stratum bassal Flashcards
stratum bassal
Stratum Basale (Basal Layer):
Location: The deepest layer of the epidermis, closest to the dermis.
Structure: This layer is connected to the dermis by a wavy border (like corrugated cardboard). This increases the surface area for nutrients to be exchanged between the dermis and the epidermis.
Function:
Stem Cells: This layer contains stem cells, which are constantly dividing (a process called mitosis).
New Cell Production: The stem cells produce new cells continuously. Some of these cells stay as stem cells to keep producing new skin cells, while others move upward to become actual skin cells (keratinocytes).
Nutrient Supply: Since it is close to the dermis, the stratum basale gets nutrients from the dermis, making it the most nourished layer of the epidermis.
Movement of Cells:
As the newly produced skin cells move up, they travel through the next layers (stratum spinosum and stratum granulosum), becoming flatter and more keratinized (i.e., they accumulate keratin, a tough protein that helps protect the skin).
Keratinization: As the cells move upward, they lose moisture and become more flattened and filled with keratin, which toughens them.
Stratum Granulosum to Stratum Lucidum:
Stratum Granulosum: As cells move from the stratum granulosum to the stratum lucidum, they undergo significant changes:
They continue to accumulate keratin (a tough protein).
They also secrete glycolipids (fatty substances) into the extracellular space, which forms a water-repellent barrier.
This process helps protect the skin from water loss and prevents harmful substances from entering.
Stratum Lucidum:
The stratum lucidum is a clear layer that forms as the cells die, becoming flat, keratinized, and filled with glycolipids.
Where It’s Found:
This layer is not present everywhere. It only appears in places where the skin is extra thick, like the palms of the hands and the soles of the feet. These areas are subject to more wear and tear, so the extra thick layer helps with protection.
Cell Death: As the cells in the stratum lucidum die, they can no longer receive nutrients or oxygen because they are far from the blood supply in the dermis. Without these vital resources, the cells die and become part of the tough, protective outer layer of the skin.
Stratum Corneum (Outermost Layer):
Thickness: The stratum corneum is the thickest layer of the epidermis, typically about 20 to 30 cell layers thick. Despite its thickness, this layer accounts for about three-quarters of the epidermal thickness.
Dead, Keratinized Cells: The cells in this layer are dead and have become completely filled with keratin, a tough protein that helps protect the skin. These dead cells are called cornified cells (or horny cells). The term “cornified” comes from cornu, meaning “horn,” because the cells are tough and resemble the hardness of a horn.
Function of the Stratum Corneum:
Durable Barrier: The stratum corneum acts like a protective overcoat for the body. The tough keratin in these cells creates a durable barrier that:
Protects deeper cells from harmful external factors (like chemicals, pathogens, and physical damage).
Helps prevent water loss, keeping the skin from drying out.
Offers protection against biological, chemical, and physical assaults (such as UV rays or environmental toxins).
Shedding and Renewal:
The stratum corneum sheds its dead skin cells regularly. These flakes rub off slowly and steadily, and some of it is what we recognize as dandruff. Over a lifetime, a person sheds about 18 kg (40 lb) of skin flakes!
These dead skin cells in the stratum corneum also become a food source for dust mites that live in our homes and bedding.
Regeneration:
New cells are constantly produced in the stratum basale (the deepest layer), and as they move up through the layers of the epidermis, they eventually become part of the stratum corneum. As a result, our epidermis is fully replaced every 25 to 45 days, ensuring the skin stays fresh and capable of protecting the body.
Summary:
The stratum corneum provides a tough, waterproof layer of dead skin cells filled with keratin. This layer protects the body from external damage, prevents water loss, and is constantly being shed and renewed.
Melanin and Melanocytes:
Melanin is a pigment that gives the skin its color. It can range from yellow to brown to black, depending on the type and amount of melanin produced.
Melanocytes are special, spider-shaped cells located primarily in the stratum basale (the deepest layer of the epidermis). These cells are responsible for producing melanin.
The concentration of melanin in specific areas causes freckles and moles. When melanin accumulates in one spot, it forms these visible skin features.
Epidermal Dendritic Cells (also called Langerhans cells):
Location: These cells are scattered throughout the epidermis.
Function: Epidermal dendritic cells act as “sentries” for the immune system. They help detect bacterial or viral invasions and alert the immune system to fight off threats. This makes them crucial for skin immunity and protection against infection.
Merkel Cells:
Location: These cells are found at the epidermal-dermal junction, which is where the epidermis meets the dermis.
Function: Merkel cells are associated with sensory nerve endings and act as touch receptors. Together with the nerve endings, they form Merkel discs, which are responsible for detecting light touch and pressure.
Melanin and UV Protection:
Melanin provides natural protection against UV radiation from the sun. The pigment absorbs and dissipates harmful UV rays, reducing the risk of DNA damage in the skin cells, which can lead to skin cancer.
People with naturally dark skin have more melanin, which is why they tend to have lower rates of skin cancer. The higher levels of melanin offer better protection against the harmful effects of UV light.
