The Integumentary System

The skin and its accessories

General Features

Body’s largest organSurface area of 1.2 to 2.2 square

meters4-5 Kilograms (7% of body weight)1.5-4.0 millimeters thick (paper towel)Damage impairs nearly every other

system

Functions

Protection-Provides a chemical, physical(mechanical) and biological barrier

Thermoregulation-Body temperature regulation

Sensory Organ-temperature, pressure, touch, and pain

Metabolic-Synthesis Vitamin D

Excretion-Small amounts of Nitrogenous wastes, water and salt

Blood reservoir

General Structure

EpidermisDermis Hypodermis /Subcutaneous (not

offically considered a part of the skin, but important none the less)

Epidermal Layers

Stratum corneum-outer most layer; 20-30 cell layers thick; 3/4 of epidermal layer

Stratum Granulosum-3-5 cell layers; last layer of the epidermis to receive nourishment

Stratum Basale/Germinativum-rapidly dividing cells; melanocytes lie directly above these cells

Epidermis Cell Types Keratinocytes Melanocytes

Keratin producing cells

Constantly rubbing off

Upper cells are dead

Forms an outer protective barrier

Melanin producing cells

Deepest layerProtect dividing

cells beneath them

Keratin

Protein found in the epidermis, hair and nails that makes those structures hard and water-repellent.

Melanin

Dark pigment formed by melanocytes; imparts color to hair and skin

EpidermisThick Skin Thin Skin

Dust Mite & Epidermal Cell

Features of the Dermis

Cell types: fibroblasts, macrophages, WBC’s

Fibers: collagen; reticular, elastic

Other Structures: nerve fibers;blood vessels; hair follicles; glands

Dermis

Dermis

“True Skin”Acts like a “body stocking” to hold

the body togetherConnective tissue; highly

vascularized

Layers of the DermisPapillary Reticular

Loosely wovenDermal papilla

form ridges to make finger-prints

Lots of blood vessels

80% of the dermisVery dense and

collagen rich

Hypodermis or Subcutaneous Layer

Although not officially considered a part of the skin, it must be examined in order to fully comprehend integumentary structure.

Features of the Hypodermis

Storage site for adipose tissue

Loosely anchors the skin to underlying muscle. Sliding allows blows to slide off and allows movement.

Factors Determining Skin Color

Melanin: Ranges from yellow to reddish-brown to black. Absorbs radiation from UV light to protect dividing cells beneath it.

Hemoglobin: Imparts a pinkish tint; lack of O2 gives a bluish cast (Cyanosis)

Carotene: Orange to yellow pigment found in many vegetables; accumulates in the stratum corneum

Effects of Aging

Fewer melanocytesFewer active hair folliclesDecreases sebaceous gland activityThin epidermisReduced sweat gland activityReduced blood supplyThinner dermis

FYI: One Square Inch of Skin Contains

65 Hairs  95-100 sebaceous glands 650 sweat glands  78 sensory apparatuses (for heat) 1,300 nerve

ending to record pain   13 sensory apparatuses (for cold) 9, 500, 000

cells  19 yards ( 17 mtrs) of blood vessels 78 yards (70

mtrs) of nerves  19,500 sensory cells at the ends of nerve fibres  160-165 pressure apparatuses for the perception

of tactile stimuli.