Unit 6: Blood and Hematopoiesis Flashcards
What is hematopoiesis?
the process of producing blood cells, including formation, development and differentiation
What are the components of blood?
plasma, erythrocytes, thrombocytes, leukocytes
What is plasma?
liquid matrix consisting of proteins and other regulatory molecules
What are erythrocytes?
Also called “red blood cells”. Cells with hemoglobin and no nucleus (oxygen transporters)
What are thrombocytes?
Formed elements (also called platelets) involved in coagulation
What are leukocytes?
Also called “white blood cells”, involved in host defense including innate and adaptive immunity.
What are the types of leukocytes?
granulocytes, mononuclear cells
What are granulocytes?
Leukocytes with specific cytoplasmic granules
What are mononuclear cells?
Agranular lymphocytes and monocytes involved in immune effector, helper and accessory functions (e.g. B cells and T cells)
What are the steps in hematopoeisis?
stem cells -> progenitor cells -> precursor cells -> differentiated, functional cell types
What are hematopoietic stem cells (HSCs)?
can self-renew and regenerate every cell type in the hematopoietic system.
What are hematopoietic stem cells capable of?
reconstituting the entire bone marrow
How often do Hematopoietic Stem Cells divide?
Relatively quiescent – resistant to chemotherapy and radiation
How are hematopoietic stem cells activated?
in response to stress
How are hematopoietic stem cells identified?
presence of specific cell surface markers: CD34, CD90
absence of other cell surface markers: CD38, other lineage markers associated with mature cell types
What are Hematopoietic Progenitor Cells (HPCs)?
more restricted in differentiation potential
Hematopoietic progenitors with different potential to form specific mature cell types are defined by…
Function
• Bone marrow transplantation
• Colony forming potential
Cell surface markers
Response to specific growth factors / cytokines
Where is the site of blood production?
depends on the stage of development in humans
Yolk Sac (Early Embryo)
• 3-10 weeks of gestation
Aorta-Gonad-Mesonephros
• Site for production of definitive HSCs
Fetal Liver (Embryo)
• 6 weeks to term
Spleen
• 10 weeks to 7 months
Bone Marrow
• 4 months to death
Where is the first phase of hematopoiesis for life? How is this characterized?
yolk sac - 3rd week of gestation
Characterized by formation of “blood islands” in wall of yolk sac.
What is the major blood forming organ in the fetus?
liver
What is the predominant cell types in the fetus?
erythroid
How much of the body is bone marrow?
4-5% of body weight
What are the compartments of bone marrow?
vascular and hematopoietic
What are the embryonic precursors to blood and bone marrow?
mesoderm
How many cells does an average human replace every day?
330 billion cells
86% of cells are blood
How does regulation of hematopoiesis occur?
Intrinsic regulatory factors
extrinsic regulatory factors
What are intrinsic regulatory factors?
(e.g. transcription factors)
coordinate gene expression
For example, the GATA2 transcription factor is required for HSC formation and function, GATA1 is needed for erythropoiesis and Pu.1 is needed to commit cells to myeloid lineages.
What are extrinsic regulatory factors?
(e.g. growth factors)
produced in stromal cells to stimulate HSC/progenitor cell survival and differentiation.
What does aplastic anemia cause?
hypocellularity
(not producing enough hematopoetic cells)
What does myeloid leukemia cause?
packed, hypercellular marrow
(too many hematopoetic cells)
What is the hematopoietic niche?
specialized microenvironment consisting of stromal cells (mesenchymal cells, adipocytes, osteoblasts, fibroblast, endothelial cells and macrophages) that produce supportive cytokines such as SCF and a local microvasculature
What do bone marrow stromal cells produce?
extracellular matrix components, growth factors, adhesion molecules, cytokines to support the developing hematopoietic stem/progenitor cells
What do cytokines and growth factors provide?
pro-survival, proliferation, and differentiation signals to stem/progenitor cells depending on the needs of the hematopoietic system
How can hematopoietic stem/progenitor cells be grown?
in vitro using semisolid media such as methylcellulose containing growth media, growth factors (see previous slide) and hematopoietic colony stimulating factors
How are characteristic colonies of hematopoietic stem/progenitor cells formed?
from a single progenitor cell, which allows for the evaluation of stem/progenitor cell potentials and frequencies in bone marrow and peripheral blood
What are characteristic colonies of hematopoietic stem/progenitor cells?
