BLOOD
1. Blood is a type of
connective tissue whose
cells are suspended in a
liquid extracellular matrix,
called plasma.
2. Blood volume varies with
body size, fluid and
electrolyte balance, and
adipose content.
- Average blood volume (70
kg male) is 5 liters.
Components
• Blood can be separated into two major
components:
• i. Blood cells or "formed elements" (about 45% of
blood), which is composed mainly of red blood
cells (RBC) i.e. 99% of blood cells are RBC and the
other 1% is white blood cells (WBC) and platelets.
• ii. Plasma (about 55% of blood), liquid portion that
contains water, plasma proteins (fibrinogen,
albumin, globulin), organic molecules (amino acids,
carbohydrates, lipids, ATP), vitamins, hormones,
electrolytes, and cellular wastes (urea, uric acid,
creatinin, bilirubin).
Physical Characteristics and Volume
a. Blood is a slightly basic (pH = 7.35–
7.45) fluid that has a higher density
and viscosity than water, due to the
presence of formed elements.
b. Normal blood volume in males is 5–6
liters, and 4–5 liters for females.
Functions
a. Blood transports substances between body cells and the
external environment and helps maintain a stable
internal environment i.e. blood is the medium for
delivery of oxygen and nutrients, removal of metabolic
wastes to elimination sites, and distribution of
hormones.
b. Blood aids in regulating body temperature, body fluid
pH, and fluid volume within fluid compartments.
c. Blood protects against excessive blood loss through the
clotting mechanism, and from infection through the
immune system.
BLOOD CELLS
Blood is composed of three types of
cells:
- erythrocytes (red blood cells)
- leukocytes (white blood cells)
- thrombocytes (platelets)
Characteristics of Red
Blood Cells (RBC) =
Erythrocytes
a. RBC has biconcave disc like shape that increases
its surface area
b. RBC are the most abundant blood cells (99.9% of
formed element) i.e. 99.9% of blood cells are RBC
c. RBC count is done as the number of RBC/ml of
whole blood. In adult 1ml whole blood contain:
i. In male there are 4.5-6.3 million RBC per
milliliter of blood
ii. In female there are 4.2-5.5 million RBC per
milliliter of blood
Characteristics of Red
Blood Cells (RBC) =
Erythrocytes
d. RBC contains hemoglobin, which is loosely bound to
oxygen.
e. Hemoglobin is a globulin protein + heme and iron
f. Hemoglobin consists of 4 polypeptides each chain holds
a Heme group containing on Iron atom.
i. Oxyhemoglobin (when hemoglobin is bound to
oxygen) = bright red
ii. Deoxyhemoglobin (when hemoglobin is not bound to
oxygen) = darker red g. Mature RBC lack nuclei (i.e.
RBC are anucleate) and organelles such as
mitochondria, leaving more room for hemoglobin and
oxygen.
Red Blood Cell Production and Its Control
a. Production (Erythropoiesis)
i. In fetuses = yolk sac, liver, spleen
ii. In adults = red bone marrow
b. Control of Production
i. RBC number remains relatively stable.
ii. Negative feedback mechanism involving the hormone
erythropoietin, which is produced and secreted by the special
cells in the kidney and liver.
1. Erythropoietin is released from kidney and liver into
circulation.
2. Erythropoietin targets red bone marrow (in epiphyses of long
bones and spongy bone of flat bones), stimulating
erythropoiesis.
Lifespan
a. Average life-span = 120 days
b. After 120 days about 10% hemolysis
(rupture) and 90 % are engulfed by
phagocytes.
LEUKOCYTES (WHITE BLOOD CELLS)
are divided into granulocytes and agranulocytes.
Granulocytes include:
- Neutrophils
- Basophils
- Eosinophils
Agranulocytes include:
- Lymphocytes
- Monocytes
Neutrophils
a. Most abundant WBC = 54%-62%.
b. Cells have very tiny light staining granules (the
granules are very difficult to see).
c. The nucleus is frequently multi-lobed with lobes
connected by thin strands of nuclear material.
Functions:
1. Phagocytosis of foreign particles (disease
organisms & debris);
2. Increased in acute bacterial infections
Eosinophils
a. 1-3% of total WBC
b. Cells have large granules (A) which are acidophilic and
appear pink (or red) in a stained preparation.
c. The nucleus often has two lobes connected by a band of
nuclear material.
d. The granules contain digestive enzymes
Functions:
1. Kill parasites and are responsible for allergic reactions;
2. Increased during parasitic infections (tapeworm,
hookworm);
3. Release histaminase during allergic reactions (inhibit
allergic reactions)
Basophils
a. <1% of total WBC
b. The basophilic granules in this cell are large, stain deep
blue to purple, and are often so numerous they mask the
nucleus.
c. Granules contain histamine (cause vasodilation) and
heparin (anticoagulant).
Functions:
1. Release heparin which inhibits blood clotting;
2. Release histamine, a vasodilator that serve as helpful
inflammatory responses;
3. May leave bloodstream and develop into mast cells,
releasing allergy mediators.
Lymphocytes
a. 5-33% of total WBC
b. cell with very clear cytoplasm which stains pale
blue.
c. nucleus is very large for the size of the cell and
stains dark purple.
d. live for several months to years (only leukocyte
that lives more than a few days);
e. smallest WBC
Functions:
1. Immunity
Monocytes
a. 3-9% of total WBC
b. the largest of the leukocytes
c. The nucleus is most often “U” or kidney bean
shaped;
d. the cytoplasm is abundant and light blue
e. leave the blood stream to become
macrophages.
Function:
1. phagocytosis (monocytes are phagocytic cells)
THROMBOCYTES – PLATELETS
a. Platelets are fragments of large cells
called megakaryocytes.
b. Normal count = 130,000-360000
platelets/ mm3 blood.
c. Formation of platelets involves
repeated mitoses of megakaryocytes
without cytokinesis.
Functions:
1. Blood clotting
BLOOD PLASMA
Composition:
1. Water:
a. 92 % of plasma is water;
b. water functions as solvent, enables
transportation of nutrients and other material,
temperature regulation, and serves as site of
metabolic reactions.
BLOOD PLASMA
2. Proteins
a. 7% of plasma volume
b. all produced in the liver
c. Three types:
i. Albumin: maintains osmotic pressure of cells,
transports fatty acids
ii. Globulins: play role in defense e.g.
antibodies = immunoglobulin
iii. Fibrinogen: blood clotting
BLOOD PLASMA
3. Plasma Gases (O2, CO2)
4. Plasma Nutrients (amino acids, glucose, fatty
acids)
5. Nonprotein Nitrogenous Substances (urea,
uric acid)
6. Plasma Electrolytes (sodium, calcium)
7. Regulatory Substances (hormones, enzymes)