BLOOD AND BLEEDING

HEMOSTASIS AND BLEEDING DISORDERS

In health blood in the Blood vessels stays in the
fluid state.
This is essential for delivery of oxygen and nutrients

**Blood composition and Formation

The Blood is made up of two components:
- The plasma and
- The cellular elements floating in it.
The plasma represents the fluid fraction and accounts for 55% of the total blood volume; plasma volume is estimated to be roughly 7% to 8% of the total body weight.
The plasma reaches the tissues and provides nutrients and soluble ions, and carries proteins (such as albumin, complement immunoglobulin, and enzymes) to the cells and tissues.
-The cellular component represents 45% of the blood volume and is divided into three major cell type erythrocytes, leukocytes, and megakaryocytes.
-Each of these cells can be traced back to a single pluripotent stem cell.
-Erythrocytes (Red Blood Cells) function is to carry oxygen to body tissues.
-Leukocytes (White Blood Cells) are a variety of more specialized cells, whose function involves host defense and immunity. The last major cell type is the megakaryocyte. -Platelets and endothelial cells are derived from this cell line and are essential for the mechanisms of hemostasis.
-The process of blood formation is called hematopoiesis. Hematopoiesis is an ongoing, lifelong process in the bone marrow in the adult.
-The production of blood cells starts in the yolk sac of the embryo and continues throughout the first trimester.
-Extramedullary hematopoiesis (outside the bone marrow) begins during the third gestational month in the fetal liver.
-The spleen, kidneys, thymus, and lymph nodes are responsible for a minor role in hematopoiesis during fetal development.
-After birth, the lymph nodes assume a primary function in the proliferation and differentiation of leukocytes and lymphocytes, while the bone marrow takes over as the major source of blood cell production.
-Similarly, the liver and spleen assume important role in the reticuloendothelial system for the destruction and turnover (apoptosis) of aged and dysfunctional cells.


Red Blood Cell
The normal red blood cell is a biconcave disk approximately to 7.5µ in diameter. It is the major component of the cellular compartment of the blood, with a circulating life of about 100 to 120 days.
The primary role of RBC is to deliver oxygen to the tissues for metabolism and carry dissolved carbon dioxide to the lungs for release into the air. The red cell depends on the hemoglobin molecule to for transport of these gases.
The number of erythrocytes in the blood ranges form 3.8 to 5.9 million cells per micro liter of blood, with a hemoglobin concentration ranging form 17 to 17g/dl and a hematocrit of 35% to 52%.
This normal range is broad for it cover men and women young and old, and with people living at altitude. Induced erythropeiesis, leading to the expansion of red cell mass, occurs in response to hypoxia, blood loss, and a variety of hormones and disease states.
The most potent stimulator of erythropoiesis is erythropoietin.
Erythropoietin is a hormone produced by the kidney in response to hypoxia. This hormone stimulates the pluripotent stem cells in the bone marrow to become mature.
The bone marrow is capable of increasing the production of red cells by 5 to 10 times normal under the influence of erythropoietin. However, because of the limiting factor of iron in diet the increase is only two to three times normal.
In patients with chronic renal failure or after a nephrectomy, the ability to generate a erythropoietin response is slower.**
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