HISTO_LC3_SKIN.pdf

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC 2 Skin and Its Appendages: Skin COLLEGE OF MEDICINE, BATCH 2026...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC 2 Skin and Its Appendages: Skin COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gallego, Gutierrez, Labingdalawa, Malonzo Dr. Ana Villanueva-De Grano | Sept. 2022 Editors: Gadaza, Gadut, Gallego, Gutierrez, Labingdalawa, Malonzo SKIN o The skin contains millions of nerve endings that transport stimuli. These nerve endings I. SKIN A. Functions allow humans to detect sensation such as B. Layers heat, cold, pain and pressure. II. EPIDERMIS 3. Homeostasis/Thermoregulation A. Layers o Thermoregulation is important because it B. Basic Skin Cell Types provides heat conservation as well as heat C. Epidermal Water Barrier loss depending on what is needed this is D. Basement Membrane Zones especially done by the fatty layer of the skin III. DERMIS and hair on the head A. Layers o Skin is the largest sensory organ in the body B. Dermal Blood Supply C. Principal Components of Dermis containing a range of receptors for touch, IV. HYPODERMIS pressure, pain, and temperature V. THICK AND THIN SKIN 4. Metabolic VI. REFERENCES o Endocrine (Cells in the skin synthesize Vitamin D3 which is needed in calcium metabolism and proper bone formation) I. SKIN o Thousands of pores on the surface of the skin can absorb vitamins, acids, water and oxygen in order to provide moisture and SKIN nourishment to our skin. largest organ in the body (both in weight and surface area) o Excretion (excess electrolyte can be removed show regional variation via sweat) 15%-20% of its total mass o Subcutaneous layer stores significant 1.5mm- 4.0mm thick amounts of energy in the form of fat 1.5 mm; lower/ upper eyelids o Functions in excretion through sweat, 4.0 mm; palms/ soles of the feet and upper back (hairless) sebaceous and apocrine gland elastic & self-renewing 5. Wound repair/Regeneration o Elastic o Self-renewing o Healthy individuals, wound heals rapidly 6. Sexual Signaling o Physical appearance influenced by pigmentation which is provided by melanocytes, body contours and actinic damage o Pheromones - sex pheromones are produced by apocrine sweat glands and other skin glands for attraction Figure 1. Anatomy of the skin A. FUNCTIONS OF THE SKIN The skin’s structure is made up of an intricate network which serves as the body’s initial barrier against pathogens, UV light, chemicals, and mechanical injury. It also regulates temperature and the amount of water released into the environment. 1. Protective Figure 2. Major functions of the skin o Physical barrier (pathogens, thermal and mechanical insults; structural integrity) B. LAYERS OF THE SKIN o Immunoregulatory (antimicrobial properties) 1. EPIDERMIS o Ultraviolet protection (melanin) - Avascular 2. Sensory Page 1 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano - Stratified squamous keratinizing epithelium (ectodermal) cuboidal to columnar mitotically active stem cells - Surface layer which is in contact with the exterior that are constantly producing keratinocytes. This layer also contains melanocytes (e.g. stem cells) 2. DERMIS and merkel cells - Vascular o Increased mitotic activity due to germinative cells - Is a layer of dense irregular C.T. (mesodermal) present - Composed of different glands, nerves and blood vessels o Desmosomes – cell attachment / cell junctions - Inferior to the epidermis o Hemidesmosomes – attachment to the basement membrane zone (BMZ) 3. HYPODERMIS / SUBCUTIS - Contains varying amounts of adipose connective tissue - Located below the dermis - Presence of adipocytes - Also known as Panniculus Figure 4. Stratum Basale STRATUM SPINOSUM o also known as prickle cell layer o 4-6 rows of cell o Numerous cytoplasmic extensions / spines ▪ Represent the sites where desmosomes are anchored to tonofilaments Figure 3. Layers of the Skin: Epidermis E, Papillary Dermis PD, ▪ Tonofilaments Reticular Dermis RD, Subcutis SC; (other structures labeled: Eccrine Maintain cell cohesion duct ED, Eccrine gland EG, Keratin K) Provide resistance to abrasions Terminate at various II. EPIDERMIS desmosome o Polyhedral cells with “intercellular bridges” EPIDERMIS o consists of desmosomes spines; represents the Outermost layer of the skin sites where desmosomes are anchored to Keratinized, stratified squamous epithelium tonofilaments – keratin intermediate filaments 0.4 to 1.5 mm thick that maintain cell cohesion and provide resistance o Thin skin - 75 to 150 μm to abrasions o Thick skin - 400 to 1400 μm o consists of fillagrin Cornification (formation of the outermost dead layer of the o Langerhans cells present skin – stratum corneum) o Synthesis of lamellar granules & distinctive proteins (keratins, filaggrin, involucrin) o Alterations of nuclei, cytoplasmic organelles, plasma membranes, & desmosomes Cornification/Keratinization o Basal cells divide by mitosis and as they move upward the cells flatten and nucleus disappears o Takes place within 28 days A. LAYERS OF THE EPIDERMIS STRATUM BASALE o also known as stratum germinativum or Basal Cell Layer o the deepest layer of the epidermis o separated from the dermis by the basal lamina. Figure 5. Stratum Spinosum o The cells found in this layer are single layer of Page 2 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano Figure 8. Ichthyosis Vulgaris STRATUM GRANULOSUM o 3-5 flattened cell layers STRATUM LUCIDUM o also known as Granular cell layer o 2-3 flat cell layers o consists of filaggrin and filled with coarse, o present in thicker skin found in soles and palms. basophilic (keratohyalin) granules. o translucent and barely visible. ▪ Keratohyalin granules are hygroscopic. o non-nucleated cells with eleidin granules It is the repeated cycles of hydration and ▪ thick skin – palms and soles dehydration. Results in the soft and o Flat cells - contains densely packed keratin flexible keratin. filaments o secretory granules not surrounded by a o Contains densely packed keratin filaments membrane o tightly packed cells that lacks nuclear or o Contains the cells that move above the spinosum organelles. and will accumulate dense basophilic o Repeated cycles of hydration and dehydration contribute to the normal desquamation of the stratum corneum results in the softand flexible keratin Figure 9. Stratum Lucidum STRATUM CORNEUM o also known as the cornified layer o 20-30 cell layers Figure 6. Stratum Granulosum o anucleate o it is the uppermost/ superficial layer of the epidermis KERATOHYALIN GRANULES o Consists of flattened, dead cells filled with o Hygroscopic soft keratin filaments o Repeated cycles of hydration and dehydration o This is the layer which varies most in thickness, o Results in the soft and flexible keratin especially in callused skin. o within this layer, the dead keratinocytes secrete defensins which are part of our first immune defense. o continuous shedding (desquamation) o Cornified layer with cornified cells called squames o Most differentiated cells in the skin it is also responsible for the formation of calluses which is a reactive process o Thick plasma membrane of the keratinized cells is coated from the outside in the deeper portion of this layer with extracellular layer of lipids that Figure 7. Keratohyalin Granules form the major constituent of the water barrier in the epidermis Clinical Correlation: Ichthyosis Vulgaris o Layer that varies most in thickness o Absent or diminished granular layer, hard and o Thickness of this layer constitutes the principal rigid keratin difference between epidermis of a thick and thin skin; thick and thin skin differs on the thickness of the skin o Cornified layer may become even thicker at the site that is subjected to unusual amounts of friction as in the formation of calluses on the palms of the hands and on the fingertips. o Callus formation is a reactive process Page 3 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano Figure 12-13. Psoriasis (left); Squamous Cell Carcinoma (right) STRATUM MALPIGHI is a combined layer of the Strata Basale, Spinosum, and Granulosum. It also constitutes the nucleated viable epidermis. Figure 14. Stratum Malpighi B. BASIC SKIN CELL TYPES 3 Basic Cell Types a. Keratinocytes – most abundant b. Melanocytes – pigment - producing c. Langerhan cells – antigen – presenting cells Additional Cells d. Merkel Cells – tactile epithelial cells Figure 10-11. Layers of the Epidermis: Stratum Corneum C, Stratum e. Indeterminate dendritic cells Granulosum G, Stratum Spinosum S, Stratum Basale B (other structures labeled: Papillary Dermis PD, Orthokeratosis OK) KERATINOCYTES o most abundant in the epidermis Clinical Correlation: Psoriasis o squamous cells o Accelerated differentiation of keratinocytes o ectodermal in origin o keratinocytes are typically produced and they o 80% of cells differentiate at accelerated rates causing a slight o Keratin thickening of the epidermis or epidermal layer and an ▪ Tough and protective that separates the increase keratinization and desquamation organism from the external o caused by overactive T lymphocytes triggering environment autoimmune reactions in the skin which can also lead ▪ Intermediate filaments about 10 nm in to inflammation with redness irritation itching and diameter scaling with a defective skin barrier These keratin squames connect at their edges and in transverse Clinical Correlation: Squamous Cell Carcinoma