Cardiovascular control mechanism

黃基礎

Introduction

• Control of blood volume and arterial pressure results in that all of the organs receive sufficient blood flow.

Central controller

Sensor Effector

Sensory nerve

Changes in BP

Sympathetic nerveParasympathetic n

Heart and arteriole

Circulatory control system

Sensors

• The animal body employs a variety of receptors for monitoring the status of the cardiovascular system.

• There are two main baroreceptors aortic baroreceptor via vagus nerve carotid baroreptor via sinus nerve

An increase in blood pressure stretches the wall of the carotid sinus, causing an increase in discharge frequency from the baroreceptors.

Chemoreceptors

Increase in CO2

Chemorecpeotr+

vasoconstriction

A rise in arterial pressure

Cardiac receptors• Atrial receptors

Increase in BPIncrease in

venous pressure

Increase in atrail filling

Stimulate the atrial receptors

Inhibition of ADH releaseLeasd to diuresis

Reduction in blood volume

Cardiac receptors• Atrial receptors

Increase in BPIncrease in

venous pressure

Increase in atrail filling

Strtch the the atrial wall

Cause atial myocytes to secrete ANP

Cause an increaseIn urine production

and sodium excretuib

Reduction in blood volume

ANP

_

ADH release

Renin release

Reduce CardiacOutput

Reduce BP

Antagonize the pressor effect of

angiotensin

Central nervous system

• Medullaray CV center 1. Pressor and depressor center 2. Cardioaccerator center 3. Cardioinhibitory center

Central nervous system

• Autonomic nervous system (ANS) 1. Sympathetic preganglionic fibers arise from cell bodies in the IML of the spinal cord of the thoracodorsal regions

• Autonomic nervous system (ANS) 2. The stellate ganglion supplies postganglionic sympathetic fibers to the heart 3. All of preganglionic sympathetic fibers are cholinergic but the postganglionic sympathetic fibers are adrenergic or cholinergic

• Parasympathetic nervous system

1. The primary effect of the parasym. n. s. on CV functionis to slow the heart rate.2. Impulses conducted by the vagus nerve affect the S-A node,A-V node and reduce artial contractivitility

Neural pathways for thr BP control

NTS: nucleus tractus of the solitarius

Medullary cardiovascular center

Control of microcirculation

• Capillary blood flow has to be adjusted to meet the demands of the tissue.

• Two control mechanisms 1. Neural control 2. Local control

Neural control of capillary blood flow

• Sympathetic stimulation and catcholamine

Stimulation of alpha receptors vasodilatation

Stimulation of beta receptors vasoconstriction

Vasoconstriction activated by -adrenergic receptors would override vasodilatation by -adrenergic receptors

• Neuropeptide Y 1. co-localized with norepinephrine within sympathetic ganglion and adrenergic nerve 2. nerve endings that surrounded the atrial and ventricular myocytes and the coronary arteries contain neuropeptide Y 3. NPY decrease coronary blood flow and the contraction of cardiac muscle by reducing the level of IP3

• Parasympathetic stimulation cause to vasodilation in arterioles

Local control of capillary blood flow

• Endothelium-produced compounds endothelium can produce NO, endothelin, and prostacyclin to affect the activity of the smooth muscle and hence, to regulate the capillary blood flow

Endothelium-derived relacing factor

(now known NO) cGMP Muscle

relaxation

Local control of capillary blood flow

• Endothelin can produce vasoconstriction prostacyclin can initiate vasodilation and act as an anticoagulant. Prostacyclin functions as an antagonist of the thromboxane A2 ,which promotes blood clotting and causes vasoconstriction. Influammators and other mediators thromboxane A2 cause vasoconstriction histamine and kinin produce vasodilatation

• Histamine, bradykinin, and serotonin cause an increase in capillary permeability

• Metabolic condition associated with activity decrease in O2, increase in CO2, and H+, a variety of metabolites (adenosine) , heart, rise in extracellular K+ , NO, prostacyclin all of the above substances produce vasodilation and a local increase in capillary blood flow.