- if a sample of blood is separated, the plasma rises to

the top, and the formed elements, being heavier, fall

to the bottom. Most of the reddish “pellet” at the
BLOOD bottom of the tube is erythrocytes or red blood cells,
the formed elements that function in oxygen
transport. There is a thin, whitish layer called the
river of life buffy coat at the junction between the erythrocytes
- transports substances such as oxygen and nutrients and the plasma. This layer contains the remaining
throughout the body and participates formed elements, leukocytes, white blood cells that
in processes such as clotting and fighting infections act in various ways to protect the body; and
- is moved through blood vessels by the pumping platelets, cell fragments that help stop bleeding
action of the heart. This fluid contains red blood cells - Erythrocytes normally account for about 45% of the
to carry oxygen, clotting proteins to stop bleeding, total volume of a blood sample, a percentage known
and white blood cells to fight infections as the hematocrit (“blood fraction”). White blood
- transportation via blood is the only way substances cells and platelets contribute less than 1%, and
can be moved to distant body locations. In addition, plasma makes up most of the remaining 55% of
clotting proteins are found only in blood whole blood
- it is the only fluid tissue in the body
COMPOSITION AND FUNCTIONS OF BLOOD PHYSICAL CHARACTERISTICS AND VOLUME
- blood is a sticky, opaque fluid that is heavier than
water and about five times thicker, or more viscous,
largely because of its formed elements
- Color: Depending on the amount of oxygen it is
carrying, varies from scarlet (oxygen-rich) to a dull
red or purple (oxygen-poor)
- blood has a characteristic metallic, salty taste
- Slightly alkaline, with a pH between 7.35 and 7.45
- Temperature: (38°C, or 100.4°F) is always slightly
higher than body temperature because of the
friction produced as blood flows through the vessels
- blood accounts for approximately 8% of body weight,
and its volume in healthy adults is 5 to 6 liters, or
about 6 quarts.
PLASMA
- straw-colored fluid
- approximately 90% water, is the liquid part of the
blood
- Over 100 different substances are dissolved here
- examples of dissolved substances include nutrients,
salts (electrolytes), respiratory gases, hormones,
plasma proteins, and various wastes and products of
cell metabolism
- Plasma proteins are the most abundant solutes in
plasma
- although blood appears to be a thick, - Except for antibodies and protein-based hormones,
homogeneous liquid, the microscope reveals that it the liver makes most plasma proteins.
has both solid and liquid components. - plasma proteins serve a variety of functions, Albumin
acts as a carrier to shuttle certain molecules through
COMPONENTS the circulation, is an important blood buffer, and
- Blood is a complex connective tissue in which living contributes to the osmotic pressure of blood, which
blood cells, the formed elements, are suspended in acts to keep water in the bloodstream. Clotting
plasma (a nonliving fluid matrix) proteins help stem blood loss when a blood vessel is
- the collagen and elastin fibers typical of other injured, and antibodies help protect the body from
connective tissues are absent from blood pathogens
- dissolved proteins become visible as fibrin strands - Plasma proteins are not taken up by cells to be used
during blood clotting as food fuels or metabolic nutrients, as are other
solutes such as glucose, fatty acids, and oxygen
- composition of plasma varies continuously as cells molecules of oxygen, so each of these tiny cells can
exchange substances with the blood. carry about 1 billion molecules of oxygen
- the composition of plasma is kept relatively constant - normal blood contains 12–18 grams (g) of
by various homeostatic mechanisms of the body hemoglobin per 100 milliliters (ml) of blood. The
- various body organs make dozens of adjustments day hemoglobin content is slightly higher in men (13–18
in and day out to maintain the many plasma solutes g/ml) than in women (12–16 g/ml).
at life-sustaining levels
- plasma helps to distribute body heat, a by-product of LEUKOCYTES
cellular metabolism, evenly throughout the body - white blood cells (WBCs)
- are far less numerous than red blood cell
- are crucial to body defense
