Connective Tissue: Types and Composition

• Connective tissue binds, supports, and strengthens body tissues
• It is a major transport system with blood and a site for energy reserves like fat or adipose tissue

Features of Connective Tissues Contrast with Epithelia

• Connective tissue isn't on body surfaces, unlike epithelia
• Cartilage and tendons show exceptions - cartilage is avascular, while tendons have minimal blood supply
• Connective tissue is usually highly vascular
• Connective tissue, like epithelia, is supplied by nerves, but cartilage is an exception

Connective Tissue Composition

• Connective tissue is composed of extracellular matrix (ECM) and cells
• CT = ECM + Cells

Extracellular Matrix Composition

• ECM consists of ground substance (GS) and protein fibers
• ECM = GS + Fibres
• Protein fibers in the ECM are secreted by the cells in the ECM/CT
• ECM structure dictates connective tissue qualities
• Cartilage has a firm and rubbery ECM, while bone has a hard and inflexible ECM

Ground Substance

• Ground substance, a component of the ECM, is a mixture containing: water, proteins (like gelatin), and polysaccharides (sugars)
• GS = H2O + proteins + polysaccharides
• The sugars consists of Glycosaminoglycans (GAGS or mucopolysaccharides)
• GAGS join with core proteins, which forms proteoglycans

Glycosaminoglycans (GAGS)

• Glycosaminoglycans (GAGS) "mucopolysaccharides" are long, unbranched polysaccharides with repeating disaccharide units
• N acetylglucosamine is an example of an amino sugar
• glucuronic acid is an example of a Uronic sugar

GAG Examples

• Sulfated GAGs like dermatan sulfate, heparin sulfate, keratan sulfate, and chondroitin sulfate bind to core proteins to form proteoglycans (PGs)
• Hyaluronic acid is a non-sulphated GAG example
• Hyaluronic acid does not bind directly to the protein backbone but links to various PGs

Hyaluronic Acid

• Hyaluronic acid is unusual because it is not sulphated or covalently bound to a core protein
• Due to its polar nature to collectively trap water, creating a jelly-like ground substance

GAG functions

• Hyaluronic Acid binds cells, lubricates joints, and maintains the shape of the eyeball
• Hyaluronidase breaks down ground substance, making it more liquid and is produced by white blood cells, sperm, and some bacteria to facilitate sperm access to the egg

GAGs Application

• Chondroitin Sulphate supports and provides adhesive features in cartilage, bone, skin, and blood vessels
• Keratan Sulphate exists Found in bone, cartilage, and the cornea of the eye
• Dermatan Sulphate exists Found in skin, tendons, blood vessels, and heart valves
• Abnormal ECM ground substance leads to the deposition of glycosaminoglycans and the influx of water increasing the orbital contents

Abnormal Periorbital ECM

• Abnormal Periorbital ECM and Thyroid Disease (Exophthalmos) is more common in younger women
• Goitre and swelling of the thyroid gland occurs
• Autoimmune over-activation of thyroid causes Goitre
• Autoimmune action on fibroblasts in ECM of eye causes exophthalmos
• The deposition of glycosaminoglycans and the influx of water increase the orbital contents

ECM Composition

• ECM is composed of ground substance and protein fibers

Types of Connective Tissue Fibres

• There are 3 different types of connective tissue fibres in the extracellular matrix (ECM): collagen fibers, reticular fibres and elastic fibres
• Proteins secreted by the cells in ECM are made of protein fibers

Collagen

• Composed of thick collagen fibers, connective tissue is strong but flexible to resist pulling forces
• Collagen features vary, such as in cartilage where there is more water content compared to bone
• Collagen makes up 25% of abundant protein of the body
• It's found in bone, cartilages, tendons, and ligaments and is arranged in parallel bundles

Reticular fibres

• Consists of composed of coating Glycoprotein collagen, in fine bundles with glycoprotein
• Made by fibroblasts
• Gives support and strength
• Forms part of the basement membrane
• Thinner, branching spreads through tissue and adipose tissue, nerve fibres, and smooth muscle tissues

Elastic fibres

• Elastic fibres are thinner than collagen fibres, are made of Fibrous network
• The protein elastin is covered by the glycoprotein fibrillin, this gives more strength and stability
• It can be stretched to 150% without breaking, and is found in skin, blood vessels, and lung

Marfan Syndrome: Genetic Connective Tissue Disorder

• The disease stems from a dominant mutation on chromosome 15, impacting the fibrillin gene
• Fibrillin, a glycoprotein (350 kDa), provides structural support for elastin
• The body produces Transforming Growth Factor beta(TGFb) which increasing growth because it does not bind normally to fibrillin to keep it inactive (theory)
• This condition occurs in 1 in 20,000 live births

Marfan Features

• Usually tall, long limbed, and often with a chest deformity (e.g. protruding or collapsed sternum)
• With medical vigilance to control blood pressure patients will hopefully have a normal life span
• Weakened heart valves and arterial walls

