Integumentary System Overview

Study Notes

The Integumentary System

Integumentary System: Skin and its accessory structures
- Makes up 16% of body weight
- Approximately 1.5 to 2 square meters in area
- The largest organ system in the body
- Protects the body, provides immune defense, synthesizes hormones, maintains fluid content, and regulates body temperature
The skin is a vital part of life and appearance.

Layers of the Skin

The skin is composed of two main layers:
- Epidermis: Made of closely packed epithelial cells
- Dermis: Made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures
Beneath the dermis lies the hypodermis, which is composed mainly of loose connective and fatty tissues.

The Epidermis

Keratinized, stratified squamous epithelium
Composed of four (sometimes five) layers:
- Thin skin: Most of the skin of the body, has four layers
- Thick skin: Palms of hands and soles of feet, has five layers
Avascular
Cells are called "keratinocytes":
- Manufacture and store keratin, a fibrous structural protein
- Keratin makes hair, nails, and skin hard/tough
- Outer layers of keratinocytes are dead and slough off regularly
Cells in the epidermis are constantly undergoing mitosis, pushing older cells upward toward the apical surface.

Layers of the Epidermis

Stratum Basale:
- Bottom layer, more cuboidal in shape
- Constantly undergoing mitosis
- Closest to nutrients obtained from the dermis
- All keratinocytes start here
- Special cells:
  - Melanocytes: Produce melanin, a pigment that protects the skin from UV damage and determines skin tone
  - Merkel Cells (Tactile Cells): Detects "light touch," most abundant in hands and feet
Stratum Spinosum:
- Appears spiny due to desmosomes connecting cells
- 8-10 cell rows thick
- Some cell division still occurs
- Cells begin synthesizing keratin protein
- Cells secrete glycolipids that make the epidermis "waterproof"
- Special cells:
  - Langerhans Cells: Immune system cells that capture pathogens and debris
Stratum Granulosum:
- 3-5 cell rows thick
- Cells are tightly interlocked, no longer divide, and become flatter and thicker
- Cells produce:
  - Keratin protein
  - Keratohyalin: Connects keratins together, making the layer "grainy"
- Nuclei and organelles disintegrate once proteins are made.
Stratum Lucidum:
- Only found in thick skin (palms and soles)
- Cells are dead, sacs of protein wrapped in a membrane
- Cells contain high amounts of eleidin protein, which doesn’t stain, making the layer translucent
Stratum Corneum:
- Cells are dead, sacs of protein wrapped in a membrane
- 15-30 rows of squamous (flattened) cells, making it the thickest layer
  - This layer is what we see and touch.
- Keratin packed tightly into these cells, giving the layer its protective qualities
- This stratum is shed regularly.

mnemonic

"Be Still…Granny Looks Crazy" – A mnemonic for remembering the layers of the epidermis from the bottom up – stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.