Unit 4 study guide

Study Notes

Epidermis: The thin outer layer, composed of stratified squamous epithelium.
- The outermost layer is the stratum corneum, made of keratin and waterproof.
- Contains melanocytes and keratinocytes.
Dermis: The thick inner layer, primarily composed of connective tissue.
- Provides support and elasticity to the skin.

Melanin: Pigment ranging from yellow to dark brown.
- Melanocytes in the base layer of the epidermis produce melanin granules which are packaged into melanosomes.
- These melanosomes are released and transferred into skin epithelial cells (keratinocytes), giving them color.
Two Types of Melanin:
- Eumelanin: Brown-black. More eumelanin results in darker skin.
- Pheomelanin: Red-yellow. More abundant in people with lighter skin.
Carotene: Yellowish pigment found in the stratum corneum and fatty layer under the skin.
- Carotene and melanin together contribute to a yellowish hue.

Highly energetic UV radiation from the sun can cause cell damage, DNA mutations, and folate breakdown (essential for reproduction).
Melanin's Protective Role:
- Melanin acts as a shield by forming a cap around a cell's nucleus, absorbing UV radiation.
- UV radiation triggers melanocytes to produce more melanin as a defensive mechanism.
Geographic UV Intensity & Skin Color:
- Stronger UV radiation is correlated with darker skin in different populations.
- Humans don't have uniformly dark skin because UVB radiation is essential for vitamin D synthesis.
Vitamin D & Skin Color:
- Vitamin D is crucial for calcium absorption, supporting bone health and a healthy immune system.
- People in areas with weaker UV radiation have lighter skin (less melanin) to absorb enough UVB for vitamin D production.

Sebaceous Glands: Secrete sebum, an oily substance that lubricates and protects the skin and hair.
- These glands are particularly active during puberty due to hormonal changes and can contribute to acne.
Sweat Glands:
- Eccrine Glands: Found throughout the body, primarily involved in temperature regulation by releasing sweat, which evaporates for cooling.
- Apocrine Glands: Mainly located in the armpits and groin, secreting a thicker sweat that can lead to body odor when broken down by bacteria

Hair: Grows in hair follicles within the dermis.
- Growth starts at the papilla (structure at the follicle base), influenced by hormones and blood flow to the papilla.
- New cells are formed, pushing existing cells upward and filling them with keratin.
- The arrector pili muscle causes hair to stand up when cold or stressed.
Nails: Formed from cells in the epidermis and composed of hard keratin.
- Key structures include the lunula (visible white part at the nail base) and the nail root (hidden under the skin where growth begins).
Sensory Receptors: Various receptors in the skin allow us to experience temperature, touch, and pain.

The skin plays a crucial role in maintaining homeostasis by regulating body temperature.
Thermoregulation Mechanisms:
- Vasodilation: Widening of blood vessels, helps release heat.
- Vasoconstriction: Narrowing of blood vessels, helps conserve heat.
- Sweat Glands: Assist in cooling through evaporation.