Biology Lab 2

Biology Lab 2 1

Blood Cells  Blood cells are formed in the bone marrow  All blood cells arise from the same bone marrow stem cells.  Stem cells are immortal, meaning they never die (at least not until you do) 2

 Stem cells are also undifferentiated meaning they have not yet developed into a particular cell type  Furthermore, stem cells are pluripotent, meaning they have the potential to become any type of blood cell.  These immortal, undifferentiated, pluripotent stem cells give rise to erythrocytes, leukocytes and platelets 3

 Leukocytes, also known as white blood cells:

 A group of related cell types that involved in immune function  Leukocytes include: 1. Neutrophils 2. Eosinophils 3. Basophils 4. Lymphocytes 5. Monocytes 4

Erythrocytes  Erythrocytes (RBCs) function to transport oxygen in the blood.  The shape of erythrocytes is ideal for this function  From the top, RBCs appear to be circular, circular but a side view shows that they are actually biconcaved discs 6

 This shape increases the surface area-to-volume ratio of the cell, cell thus increasing the efficiency of diffusion of oxygen and carbon dioxide into and out of the cell  Erythrocytes also have a flexible plasma membrane  This feature allows erythrocytes, which have a 7mm diameter, diameter to squeeze through capillaries as small as 3 mm wide  Erythrocytes contain tremendous amounts hemoglobin, hemoglobin the protein that binds oxygen

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 In order to make room for more hemoglobin to carry more oxygen, erythrocytes loose their nucleus and other organelles as they develop in the bone marrow  Because they lack a nucleus and other cellular machinery, machinery erythrocytes cannot repair themselves when damaged, consequently they have a limited life span of about 120 days  The removal of old and dying erythrocytes is carryied out by the spleen 8

 Erythrocytes, which represent the most numerous cell type in the body die at a rapid rate, 2-3 million erythrocytes die every second  Erythrocyte production must equal erythrocyte death or the cell population would decline Erythrocytes are produced through a process called erythropoesis 9

Whole Blood  Whole blood is composed of plasma (liquid), cells and platelets  If whole blood is placed into a tube and centrifuged, the cells and the plasma will separate 10

 The erythrocytes, which are heavy, will pack into the bottom of the tube  The plasma will be at the top of the tube  The leukocytes and platelets will form a thin layer (buffy coat) between the erythrocytes and the plasma 11