1-Describe Cellular and non-cellular
components of blood
2-Recognise features of blood and functions
3-Define Erythropoiesis, leucopoiesis and
thrombopoiesis.
4-Recognize sites of RBC formation at
different developmental age.
Blood:
It is a specialized circulating fluid connective tissue composed of
cells suspended in fluid intercellular substances called plasma.
It supplies O
2
and nutrients & removes CO
2
with waste products to
all regions of the body.
Characteristics of Blood
1-Bright red (oxygenated)
2-Dark red/purplish (unoxygenated)
3-Much more dense than pure water
4-pH range from 7.35 to 7.45 (slightly alkaline)
5-Slightly warmer than body temperature 100.4 F
6-Typical volume in adult male 5-6 liters
in adult female 4-5 liters
7-Nearly 7-8% of body weight
Major Functions of Blood
1. Distribution & Transport
A-oxygen from lungs to body cells
.
B-carbon dioxide from body cells to lungs
.
C-nutrients from GI tract to body cells
.
D-nitrogenous wastes from body cells to kidneys
.
E-hormones from glands to body cells
2. Regulation (maintenance of homeostasis
)
a. maintenance of normal body pH by buffer system through
blood proteins (albumin) & bicarbonate
b. maintenance of circulatory/interstitial fluid by electrolytes
c. maintenance of temperature by absorbing and distributing heat
3. Protection
.
A-platelets and proteins "seal" vessel damage
B-protection from foreign material & infections by leukocytes, antibodies&
complement proteins
Cellular components:
Red Blood Cells
(Erythrocytes)
transport O
2
White Blood Cells
(Leucocytes)
part of the immune system
Platelets
(Thrombocytes)
cell fragments involved in clotting
Plasma
( liquid “ non cellular” part )
98% water
, ions, plasma proteins (Albumin,
globulin, Fibrinogen , enzymes and
hormones)
Same
ionic composition as
interstitial
fluid
5 liter in adult
45%
is packed cells volume (PCV)
55%
is plasma volume
Plasma component
Hemopoiesis
Hematopoiesis
the formation and development of blood cells
In adults the cellular elements are produced in the bone marrow.
Some WBCs are produced in the lymphatic tissue and bone marrow.
***
All
blood cells formed come from a
hematopoietic stem cell
.
Process of producing formed elements by myeloid and lymphoid stem cells
Erythropoiesis
: Formation of RBC (erythrocytes)
Leucopoiesis:
Formation of WBC (leucocytes)
Thrombopoiesis:
Formation of platelets (thrombocytes)
In the
adult
, red blood cells, many white blood cells, and
platelets are formed in the bone marrow. In the
fetus
,
blood cells are also formed in the liver and spleen, and in
adults such extramedullary hematopoiesis may occur in
diseases in which the bone marrow becomes destroyed or
fibrosed.
In
children
, blood cells are actively produced in the
marrow cavities of all the bones.
By age 20
, the marrow in
the cavities of the
long bones, except
for the upper
humerus and femur, has become inactive . Active cellular
marrow is called
red marrow;
inactive marrow that is
infiltrated with fat is called
yellow marrow
.
Normally,
75%
of the cells in the marrow belong to the
white blood cell-producing
myeloid
series and only
25% are
maturing red cells
, even though there are over 500 times as
many red cells in the circulation as there are white cells.
This difference in the marrow reflects the fact that the
average life span of white cells is short, whereas that of red
cells is long.
The bone marrow contains multipotent uncommitted stem
cells (pluripotential stem cells) that differentiate into one or
another type of committed stem cells (progenitor cells).
These in turn form the various differentiated types of blood
cells. There are separate progenitor cells for
megakaryocytes, lymphocytes, erythrocytes, eosinophils,
basophils, neutrophils and monocytes .
The pluripotential cells are
few
in number but are capable
of completely replacing the bone marrow when i
njected
into a host whose own bone marrow has been completely
destroyed. The best current source for these hematopoietic
stem cells is umbilical cord blood.
RBCs Erythrocyte
Most abundant cell in the blood (4 million – 6 million per
microliter of blood)
—
Formed in the bone marrow
—
Mature
forms do
NOT
have a nucleus , mitochondria and
ribosomes
—
Shaped as biconcave disc (why?)
—
6-8 micrometers in diameter
***Life span of about
120 days
RBCs are narrow & flexible for excellent fluidity especially
within the small capillaries
—
Hemoglobin (iron protein)is found in the RBC , Hb carries
oxygen from the lungs to the rest of the body and carbon dioxide
binds to the RBC and is taken to the lungs to be exhaled.
•
Production of RBC
•
Early few weeks of embryo nucleated RBCs are formed in yolk sac.
•
Middle trimester mainly in liver & spleen & lymph nodes.
•
Last months RBCs are formed in bone marrow of all bones
•
Bone marrow of flat bone continue to produce RBC into adult life
•
Shaft of long bone stop to produce RBC at puberty while epiphysis
continued
Hematopoiesis and Erythropoiesis: hematopoiesis (hemopoiesis)
- the
maturation, development and formation of blood cells
A- red bone marrow (myeloid tissue) - location of hematopoiesis;
mainly in axial skeleton and heads of femur & humerus
B-hemocytoblast (stem cell) - the mitotic precursor to blood cells before
differentiation
Erythropoiesis -
the maturation, development, and formation of Red
Blood Cells
hemocytoblast ->proerythroblast ->early (basophilic) erythroblast -
>late (polychromatophilic) erythroblast ->(hemoglobin) normoblast ->
(nucleus ejected when enough hemoglobin)reticulocyte -> (retaining
some endoplasmic reticulum)
ERYTHROCYTE life span
:
hemocytoblast -> reticulocyte
3-5
DAYS
reticulocyte -> ERYTHROCYTE
2 DAYS (in blood)
ERYTHROCYTE lifespan
100-120 Days
(primarily destroyed by macrophages in the spleen)
•
Regulation of Erythropoiesis
1- Erythropoiesis is stimulated by erythropoietin hormone
produced by the kidney in response to hypoxia (low oxygen in the
blood)
•
Hypoxia caused by:
.
Less RBCs from bleeding
.
Less RBCs from excess RBC
destruction
.
Low oxygen levels (high altitude,
illness)
.
Increased oxygen demand (exercise)
.
Erythropoietin
•
Is Glycoprotein 90% from renal cortex 10% liver
•
Stimulate the growth of early stem cells
•
Does not affect maturation process
•
Can be measured in plasma & urine
•
High levels of erythropoietin
– anemia
-High altitude
Polycythemia
– Heart failure
– Lungs disease
B- Iron - essential for hemoglobin to carry oxygen
1- 65% of Fe in body is in hemoglobin
2-liver and spleen store most excess Fe bound to ferritin
and hemosiderin
.
3-Fe in blood bound to transferrin
4-daily Fe loss: 0.9 mg men/l.7 mg women
C – Vitamins as B-complex - Vit B12 and Folic Acid essential for
DNA synthesis in early mitotic divisions leading to erythrocytes
