Study Notes on Body Fluids And Circulations

Study Notes on Body Fluids And Circulations

Outcome– composition and properties of blood

Blood Composition

  • Special connective tissue
  • Consist of fluid matrix, plasma and formed elements
  • Ph- 7.4 (slightly alkaline)
  • By weight- 7-8% of body weight
  • By volume- 5-6 litres in male and 4-5 litres in female
  • Liquid part- it is the matrix ie. Plasma which consist of around 55%
  • Solid part is the blood corpuscles which is around 45% (RBC, WBC, Platelets)


  • The major part of the blood ie. 55%
  • Straw coloured, viscous fluid
  • Plasma consist of water and proteins
  • Water- 90-92%
  • proteins– 6-8%
  • proteins are of various types. The major proteins consist of
  • fibrinogen- 0.3% which is produced by liver
  • is the largest plasma protein
  • it helps in blood clotting
  • albumin – 4% which is also produced by liver
  • is the smallest plasma protein
  • it helps keeping the fluid in blood stream so that it doesnot leak into other tissues
  • globulin – 2-2.5% which is produced by the


  • helps in blood clotting and fighting infections
  • they are of α, β, ¥ types
  • there are 5 different type of ¥ immunoglobulins which are also known as antibodies which helps in fighting against foreign bodies

Formed elements

  • 45% of blood are formed elements
  • Consist of RBC (erythrocytes), WBC (leucocytes), platelets


RBC (Red Blood Cells)

  • most abundant of all the cells
  • a healthy adult has on an average, 5 millions to 5.5 millions of RBCs mm–3 of blood
  • these are formed in the red bone marrow
  • these are circular and biconcave in shape
  • the biconcave shape is due to the absence of nucleus
  • this also helps in increasing the surface area and filling of more hemoglobin
  • hemoglobin are complex protein containing iron and are red in colour
  • a healthy individual has12-16gms of hemoglobin in every 100ml of blood
  • RBC helps in transport of respiratory gases. Also they lack mitochondria and respire anaerobically and do not use any oxygen they carry
  • They also transport carbon dioxide from tissue to lungs
  • life span is around 120 days after which they are destroyed in spleen which is the graveyard of RBC


WBC (White Blood Cells)

  • These are colourless due to lack of hemoglobin
  • They are lesser in number which averages around 6000-8000mm–3
  • It is nucleated
  • WBC possess other cell organelles that can move in amoeboid fashion which allows to squeeze through pores in capillary wall and move to a site of infection. This is known as
  • These are short lived
  • These are of 2 types
  • Granulocytes
  • Agranulocytes




  • Neutrophils, Basophils, Eosinophils are different types of granulocytes
  • Granules are present in their cytoplasm
  • Nucleus is multilobed (polymorphonuclear)
  • These are produced in bone marrow


  • Lymphocytes and monocytes are different types of agranulocytes
  • Cytoplasm is clear
  • Nucleus do not divide in lobes (mononuclear)
  • These are also produced in bone marrow
Characteristics Eosinophils Basophils Neutrophils Monocytes lmyphocytes
    Number 2-3% 0.5-1% 60-65% 6-8% 20-25%
    Life Span 14 hrs 10 hrs 12 hrs Less than 24 hrs in blood 5-7 days in blood
  Nucleus shape Bilobed 2-3 lobed 3-5 lobed Kidney/ bean shaped Large, peripheral shaped
   Function Protect us against allergy and resist infections It secretes histamine, serotonin, heparin etc and involved in inflammatory actions It is phagocytic in nature and destroy foreign organisms entering the body These are blood scavengers. Also it gives rise to macrophages that engulf the foreign particles They are of 2 types ie. B and T lymphocytes which is responsible for immune responses. B lymphocytes later form antibodies which fight against foreign bodies



  • These are called thrmbocytes which are produced from megakaryocytes of bone marrow
  • Blood normally contain 1,500,00- 3,500,00 platelets mm-³
  • The life span is around 2-5 days
  • They are disc like oval shaped
  • Colourless
  • These are phagocytic in nature
  • This involves in coagulation or clotting of blood
  • Reduction of these can lead to clotting disorders which will lead to excessive loss of blood from the body



