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Fingerprints. Chapter 14. What exactly is skin?. It is an organ composed of several kinds of tissues Largest organ Performs many functions Maintains Homeostasis Prevents harmful substances such as chemicals and microorganisms from entering body Prevents water loss Maintains temperature

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Chapter 14

what exactly is skin
What exactly is skin?
  • It is an organ composed of several kinds of tissues
  • Largest organ
  • Performs many functions
    • Maintains Homeostasis
    • Prevents harmful substances such as chemicals and microorganisms from entering body
    • Prevents water loss
    • Maintains temperature
    • Houses sensory receptors
    • Contains immune cells
    • Produces chemicals such as Vitamin D
    • Excretes wastes
two main layers and one below
Two main layers and one below*
  • Epidermis

- Outer layer


  • Dermis
    • Inner layer
    • Thicker than epidermis
    • Made up of connective tissue, smooth muscle tissue, nervous tissue, blood, and other types of epithelial tissue (glands for example)

*Beneath the dermis is the subcutaneous layer

The epidermis and dermis are separated by the basement membrane that the stratified squamous epithelium is attached to

  • Lacks blood vessels
  • Made up of 4 or 5 layers
    • Stratum Basale (closest to basement membrane)
    • Stratum Spinosum
    • Stratum Granulosum
    • Stratum Lucidum (Optional)
    • Stratum Corneum

As each layer gets pushed upward, the cells change their shape and become more squamous or flattened.

stratum basale
Stratum Basale
  • The deepest layer – the contains cells that are actively dividing
    • Attached to the basement membrane
    • They are closest to the dermis, which contains blood vessels, so they receive nutrients and O2
    • As they divide, they push the older cells toward the top. Cell division prevents wear and tear – the more the use of the body part, the more the cell division (calluses, corns, etc.)
    • Specialized cells in this layer called melanocytes, produce melanin, which provides skin color
stratum spinosum

Stratum Spinosum

Stratum Spinosum
  • A thick layer of squamous epithelial cells right above the stratum basale
stratum granulosum

Stratum Granulosum

Stratum Granulosum
  • A granular layer of squamous epithelium above the stratum spinosum
stratum lucidum

