184715 integuments

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The Integumentary systemThe Integumentary system

The IntegumentThe Integument

The Integumentary System (The Integumentary System ( the the integumentintegument) or simply the skin system is ) or simply the skin system is one of the largest and heaviest organ one of the largest and heaviest organ systems of the human body. The skin systems of the human body. The skin covers the outer surface of the body and covers the outer surface of the body and is continuous with the mucous is continuous with the mucous membranes found insides the eyelids, membranes found insides the eyelids, nostrils, and other openings of the nostrils, and other openings of the human body. human body.

The Integument (skin)The Integument (skin)

The skin consist of The skin consist of two major layers, two major layers, and bed of and bed of connective tissue connective tissue of which it lays of which it lays upon called the upon called the subcutaneous subcutaneous tissue or tissue or ((hypodermishypodermis.) .)

The skinThe skin

The two major layers are:The two major layers are: -(1) The outer -(1) The outer epidermisepidermis, derived , derived

from the embryonic ectoderm, andfrom the embryonic ectoderm, and -(2) the inner-(2) the inner dermis dermis, which develops , which develops

from the mesode from the mesode Beneath the dermis is the Beneath the dermis is the

hypodermishypodermis (sometimes called the (sometimes called the subcutaneous tissue layer or the subcutaneous tissue layer or the superficial fascia)superficial fascia)

The skin and its appendages The skin and its appendages

hair, hair, nails, nails, sebaceous and sebaceous and sweat glands sweat glands

The skin and its appendagesThe skin and its appendages

make up a very complex set of organs that make up a very complex set of organs that accomplishes several functions for the accomplishes several functions for the human body, namely:human body, namely:

1. Protection for internal organs from the 1. Protection for internal organs from the outside environment,outside environment,

2. Protection from the loss of internal 2. Protection from the loss of internal fluids or dehydration,fluids or dehydration,

3. Maintenanc of homeostasis, interms of 3. Maintenanc of homeostasis, interms of body overall temperature regulation, body overall temperature regulation,

The skin and its The skin and its appendages….appendages….

4. Excretion of some waste products via 4. Excretion of some waste products via the the sebaceoussebaceous and and sweat sweat glands, glands,

5. Maintenance of the sites for reception 5. Maintenance of the sites for reception of external cutaneous sensations,of external cutaneous sensations,

6. Serves as a blood reservoir, and 6. Serves as a blood reservoir, and finally,finally,

7. The skin does some metabolic 7. The skin does some metabolic functions.functions.

The SkinThe Skin

The skin layers:The skin layers: Epidermis – specialized epithelium, derived Epidermis – specialized epithelium, derived

from the ectoderm.from the ectoderm. Dermis ( corium) – characteristics: Dermis ( corium) – characteristics: vascular dense connective tissuevascular dense connective tissue from the mesoderm. from the mesoderm. Corresponds to the Lamina propria of the mucous Corresponds to the Lamina propria of the mucous

membrane.membrane. Connected to the underlying hypodermis by Connected to the underlying hypodermis by

connective tissue fibers .connective tissue fibers . Hypodermis – lower layer, not part of the Hypodermis – lower layer, not part of the

skin.skin.

The skin…..The skin…..

Dermal ridges – patterns of ridges Dermal ridges – patterns of ridges over the skin surface consists of over the skin surface consists of whorls, loops, arches and determined whorls, loops, arches and determined by hereditary traits. Formed during by hereditary traits. Formed during 3rd and 4th months of fetal life3rd and 4th months of fetal life

Classification:Classification: thick skin = over the palms of hands thick skin = over the palms of hands

and feetand feet thin skin = over the rest of the body.thin skin = over the rest of the body.

The Epidermis.The Epidermis.

Cell types:Cell types: Keratinocyte = differentiate to keratin.Keratinocyte = differentiate to keratin. MelanocyteMelanocyte Langerhans cellLangerhans cell Merkel cellMerkel cell Basal cell layer mitotic activity Basal cell layer mitotic activity cells cells

displaced to higher level displaced to higher level elaborate keratin elaborate keratin keratin replaces the cytoplasm keratin replaces the cytoplasm cell dies cell dies shedding. shedding.

