Connective tissue

What is connective tissue

• a diverse tissue type that supports, binds, and protects body structures

General characteristics of connective tissue

• Abundant extracellular matrix (ECM)

• Composed of cells + fibers + ground substance

general functions of connective tissue

• Structural support,

• Protection and cushioning

• Transport (blood),

• Energy storage (adipose tissue)

• Immune defence

Cellular component of connective tissue

• resident cells

• transient/immune cells

Resident cells - permanently present

• Fibroblasts – ECM synthesis (collagen, elastin, ground substance)

• Chondrocytes – cartilage-producing cells and maintain cartilage

• Osteocytes – mature bone cells and maintain bone

• Adipocytes – fat storage and insulation

Transient/Immune Cells

• Macrophages – phagocytosis, immune defense

• Mast cells – secrete histamine (inflammation)

• Plasma cells – produce antibodies

• Neutrophils - First responders, phagocytose bacteria - Multi-lobed nucleus, found in pus

• Eosinophils - Defend against parasites, modulate allergies - Bilobed nucleus, eosinophilic granules

ECM is composed of?

• Ground substance

• Fibres

• all the components of the body located outside of the cells.

Key proteins in ground substance of ECM

• Composed of proteoglycans (e.g., aggrecan),

• glycosaminoglycans (e.g., hyaluronic acid)

• glycoproteins

• Provides hydration, resilience, and molecular transport

Key proteins in fibres of ECM

• Collagen – high tensile strength, found in tendons, ligaments, skin

• Elastin – provides flexibility, found in arteries, lungs, skin

• Reticular fibers – form a fine supporting network (lymphoid organs)

Ground substance appearance and functions

Appearance:

• Semifluid

• Gelatinous

• Calcified

  FUNCTIONS:

• Functions to support and bind cells together

• Provides a medium for exchange of materials between blood and cells

• Stores water

• Influences how cells/tissues develop, migrate, proliferate, change shape, influences metabolic function

Proteoglycans

• Proteoglycans are made up of a core protein to which glycosaminoglycans (GAGs) are attached

• GAGS consist of repeating units of disaccharide subunits

• Chondroitin sulphate, keratin sulphate, heparan sulphate and hyaluronan are the most common GAG

Types of connective tissue proper

1. Loose connective tissue

2. Dense connective tissue

Types of loose connective tissue

• Areolar Tissue – under epithelia, supports and cushions

• Adipose Tissue – stores energy, insulates, cushions organs

• Reticular Tissue – found in spleen, lymph nodes, and bone marrow

Types of dense connective tissue

• Dense Regular – parallel collagen fibers (e.g., tendons, ligaments)

• Dense Irregular – randomly arranged fibers (e.g., dermis, joint capsules)

• Elastic Tissue – elastin-rich (e.g., arteries, lung tissue)

Types of cartilage

• Falls under supportive connective tissue

• Hyaline Cartilage – smooth, glassy (e.g., joints, trachea)

• Elastic Cartilage – flexible (e.g., ear, epiglottis)

• Fibrocartilage – shock-absorbing (e.g., intervertebral discs)

Types of bone

• Falls under supportive connective tissue

• Compact Bone – dense, strong (outer layer of bones)

• Spongy Bone – porous, contains marrow (inner bone, ends of long bones)

Components of the blood

• Type of liquid connective tissue

• Cells: Red blood cells, white blood cells, platelets

• Matrix: Plasma (contains proteins like albumin, fibrinogen)

Areolar connective tissue proper

• is the most abundant

• Contains all three fibres (collagen, reticular and elastic)

• location: surrounds blood vessels, nerve bundles, muscles, and organs. It also fills the spaces between organs and connects your skin to your underlying muscle

• Primary functions are support, elasticity and strength

Adipose connective tissue proper

• contains adipocytes, primary function is to store triglicerides

• Primarily located beneath the skin but also found surrounding internal organs

• to provide insulation, protection and is an energy store

Reticular connective tissue proper

• only contains reticulin fibres

• is to form a protective framework/scaffold that surrounds the liver, spleen and lymph nodes

• Within spleen the RCT assists with the filter of blood and removal of old blood cells

Dense regular connective tissue

• Contain collagen fibres arranged in parallel rows

• Found in ligament and tendons

• Tissues structures withstand pulling along axis of fibres (tension)

• Does not have a good blood supply and takes longer to heal

Dense irregular connective tissue

• Collagen fibres are randomly arranged but closely knitted together

• Can withstand high pressure and pulling forces

• Found in skin, Heart and membranes surrounding cartilage and bone

Elastic connective tissue

• Contains predominantly elastic fibres with fibroblasts between them

• Located in lung tissue, walls of arteries, trachea, bronchial tubes, to name a few

• Allows stretching of organs, is strong and can recoil to original shape after being stretched

• Important property in lungs (recoils in exhaling) and arteries (recoil between heart beats to allow blood to flow)

What is cartilage

• a strong, flexible connective tissue found in various parts of the body. It provides structural support, shock absorption, and smooth movement in joints

• it is avascular

• composed of chondrocytes in ECM

Why is cartilage important?

• Essential for joint function and mobility

• Acts as a cushion to reduce friction and absorb shock

• Plays a key role in growth and development of bones

Hyaline cartilage

• Is strong and flexible

• consists of collagen fibres, cartilage cells eg chondrocytes

• Acts as a shock absorber reducing friction around joints and absorbs shock during movement

• Found in the rib cage and airways

• Plays a key role in the formation of long bones during foetal development

Fibrocartilage

• is the strongest of the three cartilages

• Its strength is provided by rows of chondrocytes and collagen

• Consists of densely packed collagen fibres

• it can withstand greater pressure

• Main function is support and protection

• distributes pressure, and provides structural support

• Provides stability and flexibility in joints that undergo repeated strain and compression

• has some regenerative capacity

Elastic cartilage

• Its has more elastic fibres than hyaline cartilage

• Can withstand greater movement and bending

• Provides flexibility while maintaining structural integrity and is more pliable

• Plays a role in sound transmission

What is bone

• a rigid connective tissue that forms the skeleton of vertebrates.

• It provides structural support, protection, and movement while serving as a reservoir for minerals and housing the bone marrow.

Key features of bone

• Mineralized tissue – primarily composed of calcium phosphate and collagen fibers, giving it strength and flexibility

• Living tissue – constantly being remodeled through bone resorption and formation

• Highly vascular – unlike cartilage, bone has a rich blood supply which aids in healing and regeneration.

• Contains osteocytes (bone cells) embedded in an ECM of collagen and mineralized components.

Bone structures

1. Compact Bone – Dense and forms the outer layer of bones, providing strength and protection

2. Spongy Bone (Cancellous Bone) – Lighter, less dense, and found primarily in the inner portions of bones, such as the ends of long bones, providing support and flexibility

3. Bone Marrow – Found in the cavities of spongy bone, bone marrow is the site of blood cell production (hematopoiesis).

Functions of bone

• Support: Provides the framework for the body

• Protection: Shields vital organs like the brain, heart, and lungs.

• Movement: Works with muscles to facilitate body movement

• Mineral Storage: Stores calcium and phosphorus for metabolic processes

• Hematopoiesis: Production of blood cells in the bone marrow.

Bone remodelling

Reabsorption:

• osteoclasts (bone-resorbing cells) breaking down old or damaged bone

• Osteoclasts secrete enzymes and acid to dissolve the mineralized bone matrix, releasing calcium and phosphates into the bloodstream.

• This phase helps to remove damaged bone and regulate mineral homeostasis

Reversal:

• After resorption, the area is prepared for new bone formation. •Preosteoblasts (precursors to osteoblasts) are recruited to the site, and the bone matrix is temporarily left in a "reversed" state, ready for new bone cells to be deposited

Formation:

• Osteoblasts produce a new osteoid (organic bone matrix) that is later mineralized with calcium phosphate to form hard bone tissue. •Osteoblasts secrete collagen and other proteins to form a soft bone matrix, which mineralizes over time into mature bone

• This new bone helps maintain bone strength and density

Mineralization:

• The osteoid produced during formation gradually becomes mineralized, primarily with hydroxyapatite crystals (calcium phosphate), which gives the bone its strength and rigidity

Components of blood

• Red Blood Cells (Erythrocytes): Carry oxygen from the lungs to tissues and carbon dioxide away from tissues to the lungs.

• White Blood Cells (Leukocytes): Play a key role in the immune response, defending the body against infections.

• Platelets (Thrombocytes): Involved in blood clotting, helping to prevent excessive bleeding.

• Plasma: The liquid portion of blood that contains water, electrolytes, proteins, nutrients, hormones, and waste products. Plasma makes up about 55% of blood volume

Function of blood

• Transport of oxygen, carbon dioxide, nutrients, hormones, and waste products

• Immunity: White blood cells defend the body against pathogens.

• Thermoregulation: Helps regulate body temperature by distributing heat

• Clotting: Platelets prevent blood loss by forming clots at injury sites

What is lymph

• it is a form of liquid connective tissue, primarily found in the lymphatic system

• is rich in white blood cells

Components of lymph

• Lymphocytes: Specialized white blood cells involved in immune responses.

• Lymph Plasma: Similar to blood plasma, but contains fewer proteins and more white blood cells.

• Intercellular Fluid: Fluid derived from tissue spaces.

Function of lymph

• Helps maintain the body’s fluid balance by collecting excess tissue fluid and returning it to the bloodstream

• Plays a critical role in immune defence, filtering out harmful pathogens and debris

• Transports fatty acids and fat-soluble vitamins from the digestive system to the bloodstream

Importance of liquid connective tissue

• essential for maintaining homeostasis

• is critical for oxygen delivery, nutrient distribution, and waste removal

• plays a vital role in the immune system, protecting the body from infection and aiding in the absorption of fats