SKIN
SKIN
It is the largest single organ of the body
accounting for about 16% of total body weight
in adults and 1.2 – 2.3 m2 o...
SKIN
•

Thick (glabrous, smooth or
nonhairy) found on the palms
and soles
> 5 mm

•

Thin (hairy) skin found in other
area...
SKIN functions:
•

The external layer of skin is relatively impermeable to water, it
prevents water loss by evaporation
• ...
SKIN functions:
•

Glands of the skin, blood vessels, adipose tissue participate in:
thermoregulation,
body metabolism,
ex...
Epidermis
Consists mainly of stratified squamous keratinized epithelium, but it
also contains three less abundant cell typ...
Epidermis - Stratum basale

Consists of five layers of keratin-producing cells (keratinocytes):
1. Stratum basale (stratum...
Epidermis - Stratum basale
•

•

•

All cells in the stratum basale
contain intermediate keratin
filaments of about 10 nm ...
Epidermis
Keratin contains at least six different polypeptides with molecular mass
ranging from 40 to 70 kDa
Three polypep...
Epidermis - Stratum basale
•

This stratum is characterized by intense mitotic activity and is
responsible (in conjunction...
Epidermis
2. Stratum spinosum consists of cuboidal or slightly flattened cells
with a central nucleus and a cytoplasm fill...
Epidermis – Stratum spinosum
•

The filaments play an important role in maitaining cohesion among the
cells and in resisti...
Epidermis
3. Stratum granulosum consists of 3-5 layers of flattened polygonal
cells whose cytoplasm is filled with coarse ...
Epidermis – Stratum granulosum

•
•

•

Lamellar bodies increase in number
These granules fuse with the cell membrane and ...
Epidermis
4. Stratum lucidum: present in thick skin, the stratum is a translucent,
thin layer of extremely flattened eosin...
Epidermis
5. Stratum corneum consists of 15-20 layers of flattened
nonnuceated keratinized cells whose cytoplasm is filled...
In psoriasis, a common skin disease, there is an increase in the number of
proliferating cells in the stratum basale and s...
Melanocytes
Melanocytes - neural crest derived cells
They have rounded cell bodies from which long irregular extensions br...
Melanocytes
The color of the skin is the result of several factors,
the most important of which are:
• content of melanin ...
Rasa czarna

Rasa
mongoidalna

Rasa biała
Langerhans cells
•

They are bone marrow–derived macrophages (Dendritic cells) they
can bind, process and present antigens...
Półpasiec

Opryszczka

Rak
Immunologic activity in the skin
SALT (Skin Associated Lymphoid Tissue)
•

Keratinocytes of the stratum basale produce:
ty...
Merkel`s cells (neural crest derived cells)

•

Merkel`s cells are generally present in the thick skin of palms and
soles
...
Dermis
•

A basal lamina is found between the stratum germinativum and the
papillary layer of the dermis
• Abnormalities o...
Dermis

•
•
•

Dermis is the connective tissue that supports the epidermis and
binds it to the subcutaneous tissue (hypode...
Dermis
•
•
•
•
•

Dermis contains two layers:
Papillary layer and reticular layer
Papillary layer is composed of loose con...
Dermis
•

Reticular layer is thicker, composed of irregular dense connective
tissue, it has more fibers (mainly type I and...
Epidermal derivatives:
•
•
•
•

The hair follicles and hair
Sebaceus glands
Sweat glands
Nails
•

Hairs are keratinized structures
present on all surface of the body,
except on the thick skin of the palms
and soles

•...
hair cortex

internal root sheath
glassy membrane –
noncellular hyaline layer

external root sheath

connective tissue she...
Sebaceus glands
•

Sebaceus gland is a holocrine saccular gland
present in the thin skin

•

The secretory portion of the ...
Sweat glands
There are two types of sweat glands:
• Eccrine sweat glands
• „Apocrine” sweat glands
Both types of sweat gla...
The fluid secreted by eccrine sweat glands is not viscous and contains little protein
Its main components are: water, sodi...
Sweat glands
„Apocrine” sweat glands:
• occur in the axilla, mons pubis, anal area,
ceruminous glands in the external audi...
Mammary gland

•

•
•
•

consist of 15-25 lobes of the compound
tubuloalveolar type whose function
is to secrete milk to n...
Mammary gland

•

During puberty breasts increase in size
and develop a prominent nipple
• Breast enlargement is a result ...
Mammary gland

Simple cuboidal epithelium covered by myoepithelial cells
Stratified columnar or cuboidal epithelium
strati...
Caseins, α-lactalbumin, Ig A,
lactose

