18.3 Formed Elements in Blood

formed elements make up __% of blood

45

erythrocytes

• fxn: transport oxygen and carbon dioxide

• life span: 120 days

• avg density: 4.8-5.4 mil

leukocytes

• fxn: initiate immune response

• life span: 12 hours (neutrophils) to years (hymphocytes)

• avg density: 4500-11,000

platelets

• fxn: hemostasis

• life span: 8-10 days

• avg density: 150,000-400,000

hematopoiesis

production of formed elements

• begins in embryonic period, fifth week of development in liver

  • 5 months when hemato. begins in red bone marrow

hemocytoblasts (stem cells)

stem cells

• multipotent: can differentiate into many types of cells

• goes into either

  • myeloid line

  • lymphoid line

myeloid line

forms erythrocytes, all leukocytes except lymphocytes, and megakaryocytes (cells that produce platelets)

lymphoid line

forms only lymphocytes

Colony-stimulating factors (CSFs)

stimulate hematopoiesis

Erythropoiesis

erythrocyte production, make up 99% of our formed elements

• Process requires iron, B vitamins, amino acids, and EPO

• Begins with myeloid stem cell—responds to multi-CSF

• Forms progenitor cell

• Forms proerythroblast—a large nucleated cell

• Becomes erythroblast—smaller, produces hemoglobin

• Becomes normoblast—still smaller, more hemoglobin, anucleate

• Becomes reticulocyte—lacks organelles except ribosomes that make hemoglobin

• Becomes erythrocyte—ribosomes have degenerated

Leukopoiesis

production of leukocytes, less than 1% of formed elements

• Involves maturation of granulocytes, monocytes, lymphocytes

• Granulocytes are neutrophils, basophils, and eosinophils

• Multi-CSF and GM-CSF cause myeloid stem cell to form progenitor cell

• Progenitor cell becomes myeloblast that becomes a granulocyte

• Monocytes also derived from myeloid stem cells

• Stem cell differentiates into progenitor cell

• M-CSF prompts progenitor cell to become a monoblast

• Monoblast becomes a promonocyte, which matures into a monocyte

Leukopoiesis (continued)

Lymphocytes are derived from lymphoid stem cells

• Stem cells differentiate into B-lymphoblasts and T-lymphoblasts

• Lymphoblasts mature into B-lymphocytes and T-lymphocytes

• Some lymphoid stem cells differentiate directly into NK (natural killer) cells

Thrombopoiesis

platelet production

• Megakaryoblast produced from myeloid stem cell

• Forms megakaryocyte under influence of thrombopoietin

• Large size and multilobed nucleus

• Megakaryocyte produces thousands of platelets

• produces proplatelets—long extensions

  • extend through blood vessel wall into bloodstream

  • Blood flow “slices” off fragments which are platelets

Erythrocytes

red blood cells

• Lack nucleus and cellular organelles; packed with hemoglobin

• Have biconcave disc structure

• Has latticework of spectrin protein providing support and flexibility

• Transport oxygen and carbon dioxide between tissues and lungs

Hemoglobin

red-pigmented protein, Transports oxygen and carbon dioxide

• oxygenated when maximally loaded with oxygen

• deoxygenated when some oxygen lost

• Each hemoglobin molecule is composed of four globins

  • Two alpha chains and two beta chains

• Each chain has a heme group: a porphyrin ring with an iron ion in its center

• Oxygen binds to the iron ion, so each hemoglobin can bind four oxygen molecules

  • 4 iron = 4 oxygen

• Carbon dioxide binds to globin protein (not iron)

erythropoiesis (EPO) steps

controlled thru negative feedback, Erythropoietin (EPO)

1. stimulus - decrease in blood oxygen

2. receptors - chemoreceptors in kidney

3. control center - cells in kidney release EPO

4. effector - Red marrow myeloid cells respond to EPO by making more erythrocytes

5. net effect - The erythrocytes increase blood’s oxygen carrying capacity

6. negative feedback - Increase in blood oxygen inhibits EPO release (negative feedback)

EPO other stimuli

• Testosterone stimulates EPO production in kidney

  • males have higher erythrocyte count, higher hematocrit

• Environmental factors (like altitude) influence EPO levels

  • Low oxygen levels at high altitude stimulate EPO

Erythrocyte destruction

Lacking organelles, erythrocytes cannot synthesize proteins for repairs

• Maximum life span is 120 days

• Globin and membrane proteins are broken into amino acids

  • Used by body for protein synthesis

hemoglobin breakdown steps

1. liver and spleen

   • globin broken down into free amino acids

   • heme converted into green pigment biliverdin

   • then into (unconjugated) bilirubin

2. blood

   • unconjugated bilirubin binds with albumin and transported to liver

3. liver

   • unconjugated bilirubin removed from blood by liver and converted into conjugated bilirubin

