Definition: This system is involved in delivering oxygen, nutrients, and hormones
throughout
the body by a complex network of vessels -- arteries, arterioles,
capillaries and veins. So it is just a transport system

The
blood is the vehicle through which it is carried and for this the motor
power is given by the heart, which is a muscular pump .so it is all
integrated system.

Types of circulatory system
   

Single circulation when blood flows through heart only once during its course of circulation e.g. invertebrates and fish.

Double circulation when blood flows through heart twice during its course of circulation e.g. amphibians, reptiles, birds, mammals.

Closed circulatory system

Vertebrates,
and a few invertebrates, have a closed circulatory system. Closed
circulatory systems have the blood closed at all times within vessels of
different size and wall thickness. In this type of system, blood is
pumped by a heart through vessels, and does not normally fill body
cavities.


 
Image taken from    www.gsu.edu  

Open circulatory system

The
open circulatory system is common to molluscs and arthropods. Open
circulatory systems (evolved in crustaceans, insects, mollusks and other
invertebrates) pump blood into a hemocoel with the blood diffusing back
to the circulatory system between cells. Blood is pumped by a heart
into the body cavities.


 
Image taken from   www.gsu.edu


The circulatory system consists of arteries veins and capillaries

Artery
is the blood vessel which carry the blood from the heart to different
parts of the body .they divide to form finer branches, the arterioles,
as they reach the destination .the arterioles finally break to form
blood capillaries .they have thicker and elastic walls with narrow lumen
.they have well developed tunica media .they normally carry oxygenated
blood with the exception of pulmonary arteries which transport
deoxygenated blood.

Vein: A blood vessel that carries
blood low in oxygen content from the body back to the heart. The
deoxygenated form of hemoglobin (deoxyhemoglobin) in venous blood makes
it appear dark. Veins are part of the afferent wing of the circulatory
system which returns blood to the heart.

Capillary the
exchange of nutrients takes place through these vessels only .They are
made up of tunica interna only that is single layered vessels.

Pulmonary circulation
is the portion of the cardiovascular system which carries
oxygen-depleted blood away from the heart, to the lungs, and returns
oxygenated blood back to the heart. The term is contrasted with systemic
circulation.

Depending upon the medium of transportation circulatory system is divided into:

A) Water vascular system in this system water circulates in instead of blood e.g. sponges (water canal system).In hydra (Gastro-vascular system)

B) Blood vascular system in this system blood is the medium of transport.like humans.

On the basis of structure, the hearts are of following types

Tubular hearts e.g. insects (cockroach-13 chambered heart)

Pulsatile vessels – Annelids, Holothurians, and amphioxus.

Chambered heart -Hearts of vertebrates and mollusc.

Ampullar accessory hearts Branchial hearts of cephalopods (octopus), insects, lymph heart of frog.

Some interesting facts:

In hepatic vein the level of glucose is minimum, and level of amino acids is maximum.

Highest level of urea is in hepatic vein and lowest in renal vein

Largest artery is Aorta

Smallest blood vessel in the body is capillary

Largest vein in the human body is Inferior vena cava

One species of Antarctic fish has white blood .it has no red pigment in its blood.

Frog has two pairs of lymph heart to pump the blood back into the veins

Thrombocytopenia: decrease in blood platelet count.

Erythropoietin Hormone secreted by the juxta-glomerular cells of the kidney

Coronary
angiography when the contrast medium dye is injected in coronary
arteries and pictures are taken for diagnostic procedures is known as
coronary angiography

Blue whale has the largest heart in the whole world

Cardiomegaly is the heart enlargement

Circulatory system in mammals

Heart
In the human body, the heart is usually situated in the middle of the
thorax with the largest part of the heart slightly offset to the left,
underneath the breastbone. The heart is usually felt to be on the left
side because the left ventricle is stronger than the right. the vessels
which supply the heart are known as coronary vessels .9which are dealt
later )

The covering of the heart is known as pericardium.

The
pericardium comprises two parts: the fibrous pericardium, made of dense
fibrous connective tissue; and a double membrane structure (parietal
and visceral pericardium) containing a serous fluid to reduce friction
during heart contractions.

The apex is the blunt point situated
in an inferior direction. It is located posterior to the 5th intercostal
space just medial of the left mid-clavicular line.

