oblique (contract from bottom up)

circumferential (contract toward center)

Why can the left ventricle create much more pressure than the right ventricle?

Using Laplace's law, explain what happens in a pressure overload or concentric hypertrophy?

The radius of the chamber increases, and this will cause a pressure decrease. Although the chamber can accomadate more blood, the chamber cannot generate enough pressure to pump blood out.

• soft, wide
• supported by papillary muscles attached to leaflets of valve via chordae tendinae
• low pressure valves (since they are supported by muscle to prevent prolapse into atria as they are closed during systole)

• narrow, rubbery, sturdy
• high pressure valves (they can withstand major pressure differences)

epicardium

myocardium

endocardium

CT

fat

CT

endothelial cells

• connected mechanically and electrically via gap junctions to form cardiac scynctium (work as team so if one fails, the other can pick up)
• if in ventricle, binucleated cells
• volume
  • most of it is myofibrils
  • rest is mitochondria
• the cells are individual, not fused

fibroblasts

endothelial cells

adipocytes

Describe refractory period of myoctyes and their purpose

It is not needed, but myoctyes can be modulated by external hormones. This will allow it to be "auto-adjustable"

• Myocyte made of myofibrils
• myofibrils made of thin and thick filaments

For the contraction of cardiac myocytes, where is the calcium coming from?

1. carries wave of depolarization inside cells
2. triggers release of calcium from SR

Differences btw skeletal and cardiac contractrion

• Dihydropyridine receptor has no link to ryanodine receptor

1. AP travels down T tublules
2. this will cause opening of dihydropyridine receptors located on T tubules to open
3. these receptors release calcium into vicinity of ryanodyne receptors
4. cause ryanodyne receptors to open and release calcium into cell
5. calcium bind to troponin and expose myosin binding sites on actin
6. to relax, calcium is put back into SR via SERCA

• if phosphorylated, it will relieve its inhibitory action on SERCA (acts as beta agonist to increase calcium uptake which increases rate of relaxation)

define preload and synonym in heart function

• aka end diastolic volume
• extent muscle is stretche before onset of contraction

• aka aortic pressure
• load lifted by muscle in isotonic contraction

Describe the relation between pressure and volume in systole curve/active curve

increase in pressure within heart cause increase in volume until there is so much pressure the heart will rupture because the actin and myosin are pulled apart to the point where they cannot form cross bridges

it will provide equality of right and left cardiac outputs

recruitment of motor units

increase frequency of nerve impulses

In cardiac muscle, how to you increase strength of contraction?

• increase amplitude and/or duration of caclium transient
• increase preload (more blood in heart) and only to the optimal stretch (maximize crossbridge formation)

Define and give examples of positive inotropes

• interventions which increase contractility
• examples: norepi., digitoxin

• interventions that decrease contractility
• ex: calcium channel blockers, ACh

1. act on beta adrenergic receptors
2. receptors linked to Gs protein that activates adenylate cyclase
3. this increase cAMP
4. increase PKA which leads to phosphorylating dihydropyridine receptors and phospholamban

1. activate muscarinic receptors
2. activate Gi proteins that block adenylate cyclase

1. inhibit Na/K pump
2. this will increase cytosolic sodium, diminishing sodium gradient that could slow Na, Ca exhange
3. cytoplasmic calcium increases, leading to enahnced SR load and improved contractility

• degree of overlap between actin myosin
• amount of calcium available