🐸 Structural Organisation in Animals

1. Animal Tissues

Tissues are organized in specific proportions and patterns to form organs.

2. Epithelial Tissue

Provides a covering or lining. Has a free surface facing body fluid or outside environment. Cells are compactly packed with little intercellular matrix.

Simple Epithelium: Single layer. Squamous (diffusion boundaries like alveoli), Cuboidal (ducts, nephrons), Columnar (lining of stomach/intestine), Ciliated (fallopian tubes).
Compound Epithelium: Multi-layered. Protective function (e.g., dry surface of skin).

Cell Junctions

Tight junctions: Stop substances from leaking across a tissue.

Adhering junctions: Cement neighboring cells together.

Gap junctions: Facilitate communication between cells by connecting cytoplasms for rapid transfer of ions/molecules.

3. Connective Tissue

Most abundant and widely distributed tissue. Functions: linking and supporting other tissues/organs. Includes soft connective tissues and specialized types.

Loose Connective: Areolar (beneath skin), Adipose (fat storage).
Dense Connective: Dense regular (Tendons - muscle to bone, Ligaments - bone to bone), Dense irregular (skin).
Specialised Connective: Cartilage, Bone, and Blood (fluid connective tissue lacking fibres).

4. Muscle Tissue

Made of long, cylindrical fibres that can contract in response to stimulation.

Types of Muscles

Skeletal: Striated, voluntary, attached to bones.

Smooth: Non-striated, involuntary, fusiform shape. Wall of internal organs.

Cardiac: Striated, involuntary, branched. Present only in the heart. Have intercalated discs.

5. Neural Tissue

Exerts greatest control over the body's responsiveness to changing conditions. Neurons are the excitable functional units. Neuroglial cells protect and support neurons, making up more than half the volume of neural tissue.

6. Morphology and Anatomy of Frog (Rana tigrina)

Frogs are cold-blooded (poikilotherms). Exhibit camouflage and mimicry. Undergo hibernation (winter sleep) and aestivation (summer sleep). Detailed study includes digestive, respiratory, circulatory, excretory, and reproductive systems.