Page 0 of 18

Human Anatomy

and physiology

Cardiovascular system

Nagabhushanam.chunduru

K . V . S . R . S I D D H A R T H A C O L L E G E O F P H A R M A C E U T I C A L S C I E N C E S ,

V J A .

CHNB Page 1

Cardiovascular system

The scientific study of the normal heart and the diseases associated with it is known as cardiology (cardio-= heart, logy-= study of).

Cardiovascular system consists of the blood, the heart, and blood vessels. In this chapter we will learn about the pump that circulates blood throughout the body-the heart. Blood must be constantly pumped through the blood vessels so that it can reach body cells and exchange materials with them. To accomplish this, the heart beats about 1,00,000 times every day, 35 million times in a year. Even while you are sleeping, your heart pumps about 5liters per each minute, 14,ooo liters per day and your heart pumps more vigorously when you are active.

Blood vessels: the heart pumps blood into vessels that vary in structure, size and function.

Arteries, arterioles, veins and venules are composed of three layer walls.

Tunica adventitia: Outer layer (fibrous layer)

Tunica media: middle layer-(muscle and elastic layer)

Tunica intima: inner layer-(epithelial layer)

Arteries:

Arteries are the blood vessels that transport blood away from the heart.

The amount of muscular tissue and elastic tissue varies in the tunica media depending upon

their size and function.

Large arteries are also called as Elastic arteries because tunica media of these consists of

more elastic and less smooth muscle. This allows the vessel wall to stretch, absorbing the

pressure wave generated by the heart.

Arteries branch many times and become smaller arteries known as arterioles.

Arterioles:

The tunica media of the arteriole almost consists of smooth muscle only. This makes the

arterioles enable to control the diameter.

Systemic blood pressure is mainly determined by the resistance offered by the arterioles to

blood flow. Hence they are also called as resistance vessels.

Arterioles divides into a number of minute vessels called capillaries.

Capillaries:

A capillary wall consists of a single layer of endothelial cells sitting on a very thin

basement membrane.

CHNB Page 2

Blood cells and large molecules such as plasma proteins normally do not pass through

capillary walls.

Capillaries form a vast network of tiny vessels that link the smallest arterioles to the

smallest venules.

The diameter of the capillaries is about

7µm.

The capillary bed is the site of exchange

of substances between the blood and the

tissue fluid, which bathes the body cells.

Entry to capillary bed is guarded by

rings of smooth muscle called

precapillary sphincters. These direct the

flow of blood.

In case of hypoxia or presence of high

levels of metabolic wastes indicating

high levels of activity dilates the

sphincters results in increased blood

flow throw the effected capillary beds.

Venules:

Venous capillaries unite to form small venules, these small venules unite to form veins.

Veins:

Veins are blood vessels that return blood to the heart at low pressures.

The walls of the veins are thinner than the arteries even though having same three layers.

These are thin because less smooth muscle and less elastic tissue present in tunica media.

When cut, the veins collapse while the thicker walled arteries will remain open. So, great

blood loss will happen in case of arterial damages.

In veins where blood is travelling a considerable distance against gravity having valves

which prevent back flow of blood.eg: lower limbs (legs).

These valves are guarded by semilunar cusps made of connective tissue.

2/3rd of the body’s blood is in venous system.

Others:

Anastamoses and end-arteries: most of the body receives blood from branches of more than

one artery, and where two or more arteries supply the same region, they usually connect. These

connections, called anastamoses, provide alternate routes called collateral circuits, for blood to

reach a particular organ or tissue.eg: palms of the hand, soles of the feet, and the heart muscle. If

one artery supplying the area is occluded anastomotic arteries provide a collateral circulation.

This is most likely to provide an adequate blood supply when the occlusion occurs gradually,

giving the anastomotic arteries time to dilate.

End-arteries are the arteries with no anastamoses. E.g. the branches from the circle of willis

in the brain, the central artery is occluded the tissues it supplies die because there is no alternate

blood supply.

CHNB Page 3

Sinusoids: sinusoids are wider than capillaries their endothelial cells usually have very

large inter cellular clefts and may have incomplete or absence of basement membranes. In

addition, sinusoids contain phagocytic cells that remove bacteria and other debris from the blood.

The spleen, anterior pituitary, and parathyroid glands contain sinusoids.