•

•
•
•

Mammary gland

In the connective tissue surrounding the alveoli there are...
Mammary gland
Epidermis
•

After keratinization, the cells consist of only fibrillar and amorfous
proteins and thickened plasma membrane...
Melanocytes
•

Eumelanin is dark brown pigment produced by the melanocytes, a
specialized cells of the epidermis found ben...
Lecture10 skin
Lecture10 skin
Lecture10 skin
Lecture10 skin
Lecture10 skin
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Lecture10 skin

  1. 1. SKIN
  2. 2. SKIN It is the largest single organ of the body accounting for about 16% of total body weight in adults and 1.2 – 2.3 m2 of surface It is composed of: • epidermis – an epithelial layer of ectodermal origin • dermis – a layer of connective tissue of mesenchymal origin Beneath the dermis lies the hypodermis (hypo=under, derma=skin) = subcutaneus tissue, a loose connective tissue which may contain adipose cells (panniculus adiposus) The hypodermis is not part of the skin, but binds skin loosely to the subjacent tissues
  3. 3. SKIN • Thick (glabrous, smooth or nonhairy) found on the palms and soles > 5 mm • Thin (hairy) skin found in other areas of the body 1 – 2 mm The designation „thick” or „thin” refers to the thickness of the epidermal layer Total skin thickness also varies according to the site of the body
  4. 4. SKIN functions: • The external layer of skin is relatively impermeable to water, it prevents water loss by evaporation • Skin is a receptor organ in continuous comunication with the environment • Skin protects the organism from impact and friction injuries • Melanin – a pigment produced and stored in the cells of epidermis protects against the UV rays
  5. 5. SKIN functions: • Glands of the skin, blood vessels, adipose tissue participate in: thermoregulation, body metabolism, excretion of various substances • Vitamin D3 is formed in the skin (from precursors) under the solar irradiation • Skin can expand and cover large areas in edema and pregnancy
  6. 6. Epidermis Consists mainly of stratified squamous keratinized epithelium, but it also contains three less abundant cell types: • • • Melanocytes Langerhans cells Merkel`s cells • The keratinizing epidermal cells are called keratinocytes
  7. 7. Epidermis - Stratum basale Consists of five layers of keratin-producing cells (keratinocytes): 1. Stratum basale (stratum germinativum) consists of the single layer of basophilic columnar cells resting on the basal lamina at the dermal-epidermal junction • Desmosomes bind the cells of this layer together in their lateral and upper surfaces • Hemidesmosomes bind these cells to the basal lamina
  8. 8. Epidermis - Stratum basale • • • All cells in the stratum basale contain intermediate keratin filaments of about 10 nm in diameter The filaments play an important role in maitaining cohesion among the cells and in resisting the effects of abrasion As the cells progress upward, the number of filaments increases until they represent half the total protein in the stratum corneum
  9. 9. Epidermis Keratin contains at least six different polypeptides with molecular mass ranging from 40 to 70 kDa Three polypeptide chains coil around one another to form subunits of the tonofilament Nine of three-chain subunits coil around each other, forming a filament of about 10 nm in diameter End-to-end aggregation of three-chain subunits increases the length of the tonofilament The composition of tonofilaments changes as epidermal cells differentiate Basal cells contain polypeptides of lower molecular weight, whereas more differentiated cells synthesize the higher-molecular-weight polypeptides
  10. 10. Epidermis - Stratum basale • This stratum is characterized by intense mitotic activity and is responsible (in conjunction with the initial portion of the next layer) for constant renewal of epidermal cells • These two layers are called malpighian layer • The human epidermis is renewed about every 15-30 days
  11. 11. Epidermis 2. Stratum spinosum consists of cuboidal or slightly flattened cells with a central nucleus and a cytoplasm filled with bundles of keratin filaments (tonofibrils) • These filaments end at and insert into the cytoplasmic densities of the desmosomes • The cells of this layer are bound together by desmosomes that punctuate the cell surface, giving a spine-studded appearance
  12. 12. Epidermis – Stratum spinosum • The filaments play an important role in maitaining cohesion among the cells and in resisting the effects of abrasion • The epidermis of areas subjected to continuous friction and pressure (such as the soles of the feet) has a thicker stratum spinosum with more abundant tonofibrils and desmosomes • The cytoplasm displays membrane-coating granules – lamellar bodies containing lamellar disks which are formed by lipid bilayers
  13. 13. Epidermis 3. Stratum granulosum consists of 3-5 layers of flattened polygonal cells whose cytoplasm is filled with coarse basophilic granules – keratohyalin granules which are not surrounded by a membrane These granules contain: Profilaggrin Involucrin Small proline-rich protein Loricrin
