a-short-review-of-histology

Red Blood Cells:

Red blood cells, or erythrocytes, are the most numerous blood cells
They are 7-8 microns in diameter with a very characteristic biconcave disc shape
Their cytoplasm consists almost entirely of the protein haemoglobin which binds oxygen or carbon dioxide for transport to/from the lungs to/from other parts of the body
The biconcave disc shape provides for a short diffusion distance for these gasses with efficiency benefits in terms of loading/off loading the gasses
Although 7-8 microns in diameter, red blood cells are highly flexible and so can squeeze through small capillaries with a diameter of only 5 microns
In the peripheral blood, red blood cells are anucleate although during their differentiation in the bone marrow the developing cells are nucleated: as part of the final stage in red blood cell formation there is an unequal division of the cell to give an anucleate portion which passes into circulating blood and a nucleated portion with little cytoplasm which is retained within the bone marrow and ingested and broken down by macrophages
Red blood cells take about 2-4 days to develop in the bone marrow, spend about 100 to 120 days in circulating blood before being broken down by macrophages, mainly in the spleen

Red Blood Cells: Image 1

In this image of a blood smear, whole red blood cells are stained a grey - pink colour
They are anucleate
Some red blood cells can clearly be seen to have the characteristic biconcave disc shape
The variety of other shapes is artefactual but reflective of the ability of red blood cells to change their shape in order to squeeze through narrow capillaries
The three nucleated cells are white blood cells

Red Blood Cells: Image 2

In this tissue section, red blood cells are present in the lumen of the blood vessel
It is less easy to appreciate their biconcave disc morphology in tissue sections than in blood smears where the whole cell is visible