Anatomy of Skin and Photophores

History of Animals and Evolution

• All animals originated from a single cell and evolved into vertebrates and non-vertebrates
• Evolution occurs to adapt to the environment, influenced by factors such as temperature, light, salinity, predators, toxins, pollution, and gravity
• Cyanobacteria produced oxygen, enabling the sea to support life
• Photosynthesis in blue-green algae helped create oxygen-rich environments

Epidermis and Its Derivatives

• The epidermis is the outermost covering of the chordate body, derived from somatic ectoderm
• Initially, the epidermis is a single layer of columnar epithelium covered by a thin film of cuticle
• In vertebrates, the epidermis differentiates into a multi-layered epithelium
• Epidermis provides mechanical and bacterial protection and prevents drying on land
• In terrestrial vertebrates, the cuticle is replaced by keratin

Kinds of Epidermal Glands

• Unicellular glands: mucous gland cells, granular cells, and beaker cells
• Multicellular glands: tubular, alveolar, and compound glands
• Specific types of glands include:
  • Mucous glands: found in fishes and amphibians, providing mucus for protection and lubrication
  • Femoral glands: found in male lizards, involved in mating and territorial behavior
  • Uropygial glands: found in birds, producing an oil used for preening and waterproofing feathers
  • Sudorific or sweat glands: found in mammals, regulating body temperature through evaporation
  • Poison glands: found in amphibians, producing toxic secretions for defense
  • Preputial glands: found in many mammals, involved in scent marking and mating
  • Mammary glands: found in mammals, producing milk for nursing young
  • Sebaceous glands: found in mammals, producing an oil (sebum) for skin and hair
  • Meibomian glands: modified sebaceous glands, producing an oil for eye lubrication
  • Scent glands: found in various animals, producing pheromones for mating and territorial behavior

This quiz covers the structure and function of tubular glands in the skin, including their formation and characteristics, as well as the role of photophores in deep-sea fish.