Cardiac Muscle Structure & Function Flashcards Preview

CVPR: CV Unit I > Cardiac Muscle Structure & Function > Flashcards

Flashcards in Cardiac Muscle Structure & Function Deck (15):
1

Composition of contractile protein

-myosin: 2 heavy chains, 4 light chains
-actin: similar to skeletal muscle actin; binds tropomyosin and troponin
-thin filament regulatory proteins:
i. TN-C: one Ca2+ binding site
ii. TH-I: N-terminal regulated by phosporylation (PK sites)
iii. TN-T: Isoforms are developmentally & pathologically regulated
iv. TM: only alpha isoform

2

Cardiac muscle structure

-interconnected mono-nucleated cells w/in collagen
-cells w/large number of myofibrils
-majority of cell volume=mitochondria
-cells coupled both electrically and mechanically

3

Regulation of calcium flow w/in muscle cells

1. depolarization --> L-type channels open --> calcium influx
2. calcium influx --> calcium release from SR via ryanodine receptors (CICR)
3. calcium binding to TN-C triggers contraction
4. calcium removed by SR Ca2+-ATPase

4

Cross-bridge cycle of cardiac muscle contraction

-@ rest: low intracell Ca2+ --> TN-TM complex inhibits actin-myosin combination
-increase myoplasmic Ca2+: TN releases inhibition, moves TM out of actin groove, myosin binds --> myosin head undergoes power stroke --> myofilaments shorten

5

Cardiac output=

Stroke volume x heart rate

6

Regulators of stroke volume

-pre-load
-afterload
-contractility

7

Molecular mechanism of length-tension relationship

xxx

8

Pre-load effects on stroke volume

-based on length-tension relationship -->
-stimulating contraction at low lengths (i.e. when heart chamber is empty) generates less tension when stimulated at increased muscle lengths (i.e. when heart chambers are full)

9

Afterload effects on stroke volume

-related to aortic (systemic) pressure
-pressure ventricles need to generate to eject blood from chamber
-inverse relationship between shortening velocity and afterload

10

Contractility definition/effects on stroke volume

-force w/which heart contracts
-regulated by norepinerphine
-"ionotropes" (positive or negative) change contractility

11

Frank-Starling Law

-stroke volume of heart increases in response to an increase in the volume of blood filling the heart (=end diastolic volume)
-i.e. increase in pre-load = increase in stroke volume

12

Factors that may contribute to Starlings Law

1. Cardiac titin isoform is very stiff
2. Ca2+-sensitivity of myofilaments increases as sarcomeres are stretched
3. closer lattice spacing: stretched sarcomeres have altered spacing between actin and myosin

13

Hypertrophy impact on cardiac muscle

1. cell growth:
i. concentric
ii. upregulation of fetal gene program
2. changes in contractility (mainly calcium sensitivity)

14

Dilation impact on cardiac muscle

1. cell growth:
i. eccentric
ii. upregulation of fetal gene program
2. changes in contractility: changes in force output (maximal)

15

Mechanism of changes in contractility

1. translational changes:
i. sarcomeric proteins (upregulation of fetal proteins)
ii. changes in signaling proteins
2. post-translational changes of sarcomeric proteins