autonomic control of the cardiovascular system Flashcards
control of CVS
- extrinsic: neurohumoral control
- intrinsic: mechanosensitivity autocrine
mean arterial pressure
slides
mechanism
Activation of neurons in the CVS occurs by multiple processes.
convergence- one neuron influenced by many
divergence- many neutrons influenced by one neuron
excitatory and inhibitory potentials
Excitatory and inhibitory potentials occur during activation of single
neural inputs.
Excitatory Post-Synaptic
Potential (EPSP)
Depolarizes the target neuron
Inhibitory Post-Synaptic
Potential (IPSP)
Hyperpolarizes the target
neuron
heart rate regulation
Autonomic nervous system primary controller of heart rate
* Both divisions (sympathetic and parasympathetic) influence
sinoatrial node activity
sympathetic pathway (heart rate regulation)
- Response to stimulation begins slowly, as:
(i) nerve terminals slowly release norepinephrine
(ii) downstream effects mediated by relatively slow second
messenger system involving production of cAMP - Response decays gradually, as nerve terminals take
up only ~70% of released norepinephrine, with
remainder carried away by blood
parasympathetic pathway (heart rate regulation)
- Rapid response to stimulation, as:
(i) nerve terminals rapidly release acetylcholine
(ii) downstream effects mediated by specialised
acetylcholine-regulated K+ channels directly coupled to
muscarinic receptors to which acetylcholine binds - Rapid decay, as SA and AV nodes rich in cholinesterase, an
enzyme that quickly hydrolyses acetylcholine - Rapid response and decay allow beat-by-beat control of SA
and AV node function
resting heart rate
Resting rate determined primarily by parasympathetic activity
* Parasympathetic effects stronger than sympathetic effects
stroke volume regulation
Stroke volume determined by:
Contractility:
- Regulated by sympathetic and parasympathetic activity
- Sympathetic activity: Increases stroke volume by
increasing magnitude and rate of force generation
(as well as rate of relaxation)
reflex regulation of blood pressure
Arterial Baroreceptors:
- Stretch receptors in the carotid sinuses and the aortic arch
- Stretch increases receptor firing, inhibiting sympathetic
outflow from pressor region (depressor effect)
arteries
- Systemic arteries have thick walls with three layers:
- Intima: Single layer of endothelial cells acting as a
metabolically active barrier between blood and vessel wall - Media: Thickest layer, composed of elastin (elasticity),
collagen (strength), and vascular smooth muscle
(contraction) - Adventitia: Layer of connective tissue containing nerves,
lymphatics and blood supply to vessel wall
arterioles
Arterioles regulate rate and distribution of blood flow
* Composed of endothelium and smooth muscle, arranged in
rings around the vessel, allowing large changes in vessel
diameter (vasoconstriction or vasodilation)
- Arterioles regulate rate and distribution of blood flow
- Under dual control: intrinsic (local conditions surrounding the
blood vessels) and extrinsic (nervous system input)
extrinsic control of blood flow
- Two sources of extrinsic (nervous system) control of flow:
(i) Sympathetic Regulation
(ii) Hormonal Regulation
sympathetic regulation (extrinsic control of blood flow)
- Under similar control as blood pressure
through regions in cerebral medulla
that influence vessel tone - Stimulation of pressor region
causes sympathetic outflow,
resulting in vasoconstriction - Stimulation of depressor region
causes inhibition of pressor region,
resulting in vasodilation - cerebral medulla influences vessel tone
- influenced by neural impulses and by blood concentration of carbon dioxide and oxygen
sympathetic regulation of vessels
- Sympathetic nerve terminal releases neurotransmitters,
neuropeptides, and other molecules which act on the
vascular smooth muscle cells and to cause vasoconstriction
or vasodilation
signalling molecules and response in sympathetic regulation
Norephinephrine (NE) –vasoconstriction
ATP —vasoconstriction
Neuropeptide Y —-vasoconstriction
Vasoactive intestinal peptide (VIP)—- vasodilation
Nitric Oxide —-vasodilation
hormonal regulation (extrinsic control of blood flow)
- Two sources of extrinsic (nervous system) control of flow:
(ii) Hormonal Regulation - Epinephrine / norepinephrine released by the adrenal
medulla influences arteriole tone - Low epinephrine concentration dilates arterioles
(-adrenergic), high concentration constricts arterioles
(-adrenergic), while norepinephrine only causes constriction
balance of intrinsic/extrinsic control
Dual control of peripheral vessels allows direction of blood flow
to areas with greatest need
- In some tissue effects fixed, in others balance is adjusted based
on activity:
a) In brain and heart (vital structures with limited tolerance for
reduced blood flow), intrinsic mechanisms are dominant
b) In skin (important for homeostasis), extrinsic vascular
control is dominant
c) In skeletal muscle (in which there can be large changes in
metabolic activity), intrinsic and extrinsic mechanisms
interact, allowing tuned response to changes in activity
ageing
Ageing alters function of parasympathetic and sympathetic inputs to the
intracardiac nervous system.
Changes in cardiac function with ageing occur as a result of tissue and
cellular-level changes.
pathological conditions
Pathological conditions result in a changes in both neuronal
and myocardial tissue functions.
Pathological disruption of cardiac function often results in predictable
physiological changes.