Colony forming unit (CFU)
CFU-Granulocyte-Erythrocyte-Macrophage-Megakaryocyte (CFU-GEMM)
CFU-Granulocyte-Macrophage
CFU- Granulocyte
Burst Forming Unit - Erythrocyte
How are hematopoetic stem cells “mobilized” to leave the bone marrow and enter circulation?
enhanced by administering granulocyte – colony stimulating factor (G-CSF)
How are hematopoetic stem cells leave circulation to reenter circulation?
stem cell homing – when an HSCs leaves the blood and re-enters the bone marrow niche.
How is stem cell homing mediated?
by stem cell derived factor 1 (SDF1) and CXCR4. The maintenance of stem cell viability during this process is mediated by secreted stem cell factor (SCF) and HSC cell surface receptors Kit and Notch.
What do the features of HSCs (mobilization and homing) permit?
Their transplantation
What are the types of HSC transplantation?
autologous (self)
allogenic (other)
Why are bone marrow transplants performed?
replace cancerous cells in the bone marrow
How are bone marrow transplants performed?
Stem cells are harvested from marrow or mobilized peripheral blood or collected from umbilical cords after birth.
HSCs can also be cultured in the lab, modified using CRISPR-Cas9.
What is the model for the differentiation states of hematopoiesis? What is this based on?
suggest a continuum of differentiation “states” as opposed to discrete populations of progenitors with fixed lineage potential
based on new techniques that allow molecular analysis of individual cells.
- Single cell RNA-sequencing
What does blood transport?
oxygen, carbon dioxide, nutrients, hormones, heat and waste
What does blood regulate?
fluid homeostasis, pH, body temperature and water content
What does blood protect?
against excessive loss by clotting.
against infections.
What is plasma and where is it secreted?
(water (90%), proteins, electrolytes, nitrogen, nutrients, gases)
secreted by liver.
What are the proteins in plasma?
albumin, globulins, fibronogen
What does albumin do in plasma?
maintains proper concentration gradients between blood and extracellular tissue fluid. Made in the liver. Albumin has a fundamental role in maintaining osmotic pressure in blood
What do globulins do in plasma?
immunoglobulins are secreted by plasma cells, and are involved in the humoral response. Non-immunoglobulins are secreted by the liver, and help maintain osmotic pressure.
What does fibronogen do in plasma?
participates in coagulation, produced in liver
What is serum? Why is is preferred in testing?
plasma minus fibronogen and some clotting factors.
For many specific tests, serum is preferred because it lacks coagulation factors.
What are formed elements?
cells and fragments of cells
What are granulocytes?
neutrophils, eosinophils, basophils
What are agranulocytes/mononuclear cells?
monocytes and lymphocytes
What does a differential blood count do?
Quantify the relative percentage of each white blood cell in the peripheral blood. These values can be compared to normal relative frequencies and give indications of potential problems
What cells makes up most of the differential blood count?
Neutrophils (60-70%)
Lymphocytes (20-25%)
What is a complete blood count?
(CBC)
one of the most commonly used, relatively inexpensive and highly informative lab test panels
What does a CBC measure?
total RBC, WBC (including differential counting), platelets, hemoglobin, hematocrit, and erythrocyte indices
How does hemoglobin change in a CBC at birth, to 10 years old, and then in adult women and men?
Highest at birth (17-23 g/dL)
Lowest at 10 years old (12-14 g/dL)
Lower in adult Women (13-15 g/dL) than Men 14-17 g/dL
What is hematocrit?
the percentage of erythrocyte volume in the whole blood (also known as packed cell volume)
What do CBC’s measure?
hemoglobin, hematocrit, erythrocyte indices
What do erythrocyte indices measure?
Mean corpuscular volume (MCV) – size of red blood cell
Mean corpuscular hemoglobin (MCH) – amount of hemoglobin in average erythrocyte
Mean corpuscular hemoglobin concentration (MCHC) – percentage of hemoglobin in erythrocyte
Erythrocyte distribution width (RDW)- are erythrocytes uniformly sized and shaped?
