Tissues That Form the Skin

Tissues that form the skin Epidermis ● Keratinised stratified squamous epithelial tissue ● Outermost layer that covers the skin surfaces ● Avascular and aneural ● Able to resist mechanical stress because it is composed of 95% keratinocytes ○ Keratinocytes = the hard substance in the keratinised stratified squamous epithelium (adds extra layer of strength) for protection of the underlying structures 5 individual layers of the epidermis 1. Stratum basale (deepest) - Junction between the epidermis and connective tissue under the dermis - Closest to blood supply (in the connective tissue) - First layer to absorb nutrients and oxygen - Production of new epithelial cells, which migrate up 2. Stratum spinosum (thickest) - Spiny projections to connect the epidermis to the dermis - Connects the epithelium to the connective tissue underneath - Precursor cells for vitamin D 3. Stratum granulosum (lipids) - End of the living area (before they get keratinised) - Releases lipids/oily substance for maintaining internal fluid and electrolyte homeostasis - Limits what can go through the skin layers 4. Stratum lucidum (clear layer) - Clear layer - **Not present in all skin areas** - First layer of dead cells (no nuclei) 5. Stratum corneum (most superficial) - Keratin fills in the dead cell layers - Creates a hardened area to protect against the mechanical stresses Thick and thin skin ● Thick skin = high mechanical stress = 5 layers of epidermis ○ No hair follicles ○ Palm of hand and plantar surface of feet ○ Many sweat glands ● Thin skin = low mechanical stress = 4 layers of epidermis ○ For lubrication and thermoregulation ○ Presence of hair follicles ○ Located everywhere else ○ Both sweat and sebaceous glands are present Dermis ● ● ● Connective tissue → loose, dense irregular Anchors the epidermis in place, provides strength and allows movement Vascular and neural Superficial (papillary layer) - Blood vessels and sensory receptors (tactile) - Pimple like projections that interlock with the overlying epidermis to keep the epidermis in place - Where the arteries and the veins meet, where the movement of waste and oxygen occurs, diffusion - Thinner layer of the dermis Deep (reticular layer) - Also has blood vessels and nerves - Physical barrier for other structures underneath the dermis - Twisting and mechanical stresses do not tear the tissue because of collagen (provides strength and prevents traumatic injury to deeper tissues) - Elastin to return to original shape - Has glands and hair follicles (thermoregulation) - Pressure and vibration sensory receptors Hypodermis - Directly under the dermis (reticular layer and hypodermis blend) - Fatty layer underneath the skin (adipose tissue and not skin tissue) - Added layer of protection for underlying structures Skin markings ● Fingerprints for grip → they form from the dermal ridges pushing up into the epidermis (extensions of the dermis that are trying to push through the epidermis) ● Wrinkles → effect of ageing and external factors on collagen and elastin ● Skin tension lines ○ ○ ○ ○ How protein fibres (collagen) pull on the dermis underneath Circular around the head and trunk Horizontal on the head and limbs Wound healing → The wound is dependant if it happens in line or at a right angle to the skin tension line ■ Wound along the line = opening is small and small scar, will heal and hold together ■ Right angle = the tension will pull it apart and make it hard to close, larger scar ■ Specific way that they cut in surgery to minimise scarring and for healing