1. The Integumentary System
Skin and its accessory structures
Lecture for medical students
Department of histology,
cytology and embryology KhNMU

2. General Functions of the Skin
Regulation of body temperature
Protection as physical barrier
Sensory receptors
Excretion and absorption
Synthesis of vitamin D

3. 2 Major layers of skin
epidermis is epithelial tissue
dermis is layer of connective tissue, nerve & muscle
Subcutaneous tissue (hypodermis) is layer of adipose & areolar tissue
subcutaneous injection
intradermal = within the skin layer

4. Development of the Skin
Epidermis develops from ectoderm
Dermis develops from mesoderm
Slippery coating of oil and sloughed off skin called vernix caseosa is present at birth

5. Cell types of the Epidermis
Keratinocytes--90%
produce keratin
Melanocytes %
produces melanin pigment
long cell processes
Langerhan cells
from bone marrow
phagocytes
Merkel cells
touch receptor

6. Layers (Strata) of the Epidermis5 4 3 2 1

7. 1. Stratum Basale Deepest single layer of cells Stratum germinativum
Combination of merkel cells, melanocytes, keratinocytes & stem cells that divide repeatedly

8. 2. Stratum Spinosum 8 to 10 cell layers held together by desmosomes
At slide cells shrink and look spiny
Melanin

9. 3. Stratum Granulosum 3 - 5 layers of flat dying cells
Nuclear degeneration
Contain dark-staining keratohyalin granules

10. 4. Stratum Lucidum Seen only in thick skin on palms & soles of feet
Three to five layers of clear, flat, dead cells
Contains precursor of keratin

11. 5. Stratum Corneum
25 to 30 layers of flat dead cells filled with keratin
Continuously shed
Barrier to light, heat, water, chemicals & bacteria
Friction stimulates callus formation

12. Keratinization & Epidermal Growth
Stem cells divide to produce keratinocytes
As keratinocytes are pushed up towards the surface, they fill with keratin

13. Dermis Connective tissue layer
Contains hair follicles, glands, nerves & blood vessels
Major layers of dermis
papillary
reticular

14. Papillary l. Top 20% of dermis Composed of loose CT
Finger like projections called dermal papillae
Functions:
contains capillaries that feed epidermis
contains Meissner’s corpuscles (touch) & free nerve endings (pain and temperature)

15. Reticular l. Dense irregular connective tissue
Collagen and elastic fibers
Contains glands & hair follicles
Provides strength, extensibility & elasticity to skin
Epidermal ridges conforms to dermal papillae = fingerprints

16. Types of Skin Thin skin - covers most of body
thin epidermis (.1 to .15 mm.) that lacks stratum lucidum
lacks epidermal ridges, has fewer sweat glands and sensory receptors
Thick skin - only on palms and soles
thick epidermis (.6 to 4.5 mm.) with distinct stratum lucidum & thick stratum corneum
lacks hair follicles and sebaceous glands
-thick hypodermis

17. Accessory Structures of Skin
Epidermal derivatives
Epithelium sinks inward during development to form:
hair
glands
nails

18. Structure of Hair medulla, cortex & cuticle Root -- below the surface
Shaft -- visible
medulla, cortex & cuticle
Root -- below the surface
Follicle surrounds root:
external root sheath
internal root sheath
base of follicle is bulb
germinal cell layer
C.t.Papilla contains blood vessels

19. Hair Related Structures
Muscle arrector pili
smooth muscle in dermis contracts with cold or fear.
forms goosebumps as hair is pulled vertically

21. © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer
Hair Color and Texture
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Eumelanin
Pheomelanin
Cuticle
Cortex
(c) Red, wavy
Air space
Eumelanin
Pheomelanin
Medulla
(b) Black, straight
(a) Blond, straight
(d) Gray, wavy
© The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer

22. Glands of the Skin Sebaceous Sweat Ceruminous (wax) glands
Mammary (milk) glands

23. Histology of skin glands

24. Sebaceous (oil) glands
Secretory portion in the dermis
Most open onto hair shafts
Sebum
combination of cholesterol, proteins, fats & salts
keeps hair and skin from soft & pliable
Acne
bacterial inflammation of glands
secretions stimulated by hormones at puberty

