Body Fluids and Circulation

All living cells require nutrients, oxygen, and other essential substances, while waste and harmful materials need continuous removal for healthy tissue function. Efficient transport mechanisms are essential for moving these substances to and from cells. Simple organisms like sponges and coelenterates circulate water through their body cavities for substance exchange, while more complex organisms use specialized body fluids like blood and lymph.

1.0Blood

• Fluid connective tissue / specialized connective tissue.
• Mesodermal in origin
• Study of Blood — Hematology
• Process of blood formation Haemopoiesis (in bone marrow).
• Color — Red
• pH — 7.4 (Slightly alkaline)
• Weight — 7 to 8% of body weight
• Volume — 5 - 6 liters in male and 4 - 5 liters in female.
• Anticoagulant present in human blood – Heparin

Composition of Blood

1. Plasma

• Plasma is a straw colored, viscous fluid constituting 55% of the blood.
• When separated from the rest of the blood, plasma is a light yellow liquid.

2. RBC (Erythrocytes)

• Red blood cells (RBC) or erythrocytes are the most abundant of all the cells in blood.
• Number of RBC in healthy adult male - 5 million to 5.5 million of RBCs mm3 of blood.
• Number of RBC in healthy adult females - 4.5 million to 5 million of RBCs mm3 of blood.
• Number of RBC in healthy newborn babies - 6.8 million of RBCs mm3 of blood.

Shape and Size

• In most mammals, mature RBCs are biconcave, disc like, circular in cross section. (Biconcave shape of RBC increases surface area).

Structural Details of RBC

• ER (Endoplasmic reticulum), GC (Golgi complex), Ribosomes & Mitochondria are absent in mature mammalian RBC. Due to absence of mitochondria, they respire anaerobically.
• A network of structural proteins called stomatin is present which forms a spongy cytoskeleton.
• Carbonic anhydrase (One of the fastest enzymes) - Zinc containing enzymes which helps in transportation of CO2.

Hemoglobin (Hb)

• RBCs have a red coloured, iron containing complex protein called hemoglobin, hence the color and name of these cells.
• In each RBC 26.5 crores molecules of Hb are present.
• Red coloured respiratory pigment which helps in transportation of O2 & CO2.

Life span of RBC 

• Human adult — 120 days
• New Born Baby — 100 days
• 1% RBC are destroyed daily but in the same number new RBC enter into the blood.
• Destruction of RBC occurs in the spleen. (Graveyard of RBC)
• Spleen also stores extra blood corpuscles so it is also called Blood Bank of Body.

3. WBCs (White Blood Cells)

• White blood cells, also known as leukocytes, are significantly fewer in number than red blood cells. 
• They range from 4,000 to 11,000 per cubic millimeter of blood and comprise less than 1 per cent of the total blood volume. 
• White blood cells are essential for the human immune system despite their relatively small numbers. 

Types of White Blood Cells

There are five distinct types of white blood cells, primarily classified based on the presence or absence of granules:

• Granulocytes
• Agranulocytes

Granulocytes: Due to the presence of lobed nuclei they are also called polymorphonuclear WBC.

Are of three types :-

Granulocytes
	Acidophiles	Basophils	Neutrophils
Staining	Acidic dye like Eosin	Basic dye like methylene blue	Combination of basic and acid dyes
Nucleus	Bilobed	S-shape, 2 to 3 lobes	3 to 5 lobes
Functions	Protect body against allergy & endo parasitic infection	Secretion & transportation of heparin, histamine & serotonin	Micropolice man of blood Destroy bacteria & viruses by phagocytosis
Microscopic view

Agranulocytes 

• Due to absence of a lobed nucleus they are also called mononuclear WBC.
• Cytoplasm is clear.
• Are of two types :-

(i) Monocytes

(ii) Lymphocytes

Agranulocytes
	Monocytes	Lymphocytes
Nucleus	Kidney shaped/bean shaped	Large and spherical
Functions	Phagocytic in nature (Macropolice man & scavenger cell)	T–Lymphocytes B–Lymphocytes
Microscopic view

3. Platelets(Thrombocytes)

• Shape is disc-like, oval-shaped or biconvex.
• Size is about 2 - 3 m.
• Life span is about : 2 – 5 days.
• Normal platelets count : 1.5 – 3.5 lakh/mm3 of blood.
• Decrease in the number of blood platelets is called Thrombocytopenia, causing clotting disorders which leads to excessive loss of blood from the body.
• Non-nucleated.
• Platelets are only found in mammals.
• The critical count of Thrombocytes is 40,000/mm3. If the number is less than the critical count then red spots or rashes appear on the skin called Purpura disease.
• In their cytoplasm basophilic granules are present which can be stained by methylene blue.