Connective Tissue Cells

• Two common types are fibroblasts and adipocytes

Fibroblasts

• Key Functions: secretes the matrix with fibers and ground substance
• Primary Location: widely distributed in connective tissues; migratory

Adipocytes

• Key Functions: store fat (triglycerides)
• Primary Location: under the skin and around organs

Other cells found in Solid CT

• Macrophages (Histiocytes); phagocytic cells fixed and wandering forms in connective tissues (CT), Wandering in CT: sites of infection/inflammation/ injury
• Plasma cells; From B-lymphocyte produce antibodies
• Mast cells; Produce histamine that dilates vessels
• Leukocytes; migrate out from blood

Classification of Connective Tissue

• Classification:
  • Embryonic
  • Mature

Embryonic Connective Tissues

• Mesenchyme embryonic Tissue consists of connective tissue cells (mesenchymal cells) in a semi-fluid ground substance containing reticular fibres
• Mucous CT is a Tissue with widely scattered fibroblasts embedded in jelly-like ground substance that supports the umbilical cord of foetus.

Mature Connective Tissues

• Fluid, Supportive and Proper
• Five variations will be reviewed

Loose Connective Tissue: Areolar

• Key Features: presence of collagen, reticular, and elastic fibers
• Key Functions:Provides strength, Elasticity, and Support
• Primary Location: widely distributed around almost every structure. Like a “packing material".

Loose Connective Tissue: Adipose

• Sub-type: Adipose
• Key Features: Adipocytes , Central triglyceride droplet
• Insulates and is a temperature control that is an energy source
• Primary Location: Found with areolar connective tissue (incl. fibroblasts). Buttocks; flanks; abdomen; orbit of eye.
• White adipose (energy storage) and Brown adipose (heat production)

Dense Regular Connective Tissue

• Structures formed from them Tendons (muscle to bone); Ligaments (bone to bone); aponeuroses (muscle to muscle)
• Collagen fibres are not a living tissue.
• Regularly arranged collagen such as tendons (pulling along the fibre axis) that has Shiny white colour.
• Slow healing but with good Attachment.
• Made of many fibres fewer cells

Supporting CT: Hyaline Cartilage

• Primarily located at anterior ends of ribs; respiratory cartilage – i.e. nose, trachea, bronchi, the Nasal septum, ends of long bones.
• Abundant. and Relatively weak but with resilient gel in which fibres are present but not obvious
• Offers good Flexibility and movement.
• Dense network of collagen and elastic fibres

CT: Bone

• Compact bone is the Outer layer of bone and forms the shaft of long bones
• Cortical bone is made of rod-shaped units which are either Osteons or Haversian systems
• Spongy bone is the Porous inner bone tissue that lies underneath compact bone
• Bone is also known as Cancellous bone and they Lacks osteons

Compact Bone

• Has osteons that Store calcium and phosphorous in bone which gives Protection & support
• Spongy compact bone lacks osteons while and produces blood cells red marrow) and stores triglycerides (yellow marrow).

Bone cells

• Four cell types are found in bone and is all the detail need to know bone

Osteogenic

• Mesenchymal stem cells that develop, starts to lay down collagen and becomes Osteoblasts

Osteoblasts

• Lay down more collagen and mineralization process starts.

Osteocytes

• Mature bone cells derived from osteoblasts trapped within the extracellular matrix and Involved in exchange of nutrients and wastes. Have gap junctions.

Osteoclasts

• Large, Multinucleated cells that are Formed from the fusion of blood monocytes and Break-down bone

Osteon (Haversian Systems) Structure

• Composed of four parts
• The basic unit of compact bone is the osteon

Structure: Lamellae

• Made of concentric rings of mineral salts for hardness with calcium phosphate and calcium hydroxide that together form hydroxyapatite
• Also composed of collagen for tensile strength

Structure: Lacunae

• They consists of small spaces between lamellae that contain mature bone cells called osteocytes

Structure: Canaliculi

• "Minute canals" contains EC fluid and minute osteocytic processes that radiate from lacunae which provide routes for oxygen, nutrients and waste

Structure: Central (Haversian) canal

• Has blood, and nerves

Bone Fracture: Remodeling

• Osteoclasts reabsorb dead bone
• Chondroblasts form hyaline cartilage callus
• Osteoblasts lay down new bone
• Osteoclasts remodel new bone

5. Liquid Connective Tissue

• Consists of blood plasma and formed elements, notably the red cells, white cells and platelets
• (Blood CT=ECM (plasma) + Cells)

Blood: Formed Elements

• Erythrocytes transport oxygen and carbon dioxide
• Leukocytes fight off combat disease:
  • Neutrophils and monocytes, phagocytic engulfing bacteria
  • Basophils mobile and Mast cells tissues are released substance’s intensifies it reaction
  • Eosinophils are involved in acute allergic response and are parasitic
  • Leukocytes or Lymphocytes
• Platelets are involved from megakaryocytes in red marrow with good clotting.
• Connective tissue has both cells and matrix between them