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ch. 19 blood
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The Blood
A unique, fluid
connective tissue
the blood constitutes about
8%
of body weight
In a healthy adult, volume is
5-6
L for a male and
4-5
L for a female
the blood is about
4-5
times as viscous as water
the blood has a pH of
7.35-7.45
blood color varies from
scarlet
(
O2-rich
) to
dark red
(
O2-poor
)
blood functions to
transport
,
regulate
, and
protect
Transport
O2
and
nutrients
to cells
CO2
and metabolic wastes away from cells
hormones
and
enzymes
Regulate
body temperature
pH of body tissues
water content of tissues
Protect
against
blood loss
(by
clotting mechanisms
)
against
infection
(by
defense mechanisms
of
white blood cells
)
Blood is composed of two portions:
Plasma
(
55%
)
Formed elements
(
45%
)
Plasma
(
55
%)
watery fluid
that contains
dissolved substances
Formed elements (
45%
)
red blood cells (
erythrocytes
)
white blood cells (
leukocytes
)
platelets (
thrombocytes
) are cell fragments
Blood Plasma
• Fluid portion of blood; straw-coloured
• Composed of 90%
water
and 10%
solutes
Solutes include:
electrolytes
: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-
nutrients
: amino acids, glucose, fatty acids, glycerol
enzymes
and hormones gases: CO2, O2
metabolic wastes-
urea, ammonia, bilirubin
plasma proteins
produced mainly by liver
Plasma Proteins account for
8%
of the 10% of dissolved
solutes
in plasma
plasma proteins have 3 main categories
Albumin
Globulins
Fibrinogen
1)
Albumin
(smallest size)
54
% of plasma protein
helps with the maintenance of
osmotic pressure
(helps keep water in blood plasma)
acts as a
blood buffer
(maintains pH)
carrier
molecule of
fatty acids
and
steroid hormones
Globulins
38% of plasma protein
i)
alpha
and
beta
globulins – transport iron, metals, lipids, fat-soluble vitamins
ii)
immunoglobulins
(antibodies) – released by plasma cells during immune response
Fibrinogen
7% of plasma protein
soluble precursor of fibrin
acts in blood clotting
Red Blood Cells
• Function in the transport of respiratory gases -
O2
and
CO2
•
Biconcave disc
- lacks nucleus and other organelles when mature
• Contain about
250 million
molecules of hemoglobin (Hb) per
cell
Hb molecule consists of:
• a
globin
molecule composed of
four polypeptide chains
(
2 alpha
&
2 beta
)
• an
iron-containing ‘heme’ pigment
bound to each of the
four chains
Each heme binds one
O2
molecule reversibly
globin
binds
CO2
Lifespan of RBCs is about
120
days
red blood cells are formed constantly by
erythropoiesisin red bone marrow
(rate of
2 million per sec
)
cells take about
one week
to mature
the main stimulus for increased erythropoiesis is a decrease in the
O2-carrying capacity
of the blood
Number of RBCs and platelets stays fairly
constant
because regulated by
negative feedback systems
Number of WBCs varies because it depends on
invading pathogens
and other
foreign antigens
blood cell formation is called
hematopoiesis
All blood cells arise from a
Pluripotent stem
cell in red bone marrow (
hemocytoblast
)
the hemocytoblast goes on to form
2
stem cell lines:
myeloid stem cells-
form RBC’s, Platelets, Eosinophils, Basophils, Neutrophils & Monocytes
lymphoid stem cells-
form Lymphocytes
Erythropoiesis
requires a dietary intake of
iron
, vitamin
B12
, and
folic acid
iron
is needed for heme synthesis
stored in the
liver
and
spleen
as
portein-iron complexes
transported in the blood by
transferrin
(
plasma protein
) to
red bone marrow
and is taken up by developing
RBCs
Vitamin
B12
• found in
dietary liver
,
eggs
, and
meat
• requires production of an
intrinsic factor
by the
stomach mucosal cells
to allow
B12
to be absorbed in the
small intestine
B12
is stored in the
liver
and transported to
red bone marrow
when needed
Vitamin
B12
AND
Folic Acid
are needed for
cell division
and
DNA synthesis
that occurs in
RBC formation
=
erythropoiesis
RBCs are
anucleate
so they can't
grow
and
divide
old or damaged RBC’s are destroyed by
macrophages
in the
spleen
,
liver
, and
bone marrow
hemoglobin
is salvaged and degraded to
heme
and
globin
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