Integument and its Derivatives | Zoology Optional Notes for UPSC PDF Download

Derivatives of Integument in Mammals: An In-Depth Look

1. Layers of the Skin: Epidermis and Dermis

• Epidermis (Outer Layer):

  • Origin: Ectodermal in origin.
  • Structure: Divided into several strata.
  • Key Layers:
    • Stratum Germinativum (Malpighian Layer):
      • Composed of tall, columnar cells perpendicular to the dermis.
      • Constant mitotic division, with new cells gradually moving toward the surface.
    • Transitional Layer:
      • Formed by flattened cells with poor stainability during their journey to the surface.
    • Stratum Corneum (Horny Layer):
      • Outermost layer comprising flat, dead cells.
      • Main constituent: Keratin, a hard, tough, and insoluble protein.
    • Variations in Certain Body Parts:
      • Thick skin on palms and soles has a less abrupt transition from Malpighian layer to corneal layer.
      • Transitional layer subdivided into stratum granulosum and stratum lucidum.
• Dermis (Inner Layer):
  • Origin: Mesodermal in origin.
  • Composition: Connective tissue fibers, smooth muscle fibers, blood vessels, nerves, and glands.
  • Thickness: Generally thicker than the epidermis.

2. Specialized Structures and Variations in Mammalian Skin:

• Blubber in Whales and Seals:

  • A thick layer of fat that serves as a food reservoir and aids in temperature regulation.
  • Provides insulation against cold environments.
• Melanin Distribution:
  • Pigments, such as melanin, are present in the cells of the deepest layer of the epidermis.
  • Melanin distribution is not confined to specialized cells.

3. Maintenance of Epidermal Thickness:

• The thickness of the epidermal part remains relatively constant due to a balance between the proliferation rate of the stratum germinativum and the loss of corneal cells.

4. Continuous Integration with Mucous Membranes:

• The integument is seamlessly connected with mucous membranes in areas like the mouth, rectum, urinogenital organs, nostrils, and eyelids.

Understanding the detailed structure and variations of the integument in mammals provides insights into the diverse adaptations and functions of this crucial organ. From temperature regulation to protection and sensory perception, the skin's derivatives contribute significantly to the survival and well-being of different mammalian species.

Functions of the Integument in Vertebrates

1. Protection:

• Mechanical Protection:
  • Prevents the entry of foreign bodies, protecting the body from infections.
  • Dermal and epidermal scales provide a protective barrier against surface abrasion.
• Defensive Structures:
  • Hair, bristles, and spines are employed for both offensive and defensive purposes.
• Water Conservation:
  • The impervious integument helps prevent the loss of water from the body.

2. Thermoregulation:

• Temperature Regulation:
  • Feathers in birds, sweat glands, and blubber in mammals aid in regulating body temperature.
  • Hair functions to conserve heat, especially during winter.

3. Storage of Food:

• Blubber in Marine Mammals:
  • Whales, seals, and sea cows store food in a sub-dermal fat layer known as blubber.

4. Excretion:

• Waste Elimination:
  • The skin in some aquatic vertebrates serves as an excretory organ.
  • Waste materials stored in the corneal layer during ecdysis are shed.
  • Sweat glands aid in removing nitrogenous wastes from the body.

5. Respiration:

• Cutaneous Respiration:
  • Moist skin in certain vertebrates (common eel, mud skippers, swamp eels) facilitates respiration.
  • Amphibians rely on the moist and glandular skin for accessory respiration.

6. Secretion:

• Glandular Functions:
  • The skin acts as an organ of secretion with various glands.
  • Mucous glands in fishes reduce resistance during swimming.
  • Poison glands in fishes, amphibians, and snakes are used for protection and predation.
  • Mammary glands, scent glands, and sebaceous glands serve different functions.

7. Locomotion:

• Integumentary Derivatives:
  • Fins in fishes, webbed structures in aquatic amphibians and birds, scutes in snakes, adhesive pads in climbing lizards, feathers in birds, and patagium in flying lizards facilitate different modes of locomotion.

Understanding these multifaceted functions highlights the adaptability and significance of the integumentary system in vertebrates across various environments and lifestyles.

Epidermal Derivatives and Integumentary Glands in Vertebrates

1. Integumentary Glands:
   • Unicellular and multicellular glands arise from the Malpighian layer of the epidermis.
   • Types: mucous cells, granular cells, and large beaker cells.
2. Epidermal Scales and Scutes:
   • Protective structures found in different patterns on the skin.
   • Present in reptiles, fish, and some amphibians.
3. Horns:
   • Developments on the skin, often found in mammals.
   • Examples include the horns of cattle and other ungulates.

Epidermal Glands:
Epidermal glands are diverse and can be classified based on structure and function.

1. Unicellular Glands:
   • Single cells, like mucous cells or goblet cells, secrete mucin for lubrication.
2. Multicellular Glands:
   • Tubular Glands:
     • Tubular, uniform diameter (e.g., glands of Moll in human eyelids).
     • Coiled (e.g., sweat glands) or compound tubular (e.g., mammary glands).
   • Alveolar Glands:
     • Downgrowths into the dermis, with rounded or flask-shaped ends (e.g., mucous and poison glands).
     • Compound alveolar glands branch into lobules (e.g., mammary glands).

Kinds of Epidermal Glands:
Based on function, epidermal glands in vertebrates include:

1. Sudorific (Sweat) Glands:
   • Long, coiled tubular glands distributed unevenly.
   • Absent in certain species like Tachyglossus, Mus, Talpa, Cetacea, and Sirenia.
   • Functions in temperature regulation and waste removal.
2. Sebaceous Glands:
   • Alveolar glands often associated with hair or found in hairless regions.
   • Absent in Pangolin, Cetacea, and Sirenia.
   • Produces sebum for body oiliness; Meibomian and scent glands are modified sebaceous glands.
3. Meibomian Glands:
   • Modified sebaceous glands in eyelids secreting an oily film on the eyeball surface.
4. Scent Glands:
   • Modified sebaceous glands producing sex attractants.
   • Location varies, e.g., near eyes in deer, near anus in carnivores, between toes in pigs and goats.

Understanding these epidermal derivatives and glands provides insights into the diverse functions they serve in different vertebrate species.