Integumentary System Statistics Covers the entire body l

Integumentary System

Statistics Covers the entire body. l Weighs between 9 to 11 lbs. l Thickness of skin in some areas can be from 1. 5 to 4 mm thick. l Flexible yet tough. l The #1 defense from bacteria and fungi. l

Hypodermis (Not technically part of the skin) l l l A. k. a. Superficial fascia. Stores fat Anchors the skin (loosely) It is important that we understand that the hypodermis anchors skin down loosely because it allows some potential trauma to slide off of the body. Hypodermis will thicken when we gain weight. (In women, thighs and breasts first, in men anterior abdomen)

Hypodermis

Epidermis l The epidermis is made up of keritanized stratified squamous epithelium.

Cell Types: Keratinocytes l Keratinocytes: cells that produce keratin. l Keratin: fibrous protein that gives skin its protective properties.

Cell Types: Melanocytes l l Melanocytes: synthesize melanin. Have a weblike appearance. Found in the deepest part of the epidermis. Melanin is created by the melanocytes, shipped up to the keratinocytes through the spider-like arms of the melanocyte, and deposited in the side of the nucleus of the keratinocyte that faces towards the sun, which creates a barrier that protects the keratinocyte’s nucleus from UV damage.

Melanocytes

Cell Types: Epidermal dendritic cells A. k. a. Langerhan’s cells l Spawn from bone marrow and work their way to the epidermis. l Key part of the immune system. l

Langerhan’s cells

Cell Types: Tactile cells l A. k. a. Merkel cells l Very intimately close to Merkel discs that act as receptors for the touch sense. l Merkel cell carinoma

Layers of the epidermis l Number of layers vary based on whether skin is thick or thin. l Thick: 5 layers l Thin: 4 layers

Thick Skin l Thick skin’s 5 layers: l l l Examples of thick skin l l l Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum Covers palms of hands Fingertips Feet *Stratum= layer *Strata= layers

Thin skin l Thin skin’s 4 layers: l Stratum basale l Stratum spinosum l Stratum granulosum l Stratum corneum l Examples of thin skin: l Everywhere else

Stratum Basale A. k. a. Basal layer l Deepest layer and attached to the dermis. l As these cells divide, they push the cells above them closer to the surface of the skin, and force the other layers to mature into fully formed keratinocytes faster. l

Stratum spinosum Several layers thick. Contains a web-like system of intermediate filament designed to resist tension. l Looks like prickly spiked balls. l

Stratum granulosum l l Thin layer (3 -5 layers). This is where the bulk of keratinization occurs. Each of the layers in this stratum will start to look very different. Cells flatten; nuclei and organelles disintegrate. Forms lamented and keratohyaline cells. l l Keratohyaline cells: helps form keratine in the upper layers Lamented cells: creates water resistant glycolipids that fill extracellular spaces in the cell.

Stratum lucidum l Consists of two clear flat dead cell layers. Uses keratin to bind together in a cable like array. (thick skin only)

Stratum corneum Outermost layer. (20 -30 cell layers thick) l Mostly all the cells of this layer are dead. Designed to be durable and take damaged. Seen most often flaking off as dandruff. l

End of Epidermis

Dermis Second major skin region. Made of strong connective tissue. l Contains connective tissue proper cell types: l l Fibroblasts l Macrophages l Few mast cells l Few white blood cells

Major layers of the dermis l Papillary layer: l Made of areolar connective tissue. l Contains interwoven elastic and collagen fibers. l Contains heavy amounts of blood vessels. l The loose connections of the tissue allows free movement of defensive cells, like the WBCs and macrophages.

continued The superior surface contains peg-like projections called dermal papillae. Others contain free nerve endings (pain receptors) and touch receptors called Meissner’s corpuscules. l On the hands and feet, papillae lay on ridges called dermal ridges. The dermal ridges have ridges on top of them called epidermal ridges. These ridges of skin are collectively called friction ridges. l Since sweat pores open on these crests, we will leave behind a small film of sweat on anything we touch. You know these as fingerprints. l

Reticular layer l The deeper and thicker of the two layers. l Course, irregular cell arrangement, dense fibrous connective tissue. l The cutaneous plexus, a layer of blood vessels that give nutrients to this layer, are between this layer and the hypodermis.

continued l In certain areas, skin that has less dense regions of the collagen fibers will form what is called cleavage. l When surgeons make an incision parallel to these lines, the skin gapes less and heals faster.

continued l Flexure lines are dermal folds that occur near joints where the dermis is firmly anchored to deeper structures. (look at the creases on the palms of your hands) l The dermis is folded due to the fact that skin cannot slide enough to conform to the joints in your hands.

