Integumentary system

• Largest single organ of the body is the skin
• Integumentary system also known as integument (L. Covering) or cutaneous layer
• Skin consist of 15-20% of the total body weight
• Functions of the skin

  • Protection
  • Sensory
  • Thermoregulatory
  • Metabolic
  • Sexual signaling
• Types of skin

  1. Thick skin - palms and soles (400-1400 um) (1.4mm)
  2. Thin skin - whole body except palm and sole (75-150um)
• General layers of the skin

  1. Epidermis
  2. Dermis
  3. Hypodermis
• Epidermis

  • Primary tissue composition: stratified squamous keratinized epithelium
  • lacks vasculature
  • receives nutrients only from the dermis
• Cells of epidermis

  • Keratinocyte - primary cell
  • Melanocyte - pigment producing cell
  • Langerhan cell - macrophage in skin/ Ag presenting cell
  • Merkel cells - Sensory (Tactile)
• KERATINOCYTES

  • Primary Cells located at epidermis
  • Originate in the deepest layer of the epidermis
  • Stratum basale move up to the final barrier layer of the skin, stratum corneum
• MELANOCYTES

  • Located at basal epidermis
  • Derived from neural crest
  • Pale staining and rounded cell bodies
  • Synthesize dark melanin pigment in melanosomes
  • Protect nuclear DNA from UV damage
  • Eumelanin - brown or black pigment (hair follicles)
  • Pheomelanin - in red hair
• Diseases related to melanocyte

  1. Albinism - less melanin than usual and due to defect in the enzyme tyrosinase.
  2. Vitiligo - patches of skin and happens when melanocyte are attacked and destroyed
• LANGERHANS CELLS/ Macrophage in skin

  • APC antigen (antigen precenting cells)
  • 2-8% of the cell in epidermis
  • located at spinous layer (stratum spinosum)
  • Bind, process and present antigens to T-lymphocytes
• MERKEL CELLS

  • Aka Epithelial Tactile Cells
  • Mechanoreceptors for light touch
  • Abundant in fingertips and bases of some hair follicle
  • Characterized by small, Golgi-derived dense-core neurosecretory granules containing peptides.
• LAYERS OF THE EPIDERMIS

  • Stratum Corneum – Thick and Thin Skin
  • Stratum Lucidum – Thick Skin
  • Stratum Granulosum – Thick and Thin Skin
  • Stratum Spinosum/Germinativum – Thick and Thin Skin
  • Stratum Basale – Thick and Thin Skin
• STRATUM CORNEUM

  • 15-20 layers of dead, flattened, anucleate, keratin-filled keratinocytes called squames.
  • Bound by hydrophobic lipid-rich segment that provides protection against friction and waterloss
  • Superficial
• STRATUM LUCIDUM

  • 2-3 layers of anucleate, dead cells
  • seen only in thick skin
• STRATUM GRANULOSUM

  • 3-5 layers of keratinocytes
  • Contains kerato-hyaline granules - which are intensely basophilic [have intense affinity in basic dyes]
  • Contains lamellar granules (golgi derived) taht produces a lipid rich, impermeable layer around the cells forming a major part of the skins barrier against water loss
• STRATUM SPINOSUM/ GERMINATIVUM

  • Thickest layer
  • consist of generally polyhedral cells having nucleoli and cytoplasm actively synthesizing keratins
  • contains tonofibrils (keartinkeratin filament bundles)
  • Prickle Cells - keratin in our stratum spinosum
  • cells may still divide
  • langerhan cell is present
• STRATUM GERMINATIVUM

  • combination of stratum basale and spinosum
  • layer where they meet
• STRATUM BASALE

  • single layer of cuboidal to low columnar cell in contact with basement membrane
  • mitosis occur here
  • melanocyte and Merkel cell is present
• DERMIS