Control of blood vessel diameter:

All blood vessels except capillaries have smooth muscle fibers in the tunica media which

are supplied by nerves of the autonomic nervous system. These nerves arise from the vasomotor

center in medulla oblongata and they change the diameter of the lumen of blood vessels,

controlling the amount of blood they contain. Medium sized and small arteries have more muscle

than elastic tissue in their walls. In large arteries, such as aorta, the middle layer is entirely elastic

tissue. Hence these show no response to nervous stimulation.

Vasodilatation and vasoconstriction:

Sympathetic nerves supply the smooth muscle of the tunica media of blood vessels. There

is no parasympathetic nerve supply to most blood vessels and therefore the diameter of the vessel

lumen and the tone the smooth muscle is determined by the degree of sympathetic nerve

stimulation. There is always some nervous input to the smooth muscle in the vessel walls which

can then be increased or decreased. Decreased nerve stimulation causes the smooth muscle to

relax, thinning the vessel wall and enlarging the lumen. This process is called vasodilatation and

results in increased blood flow under less resistance. Conversely, when nervous activity is

increased the smooth muscle of the tunica media contracts and thickens. This process is called

vasoconstriction. A small change in lumen results in considerable alteration in blood flow to the

part of the body they supply.

Autoregulation: The accumulation of metabolites in local tissues also influences the degree of

dilatation of arterioles. This mechanism ensures that local blood flow is increased in:

Increased tissue activity e.g. vasodilatation in muscles during exercise.

Following decreased blood supply to a part, e.g. in response to temporary occlusion of local

blood.

In response to tissue damage, e.g.: in inflammation.

CHNB Page 4

ANATOMY OF HEART

Location of the heart: Heart is roughly cone shaped organ. The size is about the owner’s fist. It is

about 12cm long, 9cm wide and 6cm thick, with an average weight of 250gm in adult females and

300gm in adult males. The heart is present in thoracic cavity, in the mediastinum, and in between

the lungs, extends up to 5th intercoastal space from 2nd rib. Base of the heart present superiorly and

apex present inferiorly and rests on the diaphragm. It lies obliquely, a little more to the left than the

right. The apex is about 9cm to the left of the mediastinum at level of the 5th intercoastal space.

Structure

The wall of the heart is composed of three layers of tissue: pericardium, myocardium and

Endocardium.

Pericardium: The pericardium consists of two main parts: I. the fibrous pericardium and II. The

serous pericardium. The superficial fibrous sac is composed of tough, inelastic, dense irregular

connective tissue. It continues with the tunica adventitia of the great blood vessels and it prevents

over distension of the heart. Provides protection and anchors the heart in the mediastinum.

The deeper serous pericardium is a thin membrane that forms a double layer around the

heart. The outer parietal layer of the serous pericardium is fused to the fibrous pericardium. The

inner visceral layer of the serous pericardium, also called the epicardium, is one of the layers of the

heart and adheres tightly to the surface of myocardium. Between the parietal and visceral layers of

the serous pericardium is a thin film of lubricating serous fluid known as pericardial fluid, reduces

friction between the layers of the serous pericardium as the heart moves. The space that contains

pericardial fluid is called the pericardial cavity.

Myocardium: Myocardium is composed of cardiac muscle tissue, found only in the heart and it is

striated and involuntary in nature. It makes up about 95% of the heart and responsible for its

pumping action. Each muscle fiber has a nucleus and one or more branches. The branches are very

close to each other and this helps to spread the cardiac impulses throughout the heart very rapidly.

Usually the myocardium is thicker in the ventricle side than the atrial side.

Endocardium: It is the inner most layer consists of thin, smooth and glistery membrane made up

of epithelial cells. This layer is continuous with the tunica intima of the blood vessels. The

chambers are lined with Endocardium. The important physical characteristic of the endocardium

is not its thinness, but rather its smoothness. This very smooth tissue prevents abnormal blood

clotting, because clotting would be initiated by contact of blood with a rough surface.

Interior of the heart: The heart has four chambers. The two superior receiving chambers are

the atria, and the two inferior pumping chambers are the ventricles. The right chambers of the

heart are separated from left chambers by a fibro muscular lining called septum. The upper atrial

portion of the septum is known as intra-atrial septum, consists of fibrous tissue. The ventricular

portion of is known as intra-ventricular septum, consists of fibro-muscular tissue.

