Connective Tissue

CONNECTIVE TISSUE

Connective tissue is the most abundant and widely distributed tissue in the human body.
It supports, connects, and binds various organs and tissues together.

Examples include: cartilage, bone, adipose tissue, areolar tissue, and blood.

Connective tissue contains:

• Cells
• Fibres
• Ground Substance (Matrix)

These three components give strength, elasticity, and support to the tissue.

FUNCTIONS OF CONNECTIVE TISSUE

1. Provides mechanical support to organs
2. Connects and binds tissues
3. Acts as a medium for exchange of nutrients and waste
4. Stores energy (fat tissue)
5. Provides insulation
6. Offers defence – barriers, antibodies, phagocytosis

COMPOSITION OF CONNECTIVE TISSUE

Connective tissue has fibres, cells, and ground substance.

FIBRES

1. Collagen Fibres

• Thick & strong
• Provide tensile strength
• Most abundant fibre in connective tissue

2. Elastic Fibres

• Made of elastin
• Stretch and recoil easily
• Found in skin, lungs, arteries

3. Reticular Fibres

• Thin, branched fibres
• Form delicate networks
• Provide support in soft organs (spleen, lymph nodes)

CELLS

1. Fibroblasts

• Most common cell
• Produce fibres and ground substance

2. Macrophages

• “Big eaters”
• Perform phagocytosis of foreign bodies and microbes
• Two types:
• Wandering macrophages – move to infection sites
• Fixed macrophages – remain in organs (lungs, spleen)

3. Plasma Cells

• Derived from B-lymphocytes
• Produce antibodies
• Found in respiratory and digestive tract, lymph nodes

4. Mast Cells

• Secrete histamine, important during inflammation
• Dilate blood vessels

TYPES OF CONNECTIVE TISSUE

Connective tissue is broadly classified into:

1. Loose Connective Tissue
2. Dense Connective Tissue
3. Cartilage Tissue
4. Bone Tissue
5. Blood (Fluid Connective Tissue)

1. LOOSE CONNECTIVE TISSUE

Cells and fibres are loosely arranged in a semi-fluid matrix.

a) Areolar Tissue

• Most widely distributed
• Contains all types of fibres and cells
• Fills spaces between organs

Location:
Under the skin, between muscles, around blood vessels and nerves

Functions:

• Strength
• Flexibility
• Support

b) Adipose Tissue

• Made of adipocytes (fat cells)
• Stores fat as a single large droplet

Location:
Under the skin, around heart and kidneys, yellow bone marrow

Functions:

1. Prevents heat loss (insulation)
2. Energy storage
3. Protection of organs
4. Gives shape to body

c) Reticular Tissue

• Contains reticular fibres and reticular cells
• Forms a supportive network (stroma)

Location:
Liver, spleen, lymph nodes, red bone marrow

Functions:

• Forms structural framework
• Filters worn-out blood cells (spleen)
• Removes microbes (lymph nodes)

2. DENSE CONNECTIVE TISSUE

Contains closely packed fibres and fewer cells.

a) Dense Regular Connective Tissue

• Fibres arranged in a parallel pattern
• Very strong

Location:

• Tendons (muscle → bone)
• Ligaments (bone → bone)

Function:

• Provides strong attachments

b) Dense Irregular Connective Tissue

• Fibres arranged in irregular patterns
• Can withstand tension from multiple directions

Location:

• Dermis of skin
• Organ capsules

c) Elastic Connective Tissue

• Contains freely branching elastic fibres
• Yellowish in appearance

Location:

• Lungs
• Elastic arteries
• Vocal cords
• Bronchial tubes

Function:

• Allows stretching and elasticity of organs

3. CARTILAGE TISSUE

Cartilage is firmer than other connective tissues but more flexible than bone.
Cells called chondrocytes lie in spaces called lacunae.

Types of Cartilage

a) Hyaline Cartilage

• Most common type
• Glassy, bluish-white appearance
• Chondrocytes arranged in small groups

Location:
Nose, trachea, bronchi, rib ends, fetal skeleton

b) Fibrocartilage

• Many collagen fibres
• Very strong and shock-absorbing

Location:
Intervertebral discs, pubic symphysis

c) Elastic Cartilage

• Yellow elastic fibres
• Most flexible type

Location:
External ear, epiglottis

4. BONE TISSUE

Bone is the hardest connective tissue.
Its strength comes from:

• Calcium salts (calcium phosphate & carbonate)
• Collagen fibres

Components of Bone

Bone consists of:

• Periosteum
• Compact bone
• Cancellous bone
• Bone marrow

Microscopic Structure

Functions of Bone

1. Provides structural support
2. Protects organs
3. Stores calcium
4. Produces blood cells in red bone marrow

5. BLOOD (FLUID CONNECTIVE TISSUE)

Blood is considered a connective tissue because it:

• Has cells suspended in a matrix (plasma)
• Transports materials throughout the body

Components of Blood

• RBCs (Erythrocytes)
• WBCs (Leukocytes)
• Platelets
• Plasma (matrix)

Functions

1. Transport of gases, nutrients, hormones
2. Defence against infection
3. Clotting
4. Regulation of body temperature