Stem cells

Bulge 

Stem cells are thought to reside mainly in the troughs of rete pegs, and in the outer root sheath bulge of the hair follicle

Stem Cell Niches

Ans. is ‘a’ i.e., Bone marrow

• Blood cells first appear during the third week of fetal embryonic development in the yolk sac, but these cells are generated from a primitive stem cell population restricted to the production of myeloid cells.

o Most studies suggest definitive hematopoietic stem cells arise in the mesoderm of the intraembryonic aorta/ gonad/mesonephros region, but evidence also exists for an origin within a small subset of yolk sac-derived cells.

• By the third month of embryogenesis, stem cells derived from the AGM and/or yolk sac migrate to the liver, which is the chief site of blood cell formation until shortly before birth.
• Beginning in the fourth month, stem cells migrate to the bone marrow to commence hematopoiesis at this site. o By birth, marrow throughout the skeleton is hematopoietically active and virtually the sole source of blood cells. o Up to the age of puberty, marrow throughout the skeleton remains red and hematopoietically active. o By age 18 only the vertebrae, ribs, sternum, skull, pelvis, and proximal epiphyseal regions of the humerus and femur retain red marrow, the remaining marrow becoming yellow, fatty, and inactive.

Ans. is ‘c’ i.e., Liver

o Stem cells are located in sites called niches. These include :

        Epidermal stem cells located in the bulge area of the hair follicle serve as a stem cells for the hair follicle and the epidermis.

        Intestinal stem cells are located at the base of a colon crypt, above Paneth cells.

        Liver stem cells (commonly known as OVAL cells) are located in the canals of Hering , structures that connect bile ductules with parenchymal hepatocytes.

        Corneal stem cells are located in the limbus region, between the conjunctiva and the cornea

        The bone marrow contains hematopoietic stem cells as well as stromal cells capable of differentiation into various lineages.

o There are three accessible sources of adult stem cells in humans :

1. Bone marrow, which requires extraction by harvesting, that is, drilling into bone (typically the femur or iliac crest),
2. Adipose tissue, which requires extraction by liposuction, and
3. Blood, which requires extraction through pheresis, wherein blood is drawn from the donor (similar to a blood donation), passed through a machine that extracts the stem cells and returns other portions of the blood to the donor.
4. Stem cells can also be taken from umbilical cord blood just after birth

Ans. is ‘c’ i.e., Trans-differentiation

Transdifferentiation

o Transdifferentiation takes place when a non-stem cell transform into a different type of cell, or when an already differentiated stem cell creates cells outside its already estabilished differentiation.

o Remember very important fact that it is the non-stem cell or already differentiated stem cell (i.e. mature cell) that is transformed into other type of cell. It is not stem cell that is transforming.

o Transdifferentiation is a type of metaplasia.

o Then, what is the difference between transdifferentiation and metaplasia.

         In Transdifferentiation only differentiated stem cell is transformed into other cell type, while in metaplasia any of the two, either stem cell or differentiated cell can transform into other cell type.

       So, all transdifferentiation processes are metaplasia, but not all metaplasia are transdifferentiation. o Most likely question has been wrongly framed here, there should be non-stem cell instead of stem cell in the question. Anyways answer remains the same, as no other option is related to this type of transformation.

Ans. is ‘c’ i.e., Intestine

Stem cells are located in sites called niches. These include :

Epidermal stem cells located in the bulge area of the hair follicle serve as a stem cells for the hair follicle and the epidermis.

Intestinal stem cells are located at the base of a colon crypt, above Paneth cells.

Liver stem cells (commonly known as OVAL cells) are located in the canals of Hering , structures that connect bile ductules with parenchymal hepatocytes.

Corneal stem cells are located in the limbus region, between the conjunctiva and the cornea

The bone marrow contains hematopoietic stem cells as well as stromal cells capable of differentiation into various lineages.

Limbal stem cells (also c/d corneal epithelial stem cells) are stem cells located in the basal epithelial layer of the corneal limbus.