Neurohumeral Influences of the Heart Flashcards
Where is parasympathetic (cholinergic) control located?
Medulla oblongata (cardioinhibitory center)
How does parasympathetic stimulation get to the heart?
Via the vagus nerve and cardiac plexus
- innervates the SA node, AV node and sparsely innervates myocardium; releases Ach
What does parasympathetic (cholinergic) innervation to the heart do?
- slows rate and force of myocardial contraction
- decreases myocardial metabolism
- causes coronary artery vasoconstriction
Where is sympathetic (adrenergic) control for the heart located?
medulla oblongata, cardioacceleratroy center
How does sympathetic (adrenergic) innervation get to the heart?
-Via cord segments T1-T4, upper thoracic to superior cervical chain ganglia, innervates SA node, AV node, conduction pathways, and myocytes
- Releases epinephrine and norepinephrine
What does sympathetic stimulation to the heart do?
causes an increase in the rate and force of myocardial contraction and myocardial metabolism
- coronary artery vasodilation
What do skin and peripheral vasculature receive?
- only post ganglionic sympathetic innervation
- causes vasoconstriction of cutaneous arteries
- Sympathetic inhibition must occur for vasodilation
What drugs increase sympathetic functioning?
sympathomimetics
(alpha or beta agonists)
What drugs decrease sympathetic functioning?
sympatholytics
(alpha or beta antagonists or blockers)
What is the main mechanism controlling heart rate?
baroreceptors
Where are baroreceptors located?
in walls of aortic arch and carotid sinus
- function via vasomotor center
What do baroreceptors do?
- circulatory reflex: respond to changes in blood pressure
Baroreceptors response to increased BP
- parasympathetic stimulation
- decreased rate and force of cardiac contraction
- sympathetic inhibition
- decreased peripheral resistance
Baroreceptors response to decreased BP
- sympathetic stimulation
- increased HR and BP
- Vasoconstriction of peripheral blood vessels
What does increased right arterial pressure cause
reflex acceleration of heart rate
Where are chemoreceptors located?
in the carotid body
What are chemoreceptors sensitive to?
- changes in blood chemicals
- oxygen, carbon dioxide, and lactic acide
What chemical changes cause an increase in HR
Increased CO2
Decreased O2
Decreased pH/elevated lactic acid
What chemical changes cause a decrease in HR
- increase O2 levels
Increased body temp causes HR to…
increase
Decreased body temp causes HR to…
decrease
Hyperkalemia causes
- decreased rate and force of contraction
- widened PR interval and QRS
- tall T waves
Hypokalemia causes
- flattened T waves
- prolonged PR and QT intervals
- arrythmias
- may progress to ventricular fibrillation
Hypercalcemia causes
- increased heart actions
Hypocalcemia causes
- depressed heart actions
Hypermagnesemia is
- a calcium channel blocker which can lead to arrhythmias or cardiac arrest
Hypomagnesemia causes….
ventricular arrhythmias, coronary artery vasospasm, and sudden death
Increased peripheral resistance…
increases arterial blood volume and pressure
decreased peripheral resistance…
decreases arterial blood volume and pressure
what is peripheral resistance influenced by?
arterial blood volume (viscosity of blood and diameter of arterioles and capillaries)
