This module deals with

    • composition and functions of blood
    • properties of blood


  • Blood is a fluid connective tissue that flows all over the body in the vessels of the cardiovascular
  • Transportation
  • Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs
  • Transport nutrients from GI tract to liver and other cells
  • Transport hormones from endocrine glands to target cells
  • Transport waste products from cells to excretory organs
  • Regulation
  • Maintains homeostasis
  • Regulates pH / acid base balance
  • Regulates body temperature and water balance
  • Regulates osmotic pressure
  • Protection
  • Provides immunity
  • Blood is composed of fluid in which the cells and cell fragments are suspended. The fluid portion is known as the plasma‚ and the suspended cellular elements are the
    • Erythrocytes (RBCs)
    • Leukocytes (WBCs) and
    • Thrombocytes (platelets)
  • Plasma constitutes about 55 to 70% of the blood volume, while the cellular components account roughly about 30-45% of the total It performs numerous functions that are essential for life and health.
  • Specific gravity is the ratio of weight of a given volume of a fluid to the weight of the same volume of distilled water measured at 25°
  • Plasma protein concentration is largely responsible for the specific gravity of the plasma. The cellular elements called the corpuscles have higher specific gravity than the



Species Specific gravity
Goat 1.042 (1.036 – 1.051)
Pig 1.045 (1.035 – 1.055)
Dog 1.048 (1.045 – 1.052)
Cat 1.050 (1.045 – 1.057)
Sheep 1.051 (1.041 – 1.061)
Cattle 1.052 (1.046 – 1.061)
Horse 1.053 (1.046 – 1.059)


  • The copper sulphate drop falling method is commonly used for the assessment of specific gravity of blood and plasma. Various factors influence the specific gravity of the


Specific gravity is increased in the following conditions


  • Polycythemia: High altitude, polycythemia vera, newborns etc.
  • Severe dehydration: Excessive fluid loss such as in vomiting,
  • Hemoconcentration: Loss of plasma as in


Specific gravity is decreased in the following conditions


  • Pregnancy: Increase in plasma volume causes hemodilution.
  • Renal diseases: Loss of albumin, oedema
  • Hemodilution: Hypersecretion or prolonged treatment with
  • Starvation and malnutrition: Decrease in plasma
  • Intravenous fluid
  • Viscosity is influenced by concentration of RBCs and plasma proteins. Among plasma proteins, the viscosity is mainly contributed by the gamma globulins which provide the resistance to blood flow and helps the normal pumping activity of the
  • It is normally about five times greater than water. Viscosity of blood  is  determined using viscosimeter.
  • An increase in the viscosity of blood is seen in conditions like polycythemia, congestive heart failure, jaundice, vomiting, diarrhoea etc, whereas a decrease in the viscosity is commonly noticed in anemia, oedema
  • It is the fluid portion of the blood. It is yellow to colourless depending on the quantity, species of the animal and animal’s
  • The plasma colour is golden yellow in dog, colourless or slightly yellow in sheep and goat, while it is highly yellow coloured in horse and cow which is chiefly due to bilirubin‚ and to some extent by the carotene, xanthine and other pigments.


Icterus index


  • It is a measure of the yellow colour of the plasma. It is measured by comparing the colour of the plasma with a standard solution of potassium
  • Plasma is obtained by adding anticoagulant to whole blood to prevent clotting and centrifuging it for settling down of the


Composition of Plasma


  • Plasma is made up of water to the extent of 91 – 92%; Solids : 8 – 9%; the solid portion of plasma includes proteins: 6 – 8 g %: Organic and inorganic compounds: 2 – 3 %


Organic Carbohydrates : Glucose, Lactate, Pyruvate
Inorganic Macro level : Fe, Cl, SO4, PO4, Micro level : Mn, Co, Cu, Zn, Iodide.
Plasma proteins Albumin, Globulin, and Fibrinogen
Non Protein Nitrogenous (NPN)


Urea, Uric acid, Creatine, Creatinine, Salts of Ammonia
Lipids Neutral fat, Cholesterol, Phospholipids, Lecithin
Others Enzymes, Hormones, and Vitamins


  • In the absence of the anticoagulants, the blood comes out of the blood vessels and gets coagulated to form a blood clot. On shrinking it discharges a clear watery liquid called the serum.
  • Serum is also obtained by collecting the blood without the addition of anticoagulant and allowing it to clot. Later, upon shrinkage of the blood clot the serum is
  • It differs from the plasma in lacking fibrinogen, prothrombin and other coagulation factors which are involved in blood
  • The normal pH of the blood is 4.
  • The venous blood is slightly towards acidic side because of  the  increased content of  CO2, whereas the arterial blood is slightly more towards alkaline
  • The plasma is more alkaline than the
  • The blood pH range:

o     Dog    : 7.32- 7.68

o      Cattle : 7.35 – 7.50

o      Horse : 7.35 – 7.43

  • Fowl : 56.
  • Excessive production of metabolic acid products causes abnormal reduction in the alkaline reserve leading to the condition referred to as acidosis, whereas abnormal increase in the alkaline reserve is called as alkalosis.