FORMED ELEMENTS - on average, there are 4,800 to 10,800 WBCs/mm3 of
blood, and they account for less than 1 percent of
ERYTHROCYTES total blood volume
- or red blood cells (RBCs) - contains nuclei and the usual organelles, which
- function primarily to ferry oxygen to all cells of the makes them the only complete cells in blood
body - form a protective, movable army that helps defend
- differ from other blood cells because they are the body against damage by bacteria, viruses,
anucleate (they lack a nucleus) parasites, and tumor cell
- they contain very few organelles - are able to slip into and out of the blood vessels—a
- mature RBCs circulating in the blood are literally process called diapedesis
“bags” of hemoglobin molecules - circulatory system is simply their means of
transportation to areas of the body where their
HEMOGLOBIN services are needed for inflammatory or immune
- Hemoglobin (Hb), an iron-bearing protein, transports responses
most of the oxygen that is carried in the blood. - can locate areas of tissue damage and infection in
- because erythrocytes lack mitochondria and make the body by responding to certain chemicals that
ATP by anaerobic mechanisms, they do not use up diffuse
any of the oxygen they are transporting, making from the damaged cells (positive chemotaxis)
them very efficient oxygen transporters indeed - Once they have “caught the scent,” the WBCs move
- are small, flexible cells shaped like biconcave through the tissue spaces by amoeboid motion (they
discs—flattened discs with depressed centers on form flowing cytoplasmic extensions that help move
both sides them along). By following the diffusion gradient, they
- because of their thinner centers, erythrocytes look pinpoint areas of tissue damage and rally round in
like miniature doughnuts when viewed with a large numbers to destroy microorganisms and
microscope dispose of dead cells
- their small size and peculiar shape provide a large - Whenever they mobilize for action, the body speeds
surface area relative to their volume, making them up their production, and as many as twice the
ideally suited for gas exchange normal number of WBCs may appear in the blood
- outnumber white blood cells by about 1,000 to 1 and within a few hours
are the major factor contributing to blood viscosity - A total WBC count above 11,000 cells/mm3 is
- although the numbers of RBCs in the circulation do referred to as leukocytosis (cytosis = an increase in
vary, there are normally about 5 million cells per cells). Leukocytosis generally indicates that a
cubic millimeter of blood bacterial or viral infection is stewing in the body
- when the number of RBC/mm3 increases, blood - Leukopenia count (penia = deficiency). It is
viscosity, or thickness, increases commonly caused by certain drugs, such as
- as the number of RBCs decreases, blood thins and corticosteroids and anti- cancer agents.
flows more rapidly - are classified into two major groups—depending on
- it is the amount of hemoglobin in the bloodstream at whether or not they contain visible granules in their
any time that really determines how well the cytoplasm:
erythrocytes are performing their role of oxygen
transport 1. GRANULOCYTES
- the more hemoglobin molecules the RBCs contain, - granule- containing WBCs. They have lobed
the more oxygen they will be able to carry nuclei, which typically consist of several rounded
- a single red blood cell contains about 250 million nuclear areas connected by thin strands of nuclear
hemoglobin molecules, each capable of binding 4 material. The granules in their cytoplasm stain
specifically with
 Wright’s stain Includes Neutrophils, Eosinophils, and Students are often asked to list the WBCs in order of
Basophils relative abundance in the blood—from most to least. The
following phrase may help you with this task: Never let
A. NEUTROPHILS monkeys eat bananas (neutrophils, lymphocytes,
- are the most numerous WBCs monocytes, eosinophils, basophils).
- have a multilobed nucleus and very fine granules
that respond to both acidic and basic stains
- the cytoplasm as a whole stains pink
- are avid phagocytes at sites of acute infection
- they are particularly partial to bacteria and fungi,
which they kill during a respiratory burst that deluges
the phagocytized invaders with a potent brew of
oxidizing substances (bleach, hydrogen peroxide, and
others)