The chambers of the heart:

1. Right atrium

2. Right ventricle

CHNB Page 5

3. Left atrium

4. Left ventricle

Right atrium: The right atrium is about 2-3 mm in average thickness. The right atrium receives

the impure blood through superior venacava, inferior venacava, and coronary sinus. Then this

blood sends into the right ventricle through a valve that is called the tricuspid valve or right atrio-

ventricular valve.

Right ventricle: the right ventricle is about 4-5 mm in average thickness. It receives the right

atrium blood and sends into the lungs for the purification through pulmonary arteries.

Left atrium: the left atrium is about the same thickness (2-3 mm) as the right atrium. The left

atrium receives the pure blood from lungs through four pulmonary veins. Then this blood sends

into the left ventricle through left atrio-ventricular valve or mitral valve or bi-cuspid valve.

Another function of the atria is the production of a hormone involved in blood pressure

maintenance. When the walls of the atria are stretched by increased blood volume or blood

pressure, the cells produce atrial natriuretic peptide (ANP), also called atrial natriuretic

hormone (ANH). This ANP decreases the reabsorption of sodium ions by the kidneys, so that

more sodium ions are excreted in urine, which in turn increases the elimination of water. The loss

of water lowers blood volume and blood pressure. This ANP is an antagonist to the hormone

aldosterone, which raises blood pressure.

Left ventricle: the left ventricle is the thickest chamber of the heart, averaging 10-15 mm and

forms apex of the heart. It receives blood from left atrium and sends this blood for circulation

through aorta and arteries.

The inside of the right and left ventricles the cusps of the atrio-ventricular valves are

connected to the tendon like cords, the chordae tendineae, which in turn are connected to cone

shaped structures called papillary muscles.

The valves of the heart: valves of the heart regulate the flow of blood within the heart and heart

to outside. Atrio-ventricular valves present between the concerned atrium and ventricle and these

regulate the flow of blood from atria to

ventricles. These prevent back flow of blood

from ventricles to atria.

1. Atrio-ventricular valves

a. Right atrio ventricular valve

b. Left atrioventricular valve

2. Semilunar valves

a. Pulmonary semilunar valve

b. Aortic semilunar valve.

The pulmonary semilunar

valve is present in between the right ventricle

and starting portion of pulmonary artery and it is

guarded by three cusps. Aortic semilunar valve

is present in between the left ventricle and aorta. It is guarded by three cusps. These two semilunar

valves regulate the flow of blood from heart to outside and prevent the backflow.

CHNB Page 6

Blood circulation:

The pure blood from heart goes to the tissue level becomes impure blood by loosing oxygen

and enters back into the heart. Then this impure blood from the heart goes into the lungs for the

purification and the purified blood comes back into the heart. Like this the blood passes

alternatively to the tissues and lungs through the heart. This is known as blood circulation. Blood

circulation is divided into four parts:

1. Systemic blood circulation

2. Pulmonary blood circulation

3. Portal blood circulation

4. Coronary blood circulation.

1. Systemic blood circulation: The pure blood expels from left ventricle and passes through aorta.

Then distributed into arteries and arterioles. At the tissue level the pure blood becomes impure

blood by loosing oxygen and taking CO2. This impure blood passes through venules and veins and

enters the heart through superior venacava, inferior venacava and coronary sinus. So, the systemic

blood circulation begins from left ventricle and ends at right atrium.

2. Pulmonary circulation: The impure blood expels from right ventricle goes to lungs pulmonary

arteries. In the lungs impure blood becoming pure blood by loosing CO2 and taking oxygen. This

pure blood enters the left atrium of the heart through four pulmonary veins. So, the pulmonary

circulation begins in the right ventricle and ends in the left atrium.

3. Portal blood circulation: In all the parts of the body usually the venous blood passes from the

tissues to the heart by direct route. But in the portal circulation venous blood passes from the

capillary bed of the abdominal part of digestive system, the spleen, and pancreas to the liver. It

CHNB Page 7

passes through a second capillary bed, the

hepatic sinusoids, in the liver before

entering the general circulation via inferior

vena cava. In this way a high concentration

of nutrient materials, absorbed from the

stomach and intestines, goes to the liver

first for certain modifications.