  14. 14. Epidermis – Stratum granulosum • • • Lamellar bodies increase in number These granules fuse with the cell membrane and discharge their contents (glycolipid – acylglucosylceramide) into the intercellular spaces, where they are deposited in the form of sheets containing lipid The function of this extruded material is similar to that of an intercellular cement, it acts as a water barrier and as a barrier to penetration by foreign materials
  15. 15. Epidermis 4. Stratum lucidum: present in thick skin, the stratum is a translucent, thin layer of extremely flattened eosinophilic cells The organelles and nucleus are no longer evident The cytoplasm consists primarily of densely packed keratin filaments embedded in an electron-dense matrix Desmosomes are still evident between adjacent cells
  16. 16. Epidermis 5. Stratum corneum consists of 15-20 layers of flattened nonnuceated keratinized cells whose cytoplasm is filled with a filamentous (fibrillar) scleroprotein - keratin and amorfous proteins, and have thickened plasma membranes - they are called horny cells Tonofilaments are packed together in a matrix contributed by the keratohyalin granules These cells are continuously shed at the surface of the stratum corneum
  17. 17. In psoriasis, a common skin disease, there is an increase in the number of proliferating cells in the stratum basale and spinosum as well as decrease in the cycle time of these cells. This results in greater epidermal thickness and more rapid renewal of epidermis – 4-7 days instead of 15-30 days
  18. 18. Melanocytes Melanocytes - neural crest derived cells They have rounded cell bodies from which long irregular extensions branch into the epidermis running between the cells of the strata basale and spinosum Melanocytes contain numerous, small mitochondria, a well-developed Golgi complex, short cisternae of rough endoplasmic reticulum, intermediate filaments Melanocytes are not attached to the adjacent keratinocytes by desmosomes, they are bound to the basal lamina by hemidesmosomes
  19. 19. Melanocytes The color of the skin is the result of several factors, the most important of which are: • content of melanin and carotene • the number of blood vessels in the dermis • and the color of the blood flowing in them Melanin is synthesized in the melanocytes, with tyrosinase playing an important role in the process The extensions terminate in invaginations of keratinocytes
  20. 20. Rasa czarna Rasa mongoidalna Rasa biała
  21. 21. Langerhans cells • They are bone marrow–derived macrophages (Dendritic cells) they can bind, process and present antigens to T lymphocytes • They play a significant role in immunological skin reactions • Star-shaped cells present mainly in the stratum spinosum of the epidermis, associating with keratinocytes through E-cadherin
  22. 22. Półpasiec Opryszczka Rak
  23. 23. Immunologic activity in the skin SALT (Skin Associated Lymphoid Tissue) • Keratinocytes of the stratum basale produce: tymopoietin – promotes T cell`s terminal maturation in the skin; interleukin-1 • • T lymphocytes Langerhans cells
  24. 24. Merkel`s cells (neural crest derived cells) • Merkel`s cells are generally present in the thick skin of palms and soles • Free nerve endings are present at the base of Merkel`s cells • Merkel`s cells may act as sensory mechanoreceptors or may have functions related to the diffuse neuroendocrine system
  25. 25. Dermis • A basal lamina is found between the stratum germinativum and the papillary layer of the dermis • Abnormalities of the dermal-epidermal junction can lead to one type of blistering disorder (pemphigoid)
  26. 26. Dermis • • • Dermis is the connective tissue that supports the epidermis and binds it to the subcutaneous tissue (hypodermis) The thickness of the dermis varies according to region of the body and reaches its max of 4 mm on the back The surface of the dermis is very irregular and has many projections (dermal papillae) that interdigitate with projections of the epidermis (epidermal ridges)
  27. 27. Dermis • • • • • Dermis contains two layers: Papillary layer and reticular layer Papillary layer is composed of loose connective tissue (fibroblasts, fibrocytes, mast cells, macrophages, leukocytes) It constitutes the dermal papillae From this layer special collagen fibrils (type VII) insert into the basal lamina and extend into the dermis. They bind the dermis to the epidermis and are called anchoring fibrils
  28. 28. Dermis • Reticular layer is thicker, composed of irregular dense connective tissue, it has more fibers (mainly type I and III collagen) and fewer cells than in the papillary layer • The dermis contains a network of the elastic system fibers (oxytalan, elaunin, elastic fibers) This elastic network is responsible for the elasticity of the skin The principal gycosaminoglycan is dermatan sulfate • •
  29. 29. Epidermal derivatives: • • • • The hair follicles and hair Sebaceus glands Sweat glands Nails
  30. 30. • Hairs are keratinized structures present on all surface of the body, except on the thick skin of the palms and soles • Each hair consists of two parts: hair follicle and hair shaft • The hair follicle is a tubular invagination of the epidermis and is responsible for the growth of hair • The hair bulb is the end portion of the hair follicle • Follicular bulb contains stem cells – clonogenic keratinocytes – that can migrate and regenerate the hair shaft • Dermal papilla is very well vascularized connective tissue • The hair follicle consists of external root sheath and internal root sheath