It consists
of four chambers, the two upper atria (singular: atrium) and the two
lower ventricles. .The two atria are divided by interarterial septum
into right and left auricles. On this septum a depression Fossa ovalis
is present which a remnant of embryonic Foramen ovale .Three large veins
pour blood in the right auricle by separate pores ..A coronary valve is
present at the opening of coronary sinus .Two pulmonary veins brings
oxygenated blood into the left auricle .ventricle is also divided by
inter-ventricular septum .Auricle opens into the ventricles by separate
valves,on the left side we have Mitral valve and on the right we have
tricuspid valve .these cupsid valves are connected below to the walls of
ventricles by Chordae tendinae which terminates on the papillary
muscles
Left ventricle has the thickest wall as it pumps the blood
to the whole body. It works as a pump to send oxygen-rich blood through
all parts of body. Blood contains oxygen and nutrients that every cell
in body needs to survive. The oxygen-rich blood travels throughout the
arteries and vessels, nourishing the body so that it can function
properly.

Heart will beat an average of 100,000 times per day. In
that time, it pumps more than 4,300 gallons of blood throughout the
body



Image taken from www.sudid.com/
 

The flow of blood

Heart
is divided into two sides. Each side is divided again into two
chambers, the atrium (upper chamber) and ventricle (lower chamber).
Veins carry blood to the heart from the rest of the body. This blood
carries carbon dioxide and cellular waste products. The blood goes into
the right atrium and then to the right ventricle, where it is then
pumped to the lungs to dispose of wastes and receive a fresh oxygen
supply. From the lungs, the blood returns to the heart. It returns to
the left atrium and then to the left ventricle. The blood is then pumped
out of the heart by the left ventricle into the aorta. The left
ventricle is the chamber of the heart that is responsible for pumping
blood to all parts of the body. The aorta sends this blood to small
arteries, which carry the oxygen-rich blood to the rest of the body.


 
Image taken from healthlibrary.epnet.com

The
heart shows alternate contraction and dilatation of all the chambers
.Contraction is known as systole and dilatation is called diastole. Joint diastole
is the state of heart when all the four chambers are in relaxed state.
Atrial systole forces the blood into the ventricles .the left ventricles
receives the oxygenated blood and the right ventricle receives the
de-oxygenated blood .as the ventricular systole starts the cuspid valves
closes and the blood from the ventricles is forced into the great
arteries. Oxygenated blood from the left atrium enters the aortic arch
and is carried to all parts of he body .the de-oxygenated blood from the
right ventricle reaches the pulmonary arch and is carried to the lungs
.As the ventricles began to relax ,the semi lunar valves closes and
prevent the return of blood from the two arches .

Types of circulation

There are three types of circulation

1) Pulmonary circulation from heart to lungs and back
2) Systemic circulation when blood is passed to different parts of body, it has arterial and venous system.

Arterial system

1) Carotico-systemic arch turns to left and give

a)  Coronary artery to the heart
b) Innominate gives right carotid arteries and subclavian artery (to mammary glands and the right arm)
c) Left subclavian artery arises from the arch, which supplies to the left arm

2) Dorsal aorta it gives several branches to different body organs

d) Seven pairs of intercoastal arteries
e) Pair of phrenic artery
f) Coeliac artery which divides into hepatic and lineogastric (supply to stomach and spleen)
g) Pair of renal arteries
h) Posterior mesenteric artery (to colon and rectum)
i) Many pairs of lumber arteries (to dorsal wall of body)

Iliac
artery divides into external iliac and femoral artery (to hind limb)and
internal artery (to urinary bladder and uterus in female )

Venous system

Main veins are two precavals formed by

a) Jugular veins (from head region)
b) Subclavian veins (from fore limbs)
c) Azygous vein and homozygous vein (from intercoastal muscles and dorsal wall of the body)
A post caval is formed by
a) A pair of external iliac veins (from femoral, epigastric and vesicular)
b) Hypogastric vein (formed by internal iliac and caudal)
c) A pair of ilio-lumber veins (from dorsal wall of body)
d) A pair of renal veins (from kidneys)
e) A pair of phrenic veins (from diaphragm)
f) A few pair of intercoastal veins (from the wall of thorax, pericardium)
Coronary sinus collects the blood from the wall of heart

3) Portal circulation


Image from  webanatomy.net

The
portal circulation is that circulation which is concerned with the
blood supply to the organs of digestion and its conveyance to the liver
.the following branches of abdominal aorta gives their branches for
blood supply

1 Coeliac trunk ---------------------stomach, pancreas, spleen and liver
2 Superior mesenteric arteries --------------------small intestine and first part of large intestine
3 Inferior mesenteric arteries --------------------rest of the large intestine and rectum

These
arteries break down to form capillaries and again join to form the
veins .then again individual veins from stomach, spleen, and intestines
join to form the large vein called portal vein and thus again carry the
blood to the liver ,then in the liver these portal vein again divide
into smaller veins and capillaries and ultimately they again unite to
form three large hepatic veins which after leaving the liver join
inferior vena cava ,just before IVC peirces the diaphragm.