End of Dermis

Skin Color l Three major pigments make up the skin: l Melanin l Carotene l Hemoglobin

Melanin Only one of the three pigments made in the skin. l Polymer of tyrosine amino acids. l Passed up from melanocytes to keratinocytes. l Found only in the deepest layers of the epidermis. l

Melanin

Human skin color Skin tone: l Darker skinned people are distributed more around the equator. This is due to more direct contact from the sun’s rays. l Their skin produces more melanin to protect their skin cells from harmful UV rays. l

Carotene Yellow-orange pigment found in certain plants like carrots. Accumulates in the stratum corneum, and in fatty layers of the hypodermis. l In asian people, the yellowish tint to their skin is due to varying levels of melanin and carotene. l

Carotene

Hemoglobin l The pinkish hue of hemoglobin is most evident in Caucasian people due to the fact that they lack very much pigment, allowing the reddish tint of hemoglobin to shine through the skin. Heme group

End of skin color

Glands l Appendages (added attachment) of the skin, glands function to cool down the body and expel wastes.

Sudoriferous Sweat Glands l All over the skin’s surface with the exception of the nipples and part of the external genitalia.

There can be upwards of 3 million of these glands on a body. l When myoepithelial cells contract, they squeeze out the secretion and forces the sweat to the skin surface. l

Eccrine sweat glands A. k. a. merocrine sweat glands. l Most abundant on the palms of the hands, forehead, and soles of the feet. l The secretory part is deep in the dermis, and pores (channels) allow for secretions to be brought to the surface. l The secretion from eccrine glands are what we call sweat. l

Contains small amounts of uric acid (also found in urine), which alters the p. H of sweat to between 4 -6. l Major role is to prevent overheating of the body. l

Apocrine glands Confined to the axillary (under arm) and anogential (genital region) areas. l Begin functioning around puberty. l

Ceriminous glands Modified apocrine glands. l Secrete sebum in the ear canal. l Mix with sebacous glands to form ear wax. l

Mammary glands Secrete milk. l Also included as a part of the female reproductive system. l

Oil based glands

Sebaceous Glands (oil glands) Branched alveolar glands. Found everywhere except the thick skinned parts of the hands and feet. l Most are found in hair follicles. l gland store oils, and become so stuffed with oil, it explodes! (holocrine gland) l Lipids plus cell fragments= sebum l

What happens when sebaceous glands become clogged up? l If a sebaceous gland becomes clogged with sebum, the a whitehead may form. l If that material oxidizes and dries, then a blackhead is formed.

l The inflammation of the sebaceous gland along with a pustule or cyst is called acne.

End glands

Hair covers almost all of the body. l Functions to keep us warm and help us sense insects before they bite us. l Hair on the head guards against physical trauma, heat loss, and sunlight. l

Examples of hair

Hair structure l l l Pili (hair) consists largely of dead keratinized cells. Hard keratin prominent in hair. Allows hair to be tougher and more durable, and individual cells do not flake off.

Hair anatomy Consists of a shaft, and a root. The root is the active growing region. l Flat and ribbon like hair structure results in kinky hair. l

l If the follicle is round, then the hair will appear wavy.

