Lecture 2 - Cardiac Contracile elements

Question 1

List the 4 valves

Answer 1

Tricuspid (right atria –> right ventricle) bicuspid/mitral (left atria–> left ventricle), pulmonic and aortic valves

Question 2

Describe functions of chordae tendinae, papillary muscles, and annulus fibrosus

Answer 2

chordae tendinae/papillary muscles = hold valves shut to prevent backflux
annulus fibrosus - provide structure, electrically isolate atria and ventricles

Question 3

Describe the size of the cardiomyocyte

Answer 3

20 micrometers wide, 150 micrometers long

Question 4

What happens to cardiomyocytes in response to pressure and volume overload?

Answer 4

pressure overload (hypertension) greater width, more parallel contracile units
volume overload (anaerobic exercise, valve failure) some increase in length

Question 5

What are the different bands/zones of the sarcomere?

Answer 5

Z line = where actin attaches
M line = where myosin attaches
H zone = where there is no thin filaments
I band = where there are no thick filaments
A band = length of thick filaments

Question 6

Describe the interior of the cardiomyocyte

Answer 6

50% contractile elements
30% mitochondria - either intermyofibrillar or subsarcolemnal
mono/bi nucleated
golgi/ribosomes

Question 7

Describe coupling in the cardiomyocyte

Answer 7

longitudinal and diagonal coupling via branching
physical connection via macula adherens (desmosomes)
electrical connection via gap junction - 2 connexons, each made of 6 connexins

Question 8

What are the 2 accessory proteins in sarcomeres

Answer 8

titin = extends from M-line to Z-line, acts as spring, stabilizes position of contractile elements, returns muscle to resting length
nebulin = goes from z-line to end of actin filaments, aligns and regulates thin filament

Question 9

what are the different parts of troponin?

Answer 9

troponin I - inhibitory, gets phosphorylated in smooth muscle
troponin T - binds to tropomyosin
tropinin C - 4 sites (site 1 dysfunctional in cardiac muscle, site 2 where Ca binds, site 3 and 4 high affinity, always bound to Ca)

Question 10

how does Ca2+ initiate contraction?

Answer 10

Ca 2+ binds to TnC, causes TnI and tropomyosin to roll to expose myosin binding sites

Question 11

Describe the structure of the myosin

Answer 11

2 heavy chains, 2 light chains
heavy chains have head, hinge, tail, binding sites for ATP and actin
light chains can be either regulatory or alkali

Question 12

What do the different isoforms of myosin do?

Answer 12

change rate of ATP hydrolysis therefore change the rates of contraction