Blood

  • Circulatory system is a network consisting of blood, blood vessels and the heart.
  • Circulatory system is made up of blood vessels that carry blood away from and towards the heart 
  • Arteries carry blood away from the heart and veins carry blood back to the heart.
  • Circulatory system carries oxygen, nutrients, and hormones to cells, and removes waste product, like carbon Dioxide

BLOOD

  • Blood is a combination of plasma and blood cells that circulate through the entire body 
  •  Blood is a special type of fluid connective tissue derived from mesoderm.
  • The branch of science concerned with the study of blood, blood-forming tissues, and the disorders associated with them is called haematology. ( haeme – blood and logos - study)
  • Blood is made of several components including red blood cells, white blood cells, platelets and the plasma, which contains coagulation factors and serum.
  • Blood consists of almost 7-8% of human body's weight.

Functions of Blood 

1. Transport of respiratory gases

  • It carries oxygen from the alveoli of the lungs to the tissue and eliminates carbon dioxide from the tissue to the alveoli of the lungs where it is expelled into the atmosphere.

2. Transport of nutrients

  • Blood carries digestive end products of food materials like glucose, fatty acids, amino acids, vitamins, and electrolytes from the intestine to different cells of the body for utilization in metabolic processes.

3. Vehicle for different chemicals

  • Various chemicals like hormones, enzymes, and vitamins are carried by the blood to their site of action.

4. Regulation of body temperature

  • Blood has high water content. High specific heat, high thermal conductivity, and high latent heat of evaporation of water help the blood to regulate body temperature.

5. Regulation of water and electrolyte balance

  • The water content of blood is freely interchangeable with the interstitial fluid and helps in maintaining the water and electrolyte balance of the body.

6. Regulation of pH

  • The plasma proteins and the hemoglobin act as buffers and help to maintain the acid-base balance and pH of the body fluid.

7. Storage function

  • Blood serves as a storehouse for different substances like proteins, glucose, and electrolytes and supplies these substances for utilization by the body in emergencies like starvation, fluid loss, and electrolyte imbalance.

8. Prevention of hemorrhage

  • The coagulation function of blood achieved by different proteins and the platelets prevents rupture of blood vessels and blood loss.

9. Defensive function

  • Different white blood cells present in the blood play a major role of defense mechanism of the body by destroying invading microorganisms, parasites, etc.

Physical Characteristics of Blood-

Viscosity, specific gravity, and osmotic pressure of blood have important physical effects on the circulation and flow of blood and the exchange of fluid between blood and the tissues.

  1. Color: Red, due to the presence of a red coloured pigment haemoglobin.
  2. Amount: 7-8% of total body weight.
  3. Blood volume: 4-5 Liter (female) & 4-6 Liter (male)
  4. Viscosity: 3.4-5.4 times more than water.
  5. Specific Gravity: 1.045-1.065 (specific gravity, also called relative density, ratio of the density of a substance to that of a standard substance).
  6. pH: 7.35-7.45 (slightly alkaline) pH below 0 or above 14. Anything below 7.0 is acidic, and anything above 7.0 is alkaline, or basic. 
  7. Temperature-38°
  8. Osmotic pressure-25 mm Hg

Composition of Blood 

Blood is composed of two major parts

  1. The liquid plasma
  2. Cellular elements 

The liquid plasma

Plasma is the liquid part of blood. it is composed of water (91%) and solids (9%). The solids present in plasma include-

1. Organic (8%) -

  • Plasma proteins are the most abundant and include different classes of proteins like albumin, globulin, fibrinogen, other clotting factors, and different enzymes.
  • Nutrients like monosaccharides, amino acids, fatty acids and glycerol, and vitamins are derived from the digestion of food.
  • Waste products like urea, uric acid, and creatinine.
  • Different hormones.

Functions of plasma proteins

  • Role in blood coagulation( Fibrinogen).
  • Role in Defense Mechanism: γ-globulins act as antibodies, also called immunoglobulins
  • Role in transport mechanism: Albumin,α and β- globulins are responsible for the transport of hormones and enzymes 
  • Role in viscosity of blood- Plasma proteins provide viscosity which is essential for maintaining BP. Albumin provides maximum viscosity.
  • Role in ESR- globulin and fibrinogen accelerate rouleaux formation, which in essential for ESR.
  • Role as reserve proteins- Act as last source of energy in case of starving or inadequate food intake

2 Inorganic substances (1%).

  • Various salts, like phosphates, bicarbonates.
  • Ions and electrolytes, sodium, potassium, calcium, magnesium, chloride, iron.
  • Dissolved gases, like oxygen, carbon dioxide, and nitric oxide.

Note-

  • The removal of coagulation factors from plasma leaves a fluid similar to interstitial fluid, known as serum.
  • Serum = Plasma - Fibrinogen 

Cellular Elements(Formed Elements)

Cellular elements of blood are-

  • Red blood cell (RBC) or erythrocytes,
  • White blood cells (WBC) or leukocytes,
  • Platelet or thrombocyte. 