  • layers of connective tissue [fibro-adipose tissue]
  • supports epidermis and binds it to hypodermis (physically & metabolically)
  • contains projection called dermal papillae, connects with epidermal ridges
  • filled with blood vessels, nerves, and sensory receptors
  • Basement membrane - connects with epidermis
• LAYERS OF DERMIS

  Papillary layer

  • connects to epidermis
  • more superficial layer of dermis
  • contains subpapillary vascular plexus (group of bv)
  • Contains: Loose CT, Type I and VII collagen, Mast Cells, Dendritic Cells, Fibrils of type VII collagen
• LAYERS OF DERMIS

  Reticular Layer

  • thicker than papillary layer
  • deeper layer of dermis
  • dense irregular CT surrounding hair follicles, skin gland, nerves and deep plexus of blood vessels extending into subcutaneous layer
  • Contains: Dense CT, Type I collagen, fewer cells than papillary, elastic fibers
• Both dermal regions contain a rich network of blood and lymphatic vessels
• Nutritive Vessels from two major plexuses:

  1. Subpapillary Vascular Plexus (superficial) - between papillary and reticular layer; forms a rich, nutritive capillary network just below epidermis.
  2. Deep Plexus - with larger blood and lymphatic vessels lie near the interface of the dermis and the subcutaneous layer.
• Thermoregulatory function of the dermis is done by arteriovenous anastomosesa located between both plexuses
• Subcutaneous Layer/ Hypodermis

  • Superficial fascia/ panniculus
  • Layer beneath the dermis and usually consist of adipose and loose CT
  • contains larger vessels which supply and drain the dermal blood vasculature
• Sensory Receptorss

  - specialized cells or nerve endings that transform various form of energy in the environment (heat) into electrical signals

  1. Simple nerve endings with no Schwann cells or collagenous covering (unencapsulated)
  2. More complex structures with sensory fibers enclosed by glia and delicate CT capsule (encapsulated)
• Unencapsulated Receptors

  • Merkel Cells - tonic receptors for sustained light touch and for sensing anan objects texture.
• Unencapsulated Receptors

  • Free Nerve Endings - in the papillary dermis; respond primarily to high and low temperatures, pain, and itching
• Unencapsulated Receptors

  • Root Hair Plexus - surrounding the bases of hair follicles in the reticular dermis that detects movement of the hair
• UNENCAPSULATED RECEPTORS

  1. MERKEL CELLS - tonic receptors for sustained light touch and for sensing an object’s texture.
• UNENCAPSULATED RECEPTORS

  2. FREE NERVE ENDINGS - in the papillary dermis; responds primarily to high and low temperatures, pain, and itching
• UNENCAPSULATED RECEPTORS

  3. ROOT HAIR PLEXUS -surrounding the bases of hair follicles in the reticular dermis that detects movements of the hairs
• CAPSULATED SENSORY RECEPTORS

  1. MEISSNER CORPUSCLES - initiate impulses when there is light-touch or low-frequency stimuli against skin. Numerous in fingertips, palms and soles but decline slowly in number during aging after puberty
• CAPSULATED SENSORY RECEPTORS

  2. LAMELLATED CORPUSCLES - for detection of pressure or firm

  touch.
• CAPSULATED SENSORY RECEPTORS

  3. KRAUSE END BULBS - found primarily in the skin of the penis and clitoris where they sense low-frequency vibrations.
• CAPSULATED SENSORY RECEPTORS

  4. RUFFINI CORPUSCLES - With sensory axons stimulated by stretch (tension) or twisting (torque) in the skin.
• EPIDERMAL APPENDAGES

  Help maintain the body’s homeostasis

  1. Hair
  2. Nails
  3. Glands (sweat and sebaceous glands)
• HAIR

  • keratinized structure forming within epidermal envagination called hair follicles.
  • All skin has at least minimal hair except the globrous skin of the palms, soles, lips, penis, clitoris, labia minora
  • rapidly undergoing keratinization to form the medulla, cortex, and cuticle of a hair root.