Physiology of Blood and it's Circulation | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Understanding Blood and its Circulation: Basics of Physiology

• Blood's Vital Functions:
  • Blood is a red, slightly alkaline fluid serving various crucial roles in the body.
  • It carries nutrients from the digestive system to tissues, transports oxygen to tissues and carbon dioxide to the lungs.
  • Acts as a transporter for hormones from endocrine glands.
  • Maintains proper water balance, aids in temperature control, and helps in the body's defense against bacteria and viruses.
  • Clotting ability provides a natural safety mechanism in case of blood vessel damage.
  • Contributes to maintaining the correct pH of tissues.
• Circulation System:
  • Blood circulates through arteries, capillaries, and veins, driven by the pulsations of the heart.
• Blood Composition:
  • Comprises plasma, a fluid portion where blood cells are suspended.
  • Three main types of blood cells: red blood cells (or corpuscles), white blood cells, and platelets.
• Specific Gravity of Blood (Average Range):
  • Horse: 1.046 - 1.059
  • Cattle: 1.046 - 1.061
  • Sheep: 1.041 - 1.061
  • Goat: 1.036 - 1.051
  • Pig: 1.035 - 1.055
  • Dog: 1.045
  • Cat: 1.045 - 1.057
• Erythrocyte Sedimentation Rate (ESR):
  • ESR is a blood test assessing an animal's health.
  • Provides insights into the sedimentation rate of red blood cells and is a valuable diagnostic tool.

Understanding Erythrocyte Sedimentation Rate and Blood Plasma: Basics of Physiology

Erythrocyte Sedimentation Rate (ESR)

• ESR is a measure of how quickly red blood cells settle in a tube, often used to assess an animal's health.
• Faster settling is observed in conditions like acute infections, malignant tumors, inflammation, hypothyroidism, and pregnancy.

Blood Plasma: Composition and Functions

• Constitutes 55-70% of blood, composed of water and various substances.
• Three main protein groups: fibrinogen, serum-globulin, and serum-albumin.
• Yellow to colorless, its composition remains similar across mammals.

Chemical Composition of Blood Plasma

• Water
• Gases: Oxygen, Carbon dioxide, Nitrogen.
• Proteins: Albumin, Globulins, Fibrinogen.
• Carbohydrates: Glucose, Lactose, Pyruvate.
• Lipids: Fat, Lecithin, Cholesterol.
• Non-Nitrogenous Substances: Amino acids, Urea, Uric Acid, Creatine, Creatinine, Ammonia.
• Inorganic Substances: Sodium, Potassium, Calcium, Magnesium, Sulphate, Phosphate, Iron, Manganese, Cobalt, Copper, Zinc, Iodine.
• Enzymes, Hormones, Vitamins, Pigments.

Plasma Proteins

• Mainly albumin, fibrinogen, and globulins (including y-globulins, rich in antibodies).
• Albumin dominates in man, sheep, goat, rabbit, dog, guinea-pig, and rat.
• In horse, pig, and cow, albumin and globulins are almost equal or globulins may be more.

Synthesis and Functions of Plasma Proteins

• Liver produces albumin, fibrinogen, and most globulins, while extra-hepatic cells produce y-globulins.
• Severe liver damage or protein deficiency reduces plasma protein synthesis.
• Functions include maintaining blood pressure, erythrocyte stability, regulating acid-base balance, providing antibodies, and transporting nutrients and therapeutic agents.

Understanding Blood Components and Functions: Simplified Overview

Blood Composition and Separation

• Blood is a slightly alkaline fluid that serves multiple functions in the body.
• It carries nutrients, oxygen, hormones, and assists in maintaining temperature.
• Blood separates into serum (liquid) and a solid fibrin clot when shed.

Blood Clotting Process

• Coagulation turns blood into a gelatinous mass.
• After coagulation, the clot retracts, releasing a watery fluid called serum.
• Fibrinogen transforms into fibrin during clot formation, forming fibrino-globulin and nucleo-protein in the serum.

Plasma Components

• Plasma contains non-protein nitrogenous materials, amino acids, urea, glucose, fats, and inorganic salts.
• After clotting, plasma becomes serum, lacking fibrinogen but gaining fibrino-globulin and nucleo-protein.

Red Blood Cells (Erythrocytes)

• Comprise about 32% of blood, appear as biconcave discs without nuclei.
• Contain hemoglobin for oxygen transport.
• Formed in red marrow, circulate for about three to four months before destruction.

