Histology Of Blood And Hemopoiesis Flashcards
Composition of blood
55% plasma
44% RBCs
1% “Buffy coat” (white blood cells and platelets )
Difference between plasma and serum
Serum =. Blood that has gone through the coagulation (clot) process.
-contains special growth factors and other proteins released by platelets when clotted
Plasma = blood that has not gone through the coagulation process
Red blood cell characteristics
Any clear with NO mitochondria
Lack membrane-bound organelles
contain numerous hemoglobin molecules (4 different globin peptide chains with 1 iron molecule per globin peptide chain)
- primary function is to transfer oxygen and carbon dioxide throughout the body via binding to hemoglobin (oxygen) and globin (carbon dioxide)
- Oxygen (heme) and carbon dioxide (globin chains) do not compete for the same location. *
Plasmalemma
Cell membrane of RBCs
Have peripheral and integral membranes which both function to anchor and organize the cytoskeletal proteins
possess blood type antigens on the extraceullar surface which determine your blood type.
Platelets
Membrane-bound cell fragments released by megakaryocytes that are anuclear with sparse mitochondria and possess a glycocalyx extracellular membrane.
Contains 3 types of granules
2 major categories of platelet granules and the specific names.
Alpha: PDGF, PF-4
Delta: Serotonin, ADP/ATP
Degranulation occurs rapidly when platelets adhere to collagen of endothelial cells and causes a rapid increase of cytoplasmic calcium
also has glycogen granules
What two intracellular structures serve to help rapid depolarization and release of granules from platelets?
Marginal bundles and open canalicular systems
Clotting steps (general)
Primary aggregation: glycocalyx of platelets allow platelets to adhere to the damage site and form a platelet plug
Secondary aggregation: platelets that’s re already clotted together release specific adhesive glycoproteins and ADP which promotes clotting of platelet group aggregation
Blood coagulation: proteins released from the damaged site and PGF4 promote sequential interaction of plasma protiens and other clotting activities. Forms a 3D network of fibers trapping RBCs and platelets to from the clot itself
Clot retraction: clot retraction occurs when clot contracts due to platelet-derived actin and myosin interactions
Clot removal: clot is removed by proteolytic enzyme plasmin released by the interaction of plasminogen and macrophage interaction from endothelium
Leukocyte general actions
Immune response (innate and acquired)
Allergic response (basophils and mast cells)
Inflammatory response
Repair of tissues (macrophages)
Destroy invaders
Neutrophils
Polymorphic nucleus with 3-5 lobes (looks like “stepping stones”)
Azurophilic (granules stains dark)
Contains lysozyme, defense’s and myeloperoxidase granules
Have lots of glycogen stores and few mitochondria
Function as first line of defense against most infections (mainly bacterial)
Activiely track and pursue bacteria throughout body
most common granulocyte
Eosinophils
Bi-lobed nucleus: “ on ear headphones”
Azurophilic staining and granules stain pink and red
Contains MBPs, peroxidase
Functions to modulates inflammatory responses (especially due to allergies)
Primary function is to stop parasitic infections!
granulocyte
Basophils
Bi-lobed or S-shaped nucleus (usually cant see it though and covers majority of cell)
Azurophilic granules present (stains dark purple all around cell)
Contains heparin, GAGs, histamines, PAF
Functions to mediates inflammation and is involved in allergic reactions and type 1 hypersensitivity from binding to IgE
granulocyte
Lymphocytes
smallest WBC
Contains spherical nucleus with thin ring of basophilic cytoplasm around it (approximately 70% of cell has dark purple stain, rest is light purple)
Functions to become T/B and NK cells based on their CD markers
agranulocyte
Monocytes
Indented of C-shaped nucleus with azurophilic granule staining
Functions to give rise to macrophages, osteoclasts, microglia and other mononuclear phagocyte system cells.
