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Blood

Blood. Chapter 17. Introduction. Circulatory System is subdivided into the: Cardiovascular system – blood, heart, and blood vessels Lympathetic system – lymph and lymph nodes and lymph vessels First we will look at blood – the river of life Hematology – the study of blood

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Blood

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  1. Blood Chapter 17

  2. Introduction Circulatory System is subdivided into the: • Cardiovascular system – blood, heart, and blood vessels • Lympathetic system – lymph and lymph nodes and lymph vessels First we will look at blood – the river of life • Hematology – the study of blood - clinicians examine it more often than any other tissue when investigating causes of disease in their patients

  3. Blood Circulation • Initiated by the pumping action of the heart - blood leaves the heart in arteries  tiny capillaries  enter body tissues - from capillaries oxygen-deficient blood flows into veins which return it to the heart  lungs  heart Functions of blood: • Carries respiratory gases, nutrients, hormones • Conveys cells of the defense system to infectious sites • Helps regulate body temperature – blood is diverted to or away from the skin

  4. Overview: Composition of Blood • Blood accounts for ~8% of body mass – volume in male is 5 – 6 liters; females: 4 - 5 liters • A specialized CT - Blood cells (formed elements) are suspended in plasma (fluid portion and fibrinogen) • Hematocrit (‘blood fraction’) - % of the blood volume that consists of erythrocytes - males: 47 ± 5% - females: 42% ± 5%

  5. Overview: Composition of Blood • Heavier formed elements are packed down (erythrocytes ‘red cells’) and the less dense plasma remains on top • Buffy coat junction between RBCs and plasma contains leukocytes (‘white cells’); platelets (thrombocytes) Figure 17.1

  6. Blood Plasma • Straw-colored, sticky fluid portion of blood about 90% water Contains: • Ions – Na+ and Cl- • Nutrients – sugars, amino acids, lipids, • Wastes – urea and ammonia, and CO2 • O2, hormones and vitmins • 3 main types of proteins: - albumin helps to prevent water from diffusing out - globulins include both antibodies and blood proteins that transport lipids, iron, and copper - fibrinogens are invloved in blood clotting

  7. Formed Elements Blood cells: • Erythrocytes lack nuclei and organelles • Platelets are cell fragments • Most cannot divide - survive for only a short time Staining of blood cells – cellular structures stain differentially according to their chemical makeup • Eosin an acidic dye – stains pink • Methylene blue a basic dye – stains blue and purple

  8. Figure 17.2b

  9. Erythrocytes (RBCs) • Small, oxygen-transporting cells – 7.5 um in diameter (capillary diameter 8 – 10 um) - have no organelles or nuclei - cytoplasm packed with hemoglobin - generate energy by anaerobic mechanisms • Most numerous of the formed elements – females: 4.3 – 5.2 million cells/cubic ml of blood males: 5.1 – 5.8 million

  10. An Erythrocyte • 30% more surface area for rapid diffusion of O2 • Sacs of hemoglobin (O2 and CO2) • Lives 100 -120 days • Originate in the bone marrow (expel their organelles) Figure 17.3

  11. Leukocytes (WBCs) • Less numerous 4,800 – 11,000 per cubic ml - originate in the bone marrow and are released continuously into the blood • Protect the body from infectious microorganism • Function outside the blood stream in loose CT where infections occur • Diapedesis (‘leaping through’) – circulating leukocytes leave the capillaries by squeezing between endothelial cells of the capillary walls - travel by amoeboid motion to infection sites

  12. WBCs • Bone marrow stores leukocytes -releases in large quantities during serious infections - count exceeding 11,000 per cubic ml = leukocytosis • 5 types divided into 2 groups (presence or absence of membrane-bound cytoplasmic granules): 1) Granulocytes – neutrophils, eosinophils, basophils 2) Agranulocytes – lymphocytes and monocytes Relative amount of leukocytes from most to least: Never Let Monkeys Eat Bananas

  13. Relative Percentages of the Different Types of Leukocytes Figure 17.5

  14. Granulocytes • Neutrophils – most numerous WBC (60%) • Phagocytize and destroy bacteria - also release bacteria-destroying substances into ECM of the infected tissue - pus is composed of dead neutrophils and other WBCs plus tissue debris and dead bacteria • Nucleus – 2 to 6 lobes • Granules pick up acidic and basic stains - membrane-walled sacs of digestive enzymes

  15. Neutrophil • Nucleus – has two to six lobes • Granules pick up acidic and basic stains Figure 17.4a

  16. Eosinophils: 1 – 4% of all WBCs that function during allergic reactions and parasitic infections (gather in digestive tube wall) • Granules contain digestive enzymes - phagocytose allergens then degrade histamine - attach to parasites release enzymes that digest and destroy the invaders Figure 17.4b

  17. Figure 17.4c • Basophils (base loving) – rarest, about 0.5% of all leukocytes • Nucleus – usually two lobes • Granules secrete histamines and molecules • Function in inflammation mediation

  18. Agranulocytes • Lymphocytes (T and B cells) – most important cells of the immune system (20 – 45% of WBCs) Nucleus – occupies most of the cell volume (stains dark purple) • Function in lymphoid CTs – play a crucial role in immunity - effective in fighting infectious organisms - act against antigens (‘induce against’) a specific foreign molecule that induces a response - T cells attack foreign cells directly - B cells differentiate and produce antibodies

