The Dermis and its Papillary Layer

The Dermis

• The dermis is a highly vascular layer located deep to the epidermis
• Primary functions include providing blood supply to the epidermis, housing sensory receptors, and anchoring the epidermis in place
• It consists of two distinct layers, each with unique connective tissue types

The Papillary Layer

• The papillary layer is the thinner and most superficial layer of the dermis
• It comprises of loose connective tissue
• Special collagen fibers at the dermis-epidermal junction extend into the epidermal basement membrane
• These fibers effectively anchor the epidermis to the dermis

Dermal Papillae

• Dermal papillae are tiny projections located on the surface of the papillary layer, where it interfaces with the epidermis
• These papillae contain tiny blood vessels (capillaries) arranged in loops that extend into the superficial part of the dermal papillae
• These capillaries allow for O2 and nutrients to diffuse into the extracellular fluid of the dermis, which then permeates the avascular epidermi
• Tactile (Meissner) corpuscles reside within the dermal papillae and act as sensory receptors for light touch stimuli
• Tactile (Meissner) corpuscles are especially abundant in areas where sensation is a primary function, such as fingertips, lips, face, and external genitalia

The Reticular Layer

• The Reticular Layer is a deep and thicker layer that separates the dermis from the hypodermis
• It’s composed of dense irregular connective tissue and largely arranged collagen bundles
• Collagen bundles in the reticular layer reinforce the dermis and prevent traumatic injuries from damaging deeper tissues
• Elastic fibers in the reticular layer enable the dermis to return to its original shape and size after stretching

Reticular Layer Components

• The reticular layer is rich in proteoglycans that draw water, maintaining skin firmness and hydration
• Lamellated (Pacinian) corpuscles within the reticular layer respond to changes in pressure and vibration
• Furthermore, components such as blood vessels, sweat glands, hairs, sebaceous glands, and adipose tissue are present in the reticular layer

Skin Markings

• Skin markings are small, visible lines in the epidermis caused by the interaction between the dermis and epidermis and are best observed in thick skin
• Dermal ridges are regions where dermal papillae are more prominent due to the presence of thick collagen bundles
• Dermal ridges indent the overlying epidermis, creating epidermal ridges and enhancing the gripping ability of the hands and feet
• Epidermal ridges occur in genetically determined, unique patterns like loops, arches, and whorls
• Sweat pores open along the ridges, leaving a thin film or fingerprint on touched surfaces Rreticular layer is also responsible for certain skin markings
• Tension (cleavage) lines are indentations in the epidermis resulting from gaps between collagen bundles in the dermis
• Flexure lines are deep creases found in body areas surrounding joints where the reticular layer is tightly anchored to underlying structures

Surgical Incisions and Tension Lines

• Incisions made along tension lines heal faster and with reduced scarring
• Incisions made perpendicular to tension lines heal more slowly and tend to scar

Skin Wrinkles

• Skin wrinkles are a hallmark of aging, resulting from a decrease in collagen fibers, elastic fibers, proteoglycans, and adipose tissue in the dermis
• Wrinkles reduce skin's firmness, hydration, and recoil ability after stretching, appearing more prominently in areas of repetitive muscle movement (forehead, around the eyes and mouth)
• UV exposure and cigarette smoking accelerate the formation of wrinkles
• Appearance may be minimized by botox, fillers and topical creams
• Avoiding sun exposure, using sunscreens, staying hydrated, and not smoking can delay the appearance of wrinkles

Melanin

• Melanin is a primary determinant of skin color
• It’s produced by melanocytes found in the stratum basale
• Melanin is composed of two molecules of tyrosine
• These molecules arechemically linked via a series of reactions that is catalyzed by tyrosinase within a special vesicle called a melanosome
• Melanin's primary role is to shield keratinocyte DNA from mutations induced by UV radiation
• Melanocyte arm-like extensions contact and even pierce plasma membranes of keratinocytes in both the stratum basale and spinosum
• Melanosomes migrate to the tips of these extensions and are released through exocytosis. They are then taken into the cytoplasm of surrounding kertainocytes
• Melanin is transported to the superficial side of the nucleus and effectively shields DNA, and protects against UVR damage
• Melanin must be produced consistently to maintain a stable skin color; degrades after a few days