  • Various types of blood grouping has been done
  • ABO grouping
  • Rh grouping

ABO Grouping

  • Karl Landsteiner recognised four types of blood groups in human beings
  • It is based on the presence or absence of two surface antigens on the RBC namely A and B
  • Similarly the plasma of different individuals also contain two natural antibodies called anti- A and anti- B.
  • According to Landsteiner, if an antigen is present in the RBCs, the corresponding antibody must be absent in the plasma. And if the antigen is absent on the RBCs, the corresponding antibody must be present in the plasma.
  • Also our body has self tolerant actions, ie. the immune system do not make anti- antibodies for its own RBCs

For ex if a person has blood group A, it do not produce anti- A antibodies but do produce antibodies against any B antigens.

Blood Transfusion Reactions

  • In blood transfusions the donar’s and the recipient’s blood must be compatible to avoid any serious clumping problems
  • If the blood groups are not compatible it leads to agglutination (clumping) and may further leads to blockage of small blood vessels and cause hemolysis (rupture of blood cells)


Blood groups and donor compatibility

Blood group Antigens on RBC Antibodies in Plasma Donar’s group
      A          A    anti- B      A,O
      B          B    anti- A      B,O
     AB        A,B       NIL  AB,A,B,O
      O         NIL   anti- A,B        O


  • From the above mentioned table it is evident that the person with blood group O can be donated to any other blood group and hence known as “Universal Donar
  • The person with AB blood group can accept blood from all others blood group and hence known as “Universal Recipients

Rh grouping

  • It is antigen which is similar to one present in Rhesus Monkeys hence named Rh.
  • It was discovered by Landsteiner and Wiener
  • It is observed on the surface of majority of RBCs (about 80%) of humans
  • People having these antigens are called Rh positive (Rh+ve) and those who do not have are called Rh negative (Rh –ve)
  • An Rh-ve person if exposed to Rh+ve blood will form specific antibodies against the Rh antigens. Thus Rh group need to be matched before transfusions.
  • A special case of Rh incompatibility (mismatching) has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus. Rh antigens of the foetus do not get exposed to the Rh-ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh+ve blood from the foetus. In such cases, the mother starts preparing antibodies against Rh antigen in her blood.
  • In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-ve) can leak into the blood of the foetus (Rh+ve) and destroy the foetal RBCs. This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. This condition is called erythroblastosis foetalis.
  • This can be avoided by administering anti-Rh antibodies to the mother immediately within 72hours after the delivery of the first child to destroy the foetal RBC which prevent RH.

Coagulation of Blood

  • If there’s any cut or any hurt in the finger or anywhere in the body, the wound does not continue to bleed for a long time , its because the blood has coagulation or clotting in response to it
  • This is a mechanism to prevent excessive loss of blood in the body
  • The dark reddish brown scum formed at the site of a cut or injury over a period of time. It is a clot or coagulam formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.

Mechanism of blood coagulation

  • An injury stimulates the platelets in blood to release coagulation promoting substances called thromboplastins which activates coagulation. Also tissues release tissue thromboplastins at the site of injury
  • Thromboplastins helps in the formation of the enzyme complex This complex is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive state
  • Thrombokinase converts inactive protein prothrombin present in the plasma into thrombin.
  • Thrombin is an enzyme which converts soluble fibrinogen of plasma into insoluble fibrin. Ca2+ ions are essential for both the activation and action of thrombin
  • Fibrins form a network of threads which traps dead and damaged formed elements of blood to form the blood clot or coagulum.
  • The clot heals the wound in the vessel to stop the bleeding. This is called blood clotting

Lymph (Tissue Fluid)     

  • As the blood passes through the capillaries in tissues, some water along with many small water soluble substances move out into the spaces between the cells of tissues leaving the larger proteins and most of the formed elements in the blood vessels.
  • This fluid released out is called the interstitial fluid or tissue fluid. It has the same mineral distribution as that in plasma.
  • Exchange of nutrients, gases, etc., between the blood and the cells always occur through this fluid
  • An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins. The fluid present in the lymphatic system is called the lymph.
  • Lymph is a colourless fluid containing specialised lymphocytes which are responsible for the immune responses of the body.
  • The lymphatic system comprises of lymphatic capillaries, vessels, nodes and ducts.
  • Lymph is also an important carrier for nutrients, hormones, oxygen etc.
  • It also brings the Co2 and other metabolic wastes from the body cells and pours it into venous system
  • Fats are absorbed through lymph in the lacteals present in the intestinal villi.