Effects of Excessive UV Exposure:
Leathery Skin Appearance: Prolonged exposure to UV light causes skin damage over time, leading to the development of a leathery appearance. This happens because UV rays break down the collagen and elastin fibers in the skin, which provide strength and elasticity.
Depressed Immune System: UV exposure also weakens the skin’s immune function, making it more susceptible to infections and conditions. As you mentioned, this could explain why people who are infected with herpesvirus 1 (which causes cold sores) may experience more outbreaks after spending time in the sun.
DNA Damage and Skin Cancer: Overexposure to UV rays can lead to DNA mutations in skin cells, which disrupt normal cell function and increase the risk of skin cancer. UV radiation is a major cause of basal cell carcinoma, squamous cell carcinoma, and melanoma, the deadliest form of skin cancer.
Dermis
The dermis is your “hide.” It is a strong, stretchy envelope that helps to bind the body together. When you purchase leather goods (bags, belts, shoes), you are buying the treated dermis of animals.
The connective tissue making up the dermis consists of two major regions—the papillary and the reticular areas (Figure 4.5), which are composed of areolar and dense irregular connective tissue, respectively. Like the epidermis, the dermis varies in thickness. For example, it is particularly thick on the palms of the hands and soles of the feet but is quite thin on the eyelids.
papillary layer
Location: The papillary layer is the superficial (topmost) region of the dermis, the layer beneath the epidermis. It is made of loose connective tissue and is located just below the epidermis.
Dermal Papillae:
The papillary layer has peg-like projections from its surface called dermal papillae. These projections extend into the epidermis, creating a wavy pattern. The dermal papillae help to anchor the epidermis to the underlying dermis, providing a stable connection.
The dermal papillae contain important structures like:
Capillary loops: Tiny blood vessels that supply nutrients to the epidermis. The epidermis does not have blood vessels, so it relies on these capillaries for nutrients and oxygen.
Pain receptors (free nerve endings): These detect painful stimuli in the skin.
Touch receptors: These help detect light touch.
Special Features of the Papillary Layer:
On the palms of the hands and the soles of the feet, the dermal papillae are arranged in distinctive patterns that form looped and whorled ridges. These ridges are unique to each individual and increase the friction on the skin, which helps improve the gripping ability of the fingers and feet.
Fingerprints: The ridges on the fingertips, formed by the papillary layer’s dermal papillae, are rich in sweat pores. These ridges leave unique fingerprints (a film of sweat) on any surface touched. Fingerprints are genetically determined, meaning they are unique to each individual, just like a person’s DNA.
Reticular Layer:
Location: The reticular layer is the deepest layer of the dermis, located below the papillary layer.
Composition: This layer is made of dense irregular connective tissue, which is rich in collagen and elastic fibers.
Collagen fibers provide the skin with strength and toughness.
Elastic fibers give the skin its elasticity, allowing it to stretch and return to its original shape.
F So, the reticular layer doesn’t make collagen and elastin itself, but it houses fibroblasts, which do!
Sweat glands (eccrine & apocrine) → Help regulate body temperature.
Sebaceous (oil) glands → Keep skin moisturized and waterproof.
Hair follicles → Anchor hair and allow hair growth.
Blood vessels → Supply oxygen and nutrients to the skin and help with temperature regulation.
Nerve endings → Detect pressure, vibration, and deep touch sensations.
Structures in the Reticular Layer:
Blood vessels: These supply the skin with nutrients and help in regulating body temperature.
Sweat and oil glands: These produce sweat (which helps cool the body) and oil (which keeps the skin lubricated).
Deep pressure receptors (Lamellar corpuscles): These sensory receptors detect deep pressure and vibration in the skin.
Cutaneous Sensory Receptors:
Touch receptors: Detect light touch.
Pressure receptors: Detect deeper pressure.
Temperature receptors: Detect heat and cold.
Pain receptors: Detect harmful stimuli, such as injury or extreme temperatures
Phagocytes in the Dermis:
Phagocytes are immune cells found in the dermis. They act as defenders, preventing microbes that manage to breach the epidermis from penetrating deeper into the body and causing infection.
Aging and Skin Elasticity:
Collagen and elastic fibers are key for the skin’s strength and elasticity:
Collagen fibers help keep the skin hydrated by binding water.
Elastic fibers give the skin its ability to stretch and return to its normal shape.
As we age, the number of collagen and elastic fibers decreases, and the subcutaneous tissue loses fat. This leads to the skin becoming less elastic, causing it to sag and form wrinkles.
Blood Supply and Temperature Regulation:
The blood vessels in the dermis play a critical role in regulating body temperature:
When the body is too hot: The capillaries in the dermis become engorged with warm blood, causing the skin to become reddened and warm. This allows heat to radiate from the skin and cool the body down.
When the body is too cold: The blood flow to the dermis decreases, and blood bypasses the capillaries. This helps conserve body heat and keep the internal temperature stable.
