Questions and Answers
What is the primary cell of the epidermis?
What is the function of melanin in the skin?
What is the layer of skin that contains macrophages and acts in defense against pathogens?
What is the process by which former cells are flattened and lose cellular contents to form keratin?
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What is the purpose of desmosomes in keratinocytes?
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What is the layer of skin that is composed of binding tissues of fibrous and elastic connective tissue?
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What is the function of Merkel cells in the skin?
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What is the characteristic of the reticular layer of the dermis?
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What is the primary function of the subcutaneous layer?
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What distinguishes thick skin from thin skin?
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What is the function of Langerhans' cells in the epidermis?
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What is the mechanism by which the skin loses heat through radiation?
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What type of cells contributes to the biological barrier of the skin?
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What is the structure that provides adhesion between the skin and underlying structures?
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What is the function of the glycolipid in the skin?
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What is the primary function of the dermis?
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What is the main function of Meissner corpuscle in the skin?
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Which of the following is NOT absorbed through the skin?
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What is the role of nerve endings in the skin?
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What is the function of the skin in terms of excretion?
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What happens to the air on skin surfaces when heat flows through convection?
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What is the role of vitamin D in the body?
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What is the total area of the skin in the human body?
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What is the effect of sweat evaporation on the skin?
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Study Notes
Skin Structure
- Former cells are flattened, lose cellular contents, and form keratin through a process called keratinization
- The skin surface layer is automatically removed every 14 to 28 days
- There are four main types of cells in the skin:
- Keratinocytes: produce keratin, are the primary cells of the epidermis, and arise from stem cells in the stratum basale
- Melanocytes: produce melanin, are found in the stratum basale, and transfer melanin to keratinocytes to shield the nucleus from UV radiation
- Langerhans' cells: contain macrophages, act in defense mechanisms against pathogens, and stimulate the immune system
- Merkel cells: are touch receptors
Dermis
- The dermis is the real skin, formed by binding tissues of fibrous, mostly elastic, and semi-fluid matrix
- It is divided into two layers: papillary layer and reticular layer
- Papillary layer:
- Has papillae-bumps that allow perfect adjacent placement of the epidermis and dermis layers
- Contains areolar connective tissue, several blood capillaries, sensory nerves, lymph ducts, muscles, glands, and hair follicles
- Reticular layer:
- Contains more collagen fiber compared to the papillary layer
- Has a crisscross pattern of collagen fibers that forms strong elastic netting
Subcutaneous/Hypodermis
- Located below the dermis layer
- Contains loose connective tissues, nerves, blood vessels, and adipose tissues
- Functions as an energy reservoir and provides adhesion structure of skin with underlying structures
Thick and Thin Skin
- Thick skin is distinguished from thin skin based on the thickness of the epidermis, not the entire thickness of the skin
- Thin skin has four distinct layers and covers most of the body
- Thick skin contains the stratum lucidum and may have up to 30 layers of keratinized cells
Physiology of the Skin
- The skin acts as a:
- Protective barrier
- Regulator of body temperature
- Synthesizer of vitamin D
- Sensory receptor
- Organ for absorption
- Organ for excretion
- The skin has three defense barriers:
- Chemical barrier: low pH, natural antibiotics, katelisidin, and melanin
- Mechanical/physical barrier: skin structure and keratinization
- Biological barrier: Langerhans' cells, macrophages, and DNA
Body Temperature Regulation
- The normal body temperature depends on the balance between heat production and heat loss
- The control center for body temperature is the hypothalamus in the brain
- The body regulates temperature through:
- Vasoconstriction: shrinking of blood vessels to reduce blood flow and retain heat
- Vasodilation: expansion of blood vessels to increase blood flow and lose heat
- Heat production comes from body metabolism, especially from muscles, liver, and glands in the body
- Heat loss occurs through:
- Radiation
- Conduction
- Convection (heating)
- Evaporation (sweat)
Vitamin D Synthesis
- Exposure of skin to UV light helps in the production of vitamin D
- Vitamin D is supported by calcium and phosphorus absorption from the digestive system
- Vitamin D, calcium, and phosphorus are necessary for bone formation and shape retention
Sensory Organs
- Nerve fibers found in the skin are sensory nerves that receive sensory stimulation and pass them to the brain
- Sensory receptors in the skin include:
- Meissner corpuscle: touch, especially soft touches
- Pacinian corpuscle: firm pressure, proprioception, and vibration
- Krause body: temperature (cold) and pressure
- Free nerve endings: heat, light pressure, and pain
- Ruffini endings and Merkel's discs: temperature (hot) and continuous pressure
- Hair follicles receptor: movement across the surface of the skin
Absorption and Excretion
- The skin has a limited absorption function, mainly for lipid-soluble materials, plant oleoresins, organic solvents, and metal dust
- The skin acts as a minor excretion organ for certain materials, including:
- Sodium chloride and H2O in sweat
- Urea (when kidney function is impaired)
- Aromatic materials (e.g., garlic and other spices)
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Description
This quiz covers the process of keratinization, types of skin cells, and the role of keratinocytes in the epidermis. It also explains how skin cells are formed, reproduced, and removed.
