Junqueira's Basic Histology Ch.12-13 Blood and Hemopoiesis

What are the formed elements of blood?

Erythrocytes (RBCs)
Leukocytes (WBCs)
Platelets

What does a clot include?

Formed elements (RBCs, WBCs, platelets)
Serum

What is serum?

Plasma minus the clotting factors

A pale yellow liquid that contains growth factors and other proteins released from platelets during clot formation that confer biological properties different from those of plasma

What is the hematocrit?

Volume of red blood cells
Normally about 45% of the total blood volume in healthy adults

What is the buffy coat?

When blood is centrifuged, the buffy coat is the thin gray-white layer between the red blood cell sediment at the bottom of the tube (the hematocrit) and the straw-colored, translucent, slightly viscous supernatant (the plasma).
The buffy coat makes up about 1% of the total blood volume and is comprised of leukocytes and platelets.

How many erythrocytes, platelets, and leukocytes are there per cubic mm of whole blood?

Erythrocytes: 3.9-5.5 million in women and 4.1-6.0 million in men
Platelets: 150K-400K
Leukocytes: 4.5K-11K

What is the pH of blood plasma?

7.4

What percentage (by weight) of plasma is made up of water? Protein? Other?

92% Water
7% Protein
1% Other solutes

Besides protein, what solutes does plasma contain?

Electrolytes (inorganic ions), respiratory gases, nutrients, nitrogenous waste products, hormones

What are the major plasma proteins?

Albumin (58%)
Globulins (37%)
Fibrinogen (4%)
Regulatory proteins (1%) = enzymes, proenzymes, hormones, and the complement system

What is albumin?

Most abundant plasma protein (58%)
Made in the liver and serves primarily to maintain the osmotic pressure of the blood
Contributes to blood's viscosity
Binds and transports some fatty acids, electrolytes, hormones, and drugs

What are the types of globulins in the blood?

Alpha-Globulins and Beta-Globulins:
Made by liver and other cells; include transferrin and other transport factors; fibronectin; prothrombin and other coagulation factors; lipoproteins and other proteins entering the blood from the tissues
Alpha-Globulins transport lipids and some metal ions
Beta-Globulins transport iron ions and some lipids

Gamma-Globulins:
Immunoglobulins (antibodies) that are secreted by plasma cells in many locations

What is fibrinogen?

Largest plasma protein
Made in the liver
During clotting, it polymerizes as insoluble, cross-linked fibers of fibrin that block blood loss from small vessels.

What is the differential count (percentage range) for each type of leukocyte?

Neutrophils = 54-62%
Lymphocytes = 25-33%
Monocytes = 3-7%
Eosinophils = 1-3%
Basophils = 0-0.75%

What are the dimensions of an erythrocyte?

7.5 micrometers in diameter
2.6 micrometers thick at the rim
0.75 micrometers thick in the center

What are rouleaux?

Loose stacks of RBCs adhering to one another in larger blood vessels

What are the functional reasons that RBCs have a biconcave disc shape?

High surface area-to-volume ratio = better for gas exchange; places most hemoglobin within a short distance from the cell surface
Flexibility = able to easily bend to pass through small capillaries

What are two important transmembrane proteins in RBCs and what is special about them?

Band 3 protein and Glycophorin A
Glycosylated extracellular domains of these proteins include antigenic sites that form the basis for the ABO blood typing system

What are two important peripheral membrane proteins in RBCs and what do they do?

Spectrin = dimers of this protein form a lattice bound to underlying actin filaments
Ankyrin = anchors the spectrin lattice to the glycophorins and band 3 proteins
This submembranous meshwork stabilizes the membrane, maintains cell shape, and provides the cell elasticity required for passage through capillaries.

What is the cytoplasm of a RBC comprised of?

No nucleus and no organelles
Densely packed with hemoglobin

What is hemoglobin called when bound to oxygen? Carbon dioxide?

Oxyhemoglobin
Carbaminohemoglobin

What is an increased concentration of RBCs called?

Erythrocytosis or Polycythemia

What metabolic pathway do RBCs utilize?

Glycolysis and anaerobic metabolism
Due to their lack of mitochondria

What is the lifespan of a RBC?

120 days

What are the two main groups of leukocytes?

Granulocytes = neutrophils, eosinophils, basophils
Agranulocytes = lymphocytes, monocytes

What two main types of granules do granulocytes possess?

