Integumentary System: Skin and Hair Anatomy

Melanocytes:
- Located in the deepest layer of the epidermis.
- Function: Produce melanin, a pigment that serves to protect skin cells by covering them when exposed to UV light.
- Importance of Melanin:
- Protects DNA in cells from mutations caused by UV exposure.
- Notably, melanocytes themselves are particularly susceptible to UV damage.

Synthesized in the bone marrow.
Migration: These cells move to the epidermis.
Function: Protect against infection, playing a crucial role in the immune response of the skin.

Also known as Merkel Cells.
Function: Encapsulated nerve discs that detect touch, contributing to sensory perception in the skin.

Configuration:
- Composed of 25-35 layers.
- Lacks cellular organelles.
- Characterized by very tight junctions between cells, assisting in barrier function.
Maintenance: Continuously sheds and is replaced, serving as the main layer of protection for the skin.
Abnormal thickening referred to as callus: Results from excessive friction or pressure on the skin surface leading to abnormal buildup of the stratum corneum.

Vitamin D production involves skin cells utilizing UV light:
- Skin cells produce Cholecalciferol (also known as Vitamin D3 or a hormone).
- The kidneys convert cholecalciferol to Calcitriol, the active form of Vitamin D.
- Calcitriol enhances calcium absorption in the ileum of the small intestine.

Hair growth consists of three stages:
1. Growth Stage: Lasts 2-6 years, where hair actively grows.
2. Regression Stage: Duration of 2-3 weeks, during which the follicle atrophies, and hair stops growing.
3. Resting Stage: Lasts approximately 3 months before the cycle repeats.
Fetal Hair Development:
- Begins at around 12 weeks of gestation.
- Lanugo Hairs: Fine, soft hair covering the fetus.
- Vellus Hairs: Replace lanugo hairs around the time of birth, contributing to the hair coverage in newborns.