The circulatory system (cardiovascular system)
The circulatory system (cardiovascular system) pumps blood from the heart to the lungs to get oxygen.
There are three principal fluids in our body:
- Blood, contained in the heart and in the blood vessels (arteries, veins and capillaries) of the circulatory system.
- Tissue fluid, occupying spaces between cells in the organs
- Lymph, which is contained within lymph vessels and lymphatic organs such as the spleen and the tonsils.
Non-circulating fluids: There are also some other fluids located in particular organs such as synovial fluid filled in the cavities of skeletal joints, vitreous humour in the eye, etc. They do not circulate.
Blood
Features
Never Stationary: Blood is always in motion from the heart to the arteries and back through the veins.
Colour: The blood is a somewhat thick fluid, bright red when taken from an artery or dark red when taken from a vein.
Volume: An average adult human contains 5 to 6 litres of blood by volume in his body.
Taste: saltish.
PH value: The blood is slightly alkaline with a pH of 7.3 to 7.45 (7 is neutral, neither acidic nor alkaline).
Blood is called connective tissue.
Functions of Blood
The main functions of the blood in our body can be treated under two broad headings: (A) Transport and (B) Protection.
- Transport of Digested food, oxygen, carbon dioxide, excretory substances, hormones, body heat
- Transport of digested food from the alimentary canal to the tissues. These substances are simple sugars like glucose, am acids, vitamins, mineral salts, etc.
- Transport of oxygen from the lungs to the tissues. It occurs by means of red blood cells in combination with haemoglobin in the form of an unstable compound oxyhaemoglobin, which on reaching the tissues breaks up to deliver oxygen. Hb+O 2 =Hb o2
- Transport of carbon dioxide from the tissues to the lungs. It occurs partly in combination with haemoglobin and partly as solution in blood plasma.
Hb+Co 2 = Hb.CO 2 (Carbamino haemoglobin)
- Transport of excretory material from the tissues to the liver, kidney or the skin for elimination or to render them harmless.
Composition of Blood
The blood consists of:
- Plasma – fluid part, constitutes 55-60 per cent of blood.
- Cellular elements – red and white cells, and platelets, 40-45 per cent of blood.
- Plasma- The liquid portion of blood The plasma is a light-yellow coloured, alkaline Liquid. It mainly consists of:
- Proteins, Inorganic salts
- Other substances
- 90 – 92% Water
- 7-8% Proteins
- 1% Traces The inorganic salts include mainly sodium chloride and sodium bicarbonate. Among other substances contained in the plasma are glucose, amino acids, fibrinogen, hormones, urea, etc.
The plasma from which the protein fibrinogen has been removed is called serum.
Cellular elements
The formed or cellular elements (i.e. shaped structures visible under magnification) of the blood re of three categories:
- Red blood cells (erythrocytes),
- White blood cells (leukocytes),
- Blood platelets (thrombocytes)
Flow chart of Blood composition
Composition of blood
Red blood cell
Red blood cells are also called erythrocytes (erythros: red).
Shape: These are minute biconcave disc-like structures, flat in the centre and thick and rounded at the periphery.
Origin: Bone marrow
Features: Absence of nucleus.
Function : Red blood cells bring oxygen to the tissues in our body.
An adult human male has about 5 million RBCs per cubic mm of blood and an adult female has slightly less about 4.5 million.
Constituent of RBCs. The red blood cells have a colourless spongy body or stroma which contains a respiratory pigment haemoglobin (Hb).
The haemoglobin is formed of an iron-containing part (haemin) and a protein (globin).It has the ability to combine readily with oxygen.
Number of Rbc measured by an instrument called haemocytometer.
Life and death of RBCs.
- In adults, the RBCs are produced in the marrow of long bones, especially in the ribs, breast bone and ilium of hip girdle.
- In an embryo they are produced in the liver and spleen.
- In children, the RBCs are produced in bone marrow of all bones until 5 years of age.
The average life of an RBC is about 120 days.
RBC count is higher during physical activity, pregnancy and emotional upsets.
Abnormally increased number of RBCs is called Polycythaemia, and their abnormally decreased number is known as Erythropenia.
White blood cell
Origin: Bone marrow
Features : Presence of nucleus
Function : Protect the body from disease
Their number is much less, usually about 4000-8000 per cube mm. Most WBCs are amoeboid and can produce pseudopodia with which they can squeeze through the walls of the capillaries into the tissues (diapedesis dia: across, pedesis oozing out).
Leukaemia is a cancer of the tissue forming WBCs whose number increases manifold at the cost of RBCs. It is usually a fatal disease. Currently, the treatment is only blood transfusion. Leukopenia is the abnormal decrease in the number of WBCs.
Based on shape and other characteristics, the white blood cells are classified into two major categories (granular and non-granular) and five distinct types
Blood Platelets
(Initiators of clotting of blood)
Blood platelets are minute oval or round structures, non-nucleated, floating in the blood. These are about 200,000 to 400,000 per cubic mm. Of blood in an adult.
The platelets are derived from some giant cells called megakaryocytes in the red bone marrow.
Life span: Their life span is 3 to 5 days and are destroyed mainly in the spleen (a lymphatic organ located in the abdomen).
Features : There is no nucleus.
Function: They are very important in clotting of blood. At the site of injury, the platelets disintegrate to release a chemical substance thrombokinase which initiates the process of clotting of blood.
Elements of Blood
Quick Recap
Increase of Rbc Polycythemia
Decrease of Rbc Erythropenia
Increase of WBC leukaemia
Decrease of WBC leucopenia
Lymphocyte produce Antibody
The plasma from which the protein fibrinogen has been removed is called serum.
Liver is called graveyard of RBC
The ratio of RBC and WBC 600:1
Qs Corner
1.Serum differs from blood as it lacks
- antibodies
- clotting factors
- albumins
- globulins
2.Which of the following blood cells play an important role in blood clotting?
- Thrombocytes
- Neutrophils
- Leucocytes
- Erythrocytes
3.Blood Plasma with which among the following removed is called Serum?
- Fibrin
- Fibrinogen
- Thrombin
- Thromboplastin
4.DNA is not present in
- an enucleated ovum
- hair root
- a mature spermatozoa
- mature RBCs
5.Lymph differs from blood in having
- no plasma
- more RBCs and less WBCs
- more WBCs and no RBCs
- plasma without proteins
Biology Teacher: Priyanka Dey
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