4. Coronary circulation: nutrients are not

able to diffuse quickly enough from blood

in the chambers of the heart to supply all

the layers of cells that make up the heart

wall. For this reason, the myocardium has

its own network of blood vessels, the

coronary or cardiac circulation. The right

and left coronary arteries, branch from the

ascending aorta and encircle the heart like a crown encircle the head. While the heart is

contracting, aorta propels blood through the coronary arteries, into capillaries, and then into

coronary veins. Coronary veins posteriorly open into right atria through coronary sinus.

Conduction system:

Rhythmical electrical activity is the reason for the heart’s lifelong beat. The source of this

electrical activity is a network of specialized cardiac muscle fibers called autorhythamic fibers.

These fibers repeatedly generate action potential that triggers heart chambers to contractions. This

is an intrinsic system present in the heart where by the cardiac muscle is automatically stimulated

to contract without the need for a nerve supply from the brain, but the intrinsic system can be

influenced by nerve impulses initiated in the brain and by circulating chemicals including

hormones.

Sinoatrial node: The Sinoatrial (SA) node is located in the right atrial wall, just inferior to

the entrance of the superior vena cava. The SA node typically generates impulses about 75 times

(about 70-80 beats/min) every minute. Because no other region of the conduction system or the

myocardium has a faster depolarization rate, the SA node sets the pace for the heart as a whole.

Hence, it is the heart’s pacemaker, and its characteristic rhythm, called sinus rhythm, determines

heart rate.

Atrioventricular node: From the SA node, the depolarization wave spreads via gap

junctions throughout the atria and via the internodal pathway to the atrioventricular (AV) node,

located in the inferior portion of the interatrial septum immediately above the tricuspid valve. At

the AV node, the impulse is delayed for about 0.1sec, allowing the atria to respond and complete

their contraction before the ventricles contract. Through the AV node, the signaling impulse passes

rapidly through the rest of the system. When the SA node fails to generate impulses, then the AV

node is able to initiate the cardiac impulses at the rate of 50to 60 beats/ minute. By this, it is called

as stand-in pace maker of the heart. The rhythm originated from AV node is designated as nodal

rhythm.

Bundle of His: From the AV node, the impulse sweeps to the atrioventricular (AV) bundle

(also called the bundle of His) in the superior part of the interventricular septum. The AV bundle is

CHNB Page 8

the only electrical connection between atria and ventricles. The balance of the AV junction is

insulated by the non-conducting fibrous skeleton of the heart. It divides into the right and left

branches of the bundle.

Right and left branches: The right branch is usually larger than that of the left branch.

These branches carry the impulses to their respective ventricles. When SA node, AV node is fails

to produce the cardiac impulse, then the branches are initiating the impulse, at the rate of 36 per

minute.

Purkinje fibers: the right and left branches are further divided into a small branch fibers

and spread throughout the ventricles. These are called as purkinje fibers. They help to conduct the

impulse to every part of the ventricles quickly. The fibers can also able to initiate at the rate of 30

to 35 beats/min.

Cardiac cycle: Events that are occurring in the heart during one beat are repeating in the same

order in the next beat. This cyclic repetition of the events in heart, from beat to beat, is called

cardiac cycle. (Or)

The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are

called the cardiac cycle.

The time required to complete one cardiac cycle is known as cardiac cycle time. With the

normal heart rate of 75 beats/min, the time will be 60/75= 0.8 seconds. So, every changes of the

cardiac cycle are repeated at the interval of every 0.8 sec. The cardiac cycle consists of a period of

relaxation called diastole, during which the heart fills with blood, followed by a period of

contraction called systole. There are four events occurs in the cardiac cycle. They are:

1. Atrial systole -0.1 sec

2. Atrial diastole -0.7 sec

3. Ventricular systole -0.3 sec

4. Ventricular diastole -0.5 sec

CHNB Page 9

The different events of cardiac cycle can be explained with the help of two concentric

circles. Each circle divided into 8 divisions. Each division is equals to 0.1 sec. the inner circle

represents the atrial events and outer circle represents the ventricular events.

1. Atrial systole: Atrial systole initiates the cardiac cycle, because the pace maker S.A node is

situated in the right atrium. During the atrial systole due to high atrial pressure atria will

contracts, atrio-ventricular valves opens and the atrial blood flows to their respective ventricles.

