answer 18

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

Question 19

Blood pressure

Answer 19

Cardiac output (SV x HR) x Total Peripheral resistance

Question 20

BP during aerobic exercise

Answer 20

steep initial rise, linear relationship with intensity and time

Question 21

BP after exercse

Answer 21

Cardiac output decreases before vasodilation occurs resuling in low peripheral resistance so low BP

Question 22

structure and pathway

Answer 22

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