Cell types of connective tissue proper and their function

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Connective Tissue Cells

• Cells differentiating from mesenchymal cells, spend all their life in connective tissue (resident cells):
  • fibroblasts, fibrocytes, myofibroblasts
  • reticular cells
  • adipocytes
  • stem cells

• Cells originating from hemopoietic stem cells in bone marrow, then circulate in blood, then move into connective tissue (resident cells):
  • macrophages
  • mast cells

• Transient cell population originating from hemopoietic stem cells in bone marrow, that migrate into tissue from the blood (wandering cells) in response to specific stimuli (i.e. tissue injury)
  • lymphocytes, plasma cells, neutrophils, eosinophils, basophils, monocytes

• Melanocytes (pigment cells) - neural crest origin.

1. Connective Tissue Resident Cells

• Fibroblasts
  • active cells
    • fine chromatin, prominent nucleolus, basophilic cytoplasm, abundant RER, GA, mitochondria
  • synthesis of the ECM
• Fibrocytes
  • quiescent cells
  • smaller, usually spindle-shaped, dark elongated nucleus, eosinophilic cytoplasm

Fibroblast vs. Fibrocyte - Janqueira

• Myofibroblasts
  • Actin and myosin myofilaments.
  • Wound contraction.
• Reticular Cells
  • modified fibroblasts
  • active (fine chromatin, prominent nucleolus, basophilic cytoplasm, abundant RER, GA, mitochondria)
  • synthesis of reticular fibres (type III coll.)
  • in reticular tissue (bone marrow, spleen, lymph nodes)
• Pigment Cells
  • neuroectodermal origin
  • branched shape
  • cytoplasm filled with melanin granules (dark brown)
  • iris, ciliary body, choroid, epidermis
• Adipocytes
  • unilocular
    • single lipid droplet surrounded by rim of cytoplasm with nucleus
    • white adipose tissue - subcutaneous tissue, around the kidney, neurovascular bundle
    • energy storage, insulation, cushioning of vital organs, secretion of hormones
  • multilocular
    • smaller, many small lipid droplets
    • abundance of mitochondria
    • brown adipose tissue
    • new-borns around the neck, kidney, between shoulder blades
    • thermogenin in inner mitochondrial membrane
    • heat generator

White Adipocytes (H&E) - Young, Health 2000

Brown Adipose Tissue (H&E) - Mescher 2010

2. Connective Tissue Wandering Cells

• Plasma Cells
  • eccentrically placed nucleus– cartwheel appearance (clumps of heterochromatin)
  • immunoglobulins production (abundant expanded cisternae RER, GA)

Plasma Cell (H&E) - LF1 Dp. Hist. Emb,

• Leukocytes
  • lymphocytes – lamina propria of GIT and respiratory s.
  • monocytes – precursors of macrophages
  • eosinophilic granulocytes – lamina propria of GIT; allergic reactions, parasitic infections
  • basophilic granulocytes – release of heparin and histamine; allergic reactions
  • neutrophilic granulocytes – phagocytic; inflammation
• Mast Cells (heparinocyte)
  • granules
    • heparin (anticoagulant, sulph. GAG)
    • histamine (increases permeability of venules)
    • metachromatic, PAS+, alcian blue
  • IgE receptors on the plasma membrane – hypersensitivity reaction (allergy)
  • loose CT around vessels, papillary layer of dermis, digestive and respiratory tract mucosa

Mast Cells (alcian blue) - LF1 Dep. Hist. Emb.

• Macrophages
  • phagocytic, derived from monocytes migrated from blood into CT
  • wandering macrophages migrate from blood stream into CT at sites of infection or inflammation to carry on phagocytosis
  • fixed macrophages reside in a particular tissue - alveolar macrophages in the lungs, splenic macrophages in the spleen
  • phagocytosis of bacteria and cell debris, destruction of aged red blood cells, immune response (processing and presenting antigens)
  • mononuclear phagocyte system (e.g. Langerhans cells, macrophages, microglia, osteoclasts, dendritic cells)

Macrophages in Lungs

Sources and References

• RNDr. Lucie Lantova, Institute of Histology and Embryology LF1