Podcast
Questions and Answers
Which layer of the epidermis is primarily responsible for continuous cell division and renewal?
Which layer of the epidermis is primarily responsible for continuous cell division and renewal?
What structure is primarily responsible for the adhesion of the Basal Cell Layer to the underlying basement membrane?
What structure is primarily responsible for the adhesion of the Basal Cell Layer to the underlying basement membrane?
Which type of granules found in the Stratum Granulosum aggregates to form keratin filaments?
Which type of granules found in the Stratum Granulosum aggregates to form keratin filaments?
Which layer of the epidermis consists of both the Stratum Basale and Stratum Spinosum?
Which layer of the epidermis consists of both the Stratum Basale and Stratum Spinosum?
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What characteristic feature is seen in the Stratum Spinosum layer?
What characteristic feature is seen in the Stratum Spinosum layer?
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Which of the following statements regarding Merkel's cells is incorrect?
Which of the following statements regarding Merkel's cells is incorrect?
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What is one characteristic feature of Langerhans cells as observed under a light microscope?
What is one characteristic feature of Langerhans cells as observed under a light microscope?
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Which organelle is prominent in Langerhans cells and aids in their immunological function?
Which organelle is prominent in Langerhans cells and aids in their immunological function?
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What is the primary function of melanocytes within the epidermis?
What is the primary function of melanocytes within the epidermis?
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Which layer of the skin is characterized by heavily keratinized dead cells with no nuclei?
Which layer of the skin is characterized by heavily keratinized dead cells with no nuclei?
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Study Notes
Epidermis
- The epidermis is the outermost layer of skin, composed of a keratinized stratified squamous epithelium.
- It is thicker on the soles of the feet than on the palms of the hands.
- The epidermis is avascular, receiving nutrients through diffusion from underlying tissues.
- It contains free nerve endings, giving it sensory capabilities.
- The epidermis is made up of keratinocytes (85% of cells) and non-keratinocytes.
Keratinocytes
- Keratinocytes are continuously dividing, differentiating, and accumulating keratin filaments as they progress upwards.
- Superficial layers are constantly shed.
- Based on keratinocyte maturation, the epidermis is composed of 5 distinct layers:
Stratum Basale (Basal Cell Layer)
- A single layer of cuboidal or columnar cells resting on a wavy basement membrane.
- Cells have a basophilic cytoplasm with a large, oval nucleus.
- Intense mitotic activity occurs in this layer, responsible for skin renewal.
- Melanocytes and Merkel cells reside within this layer.
Stratum Spinosum (Prickle Cell Layer)
- Consists of 4 to 8 layers of polyhedral cells above the basal cell layer.
- Cells have less basophilic cytoplasm compared to stratum basale cells.
- Cells have central, rounded nuclei.
- Desmosomes between cells create a prickly appearance due to spine-like processes.
- Langerhans cells are present in this layer.
- The malpighian layer encompasses both stratum basale and stratum spinosum.
Stratum Granulosum (Granular Cell Layer)
- Contains layers of spindle-shaped cells above the spinous layer.
- Cells have deep, basophilic, granular cytoplasm with flat, pale nuclei.
- The cytoplasm contains two types of granules:
- Keratohyalin granules: non-membranous, aggregating to form keratin filaments.
- Membrane-coated lamellar granules: release a lipid-rich secretion that fills spaces between cells.
Stratum Lucidum (Clear Layer)
- A thin, lightly stained, clear, homogeneous layer.
- Composed of flattened cells with nuclei undergoing karyolysis (nuclear breakdown).
- The cell membranes are thickened, with few remnants of desmosomes.
- Organelles disappear through lysosomal activity, leaving ghosts of nuclei or an absence of nuclei.
- Densely packed keratin filaments are embedded in an electron-dense matrix formed by keratohyalin granules.
Stratum Corneum (Horny Layer)
- Thick, eosinophilic layers formed of heavily keratinized dead cells called scales.
- Cell membranes are thickened and attached by remnants of desmosomes.
- Cells are filled with mature keratin filaments embedded in an amorphous matrix.
- No nuclei or organelles are present.
Non-Keratinocytes
- Non-keratinocyte cells represent a diverse population within the epidermis, each with specialized functions:
Langerhans Cells
- Originate from bone marrow precursors.
- Migrate through the blood to the dermis and then the epidermis.
- Represent 3-8% of epidermal cells.
- Stellate-shaped cells found mainly between cells of the stratum spinosum.
- Appear with a dark-staining nucleus and pale cytoplasm in histological sections.
- They can be identified using vital stains.
- Contain a prominent Golgi complex and numerous lysosomes.
- Possess distinctive tennis-racquet-shaped granules called Birbeck's granules.
- Some may contain hydrolytic enzymes.
- The nucleus is dark and highly irregular.
- Lack keratin filaments, desmosomes, melanin granules, and cell junctions with keratinocytes.
- Function as antigen-presenting cells, capable of binding antigens that contact the skin and presenting them to T-lymphocytes.
- Play a crucial role in skin immunological reactions such as allergic dermatitis.
Merkel Cells
- Originate from ectoderm.
- Modified epithelial cells.
- Resemble epidermal cells.
- Present in the basal layer, abundant in sensitive areas like fingertips and hair follicle bases.
- A free nerve fiber (sensory) traverses the basal lamina to terminate as disc-shaped expansions beneath Merkel cells, forming a Merkel cell-neurite complex.
- Attached to neighboring keratinocytes by desmosomes.
- Cytoplasm contains electron-dense granules similar to those of neuroendocrine cells.
- Have deeply invaginated nuclei.
- Function as mechanoreceptors for light touch sensation and exhibit neurosecretory function due to the presence of granules.
Melanocytes
- Precursors arise from the neural crest (ectoderm) and migrate to the skin early in development.
- Located in the basal layer of the epidermis.
- Do not form desmosomes with neighboring keratinocytes.
- Contain melanin granules.
- Dendritic shape allows them to transfer melanin granules to surrounding keratinocytes, contributing to skin pigmentation.
- Play a key role in protecting the skin from UV radiation.
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Description
Test your knowledge on the structure and function of the epidermis and keratinocytes. This quiz covers the composition, layers, and the sensory capabilities of the epidermis. Challenge yourself to understand the cellular mechanisms involved in skin renewal and health.