B. EOSINOPHILS
- have a blue-red nucleus that resembles earmuffs and
brick-red cytoplasmic granules
- their number increases rapidly during infections by
parasitic worms (tapeworms, etc.) ingested in food
such as raw fish or entering through the skin
- when eosinophils encounter a parasitic worm, they
gather around and release enzymes from their
cytoplasmic granules onto the parasite’s surface, PLATELETS
digesting it away - are not technically cells
- are fragments of bizarre multinucleate cells called
C. BASOPHILS megakaryocytes, which pinch off thousands of
- the rarest of the WBCs, have large histamine anucleate platelet “pieces” that quickly seal
-containing granules that stain dark blue. Histamine is an themselves off from the surrounding fluids
inflammatory chemical that makes blood vessels leaky and - appear as darkly staining, irregularly shaped bodies
attracts other WBCs to the inflamed site scattered among the other blood cells
- normal platelet count in blood is about 300,000 cells
2. AGRANULOCYTES per mm3
- lack visible cytoplasmic granules - are needed for the clotting process that stops blood
- their nuclei are closer to the norm—that is, they are loss from broken blood vessels
spherical, oval, or kidney-shaped
- include lymphocytes and monocytes
HEMATOPOIESIS (BLOOD CELL FORMATION)
A. LYMPHOCYTES - occurs in red bone marrow, or myeloid tissue. In
- have a large, dark purple nucleus that occupies most adults, this tissue is found chiefly in the axial
of the cell volume skeleton, pectoral and pelvic girdles, and proximal
- only slightly larger than RBCs, lymphocytes tend to epiphyses of the humerus and femur
take up residence in lymphatic tissues, such as the - Each type of blood cell is produced in different
tonsils, where they play an important role in the numbers in response to changing body needs and
immune response different stimuli. After they mature, they are
- the second most numerous leukocytes in the blood discharged into the blood vessels surrounding the
area. On average, the red marrow turns out an
B. MONOCYTES ounce of new blood containing 100 billion new cells
- are the largest of the WBCs every day.
- except for their more abundant cytoplasm and
distinctive U- or kidney-shaped nucleus, they HEMOCYTOBLAST
resemble large lymphocytes - a common stem cell where all the formed elements
- when they migrate into the tissues, they change into arise from which resides in red bone marrow. Their
macrophages with huge appetites. Macrophages are development differs, however, and once a cell is
important in fighting chronic infections, such as committed to a specific blood pathway, it cannot
tuberculosis, and in activating lymphocytes change
- forms two types of descendantspp00
1. LYMPHOID STEM CELL FORMATION OF WHITE BLOOD CELLS AND PLATELETS
- produces lymphocytes - formation of leukocytes and platelets is stimulated
by hormones. These colony stimulating factors (CSFs)
2. MYELOID STEM CELL and interleukins not only prompt red bone marrow
- can produce all other classes of formed elements to turn out leukocytes, but also enhance the ability
of mature leukocytes to protect the body
FORMATION OF RED BLOOD CELLS - they are released in response to specific chemical
- Because they are anucleate, they are unable to signals in the environment, such as inflammatory
synthesize proteins, grow, or divide. As they age, chemicals and certain bacteria or their toxins. The
RBCs become rigid and begin to fall apart in 100 to hormone thrombopoietin accelerates the production
120 days of platelets from megakaryocytes, but little is known
- their remains are eliminated by phagocytes in the about how that process is regulated
spleen, liver, and other body tissues - when bone marrow problems or a disease condition
- components are salvaged. Iron is bound to protein as such as leukemia is suspected, a special needle is
ferritin, and the balance of the heme group is used to withdraw a small sample of red marrow from
degraded to bilirubin, which is then secreted into the one of the flat bones (ilium or sternum) close to the
intestine by liver cells. There it becomes a brown body surface. This procedure provides cells for a
pigment called stercobilin that leaves the body in microscopic examination called a bone marrow
feces. Globin is broken down to amino acids, which biopsy
are released into the circulation.
- Lost blood cells are replaced more or less
continuously by the division of hemocytoblasts in the HOMEOSTASIS
red bone marrow. The developing RBCs divide many - blood flows smoothly past the intact lining
times and then begin synthesising huge amounts of (endothelium) of blood vessel walls. But if a blood
hemoglobin. When enough hemoglobin has been vessel wall breaks, a series of reactions starts the
accumulated, the nucleus and most organelles are process of hemostasis (hem = blood; stasis =
ejected, and the cell collapses inward. The result is standing still), or stopping the bleeding
the young RBC, called a reticulocyte because it still - his response involves many substances normally
contains some rough endoplasmic reticulum (ER). present in plasma, as well as some that are released
The reticulocytes enter the bloodstream to begin by platelets and injured tissue cells
their task of transporting oxygen. Within 2 days of
release, PHASES OF HEMOSTASIS
they have ejected the remaining ER and have - involves three major phases, which occur in rapid
become fully functioning erythrocytes sequence: vascular spasms, platelet plug formation,
- The entire developmental process from and coagulation, or blood clotting
hemocytoblast to mature RBC takes 3 to 5 days. - blood loss at the site is prevented when fibrous
- The rate of erythrocyte production is controlled by a tissue grows into the clot and seals the hole in the
hormone called erythropoietin. Normally a small blood vessel
amount of erythropoietin circulates in the blood at
all times, and red blood cells are formed at a fairly 1. Vascular spasms occur
constant rate. Although the liver produces some, the 2. Platelet plug forms
kidneys play the major role in producing this 3. Coagulation events occur
hormone. When the blood level of oxygen begins to
decline for any reason, the kidneys step up their
release of erythropoietin. Erythropoietin targets the BLOOD GROUPS AND TRANSFUSIONS
bone marrow, prodding it into “high gear” to turn
out more RBCs. - Blood is vital for transporting substances through the
- an overabundance of erythrocytes, or an excessive body. When blood is lost, the blood vessels constrict,
amount of oxygen in the bloodstream, depresses and the bone marrow steps up blood cell formation
erythropoietin release and red blood cell production. in an attempt to maintain circulation
However, RBC production is controlled not by the - the body can compensate for a loss of blood volume
relative number of RBCs in the blood, but by the only up to a certain limit.
ability of the available RBCs to transport enough ⮚ Losses of 15 to 30 percent lead to pallor and
oxygen to meet the body’s demands. weakness
⮚ Loss of over 30 percent causes severe shock,
which can be fatal
 matching is also done. Cross matching involves
⮚ Whole blood transfusions are routinely given to
testing for agglutination of donor RBCs by the
replace substantial blood loss and to treat recipient’s serum and of the recipient’s RBCs by the
severe anemia or thrombocytopenia donor serum
- the usual blood bank procedure involves collecting - typing for the Rh factors is done in the same manner
blood from a donor and mixing it with an as ABO blood typing
anticoagulant to prevent clotting