1. Erythrocytes or Red Blood Cells (RBC)-

  • RBCs also called as erythrocytes are non nucleated formed elements of the blood.
  • There red color is due to hemoglobin
  • Normal Values: Males: 5 million/cu mm Females: 4.5 million/cu mm

SHAPE AND SIZE

  • Normally disk shaped & bi-concave.
  • Central portion thinner and periphery thicker.
  • Size: Diameter = 7.2μ (6.9-7.5 μ)
  • Thickness-
  1. At periphery=2.2 μ
  2. At center = 1 μ 15
  • A healthy individual has 12-16 Gms of hemoglobin in every 100 ml of blood.
  • These molecules play a significant role in transport of respiratory gases.
  • RBCs have an average life span of 120 days after which they are destroyed in the spleen

The Production  of  RBCs is know  as erythropoiesis

Adult Red bone marrow of long bones(hip bone ribs)
Child  Bone marrow of all the bones
Foetus liver  and spleen

Note-

  • increased  in number of RBCs is known as Polycythemia 
  • Decrease in number of RBCs is known as Erythropenia 

Function  of RBSc

  • Transport O from lungs to tissue 
  • Transport CO from tissue to lungs.
  • It provides the buffering action in the form of hemoglobin and thus helps in maintaining the acid-base balance of the blood.
  • It maintains the viscosity of the blood.

2. Leucocytes are also known as white blood cells (WBC)-

  • As they are colorless due to the lack of hemoglobin.
  • They are nucleated(amoeboid) and are relatively lesser in number which averages 6000- pre microliter of blood.
  • Leucocytes are generally short lived 10 to 13 days.

The Production  of  WBCs is know  as Leucopoiesis

Adult liver, spleen,   tonsils, bone marrow 
Foetus liver, spleen 

 

Note-

  • Increase in number of WBCs is known as leucocytosis
  • Decrease in number of WBCs is known as leucopenia
  • Pathological increase in number of WBCs is known as leukemia (blood cancer)

We have two main categories of WBCs

  1.  Granulocytes
  2.  A granulocytes.

1. Granulocytes

Neutrophils, eosinophils and basophils are different types of granulocytes.

 

Type White blood cell in the body       Feature Function  Location  produced 
Neutrophils  2000 to 7500 cells per mm3 

1. Nucleus with 3-4 lobes

2. Stain with  neutral dye

Destroy bacteria by phagocytosis 

Bone marrow

Eosinophils 40-400 cells per mm3

1. Nucleus with 2 lobes

2. Stain with  Acidic dye

Combat the effect of histamine in allergic reactions  Bone Marrow 
Basophils 0-100 cells per mm3

1. Nucleus with  Indistinct lobes

2. Stain with  Basic dye

Liberate Heparin  and histamine in Allergic  reaction to intensify inflammatory response 

Bone  marrow

A. Neutrophils-

Neutrophils are the most common type of white blood cell in the body with levels of between 2000 to 7500 cells per mm3 in the bloodstream. Neutrophils are medium-sized white blood cells with irregular nuclei and many granules that perform various functions within the cell.

Function-Neutrophils function by attaching to the walls of the blood vessels, blocking the passageway of germs that try to gain access to the blood through a cut or infectious area.

B. Eosinophils-

(40-400 cells per mm3of blood.) They have large granules that help in cellular functions. Eosinophils are especially important when it comes to allergies and worm infestations.

Function-Eosinophils work by releasing toxins from their granules to kill pathogens. The main pathogens eosinophils act against are parasites and worms. High eosinophil counts are associated with allergic reactions.

C. Basophils -

Basophils are the least frequent type of white blood cell, with only 0-100 cells per mm3 of blood. Basophils have large granules that perform functions that are not well known. They are very colorful when stained and looked at under the microscope, making them easy to identify.

Function-Basophils have the ability to secrete anticoagulants and antibodies that have function against hypersensitivity reactions in the bloodstream. They act immediately as part of the immune system’s action against foreign invaders. Basophils contain histamine, which dilates the vessels to bring more immune cells to the area of injury.

 2. A granulocytes.

A. Lymphocytes-

(About 1300 to 4000 lymphocytes per mm3 of blood.)Lymphocytes are small, round cells that have a large nucleus within a small amount of cytoplasm. They have an important function in the immune system, being major players in the humeral immune system, which is the part of the immune system that relates to antibody production.

 Function-B lymphocytes make antibodies, which is one of the final steps in disease resistance. When B lymphocytes make antibodies, they prime pathogens for destruction and then make memory cells ready that can go into action at any time, remembering a previous infection with a specific pathogen. 

Type White blood cell in the blood Features Function Location produced
Lymphocyte 1300 to 4000 lymphocytes per mm3
  • Smallest of WBCs
  • Large round nucleus
Produce antibodies Bone marrow, Spleen, Tonsils
Monocyte 200-800 monocytes per mm3
  • Largest of WBCs
  • Large kidney shaped nucleus 
Ingest Micro-organisms Bone marrow

B. Monocytes-

(About 200-800 monocytes per mm3 of blood.)Monocytes are the largest of the types of white blood cells. There are only about 200-800 monocytes per mm3 of blood. Monocytes are agranulocytes, meaning they have few granules in the cytoplasm when seen under the microscope. Monocytes turn into macrophages when they exit the bloodstream.

Function-As macrophages, monocytes do the job of phagocytosis (cell-eating) of any type of dead cell in the body, whether it is a somatic cell or a dead neutrophil.

3. Platelets also called thrombocytes-

Are cell fragments produced from megakaryocytes (special cells in the bone marrow). Blood normally contains 1,500,00-3,500,00 platelets - pre microliter of blood. Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood. A reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body.

Shape Circular biconvex non-nucleated
Size  2 – 4 μm
Count 1,50,000 – 4,00,000 platelets/μL 
 Life span 5 – 9 days
Function Blood clotting

Thrombopoiesis -The production of platelets is known as thrombopoiesis.

  • Increase in number of platelets is known as thrombocytosis
  • Decrease in number of platelets is known as thrombocytopenia


 

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