Chapter 14- Connective Tissue and Bone Development

Connective tissue

Collagen and fibric substances inside tissues

Tendons

Connective tissue that connects muscle to bone

Ligaments

Connective tissue that connects bone to bone

Collagen

20-30% of the protein in the body, 33% glycine and 10% hydroxyproline, hydroxyproline measurement is used to determine meat collagen content

Procollagen

Three strands are cross linked by disulfide bonds near the c-terminal end and initiates triple helix formation, is soluble

Tropocollagen

Formed by hydrolyzing away peptide fragments at both ends, is not soluble

Collagen fiber organization

Lysines and prolines are converted into hydroxyproline and hydroxylysine that allows H-bonds in tropocollagens using Vitamin C

Collagen cross linking

Lysyl oxidase has a key regulatory role, uses lysines and hydroxylysines for oxidation, tropocollagen aligns to form collage and forms cross links

Heating in collagen cross linking

Heating destroys the structure of collagen and the collagen is converted to gelatin

Beef tenderness

Fibroblasts synthesize collagen and other fibrotic proteins in connective tissue and secrete enzymes catalyzing collagen cross linking

Fibroblasts

Derived from mesenchymal multipotent cells and come from FAPs

FAPs (Fibro/adipogenic cells)

Commitment to either adipogenic or fibrogenic lineages can be affected by TGFB or Zfp423, TGFB leads to fibrogenic differentiation

Inflammation

Induces TGFB signaling, pro-inflammatory: IL-1, IL-6, IL-12, IL-18, and TNF-a, anti-inflammatory: TGFB, IL-4, IL-10, IL-13

Injection sites

Injection induces local inflammation and collagen deposition

Bones

Accounts for a lot of waste, composed of matrix and fibers, elasticity comes from embedded collagen fibers, can be considered a specialized connective tissue

Bone growth and development

Growth determines the frame size of an animal and size of carcass, protects vital organs and serves as a storage depot for various compounds

Bone formation

Cartilage forms first and is replaced by bone tissue

Osteocytes

Originate from osteoblasts, surrounded by the bone matrix and form bone tissue

Osteoclasts

Release enzymes that digest the mineral components of bone matrix, regulate blood calcium level

Red marrow

Chief blood cell forming organ of the adult and is found in spongy bone of the epiphysis of long bones and main bodies of ribs, sternum and vertebrae

Yellow marrow

Composed mainly of adipose tissue and found in the medullary cavity of bones

Bone marrow

Aging is associated with increased adipose deposition inside bone marrow and increased mineralization

Bone maturation

Growth termination doesn’t occur simultaneously, sacral vertebrae prior to lumbar before thoracic vertebrae, and is used to judge maturity of carcasses

Bone hormones

IGFs from the liver and bone tissue, stimulate osteoblasts, promote cell division and enhance bone matrix deposition, T3 and T4 stimulate osteoblasts, and insulin increases synthesis of bone proteins

Other bone hormones

Estrogen and testosterone also stimulate growth and mineral deposition, PTH, calcitriol and calcitionin induce remodeling and calcium homeostasis

Vitamin D metabolism

Major sources are skin and diet, metabolize in liver, activate in kidney into 1,25 vit D which promotes calcium absorption and mobilization

Calcium levels

Circulatory levels regulate osteogenic cell differentiation, high levels promote osteoblast proliferation and induces osteoclast apoptosis