Blood Platelets (Thrombocytes)

• Oval discs from bone marrow, help prevent blood loss by forming clots.
• Play a crucial role in blood clotting when vessels are injured.

Hemoglobin and Its Functions

• Complex substance in red blood cells that absorbs oxygen in the lungs.
• Releases oxygen to tissues, exchanges it for carbon dioxide, and facilitates gas exchange during respiration.
• Haemolysis is the dissolution of hemoglobin from red blood cells, occurring when cells are damaged.

Serum Properties

• Natural serum from one animal may act as a haemolytic agent when injected into another animal of a different species.
• Agglutination is the process of blood cells clumping together under the influence of an agent called agglutinin.
• Heat treatment can neutralize haemolytic power, emphasizing the impact of external factors on blood components.

Understanding Blood Anticoagulants and Diagnostic Calculations: Simplified Overview

Heparin as an Anticoagulant

• Heparin is a natural anticoagulant produced by basophils and mast cells in the body.
• It prevents blood clotting by inhibiting coagulation factors.
• A concentration of 0.2 mg of heparin per ml of blood is commonly used as an anticoagulant.

Sodium Citrate and Other Anticoagulants

• Sodium citrate combines with calcium ions in plasma to form insoluble calcium salts, preventing coagulation.
• Sodium, potassium, ammonium salts of oxalates and fluorides, and chelating compounds like EDTA are also used as anticoagulants.

Role in Diagnostic Calculations

• Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH), and Mean Corpuscular Hemoglobin Concentration (MCHC) are important diagnostic parameters.
• It's crucial to maintain the size of blood cells as they are in circulation when determining the Packed Cell Volume (PCV), aiding accurate diagnostic assessments.

Blood Cell Preservation and Lifespan: Simplified Overview

Anticoagulants' Impact on Red Blood Cell (RBC) Size

• Heparin or EDTA is commonly used to maintain constant RBC size during blood analysis.
• Ammonium salts increase RBC size, while potassium salts decrease it.
• Specific combinations of Ammonium oxalate and Potassium oxalate help inhibit coagulation and preserve RBC size.

Fate of Erythrocytes (Red Blood Cells)

• Erythrocytes have a lifespan of 90 to 140 days, with an average of 120 days in humans.
• As RBCs are destroyed, the iron in hemoglobin is conserved, and the pigmented part becomes bilirubin, an excretory product.
• The liver and spleen store unused iron from destroyed RBCs, and reticulo-endothelial cells in various organs play a role in their destruction.

Haematopoiesis (Blood Cell Formation)

• Haematopoiesis is a continuous process, requiring essential nutrients.
• Vitamin B12, folie-acid, pyridoxine, riboflavin, nicotinic acid, pantothenic acid, thiamine, biotin, and ascorbic acid, along with minerals like iron, copper, and cobalt, aid in the synthesis of red blood cells.

Haemoglobin

• Haemoglobin is the pigment in RBCs, a complex protein containing iron.
• Its red color comes from heme, a compound with an iron atom.
• The synthesis involves amino acids, glycine, acetate, and a four-carbon compound from the tricarboxylic acid cycle.

Haemoglobin Formation and Types: Simplified Overview

Protoporphyrin Formation

• Four pyrrole molecules combine to form protoporphyrin.
• Protoporphyrin unites with iron to create heme.

Haemoglobin Composition

• Four heme molecules combine with globin to form haemoglobin.
• Heme is found widely in animals and plants, creating not only haemoglobin but also haemechromogen.
• Myoglobin, found in muscles, is a combination of heme and muscle globin.

Molecular Weight and Hemolysis

• The molecular weight of haemoglobin varies from 66,000 to 69,000.
• Hemolysis, the release of haemoglobin into the plasma, can occur due to factors like protozoa, toxins, or chemicals.

Hemoglobin Types

• Oxyhaemoglobin: Haemoglobin combined with oxygen.
• Carboxyhaemoglobin: Haemoglobin combined with carbon monoxide, with a stronger affinity than oxygen.
• Methaemoglobin: A derivative formed by the oxidation of haemoglobin, unable to carry oxygen like normal haemoglobin.

