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• Body membranes function to cover body surfaces, lines body cavities and form protective sheets around organs

Classification of Body Membranes

• Epithelial membranes include cutaneous, mucous, and serous types
• Connective tissue membranes have synovial membranes

Epithelial Membranes: Cutaneous Membranes

• Termed the skin
• A dry membrane that is thick and waterproof
• The outermost protective boundary of the body
• Consists of the superficial epidermis, which is composed of keratinized stratified squamous epithelium
• Also consists of the underlying dermis, which is mostly dense connective tissue

Epithelial Membranes: Mucous Membranes

• Lines all body cavities that are open to the exterior body surface
• Adapted for absorption or secretion
• Keeps the body moist to reduce friction and facilitate transfer
• Surface epithelium types include stratified squamous epithelium (mouth and esophagus) and simple columnar epithelium (the rest of the digestive tract)
• Contains underlying loose connective tissue (lamina propria)

Epithelial Membranes: Serous Membranes

• Lines open body cavities that are closed to the exterior
• The surface is a layer of simple squamous epithelium
• Covered by a thin layer of serous fluid secreted by the epithelium
• Contains underlying thin layer of areolar connective tissue
• Occurs in pairs separated by serous fluid
  • Visceral layer covers the outside of the organ
  • Parietal layer lines a portion of the wall of the ventral body cavity
• Specific serous membranes are named by their location
  • Peritoneum: abdominal cavity
  • Pleura: surrounds the lungs
  • Pericardium: surrounds the heart

Connective Tissue Membranes: Synovial Membranes

• Lines structures that are not open to the exterior, instead are a connective tissue only
• Lines fibrous capsules surrounding joints
• Secretes a lubricating fluid, called synovial fluid

The Integumentary System: Cutaneous Membrane

• Also known as the skin
• The largest organ of the body
  • Has a 2 m² surface area
  • Weighs 4.5-5 kg
• Includes skin, skin derivatives (sweat glands, oil glands, hair, and nails), blood vessels, nerve terminals, and sensory organs
• Clinical study for the medical specialty for the diagnosis and treatment of disorders of the integumentary system is dermatology
• Major functions include protection, thermoregulation, and detection of sensory input

Protection Mechanisms

• Protects deeper tissues from mechanical damage (bumps)
  • Physical barrier; contains keratin to toughen cells
  • Fat cells cushion blows
  • Pressure receptors alert the nervous system to possible damage
• Protection from acids and bases
  • Has relatively impermeable keratinized cells
  • Contains pain receptors to alert the nervous system to possible damage
• Protection from bacterial damage
  • Unbroken surface; an "acid mantle" (skin secretions are acidic, and thus inhibit bacteria)
  • Phagocytes ingest foreign substances and pathogens, preventing them penetrating deeper body tissues
• Protection from ultraviolet radiation (damaging effects of sunlight)
  • Melanin produced by melanocytes protection from UV damage
• Protection from either thermal (heat or cold) damage Contains receptors
• Protection from desiccation (drying out) Contains waterproofing glycolipid and keratin

Other Skin Functions

• Aids in body heat loss or heat retention, controlled by the nervous system
  • Heat loss occurs by activating sweat glands and allowing blood to flush into skin capillary beds
  • Heat Retention; By not allowing blood to flush into skin capillary beds
• Aids in excretion of urea and uric acid that are contained in perspiration produced by sweat glands
• Synthesizes vitamin D using modified cholesterol molecules in skin, and converts them into vitamin D via sunlight

Epidermis

• Is the outer layer of the integumentary system
• Composed of avascular stratified squamous epithelium
• Often keratinized (hardened by keratin)

Dermis

• Is deep to the epidermis
• Made of dense connective tissue
• These two layers connect by the hypodermis (adipose tissue) via subcutaneous injections, providing insulin
• Hypodermis anchors skin to organs
• Contains lamellated (pacinian) corpuscles that detect external pressure to the skin

Layers of the Epidermis From Deepest to Most Superficial

• Stratum basale
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum (thick, hairless skin only)
• Stratum corneum