Azurophilic granules = lysosomes
Specific granules = bind neutral, basic, or acidic stains and have specific functions

Contrast the life spans of different leukocytes

Neutrophils = 1-4 days
Eosinophils = 1-2 weeks
Basophils = several months
Lymphocytes = hours to many years
Monocytes = hours to years

Contrast the nuclei of different leukocytes

Neutrophils = 3-5 lobes
Eosinophils = bilobed
Basophils = bilobed or S-shaped
Lymphocytes = spherical
Monocytes = indented or C-shaped

Contrast the colors of the specific granules of different granulocytes

Neutrophils = fait/light pink
Eosinophils = red/dark pink
Basophils = dark blue/purple

What is the major function of neutrophils?

Kill and phagocytose bacteria

What are the major functions of eosinophils?

Kill helminthic and other parasites
Modulate local inflammation

What are the major functions of basophils?

Modulate inflammation
Release histamine during allergy

What granules do agranulocytes contain?

No specific granules, but they do contain azurophilic granules (lysosomes) with affinity for the basic stain azure A

What is the transendothelial migration of leukocytes called?

Diapedesis

What are the major initial events of neutrophil migration during inflammation?

1. Activated macrophages release proinflammatory cytokines (IL-1 or TNF-aplha) that signal endothelial cells of nearby postcapillary venules to rapidly insert selectins into their luminal cell surfaces
2. Passing neutrophils bind the selectins and adhere loosely to the endothelium, "rolling" slowly along its surface
3. Exposure to cytokines causes the rolling leukocytes to express integrins. The endothelial cells express the integrin ligand ICAM-1 (intercellular adhesion molecule-1). Junctional complexes between the endothelial cells are downregulated.
4. Integrin-ICAM-1 binding provides firm endothelial adhesion of neutrophils.
5. Neutrophils become mobile, probe the endothelium with pseudopodia, and finally migrate by diapedesis between the loosened cells of the venule.

What are neutrophils also called?

Polymorphonuclear leukocytes, PMNs, polymorphs

What to neutrophils' azurophilic primary granules contain?

Proteases and antibacterial proteins
Myeloperoxidase (MPO) = generates hypochlorite and other agents toxic to bacteria
Lysozyme = degrades components of bacterial cell walls
Defensins = bind and disrupt the cell membranes of many types of bacteria and other microorganisms

Describe the specific secondary granules of neutrophils

Smaller, less dense, stain faintly pink
Many functions:
Secrete various ECM-degrading enzymes (collagenases)
Deliver additional bactericidal proteins to the phagolysosomes
Insert new cell membrane components

Describe the metabolism of neutrophils

Contain glycogen and carry out glycolysis
Aerobic metabolism is unimportant due to their paucity of mitochondria
Ability to survive in an anaerobic environment is advantageous and allows neutrophils to work in poorly oxygenated damaged or necrotic regions

Describe the specific granules of eosinophils

Oval in shape with flattened, crystalloid cores containing major basic proteins (MBP), which, along with eosinophilic peroxidase and other enzymes and toxins, acts to kill parasitic worms (helminths)

How are eosinophils involved in inflammation?

Eosinophils release chemokines, cytokines, and lipid mediators that modulate inflammation
Number of eosinophils increases during allergic reactions

Describe the specific granules of basophils

Stain purple
Fewer, larger, and more irregularly shaped than the granules of other granulocytes
Strong basophilia due to presence of heparin and other sulfated GAGs
Also contain histamine, platelet-activating factor, eosinophil chemotactic factor, and phospholipase A (which catalyzes the 1st step in producing lipid-derived proinflammatory leukotrienes)

What type of antibody stimulates basophils?

Basophils have receptors for immunoglobulin E (IgE)

What happens during anaphylactic shock?

Basophils and mast cells rapidly degranulate, producing vasodilation in many organs, a sudden drop in blood pressure, and other effects comprising a potentially lethal condition

What are the three types of lymphocytes?

T Cells
B Cells
Natural Killer Cells

What are monocytes precursors of?

Macrophages, osteoclasts, microglia, Langerhans cells, and other cells of the mononuclear phagocyte system

How can you distinguish between a monocyte and a large lymphocyte?

Monocytes have large, indented, C-shaped nuclei with chromatin that is less condensed than in lymphocytes and typically stains lighter than that of large lymphocytes.

What are platelets?

Very small non-nucleated, membrane-bound cell fragments only 2-4 micrometers in diameter that promote blood clotting and help repair minor tears or leaks in the walls of small blood vessels

How do platelets originate?

They originate by separation from the ends of cytoplasmic processes extending from giant polyploid bone marrow cells called megakaryocytes.

What are the two zones of a platelet seen with staining?

Hyalomere = very lightly stained peripheral zone
Granulomere = darker-staining central zone containing granules

What structures exist in the hyalomere?

Sparse glycocalyx = involved in adhesion and activation during blood coagulation
Marginal bundle = system of microtubles and actin microfilaments that helps to maintain the platelet's shape
Two systems of membrane channels

What are the two systems of membrane channels in platelets?

