BIOLOGY: Integumentary System

Integumentary System
> consists of the skin and skin derivatives (hair, nails, glands)
> largest organ in the body


I. EPIDERMIS
> outermost layer, 10 to 30 cells thick
> composed of epithelial tissues


EPI- : meaning outside or outer or above


Types of Epidermal Cells


1. Keratinocytes - produces the keratin

Keratin: creates a barrier to protect deeper layers of the skin from injury and microbial invasion
: makes the skin water-proof

2. Melanocytes : produces the pigment melanin

Melanin: brown-black pigment that contributes to skin color
:absorbs UV light (for protection from skin cancer)

-the more the melanin, the darker the skin; the darker the skin, the more protection from skin cancer-

Layers of the Epidermis

1. Stratum Corneum : consists of flat, dead cells completely filled with keratin
> cells are continuously shed and replaced
FUNCTION: barrier against light, heat, bacteria and many chemicals

2. Stratum Lucidum : consists of layers of clear, flat, dead cells
> more obvious in the thick skin of the palms and soles

3. Stratum Granulosum : consists of layers of flattened cells that develop darkly straining granules

4. Stratum Spinosum : consists of layers of many-sided cells that fit closely together

5. Stratum : also called stratum germinativum or stratum basale
: a single layer made up of stem cells which are capable of continued cell division

Layers 1-4 (stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum) are made out of dead cells while layer 5 (stratum a.k.a stratum germinativum a.k.a. stratum basale) is made out of living cells that performs continuous cell division.

Corneum - 'horny'
Lucidum - 'clear'
Granulosum - granules
Spinosum - spiney
Germinate - to produce new cells

II. DERMIS
> composed of connective tissue containing collagen and elastic fibers

Collagen - proteins that make the skin flexible, elastic and strong
: blood vessels, nerves, glands, and hair follicles are embedded in the


Smooth Muscle/ Arrector Pili : connected to hair follicles to the tissues of the skin

Sebaceous Glands : produces sebum (oils)

Sweat Glands : produces perspiration

epidermis - means 'above the dermis'
hypodermis - means 'under the dermis' and is made of fats

III. Subcutaneous Layer (a.k.a Superficial Fascia or Hypodermis)
> fat layer which insulates the body and stored energy

EPIDERMAL DERIVATIVES:

1. Hair or Pili : composed of colums of dead keratinized cells

Arrector Pili: smooth muscle that is attached to a hair
: its contraction pull the hair into a vertical position

2. Sebaceous gland : secretes sebum (misture of fats, cholesterol, etc.)

FUNCTIONS of Sebum:
-helps keep hair from drying and becoming brittle
- prevents excessive water evaporation
- keeps skin soft and pliable

3. Suderiferous (sweat glands) : produces sweat (perspiration)

PRINCIPLE FUNCTION: helps regulate body temperature through evporative cooling also eliminates a small amount of waste from the body

4. Nail : plate of lightly packed, hard keratinized cells of the epidermis

FUNCTIONS OF THE SKIN (a.k.a. Integumentary System)
1. Regulates body temperature

2. Protects from abrasion, bacteria, dehydration and UV (Ultra Violet) rays

3. Sensation detects stimuli related to temperature, touch, pressure, and pain

4. Excretion : removes heat, water, waste materials

5. Immunity: 1st line of defense

6. Synthesis of vitamin D: begins with the activation or a starting material in the skin by UV rays