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Questions and Answers
What percentage of total body weight does the skin constitute?
Which layer of the skin serves primarily as a waterproofing barrier?
What is the primary function of the hypodermis?
What type of epithelium constitutes the epidermis?
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Which of the following is NOT a function of the skin?
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What provides the tactile sensation in the skin?
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How can skin be classified based on the thickness of the epidermis?
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What role do epidermal ridges play on the fingers and toes?
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Which layer is NOT found in thin skin?
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What is the thickness range of the epidermis in thick skin?
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Which cell type makes up approximately 95% of the epidermis?
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What is the main role of keratinocytes in the epidermis?
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What is a key structural feature of keratin that contributes to its strength?
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Which of the following correctly describes the stratum basale?
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Which of the following features is present in thick skin but absent in thin skin?
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In which layer of the epidermis do keratinocytes primarily regenerate?
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What are the primary types of keratin produced by the keratinocytes in the stratum spinosum?
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Which cells are primarily responsible for the barrier function of the stratum corneum?
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Which layer of the epidermis is primarily responsible for cell renewal?
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What structure facilitates adhesion between keratinocytes in the stratum spinosum?
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What characterizes the cells of the stratum corneum?
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What is the primary function of the membrane-coating granules found in keratinocytes?
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What type of cells make intercellular bridges in the stratum spinosum?
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Which layer of the epidermis is also known as the Malpighian layer?
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What transformation product is found in the cells of the stratum lucidum?
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Which junctions are formed between the keratinocytes in the stratum granulosum?
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What is the primary function of Langerhans cells in the skin?
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Where is the stratum lucidum prominently found?
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What component is NOT found in the contents of the lamellar bodies?
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Which statement about stratum granulosum keratinocytes is correct?
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Which layer of the basement membrane is in closest proximity to the epidermis?
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What characteristic feature is indicative of Merkel cells?
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What is the primary structural feature of the cells in the stratum corneum?
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Which of the following best describes the cells of the stratum granulosum in terms of their functionality?
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What is the significance of dermal papillae in the skin?
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How are keratin filaments aggregated in the cells of the stratum granulosum?
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Which type of collagen is predominantly found in the dermis?
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What kind of receptors are formed by the interaction of afferent nerve terminals with Merkel cells?
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What structure acts as an anchoring point between the epidermis and dermis?
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What type of connective tissue primarily composes the dermis?
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Study Notes
Integumentary System
- The integumentary system consists of skin and its derivatives: sebaceous glands, sweat glands, hair, and nails.
- The skin is the largest and heaviest organ, covering approximately 1.2-2.3 m2 and accounting for about 16% of body weight.
- The skin protects against injury, dehydration, and infection.
- Skin regulates body temperature, absorbs UV radiation for vitamin D synthesis, and contains receptors for touch, temperature, and pain.
Skin Layers
- The skin has two main layers: the epidermis (ectodermal origin) and the dermis (mesodermal origin).
- The epidermis is a keratinized stratified squamous epithelium that provides waterproofing and acts as a barrier to infection.
- The dermis is a dense fibrous connective tissue that houses the skin's appendages.
- The hypodermis, a sheath of tissue between the skin and deeper structures, is not part of the skin but attaches it to underlying bone and muscle, supplying blood vessels and nerves. It is rich in adipose tissue.
Epidermal Ridges and Dermal Ridges
- The epidermis and dermis interdigitate through the formation of epidermal ridges and dermal ridges (dermal papillae).
- Epidermal ridges, visible as fingerprints, are located where the epidermis overlies the dermal ridges.
Thick Skin vs. Thin Skin
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Thick skin is found on the palms of the hands and soles of the feet.
- It has an epidermis 400-600 µm thick with five well-defined layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
- Thick skin contains sweat glands but lacks hair follicles, sebaceous glands, and arrector pili muscles.
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Thin skin covers the rest of the body.
- Its epidermis is 75-150 µm thick and has three layers.
- The stratum granulosum and stratum lucidum are absent, but similar cells exist.
- Thin skin contains sweat glands, hair follicles, sebaceous glands, and arrector pili muscles.
