Regulation of stroke volume and heart rate Flashcards
how to increase heart rate
Tachycardia
- sympathetic system
- Release of adrenaline from sympathetic fibres
- release of noradrenaline from adrenal medulla
- acts of B1 receptors of SA node
- increases slope of pacemaker potential
How to decrease heart rate
Bradycardia
- Parasympaththetic
- release of ACH from vagus nerve
- acts of muscarinic receptors of SA node
- decrease slope of pacemaker potential
how to increase stroke volume
1-Neural
- release of adrenaline from sympathetic fibres
-release of noradrenaline from adrenal medulla
-act on B1 receptors of myocetes
-increases contractility-longer and shorter
2-increase preload
3-decrease afterload
How to decrease stroke volume
1- neural- parasympathetic has little effect
2-decrease preload
3-increase afterload
what is pre-load
- how far the muscle can stretch before contraction
- depends on sarcomere length- cannot be measured
- EDV measured
- when venous returns increase= EDV increases so stroke volume increases
what is afterload
the pressure the heart has to combat to release blood
-Total peripheral resistance: Aortic pressure
the greater the A.P., less energy is available for stroke volume as more used to overcome this
-Amount of blood being pushed out of ventricles
Pathologies of control
Hypercalcemia: increases stroke volume per given EDV- shifts curve up and left
Hypocalcemia
Barbituates
Ischemia- reduced blood flow to the heart
How to increase cardiac output
1-Electric fibrillation:
-temporarily increases C.o. by increasing heart rate
-S.V. falls as the E.D.V. decreases (cuts rapid filling phase)
-C.O. then falls
2-increase H.R. BY METHODS LISTED
3-increase S.V. BY METHODS LISTED
Starlings law
The energy of contraction of the muscle is dependant on the initial length of the cardiac muscle- the greater the length, the greater the tension
How to increase pre-load
- Skeletal muscle pump
- Respiratory pump
- Venocontriction
