Blood is a connective tissue consisting of cells suspended in an intercellular fluid (the blood plasma).

Blood functions to transport oxygen, carbon dioxide, nutrients, wastes, hormones, etc. to and from the body's cells.

Blood cells consist three types: 1. erythrocytes (red blood cells)2. leukocytes (white blood cells) 3. thrombocytes (platelets).

The above picture is a smear of human peripheral blood. The numerous small reddish cells seen here are erythrocytes (each about 7 µm across, they are by far the most numerous type of blood cell).

Blood is made up of red blood cells, white blood cells, platelets, and plasma.

Note that RBC’s in mammals do not have a nucleus when mature, which was lost during maturation in the bone marrow. Erythrocytes (red blood cells) have a reddish color (and, thus so does your blood) due to their high content of the iron - protein complex called hemoglobin. Hemoglobin is the molecule that allows erythrocytes to bind oxygen and carry it throughout the body.

RED BLOOD CELLS

RED BLOOD CELLS

Red blood cells as well as most (but not all) and platelets, are made in the bone marrow.

The normal lifespan of RBCs in the circulation is only about 120 days. Worn out RBCs are removed by the spleen and liver where hemoglobin is recycled.

A high RBC level, a condition called “erythrocytosis,” can be caused by smoking, living at high altitudes, or by disease.

Low red blood cell levels, a condition called “anemia,” can be due to a loss of blood, loss of iron, a vitamin deficiency, or other disease conditions.

This is an actual picture of White Blood Cells, in with some red blood cells. The platelets are stained purple, a T-Lymphocyte white cell is stained green, and a Monocyte white cell is stained gold as seen through a scanning electron microscope.

White Blood Cells (Leukocytes)

•Larger than RBCs•Have nuclei•Far less numerous than RBCs

Three types of Leukocytes:

1.Granulocytes2.Monocytes3.Lymphocytes (B and T cells)

Macrophages are one of many types of white blood cells (leukocytes) present in body tissues. Macrophages are important in immune response and cell stability because they mobilize in cell tissue to attack large foreign particles such as bacteria, yeast, and dead cells. Macrophages are derived from precursor cells called monocytes that first develop in bone marrow. Monocytes enter the blood and travel throughout the body in the circulatory system. When needed, circulatory monocytes move into tissue, where they become macrophages. Here a lung (alveolar) macrophage is seeking foreign bacteria (Escherichia coli) with specialized cell extensions called filopodia. Macrophages engulf and digest foreign materials in a process known as phagocytosis.

WHITE BLOOD CELLS

Platelets!

Cell fragements that play an important role in clotting.

The platelets collect at the site of injury and release fibrin. Fibrin is a protein known as the “clotting factor.” It produces a network that traps cells and this forms a clot.