Connective Tissue: Fixed Cells Overview

Study Notes

Fibroblast and Fibrocyte:
- Develop from pericytes and mesenchymal cells.
- Mature fibroblasts become less active and change into fibrocytes.
- Fibroblasts form connective tissue fibers and matrix.
- Abundant in areolar connective tissue.
- Fibroblasts can transform into contractile myofibroblasts, rich in contractile filaments.
- Crucial in wound closure during healing.
Fixed Macrophages (Histiocytes):
- Originate from blood monocytes migrating to connective tissue.
- Motile cells with multiple processes (pseudopodia).
- Irregular cell membrane due to pseudopodia.
- Cytoplasm is basophilic, containing lysosomes and phagocytosed materials.
- Indented or kidney-shaped nucleus, rich in heterochromatin (dark).
- Distinguished from fibroblasts by pale nucleus.
- Stained with vital stains like Trypan blue or black Indian ink.
Adipose Cells (Adipocytes):
- Derived from mesenchymal cells after fat accumulation.
- Unilocular:
  - Large, oval cells with flattened peripheral nucleus (signet ring).
  - Contain a large fat globule.
- Multilocular:
  - Present in newborns.
  - Many fat globules and mitochondria.
  - Rounded nucleus
  - Primarily for heat production.
  - Found in neck, shoulders, back, axilla, and para-aortic regions in newborns.

Mesenchymal Cells (UMCs):
- Embryonic, branched cells with large oval, basophilic nuclei.
- Found primarily in embryonic tissues.
- Differentiate into various connective tissue cell types.
Pericytes:
- Pale, branched cells with cytoplasmic processes.
- Located externally to endothelium of capillaries and small venules.
- Considered mesenchymal cells, persisting throughout adulthood.
- Contribute to fibroblasts and other cells.

Line the inner surface of blood capillaries and vessels.
Adults consider them connective tissue.
Functions:
- Synthesize type IV collagen.
- Can divide to form new capillaries in damaged tissue.
- Produce their own basal lamina.