What is Blood?
Blood is a specialized connective tissue that consists of
plasma and
formed elements. Plasma, the liquid component, comprises approximately 55% of blood volume and contains water, electrolytes, proteins, and other dissolved substances. The formed elements include
erythrocytes (red blood cells),
leukocytes (white blood cells), and
thrombocytes (platelets).
Histological Features of Blood
Under a microscope, blood smears reveal the different types of blood cells.
Erythrocytes appear as biconcave, anucleate discs, and their primary function is to carry oxygen.
Leukocytes are nucleated cells divided into two main categories:
granulocytes (neutrophils, eosinophils, and basophils) and
agranulocytes (lymphocytes and monocytes). Each type of leukocyte has unique functions in the immune response.
Platelets are small, anucleate cell fragments involved in clotting.
What is the Spleen?
The spleen is a vital organ located in the upper left quadrant of the abdomen. It functions as a blood filter, removing old and damaged red blood cells, and as an
immune organ that produces lymphocytes and stores platelets.
Histological Structure of the Spleen
The spleen is encapsulated by a dense connective tissue capsule from which trabeculae extend into the parenchyma, dividing it into compartments. The parenchyma consists of two main regions:
white pulp and
red pulp.
White Pulp
White pulp is composed of lymphatic tissue, primarily
lymphocytes, and forms periarteriolar lymphoid sheaths (PALS) around central arteries. It functions in the immune response, producing antibodies and activating T-lymphocytes.
Red Pulp
Red pulp consists of a network of sinusoids and splenic cords (cords of Billroth) filled with erythrocytes, macrophages, and other blood cells. Its primary function is to filter the blood, remove old or damaged erythrocytes, and recycle iron.Blood Flow Through the Spleen
Blood enters the spleen through the splenic artery, which branches into trabecular arteries and then into central arteries surrounded by white pulp. From there, blood flows into the marginal zone and red pulp, eventually draining into splenic sinusoids and then into the splenic vein.Clinical Significance
Histological examination of blood and spleen can reveal various disorders. For example, a blood smear can diagnose
anemia,
leukemia, and
infections, while spleen histology can diagnose conditions like
splenomegaly,
lymphoma, and splenic infarcts.
