The Largest Organ: Skin

Overview

Skin is the largest organ of the body, covering about 20 square feet in adults.
Different regions of skin have unique characteristics but perform similar functions:
- Sweating
- Sensation (heat, cold, etc.)
- Hair growth
Skin undergoes changes after deep cuts or wounds; it may not regain all abilities completely.

Epidermis:
- Top layer of skin, made mainly of keratinocytes.
- Provides protection and is easily repaired as it is constantly shed and renewed.
Dermis:
- Layer beneath the epidermis containing blood vessels, glands, and nerve endings.
- Responsible for the skin's various functions.

Hemostasis:
- Immediate response to blood loss and compromised skin barrier.
- Blood vessels constrict (vasoconstriction) to minimize bleeding.
- Formation of a blood clot via fibrin cross-linking to prevent blood loss and entry of pathogens.
Inflammation:
- Occurs after about three hours.
- Special cells, including macrophages (white blood cells), are sent to the wound site to fight pathogens and promote healing.
- Blood vessels expand (vasodilation) to allow cells to reach the wound.
Proliferative Stage:
- Begins two to three days after the injury.
- Fibroblast cells enter the wound to produce collagen, forming new connective tissue.
- Epidermal cells divide to reform the outer layer; dermis contracts to close the wound.
Remodeling Stage:
- The wound matures as collagen is rearranged and converted into specific types.
- This process can take over a year, improving the tensile strength of new skin.
- New tissue may regain 50-80% of original function, depending on the wound's severity.

Scarring is a significant clinical issue; skin does not fully recover.
Ongoing research aims to understand the healing process better:
- Fibroblast origin: blood vessels or adjacent skin tissue?
- Why some mammals (e.g., deer) heal more efficiently than humans?
Future goals: Improve healing processes to minimize scarring.