Formation

• These are cell fragments derived from megakaryocyte cells of bone marrow. (Special Cells)

Functions

• Coagulation of blood clotting
• Repair endothelium of the blood vascular system by the formation of platelet plug.
• Synthesize thromboplastin which helps in blood clotting.
• Synthesize serotonin.

Blood Group

• The blood of all humans appears similar but yet differ in certain aspects.
• The ABO system and Rh factors are taken into consideration.
• (A) ABO SYSTEM :
• A, B, O system was discovered by Karl Landsteiner.
• The type of blood group depends on the type of antigen or Agglutinogen (Chemicals induce immune response), which are two types A & B. These antigens are present on the wall of RBC.
• Two types of antibodies or Agglutinin (Proteins produced in response to antigen)- a/A, b/B are also found in the plasma in the blood.
• There are four types of blood groups :
• The blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping (destruction of RBC).

• During blood transfusion, the antibodies of the receiver attack on antigens of the donor if these are the same. 
• This may cause severe complications and death of the receiver.
• During blood transfusion, the antibodies of the receiver attack on antigens of the donor if these are the same. 
• This may cause severe complications and death of the receiver.
• It is evident from the table that group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors’.
• Persons with ‘AB’ group can accept blood from persons with AB as well as the other groups of blood, Therefore, such persons are called ‘universal recipients’.

Rh Factor

• Discovered by Landsteiner & Weiner in Rhesus monkey.
• Rh antigen was also found on the surface of RBC of humans (Nearly 80%).
• On the basis of this antigen blood group can be positive (+) or negative (–).
• Rh antibodies are naturally absent.
• If the receiver is positive and the donor is negative, then transfusion is always safe.
• If the receiver is negative and the donor is positive, then only the first transfusion is safe.
• Therefore Blood group O– is a universal donor and AB+ is a universal recipient (Acceptor).

• RH Factor Incompatibility : Rh antigen is due to dominant gene

Erythroblastosis Foetalis

• If mother is Rh– & father is Rh+ then offspring will be Rh+.
• In this case 1st pregnancy is completely successful due to the separation of blood through placenta, but at the time of 1st delivery, Rh antibody is formed in mother's blood due to breaking of blood vessels at the time of delivery.
• Now in subsequent deliveries Rh antibodies from the mother (Rh−ve) can leak into the blood of the fetus (Rh+ ve) and destroy the fetal RBCs.
• This could be fatal to the fetus or could cause severe anemia and jaundice to the baby. 
• So in the next pregnancy, death of the fetus will occur in the earlier stage due to agglutination of blood called erythroblastosis fetalis/HDN (Hemolytic disease of newborn).

Blood Clotting (Coagulation of Blood)

• When a person gets hurt by a sharp object, bleeding occurs and blood oozes out (exudation of blood). 
• Blood flows from cuts or wounds but after sometimes it stops automatically, it is called clotting of blood. 
• Bleeding time – 1 -3 min. 
• Clotting time – 2 - 8 min. 
• Clot or coagulum is formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. 
• Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. 
• Thrombins, in turn, are formed from another inactive substance present in the plasma called prothrombin. (In presence of vitamin K) 

2.0Circulatory Pathway

1. Open Circulatory System

• The blood or hemolymph is pumped out of the heart and the cells are directly bathed in it. 

Examples 

• Phylum Arthropoda, 
• Phylum Mollusca (except cephalopods) 
• Phylum Echinodermata 
• Lower chordates like Tunicates/urochordates 

2. Closed Circulatory System 

• The blood is circulated through a series of vessels (arteries, veins and capillaries) and does not directly come in contact with the cells. 
• Examples : Phylum Annelida, Cephalopods Mollusc, Higher Chordates

3.0Heart

Location: Present in the thoracic cavity, in space mediastinum (between both the lungs). Heart is slightly tilted to the left. 

Weight 

• Adult Male :- 300 gms. 
• Adult Female :- 250 gms.
• Coverings and Layers of Heart : Heart is protected by a double walled membranous bag.  

Structure Of Heart

• Chambers of Heart - Our heart has four chambers, two relatively small upper chambers called atria or auricles and two larger lower chambers called ventricles. 
• Septa of Heart : A thin, muscular wall called the interatrial septum separates the right and the left atria, whereas a thick-walled, the interventricular septum, separates the left and the right ventricles. 
• 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. 