25. Sweat glands most areas of skin
Eccrine (sweat) glands
most areas of skin
regulate body temperature with perspiration
Apocrine (sweat) glands
armpit and pubic region
duct opens onto hair follicle
secretions more viscous

26. Nails Tightly packed keratinized cells Nail body
visible portion pink due to underlying capillaries
free edge appears white
Nail root
buried under skin layers
lunula is white due to thickened stratum basale
Eponychium (cuticle)
stratum corneum layer

27. Skin Color melanin – most significant factor in skin color
produced by melanocytes
accumulate in the keratinocytes of stratum basale and stratum spinosum
eumelanin – brownish black
pheomelanin - a reddish yellow sulfur-containing pigment
people of different skin colors have the same number of melanocytes
dark skinned people
produce greater quantities of melanin
melanin granules in keratinocytes more spread out than tightly clumped
melanin breaks down more slowly
melanized cells seen throughout the epidermis
light skinned people
melanin clumped near keratinocyte nucleus
melanin breaks down more rapidly
little seen beyond stratum basale
amount of melanin also varies with exposure to ultraviolet (UV) rays of sunlight

28. Thermoregulation Releasing of sweat onto the skin
perspiration & its evaporation lowers body temperature
Adjusting flow of blood to the body surface
in moderate exercise, more blood brought to surface helps lower temperature
with extreme exercise, blood is shunted to muscles and body temperature rises
Shivering and constriction of surface vessels
raise internal body temperature as needed

29. Protection Physical, chemical and biological barrier
tight cell junctions prevent bacterial invasion
lipids released retard evaporation
pigment protects somewhat against UV light
langerhans cells alert immune system

30. Cutaneous Sensations
Touch, temperature, pressure, vibration, tickling and some pain sensations arise from the skin.

31. Excretion and Absorption
Only a minor role is played by the skin
400 mL of water evaporates from it daily
Small amounts salt, CO2, ammonia and urea are excreted
Lipid soluble substances can be absorbed through the skin
vitamins A, D, E and K, Oxygen and CO2
acetone and dry-cleaning fluid, lead, mercury, arsenic, poisons in poison ivy and oak

32. Synthesis of Vitamin D Sunlight activates a precursor to vitamin D
Enzymes in the liver and kidneys transform that molecule into calcitriol (most active form of vitamin D)
Necessary vitamin for absorption of calcium from food in the gastrointestinal tract

33. Epidermal Wound Healing
Abrasion or minor burn
Basal cells migrate across the wound
Contact inhibition with other cells stops migration
Epidermal growth factor stimulates cell division
Full thickness of epidermis results from further cell division

34. Deep Wound Healing
If an injury reaches dermis, healing occurs in 4 phases
inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels
migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts
proliferative phase is a completion of tissue formation
maturation phase sees the scab fall off
Scar formation
hypertrophic scar remains within the boundaries of the original wound
keloid scar extends into previously normal tissue
collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color

35. Phases of Deep Wound Healing
Which phases have been left out of this illustration?

36. Development of the Skin
Epidermis develops from ectodermal germ layer
Dermis develops from mesodermal germ layer
at 8 weeks, fetal “skin” is simple cuboidal epithelium
nails begin to form at 10 weeks, but do not reach the fingertip until the 9th month
dermis forms from mesoderm by 11 weeks
by 16 weeks, all layers of the epidermis are present
oil and sweat glands form in 4th and 5th month
by 6th months, delicate fetal hair (lanugo) has formed
Slippery coating of oil and sloughed off skin called vernix caseosa is present at birth

37. Skin Cancer 1 million cases diagnosed per year
3 common forms of skin cancer
basal cell carcinoma (rarely metastasize)
squamous cell carcinoma (may metastasize)
malignant melanomas (metastasize rapidly)
most common cancer in young women
arise from melanocytes ----life threatening
key to treatment is early detection watch for changes in symmetry, border, color and size
risks factors include-- skin color, sun exposure, family history, age and immunological status