                     CIRCULATORY PATHWAYS

  • The circulatory patterns are of two types – open or closed.
  • In open circulatory system  blood is pumped by the heart, passes through large vessels into open spaces or body cavities called sinuses. It is present in arthropods and mollusks.
  • In closed circulatory system, the blood is pumped by the heart is always circulated through a closed network of blood vessels. This pattern is considered to be more advantageous as the flow of fluid can be more precisely regulated. It is present in annelids and chordates.
  • All vertebrates possess a muscular chambered heart. Fishes have a 2-chambered heart with an atrium and a ventricle. Amphibians and the reptiles (except crocodiles) have a 3-chambered heart with two atria and a single ventricle, whereas crocodiles, birds and mammals possess a 4-chambered heart with two atria and two ventricles.
  • In fishes the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts from where deoxygenated blood is returned to the heart (single circulation).
  • In amphibians and reptiles, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. However, they get mixed up in the single ventricle which pumps out mixed blood (incomplete double circulation).
  • In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.


  • Human circulatory system also known as the blood vascular system consists of a muscular chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated.


 Structure of human heart

  • Heart is located in the thoracic Cavity, in between the two lungs, slightly tilted to the left it is derived from the mesoderm and has the size of a clenched fist.
  • This protected by a double world membranous bag pericardium. Pericardium consist of two layers an outer parietal pericardium and an inner visceral pericardium attached to the heart. All space called pericardial cavity is present between the two layers which is filled with her fluid called pericardial fluid. The pericardium protects the heart from shocks and mechanical injuries.
  • Our heart is divided into 4 chambers two relatively small upper chambers called atria (Singular, atrium) and two larger lower chambers called ventricles. The walls of the ventricles are much thicker than that of the atria. The right and the left atria are separated by a thin muscular wall called the interatrial septum whereas the right and left ventricles are separated by a thick walled interventricular septum.
  • The atrium and the ventricle of the same side are also separated by a thick fibrous tissue called the atrio ventricular septum. However each of these SEPTA are provided with an opening through which the two chambers of the same side are connected
  • The openings between the atria and the ventricles are guarded by atrioventricular valves (AV). The AV valve between the right atrium and the right ventricle has three flaps or cusps and is therefore called the tricuspid valve. The AV valve between the left atrium and the left ventricle has two flaps or two cusps is thus called the bicuspid valve or the mitral valve.
  • Special fibrous cords called the chordae tendineae are attached to the flaps of the bicuspid and tricuspid valves at one end and their other ends are attached to the ventricular wall with the special muscles, the papillary muscles. The chordae tendineae prevent the bicuspid and tricuspid valves from collapsing back into the atria during powerful ventricular contractions.
  • Three semilunar valves (half-moon shaped pockets) are found at the points where the pulmonary artery (arising from the right ventricles) and aorta (large artery arising from left ventricle) leave the heart. These valves prevent blood from getting back into the ventricles and allows the flow of blood only in one direction i.e. from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta.


Functioning of human heart

  • The entire heart is made up of cardiac muscles.
  • A specialized cardiac musculature called nodal tissue is also distributed in the heart. A patch of this tissue called the sinoatrial Node (SAN) is present  in the upper right corner of the right atrium.
  • Another mass of tissue called the atrio – ventricular node (AVN) is present in the lower left corner of the right , close to the atrio ventricular septum.
  • A bundle of noodle fibers that is atrio ventricular bundle (AV bundle) also known as Bundle of His continues from the AVN which passes through the atrio ventricular septa to emerge on the top of the interventricular septum and immediately divides into a right and left bundle
  • Branches give rise to minute fibers throughout the ventricular musculature of the respective sides and are called purkinje fibers
  • Then nodal musculature has the ability to generate action potential without any external stimuli i.e. autoexcitable. However the number of action potentials that could be generated in a minute vary at different parts of their nodal system.
  • The SAN can generate the maximum number of action potentials ie. 72- 75 minute-¹ and is responsible for initiating and maintaining their rhythmic contractile activity of the heart. Therefore it is called the pacemaker. Our heart normally beats 72-75 times in a minute.This is called heart rate.