Melanin Synthesis and Variations

• Melanin synthesis increases upon exposure to natural or artificial UV radiation, leading to skin tanning
• An immediate response involves oxidation of melanin already present in keratinocytes, leading to a quick darkening of the skin
• Delayed or secondary effects result from DNA damage in melanocytes caused by UV light, which stimulates melanin production. This appears within 72 hours and lasts longer than melanin oxidation
• Radiation from UV exposure has both immediate and delayed effects on skin pigmentation
• The amount of UV radiation that melanin can absorb is limited, restricting it's level of protection
• People of all skin pigmentations are susceptible to sunburns and face the potential risks of skin cancers
• A secondary role of melanin is to reduce vitamin D synthesis in response to UV radiation, controlling the absorption of calcium ions and maintaining calcium ion homeostasis
• People living in regions exposed to high UVR such as those from Africa developed darker skin to prevent excess vitamin D production

Skin Tone and Pigmentation Variations

• Skin color depends on the number of melanocytes in a particular body region
• Differences in melanocyte numbers can lead to uneven distribution of melanin
• For example, there are fewer melanocytes on the palms of the hands and soles of the feet
• The overall number of melanocytes is virtually identical among all individuals, irrespective of skin color
• Variations in skin tone are due to amount of tyrosinase activity and the type (color) of melanin produced
• Common pigmentation variations include freckles, moles (nevus), and albinism
• Freckles are small areas characterized by increased pigmentation and melanin production in a localized region
• Moles or nevus are also characterized by areas of increased pigmentation, as well as caused by local proliferation of melanocytes
• Individuals with albinism have melanocytes that can’t produce tyrosinase, causing a complete absence of skin pigmentation and an increased risk of DNA damage from UVR

Other Pigments

• Carotene and Hemoglobin have effect on skin pigmentation
• Carotene is a yellow-orange pigment from foods like egg yolks and orange vegetables
• It's a lipid-soluble molecule that accumulates in the stratum corneum and gives a slight yellow-orange color, especially visible in thick skin areas
• Hemoglobin, found in red blood cells, is an iron-containing protein that binds to and transports O2 throughout the body
• Oxygen binding to iron in hemoglobin results in a bright orange red color, which provides blood its characteristic color
• The effect of hemoglobin on skin redness or color is an indirect result of blood flow in the dermis
• The blood's color in the deeper dermis is visible through the epidermis

Skin Color as a Diagnostic Tool

• Color changes associated with amount of blood flow in the dermis can indicate specific diagnosis of disease
• Erythema is when the blood flow increases in dermis, causing reddish color; a normal response to exercise dissipates heat
• Other sources causing erythema include trauma, fever and infection
• Pallor, when blood flow in the dermis decreases with a loss of normal pinkish hue that can normally be seen in pale-skinned people
• It takes on a whitish color given by the collagen in the dermis
• Pallor is a natural response when body is conserving heat in cold environments
• Nervous and endocrine systems can cause pallor during fight or flight reactions
• Cyanosis indicates there are very low levels of bounds oxygen or low levels of red blood cells
• Hemoglobin causes a reddish purple hue, or faint blue, if the hemoglobin is bound with oxygen
• Difficulty breathing can be a main cause of cyanosis

Accessory Structures of the Integument

• These structures include hair, nails, and glands; are derived from epithelium; assist in overall function of system
• Hair (pili) are small filamentous structures that protrude from surface of skin
• Hair is all over the entire body except in regions with thick skin, lips, and parts of external genitalia

