Lecture 26 10/19/23 Flashcards
What does each cardiomyocyte contain?
bundles of myofibrils enclosed by the sarcolemma
Why do myofibrils have a striated appearance?
repeated pattern of sarcomeres
What are sarcomeres?
functional units of myocardial contraction
What are the characteristics of sarcomeres?
-bounded by Z lines
-actin and myosin filaments form A and I bands
-contraction pulls Z bands together and shortens muscle
What are the functionally important proteins in a sarcomere?
-actin
-myosin
-tropomyosin
-troponin
What are cytoskeletal proteins important for?
force transmission
What three molecules make up the troponin complex?
-troponin-I
-troponin-C
-troponin-T
What are the characteristics of the sarcoplasmic reticulum and T tubule structure?
-surrounds contractile elements
-T-system open to extracellular environment
-tubules extend into cells to increase sarcolemma surface area
-SR stores intracellular calcium
What initiates contraction?
Ca2+ binding to troponin-C
What structure connects individual myocytes?
intercalated discs
What happens in excitation-reaction coupling?
-Ca2+ binds troponin-C
-tropomyosin-actin complex undergoes conformational change
-myosin can now bind to actin
What is the function of ATP?
provides the energy needed for myosin head to move and shorten myofibril
What impacts the contractility/velocity of shortening?
intracellular calcium concentration
What is calcium-induced calcium release?
small amount of calcium enters cell and triggers release of larger quantity from SR
What are the general steps of excitation-contraction coupling?
-AP and Ca influx
-Ca-induced Ca release
-Ca binding troponin
-actin-myosin interaction
-removal of cytosolic Ca
What are the characteristics of the mechanical activity of the heart?
-initiated by electrical activity
-cyclic
What is systole?
contraction
What is diastole?
filling
What are the phases of the cardiac cycle?
-early diastolic filling
-diastasis
-atrial contraction
-isovolumic contraction
-AV valve closure/S1
-ejection
-semilunar valve closure/S2
-isovolumic relaxation
What do S1 and S2 mark?
the beginning and end of systole
Which sound is AV valve closure/S1?
the lub
Which sound is semilunar valve closure/S2?
the dub
What does pressure in the CV system depend on?
-anatomical site
-phase of the cardiac cycle?
What is preload?
the force that stretches the muscle prior to contraction
How is preload approximated?
end-diastolic volume or wall stress
How does preload impact contraction?
increased preload = increased force of contraction
What is afterload?
forces that oppose myocardial shortening (velocity and extent)
How is afterload approximated?
wall stress
What is contractility?
-load-independent potential to do work
-intrinsic strength of the myocardium
How does contractility impact stroke volume?
increased contractility = increased stroke volume
What is the length-tension relationship?
stretch optimizes actin-myosin interaction
What is diastolic function?
ability of ventricle to fill at low pressure
What does diastolic function depend on?
myocardial relaxation
-ventricular compliance
What is compliance?
volume/pressure relationship