sections form a folded basket-weave pattern called o Atypical keratinocytes orthokeratosis (OK). The squames are water repellent, in o characterized by highly atypical cells at all levels of partbecause they are coated with lipid-containing anti-wetting epidermis agents synthesised during maturation in the granular layer. o the disruption of the basement membrane results in a spread or metastasis of tumor cells to the lymph nodes o known for variable differentiation patterns ranging from polygonal squamous cells arranged in orderly lobules in zones of keratinization to rounded cells with foci of necrosis and occasional single keratinized cells Figure 15. Keratinocytes MELANOCYTES o produces melanin, which is responsible for the dark brown pigment of the skin o Melanin also absorbs harmful UV rays and protect Page 4 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano the skin from sun damage, also they: then migrate to the cytoplasmic Synthesized from tyrosine extensions from which they are Dark color of the skin transferred to your keratinocytes in the Protects the skin from the damaging basal cell layer of epidermis. This is also effects of UV radiation referred to as the pigment donation. o between stratum basale & spinosum ▪ They have pale-staining, rounded cell o neural crest origin bodies attached by hemidesmosomes to o long, irregular cytoplasmic and dendritic the basal lamina, but lacking extensions attachments to the neighboring o Epidermal Melanin Unit keratinocytes. ▪ 1 melanocyte : 4 basal ketaocyte (face, ▪ Eumelanins are brown or black shins, genitalia) pigments produced by the melanocyte, ▪ 1:10 (limbs) a specialized cell of the epidermis found among the cells of the basal layer and in hair follicles. The similar pigment found in red hair is called pheomelanin. ▪ SKIN COLOR o Number, size, and distribution of Melanosomes = pigment granules within the keratinocytes o Vascular pigments (oxyhemoglobin and deoxyhemoglobin) o Dietary pigments (carotene and lycopene) o Skin Color is not directly affected by melanocytes but rather by melanosomes which are within the Figure 16. Melanin and Melanocytes keratinocytes. o Fitzpatrick Scale - as the number increases, so does the pigmentation. Figure 17. (a) Normal epidermis with scattered Figure 19. Fitzpatrick Scale melanocytes M in the basal layer; (b) basal brown melanin pigment Me in dark-coloured skin Clinical Correlation: Addison Disease o UV light darkens the melanin and speeds up tyrosinase synthesis, thus increasing melanin production. Also, pituitary Adrenocorticotropic hormone also influences pigmentation. o Insufficient production of cortisol by Adrenal cortex, so there is excess ACTH produced which led to hyperpigmentation. Clinical Correlation: Vitiligo o Destruction of melanocytes o Acquired condition o Involves skin depigmentation often only in affected patches due to the loss or decrease activity of melanocytes. The causes of Figure 18. Epidermal Melanin Unit melanocytes loss are not clear, but they may include environmental, genetic, or autoimmune o Activity of melanocytes increases with exposure conditions. to X-rays and UV light ▪ Melanin is synthesized by amino acid tyrosine by melanocytes. The formed Clinical Correlation: Albinism melanin granules in the melanocytes o Normal number of melanocytes but unable to synthesize melanosomes Page 5 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano o congenital disorder which produces skin hypopigmentation due to a defect in tyrosinase or some other components of melanin producing pathway. You have a normal number of melanocytes but they are unable to synthesize the melanosome. Clinical Correlation: Freckles o Increased production of melanin by normal number of melanocytes o lay term for Ephelides and lentigines (both are flat Figure 25. Langerhans Cells macules) are the most important pigmentation characteristics observed in humans. But they differ significantly in development and morphology. Essentially, there's an increase production of melanin by a normal number of melanocytes. Clinical Correlation: Nevus o Benign proliferation of melanocytes o Increased number in melanocytes Figure 26. (a) Pale-staining Langerhans cells L in the epidermis; (b) Extensive network of cytoplasmic processes CP is highlighted in the immunohistochemical preparation Figure 20-22. Addison disease (left); Vitiligo (center); Albinism MERKEL CELLS (right) o Found in stratum germinativum in association with intraepithelial nerve endings o Palms, soles, infundibula, epithelium of nail beds, oral mucosa, genital regions o EM: possess distinctive electron-dense granules within their cytoplasm o Mechanoreceptors (gentle touch) Figure 23-24. Freckles (left); Nevus (right) ▪ Most abundant in fingertips o They are closely associated with the afferent or LANGERHANS CELLS sensory unmyelinated axons o Star shaped cells with numerous dendritic o Functions as mechanoreceptors for cutaneous processes found in stratum spinosum sensation particularly responding to gentle touch. o Originate from the bone marrow, specifically form melanocytes. They migrate via the blood stream and reside in the skin mainly in the stratum spinosum. These are antigen presenting cells are dendritic type cells and participate in the body's immune responses. o Electron microsopy, well developed RER and Golgi complex, clear cytoplasm with rodlike inclusion: Birbeck granules (Rod/Racquet inclusion) o Potent stimulators of T-cell mediated immunoreactions Figure 27. (a) Merkel cells M in the basal layer of epidermis; (b) immunohistochemical preparation with three Merkel cells M; (c) Merkel cells with pale nuclei and cytoplasm; (d) dense core granules D Page 6 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano epidermal junction or DEJ); right below the stratum basale. C. EPIDERMAL WATER BARRIER contains specialized components which provide added o Maintenance of body homeostasis adhesion to counteract disruptive external forces; it o Established primarily by two factors: maintains tissue architecture and provides resistance. o Deposition of insoluble proteins on the inner Functions: surface of the plasma membrane o Attaches the epidermis to the dermis o Lipid layer that is attached to the outer o Separates components of the epidermis and surface of the plasma membrane dermis o Provides resistance against external shearing As keratinocytes in the stratum spinosum begin to produce forces keratohyalin granules, they also produce: o Maintains tissue architecture during remodeling and repair. Lamellar bodies (membrane-coating granules) o Tubular or ovoid-shaped membrane-bound organelle o Unique to mammalian epidermis Probarrier lipids + lipid-processing enzymes o assembled into lamellar bodies o Spinous and granular cells synthesize probarrier lipids and lipid processing enzymes including sphingolipids, phospholipids, ceramides, sphingomyelinase, and phospholipase o This mixture is assembled in lamellar bodies in Golgi apparatus o Lamellar bodies contain proteases Figure 29. Basement Membrane Zone o The contents of granules are secreted via exocytosis into the intercellular spaces between stratum granulosum and stratum corneum Organization of these intercellular lipid lamellae is responsible for the formation of the epidermal water barrier has two structural elements: o The cell envelope o Lipid envelope a mature epidermis is an effective barrier which prevents dehydration from the loss of body water, poisoning from the absorption of noxious substances, and systemic infection from invading surface Figure 30. Four Zones of the BMZ microorganisms to maintain homeostasis. it resides within the most superficial layer of the skin, FOUR ZONES OF BMZ the stratum corneum. 1. HEMIDESMOSOME attachment of cells to the extracellular matrix if of crucial importance in maintenance of tissue structure and integrity. Plasma membrane of the basal keratinocytes that constitute the upper boundary of the interface Plasma membranes of the basal cells with the specialized attachment plates 2. LAMINA LUCIDA found between the epidermis and dermis. Functions to bind epithelial cells to basement membrane. Figure 28. Epidermal Water Barrier Electron-lucent region that lies beneath basal keratinocytes Portion of papillary dermis D. BASEMENT MEMBRANE ZONES (BMZ) junction between epidermis and dermis. aka(dermo- 3. LAMINA DENSA Page 7 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano consists of lattice network of structural proteins. Main o Usually, a disease of elderly with male component is type IV collagen that provides added strength predominance but can still occur in children to the basement membrane. presents as a generalized pruritic bullous Electron-dense plate below lamina lucida & above papillary eruption. Bullae are tense and develop on dermis normal orerythematous skin a.k.a basal lamina EPIDERMOLYSIS BULLOSA ACQUISITA (antibodies against 4. SUBLAMINA DENSA collagen VII) - a rare autoimmune disease characterized by lies beneath the lamina densa sub-epithelial blistering of the skin and mucosal fibrous components are present; anchoring fibrils, dermal membranes in response to injury microfibrils & collagen fibers o In general, is a group of inherited disorders characterized by blister formation in response TYPES OF COLLAGEN to mechanical trauma TYPE IV COLLAGEN o Slowly or poorly healing wounds o Major component of the basal lamina o They encompass defects in all areas of basement o Most abundant membrane TYPE VII COLLAGEN o Major component of the anchoring fibrils o Predominantly localized to the epidermal basement nmembrane zone (EBMZ) within the lamina densa and sublamina densa o Provides structural support and stability to EBMZ 2 MAJOR HEMIDESMOSOMAL PROTEINS Figure 32-33. Bullous Pemphigoid (left); Epidermolysis Bullosa o Both are basement membrane proteins Acquisita (right) o BP 230 (Bullous Pemphigoid Antigen 2) ▪ autoantibody against this is thought to SKIN CANCER be secondarily produced. is caused by unprotected long-term exposure to o BP 180 (Bullous Pemphigoid Antigen 1 or Type VII Collagen) the sun's UV radiation. 