Structure and Function of Bone Marrow: Topic 1 Flashcards
where is bone marrow found in adults?
most bone marrow is found in flat bones, such as the pelvic bones and sternum, and at the ends of long bones, such as the femur
these bones have dense bone on the outside (the cortex) and spongy bone on the inside (the medulla).
The spongy bone consists of narrow trabeculae, between which the bone marrow is situated
what does bone marrow look like under a light microscope?
low magnification: bluish-purple stuff interspersed with white dots
higher magnification: you can start to see some of the different parts of the bone marrow
bluish-purple material consists of hematopoietic cells
large white spaces are all that’s left of fat cells (which wash away during specimen processing)
what are the components of bone marrow?
- blood cells
- fat
- hematopoietic tissue
- sinusoids
- stroma
what does hematopoietic tissue give rise to?
Hematopoietic tissue gives rise to all the cells of the blood
hematopoietic tissue contains a small number of cells called stem cells, which have the capacity to self-renew and to differentiate into different types of cells
how does the composition of bone marrow change as we age?
At birth, bone marrow is virtually 100% cellular = solidly packed with hematopoietic cells
Every year, though, we lose a bit of hematopoietic tissue, replacing it with fat
general rule of thumb: the cellularity of the marrow declines at the rate of about 10% per decade, until around age 70, when it reaches an all-time low of 30%.
what are sinusoids?
Wide, thin-walled vessels that course through the marrow
they connect the arterial and venous sides of the circuulation and providing a way for cells to enter and exit the marrow
nearly impossible to see without special stains that highlight endothelial cells or basement membrane
what are stroma?
stroma of the bone marrow consists of cells and fibers that provide support and structure for hematopoietic tissue
stromal fibers, including collagen and reticular fibers, provide a nice scaffold, or network, for the blood cells and sinusoids
what are the kinds of stromal cells?
- fibroblasts: make up collagen fibers
- macrophages: digest unwanted debris
- adipose cells: fat
- osteogenic cells: produce bone
What is the bone marrow stroma made of?
Cells: fibroblasts, macrophages, adipose cells, osteogenic cells
and
Fibers: collagen and reticular fibers
what kind of hematopoietic cells are in the bone marrow?
the bone marrow contains all cell stages, from undifferentiated stem cells to fully mature blood cells
what are the two ways that hematopoietic cells in bone marrow are shown?
- densely packed block
- spread-out smear
this is because a bone marrow biopsy consists of two parts: a tissue core specimen and a fluid aspirate specimen
tissue specimen is great for looking at the overall architecture and cellularity of the marrow, but not so great for looking at the morphology of individual cells
aspirate smear is good for looking at the different types of cells (only megakaryocytes can be seen in densely packed tissue because they’re so big)
Which type of bone marrow specimen is the best for examining individual cell morphology?
The bone marrow aspirate smear
what lineage of cells takes up the most space in the bone marrow?
neutrophil series
All maturational stages of this series are clearly visible in a normal bone marrow
includes: myeloblasts, promyelocytes, myelocytes, metamyelocytes, segmented neutrophils
other granulocytes (eosinophils and basophils) are present in much smaller numbers
what is the second biggest lineage in the bone marrow?
erythroid series
all maturational stages of erythrocytes are present, but they are not usually separated out for reporting purposes
what is the myeloid:erythroid ratio?
myeloid = neutrophil series erythroid = RBC
usually between 2:1 and 4:1
there’s usually more myeloid cells than erythroid cells
M:E ratio is a quick way to get a rough idea of whether the hematopoietic cells are present in the right proportions
