Cardiovascular system

CARDIOVASCULAR SYSTEM

Introduction

Blood vascular system is closed type and double circulation. It consist of;          A. heart

                                                                                                                        B. blood vessels

                                                                                                                        C. blood

Blood vascular system balance between chemical and physical state of body fluid. The function is called homeostasis.

A. Heart

Structure

                        Human heart is myogenic (i.e. wave of muscular contraction start from the pacemaker or AV node opposite to neurogenic). It is triangular organ, situated between the lungs in thoracic cavity. It measures 25cm long and 250 gm in weight. It is made up of the three layers viz; pericardium, myocardium and endocardium. Pericardium consists of two sacs. The outer sac is made up of fibrous tissue and the inner sac consists of double layer of serous membrane. Pericardial cavity is filled with pericardial fluid to protect the heart from mechanical friction and external shock. Myocardium composes cardiac muscles. The endocardium lines myocardium and forms the valves of the heart.

                        Human heart is four chambered consisting of two upper thin walled auricles and two lower thick ventricles. The two auricles are separated each other by interauricular septum. The right auricle is larger than the left one. The right ventricle is larger than the left ventricle. Both ventricles are separated by interventricular septum. Both the ventricles are thick walled. The right ventricle is much thicker than the left ventricle. Internally both ventricles are provided with ridges called Columnae carnae.

                        Auricles open into the ventricles on the respective side by atrio ventricular apertures which are guarded by valves. Valves check the back flow of blood. The valves are connected with the wall of ventricles by chordae tendenae. The tricuspid valves guard the right atrioventricular aperture and bicuspid or mitral valves guard the left atrioventriclar aperture.

                        Sinu-auriclar node or pace maker situates on the wall of right auricle near the openings of venacavas.

                        There are three openings in the right auricle to collect venous blood. These are; i) a common opening of right and left venacava (precaval vein) ii) an opening of inferior venacava or post caval vein. iii) An opening of coronary sinuses in posterior part of right atrium.

                        There are four openings of pulmonary veins in the left auricle (2 from left lungs and two from right lung) to collect oxygenated blood.

                        The right ventricle opens into the pulmonary artery and the left ventricle opens in to the systemic aorta. The openings of these arteries are guarded by three semilunar valves.

                        Double circulation in man

There is no mixing of oxygenated and deoxygenated blood in human body. Because of double circulation that shows.

1. pulmonary circulation
2. systematic circulation

	Pulmonary circulation	Systematic circulation
Systole of ventricle 2.Significance 3. Diastole of auricles	The right ventricle pumps venous blood to the lungs via pulmonary arteries. As the blood reach the alveolar surface , carboxy haemoglobin release carbon dioxide and receive oxygen to be oxygenated Oxygenated blood from the lungs is carried into the left auricles via pulmonary veins	The left ventricle pumps oxygenated blood to the bidy parts via systematic aorta and arterial system. As the blood reach to tissue level of body parts the oxyhaemoglobin release oxygen so that oxidation of food takes place to produce energy. Carbon dioxide produce as a by product form (bend with hemoglobin). In this way the blood becomes deoxygenated. The venous blood from the parts is carried into the right auricle via two precaval and one post caval and venous system.

In this way two complete circulations take place simultaneously. Therefore there is no mixing of venous and oxygenated blood. Complete separation of auricles and ventricles and close type of blood vascular system also forbid mixing of oxygenated and deoxygenated blood. Coronary artery supplies the blood to heart from aorta. Coronary sinuses collect the venous blood from heart.    

Origin and conduction of heart beat

Sinu-auriclar node (SA-node) or pacemaker^*, which is small pea sized structure made up of specialized tissue situated the inner wall of right auricle near the opening of superior venacava initiated heart beat. Therefore human heart is myogenic. The cardiac impulse produced by the SA-node is radiated out in the form of wave not only contract the auricles it is also be passed to the muscles of ventricular wall due separation of auricles and ventricles by thin layer of fat i.e. annular pad.

The AV- node is the pacemaker like structure situated near the opening of the auriculoventricular septum. The impulses produced by pace maker reach to AV node 0.03sec so that it can generate its waves which will be transmitted to the myocardium viz AV bundle or bundle of His and network of  Perkinje,s fiber. The AV bundle arises from the AV-node, descends in the interventricular septum after crossing the fibrous ring it divides into the right and left branches. Each branch supplies a network of Purkinje fibers into the myocardium to convey electrical waves from AV nodes to the muscular apex so that ventricle or contraction is possible. 

FIG: Conduction of heart beat showing SA node and AV node

Heart beat

The rhythmic contraction and relaxation of cardiac muscle in the heart is known as heart beat. One heart beat includes atrial systole, joint diastole and ventricular systole.