Open canalicular system of vesicles = connected to invaginations of the membrane and may facilitate uptake of factors from the plasma
Dense tubular system = stores calcium
Together the two membrane systems facilitate extremely rapid exocytosis of proteins form platelets upon adhesion to collagen (or other substrates outside the vascular endothelium), activation, and calcium release

What are the two types of specific granules in platelets?

Delta granules
Alpha granules

Describe delta granules. What do they contain?

Electron-dense, 250-300 nm in diameter
Contain ADP, ATP, and serotonin (5-hydroxytryptamine) taken up from the plasma

Describe alpha granules. What do they contain?

Larger in diameter (300-500 nm) than delta granules
Contain platelet-derived growth factor (PDGF), platelet factor 4, and several other platelet-specific proteins

What are the major steps in clot formation and wound healing?

1. Primary aggregation of platelets
2. Secondary aggregation of platelets
3. Blood coagulation
4. Clot retraction
5. Clot removal

What happens during primary aggregation?

Disruptions in the microvascular endothelium allow the platelet glycocalyx to adhere to collagen. A platelet plug is formed as a first step to stop bleeding.

What happens during secondary aggregation?

Platelets in a plug release a specific adhesive glycoprotein and ADP, which induce further platelet aggregation and increase the size of the platelet plug.

How does blood coagulation occur?

Fibrinogen (from plasma), von Willebrand factor and other proteins (from damaged endothelial cells), and platelet factor 4 (from platelet granules) promote the cascade of plasma proteins that gives rise to a fibrin polymer that forms a 3D network of fibers trapping RBCs and more platelets to form a clot (thrombus)

How does clot retraction occur?

A clot that initially bulges out into the blood vessel lumen contracts slightly because of the interaction of platelet actin and myosin.

How is a clot removed?

It is mostly dissolved by plasmin, a proteolytic enzyme formed continuously through local action of plasminogen activators (from the endothelium) on plasminogen (from the plasma).

Where do blood cells arise from in the early embryo?

Yolk sac mesoderm

Where are blood cells made during the second trimester?

Liver (and spleen to a lesser extent)

Where are blood cells formed in the third trimester and throughout the rest of life?

Bone marrow
Bones throughout the body in childhood
After puberty, hematopoiesis becomes mostly restricted to bones of the axial skeleton

What are the terms for origin/maturation of RBCs, granulocytes, lymphocytes, monocytes, and platelets?

Erythropoiesis, Granulopoiesis, Lymphopoiesis, Monocytopoiesis, Thrombocytopoiesis

Hemopoietic stem cells proliferate to form which two lineages of progenitor cells?

One for lymphocytes (B cells, T cells, natural killer cells)

One for myeloid cells that develop in bone marrow (granulocytes, monocytes, erythrocytes, megakaryocytes)

What are progenitor cells commonly called?

Colony-forming units (CFUs)

What are the 4 major types of progenitor cells (CFUs)?

1. Erythroid lineage of CFU-erythrocytes (CFU-E)

2. Thrombocytic lineage of CFU-megakaryocytes (CFU-Meg)

3. Granulocyte lineage of CFU-granulocytes-monocytes (CFU-GM)

4. Lymphoid lineage of CFU-lymphocytes of all types (CFU-L)

What do progenitor cells produce?

Precursor cells (or blasts) that gradually assume the morphological characteristics of the mature, functional cell types they will become

What are the two types of bone marrow?

Red bone marrow = blood-forming, abundance of blood and hemopoietic cells

Yellow bone marrow = filled with adipocytes

What are the three histological areas of red bone marrow?

Stroma = reticular connective tissue
Hemopoietic cords = islands of cells
Sinusoidal capillaries

Describe the stroma of red bone marrow

Meshwork of specialized fibroblastic cells called stromal cells (also reticular or adventitial cells) and a delicate web of reticular fibers supporting the hemopoietic cells and macrophages

Bone matrix also contains collagen type I, proteoglycans, fibronectin, and laminin

What do macrophages in the bone marrow do?

Phagocytose older, defective red blood cells and reprocess heme-bound iron for delivery to the differentiating erythrocytes

What are the stages of erythropoiesis?

Pluripotent stem cell --> Myeloid stem cell --> Progenitor cell (CFU-E) --> Proerythroblast --> Early or basophilic erythroblast --> Polychromatophilic erythroblast --> Orthochromatophilic erythroblast --> Reticulocyte --> Eythrocyte

What are the stages of thrombopoiesis?

Pluripotent stem cell --> Myeloid stem cell --> Progenitor cell (CFU-Meg) --> Megakaryoblast --> Promegakaryocyte --> Megakaryocyte --> Platelets

What are the stages of granulopoiesis?

