Morphology of Stem Cell

Stem cells are like the building blocks of our bodies. In addition, they have a special power to change into different kinds of cells. In this article, we'll learn about the morphology of stem cells and how they change into other types of cells in stem cell series.

I can describe this all in an article, but it'll probably be easier for you if you watch the video.

What are stem cells? 

Stem cells are special because they can turn into many kinds of cells. As a matter of fact, they start off as simple cells, and then they can change into more specialized cells. There are different kinds of stem cells, like ones that can turn into any cell in the body and ones that can only turn into certain types.

Stem cells Definition
-immature cells 
-Capable of dividing and self renewing
-Unspecialized
-Potential to become specialized into different types of cells.

Classification of Stem Cells

Embryonic Stem Cells Vs Adult Stem Cells

Embryonic stem cells, originating from the inner cell mass of the blastocyst, demonstrate remarkable plasticity. To put it another way, they are capable of differentiating into various cell types. Some stem cells derive from very early embryos and are termed embryonic stem cells. Adult stem cells, also known as somatic or tissue-specific stem cells, originate from adults. These stem cells reside in different body regions and aid in tissue repair.

There are 3 types of Adult stem cells

• Bone Marrow Stem Cells.
• Neutral Stem Cells
• Epithelia Stem Cells.

Within the bone marrow microenvironment, multipotent stem cells give rise to myeloid and lymphoid progenitors, which further differentiate into specific blood cell lineages. Myeloid stem cells give rise to erythrocytes, granulocytes, monocytes, and platelets through a series of carefully orchestrated steps. Notably, the differentiation of granulocytes, such as neutrophils, involves distinct morphological changes, including nuclear segmentation and granule formation.

Differentiation In the bone marrow

Within the bone marrow microenvironment, multipotent stem cells give rise to myeloid and lymphoid progenitors, which further differentiate into specific blood cell lineages. Myeloid stem cells give rise to erythrocytes, granulocytes, monocytes, and platelets through a series of carefully orchestrated steps. Notably, the differentiation of granulocytes, such as neutrophils, involves distinct morphological changes, including nuclear segmentation and granule formation.

Haemopoiesis

One of the most well-studied aspects of stem cell biology is hematopoiesis, which denotes the process by which all blood cells form. Moreover, hematopoietic stem cells (HSCs), derived from pluripotent stem cells, undergo a series of division and differentiation steps to produce various blood cell lineages. Erythrocytes, granulocytes, lymphocytes, monocytes, and platelets all originate from common HSCs but undergo distinct lineage-specific differentiation pathways. Each of these will be discussed below.

Rate of division is determined by 

• Erythropoietin, 
• Interleukins and 
• Colony stimulating factors. 

Formation of Platelets

Megakaryocytes

• Large cells
• With Large, Irregular, Multilobular Nucleus,
• No nucleoli.
• Their cytoplasm is filled with basophilic granules. 
• The cells do not have clear margins 
• The cytoplasm is divided into 3 zones.
  1. Perinuclear zone – consisting of Golgi, rough endoplasmic reticulum, centrioles, and spindle
  2. Intermediate zone – consisting of interconnected vesicles
  3. And Marginal zone, which contains the cytoskeletal filaments

Megakaryocytes finally develop into platelets,  which are disk like, non-nucleated fragments.

There are about 200,000 to 400,000 platelets per microlitre of blood. Eventually, The spleen destroys them after about 10 days, limiting their lifespan. The process of forming platelets is termed thrombopoiesis.

The megakaryoblasts develop into megakaryocytes and then into platelets. 

Formation of Neutrophils

The formation of neutrophils, known as granulopoiesis, primarily occurs in the bone marrow. It begins with the differentiation of multipotent stem cells into myeloid stem cells, which further mature into myeloblasts. Subsequently, these myeloblasts undergo several stages of differentiation, ultimately leading to the formation of neutrophils. For this reason, various growth factors and cytokines regulate the proliferation and maturation of neutrophils, throughout this process.

Neutrophil Myelocyte

The morphology of this stem cell derivative can be described as follows

• Large
• have eccentrically located nucleus
• have prominent Golgi apparatus
• Their cytoplasm contains prominent azurophilic granules

Neutrophil myelocyte further differentiate into Neutrophil Metamyelocytes. These have a relatively smaller  nucleus with an indentation. The azurophilic granules are no loger visible. Thereafter, the Metamyelocyte develop into a Stab cell also known as Band Neutrophils. Anatomy Professors love to ask about these Minute details, probably just to make our lives a bit more miserable than they already are. Therefore, try to keep these in mind. These can be identified by the presence of a  highly segmented nucleus.