HUMAN BLOOD GROUPS

ANTIGEN
- is a substance that the body recognizes as foreign
- stimulates the immune system to mount a defence
against it
- most antigens are foreign proteins, such as those
that are part of viruses or bacteria that have
managed to invade the body
- although each of us tolerates our own cellular (self)
antigens, one person’s RBC proteins will be
recognized as foreign if transfused into another
person with different RBC antigens
- “recognizers” are antibodies present in plasma that
attach to RBCs bearing surface antigens different
from those on the patient’s (recipient’s) RBCs
- binding of the antibodies causes the foreign RBCs to
clump, a phenomenon called agglutination which
leads to the clogging of small blood vessels
throughout the body.

- there are over 30 common RBC antigens in humans,

so each person’s blood cells can be classified into
several different blood groups
- it is the antigens of the ABO and Rh blood groups
that cause the most vigorous transfusion reactions

ABO BLOOD GROUPS

- are based on which of two antigens, type A or type
B, a person inherits
- absence of both antigens results in type O blood,
presence of both antigens leads to type AB, and the
presence of either A or B antigen yields type A or B
blood, respectively. In the ABO blood group,
antibodies form during infancy against the ABO
antigens not present on your own RBCs
RH BLOOD GROUPS
- are so named because one of the eight Rh antigens
(agglutinogen D) was originally identified in Rhesus
monkeys
- the same antigen was discovered in humans
- Unlike the antibodies of the ABO system, anti-Rh
antibodies are not automatically formed by Rh− (“Rh
negative”) individuals
- however, if an Rh− person receives Rh+ blood,
shortly after the transfusion his or her immune
system becomes sensitised and begins producing
anti-Rh+ antibodies against the foreign blood type

HEMOLYSIS (rupture of RBCs)