Learning objectives 

  • This module deals with
    • types of plasma proteins
    • functions and normal concentration of plasma proteins
  • Plasma proteins contribute about 7% of the total organic molecules of the plasma. The major proteins present in plasma are:
    • Albumin (55%),
    • Globulins (38 %) and
    • Fibrinogen (7 %).
  • Liver functions as a chief site of synthesis of plasma proteins, albumin, fibrinogen, prothrombin and some of the While the gamma globulins are synthesised extra- hepatically in the lymph nodes and in the Mononuclear Phagocytic System (MPS) of spleen and bone marrow.
  • The ratio of albumin to globulin is 1:0.7. There are species variations in the ratio of plasma proteins e. albumin: globulin ratio. In humans, sheep, goats and dogs, the albumin predominates over globulin.
  • In horses, pigs, cow and cats albumin globulin ratio is equal. In new born animals (except rodents and primates plasma gamma globulin is absent or found in minute


Separation of plasma proteins


  • Salting out method: Using different concentrations of ammonium sulphate
  • Electrophoresis: Paper, starch gel, polyacrylamide gel electrophoresis are used for the separation of plasma protein



  • Transports thyroxine and Vitamin




  • Two fifth is intravascular and the rest occur extravascularly. It provides colloidal osmotic pressure because of its high concentration and low molecular weight and non-diffusible property through blood vessels, thus prevents excessive passage of fluid from the blood into the interstitial tissue and serves to control the fluid balance between blood and tissues.
  • It contributes to the amino acid pool with tissue protein and helps in transport of some anions and



  • Includes fractions α1 and α2, β1 and β2 and γ globulins which include IgA, IgD,IgE, IgG and
    • α – globulins act as carrier proteins of bilirubin, lipids, steroids and
    • α1 globulins are protease inhibitors and functions to inhibit WBC elastase and other WBC proteases and activated factor XI. The α1 lipoproteins transport lipids,fat soluble vitamins and
    • α2 globulins are the macroglobulins and inhibit plasmin, thrombin and
    • β – globulins are:
      • Ceruloplasmin: Transports
      • Ferroxidase: Transferrin transports
      • Haptaglobulin: Transports Hb to liver after haemolysis.
      • Apolipoproteins: Transports triglycerides, phospholipids and
      • Hemopexin: Aids the transport of heme from lysed
      • Transcortin: Transports
      • Transcobalamins I & II: Transports
    • γ – globulins
      • They provide viscosity to the blood, thus maintain normal blood pressure. Synthesised by -lymphocytes and plasma cells, functions to provide immunity and also helps transport of vitamin
      • The γ globulins are the immunoglobulins (Ig) and are classified into the following types:
      • IgG is responsible for most of the humoral immunity of the organism. It can cross placenta.
      • IgM is the second major immunoglobulin of the serum and it is typically the first   immunoglobulin   increase   in   concentration   in   serum during primary immune response. These are naturally occurring antibodies against erythrocytes in certain incompatible blood
      • IgA is a glycoprotein found in external secretion such as saliva, tears, colostrum etc. It forms the primary immunoglobulin in the colostrum and is responsible for natural passive immunity in the neo-natal calf, foal, lamb, kid and piglets. Plays an important role in local defence by protecting various body surfaces g., the intestinal, respiratory and uro-genital tracts, mammary gland and the eyes from bacterial and viral invasions. IgA does not cross the placenta. It is most abundantly found in normal animals.
      • IgD is involved in B-cell differentiation to form ‘clones’.
      • IgE is involved in hypersensitivity and allergic responses. It causes the release of histamine from basophils and mast cells.




