Lecture 26 10/19/23

Question 1

What does each cardiomyocyte contain?

Answer 1

bundles of myofibrils enclosed by the sarcolemma

Question 2

Why do myofibrils have a striated appearance?

Answer 2

repeated pattern of sarcomeres

Question 3

What are sarcomeres?

Answer 3

functional units of myocardial contraction

Question 4

What are the characteristics of sarcomeres?

Answer 4

-bounded by Z lines
-actin and myosin filaments form A and I bands
-contraction pulls Z bands together and shortens muscle

Question 5

What are the functionally important proteins in a sarcomere?

Answer 5

-actin
-myosin
-tropomyosin
-troponin

Question 6

What are cytoskeletal proteins important for?

Answer 6

force transmission

Question 7

What three molecules make up the troponin complex?

Answer 7

-troponin-I
-troponin-C
-troponin-T

Question 8

What are the characteristics of the sarcoplasmic reticulum and T tubule structure?

Answer 8

-surrounds contractile elements
-T-system open to extracellular environment
-tubules extend into cells to increase sarcolemma surface area
-SR stores intracellular calcium

Question 9

What initiates contraction?

Answer 9

Ca2+ binding to troponin-C

Question 10

What structure connects individual myocytes?

Answer 10

intercalated discs

Question 11

What happens in excitation-reaction coupling?

Answer 11

-Ca2+ binds troponin-C
-tropomyosin-actin complex undergoes conformational change
-myosin can now bind to actin

Question 12

What is the function of ATP?

Answer 12

provides the energy needed for myosin head to move and shorten myofibril

Question 13

What impacts the contractility/velocity of shortening?

Answer 13

intracellular calcium concentration

Question 14

What is calcium-induced calcium release?

Answer 14

small amount of calcium enters cell and triggers release of larger quantity from SR

Question 15

What are the general steps of excitation-contraction coupling?

Answer 15

-AP and Ca influx
-Ca-induced Ca release
-Ca binding troponin
-actin-myosin interaction
-removal of cytosolic Ca

Question 16

What are the characteristics of the mechanical activity of the heart?

Answer 16

-initiated by electrical activity
-cyclic

Question 17

What is systole?

Answer 17

contraction

Question 18

What is diastole?

Answer 18

filling

Question 19

What are the phases of the cardiac cycle?

Answer 19

-early diastolic filling
-diastasis
-atrial contraction
-isovolumic contraction
-AV valve closure/S1
-ejection
-semilunar valve closure/S2
-isovolumic relaxation

Question 20

What do S1 and S2 mark?

Answer 20

the beginning and end of systole

Question 21

Which sound is AV valve closure/S1?

Answer 21

the lub

Question 22

Which sound is semilunar valve closure/S2?

Answer 22

the dub

Question 23

What does pressure in the CV system depend on?

Answer 23

-anatomical site
-phase of the cardiac cycle?

Question 24

What is preload?

Answer 24

the force that stretches the muscle prior to contraction

Question 25

How is preload approximated?

Answer 25

end-diastolic volume or wall stress

Question 26

How does preload impact contraction?

Answer 26

increased preload = increased force of contraction

Question 27

What is afterload?

Answer 27

forces that oppose myocardial shortening (velocity and extent)

Question 28

How is afterload approximated?

Answer 28

wall stress

Question 29

What is contractility?

Answer 29

-load-independent potential to do work
-intrinsic strength of the myocardium

Question 30

How does contractility impact stroke volume?

Answer 30

increased contractility = increased stroke volume

Question 31

What is the length-tension relationship?

Answer 31

stretch optimizes actin-myosin interaction

Question 32

What is diastolic function?

Answer 32

ability of ventricle to fill at low pressure

Question 33

What does diastolic function depend on?

Answer 33

myocardial relaxation
-ventricular compliance

Question 34

What is compliance?

Answer 34

volume/pressure relationship