Layers of the Epidermis - The Specifics

• Stratum Basale (Stratum Germinativum)
  • Deepest layer
  • Lies next to dermis
  • Cells undergoing mitosis which turn into more superficial layers
  • Includes melanocytes to produce melanin
  • Attached to basal lamina by hemidesmosomes
  • Forms a strong bond between epidermis and dermis
• Stratum Spinosum
  • Consists of numerous keratinocytes arranged in 8–10 layers, some retain their ability to divide
    • Produces coarser bundles of keratin, which tightly join the cells to one another through desmosomes
  • Langerhans cells are active in the immune response
  • Projections of melanocytes
• Stratum Granulosum
  • Contains 3-5 layers of flattened keratinocytes undergoing apoptosis
  • Produces darkly staining granules of a protein, keratohyalin, which assembles keratin intermediate filaments into keratin
  • Produces a lipid-rich secretion = water-repellent sealant, retarding loss and entry of water and entry of foreign materials
• Stratum Lucidum
  • Formed from dead cells of the deeper strata
  • Occurs only in thick, hairless skin that is of on of the palms of hands and soles of feet
  • Consists of four to six layers of flattened clear, dead keratinocytes containing keratin, along with thickened plasma membranes
• Stratum corneum
  • Outermost layer of epidermis consisting of 25-30 layers of flattened dead keratinocytes
    • Extremely thin flat, shingle-like dead cells are filled with keratin (familiar as dandruff and dander)
  • Protective protein that prevents water loss
  • Shed and replaced every 2 weeks, accounting for three-quarters of the epidermal thickness

Cells in the Epidermis

• 90% of cells in the epidermis are there to Produce the protein keratin (protects underlying tissues) and lamellar granules (waterproof sealant)
• Other cells participate in immune responses (epidermal dendritic cells)
• 8% of the cells produce the pigment melanin
• Other cells function in sensing touch

Dermis

• A vascular area
• Is the treated dermis of animals in leather goods
• Collagen and elastic fibers are located throughout
  • Collagen fibers give skin its toughness
  • Elastic fibers give the skin elasticity
• Blood vessels play a role in body temperature regulation
• On the palms of hands/soles of feet, papillae are arranged in definite patterns that form looped/whorled ridges which increase friction and enhance gripping
• The part of the dermis responsible for itch or pain is the papillary layer
• Damage to the dermis results in stretch makes that are caused by excessive stretching of the dermis, particularly during pregnancy or weight gain
• Constant pressure in skin results in pressure ulcers, due to a constant deficiency of blood to tissues overlying a bony projection that has been subjected to prolonged pressure against an object such as a bed, cast, or splint which causes tissue ulceration

Two Layers of the Dermis

• Papillary layer is the upper dermal region containing
  • Projections called dermal papillae, with capillary loops
  • Pain receptors and touch receptors (Meissner corpuscles)
• Reticular layer is the deepest skin layer with blood vessels, sweat and oil glands, and hair follicles
  • Contains deep pressure receptors

Normal Skin Color Determinants

• Melanin is the only pigment made by the skin (yellow, brown, or black)
  • Melanocytes produce melanin and protect from UV radiation, and are mostly in the stratum basale
  • Melanin is determined by genetics and exposure to sunlight
• Carotene is an orange-yellow pigment from some vegetables (increases orange tan with large amount of carotene-rich food)
• Hemoglobin is gives the red coloring in blood cells found in dermal capillaries interrupted blood supply leads to cyanosis (blueish color)
• Accumulations of melanin includes freckles/pigmented nevi (moles) along with local accumulations of melanin in patches
• Inability to produce Melanin in an individual is Albinism, resulting in a inherited tendency the skin to burn easily on overexposure to sunlight -Vitiligo is a disease that is a Loss of melanocytes, which results in a loss of the pigment/ color
• Jaundice results with the Buildup of bile produced by liver, resulting in a yellow color
• Erythema is the Redness of the skin, caused by engorgement of capillaries with blood due to skin injury, as seen in some inflammation

Appendages of the Skin

• Includes the following structures
  • Cutaneous glands are exocrine glands made up of:
    • Sebaceous glands
    • Sweat glands (sudoriferous glands)
    • Ceruminous Glands
  • Hair
    • Hair follicles -Nails

Skin Appendages: Sebaceous Glands

• Found all over the skin, except on the palms of the hands and the soles of the feet
• Produces sebum as a lubricant for skin, preventing brittle hair while killing bacteria
• Most have ducts that empty contents into hair follicles, though others open directly onto skin surface
• More activated after puberty Acne results in inflammation as a cause bacteria colonizes these glands, destroying epidermal cells and creating cysts