4.0Cardiac Cycle

• One complete rhythmic relaxation and contraction of all the parts of the heart which result in receiving and pumping of the blood. 
• 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. 
• There are 72 cardiac cycles/minutes in an adult. 
• Duration of cardiac cycle = 60/72 = 0.8 sec.
• End Diastolic Volume (EDV) = 120 ml. 
• End Systolic Volume (ESV) = 50 ml. 
• Stroke Volume (SV) = EDV – ESV = 120 - 50 = 70 ml. 
• Stroke Volume (SV) = Amount of blood pumped by each ventricle in one cardiac cycle, it is generally 70 ml. Stroke volume is also known as beat volume. 
• Cardiac Output = $SV\times Numberofbeats/min$. = $70ml\times 72beats/min$. = 5 L/min at rest

Heart Sounds:

• 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. 
• The second heart sound (Dub) is associated with the closure of the semilunar valves.  These sounds are of clinical diagnostic significance.

5.0Double Circulation

There are two types of circulation of blood taking place in the human heart. 

(i) 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 constitutes the pulmonary circulation.

(ii) 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.

Significance of Systemic circulation

1. Double Circulation 

• Pulmonary circulation and Systemic circulation collectively called "Double circulation". 
• In double circulation, blood has to pass through the heart twice, once in the right part of heart then goes to lungs for oxygenation and comes back to the left side of the heart. 

On the basis of supply to the organ circulation is of various types 

• For Brain – Cerebral Circulation 
• For Kidneys – Renal Circulation  
• For Heart – Coronary Circulation 
• For liver – Hepatic Circulation 

2. Coronary Circulation 

A special coronary system of blood vessels is present in our body exclusively for the circulation of blood to and from the cardiac musculature.

6.0Electrocardiograph (ECG)

• ECG is a graphical representation of the electrical activity of the heart during a cardiac cycle. 
• ECG stands for Electrocardiogram. 

Significance of ECG

• ECG is of a great clinical significance as any deviation from this shape indicates a possible abnormality or disease.

7.0Blood Pressure

• Blood pressure is the pressure exerted by the flowing blood on the elastic walls of arteries. 
• Hales measured B.P. in horse first of all. 
• The instrument by which we can measure B.P. is called Sphygmomanometer. Blood-pressure is measured in two stages :- 
• (i) Systolic pressure (120 mm of Hg) 
• (ii) Diastolic pressure (80 mm of Hg) • Normal B.P. of a healthy person is 120/80 mm Hg. 

Factors Affecting B.P. 

Disorders of Circulatory System

8.0Blood Vessels and Lymph

1. Blood Vessels

In closed type of blood vascular system, blood vessels are of 3 types :

Anatomy of Blood Vessels:

Tunica Externa :- It has loose connective tissue with collagen fibers, elastin fibers and longitudinal smooth muscles. 

Tunica Media :- It is a thick layer of circular smooth muscles and a network of elastin fibers. 

Tunica Interna/ Intima :- This layer is made up of simple squamous epithelium. It is also known as Endothelium.

Difference between Artery and Vein

Capillaries 

• These are present between arteries and veins. 
• In the walls of blood capillaries, only the endothelium layer is found. It is made up of simple squamous epithelium. 
• Exchange of material between blood and tissue occurs at the level of capillaries.

Portal system

• When the vein of any organ of the body does not open in the caval vein or heart but it divides into capillaries in any other organ and its blood is transported by vein of that other organ to the heart, then this type of system is termed a portal system. or Blood circulation that starts in capillaries and ends in capillaries is called a portal system.

It is of following types:- 

I. Renal portal system 

II. Hepatic portal system 

III. Hypophysial portal system

Hepatic Portal System

• A unique vascular connection exists between the digestive tract and liver called hepatic portal system. 
• The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation. 

2. Lymph

• Lymph is a colorless fluid which is formed by the filtration of blood at capillaries level. 
• Lymph = plasma without large protein + WBCs mainly lymphocytes 
• Lymph is also called tissue fluid or ECF or interstitial fluid.

Functions of lymph

• Lymph acts as ‘Middle Man’ between blood and tissue.
• Exchange of nutrients, gasses, etc., between the blood and the cells always occur through this fluid.
• Lymph is also an important carrier for nutrients. 
• In the intestine, lymph helps in absorption of fat through special lymphatic capillaries called lacteals. 
• Lymph has lymphocytes therefore responsible for immune responses of the body.