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Chapter 17: Blood
Components of Blood
-blood is the only fluid tissue in the body
-appears as a thick, homogenous liquid but has both cellular and liquid components
-blood is a specialized type of connective tissue where living blood cells, formed elements
(such as RBCs, leukocytes / WBCs, platelets etc.), are suspended in a nonliving fluid
matrix called plasma
-dissolved fibrous proteins become visible as fibrin strands during blood clotting
-in a centrifuge, the heavier formed elements are packed down by centrifugal force and the
less dense plasma remains at the top
-most of the mass at the bottom is made up of erythrocytes (red blood cells) that transport
-a thin, white layer is present at the erythrocyte-plasma junction and is called the buffy
-buffy coat layer contains leukocytes and platelets
-leukemia patients would have a large buffy coat
-erythrocytes typically make up about 45% of the total volume of blood sample and this
blood fraction is known as the hematocrit
-leukocytes and platelets contribute less than 1% of blood volume and plasma makes up the
remaining 55%
Physical Characteristics of Blood and Volume
-blood is a sticky, opaque fluid with a metallic taste
-scarlet coloured blood = oxygen rich
-dark red blood = oxygen poor
-blood is more dense than awter and about 5 times more viscous due to its formed elements
-blood is slightly alkaline with a pH of 7.35 to 7.45 and temperature of 38C (always
slightly higher than body temperature)
-blood makes up 8% of the body weight with a volume of 5-6L in makes and 4-5L in
1) Distribution
a) delivering oxygen from the lungs, nutrients from the digestive system, and dissolved
gases to all body cells
b) transporting metabolic waste products from cells to elimination sites (to the lungs for
elimination of carbon dioxide and to the kidneys for the disposal of nitrogenous waste)
c) transporting hormones from the endocrine organs to their target organs
2) Regulation
a) maintaining appropriate body temperature by absorbing and distributing heat throughout
the body and tot he skin to encourage heat loss
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b) maintaining normal pH in body tissues; many blood proteins and other bloodborne
solutes act as buffers to prevent excessive or abrupt changes in blood pH that could
jeopardize normal cell activities
-blood acts as the reservoir for the body's alkaline reserve of bicarbonate atoms
c) maintaining adequate fluid volume in the circulatory system
-salt (i.e.:NaCl) and blood proteins act to prevent excessive fluid loos from the
bloodstream into tissue spaces
-the fluid volume in the blood vessels remains ample to support efficient blood
circulation to all parts of the body
3) Protection
a) preventing blood less
-when a blood vessel is damaged, platelets and plasma proteins initiate clot
formation, halting blood loss
b) preventing infection
-antibodies, complement proteins, and WBCs help defend the body against foreign
invaders such as bacteria and viruses
Blood Plasma
- a straw-coloured, sticky fluid
-contains about 90% water and over 100 different dissolved solutes including nutrients
(i.e.; glucose, carbohydrates, amino acids), gases (i.e.: O2 and CO2), hormones, wastes and
products of cell activity, ions / electroylyes (i.e.: sodium, potassium, calcium, chloride,
bicarbonate), proteins (i.e.: albumin, clotting proteins etc.), etc.
-plasma proteins account for 8% by weight of plasma volume
-plasma proteins, except for hormones and gamma globulins, are produced by the liver
-most plasma proteins serve a variety of functions but are not taken up by cells to be used
as fuels or metabolic nutrients like most other plasma solutes (i.e.; glucose, fatty acids,
amino acids)
-accounts for ~60% of plasma protein
- acts as a carrier to shuttle certain molecules through the circulation
-albumin is an important blood buffer
-is the major blood protein contributing to the plasma osmotic pressure which helps keep
water in the bloodstream (sodium ions are the other major solute contributing to blood
osmotic pressure)
-plasma composition is kept relatively constant by various homeostatic mechanisms
Formed Elements
-formed elements include erythrocytes, leukocytes, and platelets
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-erythrocytes of have no nuclei or organelles
-platelet cells are cell fragments
-only leukocytes (WBCs) are complete cells
-most formed elements survive in the bloodstream for only a few days
-most blood cells do not divide; they are continuously renewed by division of cells in red
bone marrow, where they originate
-erythrocytes outnumber the other types of formed elements
-red blood cells (RBCs)
-small cells shaped like biconcave discs (flattened discs with depressed centres)
-they appear lighter in color at their thin centers than at the edges
-mature erythrocytes are abound by a plasma membrane and lack a nucleus (anucleate)
-have no organelles; they are "bags" of hemoglobin which is the RBC protein that functions
in gas transport
-contains other proteins such as antioxidant enzymes that rid the body of oxygen radicals
-other proteins are used to maintain the plasma membrane and promote changes in
RBC shape
-spectrin, a network of proteins, maintains the biconcave shape of the RBC
-it is attached to the cytoplasmic face of its plasma membrane
-the spectrin net is flexible, allowing the RBC to twist, turn, and become
cup shaped as they are carried through capillaries with diameters
that are smaller than the RBC and then return to their biconcave
-RBCs are an example of complementarity of structure and function
-it picks up oxygen in the capillary beds of lungs and releases it to tissue cells
across other capillaries throughout the body
-transports 20% of carbon dioxide released by tissue cells back to the lungs
-erythrocytes are the major factor contributing to blood viscosity
-greater viscosity = greater number of red blood cells
-3 structural characteristics that contribute to erythrocyte gas transport function
1) -small size and biconcave shape provide a huge surface area relative to
-biconcave disc is suited for gas exchange because no point within the
cytoplasm is far from the surface
2) -not counting water, an RBC is over 97% hemoglobin, which binds and
transports respiratory gases
3) -they do not consume any oxygen they are transporting
-they lack mitochondria and generate ATP by anaerobic mechanisms
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