Skin Appendages: Sweat Glands

• Produce sweat (sudor)
• Two types
  • Eccrine includes:
    • Open the duct to a pore on the skin surface through perspiration, which is thermoregulatory and causes emotional sweating that's widely distributed in the body
    • Especially on palms and soles
  • Apocrine Includes:
    • Ducts are empty into hair follicles
    • Produce odorous secretion and active at puberty
    • Located in the location areas such as armpits, around nipples, and groin
• Sweat Composition
  • Mostly water Contains
  • Salts and vitamin C
  • Some metabolic waste
  • If the glands are apocrine, it contains Fatty acids and proteins, resulting in a yellowish appearance
• Sweat functions to Dissipate excess heat and to Excrete waste products
  • Has an Acidic nature inhibits bacteria growth while the Odor is caused from associated bacteria
• Some of sweat glands are modified sweat glands located in the ear canal known as Ceruminous Glands responsible making a waxy secretion called cerumen (earwax), which provides a sticky barrier to prevents the entry of foreign materials.
• The hair is also used as a appendage due to being Produced with a hair follicle
  • Consist of hard keratinized epithelial cells, with Melanocytes providing pigment for hair color.
  • Structures include; the hard central Medulla, with a rougher Cortex, finished with a Cuticle that is more heavily lined with outer keratin.
  • The hair must be attached to structures such as; The papilla surrounded hair follicle, to then also be surrounded by a nerve ending Hair Plexus that can be more sensitive to the touch, and to then be also attached to smooth Arrector Pili so that the strands can move upon being excited or from the cold.

Skin Appendages: Nails

• Modifications of the epidermis
  • Scale-like
  • Heavily keratinized
  • Responsible for growth with the underlying extends stratum basale
  • Lack of pigment, rendering a colorless appearance
• Nail Structures
  • Free edge on to a visible attached portion called the Body connected to the Root of nail embedded in skin finished with a visible Cuticle

Homeostatic Imbalances

• Burns caused by Tissue damage and cell death from heat/ electricity/UV/ chemicals that are usually connected with dangers due to body
  • Can affect/cause Blood Flow
  • Dehydration and Electrolyte imbalance
  • Kidneys failure due to Circulatory Shock
  • Skin is exposed to Infections
• The Rule of Nines are to quickly estimating how much a person has been burned by measuring every region as about 9% of the body
  • Anterior and posterior head and neck = 9% along with the other regions such as the torso, legs and arms.
• The Degrees of the Burnt areas
  • If the skin is Only epidermis is damaged and the Skin turns red and swollen it is known as a “First degree Burn”
  • If the Epidermis and upper area of the dermis becomes more badly damaged with Skin turning red while blistering on top it is known as a “Second degree burn”
  • Third-degree burns are the total destruction of the burns, becoming entirely white or black
• Critical Burns can result from the following conditions
  • Having Over 25% of body with second-degree burns
  • Over 10% of body with the already worse third-degree type burns.
  • Where the third-degree burns take place, it usually happens to be on and around the Face, Hands, & Feet.

Skin Cancer

• An abnormal cell growth the is Classified in two ways of
  1. Non-Harmful Benign a. When it Does not spread throughout and is encapsulated/ contained b. Relatively slow growth c. Rarely fatal if removed before organs fail that the cancer touches
  2. More Dangerous Malignant a. Metastasized into other parts of the structure being damaged in b. Which there Fast to start the next stage of growths.
• Where the cancer arrives in this skin is then what specifies the cancer as either:
  1. Basal cell carcinoma the more common
  2. Squamous cell carcinoma when not removed
  3. Malignant melanoma being the worst
• As an example, a squamous type cancer being a skin cancer that Metastasizes to a lymph nodes
• “ABCD” rule for finding if melanoma occurred, and to do that, this should follow”
  • A = Asymmetry with non matching sides, to confirm the pigmented mole does not match
  • B = Border irregularity, where these are tested to see of the borders that are not smooth
  • C = Colour to confirm that it is mixed and contains different colours in which the pigmented area does not match.
  • D = Diameter to confirm it has grown outside 6mm.

Developmental Aspects of Skin & Aging

• As you get into your golden years The Integument area grows thin
  • Blood flow can become more difficult decreasing
  • Cellular activity also starts down decreasing over years
• The decreases in aging skin include all factors, there can be changes with Amount collagen, sweat glands, fat, number that helps elastic, as these changes may start affecting each other.