Which are characteristics of the papillary region of the dermis?

Figure 1. This stained slide shows the two components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from one to the other, making the border between the two somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below belong to the reticular layer. LM × 10. (credit: modification of work by “kilbad”/Wikimedia Commons)

The dermis might be considered the “core” of the integumentary system (derma- = “skin”), as distinct from the epidermis (epi– = “upon” or “over”) and hypodermis (hypo– = “below”). It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts (Figure 1).

Papillary 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. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae (see Figure 1). 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.

Reticular Layer

Underlying the papillary layer is the much thicker reticular layer, composed of dense, irregular connective tissue. This layer is well vascularized and has a rich sensory and sympathetic nerve supply. 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 dermis is the second and thickest layer of the three major layers of skin, located between the epidermis and subcutaneous tissues, also known as the subcutis and the hypodermis.

The skin was previously viewed as a body part that protects us from the elements. Today, new knowledge informs us that the layers of the skin are actually very complex and have many important functions—from giving us goosebumps and cooling us down in the sauna to letting our brain know that our hand is on a burner. Let's learn more about how this layer is structured and what it does for us.

Anatomy and Structure

The dermis has two parts: a thin, upper layer known as the papillary dermis, and a thick, lower layer known as the reticular dermis. Its thickness varies depending on the location of the skin. For example, the dermis on the eyelids is 0.6 millimeters thick; on the back, the palms of hands and the soles of feet, it measures 3 millimeters thick.

The dermis contains a lot of the body's water supply and it has important roles in both regulating temperature and providing blood to the epidermis.

Structures found in the dermis include:

• Connective tissues, specifically collagen and elastin
• Blood capillaries (the smallest of blood vessels) and other small vessels
• Lymph vessels
• Sweat glands
• Sebaceous glands (oil glands)—best known for its tendency of becoming clogged and causing the dreaded white heads of acne, it actually plays an important role in protecting the body
• Nerve endings
• Hair follicles—the body contains close to 2 million hair follicles

Tissue Composition

The dermis is composed of three types of tissues that are present throughout the dermis rather than in layers:

• Collagen
• Elastic tissue
• Reticular fibers

The papillary layer, the upper layer of the dermis, contains a thin arrangement of collagen fibers. The lower layer, known as the reticular layer, is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin.

Roles It Plays

The dermis is the thickest layer of skin and arguably the most important. It plays several key roles, including:

• Producing sweat and regulating the body's temperature: Within the dermis are sweat glands that produce sweat that comes out of the pores. The body sweats as a way to cool itself off, regulate temperature and flush out toxins. There are more than 2.5 million sweat glands in the body, and there are two different types: apocrine and eccrine. Apocrine sweat glands are found in the more odorous parts of the body, including the armpits, scalp, and genital region. The sweat glands, which become active during puberty, secrete their substances into the hair follicles. The sweat that is secreted is actually odorless at first. It only starts to smell when it comes in contact with skin bacteria. Eccrine sweat glands are located throughout the rest of the body—on the palms, the soles of feet, armpits, and the forehead. These glands emit their substances directly to the surface of the skin.
• Producing oil: The sebaceous glands produce sebum or oil. Sebum inhibits bacterial growth on the skin and conditions the hair and skin. If the follicle in which sebaceous glands are located becomes clogged with excess oil or dead skin cells, a pimple develops.
• Growing hair: Hair follicles are located in the dermis. Every follicle root is attached to tiny muscles, known as arrector pili muscles, that contract when the body becomes cold or scared, causing goosebumps.
• Feeling: The dermis is full of nerve endings that send signals to the brain about how things feel—whether something hurts, itches, or feels good.
• Distributing blood: Blood vessels that are located in the dermis feed the skin, remove toxins, and supply the epidermis with blood.
• Protecting the rest of the body: The dermis contains phagocytes, which are cells that consume potentially harmful toxins and impurities, including bacteria. The dermis already protects the body, but the phagocytes provide an additional layer of protection from anything harmful that has penetrated the epidermis.
• Giving the skin structure so it holds its shape: The dermal layer is responsible for the turgor of the skin, acting in a similar way as does the foundation of a building.