Epidermis of the palms and Epidermis of the palms and solesole

1. Stratum germinativum:1. Stratum germinativum: The stratum germinatum (The stratum germinatum (SGSG) provides the ) provides the

germinal cells necessary for the regeneration germinal cells necessary for the regeneration of the layers of the epidermis. These of the layers of the epidermis. These germinal cells are separated from the dermis germinal cells are separated from the dermis by a thin layer of basement membrane. After by a thin layer of basement membrane. After a mitotic division a newly formed cell will a mitotic division a newly formed cell will undergo a progressive maturation called undergo a progressive maturation called keratinization as it migrates to the surface.keratinization as it migrates to the surface.

Tonofibrils Tonofibrils = aggregate= aggregate bundles of fine bundles of fine filaments, where mitotic activities are filaments, where mitotic activities are inititated.inititated.


2. Stratum Spinosum2. Stratum Spinosum The cells that divide in the statum germinativum soon begin to The cells that divide in the statum germinativum soon begin to

accumulate many desmosomes on their outer surface which accumulate many desmosomes on their outer surface which provide the characteristic “prickles” of the stratum spinosum provide the characteristic “prickles” of the stratum spinosum ((SSSS), which is often called the prickle-cell layer.), which is often called the prickle-cell layer.

Composed of irregular, polyhedral cells, separate and flattened Composed of irregular, polyhedral cells, separate and flattened at the surface.at the surface.

Cytoplasm is basophilic, intercellular b ridges with short Cytoplasm is basophilic, intercellular b ridges with short process to adjacent cellsprocess to adjacent cells

MALPHIGIAN layer = stra. Germinativum & stra. Spinosum:MALPHIGIAN layer = stra. Germinativum & stra. Spinosum: a. responsible for proliferation & initiation of keratinization a. responsible for proliferation & initiation of keratinization

process.process. b. contains Melanocytesb. contains Melanocytesmelanin, for pigmentation.melanin, for pigmentation. c. with scattered langerhans and Merkel cells.c. with scattered langerhans and Merkel cells.


3. Stratum granulosum3. Stratum granulosum The progressive maturation of a keratinocyte is The progressive maturation of a keratinocyte is

charcterized by the accumulation of keratin, called charcterized by the accumulation of keratin, called keratinization. The cells of the stratum granulosum keratinization. The cells of the stratum granulosum ((SGRSGR) accumulae dense basophilic keratohyalin ) accumulae dense basophilic keratohyalin granules (seen on the close-up view). These granules (seen on the close-up view). These granules contain lipids, which along with the granules contain lipids, which along with the desmosomal connections, help to form a desmosomal connections, help to form a waterproof barrierwaterproof barrier that functions to prevent fluid that functions to prevent fluid loss from the body- loss from the body- keratinosomeskeratinosomes..

Consists of 3 to 5 layers of flattened cells whose Consists of 3 to 5 layers of flattened cells whose long axis is parallel to the skin surface, contains long axis is parallel to the skin surface, contains KeratohyalinKeratohyalin granules, cells become pale, granules, cells become pale, eventually dies.eventually dies.


4. Stratum Lucidum4. Stratum Lucidum Epidermis varies in thickness throughout the body Epidermis varies in thickness throughout the body

depending mainly on frictional forces and is depending mainly on frictional forces and is thickest on the palms of the hands and soles of thickest on the palms of the hands and soles of the feet. The stratum lucidum is normally only the feet. The stratum lucidum is normally only well seen in thick epidermis and represents a well seen in thick epidermis and represents a transition from the stratum granulosum to the transition from the stratum granulosum to the stratum corneum. stratum corneum.

Clear translucent layer 3 – 5 cell layers, flattened Clear translucent layer 3 – 5 cell layers, flattened and closely packed, nuclei are indistinct or and closely packed, nuclei are indistinct or absent. Cytoplasm has keratohyalin and absent. Cytoplasm has keratohyalin and distributed among the tonofibrils.distributed among the tonofibrils.


5. Stratum Corneum5. Stratum Corneum As a cell accumulates keratinohyalin granules, it As a cell accumulates keratinohyalin granules, it

is thought that rupture of lysosomal membranes is thought that rupture of lysosomal membranes release lysosomal enzymes that eventually cause release lysosomal enzymes that eventually cause cell death. The dead and dying cells filled with cell death. The dead and dying cells filled with mature keratin form the stratum corneum (mature keratin form the stratum corneum (SCSC). ). The deeper cells of the stratum corneum retain The deeper cells of the stratum corneum retain their desmosomal junctions, but as they are their desmosomal junctions, but as they are pushed to the surface by newly forming cells of pushed to the surface by newly forming cells of the stratum germinativum (the stratum germinativum (SGSG), the dead cells ), the dead cells gradually break apart and are lost, a process gradually break apart and are lost, a process called called desquamationdesquamation..


