zoo 102 lec

• three major layers of the skin: epidermis, dermis, and hypodermis or subcutaneous
• Integumentary system - It’s your body's outermost layer. It includes your skin, hair, nails, and glands. These organs and tissues serve as your first line of defense against microorganisms while also protecting you from harm and sunlight. Your integumentary system coordinates with other systems in your body to maintain equilibrium
• Four components of the integumentary system: skin, hair, nails, and glands
• SKIN

  • The skin is often known as “the largest organ in the human body. ”
  • The largest surface area of all the organs.
  • Weighs more than any single internal organ, accounting for about 15% of body weight
  • Skin is an integumentary system organ composed of a layer of tissues that protects the muscles and organs beneath it.
• The average square inch of skin contains 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and over a thousand nerve endings. It is the most significant defense against pathogens and also helps in Vitamin D and B synthesis
• Skin main functions:

  • Protection: provides an anatomical barrier between the internal and exterior environment
  • Sensation: reacts to the environment due to variety of nerve endings
  • Heat regulation: allows precise control of energy loss
• Epidermis - made up of stratified squamous keratinizing epithelium and an underlying basement membrane. 2 main types of cells that make up the epidermis: keratinocytes and Langerhans cells
• Hypodermis - is not considered as a layer of the skin. It aims to connect the skin to the underlying bone and muscle while also supplying it with blood vessels and nerves. The hypodermis contains 95% body fat which serves as a padding and insulation for the body.
• • Dermis - contains blood vessels, nerves, hair follicles, smooth muscle, glands, and lymphatic tissue. Collagen, elastin, and reticular fibers are present. The main cell types of dermis are fibroblasts, adipocytes, and macrophages.
• Epidermis:

  • can further be divided into the following strata: corneum, lucidum, granulosum, spinosum, basale.
  • cells are formed through mitosis at the innermost layers
  • Keratinization: is a cytodifferentiation process that keratinocytes go through as they transition from their post-germinative state (stratum basale) to a differentiated, hardened cell filled with protein, constituting a structurally and functionally distinct keratin-containing surface layer.
  • This layer of skin keeps water in the body while keeping other dangerous substances and germs out.
• Dermis:

  • Papillary layer: outermost and reaches into the epidermis to provide it with vessels. Papillary ridges form the lines of the hands, giving us fingerprints.
  • Reticular layer: more dense and continuous with the hypodermis. It houses the majority of the structures such as sweat glands.
• Hypodermis:

  • is not usually classified as a layer of the skin
  • aims to connect the skin to the underlying bone and muscle while also supplying it with blood vessel and nerves.
  • contains 95% body fat
  • serves as padding and insulation for the body
• Hair:

  • Hair is derived from the epidermis but grows its roots deep into the dermis.
  • Hair covers the majority of the body with the few exceptions of the palms, soles, lips, and portions of external genitalia.
  • Hair provides mechanical protection for the skin, improves sensory function, and helps regulate body temperature.
  • Hair growth occurs in three phases: anagen (growth phase), catagen (nonproliferative phase), and telogen (resting phase), which cycle based on hormones and nutrition.
  • Hair is made of a protein called keratin.
• Stages of Hair Growth:

  • Anagen - longest phase; 3-5 years on your head
  • Catagen - last up to 10 days; about 5% of the hairs on your head
  • Telogen - last up to 3 months about 10- 15% of the hairs on your scalp
• Exogen

  • the extension of the telogen stage
  • washing and brushing aid in the removal of hair from the scalp
  • 50 to 100 hairs per day is lost
  • last for about 2-5 months
• Three Parts of the Hair:

  • Hair Follicle - the tube-like structure that holds the hair to the skin
  • Hair Shaft - the areas of your hair that you can see, touch, and style
  • Hair Bulb - located under your skin and is responsible for hair growth
• Nails:

  • The nails are an important structure composed of keratin. It generally serves two purposes: As a protective plate and Enhances sensation of the fingertip
  • Structure: The nail has six distinct parts: the root, nail bed, nail plate, eponychium (cuticle), perionychium, and hyponychium.
• Stages of Hair Growth

  A) Anagen (growing phase)

  B) Catagen (transition phase)

  C) Telegen (resting phase)

  D) Exogen (shedding phase)

  
• Parts of the Nail

  A) Proximal Nail Fold

  B) Eponychium

  C) Cuticle

  D) Lunula

  E) Distal Edge

  F) Nail Plate

  G) Lateral Nail Fold

  
• Parts of the Nail

  A) Eponychium

  B) Lunula

  C) Nail Plate

  D) Free Edge

  E) Hyponichium

  F) Nail Groove

  G) Perionychium

  H) Nail Bed

  I) Root

  
• Parts of the Nail:

  • Root - aka as the germinal matrix; produces most of the volume of the nail and nail bed
  • Eponychium - the visible part of the proximal nail fold that appears to end at the base of the nail
  • Cuticle - located between the skin of the finger and the nail plate, fusing two tissues together and providing a waterproof barrier
  • Lunula - the half-moon at the base of the nail
  • Nail Bed - called the sterile matrix; contains blood vessels, nerves, and malanocytes
  • Nail Plate - this is the actual fingernail, made of translucent keratin
• Parts of the Nails

  • Hyponychium - the area between the nail plate and the fingertip; provide a waterproof barrier
  • Nail Groove - are grooves on the skin at the edge of the free edge; serves as the nail's guideline as it grows
  • Perionychium - aka the nail wall; skin that overlies the nail plate on its sides
  • Distal Edge - aka the free edge; the anterior margin of the nail plate corresponds to the abrasive or cutting edge of the nail
  • Proximal Nail Fold - soft tissues that protects the emerging nail plate
• Glands

  • Glands are present all throughout your skin. They move things such as water, salt, and oil from beneath your skin to the surface.

  Two types of sweat glands in humans:

  1. Eccrine (merocrine) - Found all through out the body, but most common on the palms of the hands, soles of the feet, and the forehead. (for humans)
  2. Apocrine - only develop during early- to mid-puberty
  3. release greater than average levels of perspiration for around a month
  4. Produce sweat that contains fatty materials
• The integumentary system consists of the following glands:

  • Sudoriferous glands: are sweat-producing glands, which makes them important in helping to maintain body temperature
  • Sebaceous glands: are oil-producing glands that help inhibit bacteria, stay waterproof, and keep our hair and skin from drying out.
  • Ceruminous glands: produce earwax which keeps the outer surface of the eardrum pliable and prevents drying.
  • Mammary glands: produce milk
• The Embryonic Origin of:

  • skin glands - formed from the invagination of the surface epidermis
  • dermis - The dermis develops from mesoderm and mesenchyme and produces the reticular lamina
  • epidermis - The single-layered surface ectoderm proliferates to give rise to the multilayered epidermis and produces the basal lamina
  • hypodermis - Mesodermal cells differentiate into adipocytes, which are responsible for storing fat and providing insulation and cushioning.
• Dermis derivatives: dermal bone and fish scale
• Dermal bone is the outermost layer of bone that is covered by skin; ostracoderms and placoderms
• Types of Scales: Placoid, cosmoid, ganoid, ctenoid, cycloid, teleost
• Cosmoid scales - Found in Placoderms (extinct) as plates, and also typical of the Lobe Finned Fishes or Sarcopterygii, (Choanichthyes). Extinct fish had scales of enamel, cosmine and bone with pulp cavities. Modern ones, like Coelacanth and the lungfish have calcified fibers so this type of scale is almost extinct. No specimens available.
• Ganoid Scales - Made of multi-layered enamel called ganoin over lamellar bone. Primitive (now extinct) species also had a cosmine layer and vascular bone with pulp, but these were lost in modern day examples.
• Placoid Scales - Made of enamel (epidermal) and the dermal derivatives, dentine and bone with a pulp core. They are typical of cartilaginous fishes. Placoid scales are responsible for the rough feeling of dogfish skin.
• Teleost (bony fish) scales - These are thin scales of dermal bone. They have a thin covering of epidermal tissue over them. It is derived by reduction (loss) of parts of a ganoid scale. There are two types depending on their shape
• Cycloid scales - a round-ended scale
• Ctenoid Scales - A comb shaped end is characteristic of this scale type.
• WHAT ARE THE EXTERNAL COVERINGS OF VERTEBRATES?

  Serve critical functions such as:

  • Protection
  • Insulation
  • Sensory perception
  • Communication within the species
• Importance of External Coverings of Vertebrates

  • the body's primary line of defense, especially for amniotes
  • vital mission of the integument in aquatic vertebrates is mucus secretion.
  • Cornification began in amphibians, improved in reptilians, and endured in avian and mammalian epidermis
  • The organ that holds the body together, covers and protects it, and provides communication with its environment.
  • The feather, the most ostentatious and functional structure of avian skin, evolved in the Mesozoic period.
• Cartilaginous Fishes skin

  • Multilayered
  • contains mucus and sensory cells
  • denticles: contain blood vessels and nerves
• Skin


  Vertebrate integument; same basic structure in all vertebrates (fish, reptiles, birds, humans, and other mammals. Largest organ in the body
• Skin of the Jawless Fishes


  Thick skin; epidermal glandular cells; one secretes the protective cuticle; multicellular slime glands secrete large amount of mucous (for protection)
• Bony Fishes skin

  Contain scales; thin layer of dermal tissue overlaid the superficial epidermis normally covers the scales; grow at the margins and at the lower surface permeable and used in gas exchange; mucus helps to fight off bacteria