Composition and functions of blood | Human physiology

BODY FLUIDS

Two types of body fluid-
(i) Intracellular fluid(ICF)
e.g.  Cytoplasm
(ii) Extracellular fluid(ECF)
e.g. Blood,Lymph,Tissue fluid

BLOOD

• Blood is the fiberless connective tissue  formed of  55% plasma and  45% formed elements (RBC,WBC,Platelets).
• Blood is slightly alkaline(pH=7.4).
• The specific gravity of blood is about 1.055

COMPOSITION OF BLOOD

PLASMA :

• Plasma forms the matrix of blood.
Plasma has:
92% water
7-8% protein
0.5-1% ions

Plasma Protein :-

Albumin = maintain osmolarity
Globulin = Help in defence
Fibrinogen = Help in clotting
Prothrombin = Help in clotting 

Ions :-
Na+,K+,Cl-,HCO3-, sulphate,phosphate, calcium etc.

FORMED ELEMENTS IN BLOOD :

RBC / erythryocytes :-

• Formation of RBC = erythropoiesis
• Site of erythropoiesis(formation of red Blood cells) = bone marrow
• Life span of foetal RBC = 100 days
•  Lifespan of RBC(Red blood cells) after birth = 120 days
• Normal RBC count in males = 5.5 million/mm³
• Normal RBC(Red blood cells) count in females = 4.5-5 million/mm³
• Increase in red blood cells count = Erythrocytosis (hilly area, Dehydration,bone marrow tumor)
• Decrease in RBC count known as Erythrocytopenia (malaria, sickle cell anemia).
• Shape of RBC is Biconcave and disc like.
• RBC is non-nucleated  and lacks all cell organelles.

WBC / Leucocytes :-

• Formation of WBC = Leucopoiesis
• Site of formation = Bone marrow
• Life span of WBC = 3-7 days
• Normal WBC count = 6000-8000/mm³
• Increased WBC count =Leucocytosis / Leukemia (occur in cancer)
• Decrease WBC(Leucocytes) count = Leukopenia (in AIDS)
• Shape of WBC is irregular and amoeboid.
• WBC has nucleus.

Types of WBC :-

(1) Granulocytes
(2) Agranulocytes

PLATELETS / THROMBOCYTES :

• Formation of platelets = Thrombopoiesis
• Site of formation of platelets = bone marrow
• Life span of platelets = 1 week
• Shape of platelets = disc shape
• Platelets lack nucleus
• Normal platelets count = 1.5-4 lakh/mm³
• Increased Platelets count = Thrombocytosis
• Decrease platelets count= Thrombocytopenia

Note:- In dengue, number of platelets decrease. Hence Aspirin (antiplatelet) drug is not given.

FUNCTIONS OF BLOOD

Blood serves the following important functions:
1. It transports O2 and nutrients to various tissues.
2. Transports waste products.
3. Carries hormones from endocrine glands to various tissues.
4. It redistributes water(H2O) from one part of the body to the other.
5. It contains antibodies and leucocytes(WBC) which protect the body from diseases.