TBL 14: Bone Marrow

Question 1

What are the different hematopoietic organs from gestation to birth?

Answer 1

Blood islands in the mesoderm surrounding the yolk sac. From 2nd to 7th month of gestation, the liver is colonized by hemangioblast-derived hematopoietic stem cells. From 7th month on, the bone marrow is colonized by these stem cells

Question 2

What are blood smears good for?

Answer 2

cells details, maturation, differential counts, ratio of myeloid to erythroid cells, morphological changes, detect anemias, leukemias, and myeloma

Question 3

What are needle biopsies good for?

Answer 3

Panoramic view of bone marrow and normal architecture, bone marrow cellularity (index of hematopoietic cells to adipocytes)

Question 4

How do autologous and allogeneic bone marrow transplants differ?

Answer 4

Autologous - used in lymphoma where marrow is contaminated. Harvest bone marrow and reinject it after obliterating the remaining stem cells
Allogenic - bone marrow comes from another person who matches MHC

Question 5

What are the four CFU cells?

Answer 5

erythrocytic, granulocytic-monocytic, lymphocytic, megakaryocytes

Question 6

The cells of erythropoiesis and the characterization of them

Answer 6

CFU-E, proerythroblasts, basophilic, polychromatophilic, orthochromatophilic, nuclear extrusion, reticulocytes (no central pallor), erythrocyte

Question 7

What is the role of erythropoietin? How long does erythropoiesis last?

Answer 7

produced in kidneys and it stimulates and sustains erythropoiesis which takes about 7-8 days

Question 8

Why is hypoxia the principal stimulus for erythropoietin secretion?

Answer 8

Regulation exists as a feedback loop. Hypoxia tells the kidneys that not enough O2 is delivered to tissues so it produces erythropoietin to stimulate the development of more RBCs to increase the blood’s O2 carrying capacity

Question 9

Why does cytoplasmic color change from blue to reddish pink during erythropoiesis?

Answer 9

The RNA also absorbs the basic stain. Over time, the cytoplasm has less RNA as the nucleus is gone so the cytoplasm changes color

Question 10

Describe granulopoiesis

Answer 10

CFU-GM, myeloblasts, promyelocytes, myelocytes, metamyelocytes, band cells and lobulation of the horseshoe shaped nuclei completes process

Question 11

When do neutrophilic, eosinophilic, and basophilic granules become distinct?

Answer 11

Metamyelocytes

Question 12

Characterize Promyelocytes

Answer 12

large, round nuclei and reddish blue cytoplasmic granules (lysosomes)

Question 13

Characterize Myelocytes

Answer 13

Nuclei are eccentrically positioned and flattened on one side

Question 14

Characterize metamyelocytes

Answer 14

The flattened side of the nucleus becomes indented and the granules become distinct

Question 15

Characterize band cells

Answer 15

progressive deepening of the indentation results in horseshoe-shaped nuclei

Question 16

What is sepsis and when can it progress to septic shock?

Answer 16

systemic response to infection. Blood poisoning. Infection in blood leading to inflammation. Can progress to shock if hypotension and organ dysfunction fail to respond to antimicrobial treatment

Question 17

At what age are progenies of T cells established by?

Answer 17

Mid-twenties

Question 18

Describe the thymus

Answer 18

Two lobes surrounded by connective tissue capsule. Short trabeculae project into outer portions of lobe subdividing them into lobules with an dark stained cortex around a pale medulla

Question 19

What are epithelial reticular cells

Answer 19

Form a meshwork extending between trabeculae creating a scaffold supporting the T cells.. They secrete thymosin and thymopoeitin which induce T cell maturation and cell-mediated immunity

Question 20

What does lymphocytopoiesis do and describe the maturation of T cells?

Answer 20

Generates mature B cells and immature T cells in bone marrow. Immature T cells circulate to capillaries in the thyme medulla and traverse the capillary endothelium into the cortex where they become immunocompetent.

Question 21

Why do recurrent opportunist infections characterize DiGeorge syndrome?

Answer 21

Thymus does not develop properly and thus, there is a T cell deficiency leading to immunodeficiency

Question 22

What forms the blood-thymus barrier?

Answer 22

tight junctions between cortical capillary endothelial cells, thick basement membranes, macrophages, ERC processes

Question 23

Function of blood-thymus barrier and what happens when a T cell circumvents it?

