The Circulatory System
The circulatory system consists of blood, blood vessels, & the heart.
Blood
Blood is composed of plasma, thrombocytes (platelets), erythrocytes (red blood cells or RBCs), & leukocytes (white blood cells or WBCs).
The picture below shows each of the components of blood as they appear under the microscope.
Plasma
Plasma is the fluid portion of blood & makes up around 55% of total blood volume. Plasma consists largely of water – around 90% depending on the specific location in the circulatory system. The remainder of plasma is composed largely of proteins (classes – albumins, globulins, & fibrinogen). Plasma also contains some dissolved oxygen & carbon dioxide, hormones, glucose, & some minerals & ions.
The main function of plasma is to transport various nutrients & wastes to their target organs.
Thrombocytes (Platelets)
Thrombocytes are fragments of another type of cell (megakaryocytes). They live for around 10 days, are smaller than RBCs, & make up less than 1% of total blood volume.
The main function of thrombocytes is to aid in blood clotting.
Erythrocytes (Red Blood Cells – RBCs)
RBCs transport oxygen from the lungs to the cells of the body where they pick up a small portion of carbon dioxide to transport back to the lungs. They make up around 45% of total blood volume.
RBCs are among the most specialized cells in the body. They have a biconcave shape, which increases surface area for gas exchange. They lack a nucleus, mitochondria, endoplasmic reticulum, or ribosomes. They live for around 120 days.
Leukocytes (White Blood Cells – WBCs)
WBCs help defend the body against invasion by pathogens & remove toxins, wastes, & abnormal or damaged cells. They are typically larger than RBCs, live for only a few days, & make up less than 1% of total blood volume.
WBCs are grouped into two classes: granulocytes & agranulocytes. Granulocytes have visible granules in their cytoplasm, while agranulocytes do not. Each type can typically be distinguished by its nucleus.
Granulocytes
Neutrophils (AKA polymorphonuclear leukocytes) are the most numerous type of WBC, making up anywhere from 50-75% of WBCs. They have a multi-lobed nucleus. Neutrophils specialize in attacking & digesting bacteria.
Eosinophils are fairly rare, making up only around 1-4% of WBCs. Eosinophils typically have a 2-lobed nucleus that resembles a U. Eosinophil levels increase during allergic reactions or parasitic infections.
Basophils are the least common leukocyte, making up less than 1% of all WBCs. Basophils typically have a 2-lobed nucleus that resembles an H. Basophils specialize in releasing chemicals that increase the inflammation response at an injury site.
Agranulocytes
Lymphocytes are the second most numerous leukocyte, making up around 20-30% of all WBCs. Lymphocytes typically have a large nucleus that fills most of the cytoplasm. Lymphocytes may attack foreign invaders directly or indirectly (by making antibodies that attack the invaders). Lymphocytes are also responsible for destroying abnormal body cells (&, thus, help prevent cancer).
Monocytes are moderately abundant & make up around 3-9% of all WBCs. Monocytes are the largest of the leukocytes & typically have an oval or kidney bean-shaped nucleus. Monocytes directly ingest foreign invaders.
The picture below shows each of the different types of leukocytes as they appear under the microscope. They appear in the following order: Neutrophil, Monocyte, Basophil, Lymphocyte, & Eosinophil.
Now that you've reviewed each of the types of leukocytes, complete the activities below.
Review each of the components of blood by matching them to their functions.
