Integumentary System

• The integument is the largest system of the body: 16% of body weight, 1.5 to 2 m2 in area
• The integument is made up of the cutaneous membrane (skin) and accessory structures like exocrine glands, hair, nails
• The parts of the cutaneous membrane include the outer epidermis (superficial epithelium) and the inner dermis (connective tissues)
• Accessory structures like hair, nails, and multicellular exocrine glands originate in the dermis and extend through the epidermis to the skin surface
• The subcutaneous layer (hypodermis) is composed of loose connective tissue, located deep below the dermis, and is the location of hypodermic injections
• Functions of the skin include protecting underlying tissues and organs, excreting salts, water, and organic wastes, maintaining body temperature, synthesizing vitamin D3, storing lipids, and detecting touch, pressure, pain, and temperature
• The organization of the epidermis includes layers such as stratum germinativum, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum, which is keratinised stratified squamous epithelium
• It takes 15-30 days for a cell to move from the stratum germinosum to the stratum corneum
• The stratum germinativum, also known as the "germinative layer," has many germinative (stem) cells or basal cells attached to the basal lamina by hemidesmosomes, forming a strong bond between the epidermis and dermis
• The stratum corneum, also known as the "horn layer," is the exposed surface of the skin with 15 to 30 layers of keratinized cells that are water-resistant and shed and replaced every 2 weeks
• Keratinisation is the formation of a layer of dead, protective cells filled with keratin, occurring on all exposed skin surfaces except the eyes
• Skin color depends on the pigments carotene and melanin, as well as the extent of blood circulation
• Sources of pigment include melanin and carotene
• Keratinocytes contain a large amount of keratin
• Keratinocytes are the most abundant cells in the epidermis
• Sources of skin pigment

  • Melanin
  • Carotene
• Melanin is a source of pigment due to sunlight action on melanocytes
• Carotene is a source of pigment from food (e.g. carrots)
• Dermis


  • Located between epidermis and subcutaneous layer
  • Anchors epidermal accessory structures like hair follicles and sweat glands
  • Has two components: outer papillary layer and deep reticular layer
  • Characteristics: strong due to collagen fibers, elastic due to elastic fibers, flexible (skin turgor)
• The Papillary Layer

  1. Consists of areolar tissue

  2. Contains capillaries, lymphatics, and sensory neurons

  3. Has dermal papillae projecting between epidermal ridges
• The Reticular Layer


  1. Consists of dense irregular connective tissue

  2. Contains larger blood vessels, lymph vessels, and nerve fibers

  3. Contains collagen and elastic fibers

  4. Contains connective tissue proper

  5. Tissue is stronger in certain directions
• Lines of cleavage or tension lines determine the strength and alignment of fibers in the skin
• Accessory structures like hair, hair follicles, sebaceous glands, sweat glands, and nails are derived from embryonic epidermis and located in the dermis
• Sebaceous glands are holocrine glands that secrete sebum
• Sweat glands are merocrine glands that secrete watery secretions
• Sebum contains lipids and other ingredients, lubricates and protects the epidermis, and inhibits bacteria
• Merocrine sweat glands are widely distributed on the body surface, especially on palms and soles, and are responsible for sensible perspiration
• Sensible perspiration cools the skin, excretes water and electrolytes, and flushes microorganisms and harmful chemicals from the skin
• Apocrine sweat glands are found in armpits, around nipples, and groin, and their odorous secretions begin at puberty
• Mammary glands produce milk
• Ceruminous glands protect the eardrum and produce cerumen (earwax)
• Repair of skin

  1. Inflammatory

  2. Migratory

  3. Proliferation

  4. Scarring
• Hair structure

  Medulla

  Cortex

  Cuticle
• Medulla


  Containing soft keratin.
• Hair structure


  .

  
• Cortex


  Contains hard keratin
• Cuticle 


  Contains hard keratin
• Follicle structure


  Internal root sheath

  External root sheath

  Glassy membrane is wrapped in dense connective tissue sheath
• Type of exocrine glands

  Sebaceous and sweat glands
• Ceruminous gland


  The ceruminous glands in the skin of the human external auditory canal are modified apocrine glands, which, together with sebaceous glands, produce the cerumen, the ear wax.