This completes for 0.1 sec. then atrial diastole is begins.

2. Atrial diastole:

Atrial diastole begins immediately after the end of atrial systole. Atrial diastole begins with

closing of atrioventricular valves. During the atrial diastole the right atria receives the impure

blood through superior venacava, inferior venacava and coronary sinus. The left atrium receives

pure blood from lungs through four pulmonary veins. This completes for 0.7 sec.

3. Ventricular systole:

At the end of atrial systole the ventricular systole is begins and it completes for 0.3 sec. At the

end of atrial systole the atrio-ventricular valves are closes and the semilunar valves should open.

But the semilunar valves open little later about 0.05 sec. in this period the ventricles contracts in a

closed chamber without ejection of blood. So, this period is called as called as isometric

contraction period (0.05sec). After opening the semilunar valves the blood ejection is begins. In

the beginning, due to maximum pressure in these ventricles the blood ejection is maximum for

about 0.14 sec, which is known as rapid ejection period. Then blood flows with low speed. This

period is called as reduced ejection period (0.11 sec). With this the ventricular systole is ends and

ventricular diastole is begins.

4. Ventricular diastole:

The ventricular diastole is begins with the end of ventricular systole and this ends for 0.5 sec.

the ventricular diastole should begin with the closing of semilunar valves. But the semilunar valves

are closing little later of about 0.04 sec. the ventricles are in diastolic period without closing the

valves. This period is called as protodiastolic period (0.04 sec).

After closing the semilunar valves, the atrio-ventricular valves should open. But the atrio-

ventricular valves are opens a later about 0.08 sec. This period is known as isometric relaxation

period (0.08 sec). After opening the atrio-ventricular valves the blood of atria rushes towards their

respective ventricles. In the beginning, the blood filling is very rapid for about 0.12 sec because of

maximum pressure in the atria. This period is called as first rapid filling period (0.12 sec). Then,

as the pressure reduces in atriums the blood filling becomes slow of about 0.16 sec. this period is

called as slow filling period (0.16 sec). At the end due to atrial muscle contraction the blood filling

is again becomes rapid for about 0.1 sec. this period called as second rapid filling period (0.1 sec).

This completes the ventricular diastole. Like this cardiac cycle is continues.

CHNB Page 10

HEART SOUNDS:

There are four heart sounds. The first and second sounds

are classical sounds. They can be detected clinically

with the help of stethoscope. The third and fourth

sounds can’t be detected clinically, but they can

detect by graphical method. The first and second

sounds are very close to each other, after the second

sound there is a long pause. The sequence of the

sound is like as shown in the diagram.

I sound: The first sound occurs at the onset of ventricular systole. The nature of the sound is dull and

prolonged like the word L-U-B-B. The duration is 0.1to 0.17sec. The first sound occurs due to sudden

closure of AV valve and ejection of ventricular blood. The sound is identified by its nature and the

sound is produced after the pause.

The first sound indicates that the onset of ventricular systole. The duration and intensity of the sound

shows the condition of myocardium. It also indicates that the leaflets of AV valves are closing

properly.

II sound: The second sound occurs at the onset of ventricular diastole. The nature of the sound is sharp

and short, like the word D-U-P. The pitch is high and duration is 0.1 to 0.14 sec. The second sound

occurs due to sudden closure of semilunar valves. The second is identified by its nature. The second

sound occurs after the first sound and after the second sound there is a long pause.

The second indicates that the end of ventricular systole and beginning of ventricular diastole. The pitch of

second is directly proportional to blood pressure. The clear second also indicates proper closing of

semilunar valves.

III sound: The third sound occurs after the second, due to the opening of AV valves. The sound is

produced due to sudden rush of blood into ventricles.

The third sound indicates the beginning of ventricular filling. Duration of the sound is 0.04 sec.

CHNB Page 11

IV sound: The fourth sound is also known as atrial sound. This sound occurs due to the contraction of

atria i.e. during the end of ventricular diastole. The sound produced due to sudden rush of atrial blood

into ventricles.

