PHS 3504 - Skin AKA Integumentary System

• wound healing: repair of the skin

  1) injury triggers bleeding (damages to the capillaries) and mast cells get activated to initiate the inflammation

  
  

  2) blood clotting (scab/provisional matrix formation) to limit bleeding and temporarily seal the cut against microbes

  
  

  3) epithelial stem cells proliferate to replenish lost keratinocytes. macrophages chew away the scab/provisional matrix, and fibroblasts secrete collagen to fill the vacancy

  
  

  4) the scab is shed, and the epidermis is repaired. in dermis, scar tissue is deposited
• scar formation

  fibroblasts secrete collagen into wound to fill the vacancy
• inflammation

  recruitment of cells from blood vessels:

  (a) platelets - clotting

  (b) white blood cells - fight infection

  (c) fibroblasts - tissue repair/scar formation
• deep wound healing

  occurs when an injury extends deep to the dermis and subcutaneous layer --> loss of function and development of scar tissue

  
  

  cut/damage extend beyond the epidermis and blood vessels (capillaries) are damaged

  
  

  bleeding --> clot formation (hemostasis/blood coagulation)

  
  

  inflammation and scar formation are involved
• epidermal wound healing

  occurs following superficial wounds that affect only the epidermis (ex: paper cuts, first-degree burns)

  
  

  damage is not extended beyond the epidermis --> no blood vessels are damaged --> no blood clot formation

  
  

  inflammation or recruitment of cells from blood vessels is not involved

  
  

  basal stem cells divide to regenerate "stratum basale"

  
  

  cells of the "stratum basale" differentiate to replenish upper layers of epidermis
• types of wound healing

  1. epidermal wound healing

  2. deep wound healing
• wound healing

  refers to a living organism's replacement of destroyed or damaged tissue by newly produced tissue

  
  

  in undamaged skin, the epidermis and dermis form a protective barrier against external environment. when this barrier is broke, wound healing is set in motion to repair the damage

  
  

  two kinds of wound-healing processes can occur, depending on the depth of the injury
• burn healing

  1. first-degree: only damages the epidermis, the "basal stratum" of the epidermis is intact (stem cells available) and will generate new keratinocytes for repair (no scar formation)

  
  

  2. second-degree: damages extend to the dermis. fibroblasts withing the dermal layer become activated and recruit more fibroblasts (to secrete & deposit collagen --> scar formation). remaining epithelial "basal" cells (stem cells) also start to divide to replenish lost keratinocytes

  
  

  3. third-degree: all "epithelial cells" and "fibroblasts" are gone, so nothing can occur. Only skin graft will repair the skin
• third-degree burn

  a full-thickness burn (as the burn destroys the epidermis, dermis, and subcutaneous layer)

  
  

  most skin functions are lost, and region is numb because sensory nerve endings have been destroyed

  
  

  skin may appear black, white, brown, or yellow at the injury site

  
  

  no new skin will be formed
• common causes of second-degree burns

  severe sunburn, scald, flame, chemicals, and electricity
• second-degree burn

  A partial-thickness burn (destroys the epidermis and part of the dermis)

  
  

  can be superficial or deep

  
  

  deep second-degree burns can cause scarring

  
  

  some skin functions will be lost

  
  

  causes deep redness, blister formation, edema, and pain (can be severe and intense)
• common causes of first-degree burns

  mild sunburns or from using a tanning bed

  
  

  flash burns: a sudden brief burst of heat, such as light scalding
• first-degree burn

  Superficial burns

  
  

  it only damages the epidermis

  
  

  it is characterized by mild pain, swelling, and erythema (redness), but is dry without blisters, and skin functions remain intact
• dermatologists

  medical doctors who specialize in treating disorders of the integumentary system
• burn

  tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature the proteins in the skin cells

  
  

  burns disrupt skin integrity

  
  

  burns destroy the skin's functions - protection against microbial invasion, sensory, and thermoregulation

  
  

  burns are graded according to their severity: first-degree, second-degree, and third-degree burns
• integumentary system barriers

  1. physical barriers: a dense tissue combined with keratin & hair

  2. chemical barrier: secretion (acids & oils: sebum, cerumen)

