Tissue 2

• Stratum Corneum


  The outermost layer of the epidermis, composed of dead, flattened keratinocytes filled with keratin. Acts as a barrier to protect underlying tissues.
• Stratum Lucidum


  A thin, clear layer found in thick skin (palms, soles). Provides an additional barrier, making the skin more capable of handling friction.
• Stratum Granulosum


  The middle layer of the epidermis. Contains keratinocytes starting to die and have granules of keratohyalin, which contributes to keratin formation. Plays a role in waterproofing the skin.
• Stratum Spinosum


  Also known as the "spiny" layer. Consists of several layers of keratinocytes connected by desmosomes, providing strength and flexibility. Contains Langerhans cells involved in the immune response.
• Stratum Basale (Stratum Germinativum)


  The deepest layer of the epidermis. A single row of dividing keratinocytes, containing melanocytes and Merkel cells.
• Papillary Layer


  • The uppermost layer of the dermis, made of loose connective tissue with thin collagen and elastic fibers. Increases the surface area for exchange between epidermis and dermis, contains capillaries, lymphatic vessels, and sensory neurons.
• Reticular Layer


  • The deeper and thicker layer of the dermis, composed of dense irregular connective tissue with a network of thick collagen and elastic fibers. Provides the skin with strength, extensibility, and elasticity.
• Hypodermis


  The deepest layer of the skin, located beneath the dermis. Primarily composed of adipose tissue, providing insulation, energy storage, cushioning, and anchoring the skin.
• Melanocytes


  Cells located in the stratum basale that produce melanin, the pigment responsible for skin color.
• Eumelanin


  Provides brown to black pigmentation, offers better protection against UV radiation.
• Pheomelanin


  Provides yellow to red pigmentation, offers less protection against UV radiation.
• Nail Plate


  The visible, hard part of the nail made of tightly packed keratinized cells. Protects the distal phalanx and enhances fine touch and manipulation.
• Nail Bed


  The skin beneath the nail plate, composed of living skin cells. Supplies nutrients to the nail plate and supports its growth.
• Cuticle (Eponychium)


  A thin layer of skin at the base of the nail, made of dead skin cells. Protects the area between the skin and the nail from infection.
• Hyponychium


  The area under the free edge of the nail, a thickened layer of skin. Acts as a barrier to prevent pathogens from entering the space under the nail.
• Lunula


  The visible part of the matrix seen as a white, crescent-shaped area at the base of the nail
• Cuticle (Eponychium)


  • Made of dead skin cells
  • Protects the area between the skin and the nail from infection
• Hyponychium


  The area under the free edge of the nail
• Hyponychium


  • A thickened layer of skin
  • Acts as a barrier to prevent pathogens from entering the space under the nail
• Nail Folds


  Folds of skin that frame and support the nail on three sides
• Nail Folds


  • Lateral nail folds (on the sides) and the proximal nail fold (at the base)
  • Protect the edges of the nail and help anchor it in place
• Free Edge


  The part of the nail that extends beyond the fingertip
• Free Edge


  • The distal end of the nail plate
  • Protects the fingertip and aids in precision tasks
• Nails protect the distal phalanges, enhance the ability to manipulate small objects, and provide a window into the body's overall health
• Sweat glands are specialized structures in the skin that produce sweat, playing a key role in thermoregulation and excretion
• Types of sweat glands

  • Eccrine
  • Apocrine
• Eccrine Sweat Glands


  Simple, coiled tubular glands that open directly onto the skin surface through pores
• Eccrine Sweat Glands


  • Found all over the body, with high concentrations on the palms, soles, and forehead
  • Produce a watery sweat that helps cool the body when it evaporates from the skin
  • Help excrete waste products, such as urea and electrolytes
  • Assist in maintaining the hydration of the stratum corneum
  • Activated by the sympathetic nervous system, primarily in response to heat and emotional stress
• Eccrine Sweat Composition


  Mainly water (99%), with small amounts of salts, urea, and other electrolytes
• Apocrine Sweat Glands


  Larger than eccrine glands and open into hair follicles rather than directly onto the skin surface
• Apocrine Sweat Glands


  • Found mainly in the axillary (armpit) and genital regions, as well as around the nipples and in the ear canal
  • Produce a thicker, milky sweat that, when broken down by skin bacteria, produces body odor
  • Thought to be involved in pheromone signaling
  • Activated by emotional stress, pain, and sexual arousal rather than temperature
  • Begin functioning at puberty
  • Activated by the sympathetic nervous system in response to stress and hormonal changes
• Apocrine Sweat Composition


  Contains proteins, lipids, and steroids, which are broken down by bacteria on the skin, leading to the characteristic odor
• Sebaceous glands are another important accessory structure of the skin, responsible for producing sebum, an oily substance that helps to lubricate and protect the skin and hair
• Sebaceous Glands


  Comprised of lobes of glandular tissue with ducts that usually open into hair follicles, or in some areas, directly onto the skin surface
• Sebaceous Glands


  • Found throughout the skin, except on the palms of the hands and the soles of the feet
  • Particularly abundant on the face, scalp, and upper back
  • Typically connected to hair follicles, with sebum traveling up the hair follicle and onto the skin's surface
• Sebum


  A lipid-rich substance consisting of triglycerides, free fatty acids, wax esters, squalene, and cholesterol
• Function of Sebaceous Glands

  • Sebum helps to lubricate and waterproof the skin and hair, keeping them pliable and preventing dryness
  • Sebum forms a protective barrier on the skin that helps to prevent the growth of certain bacteria and fungi
  • Sebum helps to retain moisture in the skin, contributing to the skin's barrier function
  • Sebum helps to reduce water loss and can play a minor role in thermoregulation
• Hormonal Control of Sebaceous Glands

  Sebaceous gland activity is influenced by hormones, particularly androgens such as testosterone
• Sebaceous Gland Hyperactivity


  • Overproduction of sebum can lead to conditions like acne, where hair follicles become clogged with sebum and dead skin cells, providing an environment for bacterial growth and inflammation
• Sebaceous Gland Hypoactivity


  • Underproduction of sebum can lead to dry, flaky skin