Epidermal Cell Types
- The epidermis consists of four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells.
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Keratinocytes make up approximately 95% of the epidermis and are responsible for regenerating the skin every 30 days via mitosis.
- They produce keratin, the key structural protein in skin, hair, and nails.
- Keratin monomers form filament bundles, further organized into intermediate filaments, held together by hydrogen bonds.
- Keratin's high cysteine content enables disulfide bridges, adding strength and rigidity.
- Melanocytes produce melanin, the pigment that provides skin color and protects against UV radiation. Melanocytes reside in the stratum basale and stratum spinosum.
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Langerhans cells, derived from bone marrow, are located mainly in the stratum spinosum and function as antigen-presenting cells in the immune system.
- These cells phagocytose antigens and express CD1 and MHC I and II receptors.
- Merkel cells are located in the stratum basale and are believed to be of epithelial origin. They function as mechanoreceptors (touch receptors).
Epidermal Layers
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Stratum basale: The deepest layer of the epidermis. It comprises mitotically active, cuboidal to columnar keratinocytes, responsible for cell renewal.
- Keratinocytes are held to the basal lamina (basement membrane) by hemidesmosomes and to each other via desmosomes.
- This layer contains melanocytes and Merkel cells.
- Keratinocytes produce keratin 5 and 14.
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Stratum spinosum: This layer is composed of polyhedral keratinocytes (prickle cells) with numerous processes (intercellular bridges) that form desmosomes.
- Cells in the deeper layer of this stratum also display mitotic activity.
- This layer and the stratum basale constitute the malpighian layer.
- Keratinocytes produce keratin 1 and 10.
- It contains membrane-coating granules (Odland bodies, lamellar bodies) that release lipids, enzymes, and proteins into intercellular spaces, contributing to the stratum corneum's barrier function.
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Stratum granulosum: This layer is formed by migrating cells of the stratum spinosum.
- It consists of 3-5 layers of flattened keratinocytes, the most superficial layer with nuclei.
- Cells contact each other through desmosomes and tight junctions.
- Keratinocytes accumulate keratohyalin granules, which destroy nuclei and organelles, and contain filaggrin and trichohyalin that crosslink keratin filaments.
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Stratum lucidum: This layer is found only in thick skin and lies between the stratum granulosum and corneum.
- It contains keratin filaments and eleidin, a transformation product of keratohyalin.
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Stratum corneum: The outermost layer of the epidermis, it consists of 15-20 layers of flattened, nonnucleated dead cells (hulls) filled with keratin, called squames.
- This layer is continuously shed through desquamation.
The Basement Membrane
- The basement membrane is a thin sheet of fibers that separates the epidermis from the dermis.
- It is produced by both tissues and anchors the epidermis to the dermis.
- The basal lamina layer is divided into two layers: lamina lucida and lamina densa.
- The basement membrane controls the traffic of cells and molecules between the dermis and epidermis.
Dermis
- The dermis lies under the epidermis and is derived from the mesoderm.
- It consists of dense, irregular collagenous connective tissue with mostly type I collagen and numerous elastic fibers.
Dermis Layers
- The dermis has two layers: papillary and reticular.
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Papillary layer: The superficial layer, it forms dermal papillae (dermal ridges) that interdigitate with the epidermal ridges.
- This layer is composed of thin, loosely arranged fibers and cells.
- It contains capillary loops that nourish the epidermis and Meissner corpuscles (fine-touch receptors).
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Reticular layer: This deeper and more extensive layer constitutes the majority of the dermis.
- It is the location for sweat glands, hair follicles, sebaceous glands, and arrector pili muscles.
Function of Epidermal Ridges
- The raised strips of epidermis on the palms and soles, known as epidermal ridges, increase friction.
- This friction enhances traction for the feet and improves grip ability for the hands.
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Description
Explore the integumentary system, which includes the skin and its derivatives such as glands, hair, and nails. Learn about the structure of the skin, its protective functions, and the various skin layers. This quiz will test your understanding of how the skin protects and regulates body functions.
