C 5

Skin

the largest organ in the body

Cutaneous Membrane consist of

Epidermis and Dermis

epidermis

the superficial layer: keratinized stratified squamous epithelium resting on a basement membrane

dermis composed of

the epidermis and basement membrane: loose connective tissue and dense irregular connective tissue

Avascular Epidermis

Relies on diffusion of oxygen and nutrients from blood vessels in deeper dermis; limits epidermal thickness

Epidermis made of

About 50% of epidermal cells are too far from adequate blood supply to sustain life; superficial layers are made up entirelyof dead cells

Epidermis Structure

in cutaneous membrane include sweat glands, sebaceous glands, hair, and nails

Epidermis contains

sensory receptors and arrector pili muscles (small bands of smooth muscle associated with hair

Hypodermis

deep to dermis

Hypodermis job to the skin

Not part of skin; anchors skin to deeper structures like muscle and bone

Hypodermis made of

  loose connective and adipose tissues; has abundant blood supply

Functions of the Integumentary System

protecting the underlying organs or for maintaining homeostasis

Hypodermis- Protection

a.        Protects from mechanical trauma, pathogens, and the environment.

b.       Keratinized stratified squamous epithelium provides a continuous barrier against invasion.

c.        Glands also create a slightly acidic pH which inhibits pathogen growth.

d.       The skin protects against ultraviolet (UV) light;

Hypodermis- Sensation

a.        enables the nervous system to perceive changes in the body’s internal or external surroundings, which is critical to homeostasis.

b.       the skin detect changes in the internal and/or external environment such as heat, cold, and pain.

i.       detect potentially harmful stimuli (heat, cold, and pain); could lead to tissue

damage

Hypodermis- Excretion

process where waste products and toxins are eliminated from the body

Perspiration

a.        consists of water, and dissolved waste material from the breakdown of chemicals during cellular processes

i.      Whenyouperspirethebodyeliminatesthewaste,ammonia,urea,saltsandsuga

 Thermoregulation, how it works

a.        Blood vessels in dermis expand and dilate

i.       As they expand, blood flow increases, and heat is released to our skin which holds sweat glands

1.    Water (sweat) carries heat when it evaporates, produces cooling effect

Skin role for Vitamin D

required for calcium ion absorption from the small intestine.

Calcium ions are critical for nerve function, muscle contraction, building and maintaining bone tissue, and many other physiological functions

Keratinocyte

the most numerous cell type that compose the superficial layer of the skin

Keratinocytes make up

95% of the epidermis

Features of keratinocyte

 make the epidermis stronger and less susceptible to mechanical trauma

Keratinocyte manufactures

keratin, a tough fibrous protein that makes the epidermis more resistant to mechanical trauma

Keratinocytes link by

desmosomes, which makes the epidermis stronger

Stratum basale layer

single layer of stem cells resting on the basement membrane

Stratum basale cells

Closest cells to the blood supply in dermis makes these the most metabolically and mitotically  active cells in the epidermis

Stratum spinosum layer

thickest layer, sits on top of the stratum basale so it is still close to the blood supply

Stratum spinosum cells

cells in this layer are also metabolically and mitotically active

Stratum granulosum cells

have prominent cytoplasmic granules

Stratum granulosum filled with

1.    keratin bundles

2.    or a lipid-based substance,

a.     The hydrophobic nature of lipids provides a waterproofing that is critical for maintaining internal fluid and electrolyte homeostasis.

Stratum lucidum

is a narrow layer of clear dead keratinocytes found only in thick skin.

Stratum corneum

the outermost layer of the epidermis, consists of several layers of dead flattened keratinocytes with thickened plasma membranes filled mostly with keratin bundles and little else

Keratinocyte life cycle

a.        Keratinocytes begin life in the stratum basale or spinosum; pass through each epidermal layer; shed from stratum corneum

b.       Migration from deepest strata to stratum corneum takes 40–50 days to complete

Dendritic Cells

located in the stratum spinosum, are phagocytes that protect the skin and deeper tissues from pathogens

Melanocyte location

in the stratum basale, produce melanin which is a protein skin pigment ranging from orange-red to brown-black

Melanocytes function

secrete melanin into keratinocytes, protecting the “sunny” side of their nucleus

from UV

Merkel cells

found scattered throughout the stratum basale, and detect light touch and discriminate shapes and textures

• a.        They are found in regions that are specialized for touch, such as

  the fingertips, lips, and at the base of hairs.

dermis description

highly vascular layer deep to epidermis

Dermis Function

a.     Providing the blood supply for epidermis

b.    Contains sensory receptors

c.     Anchors epidermis in place

dermis is composed of

papillary layer and dermal papilla

papillary layer

the thinner most superficial of the two layers, is composed of loose

(areolar)connective tissue

•       Special collagen fibers at dermis-epidermal junction; extends into epidermal basement  membrane and anchors epidermis to dermis

dermal papillae

tiny projections found at the surface of the papillary layer where it comes into contact with the epidermis

Dermal papillae contain

capillaries arranged in loops that extend up into the most superficial part of the dermal papillae

