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B2.3.3—Stem cell niches in adult humans

Adult stem cell niches are local tissue environments that maintain stem cells, regulate their division, and control activation or differentiation.

Syllabus
First assessment 2025
Objective
B2.3.3
Level
HL

Compare Niches And Potency Levels

A two-part diagram with a potency ladder from totipotent to pluripotent to multipotent, plus small labeled sketches of a bone marrow niche and a hair follicle bulge niche.

A stem-cell niche is a local tissue environment whose signals can keep adult stem cells undifferentiated or trigger their proliferation and differentiation. Potency describes how many different cell fates a stem cell can produce.

Bone marrow niches regulate blood-forming stem cells, while the bulge region of hair follicles contains stem cells that maintain and regenerate follicle tissues. Changes in local signals switch cells between maintenance, division and differentiation.

Totipotent cells in the earliest embryo can form all embryonic cell types and extra-embryonic tissues. Cells soon become pluripotent, able to form all body cell types but not a whole organism. Adult stem cells such as those in bone marrow are multipotent and form a restricted family of related cells.

A blood-forming stem cell in bone marrow can self-renew or produce multiple blood-cell lineages, but it does not normally produce neurons; this is multipotency rather than pluripotency.

Potency is the range of possible differentiated descendants, not the rate of division. A niche is also more than a location: its surrounding cells and signals regulate stem-cell behaviour.

Cell Specialization and Size Limits

Cell specialization comes from differential gene expression after a zygote divides, stem cells provide self-renewing cells with different potencies, and cell size is constrained by surface area-to-volume ratio because exchange depends on surface area while demand depends on volume.

  • Differentiation: same genome, different active genes, different proteins.
  • Stem cells: self-renewal plus potency; specify totipotent, pluripotent, or multipotent when needed.
  • SA:V: as cells grow, exchange becomes less efficient because volume increases faster than surface area.

Concept essentials

  • A stem cell niche is a local environment that regulates stem cell behaviour.
  • Niches can maintain stem cells in an undifferentiated state.
  • Niche signals can activate division and guide differentiation.
  • Bone marrow and hair follicle bulge regions are examples of adult stem cell niches.