Neurohumoral regulation of the vascular system
Neurohumoral regulation of the vascular system
- Signals from the receptors cause the autonomic nervous system and endocrine response.
- The main homeostatic goal in cardiovascular regulation is to maintain adequate blood pressure.
Information about blood pressures provide many receptors: - Carotid sinus baroreceptors
- The renal juxtaglomerular apparatus receptors
- Pressure baroreceptors in the venous system and cardiac atria
Carotid sinus baroreceptors provide momentary feedback about arterial blood pressure. They cause the sinocarotid reflex.
The sinocarotid reflex
Afferent nerve impulses are carried from the carotid sinus nerve to the brainstem. Increased stretch of the carotid sinus, caused by a rise in blood pressure or pulse pressure, increases the action potential frequency in the carotid sinus nerve. In the medulla oblongata, this input increases inhibition of sympathetic outflow and stimulates parasympathetic outflow. The opposite occurs when BP or pulse pressure decreases and carotid sinus stretch is reduced.
The sinocarotid (baroreceptor) reflex
The adequacy of the baroreceptor reflex can be assessed by the tilt-table test (or head up tilt test), when a patient is moved from a supine to a standing position while blood pressure and HR are being monitored. The change of body position in space changes the direction of Earth gravity vector to the body that leads to redistribution of blood: the blood supply of organs above the heart level decreases (decentralization of blood circulation). This relative deficiency of blood circulation changes sinocarotid baroreceptors and it is should be balanced out by activation of sympathetic effects: heart rate increases, blood pressure rises due to vasoconstriction. As a result, the blood flow in brain and in the heart comes to the normal state.
The renal juxtaglomerular apparatus senses effective circulating blood volume and regulates the blood pressure by Renin.
- The primary site of cardiovascular control within the central nervous system is the medulla oblongata.
- In the medulla oblongata and in the lateral horns of the spinal cord are centers of sympathetic and parasympathetic system.
Parasympathetic (vagal) fibers innervate the SA and AV nodes, the conduction pathways, and the cardiac myocytes. The principal neurotransmitter released is acetylcholine, which in most cases acts via the muscarinic (M2) receptors. The main cardiovascular effects of the parasympathetic nerves are to slow HR and conduction velocity and to reduce the force of atrial contraction. Parasympathetic (vagal) fibers don’t innervate vessels.
Extensive sympathetic innervation occurs in the heart and vasculature. The primary neurotransmitter released during sympathetic innervation is norepinephrine, which mediates responses through several different adrenergic receptors. There are α1-, α2-, β1-, β2, β3- receptors.
Receptor
Localization
Activation most from…
Effects
α1
Arterioles
Norepinephrine
Smooth muscle contraction, mydriasis, vasoconstriction in the skin, viscera’s sphincter contraction of the Gastrointestinal tract and urinary bladder.
α2
Presynaptic receptors
Epinephrine
Smooth muscle mixed effects, norepinephrine (noradrenaline) inhibition, Cardiac muscle relaxation and platelet activation
β1
Heart
Norepinephrine
Increase the heart rate, conductivity and forse of contraction
β2
Bronchioles
Epinephrine
Smooth muscle relaxation (Ex. Bronchodilation)
β3
Adipose tissue
Norepinephrine
Enhance lipolysis, promotes relaxation of the bladder
Humoral regulation of cardiovascular system:
Information about blood pressures provide many receptors:
- Carotid sinus baroreceptors
- The renal juxtaglomerular apparatus receptors
- Pressure baroreceptors in the venous system and cardiac atria
Carotid sinus baroreceptors
provide momentary feedback about arterial blood pressure. They cause the sinocarotid reflex.
The sinocarotid reflex
Afferent nerve impulses are carried from the carotid sinus nerve to the brainstem. Increased stretch of the carotid sinus, caused by a rise in blood pressure or pulse pressure, increases the action potential frequency in the carotid sinus nerve. In the medulla oblongata, this input increases inhibition of sympathetic outflow and stimulates parasympathetic outflow.
The opposite occurs when BP or pulse pressure decreases and carotid sinus stretch is reduced.
The sinocarotid (baroreceptor) reflex
The adequacy of the baroreceptor reflex can be assessed by the tilt-table test (or head up tilt test), when a patient is moved from a supine to a standing position while blood pressure and HR are being monitored. The change of body position in space changes the direction of Earth gravity vector to the body that leads to redistribution of blood: the blood supply of organs above the heart level decreases (decentralization of blood circulation). This relative deficiency of blood circulation changes sinocarotid baroreceptors and it is should be balanced out by activation of sympathetic effects: heart rate increases, blood pressure rises due to vasoconstriction. As a result, the blood flow in brain and in the heart comes to the normal state.
The renal juxtaglomerular apparatus senses effective circulating blood volume and regulates the blood pressure by Renin.
- The primary site of cardiovascular control within the central nervous system is the medulla oblongata.
- In the medulla oblongata and in the lateral horns of the spinal cord are centers of sympathetic and parasympathetic system.
Parasympathetic (vagal) fibers innervate the SA and AV nodes, the conduction pathways, and the cardiac myocytes.
The principal neurotransmitter released is acetylcholine, which in most cases acts via the muscarinic (M2) receptors.
The main cardiovascular effects of the parasympathetic nerves are to slow HR and conduction velocity and to reduce the force of atrial contraction.
Parasympathetic (vagal) fibers don’t innervate vessels.
Extensive sympathetic innervation occurs in the heart and vasculature.
The primary neurotransmitter released during sympathetic innervation is norepinephrine, which mediates responses through several different adrenergic receptors. There are α1-, α2-, β1-, β2, β3- receptors.
Receptor | Localization | Activation most from… | Effects |
α1 | Arterioles | Norepinephrine | Smooth muscle contraction, mydriasis, vasoconstriction in the skin, viscera’s sphincter contraction of the Gastrointestinal tract and urinary bladder. |
α2 | Presynaptic receptors | Epinephrine | Smooth muscle mixed effects, norepinephrine (noradrenaline) inhibition, Cardiac muscle relaxation and platelet activation |
β1 | Heart | Norepinephrine | Increase the heart rate, conductivity and forse of contraction |
β2 | Bronchioles | Epinephrine | Smooth muscle relaxation (Ex. Bronchodilation) |
β3 | Adipose tissue | Norepinephrine | Enhance lipolysis, promotes relaxation of the bladder |
Humoral regulation of cardiovascular system:
