Connective Tissue

Classification (Type)

Proper

• Loose
• Dense
  • Regular
  • Irregular

Supporting

• Adipose tissue
• Elastic tissue
• Mucus tissue
• Hematopoietic

Special properties

• Cartilage
• Bone

Classification (Origin)

Hematopoietic

For more, see here: Hematopoeisis

• Red blood cells
• White blood cells
• T/B cells
• Mast cells
• Microglia
• Langerhans cells
• Osteoclasts

Undifferentiated mesenchymal

• Fibroblasts
• Adipocytes
• Chondrocytes
• Osteoblasts
• Mesothelial cells
• Endothelial cells
• Smooth muscle cells

Cellular Components

Fibroblasts

Structural, produce fibers and ground substance.

Adipose cells

Unilocular adipocytes

Function: Fat cells, energy storage.
Features: Large fat cells which include one lipid droplet. Lots of open space with a thin cytoplasm along edge.

Multilocular adipocytes

Function: Only present in neonates as a form of heat generation
Features: Include multiple lipid droplets and mitochondria

Macrophages

Function: Phagocytic cells which take up debris
Features: Visible vesicles

Plasma cells

Function: Derived from B cells, produce immunoglobulins.
Features: Eccentric nucleus, cartwheel arrangement of heterochromatin, abundant RER.

Mast cells

Function: Basophilic molecules containing pharmacologically active substances mediating allergy response. IgE on surface trigger an allergy response (heparin, histamine, leukotrienes, proteoglycans, ECF-A).
Features: Large basophilic granules around a nucleus. Stains dark.

Amorphous tissue

Known as ground substance. Molecules composed of varied protein and sugar ratios.

Glycosaminoglycans

For more, see here: Carbohydrates and Sugar Code Primer > Glycosaminoglycans
Disaccharide sugars containing amino sugars. Hold water. An example is hyaluronic acid (in eye).

Proteoglycans

A core protein connected to glycosaminoglycan chains. Brush like.

Glycoproteins

For more, see here: Protein Primer > Glycoproteins

Globular proteins with branched sugar residues found in basement membrane. Binding sites for cells, collagen, and heparan. Examples include fibronectin, laminin, and integrins.

Fibrous components

Collagen fibers

For more, see here: Protein Primer > Collagen. Seen as thick fibers with striations.

Functions

• Adhesion
• Skeletal (bones, cartilage)
• Protective (skin)
• Messenger

Synthesis

1. Pre-procollagen translated from mRNA
2. Procollagen formed after cleavage of signal peptide
3. Hydroxylation/glycosylation (using Vitamin C)
4. Alignment of chains to form triple helix
5. Packaging into secretory vesicles, secretion
6. Formation of tropocollagen
7. Bundling to form fibril → fiber → fiber bundle

Clinical pearls

Scurvy: Resulting from Vitamin C deficiency
Ehlers-Danlos (VI): Faulty hydroxylation
Ehlers-Danlos (VII): Decreased peptidase activity (step 6)

Elastic fibers

Formed from oxytalan (fibrillin) and elastin. Oxytalan resists tension while elastin provides flexibility. Appears thin and brownish-red (stains with orecin).

Clinical pearl: Marfan Syndrome

Inherited mutation in fibrillin causing a weakened aorta, potentially leading to aortic dissection.

Reticular fibers (type III collagen)

Found in lymphoid organs and tissues. Forms scaffolding allowing lymphocytes to take refuge as the mighty fluid current rushes past. Turns black with silver stains.