Animal Tissues

Just as a building is made of different materials (brick, cement, steel, wood), the animal body is made of different tissues -- groups of similar cells that work together to perform specific functions. There are four main types of animal tissues.

1. Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It serves as a protective barrier.

Types:

• Simple squamous: Flat, thin cells. Found in: blood vessel lining, lung alveoli. Function: diffusion, filtration.
• Simple cuboidal: Cube-shaped cells. Found in: kidney tubules, glands. Function: secretion, absorption.
• Simple columnar: Tall, column-shaped cells. Found in: intestinal lining. Function: absorption, secretion (may have microvilli or goblet cells).
• Stratified squamous: Multiple layers of flat cells. Found in: skin, mouth, oesophagus. Function: protection against wear and tear.
• Ciliated epithelium: Has cilia on the surface. Found in: respiratory tract, fallopian tubes. Function: moves mucus and particles.

Characteristics: Cells are tightly packed, rest on a basement membrane, lack blood vessels (avascular).

2. Connective Tissue

The most diverse and abundant tissue type. It connects, supports, and protects other tissues.

Types:

• Loose connective tissue (Areolar): Fills spaces between organs. Contains fibres and cells in a gel-like matrix.
• Dense connective tissue: Strong, with closely packed collagen fibres. Forms tendons (muscle to bone) and ligaments (bone to bone).
• Adipose tissue: Fat storage. Provides insulation and cushioning.
• Cartilage: Firm but flexible. Found in: ear, nose, tracheal rings, joints. Matrix contains chondrocytes.
• Bone: Hard, mineralized with calcium. Provides support, protection, and mineral storage. Contains osteocytes.
• Blood: Liquid connective tissue. Contains RBCs, WBCs, and platelets in plasma. Transports O₂, nutrients, and waste.

3. Muscular Tissue

Specialized for contraction and movement.

| Type | Appearance | Location | Control | |------|-----------|----------|---------| | Skeletal | Striated, multi-nucleated | Attached to bones | Voluntary | | Smooth | Non-striated, spindle-shaped | Gut, blood vessels, uterus | Involuntary | | Cardiac | Striated, branched, intercalated discs | Heart only | Involuntary |

4. Nervous Tissue

Found in the brain, spinal cord, and nerves. Specialized for conducting electrical impulses.

Neuron structure:

• Cell body (soma): Contains the nucleus
• Dendrites: Short branches that receive signals
• Axon: Long fibre that transmits signals away from the cell body
• Myelin sheath: Insulating layer that speeds up signal transmission

Supporting cells (neuroglia): Provide support and nutrition to neurons.

Key Takeaways

• Four tissue types: epithelial (protection), connective (support), muscular (movement), nervous (signalling)
• Epithelial tissue lines surfaces; connective tissue is the most diverse
• Three muscle types: skeletal (voluntary), smooth (involuntary), cardiac (involuntary)
• Neurons transmit electrical signals through dendrites, cell body, and axon