Stratum Lucidum

Stratum Lucidum
  • An optional layer of squamous epithelium – only found in thick skin
  • Found in palms of hand or soles of feet
stratum corneum
Stratum Corneum
  • Topmost layer of squamous epithelium. Flattened cells
  • These cells are called Keratinocytes, because their cell membranes thicken with a protein called keratin.
  • This hardens them, makes them waterproof.
  • The farther the keratinocytes travel from the stratum basale, the less nutrients they have, so they eventually die.
  • The older keratinocytes develop many desmosomes
  • The tough sheet of dead cells is called the Stratum Corneum and is shed (exfoliation)
melanocytes and melanin
Melanocytes and Melanin
  • Although melanocytes are found in the stratum basale, their product – melanin can be found in other cells of the epidermis and sometimes even in the cells of the connective tissue underneath
  • This is because the melanocytes transfer the melanin to the neighboring cells via cellular extensions called dendrites – this process is called cytocrine secretion
more about melanin
More about Melanin
  • Melanin absorbs UV radiation – prevents skin cancer
  • Skin color depends mainly on the amount of the brown pigment melanin produced in the skin.
  • All people have about the same number of melanocytes. However, the melanocytes of dark-skinned people produce more melanin than do those of light-skinned people. The amount of melanin produced in each person's skin is determined mainly by heredity.
  • Exposure to sunlight increases the production of melanin, causing light skin to tan. In some cases, melanin builds up in small spots, forming freckles.
  • As someone grows older, the melanocytes produce melanin at uneven rates, which causes some areas of the skin to remain light and others to darken. These dark spots are sometimes called age spots or liver spots.
sunburn solar erythema
Sunburn (Solar Erythema)
  • Too much UV radiation
  • Epidermal cells become “sick”
  • Skin becomes red, swollen and painful
  • Cell undergo Apoptosis or programmed cell death
  • Apoptosis kills damaged cells to prevent skin cancer
  • Stratum basale will replace lost cells
the dermis
The Dermis
  • Below epidermis
  • Boundary between epidermis and dermis is uneven due to dermal papillae that extend into ridges in the epidermis
dermis cont d
Dermis, cont’d.
  • Contains nerve receptors – to sense light/heavy touch or pressure
  • Contains connective tissue made of collagen and elastic fibers
  • Contains smooth muscle, blood vessels, nerve tissue, hair follicles, sweat glands, and sebaceous glands.
friction skin
Friction Skin
  • The tough skin found on the palms and soles – these have the corpus lucidum
  • This thick skin is more affected by dermal papillae
  • The dermal papillae in friction skin creates ridges and valleys in the skin on the palms of hands and soles of feet
  • Each ridge houses a single row of pores that are connected to ducts leading to sweat glands
latent prints
Latent Prints
  • Sweat comes out of the pores and coats the ridges of the palms
  • Sweat contains water, salts, and waste products of body metabolism such as urea and amino acids. some oils from oil glands can also be mixed with the sweat.
  • (The dissolved solid content of sweat is only one eighth that of an equal volume of urine, the body's main vehicle of salt excretion; however, excessive sweating may produce severe salt loss.)
  • The sweat is then deposited on any surface the fingers touch, leaving a distinctive pattern behind
characteristics of fingerprints
Characteristics of Fingerprints
  • Fingerprints are unique to a particular individual.
  • No two fingerprints have the exact same set of characteristics.
  • Fingerprints do not change over a person’s lifetime or with superficial injury.
  • Fingerprint patterns can be classified.
  • Fingerprints do not provide proof of genetic history or racial background.
  • It is not possible to change one’s fingerprints, although some have tried.
the 3 principles of fingerprinting
The 3 principles of Fingerprinting
  • Fingerprints are unique and genetically determined
  • They remain unchanged throughout one’s life – they grow with the hand, but do not change.
  • The ridge (also called minutiae) patterns can be classified
fingerprint identification points
Fingerprint Identification Points
  • A single fingerprint may contain as many as 100 or more minutiae that can be used for identification purposes.
  • Debate continues over how many details must be the same to declare two fingerprints a match.
characteristics of fingerprints28
Characteristics of Fingerprints
  • Fingerprint patterns
    • Delta: two lines diverge and form a triangle
    • Arch: lack of any deltas
    • Loop: only one delta
    • Whorl: two or more deltas
characteristics of fingerprints29
Characteristics of Fingerprints
  • Fingerprint pattern distribution in the general population
    • 65% are loops
    • 35% are whorls
    • 5% are arches
types of patterns
Types of Patterns
  • Arch loop
  • Whorl
  • Plain radial
  • Plain tented
  • Ulnar
  • Accidental double
  • Central pocket
who discovered the uniqueness of fingerprints
Who discovered the uniqueness of fingerprints?
  • The Chinese are believed to have first used fingerprints as a “signature” on legal documents, almost 3000 years ago!
  • William Herschel used the Chinese method in India several hundred years ago, to get natives to “sign” legal documents
  • Henry Fauld, a Scottish physician published a journal on fingerprints and their uniqueness
    • But because the Bertillon method of anthropometry was being used, no one paid him any attention
  • Francis Galton, an Englishman did more research into it and persuaded the British government to use the fingerprinting method as a form of I.D. – his published work was a book called Finger Prints.
types of prints
Types of Prints
  • Latent fingerprint (patent fingerprint)
    • One that occurs when the entire pattern of whorls on the finger is transferred to an object
  • Plastic fingerprint
    • When a finger presses against a plastic material and leaves a negative impression of friction ridges
  • Visible fingerprint (dust print)
    • Print that has been adulterated with foreign matter
searching for prints
Searching for Prints
  • Evidence may be located in unobvious places at the crime scene.
  • Six broad categories of techniques for lifting prints:
    • Powders
    • Iodine
    • Ninhydrin
    • Silver nitrate solution
    • Superglue fuming
    • Lasers
preservation of fingerprints
Preservation of Fingerprints
  • Methods of fingerprint preservation include photography of the print and lifting techniques.
    • Powder and tape are the most commonly employed techniques for revealing, lifting, and preserving prints.
computerized fingerprints the iafis system
Computerized Fingerprints: The IAFIS System
  • AFIS, Integrated Automated Fingerprint Identification System, is national print database run by the FBI
  • A computer is used to scan and digitize fingerprints
    • This translates the unique ridge patters of the prints into a binary code for the computer’s searching algorithm.