Cardiac Cycle

Atrial systole

Both the auricles contract simultaneously due to initiation of impulse of SA node to pump auricular blood to the respective ventricles. It takes 0.1sec

• the rest potential of pacemaker is-55 to 60mv
• the waves transmit at the rate 1m/s in auricle
• the waves transmit at the rate of (1.5-4)m/s in purkunje fibers

Joint diastole

Where the auricles contract the ventricles relax. There is a tome period when both the auricles and ventricles remain relaxed. This is known as joint diastole. It takes 0.4 sec

Ventricular systole

This is the contraction of both ventricles to pump out blood to the respective arteries. It takes place for 0.3 sec during this time period the auricles relax. In this way any cardiac cycle takes place in 0.8 sec. normally 60-80 (average 72) cardiac cycles/ heart beat takes place in a minute.

Stroke volume

This is volume of blood pump cut of the heart in each beat. It measures 70ml.

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Blood pressure

Systolic blood pressure

It is the amount of pressure excited by blood on the wall of blood vessel when cardiac contraction (ventricular) takes place. It is determined by ‘lubb’ sound. It is about 120mmof hg in a healthy adult man.

Dystolic blood pressure

This is the value of pressure exerted by blood on the wall of blood vessel when cardiac relaxation takes place. It is determined by ‘dup’ sound. It is about 80mm of Hg in a healthy adult man.

      The name of instrument which clears the auscultation of heart beat is called sphygmomanometer. It is invented by Karot Koff in 1905.

      Hypertension (High blood pressure) and hypotension are the problem of blood pressure. Mental tension fear, exercise, obesity (excessive deposition of fat and increase of weight) anxiety (unpleasant emotional state) sorrow and other emotional stresses cause hyper tension. It measured as 150/90 mm Hg. When the blood pressure becomes low as 120/80 mm Hg. It is called low blood pressure. The main factor of hypotention is loss of blood by hemorrhage, failure of pumping action of the heart. It may cause a person senseless.

Electrocardiogram (ECG)

It is graphical representation of electrical variations cause by heart beat. The instrument which shows ECG is called ECG-machine or electrocardiograph. We know that SA node generates electrical impulse and it, transmitted to AV node, bundle of his, purkunje fiber, ventricular muscle fiber and lastly surround the tissue of heart. The electric impulse that is initiated in a cardiac muscle is (will be) transmitted whole body also. If suitable electrodes (leads) are placed on body opposite to heart and connected to a very sensitive galvanometer electrical potential can be recorded. Inventor of the device is Einthoven (1903) also known as father of electrocardiography. In one second 5 waves are formed. ECG shows the abnormalities of heart or heart diseases on basis of electrical impulses produced by nodes. Normal pattern of ECG has five waves, represented by PQRST 

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P wave is atrial depolarization (contraction) QRS is wave is depolarization of ventricles. T waves are repolarization (relaxation) of ventricles.

An artificial pacemaker is a lithium halide cell with an electrode. It generates electrical current (for more ten years) to regulate the heart beat at a normal rate. It was first implanted by chardack in 1960. A pacemaker is implanted when heart rate of patient is falls about 30-40%. This device is widely used and has become boon in history of medical science.

Distribution of blood volume

About 84% of blood circulates in systemic circulation. In which 64% is in veins and venules and 13% is in arteries and about 7% remain in arterioles and capillaries. Heart itself contains 7% volume of blood and pulmonary vessels contain 9% of blood.

Blood vessels: there are three types of blood vessels

a)      arteries

b)      veins

c)      Capillaries.

Histologically arteries and veins are made up of three layers of tissue.

Outer layers made up of fibrous tissues called tunica externa. A middle layer of smooth muscle with elastic tissues is called tunica media. Inner layer of squamous epithelium called tunica interna.

Wall of capillaries made up of single thin walled squamous epithelial layer.

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Arterial blood circulation

In this circulation blood is carried away from arteries from heart to different part of body in human main arteries are

Pulmonary arteries

i) Left pulmonary arteries carry deoxygenated blood from left lung.

ii) Right pulmonary arteries carry deoxygenated blood to right lung.

B) Aorta:  it begins from anterior part of left ventricle. It makes an arch and descends behind the heart.

Four major branches are given before the arch behind from aorta.

1)      Right common carotidà external and internal carotid artery supplies the blood right and left from side of head brain eyes nose.

2)      Right subclavian arteryà neck region shoulder radial and ulnar of forearm.

3)      Left common carotidà to left side of head and face.

4)      Left subclavian arteryà neck, left shoulder and arm.

C) Thoracic segments

      As the aortic arch, curves down into the abdominal region it gives following major right number of arteries.

1)      Inferior phrenic- inferior part of diaphragm

2)      Coeliac artery -stomach, pancreases, spleen, liver gall bladder, duodenum.

3)      Superior mesenteric artery- various part of small intestine.

4)      Renal arteries- kidney and adrenal glands.

5)      Genital -ovaries and testis

6)      Lumber -posterior part of abdomen.

7)      Inferior mesenteric- large intestine.

8)      Common iliac artery- pelvic region and hind limbs.

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            Venous blood circulation

            The principle veins in human body are:

            A. A pair of pulmonary veins.

            B. One superior venacava.

            C. One inferior venacava from posterior region.

FIG :Arterial and venous circulation of blood in human body

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A.     Pulmonary vein collects the oxygenated blood from lungs and opens in the left auricle.