3 major types of skin cancer ▪ direct target of autoantibody because that originates form the epidermal layer of its location along the basement membranes Figure 34. Types of Skin Cancer THREE MAJOR TYPES OF SKIN CANCER: Figure 31. BMZ with Hemidesmosomal Proteins ▪ Basal Cell Carcinoma Most common type, microscopically resemble cells CLINICAL CORRELATIONS form thestratum basale BULLOUS PEMPHIGOID - a chronic blistering of the skin that ranges from mildly itchy welts to severe blisters & Slow growing tumor that usually does not infection and may affect a small area or spreads all over the metastasize. Typically, cancer cells arise from body. An autoimmune disorder follicular bulge of the outer root sheath if the hair o Most common autoimmune subepidermal follicle. blistering disease of the skin, their antibodies produce against the BP 230 & BP 180 which are ▪ Squamous Cell Carcinoma important membrane proteins in BMZ Second most common Usually develops a small painless nodule or a patch Page 8 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano that issurrounded by an area of inflammation. Characterized by highly atypical cells at all levels of the epidermis ▪ Malignant Melanoma Most serious form of skin cancer if not recognized at an early stage. Individual melanoma cells which originate from melanocytes will contain large nuclei with irregular contours and prominent eosinophilic nuclei. They aggregate in nest or scattered throughout the entire thickness of the epidermis. Figure 36. Layers of the Dermis With time, melanoma will undergo a radial growth phase and they grow in all directions – upward in A. PARTS OF THE DERMIS the epidermis, downward into the dermis & 1. PAPILLARY DERMIS peripherally as well Thin zone immediately beneath/below the epidermis At early stage they tend not to metastasize but in Haphazardly arranged collagen bundles the vertical growth phase they will exhibit mitotic highly irregular activity and will form round nodules that grow accounts for the whorls, loops and arches found on the tips perpendicular to the surface of skin. of fingers By this time, melanocytes will display a little or no composed of loose connective tissue that is highly vascular pigment in they usually start to metastasize to the highly developed circulation made up mostly of capillaries original lymph nodes in vertical growth phase has a lot of fibrocytes 2. RETICULAR DERMIS a deep layer forming a thick layer of dense connective tissue that constitutes the bulk of dermis collagen fibers have parallel orientation (Cleavage lines or Langer’s lines) or skin tension lines thick collagen bundles arranges in orthogonal pattern has fewer fibrocytes B. DERMAL BLOOD SUPPLY Figure 35. Skin Cancers the largest blood supply composed of arteries and veins that branch superficially into the middermis to form the cutaneous plexus. III. DERMIS Thermoregulatory function DERMIS decrease/ increase blood flow in the papillary layer to Derived from mesenchyme minimize or facilitate heat loss. middle layer of the skin Composition: collagen (70%), elastin, ground substance TWO MAJOR PLEXUSES (proteoglycans) 1. SUBPAPILLARY PLEXUS contains sweat glands, sebaceous glands and hair follicle between papillary & reticular dermis highly vascular o Layers form which your capillary Functions: supports the epidermis, feeling different branches extend into the dermal sensations, and producing sweat and hair papillae, and they form rich nutritive capillary network just below the A layer of connective tissue that supports the epidermis epidermis and binds it to the subcutaneous tissue or hypodermis. 