Stratum CorneumStratum Corneum Nucleus is absent, cytoplasm is Nucleus is absent, cytoplasm is

replaced with Keratin from the replaced with Keratin from the tonofibrils and deeper epidermal tonofibrils and deeper epidermal layer ( soft keratin) low in sulfur layer ( soft keratin) low in sulfur content.content.

Stains pink in Eosin and often Stains pink in Eosin and often shredded during preparation.shredded during preparation.

Stratum disjunctum = most Stratum disjunctum = most superficial layer , with flat horny superficial layer , with flat horny plates and desquamated constantly.plates and desquamated constantly.

Pigmentation of skin:Pigmentation of skin:

Carotene = yellow color.Carotene = yellow color. Blood = reddish hue.Blood = reddish hue. melanin pigments = shades of brownmelanin pigments = shades of brown

melanin melanin = produced by melanocytes = produced by melanocytes within the melanosomeswithin the melanosomes

melanocytes melanocytes between keratinocytes of stra. between keratinocytes of stra.

Germinativum and spinosumGerminativum and spinosum within hair follicleswithin hair follicles dermal connective tissue.dermal connective tissue.

Pigmentation of skin…..Pigmentation of skin…..

TyrosinaseTyrosinase ( enzyme from the ribosomes) ( enzyme from the ribosomes) transferred to endoplasmic reticulum transferred to endoplasmic reticulum Golgi Golgi zone zone packaged into vesicles packaged into vesicles fused into fused into premelanosomes premelanosomes mature into 4 stages with mature into 4 stages with melanin packed melanosomes melanin packed melanosomes transferred transferred to keratinocytes of stra. Germinativum and to keratinocytes of stra. Germinativum and spinosum via phagocytosis of melanosome spinosum via phagocytosis of melanosome containing processes of melanocytes containing processes of melanocytes pigments are injected into the keratinocytes.pigments are injected into the keratinocytes.

Pigmentation of skin…..Pigmentation of skin…..

MSH MSH – melanocyte stimulating – melanocyte stimulating hormones stimulates migration of hormones stimulates migration of melanosomes in dendritic process melanosomes in dendritic process and the transfer of keratinocytesand the transfer of keratinocytes

Ultraviolet rays increases the Ultraviolet rays increases the melanocytes enzymatic activitymelanocytes enzymatic activity TanningTanning

Langerhans cellsLangerhans cells

the 3rd cellular population within the epidermis.the 3rd cellular population within the epidermis. Star- shaped, with numerous dendritic process Star- shaped, with numerous dendritic process Found principally within the stra. Spinosum.Found principally within the stra. Spinosum. Berbick granules = rod-like inclusions in Berbick granules = rod-like inclusions in

cytoplasm, strat epith. In oral mucosa, cytoplasm, strat epith. In oral mucosa, esophagus, vagina, hair follicles, sebaceous and esophagus, vagina, hair follicles, sebaceous and apocrine glands, thymus and lymph nodes. apocrine glands, thymus and lymph nodes. Functions by fixing and processes exogenous Functions by fixing and processes exogenous antigens. antigens. Associated with B and T lymphosAssociated with B and T lymphos..

Merkel cellsMerkel cells

the 4th cellular population within the the 4th cellular population within the epidermis.epidermis.

Wide epidermal distribution, found in stra. Wide epidermal distribution, found in stra. GerminativumGerminativum

With irregular shaped nuclei, cytoplasm less With irregular shaped nuclei, cytoplasm less dense, concentrated at the basal region of dense, concentrated at the basal region of cells.cells.

Attached to neighboring keratinocytes by Attached to neighboring keratinocytes by numerous desmosomes.numerous desmosomes.

Functions as mechanoreceptors.Functions as mechanoreceptors. Has APUD ( amino precursor uptake and Has APUD ( amino precursor uptake and

decarboxylation) like activity.decarboxylation) like activity.

The DermisThe Dermis

1. The Papillary Dermis1. The Papillary Dermis The papillary dermis (The papillary dermis (PDPD) contains vascular ) contains vascular

networks that have two important functions. The networks that have two important functions. The first being to support the avascular epidermis with first being to support the avascular epidermis with vital nutrients and secondly to provide a network vital nutrients and secondly to provide a network for thermoregulation. The vasculature is organized for thermoregulation. The vasculature is organized so that by increasing or decreasing blood flow, heat so that by increasing or decreasing blood flow, heat can either be conserved or dissipated. The can either be conserved or dissipated. The vasculature interdigitates in areas called dermal vasculature interdigitates in areas called dermal papillae (papillae (DPDP). The papillary dermis also contains ). The papillary dermis also contains the free sensory nerve endings and structures the free sensory nerve endings and structures called Meissner’s corpuscles in highly sensitive called Meissner’s corpuscles in highly sensitive areas. areas.

