Chp. 5 Hematopoiesis

define hematopoiesis

The production, maturation, development, renewal, proliferation, and differentiation of all blood cells.

define intramedullary

Hematopoiesis occurring inside the bone marrow

define Extramedullary

Hematopoiesis outside the bone marrow (typically in the liver or spleen under stressful conditions).

define intravascular

Occurring inside the blood vessels (such as early embryonic development in the yolk sac)

define extravascular

Occurring outside the blood vessels

What is retrogression in bone marrow?

when active cell-producing red marrow becomes inactive, fat-filled yellow marrow with age.

define totipotent stem cells in the context of hematopoiesis

Capable of dividing and producing any cell type in the entire body.

define pluripotent (multipotent) stem cells in the context of hematopoiesis

can differentiate into any blood cell lineage and restricted to blood cells. (myeloid or lymphoid)

define splenomegaly

Enlargement of the spleen, often due to increased clearance of abnormal or antibody-tagged blood cells

define splenectomy

Surgical removal of the spleen

What are the three developmental phases of fetal hematopoiesis?

Mesoblastic Phase, Hepatic Phase, Medullary Phase

define Mesoblastic phase developmental phases of fetal hematopoiesis

Occurs in the yolk sac (starting around day 19 of embryonic development).

define hepatic phase developmental phases of fetal hematopoiesis

Occurs primarily in the liver (and to a lesser extent, the spleen).

define Medullary phase developmental phases of fetal hematopoiesis

Occurs in the bone marrow once bones have developed.

What are the earliest types of hemoglobin produced during the mesoblastic and early hepatic phases?

Gower 1, Gower 2, and Portland hemoglobins. These later transition to Hemoglobin F (fetal hemoglobin) in the hepatic phase.

How do megakaryocytes physically release platelets into circulation?

Megakaryocytes reside close to the blood vessel sinuses in the bone marrow. They reach physical, cytoplasmic "arms" directly through the sinus walls into the bloodstream and pinch off individual platelets directly into circulation.

How does the spleen act as a storage reservoir for platelets?

The spleen sequesters (holds in reserve) approximately one-third (1/3) of the body's total platelet population.

what are the primary functions of EPO (erythropoietin)

driving red blood cell production. (Hormone/cytokine)

What are stromal cells and what do they include?

mesenchymal-derived cells that support hematopoiesis. Include: Endothelial cells, adipocytes, osteoblasts, osteoclasts, and fibroblasts

what are the primary functions of TPO (thrombopoietin)

driving platelet (thrombocyte) production, primarily synthesized in the liver. (Hormone/cytokine)

Why are mature platelets considered "a-nuclear" and unable to proliferate or make new internal contents?

Platelets are never formed with a nucleus; they are simply pinched-off fragments of a megakaryocyte's cytoplasm. They can only acquire new internal proteins or substances through endocytosis from plasma.

What is the formula to estimate normal bone marrow cellularity?

100 - Age = Estimated % Cellularity

Why does significant liver disease (e.g., cirrhosis, hepatitis, alcoholism) cause bruising and bleeding?

Damage to the liver directly impairs the body's ability to form clots. The liver is the primary site for synthesis of coagulation factors and thrombopoietin (TPO).

What is the expected platelet reaction immediately following a splenectomy?

Transient thrombocytosis (an abnormally high blood platelet count), because the one-third reservoir of platelets normally stored in the spleen is suddenly forced to remain in active peripheral circulation.

What is a micromegakaryocyte and when is it seen in peripheral blood?

It is an extremely abnormal "bare nucleus" remnant of a megakaryocyte. It is never seen in normal blood but can appear in severe pathological conditions like Myelodysplastic Syndrome (MDS) or Primary Myelofibrosis.
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describe the hematopoietic journey (fetal to adult)

Day 19 (Embryo): Yolk sac initiates intravascular hematopoiesis.


Organogenesis: Stem cells migrate to the liver (primary) and spleen (secondary).


Skeletal Development: Final migration into the bone cavities (medullary hematopoiesis). Under extreme physiological stress, hematopoiesis can revert back to the liver and spleen (extramedullary).

state the difference between red vs yellow bone marrow

Red marrow is active

Yellow marrow is fat-filled

can yellow marrow revert back to active red marrow

Yes with increased demand of red marrow

define bone marrow scaffolding

Hematopoiesis relies on a microenvironment. This stromal matrix includes osteoclasts (break down bone), osteoblasts (build bone), and blood vessels.

define megakaryocyte location and size

largest cell in body, They sit right on the edge of marrow sinuses, using cytoplasmic extensions to "pinch off" platelets directly into blood flow.

state why the spleen is a dual threat in hemostasis with storage

Holds 1/3 of all platelets. Loss of the spleen dumps this pool into active circulation, artificially raising platelet counts until the body adjusts.

state why the spleen is a dual threat in hemostasis with clearance

The spleen filters out old red blood cells and clears antibody-tagged cells. In autoimmune disorders (like ITP), platelets tagged with autoantibodies are prematurely destroyed here, leading to thrombocytopenia.

what are Kupffer cells and their function

macrophages in the liver sinusoids that remove senescent cells and foreign debris from blood. They also secrete mediators that regulate protein synthesis in hepatocytes.

What are the two methods the spleen uses to remove abnormal RBCs from circulation?

Culling and Pitting

Define culling in the spleen method to remove RBCs from circulation

Phagocytosis and degradation

Define pitting in the spleen method to remove RBCs from circulation

removal of inclusions or damaged surface membrane from circulating RBCs

T cells develop in what organ

Thymus

What are the three main functions of lymph nodes?

1. Site of lymphocyte proliferation (more B than T)

2. Initiation of the specific immune response to foreign antigens

3. Filter particulate matter, debris, and bacteria entering via lymph