Characteristics of Hemoglobin

• Hemoglobin levels are expressed as g/100 ml of blood.
• Normal values range between 13 and 15 g/100 ml in most mammals.
• Oxyhaemoglobin carries about 1.36 ml of oxygen per gram of haemoglobin when saturated.

Abnormal Hemoglobin Types

• Carboxyhaemoglobin gives blood a bright cherry red color and can be misleading in cases of carbon monoxide poisoning.
• Methaemoglobin, formed under certain conditions or drug administration, cannot function as a respiratory pigment.

Erythrocyte Values in Blood (million/cubic mm)

• Normal erythrocyte values vary across species (e.g., 5-6 in humans, 9-12 in pigs, 6-8 in cats).
• Values indicate the number of red blood cells in a cubic millimeter of blood.

White Blood Cells: Understanding the Defenders in Blood

Identification and Characteristics

• White blood cells are colorless bodies seen under a microscope, larger and fewer than red blood cells.
• They possess amoeboid movement and nuclei, standing out from the red cells.

Types of White Blood Cells

• Neutrophils:
  • Granules in the cytoplasm, staining less distinctly.
  • Varied nuclei shapes, termed polymorphonuclear leukocytes.
  • Key role in phagocytosis, engulfing bacteria and defending against infections.
• Eosinophils:
  • Granules stain easily with eosin, a histological dye.
  • Increase in certain chronic diseases and parasitic infestations.
  • Limited phagocytic capacity, less effective against microorganisms.
• Basophils:
  • Blue-staining granules containing histamine, released during allergic reactions.
  • Have receptors for IgE antibodies, playing a role in severe reactions to parasites.
• Monocytes:
  • Few granules, engulf bacteria, important in less acute infections.
  • Enlarge and become macrophages when moving from blood vessels into tissues.
• Lymphocytes:
  • Few granules, formed in lymphoid tissues (nodes, spleen, tonsils).
  • Involved in antibody formation, creating barriers against local diseases.

Conditions and Abnormalities

• Eosinophilia: Abnormally high eosinophils, seen in severe parasitic infestations and certain diseases.
• Basophils with IgE antibodies can cause severe reactions, releasing histamine.

Temperature Variation

• Blood temperature varies, coolest near the surface and hottest in hepatic veins.
• Ranges from 100 to 105°F.

Note: White blood cells play crucial roles in the body's defense against infections and diseases.

Blood Quantity: Understanding the Volume and Components

Blood Quantity in Domesticated Animals

• It's challenging to measure the total blood amount by direct bleeding due to some left in vessels.
• Approximate proportions of body weight dedicated to blood:
  • Horse: 1/15 or 6.6%
  • Ox: 1/13 or 7.71%
  • Sheep: 1/12 or 8.01%
  • Pig: 1/22 or 4.6%
  • Dog: 1/11 to 1/18 or 9.1% to 5.5%
• An average-sized horse contains about 50 pints of blood.

Total Leucocytes (White Blood Cells) per Cubic mm of Blood

Quantities vary across species:

• Horse: 8000 - 11,000
• Cow: 7000 - 10,000
• Sheep: 7000 - 10,000
• Goat: 8000 - 12,000
• Dog: 9000 - 13,000
• Cat: 10,000 - 15,000
• Chicken: 20,000 - 30,000

Percentage of Leucocytes by Type

Different species have varying proportions of white blood cell types:

• Neutrophils: Primary defender against infections.
• Lymphocytes: Involved in immune responses.
• Monocytes: Engulf bacteria, important in infections.
• Eosinophils: Respond to allergies and parasites.
• Basophils: Release histamine during allergic reactions.
• Examples:
  • In a horse:
    • Neutrophils: 50-60%
    • Lymphocytes: 30-40%
    • Monocytes: 2-5%
    • Eosinophils: 1%
    • Basophils: Not specified
  • In a Cow:
    • Neutrophils: Not specified
    • Lymphocytes: 25-30%
    • Monocytes: 5%
    • Eosinophils: 2-5%
    • Basophils: 2-5%

Regulating Heart Function: Ensuring a Steady Beat

Sinoatrial Node (Pacemaker)

• Main Control: A specialized heart muscle, the Pacemaker, in the right auricle.
• Function: Emits electric impulses at regular intervals to stimulate heart muscle contractions.
• Process: Impulses travel through auricles, then to the Atrioventricular Node, causing sequential contractions in auricles and ventricles.

