integument

The integument includes the skin and subcutaneous layer beneath it.
Skin is the largest organ of the body, composed of two primary layers: the epidermis and the dermis.

The epidermis is the superficial layer made of stratified squamous epithelium.
It is avascular, meaning it contains no blood vessels.
Composed of several layers (strata), differentiated into:
- Thick Skin: 5 layers (found in palms and soles).
  - Stratum Corneum: Dead keratinocytes.
  - Stratum Lucidum: Only in thick skin, translucent layer.
  - Stratum Granulosum: Keratinization occurs, organelles begin to degrade.
  - Stratum Spinosum: Several layers thick, keratinocytes are beginning to mature.
  - Stratum Basale: Deepest layer with actively mitotic cells, including keratinocytes and melanocytes.
- Thin Skin: 4 layers (lacks stratum lucidum).

The dermis lies beneath the epidermis, composed of areolar and dense irregular connective tissue.
Contains blood vessels, hair follicles, and various glands.

Lies below the dermis; includes areolar and adipose tissue.
Not considered part of the skin but provides insulation, cushioning, and energy storage.

Prevents excessive water loss and gain; skin is water-resistant but not waterproof.
Engages in insensible perspiration (unnoticeable water loss) and sensible perspiration (visible sweating).

Regulates body temperature through:
- Vasodilation: Expansion of dermal vessels to release heat.
- Vasoconstriction: Constriction of vessels to retain heat.

Synthesizes Vitamin D3 (cholecalciferol) and converts it into calcitriol, important for calcium homeostasis.

Houses epidermal dendritic cells that play a role in initiating immune responses.

Contains various receptors that detect temperature, touch, and other sensory information.
- Tactile cells stimulate sensory nerve endings.

Involved in secretion of sweat and sebaceous substances for skin and hair lubrication.

Skin has a significant ability to repair and regenerate after injury, involving cell division and migration to the wound site.

Aging leads to decreased collagen production, reduced elasticity, and increased vulnerability to injury.
Changes in pigmentation and overall appearance due to decreased melanocyte activity and altered completion of skin layers.

The integumentary system develops from the ectoderm, with specialized keratinocytes providing protection and forming barriers throughout fetal development.

Hemoglobin: Blood pigment providing a red color through superficial blood vessels.
Melanin: Produced by melanocytes, responsible for skin pigmentation and UV light absorption.
Carotene: Yellow-orange pigment from diet (e.g., carrots) that accumulates in the skin.

Albinism: Lack of melanin leading to white skin, hair, and pink eyes.
Bronzing: Golden-brown appearance due to adrenal cortex hormone deficiency (Addison's disease).
Cyanosis: Bluish skin from oxygen deficiency.
Erythema: Red skin due to increased blood flow (e.g., from exercise).
Hematoma: Bruising due to trauma or bleeding under the skin.
Jaundice: Yellowing of skin due to liver issues and elevated bilirubin levels.
Pallor: Ashen skin color due to reduced blood flow.

Mole (Amoebus): Localized overgrowth of melanocytes.
Freckles: Spots due to high melanocyte activity.
Hemangioma: Benign tumor from blood vessel proliferation.
Friction Ridges: Follicles of skin increasing grip on surfaces through ridges on fingers and palms.