Agranulocyte
Steps of leukocyte extravasion
1) local activated macrophages release proinflammatory cytokines (IL-1 and TNF-a) that signal to endothelial cells to upregulated selections (P-selectin)
2) passing neutrophils bind to these selections and allow it to loosely “roll” along the endothelial cells
3) leukocytes that are “rolling” upregulate integrins on the leukocytes and integrin ligand (ICAM-1) on the endothelial cells and down regulates junctional complexes (gap junctions)
4) integrins and selectins bind and allow leukocytes to receive further stimulation and become sensative to chemokines
5) leukocytes become motile and follow chemokines and squeeze between endothelial cells via diapedesis to get to the site of infection/damage
Main sites of hemopoiesis with respect to age
1-3 months in gestation (1st trimester)= yolk sac
3-6 months in gestation (2nd trimester)= liver and spleen (more liver)
8months to birth(3rd trimester) = all bones via bone marrow
Birth - 29 years = all bones but primarily tibia, femur, sternum, vertebrae and ribs
30- 100 years of age = sternum, vertebrae and rib bone marrow
Hematopoietic cords and sinusoidal capillaries
Cords = Sites of proliferation and maturation of hematopoietic cell lines into cell lineages
Capillaries = allows for passage of mature blood cells into the blood stream via a pressure gradient
Both found in red bone marrow
Hemopoeitic stem cell differentiation
Pluripotent stem cells located in bone marrow that differentiates based on what cytokines they are exposed to during maturation
Equation used to estimate normal Cellularity
100% - patient age +/- 10%
Ex: 30 year old = 60-80% normal range
Erythropoiesis
Differentiation of pro-erythroblasts from MEP or CEP via erythropoietin (EPO) expression
Proerythroblast nucleus increases mRNA production and increases polyribosomes which in turn will slowly become hemoglobin
Overtime, mRNA is reduced and the nucleus condenses while hemoglobin content increases inversely. (basophilic and polychromatophilic erythroblasts)
- during this process, the cell stains less basophilic (purple) and more eosinophilic (Pink) overtime
Eventually releases nucleus (pyknotic nucleus) and forms a reticulocyte (immature RBC)
Reticulocytes are pushed into sinusoidal capillaries and become mature RBCs
Thrombopoiesis
Differentiation of megakaryoblast from MEP or CEP via thrombopoietin (TPO) presence.
Multiple rounds of endomitosis (DNA division, but not cellular division, results in multiple nuclei but only 1 cell) in a megakaryoblast differentiate it into a megakaryocyte.
Megakaryocytes are extended into sinusoidal capillaries which releases tips (platelets) into the blood stream directly
Granulopoiesis
Differentiation of a granulocyte progenitor cell and myeloblast driven by GM-CSF and G-CSF and specific growth factors which commit them to specific granulocyte.
Starts as myeloblast (basophilic standing cytoplasm cell with no granules)
Then becomes promyelocyte (possessing a well defined golgi and RER, also contains granules and stains more basophilic)
Then becomes myelocyte/ metamyelocyte (first signs of differentiation of granulocytes where they gain specific granules and accumulate in the cytoplasm) until this stage, it is impossible to distinguish between the 3 granulocytes
Last stage of mitotic division
Then becomes mature definitive granulocyte after its nucleus has condensed into polymorphic shape
Primary lymphoid organs vs secondary lymphoid organs
1st: Red bone marrow. And thymus
2nd: Mucosa-associated lymphoid tissue (MALT), lymph nodes and spleen
Difference is 1st = site of maturation and 2nd = site of activation
Lymphatic tissue histologically
Supported by reticular tissue (except for thymus)
- contains reticular cells and fibers (type 3 collagen fibers)
- contains T and B cells and plasma cells
- also contains macrophages, dendritic cells and APCs
Where does positive selection/ tolerance occur in the thymus?
The cortex
Negative and positive selection of T cells in thymus
Positive selection: lymphocyte survives if it binds to the MHC complexes (cortex)
Negative selection: lymphocyte survives if it does not bind to self antigens
(Medulla)
Final step of maturation in the thymus
2% of total naive lymphocytes survive positive and negative selection
- undergo selective loss of either CD4 or CD8 expression which officially gives the T-cell its properties
MALT
Found throughout the mucosa in the UG and GI and respiratory system
- usually found in the lamina propria sections of the tissue
- contain lymphoid nodules which are localized concentrations of lymphatic tissue that contain mostly T and B cells. (Can be primary or secondary)
Primary vs secondary nodules in MALT
Primary nodule: not active immune response, support cells
-stains darker
Secondary nodule: active immune response is initiated via APC cell infiltration
- causes differentiation into germinal center (B-cells) and mantle zone (T-cells)
- stains lighter than primary when active
Histologically, primary looks the same color throughout, whereas secondary has a clear germinal center in the middle
Lymph nodes
Capsules with trabeculae and contain 3 sites:
Cortex: outside and contain subcapsular sinuses and lymphoid nodules
-sites of immune response
Paracortex: does not contain lymphoid nodules and instead contain HEVs
- brings in APCs and active lymphocytes
Medulla: contains T cells in the medullary sinuses and medullary cords
Sites of entering the lymph nodes
90% = blood stream via HEVs
10% = lymph stream via afferent vessels
All stuff migrates to lymphoid nodules of the cortex, which is the site of an immune response
Spleen functions
Filtering the effete RBCs
Site of immune responses
Reservoir for blood and blood cells
Site of fetal hemopoiesis
Splenic pulp
20% = white pulp
- contain PALS, transient lymphoid nodules and central arterioles. Site of immune response
80% = red pulp
- contains penicillar arterioles, splenic sinuses, splenic cords. Site of blood filtration
Albumin
Most abundant plasma protein
- made in liver
- serves primarily to maintain osmotic pressure of blood and to bind drug components to move throughout body
Alpha and beta globulins
Include transferrin, fibronectin, prothrombin and other coagulation factors
- also include lipoproteins
- made in liver primarily
Immunoglobulins
Secreted by plasma cells as antibodies or y-globulins
Fibrinogen
Largest plasma protein and is made in liver
- during clotting, polymerizes as insoluble, cross-linked fibers of fibrin that block blood loss from small vessels
Complement proteins
Innate immune system defense that is found in the plasma of blood.
