Regulation of cardiovascular system - Part 1 

 

Importance of CVS regulation

1.    Exercise – increase blood supply to active tissue (muscles) by redistributing the blood

2.    To maintain adequate blood flow to vital argan (the heart and brain). In the face of challenges such as hemorrhage

3.    Increase or decrease the heart loss from body by redistribution of blood

·       Resistance vessels

            The wall of the arterioles contain less elastic tissue that the arteries but proportionately more smooth muscle. The muscle is extensively noradrenergic nerve fibers (constrictor). The arterioles offer considerable resistance to the flow of blood and are known as the resistance vessels.

·       Capacitance vessels

The wall of veins are easily distended and can expand to hold more blood without

much increase in intravascular pressure. Therefore, they are known as capacitance vessels. They are innervated, and their smooth muscle can contract in response to noradrenergic stimulation, pushing blood into the heart.

 

CVS – Regulation

 

·       Circulatory adjustments or cardiovascular functions can be regulated by altering the,

1.    Output of the pump (the heart)

2.    Changing the diameter of the resistance vessels (primarily the arterioles)

Vasoconstriction and Vasodilation

3.    Altering the amount of blood pooled in the capacitance vessels (the veins)

Venoconstriction and Venodilation

·       Circulatory adjustments are brought about by altering the,

1.    Output of the pump (the heart)

       By changing the cardiac output

2.    The caliber of the arterioles is regulated by,

-        The presence of autoregulation

-        Vasoregulation substances produced by endothelial cells

-        Circulating vasoactive hormones

 

      Systemic Regulation

-        Neural regulation

-        Chemical regulation

                 ( Through regulation of both cardiac output and vasculatures diameter)

 

Systemic regulation by the nervous system

-        Short term responses to changes in volume and pressure

-        Long term responses to changes in volume and pressure

 

·       Neural control of cardiovascular system

-        Most of blood vessels receive autonomic innervation

1.    Mostly from the sympathetic system that results in vasoconstriction

-        The nerve innervations to the heart resistance vessels regulates tissue blood flow and arterial pressure

-        Innervations to the venous capacitance vessels change the volume of blood “stored” in the veins

-        Splanchnic veins are well innervated when compared with the innervation of most other veins (redistribution of blood from splanchnic area)

-        The brain stem send excitability impulses to CVS (to increase blood pressure)

-        The brain stem receives inhibitory impulses from sensory receptors in the wall of blood vessels / cardiac chambers (eg – baroreceptors)

-        Thus, baroreceptors reflex help to regulate the blood pressure by altering the activity of sympathetic and parasympathetic innervations to the heart and blood vessels.

Sympathetic innervation of the heart

            Norepinephrine from postganglionic sympathetic nerves activates adrenoreceptors in the heart on

-        the sinoatrial (SA) node

-        atrioventricular (AV) node

-        his – purkinje conductive tissue

-        atrial and ventricular contractive tissue

The sympathetic stimulation will leads to increase in hear rate (positive chronotropy) , and force of contraction (positive inotropy)

                        Parasympathetic innervation of the heart

      The parasympathetic through release of acetylcholine from postganglionic parasympathetic (vagus) nerves activates nicotinic receptors on SA and AV nodes and cardiac muscle. Heart rate and contractility are reduced.