The Integumentary System: An Overview

Functions:

� Protective covering � Helps regulate body temperature � Retards water loss from deeper tissues � Houses sensory receptors � Synthesizes biochemicals � Excretes small quantities of waste

Consists of…

� Cutaneous membrane �  Epidermis � Dermis

� Accessory structures- hair, sweat glands, sebaceous glands etc.

� Subcutaneous layer (hypodermis)

Components

Figure 5.1

The Epidermis

Epidermis

� The epidermis is composed of layers of keratinocytes- cells that produce keratin

Figure 5.2

The Epidermis � Composed of stratified squamous epithelium �  Lacks blood vessels � Older cells are pushed to the top and harden

in a process called keratinization.

Layers of the epidermis:

� Stratum basale/ germinativum � Stratum spinosum � Stratum granulosum � Stratum lucidum � Stratum corneum

From deep…….

…… to superficial

Epidermis Cell Layers � Germinative

�  Basal cells (stem) are reproducing � Spinosum- spiny layer � Granulosum- grainy layer

�  Stops dividing, start producing keratin �  Lucidum

�  The clear layer found only in thick skin � Corneum

�  Exposed to surface and shed every 2 wks.

Skin color depends on… � Blood supply

�  Interrupted blood supply leads to cyanosis- blue! � Carotene

� Orange-yellow pigment found in orange vegetables � Melanin

�  Yellow-brown pigment �  Protects us from UV radiation �  Produced by melanocytes

Melanocytes

Figure 5.5a, b

Epidermal cells � Synthesize vitamin D3 (cholecalciferol) when

exposed to UV

� Aids in absorption of calcium and phosphorus- needed for bone strength

The Dermis

Dermal Organization �  Located between epidermis and

subcutaneous layer

�  Anchors accessory structures- hair follicles, sweat glands, blood vessels etc.

�  Two components: �  Outer papillary layer �  Deep reticular layer

Layers of the Dermis

� Papillary layer �  Areolar tissue � Contains blood vessels, lymphatics, sensory

nerves of epidermis

� Reticular layer � Dense irregular connetive tissue � Contains network of collagen and elastic

fibers to resist tension

Stretch Marks

� Caused by excessive stretching of the dermis

� Patterns of collagen and elastic fibers form lines of cleavage

Hypodermis

� Elastic areolar tissue and adipose tissue � Stabilizes skins position against

underlying organs and tissues � Shock absorber and insulator � Few capillaries and no vital organs � Subcutaneous injection is useful to

administer drugs

Hairs

� Composed of keratinized dead cells that are produced in hair follicles

� Project deep into the dermis and often into the hypodermis

Structures �  Hair papilla

�  Connective tissue containing capillaries and nerves

�  Root �  Anchors hair into skin

�  Shaft �  Part we see on the surface �  Consists of three layers ○  Cuticle- overlapping shingle layer ○  Cortex- underlying layer- pigments ○  Medulla- core of hair

Structures Contd.

� Sebaceous Glands � Discharge oily substance into hair follicles �  Inhibits growth of bacteria

� Arrector pili muscle �  Pulls on follicle, forcing the hair to stand up � Cold or emotional states- goosebumps

Hair Color

� Produced by melanocytes at the hair papilla

Function of Hair �  Head

�  Protection from UV light �  Cushion a light blow to head �  Insulation

�  Nostrils, ears, and eyes �  Prevent entry of particles

�  Sensory �  Sensory nerve fiber at base of every hair

Exocrine Glands- Reach Outside � Sebaceous glands (Oil glands)

�  Associated with hair �  Secrete sebum, which lubricates and inhibits

bacteria growth �  Acne- condition when they are clogged

� Sweat glands (Watery Glands) �  2 kinds ○  1- hormonal- armpits, groin, nipples ○  2- All over body

Nails

� Keratinized cells that protects the tips of fingers and toes

Structures � Nail Body

� Covers an area of the epidermis called the nail bed

� Nail Root � Where nail production occurs � Not visible on surface

� Cuticle �  Portion of stratum corneum

Structure Contd.

�  Lunula �  Pale crescent area near the root were blood

vessels are absent