Integumentary System

• Synovial membrane


  A connective tissue membrane that does not include epithelial cells
• Synovial membranes


  • Line the capsules around synovial joints, tendon sheaths, and bursae
  • Secrete synovial fluid, which cushions and reduces friction in moving structures
• Integumentary system


  Consists of the skin, sweat and oil glands, nails, and hair
• Functions of the integumentary system

  • Skin acts as a protective layer for underlying tissues and defends against injuries
  • Keratin in the skin provides structural strength and protects against chemicals
  • Skin functions as a water barrier, preventing excessive evaporation and water entry
  • Regulation of body temperature is achieved through capillaries and sweat glands in the skin
  • Skin produces melanin to protect against harmful UV radiation and synthesizes vitamin D
  • Chemical waste products are eliminated through sweat, which also helps protect against infections
  • Cutaneous sensory receptors in the skin transmit information about touch, pressure, pain, and temperature
• Skin


  Composed of two layers: the outer epidermis and the underlying dermis
• Epidermis


  • Outermost layer of the skin and consists of five layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale
  • Epidermal layers do not have a direct blood supply but receive nutrients from the underlying dermis, primarily through the stratum basale
  • Cells in the stratum basale continuously produce new skin cells, which gradually move toward the surface and eventually die
  • Majority of cells in the epidermis are keratinocytes, which produce keratin
  • Cells in the stratum spinosum and stratum granulosum become flatter and more filled with keratin, making them tough and water resistant
  • Stratum lucidum is a clear layer found in thick skin areas like palms, soles, and fingers
  • Stratum corneum consists of dead cells filled with keratin that continuously shed
  • Epidermis completely regenerates every 25 to 45 days
  • Stratum basale contains melanocytes that produce melanin, responsible for human skin colour
  • Sunlight exposure stimulates melanin production, resulting in tanning and increased sun protection
  • Extra melanin functions as a natural sunscreen, reducing the likelihood of sunburn
  • Epidermal dendritic cells initiate immune responses to foreign bacteria or viruses
  • Merkel cells in the stratum basale serve as touch receptors and transmit sensory information to the brain
• Dermis


  • Dense, fibrous tissue composed of collagen and elastic fibres
  • Collagen fibres provide toughness and bind with water to maintain skin moisture
  • Elastic fibres help keep the skin youthful without wrinkles or sagging
  • Aging leads to a decrease in collagen and elastic fibres in the dermis
  • Rich blood supply, aiding in heat regulation
  • Specialized sensory receptors for touch, vibration, pain, and temperature are present
  • Phagocytes in the dermis ingest foreign materials and dead cells
  • Papillary layer is the outer layer of the dermis, containing dermal papillae with capillaries and nerve endings
  • Dermal papillae form unique patterns on palms, fingers, toes, and soles, resulting in fingerprints
  • Reticular layer is beneath the papillary layer and has an irregular arrangement of collagen and elastic fibres
  • Reticular layer contains blood and lymphatic vessels, sweat and oil glands, muscles, hair follicles, and nerve endings
• Hypodermis


  • Consists of fibrous connective tissue and adipose tissue
  • Fat cells are present, providing padding, insulation, and energy storage
• Appendages of the skin

  • Sudoriferous glands
  • Sebaceous glands
  • Hair
  • Nails
• Sudoriferous glands


  • Found throughout the dermis, with higher concentrations under the arms, on the palms, soles, and forehead
  • Approximately 2 to 3 million sweat glands in each person's body
  • Two types: eccrine glands and apocrine glands
  • Eccrine glands are the major sweat glands, covering most of the body and opening directly onto the skin
  • Sweat from eccrine glands is a clear, watery fluid containing water, waste products (urea, uric acid, salts), and vitamin C
  • Bacteria can chemically change sweat on the skin, resulting in an unpleasant odour
  • Nerve endings in sweat glands stimulate sweat production in response to increased body or external temperature
  • Evaporation of sweat from the skin helps dissipate body heat effectively
  • Apocrine glands are larger than eccrine glands and are primarily found in the genital and armpit areas
  • Apocrine glands secrete a milky fluid containing sweat, fatty acids, and proteins
  • Apocrine gland ducts empty into hair follicles
• Sebaceous glands


  • Found throughout the body, except for the palms and soles
  • Produce an oily substance called sebum
  • Most sebaceous glands empty into hair follicles, while some secrete directly onto the skin
  • Sebum helps keep the skin and hair soft
  • Sebum also contains chemicals that have antibacterial properties
  • More active during adolescence, resulting in oilier skin for teenagers
• Hair


  • Hair follicles are structures within the dermis that produce hair
  • Base of the follicle contains a papilla of connective tissue with a rich capillary supply for nourishment
  • Specialized cells in the follicle's matrix divide and generate living hair cells
  • As the cells move upward, they fill with keratin and become non-living
  • Hair shaft is mostly composed of protein
  • Hair colour and texture are determined by melanocytes within the hair follicle
  • Reduced pigment production by melanocytes results in grey or white hair with aging
  • The shape of the hair follicle determines hair texture (straight, wavy, or curly)
  • Arrector pili muscles connect the hair follicle to the dermis
  • Stimulated arrector pili muscles cause hair to stand upright, resulting in goosebumps
  • Goosebumps help trap air close to the skin for insulation and warmth
• Nails

  • Nail bed is a specialised region of the stratum basale underlying each nail
  • Nail matrix, located at the proximal end of the nail bed, is responsible for nail growth
  • Nail growth occurs in the matrix as new cells rapidly become keratinized and die
  • Nails are transparent but appear pinkish due to the capillary supply beneath the stratum basale
  • The white, crescent moon-shaped region at the base of the nail is called the lunule
  • The lunule is positioned over the thickened nail matrix and has a curved shape similar to a crescent moon