B.     One superior venacava collects the deoxygenated blood from right and left brachiocephalic vein. Each brachiocephalic vein collect the deoxygenated blood from shoulder limbs by auxiliary vein and cephalic vein and from brain, eyes by internal jugular vein and ex j. vein. Azygous vein and hemizygous veins collect blood from thoracic area and connect with superior venacava and brachiocephalic veins.(Ex. Jugular, Internal Jugular and Subclavian vein)

C.     Venous blood of posterior region of body below the diagram is collected by inferior venacava with following veins.

1.      Common iliac veins collect the blood from leg and pelvis by external iliac vein. Similarly internal iliac vein collects the blood from rectum, ureter urinary bladder as well as reproductive organs except gonads and joins with common iliac vein.

2.      Lumber vein collect the blood from lumber region.

3.      Genital veins collect blood from gonads.

4.      Renal veins collect venous blood from kidney.

5.      Supra renal veins collect the blood from adrenal glands or suprarenal glands.

6.      Inferior phrenic veins collect the blood from lower surface of diaphragm.

7.      Hepatic vein collect the blood from liver to venacava.

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Hepatic portal system

Collection of blood from parts of alimentary canal and carried in to liver by hepatic portal vein is called Hepatic portal system. Hepatic portal vein is formed by union of following veins.

1.      Cystic vein: from gall bladder.

2.      Pancreatic vein: from pancreas.

3.      Gastric vein: from stomach and esophagus.

4.      Duodenal vein: collects blood from duodenum.

5.      Superior mesenteric vein: from small intestine and the proximal parts of large intestine(caecum)

6.      Inferior mesenteric vein: from rectum, d.colon.

7.      Splenic vein: from spleen and part of stomach

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Significance of hepatic portal system

1.      Liver store glucose in the form of glycogen and release glucose in blood as required.

2.      Fat cells are picked up by kupffer cells of liver.

3.      Excretory products are carried to the kidney.

Blood groups in human being

In 1900 Karl Landsteiner discovered three types of blood groups A, B and O. He was awarded to the work in 1931 by Novel prize. Fourth blood group AB was reported by Decastello and Sturly in 1902.

Blood contain two types of proteins—antigen or agglutinogen (type of glycoprotein) on surface of RBC (represented by A and B). Antibodies or agglutinin present in plasma (represented by a and b).

Depending upon presence and absence of antigens and antibodies four blood groups has been differentiated. These are A, B, AB and O.

1.      Blood group A have antigen A in RBC and antibody b in plasma.

2.      Blood group B have antigen B in RBC and antibody a in plasma.

3.      Blood group AB has antigen A and B in RBC but no antibody in plasma.

4.      Blood group O have no antigen in RBC but antibody a and b in plasma.

Group	Antigen on Red-cell surface	Antibodies in serum	Blood group of people can receive blood from	Blood group of people donor can give blood to
A	A	Anti-b	A,O	A,AB
B	B	Anti-a	B,O	B,AB
AB	A and B	None	A,B,AB,O	AB
O	Neither A nor B	Both A,B	O	A,B,AB,O

Fig: Table ABO blood group system

Blood transfusion

If the transfused blood or donated blood is not compatible (existing together) with blood of recipient blood agglutinates. For this, antigen of donor’s blood and corresponding antibody of recipient’s blood must not be present. Blood group AB is universal recipient and blood group O is universal donor.                

                      

Blood groups determination

1.      Taken blood is mixed with different sera separately (anti-A serum and anti-B serum)

2.      If clump with serum A it is group B, but if clump with serum B it is group A.

3.      If clump with both sera indicates it is group AB.

4.      If blood does not clump with sera A and B it is group O blood.

                                               

                        Mechanism of inheritance of blood group

A and B are dominant antigen and O is recessive antigen. Depending on the genotype of parents the group of offspring can be predicted. Examples;

Rh factor- Rh factor was discovered by K.Landsteiner and Wiener in 1940 in RBCs of Rhesus monkey (Macca rhesus).This antigen is found on the surface of RBC. Most of 85% of people have Rh factor. The presence of Rh factor in blood of a person is called Rh +Ve and absence is called Rh –Ve. Rh +Ve and Rh –Ve are incompatible and cannot be mixed. It is great importance in two conditions:

1. During transfusion of blood   2. During pregnancy

Rh incompatibility

Rh factor is very important as it is inheritable. When Rh+ man marries a Rh- woman there is a chance that some of their children will be Rh+. During pregnancy, fragments of Rh+ RBC of the foetus may enter blood of mother. It act as antigen  and mother body produce antibodies against the Rh+.The bodies passes from placenta to the foetus and destroy foetal red cell. It happens in second pregnancy because in first pregnancy the antibody will form but not enough to destroy RBC of foetus. The baby born to be premature, anaemic and jaundice. The condition is called erythroblastosis foetalis.

About one in every 10 marriages is between Rh+men and Rh- women, but only about one in 40 of these marriages is affected by the Rh- incompatibility.