Structures of the Blood
BLOOD SPLEEN
PLASMA THYMUS
BONE MARROW LYMPH
erythrocytes LYMPH NODES
reticulocytes cervical nodes
platelets (thrombocytes) axillary nodes
leukocytes epitrochlear nodes
lymphocytes: inguinal nodes
B-cells, T-cells LYMPH VESSELS
monocytes CISTERNA CHYLI
granulocytes: THORACIC DUCT
basophils, RIGHT LYMPHATIC DUCT
eosinophils, neutrophils
Functions of the Blood and LymphThe BLOOD and the LY M P H are the body’s vital
fluids, sharing responsibility for nourishment,
cleansing, IMMUNE RESPONSE, and fluid balance. The
blood primarily nourishes the cells, and the lymph
cleanses and drains the tissues. The lymph derives
from as well as returns to the blood. Though the
blood and the lymph are unique fluids that circu-
late through separate networks, they share some
structures that allow leukocytes, notably lympho-
cytes and granulocytes, to move freely between
the blood and the lymph.
The rhythm of life: the blood The adult human
body contains about five liters (just under six
quarts) of blood that the HEARTpropels on a con-
tinuous circuit through the arteries and veins.
Contained within the arteries and veins of the
pressurized cardiovascular system, the total blood
volume circulates from the heart, through the
body, and back to the heart in about a minute.
During strenuous activity the blood can pound
through six full circuits in a minute, hammering
oxygen and GLUCOSEto the cells to fuel their
increased energy output.
Though fluid the blood is a living tissue, a mix
of cells (45 percent of the blood’s composition)
suspended in a watery matrix of PLASMA(55 per-
cent of the blood’s composition). Plasma, which is
about 90 percent water, also carries numerous
substances dissolved in it including electrolytes,
glucose (sugar), hormones,NUTRIENTS, and pro-
teins such as CLOTTING FACTORSandALBUMIN. A sin-
gle drop of blood contains roughly:- 500 million erythrocytes
- 33.5 million platelets
- 830,500 leukocytes
Blood cell production: the bone marrow The
red BONE MARROW, located in cavities within the
bones called medullary canals, produces 99 per-
cent of the adult body’s blood cells and all of its
erythrocytes. This spongy, somewhat gelatinous
substance has two structures, the vascular com-
partments through which blood circulates and the
extravascular compartments that contain the
BLOOD STEM CELLS. The red bone marrow is extraor-
dinarily active tissue, releasing into circulation 2
to 3 billion erythrocytes, 2 to 3 billion platelets,
up to 100 billion granulocytes, and several hun-
dred million monocytes every 24 hours. The BONETHE BLOOD AND LYMPH
The BLOODand LYMPHare the cell-bearing fluids that nourish and protect the body. Physician specialists who treat con-
ditions of the blood and lymph are hematologists. This section, “The Blood and Lymph,” presents an overview of the
structures and functions of the blood and lymph, a discussion of hematologic and lymphatic health and disorders, and
entries about the health conditions that can affect the blood and lymph.
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