Ch 3.4 Connective Tissue Supports and Protects

What is a hallmark of connective tissue?

• its cells are typically widely dispersed within an extensive extracellular matrix (ECM).

What is a matrix?

A non-living material composed of 2 main components:

• protein fibers and ground substance

What is ground substance?

• This is an unstructured material that fills the space between the cells and contains the fibers.

  • It can range from fluid to gel-like to rigid, consisting primarily of water, interstitial fluid, cell adhesion proteins, and proteoglycans (large complexes of protein and glycosaminoglycans, e.g., hyaluronic acid, chondroitin sulfate), which trap water and provide resilience.

What are Protein Fibers?

• These provide strength and support within the matrix. The three main types are collagen, elastic, and reticular fibers.They are essential components of connective tissue that help maintain structure and flexibility.

What are Connective tissues critical functions?

Support and connect, protection, transport, energy storage, immunity & defense

What is the support and connect function of Connective Tissue?

• They form the structural framework of the body, binding organs and cells together.

  • Examples include ligaments (connecting bone to bone) and tendons (connecting muscle to bone), as well as the fibrous capsules around organs.

What is the Protection function of connective tissue?

• Connective tissues encapsulate delicate organs (e.g., fibrous pericardium, dura mater) and provide the skeletal framework (bone, cartilage) that protects vital internal structures

  • (e.g., cranium protecting the brain, rib cage protecting the heart and lungs).

What is the Transport function of Connective tissue?

• Fluid connective tissues, particularly the hematopoietic system (blood and lymph), facilitate the transport of nutrients, gases (oxygen, carbon dioxide), hormones, and waste products throughout the body.

What is the energy storage function of connective tissues?

• Adipose tissues (fat) specialize in storing energy in the form of triglycerides. Adipose tissue also serves as thermal insulation, cushions organs, and contributes to body contour.

What is the Immunity and defense function of Connective Tissue?

• Connective tissues house various immune cells (e.g., mast cells, macrophages, lymphocytes) that defend the body against pathogens and initiate inflammatory responses.

What are the Embryonic Connective Tissue

types include mesenchyme and mucous connective tissue, which give rise to other connective tissue types and are crucial for development.

What is Mesenchyme?

• the first connective tissue to develop in the embryo, originating from the mesoderm. It is a loosely organized embryonic tissue that serves as the universal stem cell source for all adult connective tissue types, including fibroblasts, chondroblasts, and osteoblasts.

What is Mucous Connective Tissue?

Also known as Wharton’s Jelly, its a specialized jelly-like material found primarily in the umbilical cord. It provides cushion, support, and protection for the umbilical blood vessels. While present at birth, it typically degenerates shortly thereafter.

What are the 3 kinds of Connective Tissue Classification?

• Connective tissue proper (Viscous ground substance and diverse population of cell types and fibers),

• Supportive Connective Tissue (Designed to provide structural support) ,

• Fluid Connective Tissue (Liquid matrix and circulates through the body)

What are the 2 kinds of Connective Tissue Proper?

Loose Connective Tissue & Dense Connective Tissue

Whats the Difference Between Dense and Loose Connective Tissue?

Dense contains high proportion of densely packed fibers, primarily collagen, w/ less ground substance and fewer cells. (offers considerable strength and resistance to tension.

Loose has fewer fibers and more ground substance and cells. (Flexible and provides cushioning)

What are the 3 kinds of Loose connective tissue?

Areolar, Adipose, Reticular

What is areolar connective tissue?

• The most widespread connective tissue proper.

  • It has a loose arrangement of all three fiber types (collagen, elastic, reticular) and various cell types (fibroblasts, macrophages, mast cells).

  • It acts as a soft, pliable cushion that binds epithelia to deeper tissues, wraps organs, and surrounds capillaries, allowing for considerable flexibility and movement. Plays a vital role in inflammation. 

What is Adipose Connective Tissue ?

• Primarily composed of adipocytes, cells specialized for storing large lipid droplets (triglycerides).

