Dr. Basim Al-Ka'abi
Blood Physiology
Eighth Lecture
1
Lecture Name: Hemostatic Abnormalities and Role of Blood in Immunity
Lecturer Name: Dr. Basim A. Al-Ka'abi
Department: Medical Physiology
Stage: First Stage Medical Students
Lecture Objectives:
By the end of this lecture the students should be able to know the following:
An idea about the abnormalities that affect blood coagulation.
General meaning of immunity.
Role of blood and its cellular elements in immunity.
References:
Barrett, K et al. (2018). Ganong's Review of Medical Physiology. Twenty-
sixth edition. USA.
Guyton, A and Hall, J (2015). Text Book of Medical Physiology.
Thirteenth edition. Philadelphia, USA.
Dr. Basim Al-Ka'abi
Blood Physiology
Eighth Lecture
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Abnormalities of hemostasis
von Willebrand disease
-Is a hereditary (and sometimes acquired) bleeding disorder caused by
missing or defective von Willebrand factor (vWF), a clotting protein. This
factor binds factor VIII and platelets in the blood vessel wall, which help
form a platelet plug during the clotting process.
Hemophilia A
-Is a common disease, characterized by greatly prolonged coagulation time
due to a deficiency of factor VIII. It is as a sex-linked hereditary bleeding
disorder resulting from abnormalities of the gene on X chromosome that
codes for factor VIII.
Hemophilia B (Christmas disease)
-A hereditary bleeding disorder caused by a deficiency of factor ΙХ.
Hemophilia C
-A hereditary bleeding disorder caused by a deficiency of factor ХΙ.
Vitamin K deficiency
-Is one of the common causes of depressed formation of clotting factors by
the liver.
-Vitamin K is necessary to promote the formation of four of the most
important clotting factors: Prothrombin, factor VII, Factor IX, and factor
X. Its absence leads to insufficient formation of these clotting factors which
can also lead to a serious bleeding tendency.
-Vitamin K is continually synthesized in the intestinal tract by bacteria, so
its deficiency rarely occurs, except in newborn children before they
establish their intestinal bacterial flora. However, vitamin K deficiency
Dr. Basim Al-Ka'abi
Blood Physiology
Eighth Lecture
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does often occur as a result of poor absorption of fats from the GIT, because
it is fat-soluble.
Thrombocytopenia
-Means the presence of a very low quantity of platelets in the circulatory
system.
-Persons with thrombocytopenia have a tendency to bleed as do
hemophiliacs, except that the bleeding is usually from many small
capillaries rather than from larger vessels, as in hemophilia.
-Ordinarily, bleeding does not occur until the number of platelets in the
blood falls below a value of approximately 50,000/mm
3
rather than the
normal 150,000-400,000/mm
3
.
-Levels as low as 10,000/mm
3
are frequently lethal.
Immunity
-Immunity is the resistance of the body to invasion by bacteria, viruses, or
other infectious agents or toxins.
-A human being is born with innate immunity, and each person is born with
a certain amount of innate immunity that results from several special
mechanisms:
1. The reticulo-endothelial system and other white blood cells.
2. Resistance of the intact skin to invasion by microorganisms.
3. Digestive enzymes and acidity of the stomach.
4. Substances circulating in the blood.
-Acquired immunity occurs following exposure to invading agent or
foreign substances which are of two types:
A- Humoral immunity.
B- Cell-mediated immunity.
Dr. Basim Al-Ka'abi
Blood Physiology
Eighth Lecture
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Humoral immunity
-In humoral immunity, the body develops circulating antibodies.
-Is mediated by B-lymphocytes which are activated to produce plasma
cells, which, in turn, produce large quantities of antibodies.
-The foreign antigens first enter the lymphoid tissue, especially the lymph
nodes.
-Once the antibodies had been formed and released into the body fluids,
a process that usually requires 1 to several weeks, they destroy the specific
invader that had caused their formation and can destroy any future invader
of this same type.
-Antibodies destroy the invading agent or make it more susceptible to
phagocytosis by the tissue macrophages or by other white blood cells, or,
in case of toxins, the antibodies can simply neutralize these agents by
combining chemically with them.
Cell-mediated immunity (cellular immunity)
-Is mediated by T lymphocyte.
-However, instead of forming antibodies when the lymph node is exposed
to antigens, these cells form the so called sensitized lymphocytes (also
called T cells).
-Large numbers of T cells are then released into the circulating blood and
spread throughout the body.
There are three major types of T cells:
A- Cytotoxic T cells
-This type of T cells combines directly with antigens on the surfaces of
invading organisms and can therefore destroy them.
Dr. Basim Al-Ka'abi
Blood Physiology
Eighth Lecture
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B- Helper T cells
-They function mainly in association with plasma cells in the lymph nodes
to regulate humoral immunity (antibody production).
-They activate macrophages and thus enhancing phagocytosis.
C- Suppressor T cells
-They suppress some of the immune reactions, to prevent the immune
system from running wild and become destructive to normal tissues.
Immune tolerance
-Normally the immune system does not attack the body’s own tissues.
-The immune process of the normal human body does not develop
antibodies or sensitized lymphocytes that can destroy the body’s own
tissues, although the body tissues are largely like bacteria in their chemical
composition.
-This is called tolerance to the body’s own proteins and tissues.
-This results mainly from destruction during fetal life of those primordial
lymphocytes in the thymus and liver that are capable of forming antibodies
or sensitized lymphocytes against the body’s own proteins and tissues.
-It is likely that special suppressor T cells also develop to help cause
tolerance.
-Failure of immune tolerance leads to autoimmune disease.
-Examples of autoimmune disease include rheumatic heart disease,
rheumatoid arthritis, thyroiditis, acute glomerulonephritis.