Human Anatomy: Hair and Skin Structure

The Integumentary System (PHC411)

• The integumentary system is a critical body system, encompassing the skin and its associated structures.
• The skin's structure is crucial for its function, with different layers having specific makeup.
• The skin is composed of the epidermis, dermis, and subcutaneous layer.
• The epidermis is the outermost layers and is composed of epithelial tissue while the dermis is the deeper layer and composed of connective tissue.
• The subcutaneous layer or hypodermis is composed of areolar and adipose tissue.
• Keratinized stratified squamous epithelium forms the epidermis, providing protection.
• Four main types of cells make up the epidermis: keratinocytes, melanocytes, dendritic (Langerhans) cells, and tactile (Merkel) cells.
• Keratinocytes are the most numerous, synthesizing keratin for protection, and contain lamellar granules for water-repellency.
• Melanocytes produce melanin, a pigment crucial for UV protection and skin color.
• Dendritic cells play a critical role in the immune system, monitoring and responding to pathogens.
• Tactile cells are responsible for touch sensation.
• The dermis houses collagen and elastic fibers, and supports other structures like blood vessels, nerves, glands, and hair follicles.
• The dermal layer has a papillary and reticular region, with the papillary region containing papillae that increase the skin's surface area.
• The reticular region has denser connective tissue holding structures within.
• Fingerprints form due to the interaction between the stratum basale and papillary layer in a growing fetus.
• The subcutaneous layer or hypodermis helps connect the skin to underlying muscles and contains fat for energy storage, insulation, cushioning of bony prominences, and regulating temperature.
• The hypodermis is composed of areolar and adipose connective tissue.
• Melanin is the most significant factor in skin color.
• Melanocytes create melanosomes where melanin is produced and deposited in the stratum basale and stratum spinosum.
• Skin color differences result from various melanin quantities and types (eumelanin and pheomelanin ).
• Exposure to UV radiation can influence melanin production.
• Hemoglobin adds a reddish to pinkish hue to the skin.
• Carotene contributes yellow/orange tones, concentrating in the stratum corneum and subcutaneous fat.
• Skin color variations signify diagnostic value.
• Cyanosis indicates low oxygen supply.
• Erythema suggests dilated blood vessels.
• Pallor implies limited blood flow.
• Jaundice indicates bilirubin buildup.
• Vitiligo involves loss of melanocytes causing white patches.

Hair

• Hair is composed of keratinized epidermal cells and is typically found all over the body with exceptions.
• Hair helps with touch and protects the body from external elements.
• A hair follicle is the part that holds the hair and aids in hair growth, composed of the shaft, the root and follicle components.
• The hair root penetrates into the dermis; it consists of the medulla, cortex and cuticle.
• The follicle features an epithelial and dermal sheath.
• Hair growth has multiple stages of growth and regrowth.
• Types of hair include lanugo, vellus, and terminal hair.
• Hair color is determined by the amount and type of melanin produced and its concentration within the cortex and medulla.
• Gray hair results from a decline in melanin production.

Nails

• Nails are composed of hard, keratinized epidermal cells covering the dorsal ends of fingers and toes.
• The nail structures include a free edge, nail body, lunula, and nail root.
• The nail root is embedded into a fold of skin.
• The hyponychium beneath the free edge secures the nail to the fingertip.
• The eponychium (cuticle) consists of stratum corneum.
• Nail matrix cells divide to produce new nail cells, its rate dependent on the age and health.

Skin Glands

• Sebaceous glands are connected to hair follicles.
• Sebaceous glands secrete sebum to prevent dehydration and inhibit bacteria growth.
• Eccrine glands are the most numerous and produce watery perspiration to regulate body temperature and eliminate wastes.
• Apocrine glands produce thick, milky sweat in regions like the groin and axilla, contributing to body odor.
• Ceruminous glands are modified sweat glands in the ear canal. They secrete cerumen, protecting the ear canal from foreign bodies.

Skin Functions

• Thermoregulation: skin balances heat through sweating and blood flow adjustments.
• Blood reservoir: the dermis houses blood vessels carrying 8-10% of the blood flow at rest.
• Protection: skin protects from microbes, abrasion, heat, chemicals, and dehydration.
• Cutaneous sensations: skin has receptors for touch, pressure, vibration, and temperature.
• Excretion: skin eliminates waste through sweat.
• Absorption: skin absorbs certain substances, including fat-soluble vitamins and drugs.
• Synthesis of Vitamin D: UV rays initiate vitamin D production, crucial for calcium absorption.

Wound Healing

• Two main types of healing, epidermal and deep, are possible.
• Epidermal healing describes the process following superficial epidermal injuries. Deep wound healing pertains to deeper injuries including dermis and subcutaneous layers.
• Epidermal healing results in normal tissue function and generally, minimal scarring. Deep wound healing may result in some loss or changes of function and likely produces scar tissue.
• In wound healing, cells or processes involved may include migration, inflammation, proliferations, and finally maturation.

Burns

• Burns are tissue injuries caused by heat, electricity, radiation, or corrosive chemicals.
• Burns are graded according to their severity.
• First-degree burns affect the epidermis only. Pain, redness, and flaking are typical.
• Second-degree burns affect the epidermis and upper layers of the dermis. Pain, blisters, and swelling are prominent.
• Third-degree burns destroy the epidermis, dermis, and subcutaneous layers, resulting in sensory loss and potential need for skin grafts.
• Major burns are graded severe burns encompassing specific criteria including surface area burned.
• The rule of nines is used to estimate the surface area of a burn.

Skin Cancer

• Skin cancer is induced by UV rays from the sun.
• It is most frequent in fair-skinned people and the elderly.
• Skin cancer is one of the cancers with favorable survival rates if caught early.
• Types of skin cancer include basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.

Common Skin Disorders

• Specific skin disorders such as alopecia (hair loss), hirsutism (excessive hair growth), dermatitis (inflammation of skin), eczema (chronic dermatitis), folliculitis (hair follicle inflammation), herpes simplex (cold sores), herpes zoster (shingles), impetigo (ooze skin lesions), ringworm, scabies, rosacea and warts are common.

This quiz delves into the anatomy of hair and skin, covering key aspects such as hair growth stages, hair follicle functions, and the role of melanin in skin color. It includes details about hair structure, the types of hair, and the effects of UV light on melanin production. Test your knowledge on these essential biological concepts!