Homeometric regulation of the heart

Characteristics

• the ability to change the force of contraction of the cardiac muscle even with a constant length of cardiomyocytes

• does not depend on changes in sarcomere length
• affects inotropy (contractility)
• in contrast to heterometric control, more beats are required for the regulation to take effect
• the goal is to change cardiact output

Means of homeometric control

Sympathetic

• Positively chronotropic, inotropic, dromotropic and batmotropic effect

Parasympathetic

• Negatively chronotropic, inotropic, dromotropic and batmotropic effect

Potassium cations

• At elevated extracellular concentrations, there is a slow depolarization of the resting membrane potential (values closer to zero) and a concomitant inactivation of some sodium channels (thus preventing the action potential), , net effect is:

• the intensity of the action potential is reduced
• heart dilated, flaccid
• heart rate slows down
• in severe hyperkalaemia –up to blockage of impulse transmission through the atrioventricular bundle

Calcium cations

• opposite effect to potassium cations
• increased concentration gradually leads to spastic contraction (calcium cations initiate contraction)
• at reduced concentration - flaccidity

Bowditch (Treppe) effect

• see Bowditch effect

Temperature

• heat increases the permeability of the membrane to ions
• frequency

• Increased temperature significantly increases frequency
• reduced temperature significantly decreases frequency
• in near-death hypothermia (15-20 °C) frequency only a few beats per minute

• frequency only a few beats per minute

• force of contraction

• temporarily strengthened when the temperature rises, then the metabolic system is exhausted and the contraction is weakened

Links

Related articles

• Frank-Starling mechanism (heterometric regulation of the heart)

Used literature

• GUYTON, Arthur C. – HALL, John E. Textbook of Medical Physiology. 11. edition. Elsevier, 2006. ISBN 978-0-7216-0240-0.