  • Cardiac cycle is a repeating pattern of contraction and relaxation of the heart. The phase of contraction is called systole the phase of relaxation is called  diastole.
  • How does the heart function? Suppose for all the four chambers of the heart are in relaxed state that is they are in joint diastole.
  • In relaxed state the tricuspid and the bicuspid valves are in open state. Thus the blood from the pulmonary veins and the vena cava flows into the left and the right ventricles respectively through the left and right atria. (The right atrium receives deoxygenated blood through coronary sinus and two large veins called vena cava. The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins )
  • This build up pressure that results causes the AV valves to open an blood to flow from Atria to the ventricles.
  • At this stage the semilunar valves are closed. The SAN now generates an action potential which stimulates both the atria to undergo a simultaneous contraction known as atrial systole.This increases the flow of blood into the ventricles by about 30%.
  • The action potential generated by the SAN in conducted to the ventricular side by the AVN and AV bundles from where the Bundle of His transmits it through the entire ventricular musculature. This causes contraction of the ventricular muscles known as ventricular systole.
  • The Atria now undergoes relaxation called the atrial diastole which coincides with the ventricular systole. This causes the ventricles to contract and the intra ventricular pressure rises which leads to the closure of tricuspid and bicuspid valves due to the attempted backflow of blood into the atria.
  • As the ventricular pressure increases for the the semilunar valves guarding the pulmonary artery(right side) and the aorta(left side) are forced open. This allows the blood in the ventricles to flow through these vessels into the circulatory pathways.
  • The ventricles now relax that is ventricular diastole and the ventricular pressure falls causing the closure of semilunar valves which prevents the backflow of blood into the ventricles.
  • The ventricular pressure declines further and the AV valves are pushed open due to the pressure in the Atria exerted by the blood which was being emptied into them by the veins. Once again the blood moves freely into the ventricles.
  • The ventricles and atria are now again in a relaxed state that is joint diastole as earlier . Soon a new action potential is generated by the SAN and the events described are again repeated in a sequence and the process continues.
  • This sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the Atria and ventricles
  • Our heartbeat 72 times per minute that is that many cardiac cycles are performed per minute from this it could be deduced that the duration of cardiac cycle is 8 seconds
  • Building a cardiac cycle each ventricle pumps out approximately 70ML of blood . this is called stroke volume. The stroke volume multiplied by the number of beats per minute gives the cardiac output. The cardiac output is 72 in 270 or 5040 milliliter per minute that is about 5 liters per minute. therefore the volume of blood pumped out by each ventricle per minute is known as the cardiac output. This is higher in case of athletes then an ordinary man.
  • During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. the first heart sound lub is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound dub is associated with the closure of the semilunar valves. this sounds are of clinical diagnostic significance.

                          LUB                              DUB
First heart sound Second heart sound
Produced by closing of AV valves (tricuspid and bicuspid valves) during the ventricular systole Produced by closing of semilunar valves and the beginning of the ventricular diastole
Low pitched and long duration High pitched and short duration

Heart Sounds



  • The pacemaker region of the heart (SA node) exhibits a spontaneous depolarisation that causes action potentials, resulting in the automatic beating of the heart.
  • Impulses which travel through cardiac muscles during the cardiac cycle produce electrical currents.
  • The electrical currents is conducted through the body fluids to the body surface, where the amplified currents can be detected by placing electrodes on the skin and recorded as an electrocardiogram (ECG). It was discovered by Einthoven
  • Electrocardiogram (ECG), is a graphical representation of the electrical activity of the heart during a cardiac cycle.
  • The machine used to obtain an electrocardiogram is known as electrocardiograph and this technique is called electrocardiography
  • To obtain a standard ECG, a patient is connected to the machine with three electrical leads one to nach wrist and one to the left ankle that continuously monitors the heart activity. For a detailed evaluation of the heart’s function, multiple regions are attached to the heart region.