Cardio-Inhibitory Centre in the Brain

• Location: Medulla Oblongata in the brain.
• Control: Communicates with Pacemaker via vagus nerves.
• Action: Slows heart rate by stimulating vagus nerves, creating a sequence of contractions.

Input to Cardio-Inhibitory Centre

• Sources: Feedback from Pacemaker, sensory surfaces, and higher brain centers.
• Information: Includes heart rate, internal/external conditions (e.g., indigestion, temperature), and emotional states.
• Action: Stimulates vagus nerves to decrease heart rate as needed.

Cardio-Accelerating Centre

• Location: Medulla Oblongata.
• Stimulation: Triggered by factors like pain sensations and anticipation of exercise.
• Effect: Releases neurotransmitter (norepinephrine) directly to heart muscles, increasing heart rate and stroke volume.

Hormonal Influence

• Thyroxine: From the thyroid gland, increases heart rate.
• Epinephrine: From the adrenal medulla, increases both heart rate and stroke volume.

Regulating Blood Flow: Adapting to Changing Needs

Adjusting Blood Flow

• Purpose: Respond to varying conditions.
• Low Cellular Activity: During sleep, blood flow rate decreases to conserve energy.
• Strenuous Activity: Increases blood flow rate to meet demands for material exchange during high cellular activity.

Cardiac Output

• Factors: Product of heart rate and stroke volume.
• Control: Sinoatrial node, cardio-inhibitory, and cardio-accelerating centers in the brain, along with thyroid and adrenal gland hormones.

Controlling Blood Flow: Navigating the Circulatory System

• Stroke Volume and Circulatory System:
  • Closed System: Blood vessels and heart form a closed circulatory system.
  • Volume Increase: Blood expelled from the heart increases when the return rate of blood to the heart rises.
• Artery Diameter Regulation:
  • Vasomotor Centers: Control artery diameter based on CO₂ levels in the blood.
  • Emotion Influence: Brain centers controlling emotions impact artery diameter.
  • Carbon Dioxide Levels: High CO₂ levels lead to arterial constriction, increasing blood pressure.
  • Emotional States: Certain emotions affect heart rate and artery diameter.
• Blood Flow Control Mechanisms:
  • Vasomotor Centers and Emotional Centers: Transmit electro-chemical impulses.
  • Arterial Constriction/Dilation: Response to emotions and CO₂ levels.
  • Veins' Blood Path: Veins collect blood from various body parts, leading to the right atrium.
• Pulmonary and Systemic Circulation:
  • Heart Chambers: Blood circulates from right atrium to right ventricle, then to the lungs and left atrium.
  • Oxygenation: Lungs oxygenate blood, brightening its color in the arteries.
  • Systemic Circulation: Bright red arterial blood circulates throughout the body.
• Portal Circulation:
  • From Organs to Liver: Veins from stomach, intestines, spleen, and pancreas form the portal vein to the liver.
  • Liver Processing: Liver processes food content before blood returns to the heart.
  • Maintaining One Direction: Valves in heart cavities and veins maintain blood flow direction.
• Blood Color Differences:
  • Arterial Blood: Bright red due to higher oxygen content.
  • Venous Blood: Dull red, charged with carbon dioxide.
  • Pulmonary Artery and Veins: Dark blood goes to the lungs, bright red returns to the heart.

Blood Pathways in the Heart: A Closer Look

• Separation of Blood in the Heart:
  • Normally, no direct connection between right and left sides of the heart.
  • Blood from the right ventricle must pass through the lungs before reaching the left atrium.
• Blood Circulation in the Umbilical Cord:
  • Two large arteries carry blood from the foetus to the placenta for oxygen and nourishment.
  • A large vein brings this oxygenated blood back to the foetus through the umbilical cord.
• Special Passages in Fetal Circulation:
  • Foramen Ovale: Allows communication between right and left atria in the fetal heart.
  • Ductus Arteriosus: Connects the aorta and pulmonary artery, bypassing the lungs in fetal circulation.
• Purpose of Fetal Passages:
  • Facilitate the exchange of oxygen and nutrients in close proximity to the maternal blood in the placenta.
  • Ensure the foetus gets essential resources without relying on its own lungs.
• Changes at Birth:
  • Extra passages close and shrink after birth.
  • Foramen ovale and ductus arteriosus close rapidly, leaving remnants in adult life.
  • In some cases, these passages may persist throughout a person's life, although it's rare.