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Pharos University in Alexandria (PUA)

Faculty of Pharmacy and Drug Manufacturing

Physiology II (PHR 273) – Spring 2017

CARDIOVASCULAR SYSTEM

(CVS)

(Lectures 1, 2 and 3)

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I- HEART

1- Properties of cardiac muscle.

2- Innervation of the heart.

3- Cardiac cycle.

4- Heart sounds.

5- Heart rate.

6- Cardiac output (COP).

II- CIRCULATION

1- Arterial blood pressure (ABP).

2- Coronary circulation.

3- Tissue fluid and edema.

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CARDIOVASCULAR SYSTEM (CVS)

INTRODUCTION

The cardiovascular system is composed of the heart which is principally a

pressure pump and a group of blood vessels which comprise arteries, arterioles,

capillaries, venules and veins. All such components of the circulatory system

contain liquid blood which is ever circulating throughout life.

The Heart is made up of two halves right and left, each half is made up of

an atrium and a ventricle with an atrio-ventricular (A-V valve) in between which

allows the blood to pass only in one direction, namely from the atrium to the

ventricle. The right heart receives the venous blood from the different tissues of the

body and pumps it into the pulmonary or "lesser" circulation where it becomes

arterialized. The left heart receives the arterial blood and pumps it to the systemic or

"greater" circulation to the different tissues where it is changes into venous blood,

which once more is returned to the right heart.

The valves of the heart

There are four sets of valves in the heart. The right atrioventricular opening

is guarded by Tricuspid valve (three cusps). The left opening by the Mitral or

bicuspid valve (two cusps). The openings of the aorta and pulmonary artery are

guarded by Semilunar valves (three cusps) aortic and pulmonary valves.

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I- THE HEART

I- PROPERTIES OF CARDIAC MUSCLE

1- Contractility:

a- Definition: it is the ability of cardiac muscle to contract and relax , thus acting

as a pump which can push blood into the blood vessels.

Contraction of the heart is called systole while its relaxation is called diastole.

b- Factors affecting cardiac contractility:

1- Initial length of cardiac muscle (Frank- Starling law).

The strength of cardiac contraction is directly proportional to the initial length of

its fibers (diastolic volume)

2- Autonomic supply (innervation).

Sympathetic stimulation increases the force of contraction while parasympathetic

supply (vagus) decreases the force of contraction of atria as the vagus does not

supply the ventricles.

3- Electrolytes (blood ions).

i- Blood calcium favors systole, so, excess calcium (hypercalcemia) prolongs the

period of systole and the heart may stop in spastic contraction called calcium

rigor.

ii- Blood potassium favors diastole , so, excess potassium (hyperkalemia) prolongs

the period of diastole and the heart becomes dilated and flaccid.

c- Inotropism: it means an influence on force of contraction of the heart

+ve inotropic factor: Increases force of contraction e.g sympathetic supply,

digitalis.

-ve inotropic factor: Decreases force of contraction e.g vagus nerve, toxins.

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2- Rhythmicity (automaticity)

a- Definition: it is the ability of cardiac muscle to beat at regular intervals.

b- Nature: it is myogenic i.e the heart can initiate its own rhythm without nerve

supply. The cardiac rhythm originated in sino-atrial node (SAN) in the right atrium

then conducted to atrio-ventricular node (AVN), then to atrio-ventricular bundle

(AVB) and finally to Pukinje fibers the terminates in the myocardium of the

ventricles.

c- The normal pace maker of the heart: is SAN because it has the highest rate of

discharge of cardiac impulses i.e highest rhythmicity.

d- Factors affecting rhythmicity:

1- Innervation of the heart: sympathetic supply increases rhythmicity of the

whole heart including ventricles while vagus nerve decreases rhythmicity of the

whole heart except ventricles.

2- Body temperature: increased body temperature about 1 0c increase heart rate

about 10-20 beat/min.

3- Reaction of the blood (PH): acidosis decreases heart rate whereas alkalosis

increases heart rate. Excessive acidosis or alkalosis stops the heart.

4- O2 supply: is essential for rhythmicity because the metabolism of the heart is

mainly aerobic.

e- Chronotropism : an influence on rhythmicity (heart rate).

+ve chronotropic factor: Increases heart rate as sympathetic supply.

-ve chronotropic factor: Decreases heart rate as vagal supply.

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3- Excitability:

a- Definition: it is the ability of cardiac muscle to respond to an adequate stimulus

by contraction.

b- Excitability changes of the heart:

Tetanus of the heart (maintained contraction) can not occur. This is important

because tetanus of the heart will stop its function as a pump and causes death.