  • It provides long-term energy reserve, insulates against heat loss, and protects individual organs by cushioning.

  • There are two types: white adipose tissue (energy storage) and brown adipose tissue (thermogenic, more common in infants).

What is Reticular Connective Tissue?

• Characterized by a delicate network of reticular fibers (a fine type of collagen fiber) and reticular cells.

  • It forms a supportive framework (stroma) for soft organs that house immune cells, such as lymph nodes, spleen, bone marrow, and the liver.

What is are the 3 kinds of Dense Connective Tissue?

Dense Regular, Elastic, Dense Irregular

What is Dense Regular Connective Tissue?

• Features bundles of collagen fibers arranged predominantly parallel to each other, imparting high tensile strength in one direction.

  • This arrangement is ideal for structures subjected to unidirectional pulling forces.

  • Found primarily in tendons (attaching muscle to bone), ligaments (attaching bone to bone), and aponeuroses (sheet-like tendons).

What is Elastic Connective Tissue?

• Similar to dense regular but with a higher proportion of elastic fibers, allowing for significant stretch and recoil.

  • Found in structures that require elasticity while maintaining shape, such as the walls of large arteries, certain ligaments in the vertebral column (ligamentum nuchae, ligamentum flava), and the vocal cords.

What is Dense Irregular Connective Tissue?

• Contains thick bundles of collagen fibers that are randomly arranged, interweaving in various directions.

  • This provides strength and resistance to tension from multiple directions.

  • Found in the dermis of the skin (reticular layer), fibrous capsules around organs (e.g., kidneys, bones, cartilages, muscles, nerves), and the submucosa of the digestive tract.

What are the 2 kinds of Supportive Connective Tissue?

Cartilage & Bone

What is Cartilage

• A tough but flexible connective tissue characterized by an extracellular matrix rich in water, which allows it to resist compression.

  • Its cells, chondrocytes, are found in small cavities called lacunae.

  • Cartilage is avascular and receives nutrients by diffusion.

What are the 3 kinds of Cartilage?

Hyaline, Elastic, and Fibrocartilage

What is Hyaline Cartilage ?

• The most abundant type, with a smooth, glassy, and translucent appearance due to fine collagen fibers.

  • It provides firm support with some pliability.

  • Found in articular cartilage of movable joints, costal cartilages (attaching ribs to sternum), nasal cartilage, trachea, larynx, and forms the embryonic skeleton.

What is Fibrocartilage

• Contains thick, discernible bundles of collagen fibers, making it the strongest and most resilient type of cartilage.

  • It is resistant to both compression and tension.

  • Found in structures subjected to heavy pressure, such as the intervertebral discs (pads between vertebrae), menisci of the knee, and the pubic symphysis.

What is Elastic Cartilage?

• Similar to hyaline cartilage but contains abundant elastic fibers, allowing for greater flexibility while maintaining shape.

  • Found where strength and stretch are required, such as the external ear (pinna) and the epiglottis.

What is Bone?

The hardest and most rigid connective tissue, providing the primary structural support for the body.

It is highly vascularized and capable of significant repair and remodeling.

What is the Composition Of Bone?

• Bone tissue consists of specialized cells (osteoblasts, osteocytes, osteoclasts) embedded in a mineralized extracellular matrix.

  • The matrix is a combination of collagenous fibers (providing flexibility and tensile strength) and an inorganic mineralized ground substance, primarily hydroxyapatite, which gives bone its exceptional hardness and rigidity.

What are the 2 Kinds of Bone?

Compact & Spongy

• Compact bone, dense and provides strength; Spongy bone, lighter and contains marrow.

What is compact bone

• the dense, hard outer layer of most bones.

• Its primary structural unit is the osteon (Haversian system), which consists of concentric rings of bone matrix (lamellae) around a central Haversian (central) canal containing blood vessels and nerves.

• Osteocytes are housed in lacunae between the lamellae, connected by tiny canals called canaliculi for nutrient exchange.

