Blood Circulation | All about Blood Circulation in Human Beings.

 CIRCULATION

1. The system in which blood is circulated throughout the body is called circulatory system.

2. Blood :- 

a) The main circulating, bright red, slightly alkaline fluid int he human body is called blood.

b) Study of blood is called hematology.

c) Blood is a fluid connective tissue derivated from mesoderm. It has pH about 7.4.

d) There are about 5 liters of blood in the body which is about 8% of the total body weight.

3. Composition of blood :- 

There are two main components of blood, viz., Plasma (55%) and blood corpuscles (45%).

(1) Plasma : Plasma is a straw coloured fluid part of blood, slightly alkaline, viscous fluid consisting of 90-92% water and 8-10% of solutes.

a. Solutes are 7% proteins (serum albumin, serum globulin, heparin, fibrinogen and prothrombin).

b. Other solutes are nutrients (Glucose, amino acids, fatty acids and glycerol). 

c. Nitrogenous wastes such as urea, uric acid, ammonia and creatinine.

d. Gases like oxygen, carbon dioxide and nitrogen.

e. Regulatory substances like enzymes and hormones.

f. Inorganic substances like bicarbonates, chlorides, phosphates and sulphates of sodium potassium, calcium, magnesium, etc.

(2) Blood corpuscles : 

Blood corpuscles are solid part of blood. They are of three types erythrocytes (RBC), leukocytes (WBCs) and thrombocytes (Platelets).

(I) Erythrocytes or RBCs :- 

a. Circular, biconcave, enucleated cells of about 7 µm in diameter and 2.5 µm  in thickness.

b. RBC cout is about 5.1 to 5.8 million RBCs/ cu mm in male and 4.3 to 5.2 million/ cu mm in female. The average life span of RBC is about 120 days.

c. Erythropoiesis is formation of RBCs. It occurs in liver and spleen in foetus and in red bone marrow in adults.

d. The old RBCs are destroyed in liver and spleen.

e. Polycythemia is increase while erythrocytopenia is decrease in number of RBCs. 

f. RBCs contain respiratory pigment called haemoglobin which helps in transport of oxygen and carbon dioxide.

g. The normal haemoglobin content in adult male is 13-18 mg/100 ml of blood and 11.5-16.5 mg/100 ml of blood in adult female.

h. Less amount of haemoglobin leads to anaemia.

i. RBCs transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs. They maintain blood pH as haemoglobin acts as a buffer. They also maintain the viscosity of the blood.

(II) Leucocytes or WBCs :- 

a. Leucocytes are colourless, nucleated, amoeboid and phagocytic cells.

b. They show diapedesis, i.e. squeezing out of blood capiollaries by amoeboid movement.

c. The size is about 8 to 15 µm .

d. Total WBC count is 5000 to 9000 WBCs/cu mm of blood.

e. The average life span of WBCs is about 3 to 4 days.

f. Leucopoiesis or formation of WBCs, occurs in red bone marrow, spleen, lymph nodes, tonsils, thymus and  Payer's patches.

g. Leucocytosis is increase while leucopenia is decrease in the number of WBCs.

h. Leukemia or blood cancer is a pathological increase in number of WBCs.

i. The dead WBCs are destroyed by phagocytosis in  blood, liver and   lymph nodes.

j. Leucocytes are of  two types. viz. neutrophils, eosinophils and basophils.

k. Agranulocytes are of two types, viz. monocytes and lymphocytes.

(III) Thrombocytes or Platelets :-

a. Thrombocytes are smallest, nonnucleated, round and  biconvex. They are of about 2.5 to 5 µm  in diameter. Their count is about 2.5 lakhs/cu mm.

b. Their life span is about 5 to 10 days.

c. Magakaryocytes of bone marrow form thrombocytes.

d. Thrombopolesis is  the formation fo f platelets. 

e. Thrombocytosis is the increase while thrombocytopenia is the decrease in platelet count. 

f. Thrombocytes help in coagulation of  blood by releasing thromboplastin. 

 4. Blood Coagulation :- 

Active anticoagulants like heparin and antithrombin are present in the intact blood vessels. But upon the rupture of a blood vessel, bleeding starts. The fluid blood is converted into semisolid jelly by the process of blood coagulation or clotting.

The events that take place during blood clotting are as follows :

(1) Release of thromboplastin from platelets and injured tissues.

(2) Formation of enzyme prothrombinase inthe blood.

(3) Conversion of prothrombin into thrombin by prothrombinase.

(4) Conversion of fibrinogen into fibrin by thrombin.

