Integumentary System Overview

Integumentary System

• Skin is the integument
• Skin and its appendages make up the integumentary system
• Two distinct regions: epidermis and dermis
• A fatty layer (hypodermis) lies beneath the dermis

Integumentary System Function

• The integumentary system is the body's outer layer, including skin, hair, nails, and glands
• These organs and structures are the body's first line of defense against bacteria and help protect the body from injury and sunlight
• The integumentary system works with other systems in the body to maintain balance

Skin as an Organ

• The skin is the largest organ in the body
• Its surface area can reach up to 2.2 square meters
• It makes up approximately 7% of the total body weight (assuming a body weight of 65 kg)
• It is waterproof, stretchable, washable, and repairs minor damage like cuts, rips, and burns
• It is sensitive to stimuli

Layers of the Skin

• Epidermis: the outermost layer of the skin, composed of four layers of cells. The main cell type is the keratinocyte that produces keratin, a fibrous protein that aids in protection. Millions of dead keratinocytes are regularly shed. It lacks blood vessels.
• Dermis: the middle layer, composed of collagen and elastin. It contains nerve endings, hair follicles, and glands.
• Hypodermis/Subdermis: lies under the dermis, primarily composed of connective tissue and fatty tissue (adipose tissue). It functions for insulation, energy storage, and cushioning, protecting against trauma.

Skin Structure and Function

• Pacinian corpuscles: specialized nerve endings in the subcutaneous tissue that detect vibratory pressure and touch.
• Free nerve endings are unspecialized nerve endings that detect pain.
• Sebaceous glands: microscopic exocrine glands that secrete sebum, oily or waxy material to lubricate and waterproof skin and hair.
• Meissner's corpuscles: mechanoreceptors that are a type of nerve ending in the skin and are sensitive to light touch.

Skin Color

• Skin color is determined by the presence of melanin (skin pigment), vascularity of the dermis (blood flow), and the number of red blood cells. Increased blood flow results in a reddened complexion; decreased blood flow leads to pale or blue/purple complexion.

Functions of the Integumentary System

• Protection: from external factors like bacteria, chemicals, and temperature.
• Waterproof: fatty secretions from sebaceous glands help prevent fluid loss
• Temperature regulation: The hypothalamus acts as the body’s thermostat. It receives signals from thermoreceptors in the skin related to temperature and activates regulating mechanisms like blood flow, sweating, and shivering. Central thermoreceptors in the hypothalamus detect changes in body temperature.
• Waste excretion: The skin eliminates metabolic wastes (urea, lactic acid, salts and water) through sweat.
• Vitamin D synthesis: involves UVB radiation penetrating the epidermal layers of the skin to produce vitamin D.
• Sensation: Detects touch, pressure, pain, and temperature through nerve endings

Hair

• Functions: warmth (less in humans than other mammals), sense light touch of the skin, and protection (scalp).
• Parts: Embedded root in skin and shaft projecting above skin surface.
• Structure: composed of hard keratin. Three concentric layers: medulla (core), cortex (surrounds medulla), and cuticle (single layers that overlap)

Diseases and Injuries

• Possible diseases and injuries include but are not limited to: rash, blisters, athlete's foot (fungal infection), infection, sunburn, skin cancer, albinism, acne, herpes, cold sores, plantar warts.

Maintaining Body Temperature

• Heat retained: When cool, arrector pili muscles contract pulling hair upright and creating a layer of insulating air around the hair.
• Cooling down: When hot, arrector pili muscles relax to flatten the hair and allow air circulation to cool the skin.
• Sweating: evaporation of sweat cools the skin.
• Vasodilation: blood vessels dilate to allow more blood to flow near the skin to dissipate heat.
• Vasoconstriction: blood vessels constrict to keep blood flow away from the skin to decrease heat loss.

Explore the intricacies of the integumentary system, which includes the skin and its appendages. Learn about the structure, function, and importance of the skin as the body's largest organ and first line of defense against external threats.