Q34.Hematopoietic stem cells are found in

(A) Bone marrow
(B) Liver
(C) Spleen
(D) Payers patches

Hematopoietic stem cells are primarily found in bone marrow, the main site of adult blood cell production. This distinguishes it from secondary or fetal sites. Option (A) is correct.

Option Analysis

• (A) Bone marrow: Correct; adult HSCs reside in red bone marrow niches (endosteal/vascular) of flat bones (pelvis, sternum) and long bones, supporting lifelong hematopoiesis.

• (B) Liver: Incorrect for adults; fetal hematopoiesis site, but postnatally minimal HSCs except in extramedullary stress conditions.

• (C) Spleen: Incorrect; occasional extramedullary hematopoiesis during demand (e.g., hemolytic anemia), but not primary HSC reservoir.

• (D) Payers patches: Incorrect; gut-associated lymphoid tissue for immune sampling, lacks significant stem cell activity.​

Introduction to HSC Locations

Hematopoietic stem cells are found in bone marrow as the primary adult site, enabling self-renewal and differentiation into all blood lineages. This niche regulates quiescence via osteoblasts and stroma.

Bone Marrow Niches

Endosteal (near bone surface) and perivascular niches maintain HSCs; red marrow in pelvis/vertebrae dominates post-puberty. Mobilization to peripheral blood occurs for transplants.

Other Sites Explained

Fetal liver/yolk sac host early HSCs; spleen/liver activate extramedullary hematopoiesis rarely. Peyer’s patches are immune, not hematopoietic.