Blood is formed through haematopoiesis from hematopoietic stem cells in bone marrow, which produces red blood cells, white blood cells, and platelets. The spleen and thymus play crucial roles in immune function and lymphocyte production, while lymph nodes filter lymph and support the immune response. Abnormalities in blood cell production can lead to conditions like aplastic anemia or leukemia, affecting the body's ability to produce or regulate blood cells.

1. Blood cell formation
• Blood is formed by the process called
haematopoiesis derived from hematopoeitic
stem cells. Hematopoeitic stem cells resides in
the medulla of the bone marrow

2. http://en.wikipedia.org/wiki/Haematopoiesis

3. Blood cell formation
• Blood is mainly synthesized in the red bone marrow.
• Some lymphocytes are produced in lymphoid tissue.
• The bones are not solid, but are made up of 2 distinct
regions.
• The outer weight bearing area is hard, compact and
calcium based.
• It surrounds a lattice-work of fibrous bone known as
cancellous tissue.
• The inner region or marrow which is one of the largest
organs of the body is located within the bones.

4. • The bone marrow may contain fat cells, fluids,
fibrous tissue, blood vessels, and hematopoietic,
or blood forming cells. Marrow looks yellow
when it holds a lot of fat cells but appears red
when it has more blood-forming material.
• The marrow is the principle site for
hematopoiesis which after birth occurs primarily
within the legs, arms, ribs, sternum and
vertebrae.

5. Stem cells
• Many of the blood cells that populate the vessels are born
and mature in the bone marrow.
• They are derived from hematopoietic cells called stem cells.
• Stem cells within the bone marrow continuously divide to
form new cells.
• Some of the new cells remain unchanged as stem cells and
have lifelong capacity for self renewal. These cells are called
pluripotent cells.
• Unipotential stem cells have limited capacity of cell
renewal.

6. • Stem cells become committed to forming only one type of
blood cell line- erythrocyte, leukocytes, or platelets.
• Colonies of progenitor cells provide offspring of increasing
differentiation or maturity.
• They react to specific compounds known as poietins.
Poietins stimulate the progenitor cells until they transform
into the appropriate young blood cell known as ‘blast’ cell.
• Although stem cells are few in number-composing not more
than 3%-5% of all cells in the marrow, they are the only cells
capable of producing the progenitor cells the eventually
form all of the blood elements.

7. • The number of blood cells produced every day is
enormous. In the normal adult, production amounts
to 2.5 billion erythrocytes, 2.5billion platelets and 1.0
billion granulocytes per kilogram of body weight.
• If stem cells stop functioning because of drugs,
radiation, infection or other toxic event they become
unable to make any of the blood cells. The circulating
blood will be deficient in all types of blood cells, a
condition called pancytopenia. The inside of the bone
marrow appear empty and will lack the normal

8. Quantity of cells.
• Progenitor cell may also die or lose the ability to
function due to drugs, radiaton, infection or other
toxic event.
• Depending on which progenitor cease to work, the person
may develop pure aplasia(lack of red blood cells),
megakaryocytic aplasia(absence of platelets) or
leukopenia(low white blood cell count).
• This stem cell disorder, which is called aplastic anemia
may be treated by bone marrow transplant or

9. Immunosuppressive medications.
• In rare circumstances, children with aplastic anemia
may respond to therapy with steroids or
androgens(male sex hormones); such treatments are
generally discouraged in adults.

10. • Other types of bone marrow abnormalities such as
myeloprolierative disorder, a disease in which bone
marrow cells multiply outside of bone marrow tissue,
or myelodysplastic (preleukemia) syndromes, are the
results of marrow dysfunction in either the stem cells
or progenitor cell lines.

11. spleen
• The spleen is a vital organ that is located on the left side
of the body under the lower rib cage. It is ductless gland
that is closely associated with the circulatory system.
• The adult spleen which holds the largest collection of
blood filtering lymphatic tissue in the body is roughly 5
inches long.
• The spleen contains a white pulp of lymphoid tissues
and red pulp that contains red blood cells and hollow
cavities called sinuses.

12. • Both white and red pulps are abundant in
phagocytes.
• The spleen manufactures lymphocytes and other
immune system cells to combat infection.
• It is a storehouse for healthy blood cells and its
lymphatic tissue filters out old and damaged blood
cells, microorganisms, and cell waste.
• Incase of bone marrow malfunction/ the spleen may
assume the role of blood cell formation.

13. • Certain leukemia patients may develop
splenomegaly( an enlarged spleen).
• In some form of leukemia such as chronic
lymphocytic leukemia (CLL) and hairy cell leukemia
(HCL) splenectomy (removal of the spleen) may
effective tretment.
• Splenectomy is one of the therapeutic option for HCL

14. Thymus
• The thymus gland to some extend is an age
dependant organ.
• It functions to create T lymphcytes (T-cells) in the
developing fetus, attains its full size when the child is
2 years, and then shrinks to undetectable size during
puberty.
• The thymus is located in front of the heart. It has 2
lobes and contains the thymacytes(immature
lymphocytes), epithelial cells(cells that cover internal
and external body surfaces, including the lining of

15. Blood vessels, etc) and macrophages. T-cells are
primarily responsible for cell-mediated immunity and
immune system regulation.
• Within the thymus, immature pre-T cells develop and
are able to recognize antigens.
• The immature pre-T cells then migrate to other
lymphoid tissues, such as the spleen and the lymph
nodes, where they mature and undergo additional
differentiation.
• Although the thymus shrinks with age it continues to

16. aid immune system through out a personsˈs lifetime.

