This document provides an overview of the structure and functions of the skin and its appendages. It notes that the skin is the largest organ and is composed of three main layers - the epidermis, dermis and hypodermis. The epidermis provides protection and waterproofing and has several layers including the stratum basale, stratum spinosum, stratum granulosum and stratum corneum. The dermis lies underneath and contains blood vessels, nerves and connective tissue. The deepest layer, the hypodermis, stores fat and anchors the skin. The document also describes skin appendages like hair, sebaceous glands, sweat glands and nails, and their structure and functions.

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Ahmed Abdulwahab
UG : (1330095)

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3. The 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
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Skin structure

5. Functions
 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
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6. Function
 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
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7. Epidermis
 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
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8. Epidermis
 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.
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9. Layer 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
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10. Layer 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
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11. Layer 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
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12. Dermis
 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.
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13. Dermis
 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
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14. Hypodermis
 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
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15. Skin 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
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16. Skin 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
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17. Skin 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)
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19. Skin Appendages
Hair Growth
influenced by: (in this order)
 nutrition - main influence
 hormones
 blood flow
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Hair Pigment
caused 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

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21. Skin 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
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Nail Structures

22. Skin Appendages
Sebaceous glands
all over except palms and soles of feet
Produce oil for waterproofing
Lubricant for skin & kills bacteria
Most with ducts that empty into hair follicles
Glands are activated at puberty: stimulated by hormones
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23. Skin Appendages
Eccrine glands
Widely distributed in skin:
abundant on palms, soles,
forehead
Sweat composition:
mostly water with a slightly
acidic 4-6 pH
Function:
thermoregulation
Apocrine glands
Ducts empty into hair follicles
Found mainly in anogenital &
axillary region
Begin to function at puberty
due to hormones /
pheromones
Organic contents: Fatty
acids and proteins – can
have a yellowish color that
stains clothes
Odor is from associated
bacteria
Ceruminous glands
Modified apocrine gland
Found in outer 1/3 of ear
canal
Produce ear wax to trap
“invaders”
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Sweat Glands

24. Thank you
for your attention
Ahmed abdulwahab
UG : (1330095)
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