  3. immunological barrier: white blood cells (leukocytes)
• cerumen function

  provides a sticky barrier to prevent entry of foreign bodies into the ear canal
• cerumen

  ear wax
• ceruminous glands

  modified sweat glands located in the ear canal

  
  

  produce a waxy secretion called cerumen
• apocrine sweat glands

  located mainly in the skin of the axilla (armpit), groin, and bearded facial regions of adult males

  
  

  secrete a slightly viscous sweat which helps reduce friction from hair

  
  

  release sweat due to excitement (sexual arousal)

  - NOT INVOLVED in thermoregulation

  - much of body odor is due to apocrine sweat
• eccrine sweat glands (merocrine)

  the most common and cover most of the body

  
  

  secrete a water solution (600mL/day) that helps cool the body and eliminates small amounts of waste

  
  

  release sweat in response to "heat" in order to "cool the body" (thermoregulation); also release due to emotional stress (fear, embarrassment) --> referred to as emotional sweating or "cold sweat"
• two types of sweat glands (sudoriferous)

  1. eccrine sweat glands

  2. apocrine sweat glands
• arrector pili muscle

  an involuntary muscle that causes the hair to stand on end
• function of sebum

  - prevents dehydration of hair and skin

  
  

  - inhibits growth of certain types of pathogenic bacteria
• sebaceous gland

  a duct that merges with hair follicle to secrete oil to skin surface for moisture

  
  

  fused to hair follicles

  
  

  secrete an oily substance called sebum
• exocrine gland


  a gland that secrete a substance to skin surface
• hair root

  the part of hair that penetrates the dermis
• hair function

  protects the body:

  1. against harmful effects of the sun

  2. against heat loss

  3. sensing touch via hair follicle receptors

  
  

  anchors:

  - connective tissue within dermal layer connecting root

  - smooth muscle within dermal layer connecting root (arrector pili muscle)
• hair

  a nonliving structure (keratinous filament) produced by hair follicles

  
  

  present on most surfaces except the palms, anterior surface of fingers, and the soles of the feet

  
  

  associated with sebaceous gland and arrector pili muscle (a type of smooth muscle)
• thermoregulation by the skin

  during strenuous physical activities, such as skiing or running, the dermal blood vessels dilated and sweat secretion increases. these mechanisms prevent the body from overheating

  
  

  in response to low temperatures, the dermal blood vessels constrict to minimize heat loss
• sensory receptors in the skin

  the skin contains different types of sensory receptors to differentiate the different tactile (touch) sensations

  
  

  light touch, pressure, vibration, itch and tickle

  
  

  these sensory receptors are found in different layers of the skin:

  a) superficial layer

  - free nerve ending - detect many stimuli, including pain and temperature

  - Merkel discs (detecting touch)

  - Meissner corpuscles (detecting touch)

  - hair follicle receptors (detecting touch)

  b) deep layer

  - Pacinian corpuscles (detecting vibration and touch)
• hypodermis


  attaches the skin to the underlying tissue and organs

  
  

  contains blood vessels and nerves that extend to the more superficial layers - dermis

  
  

  contains sensory corpuscles that detect external pressure onto the skin
• epidermal ridges

  when the thin epidermis adapts to the contours of the dermal papillae

  
  

  function as "speed bumps" on the epidermal layer to increase friction (firmness of grip)

  
  

  form the basis for fingerprints or footprints
• dermal ridge

  accumulated collagen fibers

  
• dermal papillae


  small, nipple-like extensions of the dermis underlying the epidermis

  
• regions of the dermis

  1. superficial papillary layer

  - loose connective tissue, collagen fibers

  2. deeper reticular layer

  - dense irregular connective tissue, collagen fibers, elastic fibers
• dermis

  might be considered as the "core" of the integumentary system, as distinct from the epidermis and hypodermis

  
  

  made of two layers of connective tissue that compose an interconnected mesh of collagen and fibers, produced by fibroblasts

  
  

  is composed of loose and dense connective tissue

  
  

  does NOT contain epithelial cells

  
  

  contains blood and lymph vessels, nerves, and hair follicles and sweat glands
• albinism

  a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to a defect of an enzyme involved in the production of melanin
• vitiligio

  a chronic disorder that causes depigmentation patches in the skin

  
  

  the precise pathogenesis, or cause is not known but is most likely a combination of genetic factors with a disorder of the immune system (autoimmune disease)
• malignant melanoma

  cancer of melanocytes