What are these erythrocyte indices called?
below normal
above normal
irregular shape
Below normal: microcytic
Above normal: macrocytic
Irregular shape: poikilocytic
What does a CBC’s measurement reflect? What is it used for?
reflects the body’s ability to fight infection and/or disease, levels of immune and effector cells, toxicity to drugs or radiation therapy, and monitoring change over time.
It is used to screen and diagnose disease, manage conditions such as acute/chronic infections, allergies, anemias.
What are the stages of erythropoiesis?
pluripotent hematopoietic stem cell -> proerythroblast -> erythroblast (basophilic, polychromatic, orthochromatic) -> reticulocyte -> erythrocyte
What are the bone marrow stages of erythropoiesis?
pluripotent hematopoietic stem cell -> proerythroblast -> erythroblast (basophilic, polychromatic, orthochromatic)
(before reticulocyte)
What are the blood stages of erythropoiesis?
(after reticulocyte)
erythrocyte
What is the change between a proerythroblast and erythroblast?
change in color (blue cytoplasm - basophilic, between - polychromatic, more pale - orthochromatic)
What is the change between an erythroblast and reticulocyte?
loses nucleus, some organelles
What is the change between a reticulocyte and erythrocyte?
loses remaining organelles
How do red blood cells develop into a proerythroblast?
MPP to CMP to MEP then proerythroblast
How do red blood cells develop from proerythroblast to reticulocyte?
basophilic erythroblast
polychromatic erythroblast
orthochromatic erythroblast
reticulocyte
How fast do RBCs mature? How are the changes identified?
Maturation is gradual
identified by a series of predictable molecular and morphological changes
How does the staining appearance of RBCs change as they mature?
color of cytoplasm changes from blue to pink
How does the size of RBCs change as they mature?
cells get smaller
from proerythroblast to erythroblast, size decreases from 20 um to 7.8 um
How does the nuclei appearance of RBCs change as they mature?
cell nuclei get smaller
the nuclear-to-cytoplasm ratio decreases
How does the heterochromatin of RBCs change as they mature?
it condenses
How does the RNA of RBCs change as they mature?
RNA content decreases as hemoglobin content increases
How are red blood cells described?
Biconcave disc-shaped deformable membrane.
~20-30 trillion RBC in your body
Lack organelles
- No nucleus, ribosomes, mitochondria
Life span ~100-120 days
What are the functions of RBCs?
Major function: transport oxygen from pulmonary capillaries to tissues.
RBCs are deformable
What does the deformable property of RBCs allow them to do?
to fit into small capillaries
How are the mechanical properties of deformability of RBCs determined?
by a unique cytoskeletal frame, integral membrane proteins and submembrane structure:
ankyrin, spectrin, band 3, band 4.1
What are the types of regulation of RBC production?
extrinsic, intrinsic
How is RBC production extrinsically regulated?
hormones
interleukin-3 and interleukin-4
necessary nutrients
What happens with the hormonal extrinsic regulation of RBC production? Which hormones, what do they do?
Erythropoietin
- Increases RBC maturation rate
- Released in response to hypoxia
- Produced by kidneys
Thyroid hormone and testosterone play a minor role
What are the necessary nutrients for extrinsic regulation of RBC production?
Iron (essential component of hemoglobin)
vitamin b12
folate
What controls the intrinsic regulation of RBC production?
Transcription factor GATA1 is required for terminal differentiation
What is the structure of hemoglobin?
Each molecule contains four heme groups surrounded by a globin group
Each chain bound to an iron-containing heme group.
What kind of bonding does hemoglobin do?
Hemoglobin forms an unstable reversible bond with oxygen
What is globin switching?
Different subunits of hemoglobin are created throughout different parts of development
All subunits are encoded on the same gene
What are the globin subunits that are made throughout development? When? Where are they made?
epsilon - embryonic (yolk sac)
gamma G/A - fetal (liver/spleen)
alpha/beta - adult (bone marrow)
What is sickle cell anemia?