Interactions With the Epidermis

Not only does the dermis have complex functions, but it is in constant contact and communication with the epidermis, regulating important bodily processes.

Cells in the epidermis influence the dermis, which in turn influence the turnover of cells in the epidermis (via activities of cells such as mast cells, which secrete cytokines). It is the interaction of these two layers that is, in fact, most disrupted in some conditions such as psoriasis.

Aging Process

Many people wonder about what causes the skin to wrinkle and age. There are several important changes in all three layers of our skin as we age.

The dermal layer becomes thinner with age as less collagen is produced. Elastin wears out—becoming less elastic just as the elastic waistband in a pair of shorts may lose its elasticity. This is what leads to wrinkling and sagging.

The sebaceous glands produce less sebum while the sweat glands produce less sweat, both contributing to the skin dryness characteristic of aging.

The surface area or amount of contact between the dermis and epidermis also decreases. This results in less blood being made available from the dermis to the epidermis and fewer nutrients making it to this outer layer of skin. This flattening out of the connecting region also makes the skin more fragile.

Causes and Risk Factors of Wrinkles

Tumors

Just as abnormal growths in the epidermis give rise to the all-too-common skin cancers, tumors can arise from the dermal layer of the skin as well. One type of tumor which begins in the dermis is called a dermatofibroma (or benign fibrous histiocytoma.) These fairly common tumors often occur on the legs of middle-aged women. It's not known what exactly causes these tumors, but they frequently occur following some form of trauma.

Protection

Just as it's important to protect your epidermis from too much sun, it's important to protect your dermis as well. Sun exposure damages collagen (and causes changes in elastin), which can result in premature wrinkling.

Frequently Asked Questions

• What are the three types of connective tissue?

  The three types of connective tissue include collagen, reticular fibers, and elastin. The dermis only houses collagen and elastin fibers. Dense, closely-knitted collagen fibers make up the bulk of tendons and ligaments, while elastin fibers help control the blood pressure of vascular cells. Thick collagen fibers are also found in the reticular layer. In the papillary layer, there is a more thin distribution of collagen fibers.

• Why do sweat glands become more active during puberty?

  Sweat glands become more active during puberty thanks to changing hormones. Major bodily functions can be affected by just a small shift in the number of hormones and their amount of activity - hormones during puberty lead to increased sweating, changes in mood, bodily growth, and the development of sexual function.

• What is the purpose of goosebumps?

  The purpose of goosebumps is not entirely understood. They appear when small muscles flex in the dermis as a response to fear, cold weather, or something that we find inspiring, such as music. As far as fear is concerned, goosebumps are connected to the involuntary "fight or flight" response that we experience during an unnerving situation. They offer a warning that something nearby feels unsafe or wrong in some way. Early studies suggest that goosebumps can promote hair follicle growth and tissue healing, so they may have further potential.

  Which characteristic is specific for the papillary layer of the dermis?

  The superficial papillary dermis possesses thinner elastic fibers compared to the thicker elastic fibers of the reticular dermis. The papillary dermis is composed of loose connective tissue (LCT) and is highly vascular. The reticular dermis shows thick collagen bundles and forms the bulk of the dermal layer.

  What is the papillary region of the dermis?

  (PA-pih-LAYR-ee DER-mis) The thin top layer of the dermis (the inner layer of the skin). The papillary dermis has connective tissue and blood vessels that give nutrients to the epidermis (the outer layer of the skin) and that help control the temperature of the skin.

  What are some of the features of the dermal papillae?

  It is characterized by dermal papillae, little bumps that protrude up into the bottom of the epidermis. In these papillae are capillary loops, and nerve endings (for pain reception) and Meissner's corpuscles (touch receptors). Another feature of some parts of the papillary layer is dermal ridges.

  What is the main function of the papillary layer of the dermis?

  The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body.