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32.4
Blood
Blood
In vertebrates, it is considered a connective
tissue
 Composed of various types of cells
suspended in a liquid matrix called the
plasma (more on that later)
 The average human body contains between
4-6L of it
 Average pH of 7.4 in humans
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Separation
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If a blood sample is taken, the cells can be
separated from the plasma by spinning the
whole blood in a centrifuge
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•
whole blood is blood with all its components
intact
Formed elements, the cells that occupy 45%
of the volume of blood, settle to the bottom
and leave a red pellet at the bottom with the
plasma suspended above
Plasma
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Water accounts for 90% of the plasma and has a
variety of solutes dissolved in it
Electrolytes- inorganic salts in the blood
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present in the plasma in the form of ions
The concentration of these ions is important factor in
maintaining osmotic balance between the blood and
interstitial fluid
Nerves and muscles require a concentration of key ions
in the interstitial fluid in order to function properly, which
reflects the concentration in the plasma
The kidney is responsible for maintaining plasma
electrolytes at precise concentrations, which is an
example of homeostasis
Plasma (cont’d)
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Plasma proteins are another important class
of solutes and have several functions
Act as buffers to help maintain constant pH
 Help determine osmotic strength of blood
 Contribute to blood viscosity
 Some also have specific functions
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 Some
serve as escorts for lipids (remember?)
Plasma (cont’d)
Immunoglobulins are a class of proteins that
serve as antibodies that help combat viruses
and other foreign agents that invade the
body
 Fibrinogens are a class of proteins that that
serve as clotting agents that help to plug
leaks when blood vessels are injured
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Blood plasma that has the fibrinogens removed
is called serum
Plasma (cont’d)
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Also contains various substances that are
traveling from one part of the body to another
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Nutrients
Metabolic waste products
Respiratory gases
Hormones
NB: blood plasma and interstitial fluid are similar in
composition, but blood plasma has a higher
concentration of proteins
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Because capillary walls are not permeable to proteins
Blood Cells
3
classes of cells
 red
blood cells, which transport oxygen
 white blood cells, which function in
defense
 platelets, which are involved in blood
clotting
Red Blood Cells
 Red
cells, also known as erythrocytes,
are the most numerous blood cells
 Each
cubic mm of human blood contains
about 5 million of these cells, and there
are about 25 trillion of them in the average
5L of human blood
RBC Structure
Structure fits function
 Biconcave disc, flatter at the center than at
its edges
 NB: mammalian erythrocytes have no
nuclei, which is unusual for living cells (other
vertebrate classes have nucleated
erythrocytes)
 Lack mitochondria and generate ATP only
through anaerobic metabolism
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RBC Structure (cont’d)
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Small -> great for oxygen transport
For oxygen to be transported, it needs to be
able to diffuse across the plasma membrane of
the RBC
 The smaller the cell, the greater the total area of
plasma membrane in a given volume of blood

 Biconcave
shape also adds to the surface area
RBC: Small but mighty!
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Contains 250 million molecules of hemoglobin, a
protein containing iron
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has heme’s that the oxygen bind to
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Heme’s are the deep red, nonprotein, ferrous component of
hemoglobin
As red blood cells pass through the capillary beds
of lungs, gills, or other respiratory organs, oxygen
diffuses into the erythrocytes and hemoglobin
binds the oxygen
Reversed in the capillaries of the systemic circuit
with hemoglobin unloading the oxygen
RBC Life
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Formed in the red marrow of bones, esp. the ribs,
vertebrae, breastbone, and pelvis
Marrow has stem cells (remember those?) that can
develop into any type of blood cell
Red cell production is stimulated by a negative feedback
mechanism that is sensitive to the amount of oxygen
reaching the tissues via blood
If the tissues aren’t receiving enough oxygen, the kidney
secretes a hormone called erythropoietin, which stimulates
the production of erythrocytes in the marrow
If blood is supplying more oxygen than the tissues are
using, the level of erythropoietin is reduced and RBC
production is slowed
RBC end
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On average, RBC’s live 3-4 months before
they are destroyed by phagocytic cells
primarily in the liver
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The hemoglobin is digested and the amino
acids are incorporated into other proteins made
in the liver
 Most
of the iron in the hemoglobin is cycled back to
bone marrow, where it is reused in erythrocyte
production
White Blood Cells
White cells, aka leukocytes, fight infections
 There are five types: basophil, neutrophil,
eosinophil, lymphocyte, monocyte
 Some of these are phagocytes, which eat
bacteria and debris from our own dead cells
 Lymphocytes give rise to the cells that
produce antibodies, the plasma proteins that
react against foreign substances
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WBC (cont’d)
The leukocytes we see in blood are in transit
 White cells spend most of their time outside
of the circulatory system, battling pathogens
in the interstitial fluid
 Lots of white cells, esp lymphocytes, in
lymph nodes and other parts of the
lymphatic system (more later)
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WBC Life
Arise in bone marrow from the same stem
cells that can differentiate into erythrocytes
 Some lymphocytes, after leaving the
marrow, mature in the spleen, thymus,
tonsils, adenoids, and lymph nodes – all of
which are called lymphoid organs
 Normally a cubic mm of human blood has
5000 to 10,000 leukocytes, but this number
increases when the body is fighting an
infection
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Platelets
NB: NOT ACTUALLY CELLS
 Chips of cells about 2-3 µm in diameter
 No nuclei
 Originate as pinched-off cytoplasmic
fragments of larger cells in the bone marrow
 Enter the blood and help with clotting
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Blood Clotting
Fibrinogen is the inactive form of the sealant
our body uses to plug leaks in our vessels
 Its active form, fibrin, aggregates into
threads that form the fabric of the clot
 Clotting begins with the release of clotting
factors from platelets and involves a
complex chain of reactions
 More than 12 clotting factors have been
discovered and they are still not fully
understood
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Blood Clotting (cont’d)
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Hemophilia is a disease characterized by
excessive bleeding from even minor cuts and
bruises
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Caused by an inherited defect in any step of the clotting
process
Anticlotting factors in the blood normally prevent
spontaneous clotting in the absence of injury
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Sometimes platelets clump and fibrin coagulates within
a blood vessel, blocking the flow of blood
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This clot is called a thrombus
More likely to form in someone with cardiovascular disease
The Lymphatic System
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Returns fluid to the blood and aids in body defense
Fluids and some blood proteins that leak from the
capillaries into the interstitial fluid are returned to the blood
via the lymphatic system
Fluid enters this system by diffusing into tiny lymph
capillaries intermingled among capillaries of the
cardiovascular system
Once inside the lymphatic system, the fluid is called lymph,
with a composition similar to the interstitial fluid
The lymphatic system drains into the circulatory system
near the junction of the venae cavae with the right atrium
The Lymphatic System (cont’d)
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Lymph vessels, like veins, have valves that prevent the
backflow of fluid toward the capillaries
Rhythmic contraction of the vessel walls helps draw fluid
into lymphatic capillaries
Like veins, lymph vessels depend mainly on the movement
of skeletal muscle to squeeze fluid toward the heart
Along lymph vessels are organs called lymph nodes
The lymph nodes filter the lymph and attack viruses and
bacteria
Inside a lymph node is a honeycomb of connective tissue
with spaces filled with white blood cells specialized for
defense
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When the body is fighting an infection, these cells multiply, and the
lymph nodes become swollen
facweb.northseattle.edu
 www.cafleurebon.com
 www.histology-world.com
 www.miracleofthebloodandheart.com
 www.koate-dviusa.com
 www.voxxi.com
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