CARDIAC OUTPUT (CO):

Cardiac output is the volume of blood ejected from the left ventricle (or the right ventricle) into the aorta

(or pulmonary artery) each minute. There are two terms used in the cardiac output are

1. Stroke volume / systolic discharge

2. Minute volume

1. Stroke volume: stroke volume is the cardiac output per ventricle per beat. Normal value is 70ml.

2. Minute volume: minute volume is the cardiac output per ventricle per minute. Normal value is 5 to 6

litre. So, about 5 to 6 litre of venous blood enters into the heart in one minute and the same 5 to 6 litre

of blood expels from each ventricle in one minute.

The cardiac output depends on:

i. Venous blood return

ii. Force of contraction

iii. Heart rate

iv. Peripheral resistance.

The following factors influence the cardiac output:

1) Muscle exercise increases the cardiac output up to 19.5 liter per minute

2) Posture- in standing position cardiac output is more than sitting and sleeping position.

3) Fever, hyperthyroidism, excitement, adrenaline injection, anoxia, excess of CO2 increases the cardiac

output.

Cardiac Output (ml/min) = Heart Rate (75 beats/min) x Stroke Volume (70 ml/beat)

CO = 5250 ml/min (5.25 L/min)

CHNB Page 12

Cardiac reserve is the difference between a person’s maximum cardiac output and cardiac output at rest.

The average has a cardiac reserve of four or five times the resting value. Top endurance athletes may

have a cardiac reserve seven or eight times to their resting cardiac output. People with severe heart

disease may have liter or no cardiac reserve, which limits their ability to carry out even simple tasks of

daily living.

HEART RATE: Number of heart beats per minute is known as heart rate. Normal heart rate in adult

male is 72 beats/ min. In female it is slightly higher. The heart rate may vary in the following

physiological conditions:

1. Age: In fetus - 140 to 150 beats/min

New born baby - 130 to 140 beats/ min

In third year - 95to 100 beats/ min

7th to 14th year - 80 to 90 beats / min

After 15th year (adult age) 70 to 80 beats/ min

In old age the heart rate slightly increases.

2. Metabolic rate, muscle exercise, excitement increases the heart rate.

3. Respiration: during inspiration heart rate increases, during expiration the heart rate

decreases.

4. Body temperature: raise in the body temperature causes raise in heart rate.

5. Excess carbon dioxide in the body, increases the heart rate.

Regulation of heart rate:

Heart rate is regulated by two mechanisms. They are:

1. Local mechanism

2. Nervous mechanism

1. Local mechanism: The heart rate maintained by the regular function of S.A node and other special

junctional tissues of tissues of the heart.

2. Nervous mechanism: Medulla oblongata of brain consists of cardiac center and it is under the control

of hypothalamus. The cardiac center consists of cardio inhibitory center and cardio accelerator

center. Cardio inhibitory center is connected with the parasympathetic nerves and stimulation of

these causes decrease in the heart rate. The cardio accelerator center is connected with the

sympathetic nerves and stimulation of these causes increase in the heart rate.

BLOOD PRESSURE:

Blood pressure (BP) is the lateral pressure exerted by circulating blood upon the walls of blood vessels

while the blood flowing through the blood vessel. During each heartbeat, BP varies between a

maximum (systolic) and a minimum (diastolic) pressure. The term blood pressure usually refers to

the pressure measured at a person's upper arm. It is measured on the inside of an elbow at

the brachial artery. A person's BP is usually expressed in terms of the systolic pressure and

diastolic pressure (mmHg), for example 120/80.

Blood pressure drops most rapidly along the small arteries and arterioles, and continues to decrease as

the blood moves through the capillaries and back to the heart through veins.

CHNB Page 13

Systolic pressure is peak pressure in the arteries, which occurs when the ventricles are contracting.

Normal range is 110 – 130 mmHg

Diastolic pressure is minimum pressure in the arteries, which occurs when the ventricles are in diastole

or relaxation. Normal range is 70 – 90 mmHg.

Pulse pressure is the difference between systolic and diastolic pressure.

Mean arterial pressure is the average over a cardiac cycle

An example of normal measured values for a resting, healthy adult human is 120 mmHg systolic and

80 mmHg diastolic (written as 120/80 mmHg)

Fig: Representation of variations in blood pressure in different blood vessels.

