REGULATORY MECHANISMS OF THE CARDIOVASCULAR SYSTEM, THE HEART and BLOOD PRESSURE, In PROGRESSHEART RATE
Cardiac muscle fibres are self-excitatory because of their electrical properties.

1. SA node - pace-making function. Initiates the electrical wave that passes through rest of system.

2. AV node - relays electrical activities to fibres linked to it. Capable of taking over pace-making fn. if SA node fails.

CardiacMuscle.gif


What is a syncytium
CONTORL MECHANISMS OF THE HEART
Cardiovascular centre situated in Medulla Oblongata

Responds to proprioceptors, chemoreceptors and baroreceptors.
Although regulation occurs by Autonomic Nervous System, some axons carried by Peripheral Nervous System

Cranial nerve X - Vagus carries parasympathetic axons that innervate the heart.

HeartAutonomicInnervation.jpg






Natural pace of SA node ~ 100 bpm ∴ has to be slowed down - accomplished through parasympathetic stimulation via Vagus nerve
Parasympathetic stimulation: acetylcholine - decreased HR (cholinergic effect)

Sympathetic stimulation: norepinephrine released (noradrenalin) - increased HR (adrenergic effect)


Other factors that influence heart rate
Hormones : noradrenaline - increases HR ; elevated resting HR = tachycardia
acetylcholine - decreases HR ; low resting HR = bradycardia

temperature - influences firing of SA node : faster with increased body temp.

slower with decreased body temp - cf. operations done in cold room.

age

exercise

drugs and other chemicals that enter the body



BLOOD PRESSURE
ARTERIAL PRESSURE

What is Blood Pressure : Definition:

Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood.


Values:...... 120 mmHg SBPb (systolic blood pressure) .............. 80mmHg DBP (diastolic blood pressure)

Difference 40 mmHg = Pulse pressure (PP)

Mean Arterial Pressure = DBP + PP/3
.............................. MAP = 80 + (40/3)
..........................................= 80 + 13
..........................................= 93 mmHg

Instruments: Baumanometer ; Sphygmomanometer

Baumanometer.jpgSphygmomanometer.jpg


FACTORS THAT INFLUENCE BLOOD PRESSURE:

Internal Factors/Physiologic and Anatomic

Size of blood vessels - Natural Vasoconstriction & dilation , occlusions, stenosis,
Renin-Angiotensin


Blood volume - Hypervolemia, Hypovolemia - solutes and colloids play major role
ADH ; aldosterone

Viscosity of the blood - solutes and colloids play a major role

Venous return - physical activity, posture , oedema , etc.

External (introduced) Factors
alcohol
smoking
side effects of certain medications


CONTROL OF BP [flow diagram - p 730 in Marieb 2004 sixth edition]

Normal/Natural

Long Term Mechanisms
Renal mechanisms alter blood volume and concentrations of solutes to retain BP over long periods. This would involve some of the above chemicals


Neural Control: Shunting mechanism (cf. not doing strenuous exercise after heavy meal)

MAP - heart and brain will be supplied at expense of peripherals
Vasomotor Centre: Sympathetic nerves from T1 - L2 supply smooth muscle layer in bv.to maintain reasonable vasomotor tone. Responds to baroreceptors, chemoreceptors, other stimuli from centres in brain.

Short term mechanisms
Chemical controls:

Hormonal:

epinephrine : increase Cardiac Output and promotes

generalised vasoconstriction.


nor-epinephrine : vasoconstriction

[nicotine = strong vasocontrictor– LONG TERM]
Atrial Natriuretic Peptide - produced in atria = reduces blood volume& pressure by promoting

sodium and water loss via kidneys (cf. aldosterone = opposite effect)

- causes vasodilation —> further drop in pressure

ADH ( opposite to ANP) [Vasopressin]
Angiotensin II = powerful vasoconstrictor- raises blood pressure
Endothelim derived factors - endothelin most important - Ca++ entry into smooth muscle

contraction - vasoconstriction.
PDGF - prostaglandin derived growth factor - vasoconstrictor
Nitric Oxide (NO) - elicits secretion of acetyl choline, bradykinin and nitroglycerine.
Inflammatory chemicals - histamines, prostacyclin, kinins and other inflammatory response

chemicals —> vasodilators.


Taking a Pulse
Blood pressure and lie detection

CENTRAL VENOUS PRESSURE (CVP)

Venous pressure is significantly lower than arterial pressure. Before entering the heart, the pressure in the major veins is about 20 mmHg.
When the blood falls into the heart, it is not under any pressure as it runs through into the ventricles.

Central Venous Pressure is measured using a CVP-line, procedure as per pictures.

cvpline.jpgcvplinepatient.jpg







Blood pressure and lie detection