Dermis

Dermis is the second layer of the skin, located beneath the epidermis and above the subcutaneous layer. It is composed of connective tissue, blood vessels, sweat glands, hair follicles, nerve endings, and lymphatic vessels.

Structure

The dermis is divided into two layers: the papillary dermis and the reticular dermis. The papillary dermis is the uppermost layer, which directly contacts the epidermis. It is composed of loose connective tissue and contains capillaries, lymphatic vessels, and sensory neurons. The reticular dermis, on the other hand, is the deeper and thicker layer of the dermis, composed of dense irregular connective tissue containing larger blood vessels, closely packed collagen fibers, and fibroblasts.

Functions

The dermis serves several functions in the body. It provides strength and elasticity to the skin through an extracellular matrix composed of collagen and elastin fibers. It also houses various types of cells, including fibroblasts, macrophages, and adipocytes, which play crucial roles in immunity and tissue repair. The dermis also contains the hair follicles and glands that produce sweat and sebum, contributing to temperature regulation and skin hydration.

Clinical significance

Several skin conditions and diseases affect the dermis, including dermatitis, psoriasis, and skin cancer. These conditions can cause symptoms such as redness, itching, and pain. Treatment for these conditions often involves topical medications, systemic therapies, and in some cases, surgical intervention.

Anatomy

Blood Vessels

The blood vessels supply nutrients and oxygen to the skin and take away cell waste and cell products. The blood vessels also transport the vitamin D produced in the skin back to the rest of the body.

Lymph Vessels

The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.

Hair Follicles

The hair follicle is a tube-shaped sheath that surrounds the part of the hair that is under the skin and nourishes the hair.

Sweat Glands

The average person has about 3 million sweat glands. Sweat glands are classified according to two types:

1. Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body odor.
2. Eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands can produce up to two liters of sweat an hour, however, they secrete mostly water, which doesn't encourage the growth of odor-producing bacteria.

Sebaceous Glands

Sebaceous, or oil, glands, are attached to hair follicles and can be found everywhere on the body except for the palms of the hands and the soles of the feet. These glands secrete oil that helps keep the skin smooth and supple. The oil also helps keep skin waterproof and protects against an overgrowth of bacteria and fungi on the skin.

Nerve Endings

The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, pressure and information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating body heat.

Collagen and Elastin

The dermis is held together by a protein called collagen, made by fibroblasts. Fibroblasts are skin cells that give the skin its strength and resilience. Collagen is a tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible.

Subcutis

The subcutis is the innermost layer of the skin, and consists of a network of fat and collagen cells. The subcutis is also known as the hypodermis or subcutaneous layer, and functions as both an insulator, conserving the body's heat, and as a shock-absorber, protecting the inner organs. It also stores fat as an energy reserve for the body. The blood vessels, nerves, lymph vessels, and hair follicles also cross through this layer. The thickness of the subcutis layer varies throughout the body and from person to person.

See also

• Epidermis (skin)
• Subcutaneous tissue
• Skin disease
• Dermatology

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