The skin has three layers - the epidermis, dermis, and hypodermis. The epidermis is made of stratified squamous epithelium and contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells. It provides protection, regulates temperature and moisture, and produces vitamin D. The dermis contains dense connective tissue, hair follicles, sweat and sebaceous glands. It provides strength and elasticity to the skin. The hypodermis is a layer of adipose tissue that acts as insulation for the body. The skin comes in thick and thin varieties and has eccrine and apocrine sweat glands that help regulate temperature and release scent compounds.

2. THE SKIN
By
P.D.Sanaa El-Sherbiny
Mansoura University

3. Function of the
skinand protects the body.
 Covers
 Control internal temperature.
 Produces vitamin D.
 Receptors to detect environmental stimuli.
 Regulates the movement of substances
into and out of the body
Forms the largest organ of the body
forms 16%of body weight
Bio 130 Human Biology

4. Skin structure
 Epidermis: is outermost layer.
 Stratified squamous keratinized epithelium.
 Keratinization production of a waterproof protein.
 Pigments.
 Dermis: living portion of skin mostly dense
connective tissue.
 Contains :C.T fibers &cells ,vessels, sweat glands,
sebaceous glands, hairs.
 Hypodermis :Adipose tissue
Contains receptors
Bio 130 Human Biology

5. Types:1-THICK SKIN
 EPIDERMIS IS THICK:0.8mm in palm ,1.4
mm in sole.
 Contains 4 types of cells:
 1-keratinocytes (85% of cells)
 2-Melanocytes
 3-Langerhans cells
 4-Merkel cells
 ِArranged in five layers.

6. Epidermis and
dermis
Epidermis (purple)
Dermal papillae
Dermis
•Superficial papillary layer
contains loose connective tissue,
blood vessels, nerves, and
lymphatics
•Deeper reticular layer has dense
fibrous irregularly arranged
connective tissue

7. Layers of epidermis are
 Stratum basale
(germinativum)
 Stratum spinosum
 Stratum granulosum
 Stratum lucidum (may
not be present)
 Stratum corneum

8. Layers of epidermis
 Stratum basale
(germinativum)
 Single layer of cells on basal
lamina
 Stem cells which give rise to
keratinocytes
 Contain melanin transferred
from melanocytes
 May see mitotic figures
 Desmosomes and
hemidesmomes

9. Layers of epidermis
 Stratum spinosum
 Several cells thick
 Have cytoplasmic processes
(spines)
 Desmosomes

10. Layers of epidermis
 Stratum
granulosum
 1 to 3 layers of fusiform
shaped basophilic cells
 Keratohyalin
granules contain
cystine-rich and
histidine-rich proteins
that associate with
keratin filaments

11. Layers of epidermis
 Stratum
lucidum
 Present only in
thick skin
 Cells in which
keratinization
is advanced

12. Layers of epidermis
 Stratum corneum
 Superifical keratinized layer
 Cells
 Almost filled with keratin
 Flattened, non nucleate
 Coated with extra-cellular
lipids that form water barrier
of skin
 Layer that varies most in
thickness

13. TYPES OF EPIDERMAL CELLS

14. The epidermal cells
:1-keratinocytes
 They are responsible
 For keratin
formation
 Formed of many
layers that
continuously shed
 And regenerate
every 2-4 weeks
 They are arranged
 In many layers.

15. :Melanocytes
 Found inbetween cells of the basal layer &
 At the basal part of the hair follicles.
 Branched cells with centeral nuclei
 By EM contains organells for protein
synthesizes (rER, Golgi, mitochondria
&melanosomes).
 They form melanin by tyrosinase from
tyrosine amino acid
 By converting it to dioxyphenyl alanine
DOPA

20. :Langerhans cells -3
 Found in upper layers of st.spinosum
 Have branched shape &central nuclei
 Represent 3-8%of epid. Cells
 Mesodermal in origin.
 EM not connected to keratinocytes &
contain
 Birbeck granules
 Stained with silver & vital stains
 Phagocytic & antigen presenting cells

21. Langerhans cells

22. Merkels cells-4
 Found in basal cell layer
 Are modified epidermal cells
 Sensory nerve fibers form
terminal disk under
 Merkels cells
 Function as touch
receptors

24. THIN SKIN
 ALLOVER THE BODY EXCEPT SOLE &
 PALMS.
 EPIDERMIS
ISTHINNER,ST.spinosum,2-4LAYERS,ST.GRA.
ONE INCOMPLETE
 LAYER:NO ST LUCI. ,ST,COR.THINNER
NUMEROUS SWEAT GLANDS.
*CONTAIN HAIRE, SEBACEOUS
GLANDS
*AND ERECTOR PILLI MUSCLE

25. THIN SKIN

26. The dermis
 1-Papillary layer :
 Forms dermal papillae
 Loose C.T rich in collagen type 111
 Elastic fibers,C.T cells and rich in blood capillaries
 Contain meisssners corpuscles

28. Meissner‘s )Tactile(
Corpuscle
 Located in the dermlpapillae
 Receptor for light touch 28

29. Reticular layer -2
 The thicker deep layer
 Formed of dense c.T rich in interlacing wavy
collage fibers
 It is less cellular &less vascular
 Contain many nerve receptors:
 Krause end bulbs
 Ruffini corpuscles
 Pacinian corpuscles

31. :Glands and skin appendages
 Sebaceous glands
 Clumps of epithelial tissue distributed within dermis
 Secrete “sebum”—oily, fat-based substance that is
also anti-bacterial
 Located all over body
 Sweat glands
 Microscopic clumps of epithelial tissue distributed
within dermis, duct extends out through dermis to
pore their secretion.
 More than 2.5 million glands per person
 Eccrine sweat glands, concentrated on hands and
soles of feet and forehead, secrete sweat to cool
body, also at conditions of fear and emotion.
 Apocrine glands, concentrated in armpits and groin,
analogous with sexual scent glands of other
animals, odor comes from bacteria that concentrate
here.
 Ceruminous glands: modified sweat glands in ear
canal produce ear wax

32. sweat glands
Two types of sweat glands
 Eccrine
 Not associated with hair follicle
 Duct segment
 less coiled, leads to epidermis
 Stratified cuboidal epithelium
 Secretory segment
 in deep dermis or hypodermis
 Secretory cells
 Myoepithelial cells lie between
secretory cells, contraction
expels sweat
 Apocrine
 Found in limited areas
 Empty into hair follicle

33. SWEAT GLANDS
 Merocrine glands:  Apocrine glands:
 Allover the body  Axilla,groin,pubic
 Secretory cells 2types region
 Clear cells cubical rich in  Secretory part similar
glycogen granules.
 To mero. With wider
 Dark with narrow basal
part with apical  Lumen
 Glycoprotein granules  Their ducts are lined
 Myoepithelialt cells  With 2 layers of cubical cells
 Ducts lined by 2layers of but open into hair follicles
cubical cells  Secretion stim.by sex
 hormons