Answer 23

Blocks premature exposure of non self and self antigens in the blood to maturing T cells. If a T cell is exposed, it undergoes apoptosis which prevents immune reactions in the thymus

Question 24

What part of the thymus has no blood-thymus barrier and why? What is this part not stained as darkly?

Answer 24

Medullary capillaries so that matured T cells can enter bloodstream. T cells don’t spend a lot of time in the medulla so that explains the weak stain

Question 25

What are the thymus (Hassall's) corpuscles? Where are they? What do they do?

Answer 25

In the medulla and formed by clusters of ERC. Many cells undergoing degeneration. ERCs in this produce cytokines that induce development of regulatory T cells

Question 26

In what systems are lymphatic capillaries particularly abundant in?

Answer 26

Those open to external environment. Skin, respiratory, urogenital, digestive

Question 27

What are lymphangitis and lymphadenitis and why are these conditions potentially dangerous?

Answer 27

Secondary inflammation Lymphangitis - lymphatic vessels Lymphadenitis - lymph nodes Uncontained, these conditions could lead to septicemia

Question 28

What is lymphedema

Answer 28

a localized type of edema when lymph does not drain from a particular part of the body

Question 29

What forms the MALT?

Answer 29

Aggregations of lymphocytes (lymphoid nodules) that join the lymphatic capillaries and vessels to form MALT

Question 30

What makes up the lymphoid nodules and what else is part of MALT?

Answer 30

Mostly B cells that selectively bind to invading bacterial antigens and replicate. T cells are dispersed among the lymphoid nodules in MALT

Question 31

What triggers a humoral immune response

Answer 31

Release of immunoglobulins by plasma cells that bind antigens

Question 32

What occupies the paler germinal center of a lymphoid nodule

Answer 32

Plasma cells from the activated B cells

Question 33

What is required for T cell activation?

Answer 33

They need to bind both non self antigen and self-antigen

Question 34

Why can graft-versus-host disease (GVHD) occur after allogeneic bone marrow transplantation?

Answer 34

The graft T cells see the tissue of the host as foreign inducing an inflammatory response and apoptosis of the host tissue

Question 35

How many lymph nodes are in the body?

Answer 35

500-600

Question 36

Describe lymph nodes

Answer 36

dense connective tissue capsule (type I collagen) with dark cortex and pale medulla. Lymphoid nodules form in the cortex from activated B cells. There is also a trabeculae network and reticular fiber meshwork (Type III collagen)

Question 37

What are high endothelial venules (HEV)?

Answer 37

venules lined with simple cuboidal endothelium around the boundary. They bind circulating lymphocytes to take them from the bloodstream into the cortex. The medullary and cortical capillaries drain into the HEV and the HEV empty into veins that exit the lymph node at the hilum

Question 38

Describe the path (which sinuses) and what they are?

Answer 38

Afferent lymph vessels deliver to subcapsular sinus which is continuous with the trabecular sinus which are continuous with the medullary sinuses that weave among the medullary cords

Question 39

What lines the sinuses?

Answer 39

Discontinuous epithelium

Question 40

What associates with sinuses and helps filter the lymph?

Answer 40

Macrophages and there are some surrounding B cells

Question 41

What are the medullary cords?

Answer 41

Linear aggregates of antigen-activated lymphocytes and plasma cells that migrated from the cortical lymphoid nodules to medulla. The lymphocytes and antibodies enter the percolating lymph through the porous medullary sinuses

Question 42

What accounts for pale staining of medulla in lymph nodes?

Answer 42

Extensive branching of the medullary sinuses

Question 43

What forms the single efferent lymphatic vessel at the hilum?

Answer 43

Coalescence of medullary sinuses forms the single efferent vessel that transports the lymph, lymphocytes, and Abs out of lymph nodes

Question 44

What conditions can cause lymphadenopathy?

Answer 44

enlargement of the lymph nodes. Can be caused by metastasis or antigenic stimulation in a bacterial or viral infection

Question 45

What is the course taken by activated lymphocytes from the local lymph nodes to the MALT for amplification of the humoral immune response?

Answer 45

Efferent vessels to leave local lymph nodes and the HEV in MALT causes the homing process where the lymphocytes bind selective cytokines to migrate to that tissue