Heart Physiology (05) Flashcards
Cardiac output (CO)
Amt of blood pumped by heart per min (typically refer to left ventricle)
CO=?
HR x SV
Cardiac reserve
Difference between co at rest and maximum CO
Intristic regulation
Results from normal functional characteristics, not on neural or hormonal regulation
Extrinsic regulation
Involves neural and hormonal control
Factors affecting stroke volume (3)
1.Preload 2. Afterload 3. Contractility
Preload
Amt of stretch of the ventricular walls before contraction
What determines EDV
Venous return
Afterload
The pressure the contracting ventricles must produce to overcome the pressure in the aorta
Contractility
The forcefulness of contraction of the ventricle muscle fibers (strength of contraction), controlled by inotropic agents
Positive inotropic agents
(open Ca 2+ channels): SNS: cardiac accelerator nerves: neurotransmitter – Norepinephrine (NE); hormones from adrenal medulla (Epinephrine/NE)
Negative inotropic agents
drugs: calcium channel blockers and beta blockers
Factors regulating heart rate
- Autonomic nervous system
- Hormones
- Ions
- Age
- Gender
- Physical fitness
- Temperature
Parasympathetic nerve stimulation
- Vagus nerve: ↓ heart rate
- neurotransmitter acetylcholine (Ach) hyperpolarizes the heart (more K+ channels open, takes longer to reach threshold)
Sympathetic nerve stimulation
- Cardiac accelerator nerves: ↑ heart rate (& contractility)
- NE released at SA/AV nodes (also coronary vessels & myocardium) (opens Ca 2+ channels)
Hormonal Control (SNS)
- Epinephrine & NE from the adrenal medulla.
- Occurs in response to increased physical activity, emotional excitement, stress. Slower, but lasts longer
Effect of blood pressure
- Baroreceptors monitor blood pressure (sensory neurons)
- Internal carotid arteries and aorta (carotid and aortic bodies)
- Sensory information to centers in the medulla oblongata
Effect of pH, carbon dioxide, oxygen
- Chemoreceptors detect pH and CO 2 changes in the medulla oblongata
- Chemoreceptors also monitoring O 2 in carotid and aortic bodies
Effect of extracellular ion concentration
Excess or reduced extracellular K+ decreases heart rate
Effect of body temperature
Heart rate increases when body temperature increases, heart rate decreases when body temperature decreases
