Textbook Question
In which layer(s) of the epidermis does cell division occur?
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5. Integumentary System
The Epidermis: Cells
2:27 minutesProblem 21
Textbook Question
In clinical practice, drugs can be delivered by diffusion across the skin. This delivery method is called transdermal administration. Why are fat-soluble drugs more suitable for transdermal administration than drugs that are water soluble?
Verified step by step guidance1
Understand the structure of the skin: The skin consists of multiple layers, with the outermost layer being the stratum corneum. This layer is composed primarily of dead cells surrounded by lipids, making it a hydrophobic (fat-loving) barrier.
Recognize the properties of fat-soluble drugs: Fat-soluble drugs are lipophilic, meaning they can dissolve in and pass through lipid-rich environments like the stratum corneum more easily than water-soluble drugs.
Contrast water-soluble drugs: Water-soluble drugs are hydrophilic, meaning they are attracted to water and do not easily penetrate the lipid-rich stratum corneum. This limits their ability to diffuse across the skin.
Relate to diffusion principles: Diffusion across the skin depends on the drug's ability to interact with and move through the lipid matrix of the stratum corneum. Fat-soluble drugs are more compatible with this lipid matrix, facilitating their movement into deeper layers of the skin and eventually into the bloodstream.
Conclude the suitability: Fat-soluble drugs are more suitable for transdermal administration because their lipophilic nature allows them to bypass the hydrophobic barrier of the stratum corneum, ensuring effective delivery into the body.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Transdermal Administration
Transdermal administration refers to the delivery of drugs through the skin for systemic effects. This method allows for the gradual release of medication into the bloodstream, bypassing the digestive system and first-pass metabolism. It is particularly useful for drugs that require steady plasma levels over time.
Solubility and Drug Absorption
The solubility of a drug significantly affects its absorption through the skin. Fat-soluble (lipophilic) drugs can easily penetrate the lipid-rich layers of the stratum corneum, the outermost skin barrier. In contrast, water-soluble (hydrophilic) drugs struggle to cross this barrier, making them less effective for transdermal delivery.
Skin Barrier Function
The skin acts as a barrier to protect the body from external substances, which includes limiting the absorption of drugs. The structure of the skin, particularly the stratum corneum, is composed of lipids and keratin, favoring the passage of lipophilic substances. Understanding this barrier function is crucial for developing effective transdermal drug formulations.
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