LECTURE THREE

VERTEBRATE SKIN IS MADE OF THREE LAYERS:
1. EPIDERMIS, MADE OF STRATIFIED
   EPITHELIAL TISSUE
2. DERMIS, MADE OF CONNECTIVE TISSUE
3. SUBCUTANEOUS LAYER = HYPODERMIS,
   MADE OF FATTY TISSUE

STRATUM CORNEUM
STRATUM GERMINATIVUM

KERATIN IS A STRUCTURAL PROTEIN THAT IS
NOT SOLUBLE IN WATER AND WHICH ACCUMULATES
IN EPIDERMAL CELLS

THE DERMIS LAYER CONTAINS PRIMARILY
FIBROUS CONNECTIVE TISSSUE, BUT BONE
("DERMAL BONE"), BLOOD VESSELS, NERVES,
SENSE ORGANS FOR TOUCH, TEMPERATURE,
PRESSURE AND PAIN AND FAT MAY OCCUR
THERE ALSO

FAT IN THE SUBCUTANEOUS LAYER SERVES
AS A FOOD RESERVE, AS A THERMAL INSULATOR,
AND AS A CUSHION

DERIVATIVES = OUTGROWTHS = SPECIALIZATIONS

CATEGORIES OF DERIVATIVES OF THE SKIN:
1. BONY DERIVATIVES
     BONY PLATES OF OSTRACODERMS
     SHELLS OF TURTLES AND ARMADILLOS
     ANTLERS AND HORNS

2. KERATIN DERIVATIVES
     SCUTES (= KERATIN SCALES)
     FEATHERS
     CLAWS, NAILS AND HOOFS
     HAIR    HAIR FIBER IS ALPHA KERATIN
             HAIR FOLLICLE AND HAIR PAPILLA
             ARRECTOR PILI

3. GLANDS   A GLAND IS A GROUP OF CELLS WHOSE
   PRIMARY ACTIVITY IS THE PRODUCTION AND
   RELEASE OF FLUID MATERIALS
   THE FLUID RELEASED IS THE SECRETION OF
   THE GLAND
   TWO TYPES OF GLANDS:
   A. EXOCRINE GLANDS HAVE DUCTS AND
      RELEASE THEIR SECRETION INTO A
      BODY CAVITY OR ONTO THE SURFACE
      OF THE BODY
   B. ENDOCRINE GLANDS ARE DUCTLESS AND
      RELEASE THEIR SECRETION INTO THE
      BLOODSTREAM

ALL EXOCRINE GLANDS ARE DERIVATIVES
OF THE SKIN
   MUCOUS GLANDS SECRETE MUCUS
   POISON GLANDS
   SEBACEOUS GLANDS SECRETE OIL
   SWEAT GLANDS
   MAMMARY GLANDS
   SCENT GLANDS    MUSK GLANDS

 4. PIGMENT  A PIGMENT IS ANY CHEMICAL
    COMPOUND THAT HAS COLOR
       CHROMATOPHORES CONTAIN MELANIN
       AND ARE STELLATE
       IN HIGHER VERTEBRATES, CHROMATOPHORES
       RELEASE THEIR PIGMENTS

PLANTS DO NOT HAVE A SKIN, BUT ALL HIGHER
PLANTS HAVE A LAYER OF CELLS CALLED THE
EPIDERMIS ON THE SURFACE OF ROOTS,
STEMS AND LEAVES

A LAYER OF WAX CALLED THE CUTICLE OCCURS
ON STEMS AND LEAVES

THE STEMS AND ROOTS OF GYMNOSPERMS AND
LONG-LIVED DICOTS HAVE A CORK CAMBIUM
OUTSIDE THE VASCULAR CAMBIUM
   PHELLEM = CORK, CONTAINS SUBERIN
   PHELLODERM