1-Striated Muscle Cardiac

Question 1

development sequence

Answer 1

1. pluripotent stem cells
2. mesoderm/mesenchymal cells
3. myogenic progenitor cells
4. cardiomyocyte via transcription factors and epigenetic regulation
5. embryonic cardiomyocytes
6. fetal cardiomyocytes
7. neonatal
8. adult

Question 2

cardiac muscle cell

characteristics

Answer 2

• aggregate but not fuse like skeletal cells but still repeating format
  -smaller than skeletal
  -branched
  -one or two nuclei
  adjacents are connected by intercalated discs

Question 3

intercalated disc components

Answer 3

desmosomes + fascia adherens

gap junctions facilitate spread of ions so coordinated contraction (syncytium)

Question 4

layers of CT

Answer 4

1. basement membrane
2. endomysium
3. perimysium
4. epimysium

Question 5

sarcomeric structure

Answer 5

1. bounded by z discs/lines
2. thick myosin filaments interact with thin actin
3. titin span 1/2 sarcomere from M to Z line
4. costameres @ z discs link cytoskeleton to basal lamina

same as skeletal

Question 6

causes of heart failure

Answer 6

-highest percentage is from dilated cardiomyopathy aka muscle pathology

from familial mutations of cardiac genes for dystrophin, actin, myosin, desmosomal proteins, titin

Question 7

remodeling in heart disease

Answer 7

long term mechanical stress from high arterial pressure or ischemic =
-inc size of myocytes
-activation of myofibroblasts to inc secretion of ECM to promote fibrosis
-change mechanical properties of heart

aka heart becomes fibrotic and hypertrophic

Question 8

renin-angiotensin system

Answer 8

another way to inc ECM and become fibrotic

from chronic activation of innate mechanisms /endogenous hormonal signaling

activation = inc angiotensin II > TGF beta and CT growth factor pathways activate > fibroblast differentiate to myofibros and inc deposition of ECM

Question 9

action potential transmission

Answer 9

og @ SA node then propogate to cardiac muscle cells rapidly via gap junctions

Question 10

neurotransmission

calcium induced calcium release

Answer 10

1. T tubules transmit AP from suface of cardiac muscle cell
2. depolarization = open voltage gated calcium channels, L type
3. influx of extracellular Ca into cell
4. Ca binds ryanodine receptor RYR on membrane of SR
5. conformational change in RYR so release Ca from inside SR

Question 11

Calcium in SR

Answer 11

bound by calsequestrin @ region adj to RYR by junctin and triadin proteins

come back by pumps (SERCA, Na/Ca exchanger)

Question 12

modulating force

Answer 12

inc force = inc length of muscle prior to contraction

either by inc Ca sensitivity or titin helps inc muscle tension

helps inc amount of blood pumping

Question 13

catecholamines

Answer 13

aka epinephrine or norepinephrine = inc calcium release and force production

bind to beta-adrenorecptors > adenylate cyclase > inc cAMP > activate PKA > phosphorylate LTCC and RYR to enhance CICR

or PKA can relax muscle by phos proteins that reg calcium reuptake

Question 14

muscarinic agonists

Answer 14

aka acetylcholine have oppo effect of catecholamines

Gi mechanism so inhibits adenylate cyclase and dec phos of phospholamban, troponin I, RYR, voltage gate calcium channels

Question 15

metabolic characteristics

Answer 15

ATP from oxidation of fatty acids (beta) and TCA cycle/oxidative phosphorylation

majority of acetyl CoA from beta oxidation and rest from lactate/pyruvate oxidation

creatine phosphate important for actin-myosin interactions bc rapidly regenerates ATP from ADP