Comparative Anatomy

• Integumentary System - The skin and its derivatives.
• The Integumentary System plays many functions in the survival of the species.
• ROLES OF THE INTEGUMENT

  Protection

  Exteroceptive Role

  Respiration

  Excretion

  Thermoregulation

  Locomotion

  Maintenance of homeostasis

  Nourishment

  Pheromones and sex
• Excretion - the process of removing wastes and excess water from the body
• Thermoregulation - the biological mechanism responsible for maintaining a steady internal body temperature
• Locomotion - the structure of the skin has evolved to aid animals in their different modes of locomotion
• Maintenance of homeostasis - regulation of the ratio of water to salts in body fluids.
• Vertebrate skin consists of a multi-layered epidermis derived from ectoderm.
• Vertebrate skin consists dermis derived chiefly from mesoderm.
• The epidermis is the outer epithelium made up entirely of cells which are arranged in more or less distinct layers.
• 5 layers of the epidermis:

  Stratum basale

  Stratum spinosum

  Stratum granulosum

  Stratum lucidum

  Stratum corneum
• Stratum basale is consist of cells that are columnar in shape and arranged perpendicular to the dermis. It is considered as the basement layer of the epidermis.
• Stratum spinosum - sometimes called “spines” or prickle cell layer
• Stratum lucidum – found only in thick skin (e.g., palms and soles) and is composed of clear, flattened cells containing no nuclei.
• Stratum granulosum – contains keratinized cells with large amounts of keratin, giving them their characteristic appearance under light microscopy.
• Stratum lucidum is found only in thick skins such as those of elephants and hippopotamuses. The cells here have lost most of their organelles except nuclei.
• Stratum corneum – the outermost layer of the epidermis; it is composed of dead, keratinized cells that have been shed into the environment.
• Stratum granulosum contains flattened cells filled with keratin granules.
• Stratum spinosum has cuboidal cells with spiny projections on their surface, hence its name.
• Stratum granulosum is the granular layer of epidermis.
• Stratum lucidum translucent layer which is composed of dead cells.
• Absent in thin skin is the stratum lucidum,
• Stratum corneum is the outer layer of flattened cells and is also called the horny layer and is made up of hard, tough insoluble protein called keratin.
• The dermis consists mostly of connective tissue fibers extending in all directions and forming a fairly elastic covering.
• The dermis also contains nerves, smooth muscle fibers, blood vessels, and certain glands.
• the side of the dermis in contact with the epidermis is thrown into rows of papillae, which are most prominent on the palms and soles, which provide the greatest possible friction with a surface.
• The color of the human skin depends upon the presence of certain cells called melanocytes which contain pigment, melanin.
• Black or brown pigment – melanophores
• Yellow pigment – xanthophores
• Different colors – Metachrosis (ability of certain animals to change the color of their skin)
• Blue – cyanophores
• The secretory function of the skin is subserved by glands.
• Sweat glands are distributed over the surface of the human body except on the lips, glans penis, ear drum and nail bed.
• Sebaceous glands are distributed over the greater part of the surface of the skin, being notably absent from the palms and soles.
• Small glands of Zeis on the eyelids are sebaceous glands which open into the hair follicles of the eyelashes.
• Living agnathans have no scales.
• AGNATHA - have a multilayered unstratified epidermis with abundant unicellular mucous glands, thus they are called “slime eels”.
• Agnatha - The dermis is thinner than the epidermis, which contains many melanophores.
• CHONDRICHTHYES - The epidermis of the cartilaginous fishes has more layers of cells.
• CHONDRICHTHYES - the dermis is composed of collagen fibers arranged in a less than 90-degree manner.