Integumentary System: Skin Functions, Layers, and Accessory Structures
Functions of the Skin
Protection:
Against UV light.
Prevents unnecessary water loss.
Vitamin D Production: Assists in the production of vitamin D.
Body Heat Regulation: Part of homeostasis, prevents excessive heat loss and regulates temperature.
Sensory System: Contains 4 to 5 types of receptors that send messages to the brain, sensing pressure, temperature, and pain.
Epidermis
Composed of epithelium, making it an avascular part of the skin.
Cell Renewal: The journey for cells to divide in the basal layer and move to the top takes approximately , influenced by exposure.
Layers (from bottom to top):
Basal Layer (Stratum Basale):
Location: Near the dermis.
Cell Type: Cuboidal shape.
Activity: Active cell division (mitosis) occurs here.
Nutrient Supply: Receives nutrients from the underlying dermis via the papillary layer.
Melanocytes: Present in the basal layer, they extend cytoplasm up to the corneal layer to deposit melanin.
Merkel Cells: Sensory cells also present at the base of the epidermis, receiving nutrients from the dermis.
Glenosal Layer: Contains lipids that act as a waterproof property.
Corneal Layer (Stratum Corneum):
Composition: Uppermost layer, composed of dead cells.
Cell Description: Cells flatten as they move away from the basal layer and nutrient source, forming a hard, protective layer.
Thick Skin:
Location: Found on palms of hands and soles of feet.
Stratum Lucidum: An extra layer present in thick skin; it does not stain and appears clear or lucid.
Other Epidermal Cells:
Langerhans Cells: Large defensive cells, part of the immune system within the epidermis.
Cell Shape Transformation: Cells near the dermis are cuboidal; as they move upwards and away from nutrients, they flatten into squamous (flat-shaped) cells.
Dermis
Considered the "living part" of the skin due to its rich supply of:
Blood vessels.
Nerves and sensory receptors.
Lymphatic vessels.
Connective Tissue: Consists of strong tracts of dense irregular connective tissue.
Contains: Fibroblasts, macrophages, mast cells, and white blood cells.
Strength and Elasticity: Provided by collagen, elastic fibers, and reticular fibers.
Temperature Regulation: Nerves and blood vessels here play a role in regulating body temperature.
Layers of the Dermis:
Papillary Layer:
Composition: Loose connective tissue.
Structure: Features dermal papillae—finger-like projections that extend into the epidermis.
Function: Supplies nutrients to the basal (living) cells of the epidermis.
Reticular Layer:
Composition: Deeper layer, a dense network of collagen and reticular fibers.
Function: Deals with mechanical stress on the skin, resisting stretching.
Clinical Relevance: Damage to these fibers due to excessive stretching can result in stretch marks.
Components within the Dermis:
Blood Vessels: Numerous.
Hair Follicles: Associated with sebaceous glands.
Sweat Glands: Exocrine glands that release sweat.
Sebaceous Glands: Attached to hair follicles, produce sebum (oil) which lubricates hair.
Arrector Pili Muscle: A small muscle attached to hair follicles.
Function: Contracts in response to cold or fright, causing goosebumps.
Evolutionary Function (in animals): Makes the animal appear larger, aids in ventilation and limited temperature regulation.
Human Function: Primarily residual; muscle connection remains, but its functional significance is minimal.
Hypodermis (Subcutaneous Layer)
Location: Anchors the skin to internal membranes.
Not Technically Skin: While not considered part of the skin, it is studied in conjunction with it.
Composition:
Adipose Tissue (Fat Layer): Stores fat, provides insulation, and helps regulate body heat.
Clinical Example: Newborns lack a well-formed fat layer, making them prone to heat loss; rubbing them helps prevent this.
Blood Vessels: Contains a greater number of blood vessels compared to the dermis.
Temperature Regulation Mechanism: Blood vessels in the hypodermis change path to regulate heat:
Winter: Blood vessels move deeper into the fat layer to minimize heat loss.
Summer: Blood vessels move closer to the skin surface to release heat and regulate internal body temperature (part of homeostasis).
Fat Storage: Patterns of fat storage differ between males and females and across different body parts.
Skin Color
Determined by three primary pigments:
Melanin:
Most important pigment.
Production: Produced by melanocytes located in the basal layer of the epidermis.
Distribution: Melanocytes have extended cytoplasm that delivers melanin all the way up to the corneal layer.
Function: Protects the skin from harmful UV light.
Production during winter is lower; sudden intense sun exposure in spring/summer can overwhelm melanocytes, leading to sunburn and increased risk of skin cancer.
Keratin: Forms from carrots and yellow vegetables, contributes to yellowish skin tones.
Hemoglobin: Oxygen-carrying pigment in blood, contributes to pinkish skin tones.
UV Exposure and Health Implications:
Sunburn: Severe sunburn can lead to skin cancer, which is often linked to exposure rather than genetics.
Tanning Salons: The instructor advises against using tanning salons, citing:
Lack of FDA approval or regulation regarding UV exposure levels.
Insufficient studies on light distance, age of bulbs, and UV intensity.
Potential for breaking down collagen prematurely.
Significant risk of causing cancer due to excessive UV exposure.
Vitamin D Production: While sunlight is crucial for vitamin D synthesis, excessive exposure (especially in babies and young children) can have a reverse, detrimental effect on vitamin D production.
Accessory Skin Structures
Originate in the epidermis but extend into the dermis.
Hair and Hair Follicles:
Presence: Found everywhere on the skin except the palms and soles.
Structure of Hair Follicle:
Hair Papilla: Connective tissue at the base, supplied by blood vessels.
Epithelial root sheath and external root sheath.
Connective tissue sheath and glassy membrane.
Internal Hair Structure: Cortex, medulla (innermost portion), and matrix (outer portion).
Melanocyte Cells: Located within the hair follicle, they produce melanin that colors the hair shaft.
Hair Color and Aging: As we age, melanocytes produce less melanin.
Gray hair: A mix of the original hair color with air bubbles filling the space, appearing grayish.
White hair: Occurs when melanin production ceases completely, leaving an empty space that reflects white light.
Sensory Function: Hair follicles have their own receptors, causing pain when hair is pulled.
Hair Loss (Balding): Can be influenced by testosterone levels and enzyme activity. Surgical options (hair transplants) are available but involve personal consideration.
Nails:
Composition: Hard keratin.
Growth: Grows from the nail matrix (important for identification on tests).
Parts of the Nail: Nail matrix, nail root, nail fold, lunula (judicial area), nail plate (depth), and free edge.
Health Indicator: Nails can reveal underlying health issues:
White patches: May indicate iron deficiency or issues with blood levels.
Can be affected by radiation and other health problems.
Sebaceous Glands:
Location: Attached to hair follicles.
Product: Produce sebum, an oily substance that lubricates hair and skin.
Sweat Glands (Sudoriferous Glands):
Distribution: Present over the entire skin surface, except nipples and certain parts of the genitals.
Function: Primary role is to prevent overheating through evaporative cooling.
Excretory System Component: Releases waste products through sweat.
Stress Response: Humans are highly efficient at sweating in response to stress and heat.
Clinical Relevance: Lie detector tests often measure sweat production as an indicator of nervousness or deception.
Mechanism: Part of the exocrine system, sweat glands have ducts that release sweat onto the surface of the skin.
Note:
Diagrams illustrating the layers of the skin, hair follicles, and nails are crucial for understanding and labeling these structures on exams.