Chapter+6+API

The following notes comprise Chapter 06 of the provided transcript focusing on the integumentary system, including the skin and its various components, structures, and functions. Careful adherence to detail from the transcript helps ensure a comprehensive understanding of the subject matter.

The integumentary system comprises the skin and its accessory structures, including hair, nails, glands, and sensory receptors.
Skin:
- Largest organ in the body by weight.
- Constructed from multiple tissue types.
- Also referred to as the cutaneous membrane.
- Consists of two primary layers.
- Epidermis: The outermost skin layer.
- Dermis: The thicker, inner layer.

Located beneath the epidermis and is thicker.
Composed of connective tissue and includes:
- Collagenous fibers
- Elastic fibers
- Muscle
- Blood vessels
- Nervous tissue
Subcutaneous layer (hypodermis):
- Lies beneath the dermis and serves as an insulating layer.
- Made of areolar and adipose connective tissue.
- Is not considered part of the skin but contains blood vessels that supply it.

Stratified squamous epithelium composed of multiple layers.
Lacks blood vessels.
Stratum basale: The deepest layer nourished by blood vessels in the dermis.
Older cells (keratinocytes) migrate towards the surface and undergo flattening and death as they move.
Keratinization:
- Process involving hardening, dehydration, and keratin accumulation in epidermal cells during outward migration.
- Keratin: Tough, fibrous, waterproof protein produced and stored within the cells.
- Stratum corneum, the outermost layer, is composed of tightly packed keratinized cells that eventually shed.
Thickness varies:
- Thickest on palms and soles (0.8 mm to 1.4 mm).
- Thinner elsewhere (0.07 mm to 0.12 mm).
Functions:
- Protects against water loss, harmful chemicals, mechanical injury, and pathogens.

Layer	Location	Characteristics
Stratum corneum	Outermost layer	Many layers of keratinized, dead epithelial cells that are flattened and non-nucleated
Stratum lucidum (thick skin only)	Between stratum corneum and stratum granulosum	Cells appear clear; nuclei, organelles, and membranes not visible
Stratum granulosum	Beneath stratum corneum	Three to five layers of flattened granular cells containing shrunken fibers of keratin
Stratum spinosum	Beneath stratum granulosum	Many layers of cells with large nuclei and developing keratin fibers; cells becoming flattened
Stratum basale	Deepest layer	A single row of cuboidal/columnar cells that divide and grow, housing melanocytes

Situated in the stratum basale.
Along with sensory nerve endings, form Tactile Discs in the dermis, serving as sensory receptors for light touch.

Found in the stratum basale.
Produce the pigment melanin which absorbs UV light, contributing to skin color.
Melanin distributed to keratinocytes provides protection from UV radiation, DNA damage, and skin cancer.

Skin color is primarily determined by the melanin pigment, which comes in two forms:
- Eumelanin: A brownish-black pigment.
- Pheomelanin: A reddish-yellow pigment.

All individuals have the same number of melanocytes but differ in the amount of melanin produced, a genetically controlled trait.
Variations occur in the distribution and size of melanin granules.
Albinism: An inherited condition caused by mutations in melanin genes, leading to a lack of melanin.

Blood oxygenation levels influence skin tone (pinkish vs. cyanosis).
Vasodilation or vasoconstriction of dermal blood vessels influence appearance.
Carotene accumulation from dietary sources and medical conditions like jaundice can also affect skin color.

Exposure to UV radiation, either from sunlight or tanning beds, increases melanin production, causing skin darkening.
Tanning beds administer doses of UV radiation that can surpass the body’s natural protective response, increasing skin cancer risk.
Types of skin cancers include:
- Basal Cell Carcinoma and Squamous Cell Carcinoma: Most often arise from epithelial cells in the skin.
- Melanomas: least common (4%) but account for 80%