  • Fraction from the liver, functions as a precursor to form a mesh work of fibrin threads and play a key role in blood
  • It influences the suspension stability of the erythrocytes. Increased concentration of fibrinogen and globulins alter the colloidal state of the blood, hastens agglutination of RBCs and
  1. Function as source of amino acids for the synthesis of tissue proteins. The amino acids of plasma protein and tissue proteins are in a state of dynamic
  2. Provide colloidal osmotic pressure and helps to regulate fluid balance. Around 80% of the colloidal osmotic pressure is contributed by
  3. They act as blood buffer and regulate acid-base balance, thus maintains normal pH of 4.
  4. Fibrinogen and various clotting factors are essential for coagulation of
  5. Influence the suspension stability of RBCs in the
  6. Contributes to the viscosity of plasma (by gamma globulins), thereby providing for peripheral resistance, which is essential for efficient cardiac
  7. As carrier proteins they are invloved in transport of copper, iron, heme, bilirubin, thyroxine, cortisol, sex hormones, vitamin A, vitamin D, fatty acids, triglycerides, phospholipids and
  8. Immunoglobulins provide specific antibody against specific


Species Total protein Albumin Globulin Fibrinogen
Horse 6.0 – 8.0 2.8 – 3.8 2.8 – 3.8 0.2-0.4
Cow 7.0 – 8.5 3.0 – 3.8 3.6 – 4.4 0.2-0.5
Sheep 6.0 – 8.0 3.5 – 4.5 2.5 – 3.5 0.2-0.4
Goat 6.5 – 7.5 3.7 – 4.5 2.4 – 3.2 0.2-0.5
Pig 6.5 – 8.5 3.5 – 4.0 3.5 – 4. 0 0.2-0.4
Dog 6.0 – 7.8 3.4 – 4.4 2.7 – 3.2 0.1-0.4
Cat 6.0 – 7.4 3.0 – 3.8 2.5 – 3.5 0.1 – 0.4
Fowl 4.0 – 5.2 1.2 – 3.8 2.3 – 3.3


  • Lipids are heterogenous molecules soluble in organic solvents but not in water. They are esters of fatty acids, formed by the reaction of fatty acids with
  • Blood lipids (or blood fats) are lipids in the blood and they are present either free or bound to other molecules. Blood lipids are mainly fatty acids, triglycerides, lipoproteins and
  • Since lipids are insoluble in water they are mostly transported in a protein covering, and the density of the lipids and type of protein determines the fate of the lipid and its influence on



  • The concentration of blood lipids depends on dietary intake, absorption from the intestine and excretion and uptake and secretion from cells.
  • Fatty acids are present in different forms {as in chylomicrons, Very low density lipoproteins (VLDL), Low density lipoproteins (LDL)} in In addition, the fatty acids released from adipocytes exist in the blood as free fatty acids.
  • Short- and medium chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein. Long-chain fatty acids are too large to be directly released into the intestine capillaries. Instead, they are coated with cholesterol and protein (protein coat of lipoproteins) into a compound called as chylomicrons. The chylomicrons enter into lymphatic capillary and then into the bloodstream (having bypassed the liver).
  • The concentration of blood fatty acids increase temporarily after a meal which increases the uptake of fatty acids in different cells of the body like liver cells, adipocytes and muscle cells. This uptake is stimulated by insulin from the
  • Some of the fatty acids taken up by the liver is converted into VLDL and again secreted into the blood.
  • When the concentration of fatty acids in the blood decreases, this triggers adipocytes to release stored fatty acids into the blood as free fatty acids, in order to supply the energy for the muscle cells and other cells.
  • Lipoproteins are complex aggregates of lipids and proteins that increases the solubility of lipids and enable their transport throughout the
  • Lipoproteins are synthesised mainly in the liver and
  • The most abundant lipid constituents of lipoproteins are triacylglycerols, free cholesterol, cholesterol esters and phospholipids (phosphatidylcholine and sphingomyelin); fat- soluble vitamins and anti-oxidants are also transported in this
  • The lipoproteins contain different protein components called apoproteins (or apolipoproteins). Apoproteins are required to solubilise the non-polar lipids in the circulation. These proteins determine the overall structures and metabolism, and their uptake in liver and peripheral
  • Lipoproteins are classified as chylomicrons (CM), very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL), based on the relative densities on ultracentrifugation.
  • Based on the relative mobilities on electrophoresis, lipoproteins can also be classified into α, pre-β and β lipoproteins that correspond to HDL, VLDL and LDL,


Density (g/ml) 0.94 0.94-1.006 1.006-1.063 1.063-1.210
Total lipids (wt%) 99 91 80 44
Triacylglycerol 85 55 10 6