2. DEEP PLEXUS Thickness varies with the region of the body and reaches near the interface of dermis and subcutis its maximum of 4 mm on the back. o Larger blood and lymphatic vessel Responsible for the tone and texture of the skin connection which at the interface of Also contains skin appendages, vascular supply to the skin, dermis and subcutaneous layer as well as nerves and sensory nerve endings. THERMOREGULATORY FUNCTION arteriovenous anastomoses or shunts and they are located between the two plexuses o These shunts decrease blood flow into papillary layer to minimize heat loss or increase flow to Page 9 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano facilitate heat loss depending on the need o Lymphatic vessels begin at the dermal papillae and they converge to form two plexuses located within the blood vessel Figure 38. Elastic Fibers CLINICAL CORRELATIONS KELOID o Excessive collagen deposition o Keloid and hypertrophic scars are dermal form of Figure 37. Dermal Blood Supply fibroproliferative disorders that are caused by aberrant wound healing due to the injuries in the C. PRINCIPAL COMPONENTS OF DERMIS deep dermis 1. COLLAGEN STRIAE family of fibrous proteins consisting of 15 types in o Decreased expression of collagen human skin o Striae/ Stretch marks - form of dermal scarring Major structural protein for the entire body found and they are associated with the stretching of the in tendons, ligaments and in the dermis dermis Synthesized by fibroblasts o Often result from a rapid change in weight or can Type 1 Collagen - major component of the dermis also be associated with endogenous or exogenous Collagen in papillary dermis is loosely arranged corticosteroids Proposed mechanisms are related and highly irregular to hormones, physical stretch, and structural FUNCTIONS: alterations of dermal collagen and elastic tissue. o stress-resistant material of the skin CUTIS LAXA o integrity, firmness, and elasticity o decreased elastin synthesis ▪ there is considerable increase in skin and ligament extensibility caused by defective collagen fibril processing SKIN AGING (Dermatophilosis) o Loss of collagen (wrinkling) and elastin (sagging) o With age, there are changes in the dermal ECM; like the thickening of collagen fibers, less collagen synthesis, and the loss of hyaluronan and other glycosaminoglycans that will cause skin to hang loosely. Natural aging process is affected by exposure to the sun which is why doctors advise to avoid too much sun exposure. When you age, Figure 36. Collagen epidermis becomes thinner and more transparent. 2. ELASTIC TISSUE Minority of the dermis is made of elastic tissue Elastin for retractile propertiesof the skin (or the skin's elasticity) also synthesized by fibroblasts its fibromatrix component is elastin ELASTIN – amorphous protein; fiber matrix component o Papillary dermis: thin and run at right Figure 39-40. Keloid (left); Striae (right) angles to the skinsurface o Reticular dermis: thicker and oriented parallel to skin surface o Demonstrated/ Appreciated by van- Gieson stain Figure 41-42. Aging (left); Cutix Laxa (right) Page 10 of 11 [HISTOLOGY] 1.02 SKIN – Dr. Ana Villanueva-De Grano IV. HYPODERMIS SUBCUTIS/SUBCUTANEOUS/HYPODERMIS Beneath the dermis is the subcutis or hypodermis or panniculus o Layer rich of adipose tissues o Deepest layer, derived from mesenchyme o Lobules of adipocytes separated by fibrous SEPTA ▪ Consists of adipose tissue, blood vessels Figure 45. Pt. suffering from Lipodystrophy & nerves ▪ Also contains sweat glands & bases of hair follicles V. THICK VS THIN SKIN Particularly thick in individuals who live in cold climates This layer and its associated loose connective tissue Thick skin is found in the palms and soles and is constituting of hypodermis or subcutaneous facia, it is characterized by a considerable thickness of the stratum predominantly composed of adipose tissue in many areas corneum, with abundant sweat glands, thicker and taller it is separated by a vertical fibrous septum dermal papillae, prominent surface ridges, abundant blood vessels and absent pilosebaceous unit. Thin skin is found notably on the face and is characterized by a fine checkerboard pattern of ridges and moderate number of pilosebaceous units and sweat glands. Its stratum corneum is not considerably thickened. VI. REFERENCES 6 Functions of the Skin. (2012, February 2). Scottsdale Skin Figure 43. Subcutis Rejuvenation. https://scottsdaleskinrejuvenation.com/6- functions-of-the-skin/ A. FUNCTIONS Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas Repository of energy (Fourteenth ed.). McGraw-Hill Education. Endocrine organ Young, B., Woodford, P., & O'Dowd G. (2014). Wheater’s Functional LEPTIN (body weight regulation) Histology (Sixth ed.). Churchill Livingstone. Conversion of androstenedione into estrone by aromatase o This layer produces leptin a hormone that regulates body weight via the hypothalamus. CLINICAL CORRELATIONS LOBULAR & SEPTAL PANNICULITIS o Inflammation of the adipose tissue (Lobular & Septal Panniculitis) LIPODYSTROPHY o Selective loss of body fat Figure 44. Pt. with Lobular & Septal Panniculitis on lower limbs Page 11 of 11