  19. Monocytes • Are the largest - make up 4 – 8% of WBCs • Nucleus – kidney shaped • Contain a larger proportion of cytoplasm – tiny granules • Like all leukocyes, use the bloodstream to reach CT where they transform into macrophages • phagocytic cells that move by amoeboid motion • Ingest foreign cells, molecules, debris

  20. Figure 17.4d,e

  21. Platelets • Aka thrombocytes (‘clotting cells’) – disc-shaped plasma membrane-enclosed fragments of cytoplasm (megakaryocytes) • Plug small tears in BV walls - adhere to exposed collagen in large numbers - secretory granule signal more platelets to arrive - release thromboplastin (PF3) helps initiate clotting

  22. Blood Cell Formation • Hematopoiesis (hemato = blood; poiesis = to make) - begins in the early embryo and continues throughout life - after birth all blood cells originate in the bone marrow - 100 billion new blood cells formed each day

  23. Bone Marrow – Site of Hematopoiesis Bone marrow – occupies interior of all bones • Red marrow (red due to immature erythroctyes) - actively generates new blood cells - remains in epiphyses, girdles, axial skeleton • Yellow marrow (contains many fat cells) is dormant - makes blood cells only in emergencies - located in long bones of adults • Reticular CT – basic tissue framework - fibroblasts (reticular cells) cover and secret reticular fibers; contain both fat cells and forming blood cells - blood sinusoids where mature blood cells enter the bloodstream - contain macrophages extend psuedopods, capture antigens

  24. Cell Lines in Blood Cell Formation • All blood cells originate in bone marrow from one cell type, the blood stem cell - pluripotential hematopoietic stem cell • Lymphoid stem cells - give rise to lymphocytes • Myeloid stem cells - give rise to all other blood cells - become committed cells that progressively lose ability to become certain cell types

  25. Genesis of Erythrocytes • Proerythroblasts (‘earliest red’formers’) -committed cells that form erythrocytes - give rise to early erythroblasts act as ribosome-producing factories where hemoglobin is made and accumulates during the next 2 stages - late erythroblast and normoblast (stage where cell division stops) - reticulocyte at this stage young erythrocyte contains a reticulum of ribosomes (remain here for 1-2 after entering bloodstream) • Reticulocyte count – 1 to 2% of all erythrocytes > 2% adapting to life at high altitudes < 1% degenerative bone disease

  26. Formation of Leukocytes • Myeloblasts - committed cells in each granulocyte line • Promyelocytes – accumulate lysosomes • Myelocyte stage – cell division stops • Metamyelocyte stage – nucleus stops functioning and bends into a ‘horseshoe’ • Line committing to monocytes, committed monoblasts enlarge and obtain more lysosomes to become promonocytes and then monocytes

  27. Platelet Formation • Immature megakaryoblasts undergo repeated mitoses – no nuclei or cytoplasmic division • Megakaryocyte (‘big nucleus cell’) – large multilobed nucleus with many times the normal number of chromosomes - from within the reticular CT they send cytoplasmic extensions through the walls of sinusoids and into the bloodstream - extensions break apart into platelets

  28. Figure 17.8

  29. Disorders of the Blood Disorders of Erythrocytes • Polycythemia (‘many blood cells’) – abnormal excess of erythrocytes - polycythemia vera: cancer of the bne marrow • Anemia (‘lacking blood’) – any condition in which erythrocyte levels or hemoglobin concentrations are low - blood’s capacity for carrying O2 is diminished - caused by blood loss, iron deficiency, erythrocyte destruction excees replacement - folic acid deficiency (B12) - genetic defect of hemoglobin

  30. Sickle cell disease – occurs in 1 of every 400 AAs - defect in the hemoglobin molecule causes it to crystallize when O2 blood level is low - distort into the shape of a crescent - fragile, rigid, and easily destroyed - cannot pass easily through capillaries • Hemachromatosis - inherited - abnormal excess of iron

  31. Disorders of Leukocytes • Leukemia – form of cancer resulting from the uncontrolled proliferation of a leukocyte-forming cell line in the bone marrow • Classified according to: 1) Cell line – lymphoblastic or myeloblastic 2) Rate of progression – acute (rapidly advancing) or chronic (slowly advancing) • Cancer cells crowd out normal blood cell lines - cause anemia, devastating infections and hemorrhaging

  32. Disorders of Platelets • Thrombocytopenia (‘lack of platelets’) -diminished clot formation and internal bleeding from small vessels • Result from damage to the bone marrow, chemotherapy, vit B12 deficiency, leukemia, auto-inmmune destruction of the platelets, over-activity of the spleen (functions to remove and destroy platelets and other blood cells)

  33. The Blood Throughout Life • First blood cells develop with the earliest BVs - in mesoderm around the yolk sac of 3 week old embryo • Mesenchyme cells cluster into blood islands - outer cells flatten and become the endothelial cells that form the walls of the earliest vessels - inner cells become the earliest blood cells • Late in the 2nd month – liver and spleen take over blood formation • Bone marrow becomes major hematopoietic organ by month 7

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