  • The P wave is a small upward wave that represents electrical excitation (or depolarisation of the atria) which leads to contraction of both the atria.
  • The QRS (wave) complex represents the repolarization of the ventricles, which initiates the ventricular contraction (ventricular systole). The contraction of the ventricles starts shortly after Q and marks the beginning of the systole.
  • The T-wave represents the return of the ventricles from excited (depolarised) to normal state (repolarisation). The end of the T-wave marks the end of systole.
  • Thus, by counting the number of QRS complexes that occur in a given time period, the heart beat rate of an individual can be determined.
  • ECGs obtained from different individuals have roughly the same shape for a given lead configuration. ECG is of great clinical significance as any deviation from this shape indicates a possible abnormality or disease.
  • Enlargement of P-wave indicates enlargement of the atria
  • The enlarged Q and R Waves indicate myocardial infarction (heart attack).
  • The S-T segment is elevated in myocardial infarction and depressed when the heart muscles receive insufficient oxygen
  • T-wave is flat when the heart muscles receive insufficient oxygen as in atherosclerotic heart disease
  • The monitoring machine (electrocardiogram) makes the sound “pip. pip. Pip. peeeeeeee” as the patient goes into cardiac arrest.


  • The blood flows strictly by a fixed route through blood Vessels—the arteries and veins.
  • Basically, each artery and vein consists of three layers: an inner lining of squamous endothelium, the tunica intima, a middle layer of smooth muscle and elastic fibres, the tunica media, and an external layer of fibrous connective tissue with collagen fibres, the tunica externa.
  • The tunica media is comparatively thin in the veins
  • Double circulation means that the blood passes through the heart twice for each circuit of the body.
  • It includes pulmonary and systemic circulation

Pulmonary Circulation

  • The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway is known as pulmonary circulation.

 Systemic Circulation

  • The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation.
  • Thus, the systemic circulation provides nutrients, oxygen and other essential substances to the tissues and takes Co2, and other harmful substances away for elimination
  • The systemic circulation has numerous small muscular arteries and arterioles that offer greater resistance to blood flow than that in the pulmonary circulation.
  • Despite the differences in resistance, the rate of blood flow through the systemic circulation must be matched to the flow rate of the pulmonary circulation. As the amount of work performed by the left ventricle is greater than that performed by the right ventricle, so the musculature wall of the left ventricle is thicker than that of the right ventricle.

Special Region Circulation

  • A unique vascular connection exists between the

digestive tract and liver called of a standard hepatic portal system.

  • The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.
  • A special coronary system of blood vessels is present in our body exclusively for the circulation of blood to and from the cardiac




  • Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.
  • A special neural centre in the medulla oblongata (in thr brain) can moderate the cardiac function through autonomic nervous system (ANS).
  • Neural signals ie. noradrenaline through the sympathetic nerves (part of ANS) stimulates the SAN that can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.
  • On the other hand, parasympathetic neural signals (another component of ANS) releases acetycholine which decreases the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.
  • Adrenal medullary hormones i.e adrenaline and noradrenaline can also increase the cardiac output.




  • High Blood Pressure (Hypertension): Hypertension is the term for blood pressure that is higher than normal (120/80). In this measurement 120 mm Hg (millimetres of mercury pressure) is the systolic, or pumping, pressure and 80 mm Hg is the diastolic, or resting, pressure. If repeated checks of blood pressure of an individual is 140/90 (140 over 90) or higher, it shows hypertension. High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.
  • Coronary Artery Disease (CAD): Coronary Artery Disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle. It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.
  • Angina: It is also called ‘angina pectoris’. A symptom of acute chest pain appears when no enough oxygen is reaching the heart muscle. Angina can occur in men and women of any age but it is more common among the middle-aged and elderly. It occurs due to conditions that affect the blood flow.
  • Heart Failure: Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body. It is sometimes called congestive heart failure because congestion of the lungs is one of the main symptoms of this disease.
  • Cardiac arrest: When the heart stops beating or the stoppage of heart beat
  • Heart attack: When the heart muscle is suddenly damaged by an inadequate blood supply