17. Lymph nodes
• Lymph nodes are small oval or bean shaped that are
strung along the vessels that channel lymph and chyle on
the way back to the blood.lymph is the transparent and
slightly yellow, liquid that is collected from the body
tissues and chyle is the milky fluid taken from food in the
intestine during digestion.
• They contain a collection of lymphocyts(a specilized white
blood cells); nongranular leukocytes; plasma cells
(antibody releasing cells) and macrophages(large cells the
ingest foreign substance and help lymphocyts to launch
immune system response.

18. • The lymph nodes are arranged along the route of large
blood vessels and are concentrated in areas such as the
abdomen, under arms, groin and neck. Small sacs called
follicles within the lymph nodes contain B lymphocytes(B-
cells).
• T-cells deep within the lymph nodes play a role in the
induction of B-cells response.
• B-cells eventually matures into plasma cells that produce
antigen specific antibody, which is an immune system
chemical that is directed against a specific foreign
substance.

19. • During an infection the lymph node increase in size,
especially in infants and children.
• They return to normal after the infection has passed.
• Occasionally, a lymph node that appears
permanently enlarged may reflect cancerous
condition.
• For example, in rare instances, leukemia that has
spread outside of the bone marrow may cause
enlargement of lymph node(s).

20. Erythrocytes(erythropoiesis)
• The erythrocytes, or red cells(corpuscles), contain
hemoglobin- a substance that is able to bind with
oxygen.
• Oxygen from the lungs is carried by the erythrocytes to
all the tissues of the body.
• A person who has anemia will experience symptoms
such as weakness, fatigue, and shortness of breath.
• Erythropoeisis which is the process of development of
red cells takes about 7 days and the immature red cells
are released into the blood stream as reticulocytes

21. • Pluripotential stem cell differentiate into
proerythroblast-erythroblast-reticulocyte and finally
to erythrocyte. Both vitamin B12 and folic acid are
required for red cell formation.

22. Erythropoiesis

23. Leukocytes
• There are 5 different types of leukocytes within the
body.
• Neutrophils
• Basophils
• Eosinophils
• Monocytes and
• Lymphocytes.
• Neutrophils, eosinophils and basophils are granulocytes.
Granulocytes undergo many stages of development
before becoming mature neutrophils,

24. Basophils and eosinophils.
• The more immature, myeloid series of granulocytes
includes cells known as myeloblast-promyelocytes,
myelocytes-metamyelocytes-band forms(stab
cells/young cell) and polymorphonucler
leukocytes(PMNs).
• If there is block in the development of an individual’s
myelogenous(granulocytic) cell line, either chronic
myelogenous leukemia(CML) or accute myelogenous
leukemia(AML) may result.

25. Granulopoiesis

27. Monocytes
• Monocytes originate in the bone marrow as
monoblast and promonocyts.
• Once these early cell forms develop to
monocytes, they circulate in the blood stream
for about 24 hours.

28. Lymphocytes
• Lymphatic tissues have both fixed and circulating
elements. Many different types of lymphatic cells interact
to combat infection and recognize abnormal cells within
the body.
• Fixed lymphoid tissue is found in the lymph nodes, spleen,
thymus, tonsil and adenoid, bone marrow and various site
within the gastrointestinal tract, respiratory system and
liver.
• Circulating lymphatic cells such as the lymphocytes and
monocyte/macrophage cells originate from stem cells in
the blood forming tissue.

29. • The stem cells give rise to daughter cells that
ultimately develop into B-cells or T-cells.
• Daughter T-cells migrate to the thymus where they
mature into T-cells.
• It is believed that daughter B-cells mature in the bone
marrow.
• B-cells combat infection by changing into plasma cells
which secrets antibodies. Plasma cell antibodies
become attached to invading which is then
recognized and destroyed by the blood granulocytes.

30. • T-cells are able to detect virus infected cells within
the body. They interact with macrophages to rid the
body of virus.
• If there is a problem in the development of an
individual lymphocytes either chronic lymphocytic
leukemia(CLL) or acute lymphocytic leukemia(ALL)
may result.

32. Platelets
• Although platelets are classified s type of blood cell,
thy are just pieces of megakaryocytes ie bone
marrow giant cells that contain a many lobed
nucleus.
• Platelets are the major clotting elements of the body.
They group together to seal of blood vessel damage
caused by cuts or other traumatic injuries.
• A person with low level of platelets in the circulating
blood-thrombopenia may experience excessive
bleeding.

33. • The end