Case Study 5: Blood and Its Components

The process of formation and development of blood cells is termed:

• Hematopoiesis

• Hematemesis

• Hematocytometry

• Hematorrhea

Answer explanation

Hematopoiesis is a continuous, regulated process of blood

cell production that includes cell renewal, proliferation, differentiation,

and maturation. These processes result in the

formation, development, and specialization of all the functional

blood cells.

During the second trimester of fetal development, the primary site of blood cell production is the:

• Spleen

• Lymph nodes

• Liver

• Bone marrow

Answer explanation

During fetal development, hematopoiesis progresses through

the mesoblastic, hepatic, and medullary phases.

Organs that function at some point in hematopoiesis include

the liver, spleen, lymph nodes, thymus, and bone

marrow.

The bone marrow is the primary site of hematopoiesis at

birth and throughout life. In certain situations, blood cell

production may occur outside the bone marrow; such production

is termed extramedullary.

Which one of the following organs is responsible for the maturation of T lymphocytes and regulation of their expression of CD4 and CD8?

• Spleen

• Liver

• Thymus

• Bone marrow

Answer explanation

In adults, T cell progenitors migrate to the thymus from the bone marrow for further maturation.

The best source of active bone marrow from a 20 year old would be:

• Iliac crest

• Femur

• Distal radius

• Tibia

Answer explanation

Hematopoietically active bone marrow is referred to as red

marrow, as opposed to inactive yellow (fatty) marrow. At the

time of birth, the bone marrow is fully active and almost completely

cellular, with all hematopoietic cell lineages undergoing

cellular differentiation and amplification.

Physiologic programmed cell death is termed:

• Angiogenesis

• Apoptosis

• Aneurysm

• Apohematics

Answer explanation

Apoptosis is a self-inflicted cell death originating from

the activation signals within the cell itself. Most apoptosis

occurs as a normal physiologic process to eliminate potentially

harmful cells (e.g., self-reacting lymphocytes), cells

that are no longer needed (e.g., excess erythroid progenitors in

oxygen-replete states or neutrophils after phagocytosis),

and aging cells. Apoptosis of older terminally differentiated

cells balances with new cell growth to maintain needed

numbers of functional cells in organs, hematopoietic tissue, and

epithelial cell barriers, particularly in skin and the intestines. On

the other hand, apoptosis also initiates in response to internal or

external pathologic injury to a cell. For example, if DNA damage

occurred during the replication phase of the cell cycle and the

damage is beyond the capability of the DNA repair mechanisms,

the cell will activate apoptosis to prevent its further progression

through the cell cycle. Apoptosis can also be triggered in virally

infected cells by the virus itself or by the body’s immune

response. This is one of the mechanisms to remove virally

infected cells from the body.

Which organ is the site of sequestration of platelets?

• Liver

• Thymus

• Spleen

• Bone marrow

Answer explanation

Abnormal distribution of platelets can be caused by splenic sequestration.

Which one of the following morphologic changes occurs during normal blood cell maturation?

• Increase in cell diameter

• Development of cytoplasm basophilia

• Condensation of nuclear chromatin

• Appearance of nucleoli

Answer explanation

As cells mature, certain morphologic characteristics of maturation

allow specific lineages to be recognized. General characteristics

of maturation include decreased cell diameter, decreased

nuclear diameter, loss of nucleoli, condensation of

nuclear chromatin, and decreased basophilia in cytoplasm.

Some morphologic changes are unique to specific lineages

(e.g., loss of the nucleus in red blood cells).

Which one of the following cells is a product of the common lymphoid progenitor?

• Megakaryocyte

• T lymphocyte

• Erythrocyte

• Granulocyte

Answer explanation

The undifferentiated HSCs can differentiate into progenitor

cells committed to either lymphoid or myeloid lineages.

These lineage-specific progenitor cells are the common

lymphoid progenitor, which proliferates and differentiates into

T, B, and natural killer lymphocyte and dendritic lineages;

and the common myeloid progenitor, which proliferates and differentiates

into individual granulocytic, erythrocytic, monocytic,

and megakaryocytic lineages.

What growth factor is produced in the kidneys and is used to treat anemia associated with kidney disease?

• EPO

• TPO

• G-CSF

• KIT ligand

Answer explanation

The primary oxygen-sensing system of the body is located

in peritubular fibroblasts of the kidney. Hypoxia, too little

tissue oxygen, is detected by the peritubular fibroblasts, which

then produce erythropoietin (EPO), the major stimulatory cytokine for RBCs.

Which one of the following cytokines is required very early in the differentiation of a hematopoietic stem cell?

• IL-2

• IL-8

• EPO

• FLT3 ligand

Answer explanation

FLT3 is a receptor-type tyrosine-protein kinase. KIT

ligand and FLT3 ligand work synergistically with IL-3, GM-CSF,

and other cytokines to promote early HSC proliferation and

differentiation.