I- Function

II- Composition

            a- Plasma

            b- Formed elements:

                        b1- Erythrocyte

                        b2- Leukocyte

                        b3- Thrombocyte

III- Hemostasis

            - Vasospasm

            b- Platelet plug formation

            c- Coagulation

            d- Clot retraction and fibrinolysis

IV- Blood group

            a- ABO blood group

            b- Rhesus blood group




40% solid matter

60% of fluid:

=>2\3 intracellular

=>1\3 extracellular

=>80% interstitial (in between cells) = lymph

20% circulation = plasma

Percent varies depending on age of person, sex; women have more fluid because of more fat, babies have 80% fluid.




1. transport nutrients to cells and remove wastes.

2. regulation of temperature, pH, osmotic pressure, glucose, calcium...

3. protection = fight infection (white blood cells)



Hematocrit - proportion of formed elements in blood.

Enable to detect anemic state. separation of formed elements from plasma.

a- plasma - yellowish clear liquid, composed of water, proteins and other solutes.

Water = 90%

Proteins = (all synthesized by the liver)

Albumin = 54%, regulates osmotic pressure

Globulins = 38%, alpha and beta globulins in transport,

gamma globulins in defense (antibodies)

Fibrinogen = 7%, coagulation

Other solutes =

Electrolytes - Na+, K+, Ca++, Mg++

Nutrients - glucose, amino acids, fatty acids

monoglycerides ...

Gases - O2, N2, CO2

Regulatory substance - hormones, enzymes





Osmotic Pressure:

Due to concentration of solutes in the blood, such as electrolytes, glucose and proteins. Proteins, among the albumin, are the main regulators of blood osmotic pressure. It controls the distribution of fluid in the major compartments.

Basic concept: The glucose molecules diffuse into the water. They go from an area of high concentration to another area of low concentration (or going down a concentration gradient)

After a while, there is an even concentration of glucose on both sides.

When a semipermeable membrane (a membrane permeable to some compounds but not to other) separates 2 compartments, the solutes on each side diffuse, if permitted, to the other side, following the concentration gradient. If one of the compound is too big and cannot cross the semipermeable membrane, it is stuck on the same side. But water, a small molecule also follows the concentration gradient and crosses to the other side, thus increasing the volume on the side container the large molecule. This is osmosis.

Examples of conditions affecting osmotic pressure:

-malnutrition due to low albumin level

-kidney disease due loss of blood protein

b- Formed elements - formed from precursor cells or stem cells (hemocytoblast) located in bone marrow:

formed elements

=>red blood cells or erythrocytes- not true cells

=>white blood cells or leukocytes

=>platelets or thrombocytes- not true cells


Hematopoiesis or Hemopoiesis = blood cell formation



Erythropoiesis = red blood cell formation


Proerythroblast => reticulocytes (immature RBC) => erythrocytes (RBC)


Myeloblast (white blood cells) => granulocytes eosinophils




Monoblasts (white blood cells) => Monocytes

Lymphoblast (white blood cells) => B-lymphocyte (bone) or

T-lymphocyte (thymus)


Megakaryoblast => thrombocytes = platelets

b1- Erythrocytes (RBC) - 99% of formed elements, bag" filled with hemoglobin (15g/100ml of blood). about 4 to 5 millions RBC per mm3 blood.





Hemoglobin = Globin + Heme : role: carry oxygen





Life Cycle of RBC

RBCs are formed in red bone marrow which synthesizes hemoglobin from 4 globin molecules, each containing 1 heme (each heme contains 1 iron (Fe).

proerythroblasts => reticulocyes => erythrocytes ----> circulate in body for 120 days

When RBCs become old and damaged they are destroyed in spleen and liver by macrophages

Hemoglobin = globin and heme, globin is recycled; heme is degraded and made of biliverdin and Fe; biliverdin is green bile pigment which turns into bilirubin (yellow). A small amount passes into the blood and is eliminated into the urine, giving it its yellow color. In the intestine, bilirubin is converted into stercobilin (which gives the stools their brown color). The iron is recycled and transported back to bone marrow.

Factors influencing RBC synthesis:

- globin

- Fe

- vitamin B-12 (found in food)

=>Intrinsic factor secreted in stomach is needed in order to absorb B-12 in the duodenum.

