HSBTE DMLT II Semester Circulatory System: Composition and Functions of Blood, Unit II

Circulatory system

The human circulatory system consists of the blood-vascular system and lymphatic system. Human blood circulation (blood vascular system) comes under the category of double circulation of blood. There is a separate circulatory system for oxygenated blood and deoxygenated blood. The oxygenated blood and deoxygenated blood never mix.

1.1 Composition and functions of blood

COMPOSITION OF BLOOD: Blood consists of two components Plasma and blood cells.

Plasma: It is non-living, yellowish, clear, viscous ECF slightly alkaline slightly alkaline with pH 7.4. Blood has 55% plasma. Plasma consists of 91-92% water. Blood plasma has the following components in water.

• 1. Inorganic salts: Chloride, bicarbonate, phosphate, sulfate, etc. of calcium, magnesium, iron, potassium, sodium etc.

• 2. Plasma proteins: Albumin, globulin, prothrombin and fibrinogen.

• 3. Organic materials: Glucose, fat, urea, uric acid, Cholesterol, fatty acids, amino acids, etc.

• 4. Gases: carbon dioxide, oxygen, Nitrogen.

• 5. Hormones: Secretions of endocrine glands.

• 6. Vitamins/enzymes,

• 7. Anticoagulant: Heparin.

• 8. Immunoglobulins: Lysozomes, propendine.

Blood cells: Blood consists of 45% of blood cells that float in plasma. Blood has three types of blood cells. These are Erythrocytes or RBCs (Red blood cells), Leucocytes or WBCs (White blood cells), and Thrombocytes or Platelets

1. Erythrocytes (Red Blood Cells): An adult healthy male body has 5.5±1% RBCs in per cubic mm of blood. An adult healthy female body has 4.8±1% RBCs in per cubic mm of blood.

• · Erythrocytes are nonnucleated, circular, biconcave disc-shaped cells. The biconcave structure of RBCs increases surface area by 20-30% and increases its flexibility.

• · Biconcave shape helps RBCs to pass through blood capillaries.

• · The average life period of RBCs is 120 days.

• · RBCs disintegrate inside the reticulo-endothelial system present in the liver and spleen into haem and globin.

• · Spleen is considered a graveyard of RBCs. The breakdown of RBCs is called hemolysis.

• · Haemoglobin occupies maximum space inside RBC due to the absence of cellular organelles.

• · Haemoglobin is a conjugated protein consisting of iron (haem) and protein (globin).

• · Single RBC appearance is pale buff color (pale yellow color). In the group, it appears red color due to the presence of hemoglobin in RBCs.

• · Adult healthy male blood contains haemoglobin 13.5 to 17.5±2% gm/100 ml of blood. Adult healthy female blood contains hemoglobin 12.5-15.5gm/100ml of blood.

2. Leucocytes (White Blood Corpuscles):

The number of WBCs in adult humans varies from 7000 to 10,000 per cubic millimeter. It is called TLC (Total Leucocyte Count).

• · Its number is very high in newborns and in pregnant women.

• · Increase in WBC number is called Leucocytosis.

• · A decrease in WBCs number below 5000 per cubic millimeter is called leukopenia.

• · The size of WBCs is larger than RBCs. WBCs consist of cytoplasm and nucleus.

Types of Leucocytes:

There are two types of WBCs: Granulocytes and Agranulocytes.

A) Granulocytes:

• · Granulocytes have granules in the cytoplasm.

• · They have irregular lobulated nuclei.

• · There are three types of granulocytes depending upon their staining properties. These are Eosinophils, Basophils, and Neutrophils.

Eosinophils:

• a) The cytoplasm of eosinophils has granules that accept the color of acidic stains like eosin. Thus they are also called acidophils or eosiniphils.

• b) Cytoplasm has a bilobed nucleus, a narrow strand connecting both lobes.

• c) The life period of eosinophil is a few days.

Basophils:

• a) Basophils have a lesser number of granules than eosinophils.

• b) These granules quickly accept the color of basic stains like methylene blue.

• c) There are three lobes in the nucleus of basophils,

• d) Basophil's life span is longer than eosinophils.

Neutrophils:

• a) Neutrophils in non-motile state are round.

• b) In motile state they are flat and amoeboidal.

• c) Cytoplasm has a multilobed nucleus. These lobes are attached by narrow strands, and the lobes are arranged in horseshoe-shaped.

• d) They have coarse granules in the cytoplasm than eosinophils and basophils. Cytoplasmic granules have two sizes – small and large granules.

• e) Larger granules accept the color of neutral red dyes

• f) Smaller granules accept the color of Giemsa and Leishmen’s stain.

B) Agranulocytes: The cytoplasm of these leucocytes (WBCs) does not have granules. There are two types of agranulocytes: Lymphocytes and Monocytes.

i. Lymphocytes:

• · They have a large round nucleus with a small amount of cytoplasm.

• · The nucleus accepts basic dye color more than the cytoplasm.

• · Their life period varies from a few days to several years.

• · Lymphocytes have two sizes: large and small. Large lymphocytes are young lymphocytes while small lymphocytes are mature lymphocytes.

· Small lymphocytes are of two types: T-lymphocytes (85%) and B-lymphocytes (15%).

ii. Monocytes:

• · Monocyte cytoplasm has a bean-shaped nucleus.

• · They are the largest leucocytes (WBC) and have an amoeboidal shape.

• · Their life period is a few days to several days.

Thrombocytes (Platelets):

• · The number of platelets in blood is 2,50,000 per cubic mm of blood.

• · They are colorless, non-nucleated, round, oval, biconvex, or irregular,.

• · Increase in the number of platelets is called thrombocytosis

· A decrease in a number of platelets is called thrombocytopenia.

Functions of blood:

Blood is composed of plasma and blood cells. Each component performs its own function. These components help to perform the following functions: Transportation, Excretion, Respiration, Homeostasis, and Immunity.

A. Functions of Blood Plasma:

Blood plasma performs the following functions

• 1. Transportation: Blood plasma transports absorbed food, Respiratory gases, Hormones, Blood cells, plasma proteins, etc.

• 2. Blood fluid retention: Plasma proteins like albumin maintain body water balance, body fluid volume, and osmotic pressure,

• 3. Maintenance of blood pH: Blood behaves like a buffer. Plasma maintains blood pH around 7.4.

• 4. Blood clotting: Plasma has various blood clotting factors like fibrinogen, prothrombin, etc. They help to prevent blood loss.

• 5. Maintenance of body temperature: Blood plasma distributes heat from one organ to another organ to maintain normal body temperature.

B. Functions of Red Blood Cells (RBCs or Erythrocytes):

Respiratory gas transportation: Inside the lungs, oxygen combines with hemoglobin of RBCs to form oxyhemoglobin. Carbon dioxide from cells combines with the hemoglobin of RBCs and forms carboxyhemoglobin.

C. Functions of white blood cells (WBCs or Leucocytes):

• 1. Monocytes & Neutrophils: They have phagocytic action to engulf pathogens. It protects the body from infectious diseases,

• 2. Lymphocytes: They produce antibodies that develop immunity.

• 3. Basophils: They secrete heparin and histamine. Heparin acts as a natural anticoagulant inside blood vessels.

• 4. Eosinophils: They secrete antigens that counter the allergic effects of histamine,

D. Functions of blood platelets/ thrombocytes:

• 1. Haemostasis: Platelets block bleeding from injured tissues and blood capillaries. This is called hemostasis.

• 2. Blood Clotting: Platelets promote blood clotting.

Blood platelets secrete hormone serotonin that acts as a vasoconstrictor.