(5) Formation of mesh by the fibrin fibres forming the  clot.

(6) The normal clotting time is 2 to 8 minutes.

5. Blood Groups :-

There are four blood in human beings, viz., A, B, AB and O.

6. Heart :- 

a. Heart is hollow, muscular, conical organ about the size of one's first with broad baseand narrow apex tilted towards the left.

b. It is mesodermal in origin.

c. It is situated in middle of the thoracic cavity in a space called mediastinum, between the two lungs.

d. The heart is 12 cm in length, 9 cm in breadth and 250 to 300 grams in weight.

7. Pericardium :- 

Double layered membrane. Two layers are as follows :- 

a. Fibrous pericardium : Outer, tough layer of inelastic fibrous connective tissue.

b. Serious pericardium : This inner pericardium has two layers, outer parietal layer and inner visceral layer.

c. Parietal layer forms the inner linning of fibrous pericardium.

d. Visceral layer or epicardium is next to heart on the outer side.

e. Pericardial fluid is present between the parietal and visceral layers of serous pericardium.

8. Heart wall :- 

a. The heart wall has three layers, viz. outer epicardium, middle myocardium and inner endocardium.

b. Epicardium has single layer of flat epithelial cells mesothelium.

c. Myocardium has cardiac muscle fibers responsible for movements of the heart.

d. Endocardium has single layer of flat epithelial cells called endothelium.

9. External structure of heart :- 

a. Human heart consists of two superior, small, thin walled receiving chambers called atria or auricles and two inferior, large, thick walled, distributing chambers called ventricles.

b. Atrio-ventricular groove or coronary sulcus, a transverse groove which is present between the atria and the ventricles is seen externally.

c. The interventricular sulcus is present between the right and left ventricles. Coronary arteries and coronary veins are present in the sulci. The coronary veins join to form coronary sinus which opens into the right atrium.

d. The right atrium receives deoxygenated blood from all over the body through superior vena cava and inferior vena cava.

e. Left atrium receives oxygenated blood from lungs through two pairs of pulmonary veins.

f. From the right ventricle deoxygenated blood is sent to lungs through pulmonary trunk.

g. From the left ventricle oxygenated blood is sent to entire body by systemic aorta.

h. Ligamentum arteirosum connects the pulmonary trunk and systemic aorta. It represents ductus arteriosus of foetus. 

10. Internal structure of heart :- 

a. There are four chambers in the heart, viz., two atria and two ventricles which can be demarcated internally.

b. Atria are thin walled upper receiving chambers separated from each other by interatrial septum. 

c. The right atrium receives deoxygenated blood from all over the body through superior vena cava, inferior vena cava and from the heart through coronary sinus. 

d. the opening of inferior vena cava is guarded by Eustachian value while the opening of coronary sinus is guarded by Thebesian valve.

e. The fossa ovals is oval depression that is present on the right side of interatrial septum. It is the remnant of foramen ovale, an oval opening int he interatrial septum of the foetus.

f. The left atrium receives oxygenated blood from the lungs through four openings of pulmonary veins.

g. Right and left atria open into the right left ventricles respectively through atrioventricular apertures. These are respectively guarded by tricuspid and biscupid and biscupid valves made up of connective tissue.

h. The right atrioventricular valve has three flaps hence called tricuspid valve while left atrioventricular valve has two flaps hence called bicuspid valve or mitral valve.

i. These valves are attached to papillary muscles of ventricles by chordae tendinae. The valves are prevented from turning back into the atria during the contraction of ventricles due to chordae tendinae.

j. Ventricles are two thick walled lower, distributing chambers seperated from each other by interventricular septum.

k. Left ventricle has thick wall. The inner surface of the ventricle is thrown into a series of irregular muscular ridges called columnae carnae or trabeculae carnae.

l. Pulmonary trunk or aorta arises from the right ventricles carrying deoxygenated blood to lungs for oxygenation. Systemic aorta arises from the left ventricle carrying oxygenated blood to all parts of the body.

m. Pulmonary aorta and systemic aorta have three semilunar valves at the base which prevent the backward flow of blood during ventricular diastole.

11.Pumping action of heart :- 

Heartbeat is the rhythmnic contraction, i.e. contraction (systole) and relaxation (diastole) of the heart. The rate of heartbeat is about 72 times per minute during which it pumps out about 5 litres of blood.

12. Conducting system of heart :- 

a. The heartbeat in human beings originates in modified cardiac muscles called sinoatrial node (S.A. node) therefore, the heart is said to be myogenic.

b. The conducting system of heart consists of sinoatrial node (SAN), atrioventricular node (AVN), Bundle of His and Purkinje fibres.