Blood functions
Transfer of respiratory gases bound to hemoglobin
Moves hormones and regulatory proteins
Moves immune cells nutrients and metabolites
Moves wastes products
Maintains homeostatic regulation
- osmotic balance, acid-base balance and body temp
Clotting and healing of vasculature
Plasma composition
92% water
7% plasma protiens
1% other solutes
- wastes
- minerals/electrolytes
- nutrients
- dissolved gases
Peripheral membrane proteins in plasmalemma
Band 4.1 and ankyrin
- interact with other proteins such as spectrin to from structural support
Integral plasmalemma proteins
Band 3 and glycoproteins
proteins that serve as anchors under the protein complexes formed by the peripheral membrane proteins
- serve together with peripheral proteins to increase structural integrity and produce the biconcave disc shape. Also increase flexibility since the interacts between peripheral and integral membrane proteins can be rearranged
What are progenitor cells called?
Colony-forming units (CFUs)
Yellow vs red bone marrow
Red bone marrow = site of hemopoiesis
Yellow bone marrow = adipocyte filled marrow that is arrested
- site of nutrients storage and promoting bone growth
- as you get older, red gradually changes to yellow.
- some can be reverted back to red in times of hypoxia and/or severe bleeding*
Band cell
Intermediate stage of neutrophils granulocytes prior to complete maturation
- marked by elonged nucleus but not yet polymorphic.
- can enter blood stream and continue to mature
4 compartments of neutrophils
Granulopoetic compartment: found in active red marrow and move when needed
Storage compartment: mature cells that remain in the marrow and not move
Circulating population: mature and band neutrophils that are within the blood stream
Marginating population: cells that adhere loosely and accumulate transiently on the endothelial surface of venules and small veins.
- dont undergo diapedesis
Functions of blood
Transport and distribution
Homeostatic regulation
Clotting and healing of vasculature
Plasmalemma proteins
Ankyrin proteins: bind to integral proteins
Spectrins: give stability/flexibility and biconcave shape to the RBC
band dimers: integral proteins in RBCs
Common myeloid progenitor cell types (CMP)
Erythrocytes
Megakaryocytes: Platelets
Both myeloblast and monoblasts
myeloblast cells:
- eosinophils
- leukocytes
- basophils/mast cells
Monoblast cells:
- microglia
- osteoblasts
- macrophages
Common lymphoid progenitor cell types (CLP)
Lymphocytes
- B cells
- T cells
- NK cells
Marginating cells
Neutrophils that bind to endothelium but dont extravate into tissues, they just hang onto the endothelium until they are needed
(NOT CIRCULATING)
Monocytopoiesis
Differentiation of a CMP progenitor cell into a monocyte via M-CSF
Promonocyte: first stage and is completely indistinguishable from a pro granulocyte
- basophilic staining and “dented” nucleus
Monocyte: nucleus is C-shaped with azurophilic granules accumulation
- can be distinguished from granulocytes
Maturation sites of lymphocytes
Immature T cells: thymus
Immature B cells: bone marrow
Immature NK cells: bone marrow and secondary lymphoid organs
Difference between dendritic cells and follicular dendritic cells
DCs = not found in lymphoid tissues and do not currently possess antigens
FDCs = found in lymphoid tissues and present antigens for B cells
Types of cortex thymus epithelium
Type 1: squamous between capsule and cortex
- isolate cortical compartments and contribute to creating the blood-thymus barrier. Prevent unregulated exposure
Type 2: stellate
- support macrophages and lymphocytes and act as APCs for maturation of T cells and present MHC for positive tolerance/selection
Type 3: squamous between cortex and medulla
- create barrier between cortex an medulla as well as present MHC for positive tolerance/selection
Types of medulla thymus epithelium
Type 4: similar to type 3 in cortex
Type 5: support maturing T-cells and present self-antigens for negative selection
Type 6: “hassall corpuscles” that regulate local DC activity and development of regulatory T cells by secreting cytokines
