Integumentary System

The Integumentary System is part of the Anatomy and Physiology section which provides High Yield information for the MCAT exam needed for Medical School.

Table Of Contents
1 Structure of the Skin
2 Layers of the Skin
2.1 Epidermis
2.2 Dermis
2.3 Hypodermis
3 Functions of Integumentary System
4 Derivatives of the Epidermis (skin appendages)
5 Surface Anatomy
6 Tissues Anatomy

Structure of the Skin

Human skin structure
Tomáš Kebert & umimeto.org / CC BY-SA

Layers of the Skin

Epidermis
  • – Keratinized stratified squamous epithelium
    • 1. keratinocytes (90% of cells)
      • a. produce fibrous protein keratin (as intermediate filaments of cytoskeleton)
      • b. help provide protective properties of skin
    • 2. melanocytes (8%)
      • a. produce pigment melanin that protects from UV light
      • b. have projections that extend between keratinocytes, keratinocytes phagocytize projections to take in melanin
    • 3. dendritic cells
      • a. produced in red bone marrow
      • b. important in immune response
      • c. projections form a network in some layers
    • 4. tactile epithelial cells
      • a. associated with nerve endings (tactile discs)
      • b. important in sense of touch
  • – Thickness ranges from .1 mm – 2 mm
  • – Layers of epidermis (strata, from deep → superficial)
    • 1. stratum basale
      • a. one row of mainly cuboidal or columnar keratinocytes
      • b. melanocytes and tactile cells scattered among keratinocytes
      • c. divide often, older cells push upward and become parts of other layers (accumulate more keratin)
      • d. also known as stratum germinativum
    • 2. stratum spinosum
      • a. 8 – 10 cells thick, more superficial keratinocytes are flatter
      • b. some keratinocytes can still divide
      • c. dendritic cells and projections of melanocytes
    • 3. stratum granulosum
      • a. 3 – 5 cells thick, flattened keratinocytes
      • b. nuclei and organelles degenerate, lots of keratin (many cells dead)
      • c. cells contain keratohyaline granules (no membrane, bundles together keratin filaments)
      • d. also lamellar granules (membrane, lots of lipids, forms waterproof barrier between this and superficial layers)
    • 4. stratum lucidum
      • a. only in thicker skin (palms and soles)
      • b. 3 – 5 cells thick, very flat, dead keratinocytes
      • c. lots of keratin and keratohyaline
    • 5. stratum corneum
      • a. 25 – 30 cells thick, very flat, dead keratinocytes
      • b. lots of keratin, keratohyaline and lipids from lamellar granules
      • c. waterproof barrier that protects from light, heat, chemicals and invaders
      • d. constantly shed
Dermis
  • – Connective tissue with other embedded structures
    • 1. cells include fibroblasts, macrophages
    • 2. contains blood vessels and nerves
    • 3. glands and hair follicles are embedded
  • – Regions of dermis
    • 1. papillary region
      • a. areolar CT with elastic fibers
      • b. projects into epidermis as dermal papillae
      • c. loops of capillaries
      • d. touch receptors
      • e. cause ridges in epidermis (fingerprints)
    • 2. reticular region
      • a. dense irregular CT with lots of collagen and some elastin
      • b. contains bits of adipose, hair follicles, nerves, oil and sweat glands
      • c. differs in thickness in different body areas (up to 2 mm)
Hypodermis
  • – Attaches dermis to underlying structures
    • 1. areolar and adipose
  • – Also known as subcutaneous layer or superficial fascia
  • – Contains blood vessels and nerves

Functions of Integumentary System

  • – Temperature regulation
    • 1. evaporation of sweat decreases body T
    • 2. changes in blood flow (more blood → lose heat, less blood → conserve heat)
  • – Protection
    • 1. physical barrier to invasion, dehydration and UV radiation
    • 2. contains cells of immune system
  • – Sensation
    • 1. nerve cells with receptors for pain, touch, pressure, temperature
  • – Excretion
    • 1. water and dissolved substances in sweat
  • – Acts as a blood reservoir
    • 1. flow can be shifted to hard-working muscles if needed
  • – Vitamin D synthesis
    • 1. epidermis makes inactive form of vitamin D upon exposure to UV
    • 2. important in absorption of calcium

Derivatives of the Epidermis (skin appendages)

  • – Hair
    • 1. dead, keratinized cells
    • 2. shaft projects from surface of skin
    • 3. root is beneath skin surface
      • a. surrounded by hair follicle (from epidermis)
      • b. root plexus consists of nerve endings that contribute to sense of touch
    • 4. arrector pili
      • a. smooth muscle
      • b. can make hair “stand up” with cold or emotional stress
    • 5. functions
      • a. protect from light
      • b. decrease heat loss
      • c. protect eyes and nose from particles
      • d. sense of touch
      • e. hold chemical signals (pheromones)
  • – Sebaceous (oil) glands
    • 1. holocrine glands
    • 2. ducts usually open to hair follicle
    • 3. secrete sebum
      • a. mix of fats, cholesterol, proteins, salts, pheromones
      • b. coats hairs
      • c. holds moisture in the skin
      • d. inhibits most bacterial growth
  • – Sudoriferous (sweat) glands
    • 1. eccrine sweat glands (functionally merocrine)
      • a. on most skin
      • b. ducts open to skin surface
      • c. secrete sweat
        • 1) water, salt, some wastes (urea, ammonia)
        • 2) mainly for cooling body, some excretion, acidity protects from bacteria
    • 2. apocrine sweat glands (functionally merocrine)
      • a. axillary, genital and anal regions
      • b. ducts open to hair follicles
      • c. secrete sweat, fats and proteins
      • d. may function in sexual signaling (pheromones)
  • – Nails
    • 1. hard, keratinized cells
    • 2. nail body is visible
    • 3. root is under skin
    • 4. functions – grasp and manipulate objects, scratching

Surface Anatomy

Tissues Anatomy