Severe genetic disease that causes chronic pain and often premature death
What is the molecular basis for sickle cell anemia?
Single point mutation in 6th codon of beta-globin gene
About 5% of the world’s population are carriers for this mutation
What is the size of platelets?
small (2-4 um in diameter)
What is the function of platelets?
hemostasis/coagulation
What are the properties of platelets?
sticky but do not adhere to normal endothelium
What are the function phases of platelets?
cell phase
enzyme phase
contraction phase
What happens in the cell phase for platelets?
tissue/vascular injury -> platelet adherence -> activation -> platelet thrombus -> hemostatic plug
What happens in the enzyme phase for platelets?
enzymes released by platelets help form a clot
What happens in the contraction phase for platelets?
platelets contract to constrict injured vessel
How do granulocytes originate?
from multipotent common myeloid progenitors (CMP)
What are the morphologically identifiable stages that are involved in neutrophil maturation?
Myeloblast
Pro-myelocyte
Myelocyte (neutrophilic, eosinophilic, basophilic)
Metamyelocyte
Band cell
Mature neutrophil
What is the granulopoiesis maturation process similar to?
the process for eosinophils and basophils
(in response to distinct growth factor stimulation)
What are the phases of granulopoiesis?
mitotic/proliferative phases
post-mitotic phases
What do the mitotic/proliferative phases of granulopoiesis involve?
lasts ~ 1 week and proliferation stops after the myelocyte stage
myeloblast -> promyelocyte -> neutrophilic/eosinophilic/basophilic myelocyte
What do the post-mitotic phases of granulopoiesis involve?
specific granule formation in bone marrow also lasts ~ 1 week. These phases are characterized by a reduced cell size, changes to the nuclear shape from round to “kidney shaped” to “horseshoe shaped” to lobular
neutrophilic/eosinophilic/basophilic metamylocyte -> band stage (eosinophil/basophil) -> neutrophil
What is the life cycle of a neutrophil?
half-life in blood circulation is 6-8 hours.
After leaving the bloodstream and entering tissues, a neutrophil dies by apoptosis after 1-2 days.
What is the most abundant granulocyte produced by granulopoiesis?
neutrophils (~100 billion/day)
How are basophils formed
formed from a common Basophil-Mast Cell Progenitor
How is development of a basophil triggered?
by increased expression of CCAAT/enhancer-binding protein a (CEBPα)
Where are basophils developed?
develop and differentiate in the bone marrow and are released into the peripheral blood as mature cells
Where are eosinophils developed?
develop and mature in the bone marrow.
They migrate from bone marrow, to peripheral blood to connective tissues.
How is differentiation of GMPs to eosinophils induced?
IL-3
IL-5
What are the functions of granulocytes?
Function in phagocytosis, “neutralizing” invading bacteria
Contain common cytosolic granules (lysosomes) with acid hydrolases and myeloperoxidases, along with other cell-type specific enzymes/molecules.
Some cell type specific granule-containing proteins.
What are the cell type specific granules-containing proteins of neutrophils?
gelatinase, cathepsin
What are the cell type specific granules-containing proteins of basophils?
heparin, histamine, IL-4, IL-13
What are the cell type specific granules-containing proteins of eosinophils?
major basic protein, neurotoxin
Inappropriate or hyperactive granule release can be involved in?
inflammatory diseases
Where/how are monocytes produced?
in bone marrow from the same common progenitor that also produces granulocytes
What are the distance stages of monocyte differentiation?
Promonoblast
Monoblast
Promonocyte
Monocyte
What controls the extrinsic regulation of monopoiesis?
IL-3
What controls the intrinsic regulation of monopoiesis?
Pu. 1 and Egr1 transcription factors
How do monocytes circulate? What does this require?
in peripheral blood prior to migrating into tissues for the final stage of maturation into tissue macrophages
requires GM-CSF and M-CSF
What are examples of tissue specific mature cells?
Macrophages, osteoclasts, Langerhans cells, Kupfer cells
What is lymphopoiesis?
process of producing lymphocytes
What does lymphopoiesis create?
T lymphocytes
B lymphocytes
NK cells
What does differentiation of NK cells dependent on?
IL-2
IL-15