=>not enough B-12 causes pernicious anemia

- erythropoietin - hormone synthesized by kidney

decreased O2 in blood stimulates secretion of erythropoietin by the kidney. This hormone stimulates the bone marrow to produce more red blood cells

Example: increased altitude => athlete training and blood doping

b2- Leukocytes - formed in bone marrow, life cycle varies from hours to several years. about 10 000 WBC per mm3 blood

- granular leukocytes

- neutrophils - most numerous 70%

role: phagocytosis of bacteria, debris; work within the blood vessels

- Eosinophils - 3%, destroy parasites

- Basophils - triggers allergic reactions (in the tissue they become mast cell)


- agranular leukocytes

- lymphocytes - 20%, form antibodies

B-lymph (bone marrow) and T-lymph (bone => thymus)

- monocytes - phagocytosis of bacteria and debris, in tissue they are called macrophages (cause pus which is dead bacteria and dead macrophages)






neutrophil                      basophil                 eosinophil


monocyte                               lymphocyte


b3- thrombocytes


Derived from breakage of the megakaryocyte cytoplasm. about 200 000 per mm3 blood. role in hemostasis.



Is the ability of the body to stop bleeding.

Trauma to body, such as a cut, exposes connective tissue into the lumen of the blood vessel


1- Vasospasm (reflex from blood vessel wall), temporary


2- Platelet plug formation - platelets block opening in blood vessel by sticking to collagen fibers exposed into lumen. They also release serotonin which maintains vasospasm.


3- Coagulation - damaged tissue releases the tissue thromboplastin factor (TTF)- tissue factor - extrinsic factor-->Extrinsic pathway

tissue trauma => TTF => factor VII activated => factor X activated => prothrombin => thrombin =>fibrinogen => fibrin


Intrinsic pathway: Triggered by contact with foreign matter (collagen, glass, plastic...)

factor XII => IX => VIII => => => X => => => fibrin



Hemophilia - due to bad coagulation factors, often VIII and IX


Anticoagulants - helps prevent clotting


-Heparin - Is a thrombin inhibitor. normally secreted in small amount by basophils and

blood vessel lining.


-Coumadin = Warfarin - "rat poison", interferes with vitamin K action which is necessary for the synthesis of several coagulation factors.

When we cut ourselves why don't our entire body clot?

(animation of the hemostasis process)


4- clot retraction

after about 1 hour, fibrin contracts: a yellow fluid, the serum comes out of clot

(serum = plasma - fibrinogen)

then, fibrin is dissolved by an enzyme (fibrinolysis) as tissue are being repaired



1- ABO


agglutinogens and agglutinins

Agglutinogens - are antigens (foreign substances) often made of glycoproteins, embedded into the red blood cell membrane, A or B.

Agglutinins - are antibodies which react with the antigens (anti A or anti B). located in plasma. Blood group A with agglutinogen A on RBC has the opposite agglutinin (anti B) in plasma and can never have/make the matching ones.

Why can a person A blood type can receive O?  Why does this work?

Because RBC can be separated from plasma, so there is no reaction between agglutinogens and agglutinins.

2- Rh = Rhesus

Blood group RBC plasma, agglutinin

Rh+ Rh + can not make anti Rh+

Rh- no Rh+ on RBC able to make anti Rh+ if exposed to Rh+


At birth, there is no Rh agglutinin in the plasma, but a Rh- person is born with ability to make it. Examples:

Rh- gets blood with Rh+

1st transfusion - nothing happens = no physical sign but antibodies anti Rh+ are made

2nd transfusion- Rh+ blood cells are killed by anti Rh+ => hemolytic reaction

What happens in pregnant women?

-baby Rh- and mother Rh+: Nothing

-baby Rh+ and mother Rh-: 1st child: no physical sigh but the mother makes antibodies anti Rh+ after the birth of the child. When the second child Rh+ comes along, the baby's blood cells can be destroyed => hemolytic reaction (erythroblastosis fetalis). To save the baby, he will need to have a blood transfusion with Rh- to remove the toxins formed from the hemoglobin degradation and to avoid more hemolysis. To prevent the formation of these agglutinins anti Rh+ by the mother, she is given Rhogam. This drug prevents mother form producing antibodies. Rhogam is nothing else than the antibodies themselves, anti Rh+. They destroy the fetus Rh+ RBC before the mother's immune system has time to react to them. Can only be given early in pregnancy or after the child is born.

Blood types distribution in the world:


Internet sites of interest:


Blood groups:

Facts about blood donations:


Aplastic anemia:


Thalassemia and sickle cell anemia: