Keratinocyte

Key takeaways

Keratinocyte belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Keratinocyte to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Keratinocyte from memory before moving on to harder problems.

Reference excerpt

Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (stratum basale) of the skin are sometimes referred to as basal keratinocytes. Keratinocytes form a barrier against environmental damage by heat, UV radiation, water loss, pathogenic bacteria, fungi, parasites, and viruses. A number of structural proteins, enzymes, lipids, and antimicrobial peptides contribute to maintain the important barrier function of the skin. Keratinocytes differentiate from epidermal stem cells in the lower part of the epidermis and migrate towards the surface, finally becoming corneocytes and eventually being shed, which happens every 40 to 56 days in humans.

Function The primary function of keratinocytes is to act as a barrier. They protect the body from environmental damage by heat, UV radiation, dehydration, pathogenic bacteria, fungi, parasites, and viruses. Pathogens invading the upper layers of the epidermis can cause keratinocytes to produce proinflammatory mediators, particularly chemokines such as CXCL10 and CCL2 (MCP-1) which attract monocytes, natural killer cells, T-lymphocytes, and dendritic cells to the site of pathogen invasion.

Structure A number of structural proteins (filaggrin, keratin), enzymes (e.g. proteases), lipids, and antimicrobial peptides (defensins) contribute to maintain the important barrier function of the skin. Keratinization is part of the physical barrier formation (cornification), in which the keratinocytes produce more and more keratin and undergo terminal differentiation. The fully cornified keratinocytes that form the outermost layer are constantly shed off and replaced by new cells.

Cell differentiation Epidermal stem cells reside in the lower part of the epidermis (stratum basale) and are attached to the basement membrane through hemidesmosomes. Epidermal stem cells divide in a random manner yielding either more stem cells or transit amplifying cells. Some of the transit amplifying cells continue to proliferate then commit to differentiate and migrate towards the surface of the epidermis. Those stem cells and their differentiated progeny are organized into columns named epidermal proliferation units. During this differentiation process, keratinocytes permanently withdraw from the cell cycle, initiate expression of epidermal differentiation markers, and move suprabasally as they become part of the stratum spinosum, stratum granulosum, and eventually corneocytes in the stratum corneum. Corneocytes are keratinocytes that have completed their differentiation program and have lost their nucleus and cytoplasmic organelles. Corneocytes will eventually be shed off through desquamation as new ones come in. At each stage of differentiation, keratinocytes express specific keratins, such as keratin 1, keratin 5, keratin 10, and keratin 14, but also other markers such as involucrin, loricrin, transglutaminase, filaggrin, and caspase 14. In humans, it is estimated that keratinocytes turn over from stem cells to desquamation every 40–56 days, whereas in mice the estimated turnover time is 8–10 days. Factors promoting keratinocyte differentiation are:

A calcium gradient, with the lowest concentration in the stratum basale and increasing concentrations until the outer stratum granulosum, where it reaches its maximum. Calcium concentration in the stratum corneum is very high in part because those relatively dry cells are not able to dissolve the ions. Those elevations of extracellular calcium concentrations induces an increase in intracellular free calcium concentrations in keratinocytes. Part of that intracellular calcium increase comes from calcium released from intracellular stores and another part comes from transmembrane calcium influx, through both calcium-sensitive chloride channels and voltage-independent cation channels permeable to calcium. Moreover, it has been suggested that an extracellular calcium-sensing receptor (CaSR) also contributes to the rise in intracellular calcium concentration. Vitamin D3 (cholecalciferol) regulates keratinocyte proliferation and differentiation mostly by modulating calcium concentrations and regulating the expression of genes involved in keratinocyte differentiation. Keratinocytes are the only cells in the body with the entire vitamin D metabolic pathway from vitamin D production to catabolism and vitamin D receptor expression. Cathepsin E. TALE homeodomain transcription factors. Hydrocortisone. Since keratinocyte differentiation inhibits keratinocyte proliferation, factors that promote keratinocyte proliferation should be considered as preventing differentiation. These factors include:

The transcription factor p63, which prevents epidermal stem cells from differentiating into keratinocytes. Mutations in the p63 DNA-binding domain are associated with ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome. The transcriptome of p63 mutant keratinocytes deviated from the normal epidermal cell identity. Vitamin A and its analogues. Epidermal growth factor. Transforming growth factor alpha. Cholera toxin.

Interaction with other cells Within the epidermis keratinocytes are associated with other cell types such as melanocytes and Langerhans cells. Keratinocytes form tight junctions with the nerves of the skin and hold the Langerhans cells and intra-dermal lymphocytes in position within the epidermis. Keratinocytes also modulate the immune system: apart from the above-mentioned antimicrobial peptides and chemokines they are also potent producers of anti-inflammatory mediators such as IL-10 and TGF-β. When activated, they can stimulate cutaneous inflammation and Langerhans cell activation via TNFα and IL-1β secretion. Keratinocytes contribute to protecting the body from ultraviolet radiation (UVR) by taking up melanosomes, vesicles containing the endogenous photoprotectant melanin, from epidermal melanocytes. Each melanocyte in the epidermis has several dendrites that stretch out to connect it with many keratinocytes. The melanin is then stored within keratinocytes and melanocytes in the perinuclear area as supranuclear "caps", where it protects the DNA from UVR-induced damage.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Keratinocyte

Start with the simplest possible case. Write down what Keratinocyte claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Keratinocyte before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Keratinocyte ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Keratinocyte

In research: Keratinocyte appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Keratinocyte in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Keratinocyte is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human cells, Sequestering cells, Skin anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Keratinocyte outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Keratinocyte in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Keratinocyte means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Keratinocyte out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Keratinocyte in simple terms?

Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells.

Why does Keratinocyte matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Keratinocyte?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Keratinocyte.