Integumentary System Part 2

Integumentary System Part 2

• Dermis is composed of connective tissue containing collagen and elastic fibers, providing strength, extensibility, and elasticity to the skin.

• Papillary layer is the superficial layer of the dermis, composed of areolar connective tissue, housing dermal papillae, corpuscles of touch (Meissner’s corpuscles), and free nerve endings for sensations.

• Reticular layer is the deeper layer of the dermis, composed of dense, irregular connective tissue containing bundles of collagen fibers and some elastic fibers, containing adipose cells, hair follicles, sebaceous glands, and sudoriferous glands.

• Epidermal Ridges increase friction for gripping and provide the basis for fingerprints and footprints, reflecting contours of the underlying dermis.

Accessory Structures of the Skin

• General Characteristics of accessory structures: develop from the embryonic epidermis, including hair, glands, and nails.

• Hair is present on most skin surfaces except the palms, digits, soles, and digits, consisting of a shaft, root, cuticle, and hair follicle.

• Anatomy of Hair:

  • Medulla is the innermost layer, composed of irregularly shaped cells containing pigment granules, sometimes absent in thinner hair.
  • Cortex is the major part of the shaft, consists of elongated cells.
  • Cuticle is the outermost layer, consists of a single layer of heavily keratinized, thin, flat cells.
  • External root sheath is a downward continuation of the epidermis.
  • Internal root sheath is produced by the matrix.
  • Hair matrix cells arise from the stratum basale, responsible for new hair growth.

• Hair Follicle is associated with sebaceous (oil) glands, arrector pili muscles, and root plexuses.

Skin Glands

• Sebaceous (oil) glands are connected to hair follicles, absent in palms and soles, producing sebum to moisturize hair, waterproof and soften the skin, and inhibit bacterial growth.

• Sudoriferous (sweat) glands are divided into apocrine and eccrine types.

• Eccrine sweat glands: have an extensive distribution, terminating at pores on the epidermis, helping regulate body temperature and eliminating wastes like urea.

• Apocrine sweat glands: limited to axilla (armpit), pubis, and areolae, opening into hair follicles.

• Ceruminous glands: modified sudoriferous glands found in the external auditory meatus, producing earwax.

Nails

• Nails are hard, keratinized epidermal cells on the dorsal surfaces of fingers and toes.

• Nail structure: body, free edge, root, lunula, eponychium, and matrix.

• Nail growth occurs through cell division of the matrix cells.

• Nail function: grasping and manipulating small objects, protecting the ends of the digits.

Functions of Skin

• Thermoregulation is regulated by the skin through sweat liberation and adjusting blood flow in the dermis, contributing to homeostasis of body temperature.

• Blood Reservoir: The dermis contains an extensive network of blood vessels, holding 8-10% of the total blood flow in resting individuals.

• Protection: skin provides physical, chemical, and biological barriers against external threats.

• Cutaneous sensations: touch, pressure, vibration, tickle, heat, cold, and pain arise in the skin.

• Excretion and Absorption: The skin plays a minor role in eliminating waste and absorbing materials from the environment into body cells.

• Vitamin D synthesis: requires UV light activation of a precursor molecule in the skin, with enzymes in the liver and kidneys modifying it to produce calcitriol.

Structure of the Skin

• Epidermis is the superficial layer of the skin, composed of epithelial tissue and containing keratinocytes, melanocytes, Langerhans cells, and Merkel cells.

• Dermis is the deeper layer of the skin, primarily composed of connective tissue.

• Subcutaneous layer (hypodermis): consists of areolar and adipose tissue, serves as fat storage, blood vessel passage, and pressure nerve ending location.

Epidermis

• Layers of the Epidermis:
  • Stratum basale (stratum germinativum): deepest layer, contains stem cells for new cell formation, houses keratinocytes and melanocytes.
  • Stratum spinosum: provides strength and flexibility, composed of keratinocytes.
  • Stratum granulosum: transitional layer between deeper layers and superficial dead cells, shows water-repellant sealant formation and contains keratinocytes undergoing apoptosis, forming keratohyalin for keratin conversion.
  • Stratum lucidum: only present in palms and soles.
  • Stratum corneum: most superficial layer, consists of dead keratinized cells, responsible for water-repellency, thickening into calluses due to friction.

Types of Skin

• Thin Skin: covers most of the body except palms and soles, lacks epidermal ridges, and has a sparser distribution of sensory receptors compared to thick skin.

• Thick Skin: covers palms, digits, and soles, features a stratum lucidum and thick epidermal ridges, lacks hair follicles, arrector pili muscles, and sebaceous glands, but has more sweat glands than thin skin.

Structure and Basis of Skin Color

• Melanin, Hemoglobin, and Carotene: pigments contributing to skin color.
• Melanocytes synthesize melanin from tyrosine using tyrosinase enzyme.

Explore the intricate details of the dermis and its structures in this quiz on the integumentary system. Learn about the papillary and reticular layers, as well as the significance of epidermal ridges and accessory structures like hair and glands. Test your knowledge and understanding of skin anatomy and physiology.