Lecture 3: Connective Tissue

Overview of Connective Tissues

• Functions of Connective Tissue (CT):

  1. Binds, supports, and strengthens other body tissues.

  2. Acts as a major transport system (e.g., blood is a connective tissue).

  3. Serves as a major storage site for energy reserves (e.g., adipose tissue).

Features of Connective Tissues

• Differences from Epithelial Tissues:

  • CT is NOT found on body surfaces (e.g., bones, cartilage, blood).

  • CT can be highly vascular (exception: cartilage is avascular, tendons have little blood supply).

• Similarities to Epithelial Tissues:

  • CT is supplied by nerves (exception: cartilage).

Composition of Connective Tissue

• CT = ECM + Cells

• The structure of the ECM largely dictates the qualities of connective tissues

  • Example:

    • Cartilage: ECM is firm and rubbery.

    • Bone: ECM is hard and inflexible.

CT Extracellular Matrix (ECM)

• Components of ECM:

  • Ground Substance (GS)

  • Protein Fibres

  • ECM = GS + Fibres

Ground Substance

• GS can be composed of:

  • Water

  • Proteins (e.g., gelatin)

  • Polysaccharides (sugars)

  • Glycosaminoglycans (GAGS or mucopolysaccharides) which combine with core proteins to form proteoglycans. - Proteoglycans = Core protein + GAG

Terminology

• Glycosaminoglycans (GAGS):

  • Long unbranched polysaccharides with repeating disaccharide units e.g amino sugar, uronic sugar

Types of GAGS

• Sulphated GAGs:

  • Dermatan sulphate - In skin, tendons, BV

  • Heparin sulphate

  • Keratan sulphate - In bone, cartilage

  • Chondroitin sulphate - Support and provide structural integrity to cartilage, bone, skin, BV

    -These bind directly to core proteins to form proteoglycans

• Non-sulphated GAG:

  • Hyaluronic acid (not directly bound to protein, attracts water for jelly-like consistency). Instaed it’s joined to multiple Proteoglycans, which is good at retaining water (acts as physcial buffer, traps water)

Applications of GAGS

• Hyaluronidase:

  • Enzyme produced by white blood cells and some bacteria, which liquefies ground substance for easier movement.

• Hyaluronic Acid:

  • Functions to bind cells, lubricate joints, and maintain shape of eyeballs.

    -These make GS more liquid allow for easier movement

Abnormal ECM and Diseases

• Exophthalmos:

  • Condition caused by abnormal deposition of glycosaminoglycans affecting the eye, particularly in cases of autoimmune thyroid disease.

Types of Connective Tissue Fibres

• There are three main types of CT fibres in the ECM:

  1. Collagen Fibres:

     • Thick, strong, flexible to pulling forces, found in bone, cartilage, tendons, and ligaments, comprising 25% of the body.

  2. Reticular Fibres:

     • Composed of fine bundles of collagen with glycoprotein coating, providing support and forming networks in tissues like blood vessels and adipose tissue. Made by fibroblasts

  3. Elastic Fibres:

     • Thinner than collagen, composed of elastin and fibrillin, allowing tissues to stretch, stability, and strength (found in skin and blood vessels).

Marfan Syndrome

• A hereditary defect affecting elastic fibres caused by mutations in the fibrillin gene, leading to cardiovascular issues. Individuals often have tall stature and long limbs.

Cell Types in Connective Tissue

• Fibroblasts:

  • Widely distributed, secrete ECM components (fibres and ground substance).

• Adipocytes (fat cells):

  • Stores fat (triglycerides), found under skin and around organs.

• Macrophages:

  • Phagocytic cells involved in immune response, sites of inflammation, injury

• Plasma cells:

  • Produce antibodies, derived from B-lymphocytes. Found in gut, lung, spleen, salivary glands

• Mast Cells:

  • Produce histamine for inflammation Found alongside BV’s

• Leukocytes:

  • White blood cells involved in immune defence. e.g neutrophils, eosinphils

Classification of Connective Tissue

• Embryonic:

  • Mesenchyme and Mucous CT.

• Mature:

  • Connective Tissue Proper (loose and dense varieties), Fluid (blood and lymph), Supporting (cartilage and bone).

Types of Embryonic Connective Tissues

1. Mesenchyme: The first connective tissue to develop in the embryo, giving rise to all other connective tissues.

2. Mucous CT: Also known as Wharton's jelly, found in the umbilical cord, providing support and flexibility.

Types of Mature Connective Tissues

1. Loose Connective Tissue:

   • Loose Areolar Tissue - Has collage, reticular, elastin fibres. Strength, elasticity, support

   • Loose Adipose Tissue - Adipocytes dominant (Fat). Insulation, energy source, temp control

   • Dense Regular Tissue - Reguarly arranged collagen for slow healing and attatchement. Tendons, ligaments, aponeuroses.

2. Dense Connective Tissue:

   • Dense Irregular Tissue - Made of collagen fibres providing strength and resistance. Ski. lymph nodes, digestive tract.

   • Dense Elastic Tissue - Has elastin and collagen fibres for stretch found in arteries and aorta

3. Supporting Connective Tissues Cartilage:

   • Hyaline Cartilage - Dense network of collagen and elastin Fibres for movement. Nose, trachea, brnochi

   • Elastic cartilage - Elastin, collagen fibres, chondrocytes for flexiblity and strength

   • Fibrocartilage - Tough, inflexible found in joints and tendons

4. Fluid Connective Tissues:

   • Blood - Consists of blood plasma (liquid ECM) and formed elements (red cells, white cells, platelets)

     “Formed elements” of blood:

     1. Erythrocytes - Transport oxygen and carbon dioxide

     2. Neutrophils, Monocytes (Macrophages) - Engluf bacteria and are phagocytic

     3. Basophils (mobile), mast cells (immobile) - Release substances to intensify the inflammatory reaction

     4. Eosinophils - used in acute alergic responses

     5. Lymphocytes - Involved in the immune response

     6. Platelets - For clotting

5. Supporting CT - Bone or osseous Tissue:

   • Bone tissue can either be spongy or compact

   • Spongy Bone - Lacks osteons, stores trioglycerides (yellow marrow) and produces blood cells

   • Compact Bone - Contains osteons, function is protection and support, stores calcium and phosphorous

Structure of Bone

1. Osteogenic Cells - Start to lay down collagen, become trapped and become osteoblasts

2. Osteoblasts - Bone-forming cells, lays down more collagen, mineralization process starts

3. Osteocytes - Mature bone cells trapped in the ECM, they maintain bone tissue and involved in exchange of nutrients and waste

4. Osteoclasts - They break down bone, and formed from the fusion of blood monocytes

Structure of Osteons

1. Lamellae - Rings of mineral salts for hardness which form collagen and others for strength

2. Lacunnae - Small spaces between lamellae othat contain mature bone cells (osteocytes)

3. Canaliculi - Coontains EC fluid and porovides routes for oxygen, nutrients and waste

4. Central (Haversian) Canal - Has blood, lymph, and nerves

Bone Remodeling Process

• Involves osteoblast and osteoclast activity to maintain or repair bone structure, particularly after fractures.

Summary of Connective Tissues

• Composed of cells and the ECM, including types of fibres and ground substance. Key functions include support, binding, protection, storage, and transportation of substances.