Cholesterol esters 3 18 50 40
Cholesterol 2 7 11 7
Phospholipids 8 20 29 46


  • Lipoproteins are spherical in shape with the core containing non-polar lipids, triacylglycerols and cholesterol esters, and a surface layer consisting of phospholipids and non-esterified cholesterol, which also serve to present a hydrophobic face to the aqueous phase.
  • The principal role of the chylomicrons and VLDL is to transport triacylglycerols as a source of fatty acids from the intestines or liver to the peripheral
  • Chylomicrons: They are largest of the lipoproteins; they are formed in the intestinal mucosa and transport triacylglycerols from the intestinal mucosa to the liver or to other tissues; they carry mostly fats in the form of triglycerides and cholesterol. In the liver, chylomicron particles release triglycerides and some
  • VLDL: They are synthesised in liver. The liver converts the excess fatty acids (dietary or synthesised) into very low density lipoproteins (VLDL) and secretes them into plasma; in the plasma they are converted to intermediate density lipoproteins(IDL), and then to low- density lipoprotein (LDL) particles. VLDL transports triacylglycerols from liver to peripheral
  • LDL: It is the main transporter of cholesterol to the peripheral tissues. When they are present in excess they are strongly associated with the formation of atheromatous (plaque formation within arterial wall) disease within the For this reason, LDL is referred to as “bad cholesterol”.
  • HDL: They are synthesised in liver. The HDL removes excess cholesterol from peripheral tissues and delivers them to the liver for excretion in bile in the form of bile acids, a process that has been termed ‘reverse cholesterol transport’, helps to lower blood cholesterol level and hence HDL is commonly called “good cholesterol”.
  • After being transported to the liver by HDL, cholesterol is delivered to the intestines via bile production. However, 92-97% is reabsorbed in the intestines and recycled via enterohepatic circulation
  • It is lipid, waxy steroid found in the cell membranes and transported in the blood plasma of all animals.
  • It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and
  • In addition, cholesterol is an important precursor molecule for the biosynthesis of bile acids, and several fat soluble vitamins, Vitamin D3 and the steroid hormones, includingthe adrenal gland hormones such as cortisol and aldosterone as well as the sex hormones like progesterone, estrogens, and testosterone and their
  • Within the cell membrane, cholesterol also functions in intracellular transport, cell signalling and nerve
  • Since cholesterol is essential for life, it is primarily synthesized de novo, within the body, with smaller contributions from the diet.
  • Excessive levels of cholesterol in blood circulation however are strongly associated with progression of


  • The fate of cholesterol in the blood is highly determined by its constitution of lipoproteins

– some types (LDL) favour transport towards body tissues and others (HDL) towards the liver for excretion into the intestines.

  • The average amount of blood cholesterol varies with age, typically rising gradually as age advances.
  • Hyperlipidemia refers to the elevated or abnormal levels of cholesterol and triacylglycerols in the blood. One of the most clinically relevant lipid substances is cholesterol, especially on atherosclerosis and cardiovascular
  • Lipemia is a term used to refer marked hyperlipidemic condition resulting in plasma presenting a milky white
  • Postprandial hyperlipidemia is most common in animals consuming fatty diet; hence to evaluate lipid status, blood samples have to be taken from fasting
  • Hyperlipidemia is noticed in dogs and man with hypothyroidism – main lipid increased is cholesterol. Pancreatitis, uncontrolled diabetes, cholestasis, hyperadrenocorticism are some other conditions causing
  • Hypercholesterolemia is the presence of high levels of cholesterol in the blood. It is not a disease but a metabolic derangement that can be secondary to many diseases and can contribute to many forms of disease, most notably cardiovascular




  • Animal fats are complex mixtures of triglycerides with phospholipids and cholesterol; hence, all foods containing animal fat contain cholesterol to varying
  • Cholesterol is not present in plant based food sources. However, plant products such as flax seeds and peanuts contain cholesterol-like compounds called phytosterols, which are suggested to help lower serum cholesterol levels.
  • About 20–25% of total daily cholesterol production occurs in the liver; other sites of high synthesis rates include the intestines, adrenal glands and reproductive
  • Synthesis within the body starts with one molecule of acetyl CoA and one molecule of acetoacetyl-CoA. HMG-CoA reductase is an important enzyme in the cholesterol synthesis. Total cholesterol is the sum of HDL cholesterol, LDL cholesterol and 20% of triglycerides.


Blood cholesterol levels in human beings


Type Level Remarks
Total cholesterol < 200 mg/dl Desirable level. Low risk for coronary disease
240 & above Hypercholesterolemia, high risk for coronary heart disease
HDL cholesterol <40 mg/dl Low HDL levels is the risk factor for cardiac disease
60 & above High HDL, protective to heart
LDL cholesterol < 100 mg/dl Desirable level
> 160 mg/dl High, risk of heart disease
Triglycerides < 150 mg/dl Normal
>200 mg/dl High




Total blood cholesterol levels (mg/100 ml) in animals


Species Blood cholesterol levels (mg/100 ml)
Horse 75-150
Cow 60-190
Sheep 52-90
Goat 80-130
Pig 80-134
Dog 135-270






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