The Dermis….The Dermis….

2. The Reticular Dermis2. The Reticular Dermis The main fibrous bed of the dermis.The main fibrous bed of the dermis. The reticular layer of the dermis (The reticular layer of the dermis (RDRD) consists of dense ) consists of dense

irregular connective tissue, which differs from the papillary irregular connective tissue, which differs from the papillary layer (layer (PDPD), which is made up of mainly loose connective ), which is made up of mainly loose connective tissue. The reticular layer of the dermis is important in tissue. The reticular layer of the dermis is important in giving the skin it overall strength and elasticity, as well as giving the skin it overall strength and elasticity, as well as housing other important epithelial derived structures such housing other important epithelial derived structures such as glands and hair follicles.as glands and hair follicles.

Langer lines = Langer lines = direction of fiber lines of skin tension, of direction of fiber lines of skin tension, of surgical importance, incisions heal with less gap and scar surgical importance, incisions heal with less gap and scar tissues. Ground substance is of amorphous matrix. tissues. Ground substance is of amorphous matrix.

Skin……Skin……

3 principal glycosaminoglycans of 3 principal glycosaminoglycans of the skin a. hyaluronic acid, the skin a. hyaluronic acid,

b. dermatan sulfates,b. dermatan sulfates,

c. chondroitin sulfates.c. chondroitin sulfates.

Cellular elements:Cellular elements:

fibrblastsfibrblasts macrophagesmacrophages fat cellsfat cells chromatophoreschromatophores connective tissue cellsconnective tissue cells true dermal melanocytes is raretrue dermal melanocytes is rare dopa positivedopa positive accumulate in the sacral region = Mongolian spotsaccumulate in the sacral region = Mongolian spots accumulate in dermal tumors = blue neviaccumulate in dermal tumors = blue nevi generally papillary layer has more cells and generally papillary layer has more cells and

smaller and finer connective tissue fibers and smaller and finer connective tissue fibers and reticular fibers.reticular fibers.

Muscle fibersMuscle fibers

maybe found in the dermis maybe found in the dermis arrectores pilorum muscles.arrectores pilorum muscles.

Scattered in the dermis = nipple, Scattered in the dermis = nipple, penis, scrotum, parts of the penis, scrotum, parts of the perineum, contraction gives a perineum, contraction gives a wrinkled appearance.wrinkled appearance.

Hypodermis Hypodermis

the subcutaneous layer( superficial)the subcutaneous layer( superficial) not part of the skinnot part of the skin deep extension of the dermisdeep extension of the dermis density and arrangement determines the mobility density and arrangement determines the mobility

of the skinof the skin panniculus adiposuspanniculus adiposus = a fat pad due to a = a fat pad due to a

continuous lobules of fat present up to 3 cm in continuous lobules of fat present up to 3 cm in the abdomen.the abdomen.

Devoid of fats = eyelids, penis and scrotum.Devoid of fats = eyelids, penis and scrotum. Superficial zone contains hair follicles and sweat Superficial zone contains hair follicles and sweat

glands.glands.

Skin AppendagesSkin Appendages

NailsNails Horny plates of epidermis that forms a protective covering on the Horny plates of epidermis that forms a protective covering on the

dorsal plates of the terminal phalanges, do not desquamate. The dorsal plates of the terminal phalanges, do not desquamate. The body is translucent, pink color due to vascularity in the nail bed. The body is translucent, pink color due to vascularity in the nail bed. The root is more opaque and becomes continuous with the body of the root is more opaque and becomes continuous with the body of the nail. nail.

3rd month, the begin to form as nail groove 3rd month, the begin to form as nail groove differentiate into soft differentiate into soft matrix nail plates matrix nail plates advance into the dorsal surface of the digits top advance into the dorsal surface of the digits top form nail beds. It lacks sweat glands and hair follicles.form nail beds. It lacks sweat glands and hair follicles.

