SILVERTHORN
CHAPTER 16 – BLOOD
PLASMA AND THE CELLULAR ELEMENTS OF BLOOD
Plasma is the fluid matrix of the blood, within which cellular elements are suspended. Water is the
main component of plasma:
– 92 % water
– 7 % proteins
– 1 % dissolved organic molecules (amino acids, glucose, lipids, ions etc.)
Plasma is identical in composition to interstitial fluid except for the presence of plasma proteins.
Albumins are the most prevalent type of protein in the plasma. The liver makes most plasma
proteins and secretes them into the blood. The presence of proteins in the plasma makes the
osmotic pressure of the blood higher than that of the interstitial fluid. This osmotic gradient tends
to pull water from the interstitial fluid into the capillaries and offset filtration out of the capillaries
created by blood pressure.
Cellular elements
Three main cellular elements are found in blood:
1. Red blood cells / erythrocytes
2. White blood cells / leukocytes
o Lymphocytes
o Monocytes develop into macrophages.
o Neutrophils
o Eosinophils
o Basophils
3. Platelets / thrombocytes
The types of white blood cells may be grouped according to common morphological or functional
characteristics. Neutrophils, monocytes and macrophages are phagocytes. Lymphocytes are
called immunocytes. Basophils, eosinophils, and neutrophils are called granulocytes.
BLOOD CELL PRODUCTION
All different types of blood cells arise from a single precursor cell type called the pluripotent
hematopoietic stem cell, which is primarily found in the bone marrow. As this cell type specialize,
it narrows its possible fates. First they become uncommitted stem cells, then progenitor cells,
which then differentiate into RBCs, lymphocytes or other white blood cells, and megakaryocytes,
which are the parent cells of the platelets.
Haematopoiesis is the synthesis of blood cells, which starts during embryonic development. Active
bone marrow is red, because it contains haemoglobin, the oxygen-binding protein of RBCs. Inactive
marrow is yellow, because of an abundance of adipocytes. RBCs live for nearly four months in the
circulation. Haematopoiesis is controlled by cytokines. Most important cytokines are the colony-
stimulating factors, molecules made by endothelial cells and white blood cells. Other important
cytokines are the interleukins and erythropoietin, which controls red blood cell synthesis.
Silverthorn – chapter 16: Blood Page 1 of 5
CHAPTER 16 – BLOOD
PLASMA AND THE CELLULAR ELEMENTS OF BLOOD
Plasma is the fluid matrix of the blood, within which cellular elements are suspended. Water is the
main component of plasma:
– 92 % water
– 7 % proteins
– 1 % dissolved organic molecules (amino acids, glucose, lipids, ions etc.)
Plasma is identical in composition to interstitial fluid except for the presence of plasma proteins.
Albumins are the most prevalent type of protein in the plasma. The liver makes most plasma
proteins and secretes them into the blood. The presence of proteins in the plasma makes the
osmotic pressure of the blood higher than that of the interstitial fluid. This osmotic gradient tends
to pull water from the interstitial fluid into the capillaries and offset filtration out of the capillaries
created by blood pressure.
Cellular elements
Three main cellular elements are found in blood:
1. Red blood cells / erythrocytes
2. White blood cells / leukocytes
o Lymphocytes
o Monocytes develop into macrophages.
o Neutrophils
o Eosinophils
o Basophils
3. Platelets / thrombocytes
The types of white blood cells may be grouped according to common morphological or functional
characteristics. Neutrophils, monocytes and macrophages are phagocytes. Lymphocytes are
called immunocytes. Basophils, eosinophils, and neutrophils are called granulocytes.
BLOOD CELL PRODUCTION
All different types of blood cells arise from a single precursor cell type called the pluripotent
hematopoietic stem cell, which is primarily found in the bone marrow. As this cell type specialize,
it narrows its possible fates. First they become uncommitted stem cells, then progenitor cells,
which then differentiate into RBCs, lymphocytes or other white blood cells, and megakaryocytes,
which are the parent cells of the platelets.
Haematopoiesis is the synthesis of blood cells, which starts during embryonic development. Active
bone marrow is red, because it contains haemoglobin, the oxygen-binding protein of RBCs. Inactive
marrow is yellow, because of an abundance of adipocytes. RBCs live for nearly four months in the
circulation. Haematopoiesis is controlled by cytokines. Most important cytokines are the colony-
stimulating factors, molecules made by endothelial cells and white blood cells. Other important
cytokines are the interleukins and erythropoietin, which controls red blood cell synthesis.
Silverthorn – chapter 16: Blood Page 1 of 5
