how does the heart work? Flashcards
At the level of the myocyte and myofibril, _____ are key determinants of contractile performance
calcium handling and calcium sensitivity
How do we think about cardiac muscle physiology?
- Force – calcium relationships
- Frank-Starling relationships
- PV loops
Integrated cardiac performance
Force
- calcium relationships
Biochemical interactions - Highlights calcium regulation and biochemistry
Frank-Starling relationships
- Intact muscle physiology
2. Highlights length tension relationships
PV loops
Integrated cardiac performance
Mechanisms by which the heart moderates its performance
throughout the day include:
- Length dependent activation (Frank-Starling effects)
- Enhanced contractility,
- enhanced chronotropy.
The effect of increasing preload on force of contraction:
- the greater the volume of blood entering the heart during diastole (end-diastolic volume),
- the greater the volume of blood ejected during systolic contraction (stroke volume) and vice versa.
So, how does increasing preload affect cardiac performance?
- This is the basis of the Frank-Starling law of the heart.
- The Frank-Starling law of the heart describes the effect of increasing preload on the force of contraction.
- the greater the volume of blood entering the heart during diastole, the greater the volume of blood ejected during contraction.
- due to increase the fiber length, the force of contraction for a given stimulus is increased.
phosphorylation of Ca channels (SA node cells) will cause
- ↑ Heart rate
2. Improved CO
Phosphorylation of Ca channels
(ventricular cells)
will cause
- ↑ Ca entry
- ↑ Force of contraction
- improved ejection fraction (+ inotropy)
Phosphorylation of Na pump
will cause
- ↑ Ca efflux (via Na-Ca exchange)
2. enhanced relaxation and diastolic filling
Phosphorylation of Phospholamban
will cause
- Disinhibition of SR calcium pump (SERCA2)
- Increased SR calcium load
- improved diastolic filling
Phosphorylation of FKB
will cause
- Enhances Ryr receptor mediated calcium release
3. enhanced contractility
Phosphorylation of troponin I
will result in
- ↓ Ca affinity for TnC
2. enhanced relaxation
How do we get through the day?!?!
- postural accomodation
- isotonic (exercise: cardio)
- isometric (weight training)
postural accomodation
- Venous pump: skeletal musculature
- Increase venous return
- Increased EDV → increased SV
isotonic
- Decrease peripheral vascular resistance
- Increase venous return (Frank-Starling)
- Increase heart rate
- Increase inotropy
Isometric (weight training)
- Increased peripheral vascular resistance (maintain blood flow to exercising muscle group)
- Increased HR
- No increase (or decrease) in CO
What happens acutely during a heart attack?
- Loss of functional myocardium
- Increased catecholamine surge
- Increased inotropy to maintain CO despite increase BP (afterload)
- Heterogeneous cellular environment
Increased catecholamine surge symptoms are
Sweating, tachycardia, ± hypertension
Heterogeneous cellular environment symptoms are
- Local /regional changes in pH
- change in membrane potential
- secondary effect on cytosolic calcium
Ca regulated by
phospholamban and serca 2a pump.
Phospholamban
- typically inhibitits the pump
- Ryanodine receptor is how ca gets out.
- A little leaks out then a lot flows out of the SR
which part of myosin has ATPase activity?
head of myosin
muscle shortening is an ATP dependent process