HyponychiumHyponychium = thickened epidermis at the junction of stra. Corneum. = thickened epidermis at the junction of stra. Corneum. Lonule Lonule = a crescentric margin at the nail bed.= a crescentric margin at the nail bed. Nail grooveNail groove is lined by modified epidermis is lined by modified epidermis Eponychium Eponychium = = cuticlecuticle, extension of the stra. Corneum from nail bed , extension of the stra. Corneum from nail bed

to free surface of the nail plate.to free surface of the nail plate. Growth rates is Growth rates is 0.5 mm per week0.5 mm per week Faster growth Faster growth in the fingernail than in toenails. in the fingernail than in toenails.

Hair FollicleHair Follicle

Hair Follicles Hair Follicles elastic keratinized threads that developed from the elastic keratinized threads that developed from the

epidermis.epidermis. Distributed thru out the entire skin surface except:Distributed thru out the entire skin surface except: palmspalms solesole dorsal surface of distal phalangesdorsal surface of distal phalanges anal appertureanal apperture urogenital appertureurogenital apperture has shaft and root embedded in the skinhas shaft and root embedded in the skin hair follicle consists of epidermal and dermal tissueshair follicle consists of epidermal and dermal tissues


Structure =Structure = dermal root sheath derive from external dermal root sheath derive from external

connective sheath. connective sheath. With 3 layers: With 3 layers:

outer poorly defined, coarse bundle of collagen fibers outer poorly defined, coarse bundle of collagen fibers ( corresponds to reticular layer)( corresponds to reticular layer)

midlayer = thicker, corresponds to papillary layer, midlayer = thicker, corresponds to papillary layer, cellular and with fine connective tissue layer.cellular and with fine connective tissue layer.

Inner layer, glassy membrane, corresponds to basal Inner layer, glassy membrane, corresponds to basal lamina, consists of amorphous ground substance.lamina, consists of amorphous ground substance.


epithermal (epithelial root sheath) = epithermal (epithelial root sheath) = from the epidermisfrom the epidermis

outer epithelial root sheath = posses a outer epithelial root sheath = posses a single row of tall cells and an inner single row of tall cells and an inner polygonal stratum.polygonal stratum.

Inner sheath = keratinized root sheathInner sheath = keratinized root sheath

Inner layer of hair follicle Inner layer of hair follicle layers:layers:

Henle’s layer = a single layer of Henle’s layer = a single layer of flattened, clear cells with hyalineflattened, clear cells with hyaline

Huxley’s layer = several layers of Huxley’s layer = several layers of flattened cells with trichohyaline granule flattened cells with trichohyaline granule like keratohyaline and tonofibrils.like keratohyaline and tonofibrils.

cuticle of root sheath = lie against the cuticle of root sheath = lie against the hair cuticle. A single layer of transparent hair cuticle. A single layer of transparent horny scales and interdigitate.horny scales and interdigitate.

Inner layer of hair follicle Inner layer of hair follicle layers…layers…

Henle’s layer = a single layer of Henle’s layer = a single layer of flattened, clear cells with hyalineflattened, clear cells with hyaline

Huxley’s layer = several layers of Huxley’s layer = several layers of flattened cells with trichohyaline granule flattened cells with trichohyaline granule like keratohyaline and tonofibrils.like keratohyaline and tonofibrils.

cuticle of root sheath = lie against the cuticle of root sheath = lie against the hair cuticle. A single layer of transparent hair cuticle. A single layer of transparent horny scales and interdigitate.horny scales and interdigitate.

Growth = follows mitosis of the Growth = follows mitosis of the undifferentiated matrix of epidermal undifferentiated matrix of epidermal cells. cells.

Definite period for growth:Definite period for growth:

Definite period for growth:Definite period for growth: Head hair = growth is 2 – 4 yearsHead hair = growth is 2 – 4 years Eyelashes = 3 – 4 months.Eyelashes = 3 – 4 months. Upon cessation of growth, Upon cessation of growth,

multiplication at the bases stopped multiplication at the bases stopped root detach from matrix root detach from matrix hair falls hair falls out or is pulled. After a period of rest, out or is pulled. After a period of rest, a new germinal matrix develops to a new germinal matrix develops to grow up the reformed follicle.grow up the reformed follicle.

The HairThe Hair

Structure of the HairStructure of the Hair Layers:Layers:

medullamedulla cortexcortex cuticlecuticle

Medulla: Medulla: forms loose axisforms loose axis with 2 – 3 layers of shrunken with 2 – 3 layers of shrunken cornified, cuboidal cellscornified, cuboidal cells Absent in fine short hairs, downy type hair, some scalp hair, Absent in fine short hairs, downy type hair, some scalp hair,

blonde hair. blonde hair. Cells contains pigments, medulla is of soft type.Cells contains pigments, medulla is of soft type.

