# Integumentary System

<p class="callout info">Apparently there is no chapter/section for this in the book?</p>

## Integument

- the skin and all accessory structure (hair, feathers, scales)

## Skin

- The largest vertebrate organ
- major part of the integument system

## Vertebrate integument and derivatives

### Functions

- Protection form abrasion
- protects against water loss
- barrier to disease causing pathogens
- protection from UV light
- temperature regulation
- contains sensory receptors
- excretion (limited)

### Vertebrate Integument

- skin and all other accessories
- skin is the largest organ o vertebrates
- skin consists of 2 layers 
    - epidermis
    - dermis

### Epidermis

- outer layer
- nutrients diffuse into the epidermis form the dermis
- stratified squamous epithelial cells

#### Cell types

- langerhans cells 
    - defensive cells
- Melanocytes 
    - produce pigment melanin
    - skin coloration
    - protect form UV light
- Merkel cells 
    - touch receptors
- Keratinocytes 
    - primary cell type
    - produce insoluble protein Keratin
    - amount of keratin increases from the inside to outside
    - keratin fill cytoplasm and impairs nutrient diffusion, cell dies

### Dermis

- Inner layer of skin 
    - thinner than dermis
- highly vascularized
- contains: 
    - sensory structures
    - vessels
    - nerves
    - glands
- Origin of hair/scales/feathers in vertebrates
- Sensory structures 
    - Meissner's corpuscles 
        - light touch
    - Pacinian corpuscles 
        - deep vibrations

#### Sweat Glands

- temperature regulation
- produce sweat (primarily water) 
    - evaporating cooling
    - release of waste ions
- 2.5 million on the body
- release of heat

#### Sebaceous Glands

- all over body, except palms and soles
- large on face, neck, and upper chest
- produce sebum 
    - lubricates and soften hair and skin
    - water proofing in aquatic mammals

### Hypodermis

- subcutaneous layer 
    - below the dermis
- not a layer of the skin
- contains much adipose (fat) tissue
- females have thicker layer of adipose tissue than males

#### Function

- body contour
- insulation
- support the skin