The Integumentary System

Protection (from foreign bodies/bacteria),

Sensation (tactile/pain receptors),

Thermoregulation (sweat/vasodilate/vasoconstrict),

Vitamin D Synthesis

The epidermis.

Holds in water to keep the skin hydrated/healthy, produces new skin cells from the deepest layer, and protects the body from external harm such as UV radiation, pathogens, and chemicals.

The dermis.

Supports the epidermis by providing strength, flexibility, and a blood supply via blood vessels. Nerve endings and tactile/pain receptors allow for sensation such as pressure, pain, heat, cold, or itchiness. Contains sweat glands (in humans) which produce sweat to aid in thermoregulation. Contains sebaceous glands which secrete oils to keep skin and hair hydrated. Contains hair follicles which produce hair that aids in thermoregulation.

Nerve endings, sweat glands (in humans), sebaceous glands (oil glands), and hair follicles.

The hypodermis (subcutaneous).

Stores energy by producing fat cells, acts as a shock absorber that protects your organs/muscles/bones from harm, adds insulation and produces sweat to regulate your body temperature, and acts as connective tissue which connects your dermis layer to your muscles/bones.

When too cold: hairs stand up, trapping air and creating an insulated layer next to the skin to help retain heat. Muscle contracts to prevent heat from escaping, blood vessels in the dermis vasoconstrict to retain heat.

When too hot: hairs flatten and reduce the amount of trapped air, enhancing heat loss. Muscles relax and the blood vessels vasodilate which allows the body to lose heat through the dermis. The dermis produces sweat which evaporates on the epidermal layer.

The hypothalamus using negative feedback loops.