• Compact bone provides resistance to forces from a single direction and forms the diaphysis (shaft) of long bones.

What is Spongy Bone? (Cancellous or Trabecular Bone)

• The lighter, less dense inner layer, found deep to compact bone, particularly in the epiphyses (ends) of long bones and within flat bones.

• It consists of a network of interwoven bony plates or rods called trabeculae, which are oriented along lines of stress to provide strength without excessive weight.

• The spaces between trabeculae are filled with red or yellow bone marrow.

• Spongy bone is well-suited to withstand stresses from multiple directions and houses bone marrow, important for hematopoiesis (blood cell formation).

What are the 2 kinds of Fluid Connective Tissue?

Blood and Lymph

What is Blood?

• A unique fluid connective tissue circulating within the cardiovascular system.

• Its liquid matrix, plasma, is primarily water and contains dissolved proteins, nutrients, gases, hormones, and waste products.

• Blood's primary role is transport.

What are the formed elements of Blood?

• Composed of erythrocytes (red blood cells, for oxygen transport), leukocytes (white blood cells, for immune defense), and platelets (for blood clotting).They are essential components that perform critical functions in the circulatory system.

What is Lymph?

• Formed from interstitial fluid that enters lymphatic vessels.

  • It collects and transports dietary fats, pathogens, and immune cells (lymphocytes) throughout the lymphatic system, playing a crucial role in fluid balance and immune responses.

What are Fibroblasts

• The most abundant cell type in connective tissue proper.

• They are actively involved in synthesizing and secreting the protein fibers (collagen, elastic, reticular) and the components of the ground substance that form the extracellular matrix.

• They are essential for tissue development, maintenance, and repair.

What are Adipocytes?

• Specialized cells for fat storage.

• White adipocytes store triglycerides for long-term energy reserves, insulation, and cushioning.

• Brown adipocytes are specialized for thermogenesis (heat production), particularly important in infants.

What are Macrophages?

• Large phagocytic cells derived from monocytes (a type of white blood cell).

  • They engulf and digest cellular debris, foreign substances, bacteria, and dead cells.

• They also play a crucial role in immune defense by presenting antigens.

What are Mast Cells?

• Large, oval-shaped cells usually found near blood vessels.

• They store and release chemical mediators like histamine (involved in inflammation and allergic responses) and heparin (an anticoagulant).

What are Plasma Cells?

• Differentiated B lymphocytes that produce and secrete large quantities of antibodies, playing a key role in humoral immunity.

What are Leukocytes?

• Various types (e.g., neutrophils, eosinophils, lymphocytes) that migrate from the bloodstream into connective tissues, especially during inflammation and infection, to perform immune surveillance and defense functions.

What are Connective Tissue Fibers?

Collagen, Elastic, and Reticular Fibers that provide strength and elasticity to the matrix

What are collagen fibers

• The strongest and most abundant type of fiber.

• Made of the protein collagen, these fibers are tough, thick, and resistant to stretching (high tensile strength), providing structural integrity and linking tissues together.

  • They are particularly prominent in tendons, ligaments, and bone.

What are Elastic Fibers?

• Composed of the protein elastin, these fibers have the ability to stretch and recoil, allowing tissues to resume their original shape after deformation.

  • They are particularly present in structures needing flexibility, such as the skin, lungs, and blood vessel walls.

What are Reticular Fibers?

• Short, fine, highly branched collagenous fibers that form a delicate, net-like framework (stroma) supporting soft tissues and organs (e.g., lymph nodes, spleen).

  • They provide additional support and strength where flexibility is also needed.

What is Ground Substance?

• The unstructured material that fills the space between cells and contains the fibers. It is primarily composed of glycosaminoglycans (GAGs) (e.g., hyaluronic acid, chondroitin sulfate) and proteoglycans.

  • These molecules are highly hydrophilic, allowing the ground substance to trap large amounts of water, forming a viscous, gel-like matrix. This hydration facilitates nutrient diffusion, waste transport, and acts as a molecular sieve.