CortexCortex

make up the bulk of the hairmake up the bulk of the hair composed of several layers of long composed of several layers of long

flattened spindle shaped cornified cells.flattened spindle shaped cornified cells. Keratin is of the hard typeKeratin is of the hard type Keratin fibrils are oriented parallel to the Keratin fibrils are oriented parallel to the

long axis of the hairlong axis of the hair Pigment granules are found in between Pigment granules are found in between

cells and are oxidizedcells and are oxidized Air accumulates in the intercellular spaces, Air accumulates in the intercellular spaces,

modifies hair color.modifies hair color.

CuticleCuticle

single layer of thin clear cellssingle layer of thin clear cells cornified cells, have lost their nucleicornified cells, have lost their nuclei cells overlap with free edges directed cells overlap with free edges directed

upwardsupwards x section, round = Chinese, Eskimos, x section, round = Chinese, Eskimos,

American Indians.American Indians. Oval = CaucasiansOval = Caucasians Elliptical or reniform = wooly hair of blacks.Elliptical or reniform = wooly hair of blacks.

Sweat GlandsSweat Glands

Eccrine or merocrine sweat Eccrine or merocrine sweat glands or ordinary sweat glands or ordinary sweat glands. glands.

Coiled, tubular, distributed Coiled, tubular, distributed thru out the skin. thru out the skin.

Not found in:Not found in: nail bedsnail beds margin of lipsmargin of lips glans penisglans penis eardrumeardrum

Most numerous in the:Most numerous in the: palms palms solesole Apocrine sweat glands Apocrine sweat glands

= found in axilla, nipple, areola, = found in axilla, nipple, areola, labia majora, circumanal labia majora, circumanal region.region.

= has a thicker secretion, = has a thicker secretion, opens into the upper part of opens into the upper part of hair follicles. Less coiling, the hair follicles. Less coiling, the lumen is much wider., myo-lumen is much wider., myo-epithelial cells are much larger epithelial cells are much larger and form a complete layer, and form a complete layer, begins to function only at begins to function only at puberty. Secretes a waxy puberty. Secretes a waxy substance = cerumen from substance = cerumen from glands of the external glands of the external audoitory meatus and the audoitory meatus and the eyelids glands of Moll.eyelids glands of Moll.

Sebaceous glandsSebaceous glands

connected with hair folliclesconnected with hair follicles several drain into a single follicleseveral drain into a single follicle others drain into free surface, e.g., glans penis, others drain into free surface, e.g., glans penis,

labia minora, tarsal ( meibomian) glandslabia minora, tarsal ( meibomian) glands absent in palms and solesabsent in palms and soles each is encapsulated by a thin layer of connective each is encapsulated by a thin layer of connective

tissue.tissue. alveolar ( saccular) glands which synthesize alveolar ( saccular) glands which synthesize

lipids.lipids. Alveoli are completely filled with stratified Alveoli are completely filled with stratified

epithelium epithelium

Sebaceous glandsSebaceous glands

Alveoli are completely filled with stratified Alveoli are completely filled with stratified epithelium, the internal surface is a single row of epithelium, the internal surface is a single row of small cuboidal cells small cuboidal cells continuous with basal cells continuous with basal cells of epidermis of epidermis incr. agranular endoplasmic incr. agranular endoplasmic reticulum reticulum becomes active in Lipogenesis becomes active in Lipogenesis center of alveoli nucleus becomes largercenter of alveoli nucleus becomes larger cytoplasm is distended with droplets, containing cytoplasm is distended with droplets, containing cholesterol, phospholipids, triglycerides cholesterol, phospholipids, triglycerides nuclei nuclei gradually shrinks and disappears gradually shrinks and disappears cells cells breakdown into fatty mass of debris breakdown into fatty mass of debris

SEBUM , holocrine type, total destruction of SEBUM , holocrine type, total destruction of epithelial cells.epithelial cells.

* discharge of sebum is aided by the arector pili * discharge of sebum is aided by the arector pili muscle and pressure within alveolus.muscle and pressure within alveolus.

Sebaceous gland…..Sebaceous gland…..

VascularityVascularity = rete cutaneum , around the = rete cutaneum , around the

junction zone between the dermis junction zone between the dermis and the hypodermisand the hypodermis rete rete subpapillare ( network between subpapillare ( network between papillary and reticular layer) papillary and reticular layer)

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184715 integuments

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