Learning Objectives
- Understand animal tissues: epithelial, connective, muscular, and neural
- Study the morphology and anatomy of earthworm, cockroach, and frog
- Learn the organ systems in these representative organisms
Key Concepts
Animal Tissues
Epithelial Tissue: Covers body surfaces, lines cavities. Types: Squamous (flat, in blood vessels — endothelium), Cuboidal (in kidney tubules, salivary glands), Columnar (in intestinal lining), Ciliated (in respiratory tract, oviducts), Glandular (in glands). Compound epithelium (stratified) in skin for protection. Basement membrane anchors epithelium to underlying tissue.
Connective Tissue: Most abundant tissue. Types: Loose CT (areolar — found beneath skin, fills spaces; adipose — stores fat, insulation), Dense CT (tendons — connect muscle to bone; ligaments — connect bone to bone), Specialized CT (cartilage — chondrocytes in matrix; bone — osteocytes in hard matrix with Haversian system; blood — fluid CT with RBCs, WBCs, platelets in plasma).
Muscular Tissue: Skeletal/Striated (voluntary, multinucleated, attached to bones), Smooth/Visceral (involuntary, uninucleated, in gut wall), Cardiac (involuntary, uninucleated, branched, intercalated discs, in heart).
Neural Tissue: Neurons (nerve cells) with cell body (cyton), dendrites, and axon. Neuroglia provide support. Myelinated (white matter) and non-myelinated (grey matter) nerve fibres.
Earthworm (Pheretima posthuma)
Segmented body (100-120 segments). Clitellum on segments 14-16 (secretes cocoon). Closed circulatory system. Excretion by nephridia (septal, pharyngeal, integumentary). Nervous system: ventral nerve cord with ganglia. Hermaphrodite (monoecious) but cross-fertilization. Testes in segments 10-11, ovaries in segment 13. Fertilization in cocoon.
Cockroach (Periplaneta americana)
Body: Head, Thorax (3 segments, 3 pairs of legs, 2 pairs of wings), Abdomen (10 segments). Open circulatory system with haemolymph. Respiration through tracheae opening via spiracles. Excretion by Malpighian tubules. Mosaic vision (compound eyes). Hepatic caeca for digestion. Unisexual. Females have ootheca (egg case) containing 14-16 eggs. Blood: colourless haemolymph (no haemoglobin).
Frog (Rana tigrina)
Amphibian — lives on land and in water. Moist skin for cutaneous respiration. Buccal cavity respiration and pulmonary respiration. Three-chambered heart (2 atria + 1 ventricle). Poikilothermic (cold-blooded). Hepatic portal system and renal portal system present. Sexual dimorphism: males have vocal sacs and copulatory pads. External fertilization in water. Tadpole larva undergoes metamorphosis.
Summary
Animal tissues are classified into epithelial (covering), connective (support), muscular (movement), and neural (coordination). Earthworm demonstrates closed circulation and nephridial excretion. Cockroach shows open circulation, tracheal respiration, and Malpighian tubule excretion. Frog has dual respiration modes and undergoes metamorphosis from aquatic larva to terrestrial adult.
Important Terms
- Haversian system: Structural unit of compact bone with central canal
- Intercalated discs: Specialized junctions between cardiac muscle cells
- Clitellum: Glandular structure in earthworm for cocoon secretion
- Malpighian tubules: Excretory organs in cockroach
- Nephridia: Excretory organs in earthworm
- Spiracles: External openings of tracheal system in insects
- Haemolymph: Colourless blood in cockroach
- Metamorphosis: Transformation from larva to adult (e.g., tadpole to frog)
Quick Revision
- Epithelial tissue: covers surfaces; types — squamous, cuboidal, columnar, ciliated
- Tendon = muscle to bone; Ligament = bone to bone
- Skeletal muscle = voluntary; Smooth = involuntary; Cardiac = involuntary with intercalated discs
- Earthworm: closed circulation, nephridia, hermaphrodite
- Cockroach: open circulation, tracheal system, Malpighian tubules, mosaic vision
- Frog: 3-chambered heart, cutaneous + pulmonary respiration, external fertilization
- Blood is a connective tissue (fluid CT)