It
must be well remembered that hepatic artery only supplies to the liver
it does not take any active part in the formation of portal vein.

Coronary arteries:

 

Image taken from   courses.stu.qmul.ac.uk


The
right and left coronary arteries branch off the aorta and then divide
into smaller branches, supplying all portions of the heart with blood
and oxygen. In order for the heart to function properly, it must receive
a continuous supply of fresh oxygen-enriched blood. The coronary
arteries surround the heart and carry the blood which nourishes the
heart muscle. The right coronary artery supplies blood to the right and
back sides of the heart. The left coronary artery divides into two main
branches--the circumflex and the left anterior descending--supplying
blood to the left side of the heart.
Heart valves

There are four heart valves. They are all one-way valves to keep blood moving through the various chambers of the heart.

1) The mitral valve
guards the opening between the atrium and the ventricle in the left
side of the heart. It allows blood to flow forward from the atrium to
the ventricle, and prevents blood from flowing backwards.

2      The aortic valve,
also called a semi-lunar valve, has three segments that prevent the
return of the blood from the aorta to the left ventricle. This valve is
stronger than the mitral valve. It looks like three half Ping-Pong
balls.

3      The pulmonary valve is located at the
junction of the pulmonary artery and the right ventricle. When the right
ventricle contracts, the pulmonary valve opens, forcing the blood into
the artery which leads to the lungs. It is also a semi-lunar valve. When
the chamber relaxes, this valve closes and prevents a backflow of the
blood.

4 The tricuspid valve is located between the upper
and lower chamber in the right side of the heart. Its position
corresponds to the mitral valve in the left side of the heart.

Heart sounds are due to closure of cuspid and semi lunar valves and are respectively called LUBB and DUP.


CARDIAC CYCLE

The
heart beats in a cyclic manner this refers to a cardiac cycle The
frequency of the cardiac cycle is the heart rate The cardiac cycle is
co-coordinated by a series of electrical impulses that are produced by
specialized heart cells found within the sino-atrial node and the
atrioventricular node.there are rythmic phases in this cycle ,which are
as follows .

Cardiac Cycle: Diastole Phase

Following events take place

1 The atria and ventricles are relaxed.
2   Blood flows into the right and left atria.
3   The valves located between the atria and ventricles are open, allowing blood to flow through to the ventricles.


Cardiac Cycle: Systole Phase

During
the systole phase, the ventricles contract pumping blood into the
arteries. The right ventricle sends blood to the lungs via the pulmonary
artery. The left ventricle pumps blood to the aorta. Here is a summary
of the events that occur during the systole phase:

•    The ventricles contract.
•    Atrioventricular valves close and semi lunar valves open.
•    Blood flows to either the pulmonary artery or aorta.

One heart beat completes in 0.8 second (Atrial systole 0.1 seconds)
                                                          (Atrial diastole 0.7 seconds)
                                                          (Ventricular systole 0.3 seconds)
                                                         (Ventricular diastole 0.5 seconds)

Thus there are 72 heart beats per minute on an average person performing normal work.

Phase of filling      Atria full,------- A-V node closed

Beginning of ventricular diastole ------A-V Valve opens

Rapid filling phase (75%of filling occurs .Middle third small amount of blood

Last
third of diastole atria contracts –rest 25% of blood injected into
ventricles Ventricular volume -110to 120 ml –end diastolic volume    

Phase of iso volumetric contraction –in this phase the volume of the ventricles remains same so called as iso –volumetric phase.

Period of ejection
Ventricular systole starts ,semi lunar valve opens –blood starts
flowing into aortic and pulmonary aorta .volume of ventricles reduced to
40-50 ml(end systolic volume )is called stroke volume (70ml).

Period of isovolumic relaxation
aortic valves closes (dub)sound ,pressure in aorta rises .complete
heart is in diastole .Atrium being filled up passively .A-V valve closed
hence ventricle is in isovolumic relaxation .

There are some
structures in the heart which are concerned with the generation of the
heart beat thus called pace-makers of the heart.they include

1) Sino Atrial node
2) Atrio-ventricular node
3) Bundle of His
4) Purkinje fibres i.e. branches of bundle of his

1) Sino-Atrial node

It
is located posteriorly at the junction of Superior vena cava with right
atrium. These fibres normally can generate and discharge impulses more
rapidly than any other pacemaker tissue and their rate of discharge
determines the rate at which heart will beat .That is why this is called
pacemaker of heart.

2) Atrio-ventricular node it is located posteriorly on the right side of interatrial septum.

