Integument

Integument

The integumentary system includes the skin and the related structures that cover and protect the body. The human integumentary system is made up of the skin, which includes glands, hair, and nails. The skin protects the body, prevents water loss, regulates body temperature, and senses the external environment. Examination of the integument can also provide the forensic scientist with clues regarding the identity of a crime victim, the nature of the crime committed, and even the perpetrator of the crime.

The human integumentary system serves many protective functions for the body. Keratin, an insoluble protein in the outer layer of the skin, helps prevent water loss and dehydration. Keratin also prevents excessive water loss, keeps out microorganisms that could cause illness, and protects the underlying tissues from mechanical damage. Keratin is also the major protein found in nails and hair. Pigments in the skin called melanin absorb and reflect the sun's harmful ultraviolet radiation. The skin helps to regulate the body temperature. If heat builds up in the body, sweat glands in the skin produce more sweat that evaporates and cools the skin. In addition, when the body overheats, blood vessels in the skin expand and bring more blood to the surface, which allows body heat to be lost. Conversely, if the body is too cold the blood vessels in the skin contract, resulting in less blood at the body surface, and heat is conserved. In addition to temperature regulation, the skin serves as a minor excretory organ, because sweat removes small amounts of nitrogenous wastes produced by the body. The skin also functions as a sense organ as it contains millions of nerve endings that detect touch, heat, cold, pain and pressure. Finally, the skin produces vitamin D in the presence of sunlight, and renews and repairs damage to itself.

In an adult, the skin covers about 21.5 square feet (2 square meters), and weighs about 11 pounds (5 kilograms). Depending on location, the skin ranges from 0.02–0.16 inches (0.5–4.0 millimeters) thick. Its two principal parts are the outer layer, or epidermis, and a thicker inner layer, the dermis. A subcutaneous layer of fatty or adipose tissue is found below the dermis. Fibers from the dermis attach the skin to the subcutaneous layer, and the underlying tissues and organs also connect to the subcutaneous layer.

Ninety percent of the epidermis, including the outer layers, contains keratinocytes cells that produce keratin, a protein that helps waterproof and protect the skin. Melanocytes are pigment cells that produce melanin, a dark pigment that adds to skin color and absorbs ultraviolet light thereby shielding the genetic material in skin cells from damage. Merkel's cells disks are touch-sensitive cells found in the deepest layer of the epidermis of hairless skin.

In most areas of the body, the epidermis consists of four layers. On the soles of the feet and palms of the hands where there is a lot of friction, the epidermis has five layers. In addition, calluses, abnormal thickenings of the epidermis, occur on skin subject to constant friction. At the skin surface, the outer layer of the epidermis constantly sheds the dead cells containing keratin. The uppermost layer consists of about 25 rows of flat dead cells that contain keratin.

The dermis is made up of connective tissue that contains protein, collagen, and elastic fibers. It also contains blood and lymph vessels, sensory receptors, related nerves, and glands. The outer part of the dermis has fingerlike projections, called dermal papillae that indent the lower layer of the epidermis. Dermal papillae cause ridges in the epidermis above it, which in the fingers give rise to fingerprints. The ridge pattern of fingerprints is inherited, and is unique to each individual. The dermis is thick in the palms and soles, but very thin in other places, such as the eyelids. The blood vessels in the dermis contain a volume of blood. If a part of the body, such as a working muscle, needs more blood, blood vessels in the dermis constrict, causing blood to leave the skin and enter the circulation that leads to muscles and other body parts. Sweat glands whose ducts pass through the epidermis to the outside and open on the skin surface through pores are embedded in the deep layers of the dermis. Hair follicles and hair roots also originate in the dermis and the hair shafts extend from the hair root through the skin layers to the surface. Also in the dermis are sebaceous glands associated with hair follicles that produce an oily substance called sebum. Sebum softens the hair and prevents it from drying, but if sebum blocks up a sebaceous gland, a whitehead appears on the skin.

The skin is an important sense organ, and as such includes a number of nerves that are mainly in the dermis, with a few reaching the epidermis. Nerves carry impulses to and from muscles, sweat glands, and blood vessels, and receive messages from touch, temperature, and pain receptors. Some nerve endings are specialized such as sensory receptors that detect external stimuli. The nerve endings in the dermal papillae are known as Meissner's corpuscles, which detect light touch, such as a pat, or the feel of clothing on the skin. Pacinian corpuscles, located in the deeper dermis, are stimulated by stronger pressure on the skin. Receptors near hair roots detect displacement of the skin hairs by stimuli such as touch or wind. Bare nerve endings throughout the skin report information to the brain about temperature change (both heat and cold), texture, pressure, and trauma.

Some skin disorders result from overexposure to the ultraviolet (UV) rays in sunlight. At first, overexposure to sunlight results in injury known as sunburn. UV rays damage skin cells, blood vessels, and other dermal structures. Continual overexposure leads to leathery skin, wrinkles, and discoloration and can also lead to skin cancer.

see also Crime scene reconstruction; DNA.