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Blood
Blood Circulation
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Circulatory system is divided into
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Cardiovascular system
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Lymphatic system
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Blood
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Transport mechanism for
• Nutrients
• Signaling molecules
• Respiratory gases
• Waste products
Blood Circulation
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Powered by the pumping action of the heart
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Oxygen and nutrients diffuse across capillary walls to body tissues
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Transports hormones from endocrine glands
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Conveys cells of immune system
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Regulates body temperature
Composition of Blood
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Blood volume
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Males: 5–6 liters
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Females: 4–5 liters
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Blood has cellular and liquid components
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Is a specialized connective tissue
• Blood cells—formed elements
• Plasma—liquid portion of blood
Composition of Blood
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Hematocrit
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Is the measure of % RBC
• Males: 47% ± 5%
• Females: 42% ± 5%
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Buffy coat
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Is portion of blood composed of leukocytes and platelets
• Present at junction of plasma and RBCs
Blood Plasma
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Straw-colored, sticky fluid portion of blood
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Approximately 90% water
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Contains over 100 kinds of molecules
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Ions—Na+ and Cl–
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Nutrients
• Sugars, amino acids, lipids
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Wastes
• Carbon dioxide, urea, ammonia
Proteins
Blood Plasma
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Three main proteins
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Albumin
• Prevents water from diffusing out of blood vessels
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Globulins
• Include antibodies and blood proteins that transport lipids, iron, and copper
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Fibrinogen
• One of the molecules involved in chemical reactions for blood clotting
Formed Elements
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Blood cells
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Erythrocytes, leukocytes, and platelets
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Staining of blood cells
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Acidic dye—eosin; stains pink
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Basic dye—methylene blue; stains blue and purple
Erythrocytes
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Oxygen-transporting cells—7.5 µm in diameter (diameter of capillary 8–10mm)
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Most numerous of the formed elements
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Females: 4.3–5.2 million cells/cubic millimeter
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Males: 5.2–5.8 million cells/cubic millimeter
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Have no organelles or nuclei
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Are the ideal measuring tool for estimating sizes of nearby structures
Erythrocytes
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Are packed with oxygen-carrying hemoglobin
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Hemoglobin molecule bears four oxygen molecules
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Each O2 molecule bears an iron molecule
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Oxidation of iron atoms of hemoglobin molecules
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Gives blood its red color
Erythrocytes
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Pick up O2 at lung capillaries
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Release O2 across other tissue capillaries
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Structural characteristics contribute to respiratory function
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Biconcave shape  30 more surface area
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97% hemoglobin
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Lack mitochondria
• Do not consume O2 they pick up
Leukocytes—White Blood Cells (WBCs)
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4800–11,000/cubic millimeter
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Protect the body from infectious microorganisms
Function outside the bloodstream in loose connective tissue
Diapedesis—circulating leukocytes leave the capillaries
Originate in bone marrow
Leukocytes—White Blood Cells (WBCs)
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Two types of leukocytes
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Granulocytes
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Agranulocytes
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Mnemonic: “Never Let Monkeys Eat Bananas”
Granulocytes
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Neutrophils
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Most numerous WBC—granules pick up acidic and basic stains
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Nucleus—has two to six lobes
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Attracted by bacterial products and are first line of defense in inflammatory response
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Phagocytize and destroy bacteria
• Also release enzymes into extracellular matrix of infected tissue
Granulocytes
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Eosinophils
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Represent 1–4% of all WBCs
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Granules are large and stain red
• Granules contain enzymes active during allergic reactions and parasitic infections
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Play a role in ending allergic reactions by phagocytizing allergens
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Secrete enzymes that degrade histamines
Granulocytes
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Basophils—about 0.5% of all leukocytes
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Nucleus—usually two lobes
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Granules secrete histamines
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Function in inflammation mediation
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Similar in function to mast cells
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Direct later stages of inflammation in allergies and parasitic infections
Agranulocytes
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Lymphocytes—comprise 20–45% of WBCs
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The most important cells of the immune system
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Nucleus—stains dark purple
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Effective in fighting infectious organisms
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Act against a specific foreign molecule (antigen)
Agranulocytes
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Two main classes of lymphocyte
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T cells—attack foreign cells directly
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B cells—multiply to become plasma cells
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Secrete antibodies
Agranulocytes
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Monocytes—compose 4–8% of WBCs
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The largest leukocytes
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Nucleus—kidney shaped
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Transform into macrophages
• Phagocytic cells
Platelets
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Cell fragments
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Break off from megakaryocytes
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Function in clotting of blood
Blood Cell Formation
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Hematopoiesis—process by which blood cells are formed in red marrow
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100 billion new blood cells formed each day
Bone Marrow as the Site of Hematopoiesis
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Bone marrow—located within all bones
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Red marrow—actively generates new blood cells
• Contains immature erythrocytes
• In adults, red marrow is located
• Between trabeculae of spongy bone of axial skeleton
• Girdles
• In proximal epiphyses of humerus and femur
Bone Marrow as the Site of Hematopoiesis
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Yellow marrow—dormant
• Contains many fat cells
• Located in the long bones of adults
Bone Marrow as the Site of Hematopoiesis
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Tissue framework of bone marrow
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Reticular connective tissue
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Fibroblasts covering and secreting the fiber network are reticular cells
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Blood sinusoids run throughout the reticular tissue
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Mature blood cells enter the blood stream through endothelial cells of sinusoids
Bone Marrow as the Site of Hematopoiesis
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Reticular tissue of bone marrow
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Contains macrophages that extend pseudopods to capture antigens
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Some cells of the reticular network are mesenchymal stem cells
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Can give rise to
• Fat cells, osteoblasts, chondrocytes, fibroblasts, and muscle cells
Cell Lines in Blood Cell Formation
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All blood cells originate in bone marrow
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All originate from one cell type
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Hemopoietic blood stem cell (pluripotential hematopoeitic stem cell)
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Lymphoid stem cells
• Give rise to lymphocytes
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Myeloid stem cells
• Give rise to all other blood cells
Cell Lines in Blood Cell Formation
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Genesis of erythrocytes
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Committed cells are proerythroblasts
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Remain in the reticulocyte stage for 1–2 days in circulation
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Make up about 1–2% of all erythrocytes
Cell Lines in Blood Cell Formation
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Formation of leukocytes
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Committed cell type in each granulocyte line are myeloblasts
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Monoblasts enlarge and form monocytes
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Megakaryoblasts differentiate into megakaryocytes
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Break apart into platelets
Disorders of the Blood
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Disorders of erythrocytes
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Polycythemia
• Abnormal excess of erythrocytes
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Anemia
• Erythrocyte levels or hemoglobin concentrations are low
Disorders of the Blood
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Disorders of erythrocytes (continued)
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Sickle cell disease
• Inherited condition
• Results from a defective hemoglobin molecule
• Erythrocytes distort into a sickle shape
Disorders of the Blood
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Disorders of leukocytes
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Leukemia—a form of cancer
• Classified as lymphoblastic or myeloblastic
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Disorders of platelets
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Thrombocytopenia
• Abnormally low concentration of platelets
The Blood Throughout Life
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First blood cells develop with the earliest blood vessels
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Mesenchyme cells cluster into blood islands
Late in month 2:
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Liver and spleen take over blood formation
Bone marrow becomes major hematopoietic organ at month 7