Connective Tissue – Anatomy & Physiology

TISSUE

• Tissue are group of similar cells that perform similar functions in the body.

TYPES OF TISSUE

1. Epithelial tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue

CONNECTIVE TISSUE

• Connective tissue are named because of their function of linking and supporting other organ of the body.
• Most abundant & widely distributed in the body.
• Cells are more widely separated from each other than epithelial tissue.
• Intercellular matrix is present in large amount.

Major Functions

• Binding & structure Support.
• Transport.
• Media for exchange of nutrients & waste product.
• Insulation & energy store.
• Protection.

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COMPONENTS OF CONNECTIVE TISSUE

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I. Fibres

1. Collagen fibres

• Made up of collagen proteins have a high tensile strength.
• Collagen fibres seen in bundles.
• The bundles may be straight or wavy bundles.
  

2. Elastin fibres

• Thin, long, highly elastic, yellowish branched fibres.
• Made up of the protein elastin.
• Also known as yellow fibres.

3. Reticular Fibres

• Reticular fibers are thin fibers made of collagen and are organized in a network-like pattern.
• Support the structure of organs and tissues.
  
  
  

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II. Ground substance

• The ground substance is an amorphous, gel-like substance that surrounds cells and fibers.
• It plays a key role in supporting and binding the cells and fibers together, allowing for exchange of nutrients and waste.
• It consists of:
• Proteoglycans: Large molecules that attract water, providing a gel-like consistency.
• Glycosaminoglycans (GAGs): Long unbranched polysaccharide chains that help maintain the structure and function of tissues.
• Glycoproteins: Proteins that bind cells to the extracellular matrix.

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III. Cells

1. Fibroblast

• Fibroblast are flat, branched, irregular cells with multiple processes.
• They are responsible for production of fibres and ground substance.

2. Fat Cells (Adipocytes)

• Also known as adepocytes.
• Fat cells are large cells with a single lipid droplet, displacing the nucleus to one side.
• They are found in adipose tissue.
• Adipocytes store energy in the form of fat.
• Provide insulation and cushioning to organs.
  
  
  

3. Macrophages

• They are large, irregularly shaped cells with a large nucleus.
• Macrophages are a type of white blood cell that are essential for the immune system.
• They involved in phagocytosis (engulfing and digesting pathogens, debris, and dead cells).
  
  
  

4. Leukocytes

• Leukocytes, or white blood cells, are crucial components of the immune system.
• Normally found in small number in healthy connective tissue.
• Their number increases in infection.

5. Mast Cells

• Mast cells are large usually present in groups.
• They are found in tissues near blood vessels.
• They release histamine, heparin.

6. Plasma Cells

• Plasma cells are a type of white blood cell that produce antibodies in response to foreign antigens.

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CLASSIFICATION

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I. LOOSE CONNECTIVE TISSUE

• It is characterized by a loose arrangement of fibers and cells.

1. Areolar tissue

• Areolar tissue is the most common type of loose connective tissue.
• It consists of a gel-like matrix containing collagen fibers, elastin fibers, and various cell types such as fibroblasts, macrophages, and mast cells.
• Location: Beneath epithelial tissues (e.g., under the skin, mucous membranes, and around blood vessels).
• Functions:
• Supports and binds other tissues.
• Elasticity and flexibility.
• Plays a role in the immune response through the presence of immune cells.

2. Adipose tissue

• Adipose tissue consists of adipocytes (fat cells) that store energy in the form of lipid droplets.
• Types of adipose tissue:
• White fat: 
• Large fat cell with non pigmented single large lipid droplet. 
• Found in the subcutaneous tissue, around internal organs. 
• It stores energy, provides thermal insulation, and cushioning.
• Brown fat: 
• Present more in newborns. 
• Cell contains multiple pigmented smaller lipid droplets. 
• Produce less energy and more heat.

3. Reticular tissue

• Reticular tissue is made up of of reticular fibers and reticular cells.
• Location: Found in lymphoid organs (lymph nodes, spleen, bone marrow), liver, kidneys, and other soft organs.
• Functions: Provides a supporting framework for cells. Assists in the filtration and cleaning of bodily fluids.

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II. DENSE CONNECTIVE TISSUE

• Dense connective tissue, also called dense fibrous tissue, is characterized by a high density of collagen fibers and a relatively low number of cells.

1. Dense Regular Connective Tissue 

• Collagen fibers are arranged in parallel bundles.
• Fibroblasts are aligned between the fibers.
• Location: Tendons (Connect muscle to bone), Ligaments (Connect bone to bone), Periosteum (outermost layer of the bone).
• Function: Provides strength & connect & support, Protection.

2. Dense irregular Connective Tissue

• Collagen fibers are arranged in an irregular pattern, providing strength in multiple directions.
• Location: Found in the dermis (inner layer of the skin), Joint capsules, advantitia of blood vessel.
• Function: Provides strength and resistance to tension in multiple directions. Helps to protect organs and provides structural support.

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III. SPECIAL CONNECTIVE TISSUE

• Special connective tissues are specialized forms of connective tissue with unique structures and functions.

1. Cartilage

• Cartilage is a flexible, tough connective tissue that protects joints and bones, and provides structure to the body.
• Made up of thin cells and collagen & elastic fibres.
• Tissue that lacks blood vessels (avascular) and nerves.
• Types of Cartilage:
1. Hyaline Cartilage: Most common, smooth, glassy appearance. Found at ends of long bones, costal cartilages, trachea, nasal septum. Reduces friction and provides structural support.
2. Elastic Cartilage: Contains more elastic fibers, making it more flexible. Found in external ear (pinna), epiglottis, Eustachian tube. Provides elasticity and shape retention.
3. Fibrocartilage: Strongest type, with a dense network of collagen fibers. Found in intervertebral discs, pubic symphysis, menisci of the knee. Resists compressive forces and acts as a shock absorber.

2. Bones

• A rigid connective tissue that forms the skeleton, providing support and protection.
• Highly vascularized and capable of self-repair.
• Components:
• Cells: Osteoblasts (bone formation), Osteocytes (maintain tissue), Osteoclasts (break down tissue).
• Matrix: Composed of collagen fibers and calcium phosphate, making it strong and hard.
• Types:
• Compact Bone: Dense, solid, forms the outer layer. Provides strength.
• Spongy Bone: Porous, lightweight, found within ends of long bones. Contains red bone marrow for blood cell production.

3. Blood

• A fluid connective tissue that circulates throughout the body, transporting nutrients, gases, waste, and hormones.
• Components:
• Plasma: Liquid matrix that carries nutrients and hormones.
• Cells: Red Blood Cells (transport oxygen), White Blood Cells (immune defense), Platelets (blood clotting).
• Functions: Transport, Immune defense, Regulation of temperature and pH.

4. Lymph

• Lymph is a clear or watery fluid that carries white blood cells, nutrients, and other substances.
• Components: Fluid matrix containing proteins and lymphocytes.
• Functions: Managing fluid levels, absorbing dietary fats, immune defense (filters pathogens), and filtration in lymph nodes. 

 

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