3) Bundle of his
It takes origin from AVN and then divides into right and a left branch
both branches divide repeatedly to form a network of fibres in the
ventricles.

4)Purkinje fibres  they take origin from
terminal divisions of right and left branch of bundle of his to
penetrate the ventricular wall .they transmit the impulse at a fast velocity of 4mts/sec as compared to other conducting tissue

Properties of cardiac muscles these are specialized muscle fibres having some important characteristics as being

Involuntary, striated, and being highly vascular in nature 

Electrical properties are as follows

A) Excitability
B) Auto-rhythimicity
C) Conductivity

Mechanical properties include

A) Contractility

B) All or none law
responses in cardiac muscle are also called all or none law this means
that when there is contraction or relaxation the muscles responds in a
unit manner all the fibres follows the same order

C) Refractory period Cardiac muscle is refractory it means that they will not respond when there is any command in the action potential

Jugular venous pressure (JVP)

There
is no valve at the junction of superior vena cava and right atrium
therefore right atrial pressure changes are transmitted to the jugular
vein in the neck producing 3 characterstic waves

The a wave is due to atrial systole

The c wave
is i due to rise in atrial pressure produced by the bulging of the
tricuspid into the right atrium during iso-vouumetric ventricular phase

The v wave is due to rise in arterial pressure before the tri-cuspid valve opens during diastole.

Arterial blood pressure

The arterial blood pressure is the pressure of the column of blood in the arterial system.

Systolic blood pressure (SBP) is the maximum pressure exerted during systole Range is 100-130 mmhg

Diastolic blood pressure (DBP) is the minimum pressure exerted during diastole

Pulse pressure (PP systolic blood pressure --------diastolic blood pressure.)

Mean blood pressure (MBP) it is the average pressure throughout the cardiac cycle it can be computed as MBP=DBP+1/3PP


Classification of blood pressure for adults



Factors affecting Blood pressure

Sex
In females before menopause SBP is 4-5 mmhg is less than males of same
age .After menopause SBP is 4-5 mmhg more than males of same age .this
effect may be due to estrogen.

Built In obese individuals,
brachial arterial pressure gives higher readings, because there is more
tissue between the cuff and the artery.

Diurnal variation
there is rise in BP in the afternoon about 5-10 mmhg and lowest during
early hours of morning and reverse rhythm is observed in night workers

Familial tendency of hypertension or hypotension are commonly run in families

Meals
SBP increases by 5-6 mmhg up to one hour after meals due to increase
epinephrine release from adrenal medulla .DBP remains same or slightly
decreases due to vasodilatation in digestive organs.

Sleep
SBP falls in early hours of sleep by 15-30 mmhg, because of general
vasodilatation of vessels in complete relaxed state .however disturbed
sleep increases SBP due to increased sympathetic discharge secondary to
skeleton muscle tensioning.

Posture sudden standing
increases DBP, if recorded within 30 -60 seconds of change in posture
after that it comes back to normal via the operation of baroreceptors
reflexes.

Regulation of arterial Blood pressure

Blood pressure is regulated in the body by various mechanisms which are as follows

BARORECEPTOR REFLEX
RENIN ANGIOTENSIN SYSTEM
ALDOSTERONE

HEART RATE

Normal resting heart rate in adults is 70-80 beats /min
It
is generally accepted that listening to heart beats using a
stethoscope, a process known as auscultation, is a more accurate method
of measuring the heart rate

Factors affecting heart rate:

AGE
after birth as the age increases vagal tone increases and heart rate
decreases, but in old age HR is slightly higher due to fall in vagal
tone

Foetal heart rate                            140-160bpm
At birth                                         130-140bpm
Adult’s                                             70-80bpm
Old age                                            up to 100bpm

SEX  
heart rate is slightly higher in females than males due to lower
systemic blood pressure and due to more resting sympathetic tone

BODY TEMPRETURE  
for each 1degree rise in internal body temperature, HR increases by
about 10bpm due to its effect on SA node. It also produces Cutaneous
vasodilatation causing fall in systemic B.P.

Conversely, fall in internal body temperature decreases the HR .it also produces vasoconstriction causing B.P to raise.

Exercise HR increases in linearity with the severity of exercise.

Respiration HR increases with inspiration and decreases during expiration, a phenomenon called sinus arrhythmia.

CONTROL OF HAERT RATE

Control of HR is primarily determined by two mechanisms:

1) Cardiac innervations it consists of innervations of the heart by two divisions of ANS via sympathetic and parasympathetic

2) Medullary cardiovascular centers

ELECTROCARDIOGRAM (ECG)


An
electrocardiogram (ECG or EKG) is a recording of the electrical
activity of the heart over time produced by an electrocardiograph,
usually in a noninvasive recording via skin electrodes.

