Unit I

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12. Integumentary SystemThin skin : (Epidermis-Dermis- Arrector pilorum-Sweat gland- Sebaceous glands- Hair follicle)Thick skin : (Strata basale- spinosum- granulosum- lucidum- corneum of epidermis-Papillary andreticular layers of dermis)62
12. Integumentary SystemSkin, the largest organ of the body consists of two layers, namely, epidermis and dermis which are firmlyattached to each other.Epidermis is made up of keratinised stratified squamous epithelium. It is avascular and is nourished bydiffusion. The basal layer of columnar cells rest on a basement membrane and is called stratum basale.Nuclei are distinct and show mitosis. Melanocytes are derived from melanoblasts and they are situated inthe basal layer of epidermis. They produce the pigment melanin, which is taken up by epithelial cells ofepidermis by phagocytosis. Langerhans cells are seen in metallic preparation showing branching processes.Next layer is stratum spinosum of polyhedral cells. Cells show many spine like processes loaded withtonofilaments. Third layer is stratum granulosum, which is 2 to 4 cell thick. They show keratohyalinegranules in the cytoplasm, which is basophilic in nature. Fourth layer is stratum lucidum; it is thin, clear,bright and homogenous line consists of eleidin substance. Eleidin is the transformed product of keratohyaline.Outermost layer is stratum corneum or layer of keratin. Here nuclei and cytoplasmic organelles disappearand keratohyaline granules fade away due to intracellular activity of lysosome-derived enzymes. The granulesare converted into a homogenous matrix in which all the previously formed filamentous material of the cellbecomes embedded. Each cell is transformed into one of the squames of keratin. In some specieskeratinisation can be in the absence of keratohyaline granules.Deepest cell layers proliferate throughout lifeand newer cells are pushed towards the surface. Here they die and are transformed into horny materialcalled as keratin. Keratin is water-proof and is a barrier for pathogenic micro-organisms. Keratin is toughfibrous protein highly resistant to chemical changes.Dermis is made up of connective tissue showing dermal papillae extending into epidermis, and epidermisshows epidermal papillae extending into dermis. Outer layer of dermis is called papillary layer because itshows the papillae. Deeper layer of dermis is called reticular layer, which is made up of thicker denseirregularly arranged connective tissue. Elastic fibres form network of very fine fibres in papillary layer whilein reticular layer they form a network of randomly distributed coarse fibres. Apart from various skinappendages and fibres, the dermis shows many fibroblasts, few macrophages and adipose cells.Theintegument consists of skin, hair, nail, sweat and sebaceous glands. The thickness of skin varies from0.5mm to 4 mm. It rests on the subcutaneous tissue. Depending on the thickness of the epidermis, skin isclassified into ‘Thin Skin’ and ‘Thick Skin.’Thin Skin: The epidermis is thin in ‘Thin Skin.’ Only three layers of epidermis nly. stratum corneum,stratum granulosum and stratum basale are clearly seen. Sections of sweat and sebaceous glands, hairfollicles, blood vessels are also seen. This type of skin is seen in the scalp, flexor aspect of limbs etc.Thick Skin: The epidermis is thick in ‘Thick Skin.’ All the five layers of epidermis are clearly seen. Thickskin may be hairy e.g. extensor aspect of limbs, back. Thick skin which is not hairy or ‘Glabrous’ is seenin the skin of palm, sole of foot.Notes:63
Page 4:
Mitochondrion Golgi apparatusSmooth
Page 7 and 8:
. Nonmembrane bound: These organell
Page 9 and 10:
Nucleus: It is made up of deoxyribo
Page 11 and 12: Intercellular contactsThe plasma me
Page 13 and 14: 3. Epithelial tissueHuman body is m
Page 15: Compound epithelium: They have two
Page 18 and 19: 4. Connective tissueFibroblast. Fib
Page 20 and 21: Collagen fibres Elastic fibresLoose
Page 22: 5. Muscular TissueStriated muscle L
Page 25 and 26: Sarcomere (Relaxed): Each myofibril
Page 27 and 28: Smooth muscle (LP): Smooth muscle f
Page 30 and 31: Astrocyte (Fibrous) Astrocyte (Prot
Page 32: Peripheral nerve T.S: (Epineurium -
Page 35 and 36: 7. CartilageIt is a specialised con
Page 37 and 38: White fibrocartilage: It shows bund
Page 40 and 41: Decalcified bone T.S.: (Fibrous and
Page 42 and 43: 9. Blood VesselsElastic artery: (Tu
Page 44 and 45: VeinCapillaries: (Endothelium- Basa
Page 46 and 47: 10. Lymphoid TissueLymph node (LP):
Page 48 and 49: Spleen (LP): ( Capsule - Trabeculae
Page 50 and 51: Thymus: (Capsule-Septa-Lobules-Cort
Page 52 and 53: Palatine Tonsil (LP): (Stratified s
Page 54 and 55: Morphological classification of exo
Page 56 and 57: Serous salivary gland e.g Parotid g
Page 58 and 59: Mucous salivary gland (LP): (Interl
Page 61: Mixed salivary gland (LP): A saliva
Page 65 and 66: Hair: In humans, hairs are not impo
Page 67 and 68: Sebaceous gland: It is seen on the
Page 69: Tooth: The tooth shows a projected
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Unit I

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