Blood physiology 1

The blood:-

-Blood is specialized connective tissue consisting of cellular elements suspended in plasma .
-The cells make up approximately 45% of the total blood volume .
-The blood is one of the largest organs of the body, which a volume of about 5 liters & a weight of 5.5 kg an average 70 kg man .
-Blood circulates throughout the body , supporting the function of all other body tissues .
-Normal peripheral blood is composed of three types of cell , red blood cells , white blood cells & platelets , suspended in a pale yellow fluid called plasma .

(1) The cellular elements:-

A- Red blood cells ( erythrocytes )
B- White blood cells ( leucocytes )
C- platelets .




(A):-Red blood cells (RBCs ) :-

-Mature RBCs , or erythrocytes , are the most
numerous of the blood cells : about 5x1012 normally are present in each liter of blood .
-RBCs are biconcave discs approximately 7.5 microne in diameter & 2 micron thick , but their extreme pliability allow them to squeeze through capillaries less than 5 microne diameter .
-The human body contains about 25 trillion red blood cells in an average concentration of about 5 million per microliter .
-In mammals , they lose their nuclei & its cytoplasmic organelles during development .
-Red blood cells survive in the circulation for about 120 days before being sequestered in the spleen & consumed by the phagocytic cells of the reticuloendthelial system .
-The senecent red cells that are destroyed within spleen are constantly replaced by juvenile cells synthesized & released by the bone marrow .
-An average 70 kg adult male produces about 2.3x106 red cells every second .
-Less than 1% of RBCs are the newly formed reticulocytes , which take 1-2 days to develop into mature red cells .
-This cells exhibit slight bluish network after staining, because of the present remnant RNA .


-The red cell membrane is freely permeable to water & anions ( chloride & bicarbonate) transverse the membrane in less than second, & is relatively impermeable to cations .
-The chemical composition of membrane is approxiametely 42% lipid , 50% proteins & 8% carbohydrates .
-The major function of red cells is to transport hemoglobin , which in turn carries oxygen from the lungs to the tissues & transport CO2 from tissues back to the lungs . Also , hemoglobin is an excellent acid – base buffer .
-Red blood cells contain a large quantity of carbonic anhydrase , which catalyzes the reaction between CO2 & water , increasing the rate of this reaction many thousand fold .
-The rapidity of this reaction make it possible for the water in blood to react with large quantities of CO2 & thereby transport it from the tissues to the lungs in the form of the bicarbonate ion (HCO3-) .
-The percentage of the total blood volume comprised of red blood cells is called the hematocrit , & this is normally about 40% in women & about 45% in men .

(B):-White blood cells ( leucocytes ) :-

-The leucocytes are the mobile units of the body’s protective system .
-They are formed partially in the bone marrow ( the granulocytes & monocytes , & a few lymphocytes ) & partially in the lymph tissue (lymphocytes & plasma cells ) , but after formation they are transported in the blood to the different parts of the body where they are to be used .
-The number of white blood cells in the blood is normally only 1/600 the number of red blood cells .

-Leucocytes are of two main types :-

(1) Granular leucocytes .
(2) A granular leucocytes .

(1):- Granular leucocytes :-

- Are the most numerous . Always contain specific granules , & they are characterized by the presence of many lobed nucleus for this resons they are referred to as polymorphonuclear leucocytes .

-There are three types of granular leucocytes :-

(a):-Neutrophils (b):- Eosinophils
(c):- Basophils .

(a):-Neutrophils :-

-They are the most numerous of the leukocytes in human blood which constitute 50-70% of the total white blood cells .


-The neutrophil nucleus is highly polymorphus,
which usually consist of from 3 to 5 irregular ovoid lobes connected by a thin chromatin strand .
-Neutrophil cytoplasm contains numerous fine neutrophilic granules , which are a special types of lysosomes that contains principally hydrolytic enzymes .
-Neutrophils constitute the first line of defense against invading organism so the main function of neutrophils is bacterial killing by phagocytosis .
-Neutrophils are highly motile , highly phagocytic , & are attracted out of the blood into tissue areas where tissue destruction is occurring by a process called chemotaxis ,which means attraction by the destruction products from the damaged tissues .
-Once in the tissue area , the neutrophils phagocytized bacteria & small amounts of dead tissue debris .

(b):-Eosinophil :-

-They normally constitute about 1 to 4 percent of the total white blood cells .
-The nucleus is usually bilobed .
-This name is derived from the staining
characteristic of the large cytoplasmic granules of uniform sized which stain strongly with the acidic dye eosin .
-Eosinophils are similar to the neutrophils except that they are less chemotactic & less phagocytic.
-They are phagocytose antibody – antigen complex .
-Eosinophils are produced in large numbers in persons with parasitic infections .
-The parasites are usually too large to be phagocytized , but the eosinophils attach themselves to the surface & release lethal substances that can kill many of the parasites.
-Large numbers of eosinophils also appear in the blood in allergic conditions & may help detoxify toxins that are released by allergic reactions .

-(c) Basophils :-

-These cells are difficult to find in human blood , since they constitute only about 0.5 to 1 percent of the total number of leucocytes .
-The nucleus often is irregular in outline & partially constricted into two lobes ( S shape like ).
-The cytoplasmic granules are round & variable in size , which stain with basic dyes .
-The basophils are very similar to though not identical with the large mast cells located immediately outside many of the capillaries in the body .
-Basophils & mast cells are important for allergic reaction .
-Since , the type of antibody , the IgE type , that causes allergic reaction binds to mast cells & basophils causing them to release various inflammatory products that in turn cause many of the manifestations of allergic reactions .
-Also , basophils & mast cells liberate heparin into the blood , a substance that can prevent blood coagulation . As well as histamine & small quantities of bradykinin
-Eosinophils can reduce the inflammation by inactivating the heparin & histamine , which are among the collection of substances released by allergen – stimulated mast cells & basophils , thus preventing spread of local inflammatory process , so the number of eosinophils is greatly increased in allergic conditions & parasitic infections .
-Basophils differ from neutrophils in that they are no phagocytic .

(2) – A granular leucocytes :-
- This cells have cytoplasm that appears homogenous & nuclei that are spherical to reniform in shape .