13. Cardial cycle or working of heart :- 

a. One atrial systole (0.1 sec.), One ventricular systole (0.3 sec), followed by a joint diastole (0.4 sec) is called a cardiac cycle. 

b. One cardiac cycle takes placein about 0.8 second and is also called a heartbeat.

14. Regulation of cardiac activity :- 

a. Cardiovascular centre present in the medulla oblongata of brain regulates the working of the heart.

b. Sympathetic nerves secrete adrenaline, which increases the ratr of the heart.

c. Parasympathetic nerves secrete acetyulcholine, which decreases the rate of the heart.

15. Blood Vessels :-

a. Angiology is the study of blood vessels.

b. Blood vessels are of three types viz. arteries, veins and capillaries. 

(1) Arteries :- Blood vessels carrying blood away from the heart are called arteries. Arteries form arterioles which in turn divide and redivide to form capillaries.

(2) Veins :- Blood vessels carrying blood to the heart are called veins. They have broad lumen and show low blood pressure.

(3) Capillaries :- Capillaries are thinnest of blood vessels and formed by division and redivision of arteriole. Capillaries unite to form venules. Venules join to form veins.

16. A chart showing the differences between arteries, veins and blood capillaries :- 

Arteries	Veins	Capillaries
(1) Carrying blood from the heart to other parts of the body.	Carrying blood from the different parts of the body  to the heart.	Arteries break into capillaries and capillaries unite to form veins.
(2) Thick walled	Thin walled.	Very thin with permeable walls.
(3) Arteries break up into arterioles.	Venules unite to form larger veins.	Exchange of materials take place through the capillary walls.
(4) Show high blood pressure.	Show least blood pressure.	........
(5) Shows three layers : Tunica adventitia or externa Tunica media Tunica interna or intima	Show three layers : Tunica externa Tunica media Tunica interna	........

17. Pulmonary and systemic circulation :- 

a. Human heart shows double circulation as blood passes twice through the heart during one cardiac cycle. The blood follows two routes viz. pulmonary and systemic.

b. Pulmonary circulation is the circulation between the heart and the lungs. The course of blood during pulmonary circulation is from the first ventricle (by pulmonary trunk) to the left atrium (by two pairs of pulmonary veins) of heart through lungs.

c. Systemic circulation is the circulation between the heart and the body organs (except lungs). The course of blood during systemic circulation is from left ventricle (by systemic aorta) to all body organs and from the body back to right atrium (by vena cavae).

d. Coronary circulation is circulation to the cardiac muscles of the heart. Coronary arteries supply oxygenated blood whereas coronary veins join to form coronary sinus and collect deoxygenated blood. This sinus opens into the right atrium.

18. Heartbeat and pulse :- 

a. Heartbeat is the rhythmic contraction and relaxation of the heart.

b. One systole and one diastole makes one heartbeat.

c. Heart rate is number of beats per minute (72 times per minute).

d. Stroke volume is amount of blood pumped out of ther ventricles each time. (about 70 ml of blood).

e. Cardiac output is amount of blood pumped out of the ventricles per minute, i.e. 72 x 70 ml = 5040 or about 5 liters of blood per minute.

f. Tachycardia is faster heart rate (Over 100 beats per minute).

g. Bradycardia is slower heart rate (Below 60 beats per minute).

h. Pulse is a pressure wave travelling through the arteries after each ventricular systole.

i. Pulse in the radial artery at the wrist is commonly measured.

j. The pulse rate per minute indicates the heart rate. it is same as that of heart rate (72 per minute).

k. Pulse rate changes with age, sex, posture, exercise and emotional state.

19. Autorhythmicity :- 

a. The heart shows autorhythmicity as the impulse for its rhythmic movement during beating is developed inside the heart.

b. The autorhythmic fibres are developed during embryonic life. They act as pace maker by setting the rhythm for the heart. They also form conducting system for conducting impulses throughout heart muscles.

d. The impulse travels in the heart in the following manner :- 

* Sinoatrial node (Pace Maker) -----> inter-nodal pathway -----> Atrioventricular node ------> Bundle of His -----> Right and left bundle branches ------> Purkinje fibres.

20. Blood pressure :- 

Arterial blood pressure is the lateral pressure of force exerted by following blood on the wall of arteries.

a. Sphygmomanometer is the instrument used for measuring the blood pressure.

b. The units of blood pressure are mm Hg (millimetres of mercury). 

c. Blood pressure is of two types systolic blood pressure and diastolic blood pressure.

d. Systolic blood pressure : It is the maximum pressure of blood during ventricular systole. Normal systolic pressure is 80 mm Hg.

e. The normal blood pressure is 120/80 mm Hg.

