Which layer of epidermis undergoes mitosis

Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum or stratum lucidum in the case of the palms and soles of feet. The cells in this layer can still be anchored to each other by desmosomes which is why the peeling that occurs with a sunburn peels the damaged epidermal layers in one sheet. The entire layer is replaced during a period of about 4 weeks. It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands.

The epidermis is avascular and cells of this layer must get their oxygen and nutrients from capillaries in the dermis. The dermis is made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts Figure 5.

The more superficial papillary layer serves as an anchor point for the epidermis above and is intimately connected to the deeper reticular layer. The papillary layer is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh with abundant ground substance supporting the hydration of the skin.

This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae see Figure 5. Within the papillary layer are fibroblasts, a small number of fat cells adipocytes , and an abundance of small blood vessels. In addition, the papillary layer contains phagocytes, defensive cells that help fight bacteria or other infections that have breached the skin.

This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles. In a growing fetus, fingerprints form where the cells of the stratum basale of the epidermis meets the papillae of the underlying dermal layer papillary layer , resulting in the formation of the ridges on your fingers that you recognize as fingerprints.

Dermal papillae push up on the epidermis creating unique epidermal ridge patterns. Fingerprints are unique to each individual and are used for forensic analyses because the patterns do not change with the growth and aging processes. Underlying the papillary layer is the much thicker reticular layer , composed of dense irregular connective tissue which resists forces in many directions attributing to the flexibility of the skin.

The reticular layer appears reticulated net-like due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the skin, enabling movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. In addition, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.

The hypodermis also called the subcutaneous layer or superficial fascia is a layer directly below the dermis and serves to connect the skin to the underlying fascia fibrous tissue surrounding the muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and abundant adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.

Fascia is a thick connective tissue wrapping that surrounds skeletal muscles anchoring them to surrounding tissues and investing groups of muscles.

The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes.

This stored fat can serve as an energy reserve, insulate the body to prevent heat loss, and act as a cushion to protect underlying structures from trauma. Where the fat is deposited and accumulates within the hypodermis depends on hormones testosterone, estrogen, insulin, glucagon, leptin, and others , as well as genetic factors. Fat distribution changes as our bodies mature and age. Men tend to accumulate fat in different areas neck, arms, lower back, and abdomen than do women breasts, hips, thighs, and buttocks.

The body mass index BMI is often used as a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight mass to height.

Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit. In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people.

Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat.

Not only is this a problem for the individuals affected, but it also has a severe impact on our healthcare system. Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation, especially when it reaches levels that increase the risk of heart disease and diabetes. The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin.

Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome Figure 5. Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color.

Dark-skinned individuals produce more melanin than those with pale skin. Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes.

The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid, a nutrient necessary for our health and well-being.

In contrast, too much melanin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption. There is a dynamic interplay between the amount of protection from UV radiation that melanin provides and the amount of vitamin D produced.

The amount of melanin produced, and therefore UV protection, is directly correlated with the amount of sunlight exposure. The more sunlight, the more UV protection, but the compromise is that with increased melanin there is a decrease in vitamin D produced. It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially.

Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.

Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin, and in severe cases, can cause sufficient DNA damage to result in skin cancer. How do the integumentary and immune systems work together? What is the name of the outer layer of epidermis? What is the name for the glands that are Why is the skin the main organ of integumentary system?

What is an example of a genetic disorder of the integumentary system? What effects does an allergen have on the integumentary system? Answer: Integrins along along the basal surface are organized into hemidesmosomes. The integrins interact with structural proteins in the basement membrane.

The dark staining material is melanin. The connections between cells that give rise to the prickly appearance are desmosomes. The prominent nucleoli indicate that a large amount of protein synthesis is occurring.