  31. 31. hair cortex internal root sheath glassy membrane – noncellular hyaline layer external root sheath connective tissue sheath
  32. 32. Sebaceus glands • Sebaceus gland is a holocrine saccular gland present in the thin skin • The secretory portion of the sebaceus gland lies in the dermis, excretory duct opens into the hair follicle (or directly on the skin surface of the lips, the corner of the mouth, the glans penis, the labia minora and mammary nipple) • The secretory portion of the sebaceus gland consists of groups of alveoli connected to the excretory duct by a short ductule. Each alveolus is lined by cells resembling adipocytes with numerous small lipid droplets • The excretory duct is lined by stratified squamous epithelium continuous with the external root sheath of the hair • The oily secretion of the gland (sebum) is released on the surface of the hair and the epidermis
  33. 33. Sweat glands There are two types of sweat glands: • Eccrine sweat glands • „Apocrine” sweat glands Both types of sweat glands are tubular glands and both release their secretion by a merocrine process Eccrine sweat glands: • are present in the all regions of the skin • are functional through a whole life • participate in control of body temperature The secretory portion of eccrine sweat glands is convoluted tube composed of three cell types: • clear, dark, myoepithelial cells
  34. 34. The fluid secreted by eccrine sweat glands is not viscous and contains little protein Its main components are: water, sodium chloride, urea, ammonia, uric acid After its release on the skin surface, sweat evaporates, cooling the surface Mucoid cells are pyramidal cells Line most of the luminal surface of secretory portion Clear cells are devoid of secretory granules Their basal plasmalemma has numerous invaginations characteristic of cells involved in transepithelial salt transport
  35. 35. Sweat glands „Apocrine” sweat glands: • occur in the axilla, mons pubis, anal area, ceruminous glands in the external auditory meatus and the glands of Moll of the margin of the eyelids • are functional after puberty • are supplied by adrenergic nerves The secretory portion of „apocrine” sweat gland is located in the dermis or in hypodermis The excretory duct opens into the hair follicle The glands produce a viscous secretion which is odorless but may acquire odor as a result of bacterial decompositon
  36. 36. Mammary gland • • • • consist of 15-25 lobes of the compound tubuloalveolar type whose function is to secrete milk to nourish newborns The histologic structure of the mammary gland varies according to sex, age and physiologic status Each lobe is separated from the others by dense connective tissue and adipose tissue, and is embedded in intralobular loose connective tissue Each lobe has its own excretory lactiferous duct which opens in the nipple
  37. 37. Mammary gland • During puberty breasts increase in size and develop a prominent nipple • Breast enlargement is a result of the accumulation of adipose tissue and connective tissue with increased growth and branching of lactiferous ducts (due to increase of ovarian estrogens) • In adult woman each lobe is embeded in loose connective tissue; a denser, less cellular connective tissue separates the lobes • Near the opening of the nipple the lactiferous ducts dilate to form the lactiferous sinuses – lined with stratified squamous epithelium at the external openings
  38. 38. Mammary gland Simple cuboidal epithelium covered by myoepithelial cells Stratified columnar or cuboidal epithelium stratified squamous epithelium
  39. 39. Caseins, α-lactalbumin, Ig A, lactose • • • • Mammary gland In the connective tissue surrounding the alveoli there are lymphocytes and plasma cells, which population increases during pregnancy - toward the end of pregnancy; it is responsible for the secretion of immunoglobulins (Ig A) that confer passive immunity on the newborn The mammary glands undergo intense growth during pregnancy as a result of the proliferation of alveoli at the ends of the terminal interlobular ducts Alveoli are spherical collections of epithelial cells which secrete milk A fat droplets and membrane-limited secretory vacuoles containing dense aggregates of milk proteins are visible in apical part of cells
  40. 40. Mammary gland
  41. 41. Epidermis • After keratinization, the cells consist of only fibrillar and amorfous proteins and thickened plasma membranes, they are called horny cells • These cells are continuously shed at the surface of the stratum corneum • The human epidermis is renewed about every 15-30 days
  42. 42. Melanocytes • Eumelanin is dark brown pigment produced by the melanocytes, a specialized cells of the epidermis found beneath or between the cells of the stratum basale and in the hair follicles • The pigment found in red hair is called pheomelanin and contains cysteine as part of its structure

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