• a.      loops allow oxygen and nutrients to diffuse into the extracellular fluid of the

  dermis, and then into the cells of the avascular epidermis

reticular layer

the deep thicker layer that separates the dermis from the hypodermis

reticular layer contains

• Collagen bundle

• Elastic fiber

• Proteoglycan

• Blood vessels

Collagen bundle

strengthen dermis; prevent traumatic injuries from damaging deeper tissues

Elastic Fibers

allow the dermis to return to its original shape and size after stretching

Proteoglycans

draw water into ground substance; keeps skin firm and hydrated

melanin

Skin color, mostly determined by various amounts of the orange-red to brown-black protein pigment

Tyrosinase

(an enzyme that joins two amino acids, tyrosines), to make melanin in the melanosomes

Albinism

a condition in which melanocytes fail to make tyrosinase… failing to make melanin

Vitiligo

an autoimmune disorder, where the immune system attacks and

destroys scattered melanocytes

Primary function of melanin

protecting keratinocyte DNA from mutations induced by UV radiation.

Melanocytes extensions of plasma membrane

in contact with neighboring keratinocytes in the stratum basale and spinosum.

Melanin

produced continuously to maintain consistent skin color; it degrades after a few days.

Melanin synthesis

  increases with exposure to natural or artificial UV radiation which leads to tanning

or darkening of the skin pigmentation

UV radiation

has immediate and delayed effects of skin pigmentation

Immediate response to UV radiation

Oxidation of melanin already present in keratinocytes which causes melanin to quickly darken

Delayed effect of UV radiation

causes DNA damage in melanocytes, which stimulates melanin production, leading to the delayed or secondary effects of UV exposure appearing within 72 hours and lasting longer that melanin oxidation

overall number of melanocytes

virtually identical among all individuals, irrespective of skin color

spectrum of human skin tones

is due to differences in amount of and type (color) of

melanin produced.

fewer melanocytes

found on the palms of the hand and the soles of the feet

Skin pigmentation across the body

depends on the number of melanocytes found in a particular body region, leading to uneven distribution of melanin

Variations of pigmentation

mole and freckle

freckle

  small area of increased pigmentation resulting from a local increase in melanin production concentrated in one spot.

mole

another area of increased pigmentation that is due to a local proliferation of melanocytes instead of an increase in melanin production

Carotene

a yellow-orange pigment found in food items, such as egg yolks and orange vegetables

Carotene Effect

this lipid-soluble pigment accumulates in the stratum corneum giving it a slight yellow- orange color

Hemoglobin

ifound in red blood cells, is an iron-containing protein that binds to and transports oxygen throughout the body

Hemoglobin’s effect on skin color

  is an indirect result of blood flow in the dermis.

• The color of blood in the deeper dermis is visible through the epidermis.

accessory structures or appendages of the integumentary include

hair, nails, and glands that are derived

from the epithelium and assist in the overall function of the integumentary system.

Hair or pili

are small filamentous structures that protrude from the surface of the skin over the entire body except in the regions with thick skin, the lips, and parts of the external genitalia

Hair protection

preventing substances and organisms from the external environment from entering the eyes and the nose

Hair on the Head

protects the underlying skin of the scalp from UV radiation and mechanical trauma.

Hair association with

small sensory neuron that plays a role in detecting changes in the

environment.

Hair structure

composed of two main parts; the shaft and the root, both made up of keratinized stratified squamous epithelial cells

Hair shaft

a.     is the portion of hair that projects from the skin’s surface.

• made up of columns of dead keratinized epithelial cells that have completed the keratinization process.

The root

segment of hair that is embedded in the dermis where it is surrounded by a small sensory neuron.

hair  papilla

indented at its base by a projection of blood vessels from the dermis

hair bulb

root and the hair papilla are collectively known

matrix

A small number of keratinocyte, found at the base of the root, actively divide by mitosis.

hair follicle

is an in-folding of the epidermis called the epithelial root sheath which extends deep into the dermis or even hypodermis.

dermal root sheath

Surrounding the epithelial root,   consisting of connective tissue that supports the follicle and separates it from the dermis.

Lanugo

a thin, nonpigmented hair found covering nearly the entire body of a fetus

Terminal hair

thick, coarse, and pigmented hairs. They are found surrounding the eyes and on the scalp.

Vellus hair

hairs are thinner, nonpigmented hairs. They are found over the remaining regions of the body.

Terminal hair replaces

the vellus hair after puberty, which varies by genetic sex with more hair replacement occurring in males than females.

little melanin

Blond hair

lot of melanin

Black hair

Red hair

has a special reddish pigment containing iron

aging

Melanocytes produce less melanin so hair eventually turns gray or white

Nails

are hard accessory structures that are located at the ends of the digits, are composed of stratified squamous epithelium filled with hard keratin

nail plate

       the most visible component of the nail, sits on top of an underlying epidermal

nail bed

nail root

lies under the skin where the nail matrix actively divides and produces new cells

keratinization

Keratinocytes die and have been cut off from the blood supply.

lunula

is a half-moon shaped region of the proximal nail plate that represents an accumulation of keratin.

primary function of nails

protection of the underlying tissue in the distal tips of the fingers and toes, from trauma

skin contains two basic types of glands

Sebaceous and Sweat gland

Sebaceous gland

produce oily sebum that empties into a hair follicle or a small pore

Sebaceous glands

found everywhere on the body except the palms and soles with the greatest number found on the face and scalp