BIO REVIEW

• Skin

  The external organ of the body
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis (subcutaneous)
• Epidermis


  • Outermost layer of the skin with no blood vessels
  • Functions include external surface protection, waterproofing, formation of hair and nails, natural hair color
• Dermis


  • Second layer of the skin that acts as skin glue
  • Functions include providing elasticity to the skin, nourishes the epidermis, receiving sensory stimulation, and the fingerprints and footprints
• Hypodermis (subcutaneous)


  • Innermost layer of the skin made up of adipose tissue and fats
  • Functions include providing more energy reserve, insulation, cushion, and give the body contour
• Layers of the epidermis

  • Stratum Corneum
  • Stratum Lucidum
  • Stratum Granulosum
  • Stratum Spinosum
  • Stratum Basale
• Stratum Corneum


  • First (upper) multi-layer of dead, keratinized, cornified, squamous, cells (dead because there are no blood vessels)
  • Has the protein keratin that acts as a waterproofing substance
  • Keratin continuously sheds off through exfoliation
• Stratum Lucidum


  • Only found in thick skin (soles of feet and palm of hands)
  • Provide extra fitness since these areas are prone to shock and pressure
• Stratum Granulosum


  Has active keratinocytes, cells that produce protein
• Stratum Spinosum


  • Irregular cells that help with skin strength and flexibility
  • Has dendritic cells that help boost immune response
• Stratum Basale


  • Lowermost layer composed of one layer of columnar cells
  • Mitosis layer (cells activity divide)
  • Site for the formation of hair and nails
  • Contains melanocytes
• Melanin


  • A group of pigments responsible for the color of our eyes, skin, and hair
  • Protects us against UV Light by scattering UV Rays
• Melanocytes


  • Cells that produce melanin
  • Their golgi apparatus' packages the melanin into vesicles called melanosomes
• Large amounts of melanin can form freckles and moles, or darker areas in the genitals, nipples, and areola
• Eumelanin


  A photoprotective and stable melanin, is in higher quantities for dark skin and dark eyes than pheomelanin
• Vitamin D synthesis


  • When exposed to UVB, the epidermis synthesizes a form of Vitamin D called cholecalciferol
  • Calcitriol is the active form of Vitamin D that the body uses to absorb calcium and phosphorus for bone nourishment and repair
• Structures in the dermis

  • Abundant Areolar Connective Tissue
  • Blood Vessels
  • Sensory Receptors
• Abundant Areolar Connective Tissue

  The connective tissue has elastin fibers which provide the skin's elasticity
• Blood Vessels


  • Veins, arteries, and capillaries are all found in the dermis and they nourish the skin cells via nutrients and oxygen
  • They also have thermoregulatory functions
• Sensory Receptors

  • Mechanoreceptors
  • Thermoreceptors
  • Pain Receptors (nociceptors)
• Mechanoreceptors


  Detect physical deformation via pressure, touch, stretch, or motion
• Thermoreceptors

  Detect temperature
• Pain Receptors (nociceptors)


  Detect any harmful conditions that may be thermal, physical, or chemical
• Hair


  • Formed in the basale layer from keratin protein and cuticle
  • Around 100,000 hairs are found all over the body excluding the palm (hands) and soles (feet)
  • Its main purpose is for insulation
  • When it gets too cold, the hair helps the arrector pili muscle rise to form an additional layer of insulation (goosebumps)
  • It can be modified as quills/spikes
  • When moved, it can be sensed by mechanoreceptors
• Nails

  • Thin hard coverings on the tips of fingertips and toes made of cuticle and keratin
  • Protects the toes and fingers
  • Some animals use it for grasping small objects or as a modified defensive structure (claws)
• Glands in the skin

  • Sebaceous Glands
  • Meibomian Glands
  • Sweat Glands
• Sebaceous Glands


  • Sac-like exocrine gland whose duct opens into the hair and exits through the skin surface
  • Secretes sebum or oil that helps lubricate the skin and hair, prevents dryness, and contributes to the acidity of the skin
• Meibomian Glands


  Modified sebaceous glands found in the eyelid that lubricate the eyelashes
• Types of Sweat Glands

  • Eccrine Sweat Glands
  • Apocrine Sweat Glands
  • Ceruminous Sweat Glands
  • Ciliary Sweat Glands
  • Mammary Sweat Glands
• Eccrine Sweat Glands


  • Found almost everywhere in the body
  • Secretes a mixture of water, salt, and very small amounts of urea, uric acid, and phosphorus
  • Main purpose is for thermoregulation and minor excretion
• Apocrine Sweat Glands


  • Found in only some areas such as the armpits and anogenital areas
  • Secretes water, protein and amino acids that is active during puberty, emotional stress, or sexual stimulation
  • Can contribute to body odor when left unchecked
• Ceruminous Sweat Glands

  Modified sweat glands that secrete earwax
• Ciliary Sweat Glands

  Modified sweat glands that produces a tear-like substance that lubricates and protects the eyes
• Mammary Sweat Glands


  Modifies sweat glands that secrete milk that nourishes developing infants and fetuses
• Effects of skin aging

  • Rougher and dryer skin due to loss of cuticle in the surface
  • May develop benign tumors and lesions
  • Slack or soggy due to loss of elastin fibers in connective tissue of the dermis
  • Transparent due to loss of layers in the epidermis
  • Fragile due to continuous death of connective tissue in the dermis
  • Easily bruised due to thinning of walls of the blood vessels of the dermis
  • Losses fat in areas of the hypodermis (cheek, temple, chin , nose and eyes)
  • Discoloration due to decline in activity for melanocytes
  • Hair turns gray as it enters its final stage (telogen)
• Skin care tips

  • Regularly cleanse skin with suitable products
  • Carefully wash skin with soap without harmful substances
  • Wear sunscreen
  • Avoid 10am - 2pm sun exposure
  • Control hypertension (high BP) and diabetes
  • Avoid smoking
  • Regularly exercise
  • Adequate sleep
  • Take supplements, minerals, vitamins and antioxidants
• Skeletal and muscular systems

  Used to support and protect and are used for locomotion
• Types of skeletal systems

  • Hydrostatic Skeleton
  • Exoskeleton
  • Endoskeleton
• Hydrostatic Skeleton


  • Has a fluid held under pressure and a closed body compartment
  • Commonly used by cnidarians, flatworms, annelids, and nematodes
• Exoskeleton

  • A hard covering deposited on the animals surface
  • Shells of clams and some mollusks are from Calcium Carbonate from their mantle, an extension of their body cavity
  • Arthropods have a joint skeleton called a cuticle made up of 30 % chitin secreted by the epidermis (shedded off in molting)