Physiological factors vary the blood pressure:

1. Age: The blood pressure rises with the age. The systolic blood pressure in infants is 70 -90 mmHg,

childhood 90 – 110 mmHg, in puberty 110 – 130 mmHg and in old age 140 – 150 mmHg.

2. Sex: In female both systolic and diastolic pressures are lower than male.

3. Systolic pressure may rise up to 180 mmHg in exercise.

4. Posture: In standing posture the diastolic pressure is slightly higher.

5. After meal, in emotion and excitement systolic pressure will rise.

Methods to determine the blood pressure:

1. Oscillatory method

2. Palpatory method

3. Auscultatory method

The auscultatory method is the predominant method of clinical measurement.

The auscultatory method (from the Latin word for "listening") uses a stethoscope and

a sphygmomanometer. A cuff of appropriate size is fitted smoothly and then inflated manually by

repeatedly squeezing a rubber bulb until the artery is completely occluded. Listening with the

CHNB Page 14

stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff.

When blood just starts to flow in the artery, the turbulent flow creates a Korotkoff sound. The pressure

at which this sound is first heard is the systolic BP. The cuff pressure is further released until no sound

can be heard (fifth Korotkoff sound), at the diastolic arterial pressure.

REGULATION OF BLOOD PRESSURE: Regulation of blood pressure is done through neuronal

and hormonal activities. Short term regulation of blood pressure is done by neuronal regulation and

long term regulation of blood pressure is done by hormonal regulation.

Neural Regulation of Blood Pressure:

The nervous system regulates blood pressure via negative feedback loops that occur as two types of

reflexes: baroreceptor reflexes and chemoreceptor reflexes.

Baroreceptor Reflexes:

Baroreceptors, pressure-sensitive sensory receptors, are located in the aorta, internal carotid arteries

(arteries in the neck that supply blood to the brain), and other large arteries in the neck and chest. They

send impulses to the cardiovascular center to help regulate blood pressure.

The two most important baroreceptor reflexes are the carotid sinus reflex and the aortic reflex.

Baroreceptors in the wall of the carotid sinuses initiate the carotid sinus reflex. Blood pressure

stretches the wall of the carotid sinus, which stimulates the baroreceptors. Nerve impulses propagate

from the carotid sinus baroreceptors over sensory axons in the glossopharyngeal (IX) nerve to the

cardiovascular center in the medulla oblongata. Baroreceptors in the wall of the ascending aorta and

arch of the aorta initiate the aortic reflex and it reach the cardiovascular center via sensory axons of

the vagus (X) nerve.

When blood pressure falls, the baroreceptors are stretched less, and they send nerve impulses at a

slower rate to the cardiovascular center. In response, the CV center decreases parasympathetic

stimulation of the heart by way of motor axons of the vagus nerves and increases sympathetic

stimulation of the heart via cardiac accelerator nerves. Another consequence of increased sympathetic

stimulation is increased secretion of epinephrine and norepinephrine by the adrenal medulla. As the

heart beats faster and more forcefully, and as systemic vascular resistance increases, cardiac output

and systemic vascular resistance rise, and blood pressure increases to the normal level. Conversely,

CHNB Page 15

when an increase in pressure is detected, the baroreceptors send impulses at a faster rate. The CV

center responds by increasing parasympathetic stimulation and decreasing sympathetic stimulation.

The resulting decreases in heart rate and force of contraction reduce the cardiac output. The

cardiovascular center also slows the rate at which it sends sympathetic impulses along vasomotor

neurons that normally cause vasoconstriction. The resulting vasodilation lowers systemic vascular

resistance. Decreased cardiac output and decreased systemic vascular resistance both lower systemic

arterial blood pressure to the normal level.

Chemoreceptor Reflexes:

Chemoreceptors, sensory receptors that monitor the chemical composition of blood, are located

close to the baroreceptors of the carotid sinus and arch of the aorta in small structures called carotid

bodies and aortic bodies, respectively. These chemoreceptors detect changes in blood level of O2, CO2,

and H+. Hypoxia (lowered O2 availability), acidosis (an increase in H+ concentration), or hypercapnia

(excess CO2) stimulates the chemoreceptors to send impulses to the cardiovascular center. In response,

the CV center increases sympathetic stimulation to arterioles and veins, producing vasoconstriction and

an increase in blood pressure. These chemoreceptors also provide input to the respiratory center in the

brain stem to adjust the rate of breathing.

