blood

1. BLOOD
BLOOD IS A BODILY FLUID IN ANIMALS THAT DELIVERS NECESSARY SUBSTANCES SUCH AS NUTRIENTS AND OXYGEN TO
THE CELLS AND TRANSPORTS METABOLIC WASTE PRODUCTS AWAY FROM THOSE SAME CELLS.
IN VERTEBRATES, IT IS COMPOSED OF BLOOD CELLS SUSPENDED IN BLOOD PLASMA. PLASMA, WHICH CONSTITUTES
55% OF BLOOD FLUID, IS MOSTLY WATER (92% BY VOLUME),[1] AND CONTAINS DISSIPATED PROTEINS, GLUCOSE,
MINERAL IONS, HORMONES, CARBON DIOXIDE (PLASMA BEING THE MAIN MEDIUM FOR EXCRETORY PRODUCT
TRANSPORTATION), AND BLOOD CELLS THEMSELVES. ALBUMIN IS THE MAIN PROTEIN IN PLASMA, AND IT FUNCTIONS
TO REGULATE THE COLLOIDAL OSMOTIC PRESSURE OF BLOOD. THE BLOOD CELLS ARE MAINLY RED BLOOD CELLS (ALSO
CALLED RBCS OR ERYTHROCYTES) AND WHITE BLOOD CELLS, INCLUDING LEUKOCYTES AND PLATELETS. THE MOST
ABUNDANT CELLS IN VERTEBRATE BLOOD ARE RED BLOOD CELLS. THESE CONTAIN HEMOGLOBIN, AN IRON-CONTAINING
PROTEIN, WHICH FACILITATES TRANSPORTATION OF OXYGEN BY REVERSIBLY BINDING TO THIS
RESPIRATORY GAS AND GREATLY INCREASING ITS SOLUBILITY IN BLOOD. IN CONTRAST, CARBON DIOXIDE IS ALMOST
ENTIRELY TRANSPORTED EXTRACELLULARLY DISSOLVED IN PLASMA AS BICARBONATE ION.
VERTEBRATE BLOOD IS BRIGHT RED WHEN ITS HEMOGLOBIN IS OXYGENATED. SOME ANIMALS, SUCH AS CRUSTACEANS
AND MOLLUSKS, USE HEMOCYANIN TO CARRY OXYGEN, INSTEAD OF HEMOGLOBIN. INSECTS AND SOME MOLLUSKS USE
A FLUID CALLED HEMOLYMPH INSTEAD OF BLOOD, THE DIFFERENCE BEING THAT HEMOLYMPH IS NOT CONTAINED IN A
CLOSED CIRCULATORY SYSTEM. IN MOST INSECTS, THIS "BLOOD" DOES NOT CONTAIN OXYGEN-CARRYING MOLECULES
SUCH AS HEMOGLOBIN BECAUSE THEIR BODIES ARE SMALL ENOUGH FOR THEIR TRACHEAL SYSTEM TO SUFFICE FOR
SUPPLYING OXYGEN.

2. WHITE BLOOD CELLS
• White blood cells (WBCs), also called leukocytes or
leucocytes, are the cells of the immune system that are
involved in defending the body against both infectious
disease and foreign invaders. Five[1] different and
diverse types of leukocytes exist, and several types
(including monocytes and neutrophils) are phagocytic.
All leukocytes are produced and derived from a
multipotent cell in the bone marrow known as a
hematopoietic stem cell. They live for about three to
four days in the average human body. Leukocytes are
found throughout the body, including the blood and
lymphatic system.[2]
• The number of leukocytes in the blood is often an
indicator of disease. In the U.S. there are normally
approximately 7000 white blood cells per microliter of
blood.[3] They make up approximately 1% of the total
blood volume in a healthy adult.[4] An increase in the
number of leukocytes over the upper limits is called
leukocytosis, and a decrease below the lower limit is
called leukopenia. Physical properties of leukocytes
(such as volume, conductivity, and granularity) may
change. These changes can be due to activation, the
presence of immature cells, or the presence of
malignant leukocytes in leukemia.

3. RED BLOOD CELLS
• Red blood cells (RBCs), also called erythrocytes, are the
most common type of blood cell and the vertebrate
organism's principal means of delivering oxygen (O2) to
the body tissues via the blood flow through the
circulatory system.[1] They take up oxygen in the lungs
or gills and release it into tissues while squeezing
through the body's capillaries.
• The cytoplasm of erythrocytes is rich in hemoglobin, an
iron-containing biomolecule that can bind oxygen and is
responsible for the red color of the cells. The cell
membrane is composed of proteins and lipids, and this
structure provides properties essential for physiological
cell function such as deformability and stability while
traversing the circulatory system and specifically the
capillary network.
• In humans, mature red blood cells are flexible and oval
biconcave disks. They lack a cell nucleus and most
organelles, in order to accommodate maximum space
for hemoglobin. Approximately 2.4 million new
erythrocytes are produced per second.[2] The cells
develop in the bone marrow and circulate for about
100–120 days in the body before their components are
recycled by macrophages.

4. PLATELETS
• Platelets, also called "thrombocytes", are
blood cells whose function (along with the
coagulation factors) is to stop bleeding.[1]
Platelets have no nucleus: they are
fragments of cytoplasm which are derived
from the megakaryocytes[2] of the bone
marrow, and then enter the circulation.
These un activated platelets are biconvex
discoid structures [3][4] shaped like a lens,
2–3 μm in greatest diameter.[5] Platelets are
found only in mammals, an adaptation that
may have evolved to offset the risk of death
from hemorrhage at childbirth – a risk
unique to mammals.[6]
• On a stained blood smear, platelets appear as
dark purple spots, about 20% the diameter
of red blood cells. The smear is used to
examine platelets for size, shape, qualitative
number, and clumping. The ratio of platelets
to red blood cells in a healthy adult is 1/10 to
1/20.

5. COMPONENTS OF WHITE BLOOD CELLS