W35N Skin/Integumentary System

Integumentary System

• The integumentary system is the body's covering, which includes skin, hair, glands, oils and sensors
• The integumentary system functions to regulate body temperature and store blood
• It provides protection, detects sensations, excretes/absorbs substances and synthesises vitamin D
• Several conditions affect the skin, including melanoma, skin cancer, rosacea, lupus, vitiligo and hives
• Other conditions of the skin are warts, cold sores, fungal infections, athlete's foot, ring worm, carbuncles and cellulitis
• Further skin conditions are impetigo, dandruff, chicken pox, measles, shingles, seborrheic keratosis, keloid scarring, spider veins and varicose veins
• Additional conditions include allergy, psoriasis, eczema, acne, dermatitis, moles, and ulcers

Skin Layers

• The skin is a sheet-like organ, a barrier between the internal and external environments
• It consists of two primary layers: the epidermis and the dermis
• The epidermis is the superficial, thinner layer of the skin
• The dermis is the deep, thicker layer of the skin

Thick and Thin Skin

• Most of the body surface is covered by thin skin
• Thick skin is hairless and located on the palms, fingertips, and soles of the feet, areas subject to friction

Epidermis Cell Types

• Consists of keratinocytes, melanocytes, dendritic cells, and tactile epithelial cells
• Keratinocytes comprise 85% of epidermal cells, arranged in 4-5 layers, and produce keratin
• Keratin provides a tough, fibrous protein structure to the skin
• Melanocytes comprise 8% of epidermal cells
• Dendritic cells comprise 5% of the epidermis, searching for accumulation of bacteria/viruses and initiating immune responses
• Tactile epithelial cells/ Merkel cells comprise 2% of epidermal cells

Skin Regeneration

• Turnover and regeneration times describe the time it takes for a population of cells to mature and reproduce
• As surface cells are lost, keratinocytes must be replaced through mitotic activity
• New cells must form at the same rate that old cells flake off to maintain a constant thickness
• Cell-signaling proteins affect the skin regeneration rate
• Epidermal Growth Factor (EGF) regulates the epidermis' generation and repair to promote growth, mutated cells become cancerous
• Growth hormone (GH) also has a growth-promoting effect on epidermal cells
• The dermo-epidermal junction (DEJ) joins the epidermis and dermis
• The DEJ is a basement membrane with a polysaccharide gel that cements the epidermis to the dermis
• It "glues" the layers together, provides support, and attaches to the upper surface

Epidermis Functions

• Skin repair and prevention of fluid loss
• UV protection, vitamin D3 production and prevents damage/abrasion at DEJ, acts as immune barrier

Dermis Layers and Function

• The dermis is the 'true' skin layer with 2 layers; it gives the skin its strength
• The papillary layer has loose connective tissue and thin collagenous/elastic fibres
• Dermal papillae increase the surface area of the DEJ that binds skin layers helps form distinct fingerprints
• The papillary layer provides sensory information
• The reticular layer is a dense layer of tough, interlacing white collagenous and elastic fibers that make the skin stretchable
• The dermal layer anchors hairs
• Hair follicles have involuntary arrector pili muscles, which control hair position

Sensors in the Dermis

• Millions of somatic sensory receptors are in the dermis which allow the skin to serve as a sense organ for transmit pain, pressure, and touch sensations

Hypodermis

• The hypodermis/subcutaneous layer is the innermost layer of the skin; it contains fat and nutrients
• It connects the skin to underlying adipose tissue
• This layer lies deep in the dermis, forming a connection between the skin and the body's underlying structures
• This is the layer targeted by a hypodermic needle for subcutaneous injections

Skin Color

• The number of melanocytes is generally consistent across individuals
• Skin colour variability depends on the amount and type of melanin produced
• Eumelanin is brown to dark brown
• Pheomelanin is red to orange
• Melanocytes convert tyrosine into melanin pigments released by melanosomes
• Melanin protects cells from UV light, preventing DNA mutations and skin cancer

Melanin and Albinism

• Albinism is a rare genetic mutation impacting melanin synthesis
• An inability of melanocytes to produce melanin increases the risk of DNA damage/skin cancer
• Individuals with albinism tend to have pale skin/hair and need more protection from UV radiation and are prone to sunburns

Vitamin D Synthesis

• Vitamin D can be synthesized in the skin when ultraviolet (UV) rays activate a precursor cholesterol molecule
• Brief sun exposure (10-15 minutes, twice a week) is sufficient for Vitamin D synthesis
• People in colder climates may need Vitamin D supplements due to less sun exposure

Accumulation of Pigments

• Beta carotene, an orange pigment found in carrots, can turn the skin orange if high consumption
• Bilirubin, a breakdown product of red blood cells usually processed by the liver; accumulates in the skin/eyes(jaundice) if liver is damaged
• Hemoglobin volume affects blood flow through skin capillaries related to blood pressure, heat, cardiac issues, stress, inflammation and is reddish in color

Integument Functions

• The integument provides protection, sensation, permits movement, performs endocrine functions, excretion, provides immunity
• It protects against microorganisms/dehydration/UV radiation, offers mechanical support through tissue strength
• Somatic sensory receptors pick up pain/ heat/ cold/ pressure/ touch
• Body movement from skin/ subcutaneous tissue, synthesizes vitamin D, excretes water/urea/ammonia/uric acid
• It destroys microoganisms, interacts with immune cells and aids in temperature regulation via blood-flow/sweat

Skin Functions

• Keratinized cells create a protective barrier from microorganisms/chemicals
• A supply of immune cells and chemicals that resist microbes/ pathogens
• The skin protects from dehydration
• Melanin protects from the sun
• A surface film creates a skin microbiome and is comprised of residue/ secretions from sweat and sebaceous glands where epithelial cells are constantly cast off from the epidermis ex: desquamation

Sweat Glands

• Eccrine glands are distributed throughout the body (excluding lips, ear canal, nail beds)
• These simple, coiled, tubular glands produce sweat and it's primary for temperature regulation
• Apocrine glands produce pheromones and are deep in the subcutaneous layer and produce body odors cause by secretion by skin bacteria

Sebaceous Glands

• Sebaceous glands secrete oil/sebum for hair and skin, keeping them soft
• Sebum prevents water loss and contains oils, triglycerides, fatty acids, wax esters, squalene, and cholesterol
• Sebum is antifungal, and sebum production increases hormones during adolescence, can enlarge to form pimples/blackheads

Ceruminous Glands and Mammary Glands

• Ceruminous glands are special sweat glands, which produce earwax
• Earwax protects against dehydration and blockage
• Mammary glands produce milk for offspring, are supported by hormones, and develops cancer

Hormone Impact on Glands and Proliferation

• During pregnancy, mammary gland lobules enlarge and proliferate
• Acini increase, and prolactin is needed for lactation
• Breastfeeding cessation causes structural changes