The heart and cardiac muscle

Question 1

Where are the base and apex of the heart found?

Answer 1

Base is at top, apex is at bottom

Question 2

What is the pericardium?

Answer 2

Covers heart; protects heart by providing lubrication during its constant movement; enveloped pericardia fluid

Question 3

Which side of the heart is thicker, and what does this indicate?

Answer 3

Left, as it pumps blood around the systolic system, whilst right pumps blood around pulmonary system

Question 4

What is the function of the vena cava (inferior and superior)?

Answer 4

Carry blood from the body to the heart; supplies deoxygenated blood to the right atrium

Question 5

What is the function of the pulmonary artery?

Answer 5

Carry deoxygenated blood to the lungs

Question 6

What is the function of the pulmonary veins?

Answer 6

Carry blood from the lungs; supplies oxygenated blood to the left atrium

Question 7

What is the function of the aorta?

Answer 7

Carry blood to the body; supplies oxygenated blood

Question 8

Which valve separates the right chambers?

Answer 8

Tricuspid valve; has three cusps

Question 9

Which valve separates the left chambers?

Answer 9

Mitral valve; has two cusps

Question 10

What are the names of the valves separating the ventricles from the arteries?

Answer 10

Pulmonary and aortic valves

Question 11

What is the difference between the atrioventricular and semilunar valves?

Answer 11

Semilunar valves are stronger and more rigid

Question 12

What feature prevents prolapse of the valves?

Answer 12

The papillary valves ensure valves shut but do not prolapse

Question 13

What is the purpose of the valves within the heart?

Answer 13

Prevent backflow

Question 14

How is cardiac muscle similar to skeletal muscle?

Answer 14

Striated; SR is a source of Ca ions; have t-tubules

Question 15

How is cardiac muscle different to skeletal muscle?

Answer 15

Wider and shorter cells; mononucleate, centrally located; no attachments; less and smaller SR; less t-tubules; extracellular fluid a source of Ca2+; highly oxidative; more capillaries; muscle fibres lengthen when relaxed due to heart chambers filling

Question 16

How is cardiac muscle similar to smooth muscle?

Answer 16

Is involuntary

Question 17

Why can cardiac muscle not undergo tetanic contraction?

Answer 17

Prolonged duration of L-type Ca2+ channel current = prolonged ap = sarcolemma remains refractory for the duration of the twitch

Question 18

What is the purpose of cardiac muscle not undergoing tetanic contraction?

Answer 18

Allows heart to be oscillating pump and alternate between being relaxed and contracting (filling and ejecting)

Question 19

Outline the signal propagation in cardiac muscle?

Answer 19

SAN originated electrical current; electric current spreads by intercalated discs; contraction of muscle cells dependent on extracellular Ca2+; L-type v-gated Ca2+ channels (modified dihydropyridine receptors) open in t-tubules by depolarisation of membrane; Ca2+ enters cell from outside; trigger Ca2+ binds to ryanodine receptors on SR membrane; ryanodine receptor Ca2+ channel open; Ca2+ from SR into cytosol; cytosolic Ca2+ increased; enables muscle contraction; Ca2+-ATPase pumps within SR membrane sarcolemma and Na2+/Ca2+ transporters return Ca2+ to SR and extracellular fluid

Question 20

How is force of cardiac cell contraction graded?

Answer 20

Graded with Ca2+ levels