Integumentary System

• Keratinocytes


  Cells of the epidermis that contain large amounts of the protein keratin
• Keratin


  A tough, fibrous protein that is also the basic structural component of hair and nails in humans
• Layers of the epidermis

  • Thin skin (4 layers of keratinocytes)
  • Thick skin (5 layers of keratinocytes, found in palms and soles)
• Epidermal growth factors (EGF)


  Peptide growth factor produced by the salivary glands and duodenal glands
• Roles of EGF


  • Promoting the divisions of basal cells in the stratum basale and stratum spinosum
  • Accelerating the production of keratin (keratinization) in differentiating keratinocytes
  • Stimulating epidermal development and epidermal repair after injury
  • Stimulating secretory product synthesis and secretion by epithelial glands
• Layers of the dermis

  • Papillary layer (areolar tissue, contains capillaries, lymphatic vessels, and sensory nerve fibers)
  • Reticular layer (interwoven meshwork of dense irregular connective tissue containing collagen and elastic fibers)
• Collagen fibers


  Very strong and resist stretching, but they are easily bent or twisted
• Elastic fibers


  Permit stretching and then recoil to their original length
• Aging, hormones, and the destructive effects of UV radiation permanently reduce the amount of elastin in the dermis, preventing it from recoiling to its original size after delivery or weight loss
• Epidermal pigmentation and dermal circulation


  Influence skin color
• Melanin


  The primary determinant of skin color
• Melanin in keratinocytes protects the epidermis and dermis from the harmful effects of sunlight, which contains significant amounts of ultraviolet (UV) radiation
• Hemoglobin is bright red, giving capillaries in the dermis a reddish tint that is most apparent in lightly pigmented individuals. When dilated, the red tones are more pronounced
• Sunlight converts steroids to vitamin D3

  1. Sunlight exposure

  2. Epidermal cells in the stratum spinosum and stratum basale convert a cholesterol-related steroid compound into cholecalciferol or vitamin D3

  3. Liver then converts cholecalciferol into an intermediary product used by the kidneys to synthesize the hormone calcitriol
• Too much sunlight can damage epithelial cells and deeper tissues, but limited exposure to sunlight is beneficial
• Vellus hairs


  Fine "peach fuzz" hairs located over much of the body surface
• Terminal hairs


  Heavy, more deeply pigmented, and sometimes curly
• After puberty, the follicles produce terminal hairs in response to circulating sex hormones
• The cross-sectional shape of the hair shaft and its hair follicle


  Determine whether hairs are curly or straight
• Mammary glands


  Anatomically related to apocrine sweat glands
• Ceruminous glands


  Modified sweat glands in the passageway of the external ear
• Ceruminous gland secretions combine with those of nearby sebaceous glands, forming a mixture called cerumen, or earwax, which helps trap foreign particles and prevent them from reaching the eardrum
• Compact bone


  Solid, dense bone
• Spongy bone


  Porous, less dense bone
• Endochondral ossification


  Bone formation process
• Intramembranous ossification


  Bone formation process
• The skeletal system has major functions, including protecting organs, providing support and structure, facilitating movement, and storing minerals
• Common disorders of the skeletal system include osteoporosis, Paget's disease, gigantism, dwarfism, spina bifida, and herniated disks
• The human skeletal system is divided into the axial skeleton and the appendicular skeleton
• Bones of the axial skeleton

  • Cranial bones
  • Facial bones
  • Sternum
  • Ribs
  • Vertebrae
• Bones of the appendicular skeleton

  • Shoulder girdle
  • Arm
  • Forearm
  • Wrist
  • Hand
  • Fingers
  • Pelvic girdle
  • Thigh
  • Lower leg
  • Ankle
  • Foot
• The three types of bone cells developmentally related are osteoblasts, osteoclasts, and osteocytes, progressing from the earliest to the latest stage
• Bone remodeling and homeostatic mechanisms are important for the skeletal system