4. liver

   • bilirubin then eliminated from liver into small intestine

5. small intestine

   • bilirubin converted into urobilinogen 

   • then two fates:

1. small and large intestine (80%)

   • urobilinogen > stercobilin > feces

2. blood and kidneys (20%)

   • urobilinogen absorbed back into blood into urobilin, yellow pigment excreted by kidneys

transferrin

transports iron form hemoglobin to liver

• Bound to storage proteins: ferritin, hemosiderin

• Most is bound to ferritin and stored in liver and spleen

• Transported to red bone marrow as needed for erythrocyte production

ABO antigens

• Type A blood: erythrocytes have surface antigen A only

• Type B blood: erythrocytes have surface antigen B only

• Type AB blood: erythrocytes have both antigens

• Type O blood: erythrocytes have neither antigen

ABO antibodies

• Type A blood has anti-B antibodies in its plasma

• Type B blood has anti-A antibodies in its plasma

• Type AB blood has neither anti-A nor anti-B antibodies in its plasma

• Type O blood has both anti-A and anti-B antibodies in its plasma

Rh blood types

Presence or absence of Rh factor (surface antigen D) determines if blood type is positive or negative

• present = Rh positive

• absent = Rh negative

ABO donation

agglutination

someone receives an incompatible transfusion

• Recipient’s antibodies bind to transfused erythrocytes and clump them together

• Can block blood vessels, prevent normal circulation, can cause hemolysis, rupture of erythrocytes, organ damage

agglutination test

type A blood clumps due to anti-A antibodies from type B blood

leukocyte cheat sheet

Leukocyte characteristics

• Defend against pathogens

• Contain nucleus and organelles, but not hemoglobin

• Motile and flexible—most not in blood but in tissues

  • Diapedesis: process of squeezing through blood vessel wall

  • Chemotaxis: attraction of leukocytes to chemicals at an infection site

• Five leukocyte types divided into two classes

leukocyte classes

• Granulocytes have visible granules seen with light microscope

  • Neutrophils, eosinophils, basophils

• Agranulocytes have smaller granules that are not visible with light microscope

  • Lymphocytes, monocytes

granulocytes: neutrophils

Most numerous leukocyte in blood, 50-70% of all white blood cells

• Multilobed nucleus

• Cytoplasm has pale granules when stained

• Enter tissue spaces and phagocytize infectious pathogens

• Numbers rise dramatically in chronic bacterial infection

granulocytes: eosinophils

less common, 1–4% of leukocytes

• Bilobed nucleus connected by thin strand

• Cytoplasm has reddish granules

• Phagocytize antigen-antibody complexes or allergens

• Active in cases of parasitic worm infection

granulocytes: basophils

rare, 0.5–1% of leukocytes

• Bilobed nucleus

• Cytoplasm has blue-violet granules with histamine and heparin

• Histamine release causes increase in blood vessel diameter (vasodilation) and capillary permeability (classic allergy symptoms)

• Heparin release inhibits blood clotting (anticoagulation)

agranulocytes: monocytes

2–8% of blood leukocytes

• C-shaped nucleus

• Take up residence in tissues

• Transform into large phagocytic cells, macrophages

• Phagocytize bacteria, viruses, debris

agranulocytes: lymphocytes

20–40% of blood leukocytes

• Reside in lymphoid organs and structures

• Dark-staining round nucleus

• Three categories:

1. T-lymphocytes manage immune response

2. B-lymphocytes become plasma cells and produce antibodies

3. NK (natural killer) cells attack abnormal and infected tissue cells

differential count

measures amount of each type of leukocyte and whether any are immature

Neutropenia

decreased neutrophil count

• May occur with anemia, drug or radiation therapies

eosinophilia

Eosinophil numbers rise during allergic reactions, parasitic infections, and some autoimmune diseases

Lymphocytosis

increase in lymphocytes

• Caused by viral infections (for example, mumps, mononucleosis)

• Also caused by chronic bacterial infections, some leukemias, and multiple myeloma

Platelets

Small, membrane-enclosed cell fragments

• No nucleus

• Break off of megakaryocytes in red marrow

• Important role in blood clotting

• Normally 150,000 to 400,000 per cubic millimeter blood

• 30% stored in spleen

• Circulate for 8 to 10 days; then broken down and recycled