Cardiac muscle can not be tetanized because of its long absolute refractory period

(ARP) during which the cardiac muscle does not respond to any stimulus

whatever its strength.

4- Conductivity:

a- Definition: it is the ability of cardiac muscle to transmit cardiac impulses that

originated in SAN to the rest of the heart.

b- The special conducting system of the heart:

These are tissues concerned with the formation and propagation of cardiac

impulse. It involves SAN, AVN, AVB and finally Purkinje fibers that end into the

ventricular wall.

c- The slowest conduction of impulses occurs at AVN to allow complete filling of

the ventricles.

d- The fastest conduction of impulses occurs at Purkinje fibers to allow

contraction of both ventricles at the same time.

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II- INNERVATION (NERVE SUPPLY) OF THE HEART

Sympathetic supply

Parasympathetic (vagal) supply

1- It supplies Atria, ventricles and coronary arteries.

Atria and coronary arteries but not the ventricles

2- Effect of stimulation 1- Increases all properties of the heart. 2- Vasodilatation of coronary arteries. 3- Increases O2 consumption.

1- Decreases all properties of the heart. 2- Vasoconstriction of coronary arteries. 3- Decreases O2 consumption.

Innervation of the heart

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III- CARDIAC CYCLE = One beat

a- Definition: It is the phases of cardiac systole and diastole and the

accompanying changes in pressure and volume of different cardiac chambers.

b- Duration of the cardiac cycle:

Duration= 60 seconds (1min.) divided on the heart rate (75 beat/min.)

i.e 60/ 75 = 0.8 second.

c- Phases of cardiac cycle: it occurs in the following sequences

i- Atrial systole (0.1 sec)

ii- Ventricular systole (0.3 sec)

iii- Diastole of the whole heart (0.5 sec). Diastole is more important than systole

because during which there is filling of the ventricles as well as filling of the

coronary arteries that supply the heart.

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IV- HEART SOUNDS

First heart sound

Second heart sound

a- Nature Dull, low pitched, prolonged and like word

LUB

Sharp, high pitched, short and like word DUP

b- Causes 1-Mainly closure of A-V valves( tricuspid and

mitral) 2- Contraction of the ventricles

Closure of semilunar valves of pulmonary

artery and aorta

c- Importance It indicates the beginning of ventricular systole

It indicates the beginning of ventricular diastole

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V- HEART RATE (HR)

a- Normal value: under normal resting condition, the heart rate is maintained at

its basal level which is equal to 70-80 beat/ min. physiologically, heart rate is

higher in children, females, during exercise and it is lower in adult, males, athletes

during rest and during sleep.

Tachycardia: increased heart rate above 100 beat/min.

Bradycardia : decreased heart rate below 60 beat/min.

b- Heart rate is increased by:

1- Decreased ABP.

2- Inspiration.

3- Emotions.

4- Exercise.

5- Thyroid hormones.

6- Adrenaline (epinephrine)

7- Hypoxia.

8- Fever.

c- Heart rate is decreased by:

1- Increased ABP.

2- Expiration.

3- Sleep.

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VI- CARDIAC OUTPUT (COP)

a- Definitions:

i- Stroke volume: it is the volume of blood by each ventricle per beat.

Normally, it is 70 ml/beat.

ii- Cardiac output (COP)( minute volume): it is the volume of blood pumped by

each ventricle per minute.

In adult male it is about 5 liters/min during rest. In adult female, it is 10% less.

COP= stroke volume X heart rate.

b- Factors affecting COP:

1- Venous return 2- Pumping capacity of the heart

Venous return

a- Definition: it is the volume of venous blood returning to the right atrium via

venae cavae per min. normally COP is directly proportional to venous return.

b- Normal value:

i- During rest: 5 liters/min.

ii- During exercise: in non- athletes 25 liters/min and in athletes is 35 liters/min.

c- Factors affecting venous return:

1- Rate of tissue metabolism: increased tissue activity as in case of exercise leads

to increased venous return.

2- Respiration: venous return is increased during inspiration.

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3- Muscle pump: contraction of skeletal muscle can squeeze venous blood from

peripheral veins toward the heart, so, voluntary muscles are called peripheral

hearts.

4- Arteriolar diameter: arteriolar vasodilatation increases venous return and vice

versa.

5- Capillary tone: which is the number of partially or totally closed blood

capillaries, normally equal 80-90%. This tone keeps normal venous return.

6- Gravity: it helps the venous return from veins above level of the heart but

antagonizes venous return from lower parts of the body.