Hormonal Regulation of Blood Pressure:

Several hormones help regulate blood pressure and blood flow by altering cardiac output, changing

systemic vascular resistance, or adjusting the total blood volume:

1. Renin–angiotensin–aldosterone (RAA) system. When blood volume falls or blood flow to the kidneys

decreases, juxtaglomerular cells in the kidneys secrete renin into the bloodstream.

In sequence, renin and angiotensin converting enzyme (ACE) act on their substrates to produce the active

hormone angiotensin II, which raises blood pressure in two ways. First, angiotensin II is a potent

vasoconstrictor; it raises blood pressure by increasing systemic vascular resistance. Second, it stimulates

secretion of aldosterone, which increases reabsorption of sodium ions (Na+) and water by the kidneys.

The water reabsorption increases total blood volume, which increases blood pressure.

CHNB Page 16

2. Epinephrine and norepinephrine. In response to sympathetic stimulation, the adrenal medulla releases

epinephrine and norepinephrine. These hormones increase cardiac output by increasing the heart rate and

force of heart contractions. They also cause vasoconstriction of arterioles and veins in the skin and

abdominal organs and vasodilation of arterioles in cardiac and skeletal muscle, which helps increase

blood flow to muscle during exercise.

3. Antidiuretic hormone (ADH). ADH is produced by the hypothalamus and released from the posterior

pituitary in response to dehydration or decreased blood volume. Among other actions, ADH causes

vasoconstriction, which increases blood pressure. For this reason ADH is also called vasopressin.

4. Atrial natriuretic peptide (ANP). Released by cells in the atria of the heart, ANP lowers blood

pressure by causing vasodilation and by promoting the loss of salt and water in the urine, which reduces

blood volume. Relaxation of precapillary sphincters, blood flow into capillary networks is increased,

which increases O2 level.

The ability of a tissue to automatically adjust its blood flow to match its metabolic demands is called

autoregulation. In tissues such as the heart and skeletal muscle, where the demand for O2 and nutrients

and for the removal of wastes can increase as much as tenfold during physical activity, autoregulation is

an important contributor to increased blood flow through the tissue. Autoregulation also controls regional

blood flow in the brain; blood distribution to various parts of the brain changes dramatically for different

mental and physical activities. During a conversation, for example, blood flow increases to your motor

speech areas when you are talking and increases to the auditory areas when you are listening.

CHNB Page 17

Electrocardiogram: (ECG or EKG)

As action potentials propagate

through the heart, they generate

electrical currents that can be

detected at the surface of the body.

An electrocardiogram (ECG or

EKG), is a recording of these

electrical signals.

The instrument used to record the

changes is an electrocardiograph.

By comparing these records with one

another and with normal records, it is

possible to determine (1) If the

conducting pathway is abnormal, (2)

If the heart is enlarged, (3) If certain

regions of the heart are damaged, and

(4) The cause of chest pain.

In a typical record, three clearly

recognizable waves appear with each heart beat.

The first, called the P wave, is a small upward deflection on the ECG. The P wave

represents atrial depolarization.

The second wave, called the QRS complex, begins as a downward deflection, continues as

a large, upright, triangular wave, and ends as a downward wave. The QRS complex

represents rapid ventricular depolarization, as the action potential spreads through

ventricular contractile fibers.

The third wave is a dome-shaped upward deflection called the T wave. It indicates

ventricular repolarization.

In reading an ECG, the size of the waves can provide clues to abnormalities.

Larger P waves indicate enlargement of an atrium.

An enlarged Q wave may indicate a myocardial infarction.

An enlarged R wave generally indicates enlarged ventricles.

The T wave is flatter than normal when the heart muscle is receiving insufficient oxygen—

as, for example, in coronary artery disease.

The T wave may be elevated in hyperkalemia (high blood K+ level).

CHNB Page 18

The P-Q interval represents the conduction time from the beginning of atrial excitation to

the beginning of ventricular excitation.

The S-T segment is elevated (above the baseline) in acute myocardial infarction and

depressed (below the baseline) when the heart muscle receives insufficient oxygen.

The Q-T interval may be lengthened by myocardial damage, myocardial ischemia

(decreased blood flow), or conduction abnormalities.