Electrical
impulses in the heart originate in the sinoatrial node and travel
through the heart muscle where they impart electrical initiation of
systole or contraction of the heart A typical ECG tracing of a normal
heartbeat (or cardiac cycle) consists of a P wave, a QRS complex and a T
wave.


Image taken from   zone.ni.com

P wave

This
wave corresponds to the depolarization of the atrium During normal
atria depolarization, the main electrical vector is directed from the SA
node towards the AV node, and spreads from the right atrium to the left
atrium. This turns into the P wave on the ECG

QRS complex 

Is a structure on the ECG that corresponds to the depolarization of the ventricles..

PR/PQ interval

The
PR interval is measured from the beginning of the P wave to the
beginning of the QRS complex. . On an ECG tracing, this corresponds to 3
to 5 small boxes.

ST segment

The ST segment connects the QRS complex and the T wave and has duration of 0.08 to 0.12 sec

T wave

The T wave represents the repolarization (or recovery) of the ventricles

QT interval

The
QT interval is measured from the beginning of the QRS complex to the
end of the T wave. Normal values for the QT interval are between 0.30
and 0.44 seconds.

Stokes –Adams syndrome

Attack of
temporary loss of consciousness that occur when flow of blood ceases
due to ventricular fibrillation is called Stokes –Adams syndrome .in
this syndrome, the arterial impulse suddenly fails to be transmitted to
the ventricle, which may last for few seconds to few hours .It is
treated by artificial pacemaker .the pacemaker is connected to right
ventricle for controlling its rhythm. 

LYMPHATIC SYSTEM

The lymphatic system
in vertebrates is a network of conduits that carry a clear fluid called
lymph. it also includes lymphatic organs like spleen, lymph nodes, and
thymus

Lymph is a clear fluid derived from blood and other
tissues, which, accumulates in interstitial spaces as the interstitial
fluid .Lymph contains leucocytes mainly as lymphocytes .the composition
is similar to plasma except that it is low in proteins.

Functions The lymphatic system has three interrelated functions.

1) It is responsible for the removal of interstitial fluid from tissues.
2) It absorbs and transports fatty acids and fats as chyle to the circulatory system.
3) It transport of antigen presenting cells such as dendritic cells, to the lymph nodes where an immune response is stimulated.

Lymphoid
tissue associated with the lymphatic system is concerned with immune
functions in defending the body against the infections and spread of
tumors

DISEASES OF CIRCULATORY SYSTEM

1) Hypertension also referred to as high blood pressure, HTN,
is a medical condition in which the blood pressure is chronically
elevated. The normal arterial systolic and diastolic blood pressure in
120mmhg and 80 mmhg respectively.  Hypertension has a variety of causes
it may be idiopathic. It may also result from kidney disease ,endocrine
disease or diseases of arteries .

2) Atherosclerosis It
refers to deposition of lipids on the wall lining of large and medium
sized arteries .such a deposition is called atheroma or plaque.

3) Cardiomyopathy,
which literally means "heart muscle disease," is the deterioration of
the function of the myocardium for any reason.Cardiomyopathies can
generally be categorized into two groups,: extrinsic cardiomyopathies and intrinsic cardiomyopathies

Extrinsic cardiomyopathies These are cardiomyopathies where the primary pathology is outside the myocardium itself. Most cardiomyopathies are extrinsic.

An intrinsic cardiomyopathy is weakness in the muscle of the heart that is not due to an identifiable external cause

4) Angina pectoris, this refers to chest pain due to ischemia of the heart muscle due to obstruction or spasm of the coronary arteries.

Coronary
artery disease, the main cause of angina, is due to atherosclerosis of
the cardiac arteries most patients with angina complain of chest
discomfort rather than actual pain: the discomfort is usually described
as a pressure, heaviness, tightness, squeezing, burning, or choking
sensation. Apart from chest discomfort, anginal pains may also be
experienced in the epigastrium, back, neck, jaw, or shoulders, following
skin dermatomes.

5) Cardiac arrhythmia is a term for any
of a large and heterogeneous group of conditions in which there is
abnormal electrical activity in the heart. The heart beat may be too
fast or too slow, and may be regular or irregular. The most common
symptom of arrhythmia is an abnormal awareness of heartbeat, termed
palpitations.

6) Ischemic heart disease (IHD), or myocardial ischemia,
is a disease characterized by reduced blood supply to the heart muscle,
usually due to coronary artery disease (atherosclerosis of the coronary
arteries).

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