7- Contraction of blood reservoirs: contraction of spleen, cutaneous vessels and

hepatic sinusoids leads to increased blood volume and venous return.

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II-CIRCULATION

I- ARTERIAL BLOOD PRESSURE (ABP)

a- Definitions:

1- Arterial blood pressure (ABP): it is the lateral pressure produced by the blood

on arterial wall.

2- Systolic blood pressure: it is the maximal pressure in the systemic arteries

occurring during systole. The average value is 120 mmHg.

3- Diastolic blood pressure: it is the minimal pressure in the systemic arteries

occurring during diastole. The average value is 80 mmHg.

4- Pulse pressure: it is the difference between systolic and diastolic blood

pressure. The average value is 40 mmHg.

5- Mean pressure: it is the average pressure throughout the cardiac cycle. It is

about 93 mmHg.

b- Normal standards and physiological variations:

i- Average: 120/80 mmHg.

Normal range: Systolic from 90 – 140 mmHg.

Diastolic from 60- 90 mmHg.

ii- Physiological variations:

1- Age: ABP is lower in young age.

2- Sex: women have a slightly lower ABP than men.

3- Body build: it is usually high in obese persons and the increases of pathological

hypertension in the obese are greater than in those of normal weight.

4- Exercise: blood pressure increased during exercise.

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5- Emotions: this may raise the ABP to abnormally high levels.

6- Meals: the ABP rises slightly after meals.

7- Sleep: it is slightly decreased during sleep.

c- Factors affecting ABP:

ABP= COPX total peripheral resistance

1- COP: any factor increases COP will cause an increase in ABP.

2-Peripheral resistance (PR): It is the resistance which the blood meets during its

passage through the peripheral arterioles and capillaries.

It is affected by diameter of vessels i.e dilatation of the arterioles decreases PR,

thus decreasing ABP whereas, constriction of the arterioles increases PR and ABP.

3- Elasticity of aorta and arteries: is essential to maintain normal ABP.

4- Blood volume: increased blood volume will raise ABP due to increased quantity

of blood in the arterial system.

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II- CORONARY CIRCULATION

a- Normal value:

i- During rest: it is about 225 ml/min.

ii- During severe muscular exercise: it is about 1000 ml/min.

The maximal coronary blood flow occurs during diastole of the heart.

b- Factors controlling coronary blood flow:

1- O2 need: coronary blood flow is regulated according to the need of cardiac

muscle for O2. Hypoxia leads coronary vasodilatation. (Most powerful coronary

vasodilator)

2-Metabolic factors: metabolic waste products e.g CO2, hydrogen ions, potassium

ions and lactic acids dilate coronary vessels.

3- Cardiac output (COP): coronary blood flow is directly proportional to COP.

4- Arterial blood pressure (ABP): coronary blood flow is directly proportional to

ABP especially diastolic BP.

5- Nervous control: sympathetic stimulation causes coronary dilatation while

parasympathetic stimulation causes coronary constriction.

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III- TISSSUE FLUID AND EDEMA

a-Total body water

In adult male of about 70 kg, the total body water is about 40 liters divided as

follows:

1- Intracellular fluid (ICF): about 25 liters

2- Extracellular fluid (ECF): about 15 liters (3liters plasma and 12 liters tissue fluid

(interstitial fluid in between the cells)

Regarding tissue fluid formation, the main force that pushes the fluid to tissue at

arterial end of capillary is capillary pressure while the main reabsorbing force of

fluid from tissues at venous end of capillary is colloid pressure of plasma

proteins.

b- Edema:

1- Definition: it is abnormal accumulation of tissue fluid in tissue spaces leading

to swelling of the affected part.

2- Causes:

i- Increased capillary blood pressure: as in heart failure.

ii- Increased capillary permeability: caused by histamine, O2 lack, kinins.

iii- Decreased plasma proteins colloid pressure: as in liver, kidney diseases and

nutritional deficiency as in starvation.

iv- Decreased lymphatic drainage (Obstruction of lymphatics) : e.g filariasis

leading to elephantiasis.

v- Salt and water retention: e.g increased aldosterone and glucocorticoids.

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3- Types of edema:

a- Generalized edema: caused by:

i- Heart failure.

ii- Renal failure.

iii- Hepatic failure.

iv- Nutritional edema.

b- Localized edema: caused by:

i- pregnancy edema.

ii- allergic edema.

iii- trauma.

iv- obstruction of venous or lymphatic system( elephantiasis) by filaria parasite.