21. Hypertension :- 

a. Hypertension means higher values of blood pressure (More than 140/90 mm Hg blood pressure values).

b. Excessive high blood pressure of about 220/120 mm Hg may cause rupturing of blood vessels of eyes (causing blindness). Kidneys (nephritis) and brain (stroke or paralysis).

c. Factors such as arteriosclerosis, atherosclerosis, obesity, physical or emotional stress, alcoholism, smoking, cholesterol rich diet, increased secretion of renin,, epinephrine or aldosterone, etc. can cause blood pressure.

22. Coronary artery disease (CAD) :- 

a. Atherosclerosis (narrowing of coronary arteries) can cause coronary artery disease.

b. In CAD the heart muscle is damaged because of an inadequate amount of blood due to obstruction of its blood supply.

c. Depending on the degree of obstruction, symptoms may be mild chest pain (angina pectoris) or heart attack (Myocardial infarction).

23. Atherosclerosis :- 

Deposition of fatty substances in the lining of arteries, resulting in the formation of an atherosclerotic plaque. These depositions decrease the size of the material lumen.

24. Angina pectoris :- 

Angina pectoris is the pain in the chest due to reduction in blood supply to cardiac muscle caused by narrowed and hardened coronary arteries.

25. Heart failure :-

Heart failure is the result of progressive weakening of heart muscle and the failure of the heart to pump blood effectively. Degeneration of heart muscles results in heart failure. Factors responsible for such heart failure are advanced age, malnutrition, chronic infections, toxins, severe anaemia and hyperthyroidism.

26. ECG :-

a. Electrocardiogram or ECG is graphic record of electrical variations produced by the heart during one heart beat or cardiac cycle.

b. Electrocardiograph or ECG machine is the instrument used to record action potentials generated by heart muscles.

c. Einthoven in 1903 discovered this technique, hence he is known as the “Father of Electrocardiography”.

d. A normal ECG consists of different types of waves such as P-Wave, QRS-complex wave and T-wave.

Wave	Characteristic	Cause	Indication
P-wave	Upward and small	Impulse generated by SA node	Atrial depolarization causing atrial contraction
QRS-complex	Downward, large upright triangular	Spreading of impulse from SA node to AV node then to bundle of His and Purkinje fibers.	Ventricular depolarization causing ventricular contraction.
T-wave	Broad upward	No new impulse	Ventricular repolarization causing ventricular relaxation.

 

e. Abnormal functioning of heart such as in coronary artery diseases, heart block, angina pectoris, tachycardia, ischemic heart disease, myocardial infarction, cardiac arrest, etc. can be diagnosed by ECG.

27. Lymphatic system :-

Lymph, lymphatic capillaries, lymphatic vessels and lymph nodes together constitute lymphatic system.

(1)Lymph is the tissue fluid bathes the cells and is collected in lymphatic capillaries. Lymph is a fluid connective tissue just like blood but is without RBCs, platelets and some plasma proteins. It contains carbon dioxide and metabolic wastes.

(2) Lymphatic capillaries are thin walled vessels interwoven  with the blood capillaries, present in all the tissue spaces. They are not connected with blood capillaries and are lined by endothelium of thin and flat cells.

(3) Lymphatic vessels are formed by the union of lymphatic capillaries. These are thin walled having numerous valves to prevent backflow. Thoracic or left lymphatic duct and right lymphatic duct are the main lymphatic vessels in the body.

(4) Lacteals are the lymphatic vessels coming from the intestine. They have milky appearance due to absorbed fats.

(5) The thoracic duct is the main collecting duct of the lymphatic system. It receives lymph from left side of the head, neck, chest, left upper extremity and entire body below the ribs. The right lymphatic duct drains lymph from the upper right side of the body.

(6) Lymph nodes are small, oval or bean shaped bodies situated in the course of lymphatic vessels. Lymph nodes are maximum in neck, armpit and groin. They act as filters as macrophages of lymph nodes, remove bacteria, foreign material and cell debris. They also produce lymphocytes and antibodies.

(7) Function of lymphatic system :-

a. Draining of the excess tissue fluid from the extracellular spaces back into the blood.

b. Transport of carbon dioxide and metabolic wastes from the tissue fluid. Transport of lymphocytes and antibodies from the lymphatic nodes to the blood.

c. Transport of absorbed fats from the intestine to the blood.

d. Destruction of invading microorganisms and foreign particles in the lymph nodes.