Human Hair and its Functions

• Human hair is too sparse to be very effective in thermoregulation
• Human hair provides protection by preventing substances and organisms from entering eyes and nose
• Human hair protects underlying skin of scalp from UV radiation and mechanical trauma
• It's associated with small sensory neurons and detects changes in environment

Hair main parts

• Hair is composed of two main parts: shaft and root and both contain stratified squamous keratinized epithelial cells in various stages of development
• The hair shaft projects from the skin
• The shaft’s columns of dead keratinized epithelial cells complete keratinization process
• The hair root is embedded in the dermis
• It then becomes indented by projection of blood vessels from dermis, known as the hair papilla
• The hair bulb consists of both a root and hair papilla
• Many epithelial cells in the roots are still alive, but not completed with the keratinization process
• The matrix is the small layer of keratinocytes at the base of the root that has actively dividing cells
• The root is embedded in the hair follicle where epidermis folding creates the epithelial root sheath that extends deep into the dermis and the hypodermis

Hair Structure components

• The root sheath has two components: outer anchors follicle; components in inner anchored tightly to hair root
• Strand has three visible regions in transverse section: Inner medulla with soft core of keratin and middle cortex with highly structured layers of keratinocytes
• Outermost Cuticle: Single layer of overlapping keratinocytes also containing hard keratin, adding additional mechanical strength to the hair follicle
• Dermal root sheath surrounds the epithelial root
• Connective tissues supports follicle, keeping it separate from the dermis
• Arrector pili muscles have smooth muscle bands that attach to dermis and are connected with a papillary layer
• Contraction of arrector pili causes hair to stand up (piloerection), thus the skin dimples during response to stimuli and external factors (goosebumps)

Hair Growth

• Hair Growth averages 1-1.5 mm per month
• It varies from each individual
• The main phases are growth and resting, each has its own separate functions and cycle
• The Growth phase consists of constant mitosis, and blood supply of keratin and cells, division keeps the cycle going
• A Growth Stage depends on location of hair, but one stage can vary from month to as long as 6 years
• During the resting stage, mitosis comes to end as cells die

Hair Pigment

• Hair pigment differs by type
• Lanugo: thin, nonpigmented hair covering a fetus and generally falls after birth
• Terminal Hair: Thick coarse and pigmented
• Terminal hair is found around the eyes and on the scalp
• Vellus Hair: Thinner, non-pigmented and covers remaining regions of the body
• Puberty varies from gender
• After puberty, terminal hair replaces vellus hair
• If comparing gender in hair growth, males contain a more rapid hair replacement than that of females
• Hair color in general is largely determined by production of melanin via melanocytes
• Blond hair has little melanin produced, black hair has lots produced
• In some cases there can be red hair due to a special red pigment containing iron
• Less melanin produced can also result in becoming gray or white

Nails

• Nails: Hard accessory structures that are at the ends of digits
• Nails are made of stratified and are filled with keratin and epithelium
• Nail Plate: Made visible to the epidermal nail
• Consists of two parts: nail body and root
• The nail body section is usually the visible portions you can see, nail root locations are where new growth matrix’s divide and create more structures/growth

Nail Reinforcement

• Made up of Folded regions of skin surround and reinforce nail plate; also helps keep the underlying bone or dermis in place
• Consists of two additional components to allow and promote nail structures Proximal
• Proximal and Distals Ends: Fold and help keep root and nail plate where they need to be, distal edge folds consist of stratum corneum called hyponychium

Growth:

• Actively dividing cells that push neighboring cells, while that is occurring, the dead keratinization of blood supply keeps a cycle constantly progressing by .5mm
• The nail plate has no melanocytes instead the matrix is translucent, helps promote precision grip
• This process usually offers protections against underlying trauma

Learn about the dermis, a vascular layer beneath the epidermis. Its primary functions include supplying blood to the epidermis, housing sensory receptors, and anchoring the epidermis. Discover the papillary layer, the dermis' thinner, superficial layer of loose connective tissue.