Upload
ahmed-abdulwahab
View
40
Download
0
Embed Size (px)
Citation preview
3The skin and hypodermis
Skin – our largest organ Accounts for 7% of body weight The skin varies in thickness from 1.5 to 4mm
distinct region The superficial region is a thick epithelial
tissue Divided into two distinct layers
Epidermis Dermis
Hypodermis – lies deep to the dermis
5Functions
Protection : Skin cushions and insulates the deeper body organs Protects the body from scrapes ,chemicals
and invading microorganisms The epidermis is waterproof, preventing
unnecessary loss of water across the body surface
produce pigment to protect the skin from the harmful effects of ultraviolet (UV) radiation
6Function
Body temperature regulation :The skin’s rich capillary networks and sweat glands regulate the loss of heat from the body
Excreation : The skin acts as a miniature excretory system when urea, salts, and water are lost through sweat.
Production of vitamin : The epidermal cells use UV radiation to synthesize vitamin D
Sensory reseption : touch, pressure, temperature, and pain
7Epidermis
A keratinized stratified squamous epithelium that contains four distinct types of cells Keratinocytes – most abundant
epidermis cell Produce keratin – a tough fibrous protein that
gives the epidermis its protective properties. Produce antibodies and enzymes Arise from deepest layer of epidermis Keratinocytes are dead at skin's surface
Merkel cells ,Tactile epithelial cells – associated with sensory nerve ending and function as a receptor for touch
8Epidermis
Melanocytes – secrete the pigment melanin Melanin is made in membrane-walled granules and then
transferred through the cell processes to nearby keratinocytes
Langerhans cells : macrophage like dendritic cells Millions of these dead cells rub off every day, giving us an
entirely new epidermis every 35 to 45 days—the average time from the birth of a keratinocyte to its final wearing away.
9Layer of the Epidermis
Stratum basale Deepest layer of epidermis Attached to underlying dermis Also called the Stratum
germinativum these Cells divide rapidly
Merkel cells – associated with sensory nerve ending
Melanocytes – secrete the pigment melanin
10Layer of the epidermis
Stratum spinosum (spiny layer) "Spiny" appearance caused by artifacts of histological preparation Contains thick bundles of intermediate filaments Contains star-shaped cells are part of the immune system Dendritic cells police the outer body surface, using receptor-mediated
endocytosis to take up foreign proteins (antigens) that have invaded the epidermis
Stratum granulosum Consists of one to five layers of flattened keratinocytes and intermediate
filaments intermediate filaments contain Keratohyaline granules – help form keratin Lamellated granules – contain a waterproofing glycolipid
11Layer of the epidermis
Stratum lucidum (clear layer) Occurs only in thick skin but not in thin skin Consists of a few rows of flat, dead
keratinocytes It is also named the transition zone
Stratum corneum (horny layer) Thick layer of dead keratinocytes and
thickened plasma membranes Protects skin against abrasion and
penetration
12Dermis
Second major layer of the skin Strong, flexible connective tissue Richly supplied with blood vessels and nerves fibers The deep dermal plexus is located between the
hypodermis and the dermis It nourishes the hypodermis and the structures located within
the deeper portions of the dermis subpapillary located just below the dermal papillae
perform a critical role in temperature regulation. These vessels are so extensive that they can hold 5% of all blood in the body.
13Dermis
The dermis has two layers papillary layer the superficial 20% of the
dermis is areolar connective tissue containing very thin
collagen and elastic fibers It includes the dermal papillae
increase the surface area for exchange of gases, nutrients, and waste products between these layers
reticular layer the deeper – 80% of thickness of dermis. is dense irregular connective tissue
14Hypodermis
Deep to the skin – also called superficial fascia
Contains areolar and adipose connective tissues
Besides storing fat, the hypodermis anchors the skin to the underlying structures
is also an insulator because fat is a poor conductor of heat, it helps prevent heat loss from the body
15Skin color
Three pigments contribute to skin color Melanin – most important pigment – made
from tyrosine Carotene – yellowish pigment from carrots
and tomatoes Hemoglobin – Caucasian skin contains
little melanin Allows crimson color of blood to show through
16Skin color
Melanin in granules passes from melanocytes (same number in all races) to keratinocytes in stratum basale Digested by lysosomes Variations in color Protection from UV light vs vitamin D?
Derived from epidermis but extend into dermis Include
Hair and hair follicles Sebaceous (oil) glands Sweat (sudoriferous) glands Nails
17Skin Appendages
Hair Minor protective functions (retain heat, decrease sunburn,
eyelashes protect eyes) Structure shaft – projects from skin follicle – extends into dermis root – lies within the follicle bulb – contains CT, vessels and nerves sebaceous gland – lubricates hair arrector pili muscle – attached to follicle and contracts to move
hair (hair growth, goosebumps)
19Skin Appendages
Hair Growth influenced by: (in this order) nutrition - main influence hormones blood flow
Hair Pigmentcaused by proportions of 3 melanin types
• dark hair – true melanin• blonde and red – melanin with iron and sulfur• gray/white hair - melanin replaced by air bubbles in shaft
21Skin Appendages
Nails Scale-like modifications of the epidermis Heavily keratinized Stratum basale extends beneath the
nail bed to form nail matrix Responsible for growth ( matrix region) Lack of pigment makes them colorless Lunula “little moon” – area of cell
growth (white semicircle at base of nail) Cuticle – area of skin that covers base
of nail
Nail Structures
22Skin Appendages
Sebaceous glands all over except palms and soles of feetProduce oil for waterproofingLubricant for skin & kills bacteriaMost with ducts that empty into hair folliclesGlands are activated at puberty: stimulated by hormones
23Skin Appendages
Eccrine glandsWidely distributed in skin: abundant on palms, soles, foreheadSweat composition: mostly water with a slightly acidic 4-6 pHFunction: thermoregulation
Apocrine glandsDucts empty into hair follicles Found mainly in anogenital & axillary regionBegin to function at puberty due to hormones / pheromonesOrganic contents: Fatty acids and proteins – can have a yellowish color that stains clothesOdor is from associated bacteria
Ceruminous glands
Modified apocrine gland Found in outer 1/3 of ear canalProduce ear wax to trap “invaders”
Sweat Glands