Hair Contains three keratinized layers of cells. l Middle layer called the medulla, consists of large cells and spaces. l The cortex surrounds the medulla, and consists of several layers of flattened cells. l The cuticle is the outermost layer that forms by having a single layer of cells overlap each other like shingles on a roof. l

Hair root The root of the hair contains the hair bulb, which is beneath the skin’s surface. l The hair bulb has a sensory nerve ending wrapped it called the hair follicle receptor, which allows transmissions of messages to the brain when a stimulus is applied. l

Hair follicle Wall is composed of connective tissue root sheath, which is derived (came from) dermal tissue. l This is an invagination in the epidermis formed by the inner root sheath. l

The arrector pilli A muscle associated with the hair follicle. l Most hairs grow in at an angle. The arrector pilli pull hairs into an upright position. l When the body cools too low, the arrector pilli is responsible for creating bumps on the skin surface. l

l Not very useful in humans because we have short hairs, but in long haired animals it allows them to retain heat.

Types of Hair l Vellus hair- thin hair. Mostly on children and adult females.

Types of Hair l Terminal hair-Longer thicker hair, found on eyebrows and scalp.

Growth Rates of Hair l Varies , but the greatests rates of hair growth occur on the scalp and armpits. l The hair on the legs can be stimulated by shaving, due to a physiological response to the cold. (Even when it is hot)

Growth of hair is the fastest between your teens through your 40’s. l Male pattern baldness is a genetic sexlinked trait, and doesn’t just “happen”. l

End hair

Nails l Scale like modification to hands. Protective covering for the fingers, allows us to pry open objects. l Nails correspond to claws and hooves in other animals.

The Nail bed l In the nail bed, the thickened portion is called the nail matrix. The nail matrix is the place where the nail grows.

Anatomical terms for the nail Nail folds- lateral parts of the nail that the skin folds over. l Eponychium- the nail body (cuticle) l Hyponchium- below the nail. l

End Nails

Functions of the Integumentary system Protection l Body temperature regulation l Cutaneous sensation l Metabolic function l Blood reservoir l Excretion l

Protection l l Chemical barriers: i. e. melanin in the skin. The acid mantle, due to a lower p. H of the skin, the skin tends to ward off or slow down most bacterial growth. Skin produces an antibiotic called defensins, which fight off microbial growth. Cathelicidians- wounded skin produces a multitude of peptides called cathelicidians, which fight off bacteria (especially streptococcus)

Physical barriers Provides a physical continuity to skin. Thicker skin could be beneficial, but we would lose softness and agility. l Glycolipids in the epidermis prevent diffusion directly through the skin. Prevents water loss and water entry in the skin. l

Biological barriers Includes DNA, macrophages on the dermis and dendritic cells of the epidermis. l Electrons in DNA can absorb UV rays to a degree, which allows for DNA to resist some of sun the sun’s rays. l

Body Temperature Regulation Under normal conditions, the body will lose 0. 5 L of sweat per day. l When your body temperature rises, your nervous system sends a signal to your sweat glands to begin perspiration. l

Cutaneous sensation l Cutaneous sensory receptors (part of the nervous system). Allows us to sense when there is a change in the environment, like the wind blowing.

Metabolic functions l The skin uses a modified form of cholesterol, along with the sun’s rays, to create a vitamin D precursor to ultimately create vitamin D.

Blood reservoirs The skin can hold up to 5% of the body’s blood. l When the blood vessels constrict, excess blood may be forced out of the blood vessels and into the skin, making you look flushed. l

Excretion l Ammonia and uric acid are removed from the body through sweat.

End Functions

Imbalances in the skin (Bad stuff) l Skin cancer- damage to the p 53 gene, which is a tumor supressing gene. Usually requires frequent dermal irritation. (frequent tanning, sun burn)

l Basal cell carcinoma- appears shiny and dome shaped. Accounts for 80% of all skin cancers. Sun exposed areas usually where lesions occur. Relatively slow growth. Unlikely to metastasize.

l Squamous cell carcinoma-grows rapidly and has a higher metastasis rate. Usually scaly and red, slightly raised.

l Melanoma- cancer of melanocytes. Usually appears as an irregular black patch.

Know your ABCD’s A. Asymmetry- the sides of the mystery mole do not match. l B. Border irregularity- borders of mole have indentations l C. Color- contains blacks, browns, blues, and other colors. l D. Diameter- spot is larger than 6 mm in diameter. l