Pluripotent stem cell --> Myeloid stem cell --> Progenitor cell (CFU-GM) --> Myeloblast --> Promyelocyte --> (Eosinophilic/Basophilic/Neutrophilic) Myelocyte --> (Eosinophilic/Basophilic/Neutrophilic) Metamyelocyte --> Eosinophil/Basophil/Neutrophil

What are the stages of monocytopoiesis?

Pluripotent stem cell --> Myeloid stem cell --> Progenitor cell (CFU-GM) --> Monoblast --> Promonocyte --> Monocyte

What are the sources, target cells, and effects of stem cell factor (SCF)?

Sources: stromal cells of bone marrow

Mitogen for all hemopoietic progenitor cells

What are the sources, target cells, and effects of erythropoietin (EPO)?

Sources: peritubular endothelial cells of the kidney; hepatocytes

Mitogen for all erythroid progenitor and precursor cells, also promoting their differentiation

Stimulates production of mRNA for globins, the protein components of hemoglobin

What are the sources, target cells, and effects of thrombopoietin (TPO)?

Sources: kidney and liver

Mitogen for megakaryoblasts and their progenitor cells

What are the sources, target cells, and effects of granulocyte-macrophage colony-stimulating factor (GM-CSF)?

Sources: endothelial cells of bone marrow and T lymphocytes

Mitogen for all myeloid progenitor cells

What are the sources, target cells, and effects of granulocyte colony-stimulating factor (G-CSF)?

Sources: endothelial cells of the bone marrow and macrophages

Mitogen for all neutrophil precursor cells

What are the sources, target cells, and effects of monocyte colony-stimulating factor (M-CSF)?

Sources: endothelial cells of the bone marrow and macrophages

Mitogen for monocyte precursor cells

What are the sources, target cells, and effects of IL-1?

Sources: macrophages and T helper cells

Regulates activities and cytokines secretion of many leukocytes and other cells

What are the sources, target cells, and effects of IL-2?

Source: Helper T cells

Mitogen for activated T and B cells; promotes differentiation of natural killer cells

What are the sources, target cells, and effects of IL-3?

Source: Helper T cells

Mitogen for all granulocyte and megakaryocyte progenitor cells

What are the sources, target cells, and effects of IL-4?

Source: Helper T cells

Promotes development of basophils and mast cells and B-lymphocyte activation

What are the sources, target cells, and effects of IL-5?

Also known as eosinophil differentiation factor (EDF)

Source: Helper T cells

Promotes development and activation of eosinophils

What are the sources, target cells, and effects of IL-6?

Sources: macrophages, neutrophils, local endothelial cells

Mitogen for many leukocytes; promotes activation of B cells and regulatory T cells

What are the sources, target cells, and effects of IL-7?

Sources: stromal cells of bone marrow

Major mitogen for all lymphoid stem cells

What general changes occur during erythropoiesis?

Cell and nuclear volume decreases
Nucleoli diminish in size and disappear
Chromatin density increases until the nucleus has a pyknotic appearance and is finally extruded from the cell
Gradual decrease in number of polyribosomes (dec. basophilia)
Gradual increase in amount of hemoglobin (inc. acidophilia or eosinophilia)

Describe a proerythroblast

Large cell with loose, lacy chromatin, visible nucleoli, and basophilic cytoplasm (lots of polyribosomes synthesizing hemoglobin)

Describe a basophilic erythroblast

Condensed nucleus with no visible nucleolus
More strongly basophilic cytoplasm (lots of polyribosomes making hemoglobin)

Describe a polychromatophilic erythroblast

Reduced volume
Fewer polyribosomes
Some cytoplasmic areas filled with hemoglobin (acidophilia) while others continue to have lots of polyribosomes (basophilia)

Describe an orthochromatophilic erythroblast

Cell and nuclear volume decrease further
No basophilia is present; cytoplasm is uniformly acidophilic
Cell ejects nucleus late in this stage

Describe a reticulocyte

Still has a small number of polyribosomes that form a faint network within the cell

Passes into circulation, quickly loses its polyribosomes, and matures into an erythrocyte

What is the general pattern of changes in granulopoiesis?

Initial production of azurophilic granules by the RER and Golgi

Golgi activity changes to produce proteins for specific granules

Describe a myeloblast

Finely dispersed chromatin, faint nucleoli, no cytoplasmic granules

Describe a promyelocyte

Basophilic cytoplasm with azurophilic granules containing lysosomal enzyme and myeloperoxidase

Different genes are activated based on whether the cell will become an eosinophil, basophil, or neutrophil

Describe a myelocyte

Specific granules gradually increase in number