integumentary_system

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The Integumentary System:

The Integumentary System

Layers of the Skin:

Layers of the Skin There are two main layers to the skin and a deeper layer that supports the skin and connects it to underlying tissues. The EPIDERMIS is the outer part of skin and is composed of stratified squamous epithelium The DERMIS is the deeper part of skin and is composed of connective tissue containing collagen and elastic protein fibers The HYPODERMIS (Subcutaneous Layer) is composed of areolar connective tissue

Layers of Skin:

Layers of Skin

Structure of the Skin:

Copyright 2009, John Wiley & Sons, Inc. 4 Structure of the Skin The epidermis has a number of important characteristics: the epidermis is composed of keratinized stratified squamous epithelium it contains four major types of cells: Keratinocytes (90% of the cells) produce keratin which is a tough fibrous protein that provides protection

EPIDERMIS of the Skin:

EPIDERMIS of the Skin The epidermis is composed of keratinized stratified squamous epithelium. There are about 40-50 layers of cells that gradually vary in shape until the outer layers are very flat It takes about 4 weeks for a cell to move from the bottom layer to the top layer where it is then shed from the body The outer layers of cells are dead since they are no longer able to absorb nutrients from the deeper layers of the skin

Epidermal cells: keratinocytes:

Epidermal cells: keratinocytes KERATINOCYTES These are the majority (90%) of cells in the skin They contain the protein Keratin These cells help to “waterproof” the skin and protect underlying tissues from heat, bacteria and most chemicals

Structural Basis of Skin Color:

Copyright 2009, John Wiley & Sons, Inc. 7 Structural Basis of Skin Color Variations in skin color arise from variations in the amounts of three pigments: melanin, carotene, and hemoglobin Melanin - a yellow-red or brown-black pigment produced by melanocytes (located mostly in the epidermis, where it absorbs UV radiation ) The amount of melanin causes the skin’s color to vary from pale yellow to red to tan to black The number of melanocytes are about the same in all people ; differences in skin color is due to the amount of pigment produced

Epidermal cells: Melanocytes:

Epidermal cells: Melanocytes These cells produce the pigment Melanin that gives skin is characteristic color (from yellow-red to brown-black) Melanin protects neighboring cells from the harmful affects of UV radiation from the sun

Epidermal cells: LANGERHANS Cells:

Epidermal cells: LANGERHANS Cells white blood cells that function to destroy invading pathogens, but are easily destroyed by UV radiation Hint: Langerhan sounds like a great name for a doctor or hospital (Langerhan Memorial) = keeping us healthy

Epidermal Cells: MERKEL Cells :

Epidermal Cells: MERKEL Cells specialized tactile (touch) receptors that detect light pressure and texture Hint: Merkel sounds like Mackerel (a fish) and these cells let you experience the slippery, slimy texture of the fish

Epidermis:

Epidermis

The Epidermis is divided into distinct layers of cells:

The Epidermis is divided into distinct layers of cells STRATUM BASALE Bottom layer that undergoes mitosis making more cells and contains the merkel cells (sensory touch receptors)

The Epidermis is divided into distinct layers of cells:

The Epidermis is divided into distinct layers of cells STRATUM SPINOSUM Cells have an irregular shape with pointed ends that look like spines and contains the Langerhans cells (for immunity)

The Epidermis is divided into distinct layers of cells:

The Epidermis is divided into distinct layers of cells STRATUM GRANULOSUM Cells appear to have “spots” or granules which are actually ribosomes making large amounts of the protein keratin The cells die in this layer and the nucleus fragments and is not visible in layers above this one

The Epidermis is divided into distinct layers of cells:

The Epidermis is divided into distinct layers of cells STRATUM LUCIDUM This layer is only found in the thick skin on the palms of the hands and soles of the feet The cells have a very thick phospholipid cell membrane so appear white (like adipocytes) STRATUM CORNEUM This layer contains the dead squamous cells

Photomicrograph of skin:

Photomicrograph of skin

Dermis:

Copyright 2009, John Wiley & Sons, Inc. 17 Dermis The dermis has several important characteristics: is composed of connective tissue containing collagen and elastic fibers contains two layers the outer papillary region consists of areolar connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops ) , corpuscles of touch and free nerve endings

Dermis:

Dermis Lines of cleavage - “tension lines” in the skin indicate the predominant direction of underlying collagen fibers Dermatoglyphics - the study of the pattern of epidermal ridges Copyright 2009, John Wiley & Sons, Inc. 18

Epidermal Ridges:

Epidermal Ridges Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints (and footprints); their function is to increase firmness of grip by increasing friction.

Dermis:

Copyright 2009, John Wiley & Sons, Inc. 20 Dermis The dermis has several important characteristics: is composed of connective tissue containing collagen and elastic fibers contains two layers the outer papillary region consists of areolar connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops ) , corpuscles of touch and free nerve endings

The Dermis is divided into two regions:

The Dermis is divided into two regions The outer PAPILLARY Region consists of areolar connective tissue (with primarily smaller reticular fibers) It is called the papillary region because it has many small nipple-shaped elevated projections called dermal papilla

Features of papillary region of dermis:

Features of papillary region of dermis Rows of tissue cause fingerprints This region contains the FREE NERVE ENDINGS that are responsible for sensations of temperature, pain, tickling and itching.

Features of papillary region of dermis:

Features of papillary region of dermis It also contains the MEISSNER CORPUSCLES that are responsible for sensing light pressure and slow vibrations There are numerous small blood vessels in this region

Dermis:

Copyright 2009, John Wiley & Sons, Inc. 24 Dermis The deeper reticular region consists of dense irregular connective tissue containing collagen and elastic fibers adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands Striae or stretch marks can appear if the skin is stretched too much

The Dermis is divided into two regions:

The Dermis is divided into two regions Striae or stretch marks that may appear if skin is stretched too much are due to scar tissue that forms. Their location indicates “lines of cleavage or tension lines” in the skin demonstrating the predominant direction of the collagen fibers in this region

Dermis:

Dermis

The Dermis is divided into two regions:

The Dermis is divided into two regions The inner RETICULAR Region consists of dense irregular connective tissue (with more collagen fibers) This region contains the hair follicles, sweat and oil glands, some adipose tissue, nerves and larger blood vessels It also contains the LAMELLATED (PACINIAN) CORPUSCLES that are responsible for sensing deep pressure and rapid vibrations

Pictures of dermis :

Pictures of dermis

Subcutaneous (subQ) layer (also called the hypodermis) :

Subcutaneous (subQ) layer (also called the hypodermis) This is technically not part of the skin but it attaches the skin to the underlying tissues and organs Loose areolar c.t. “subcutaneous fat” lamellated (pacinian) corpuscles which detect deep external pressure applied to the skin.

Subcutaneous (subQ) layer (also called the hypodermis) :

Subcutaneous (subQ) layer (also called the hypodermis) Due to the large amount of blood vessels in this area it serves as a good location for administering some drugs (subcutaneous injections).

Sensory Detection in the Skin:

Sensory Detection in the Skin Free Nerve Endings: Located in outer papillary region of the dermis and provide sensations of temp, pain, tickling and itching

Sensory Detection in the Skin:

Sensory Detection in the Skin Merkel Cells: These are found in deepest layers of the epidermis (Stratum Basale). They provide the sensation of light touch and pressure

Sensory Detection in the Skin:

Sensory Detection in the Skin Meissner’s Corpuscles These are found in the outer papillary region of the dermis on skin surfaces that lack hair and also provide the sensation of touch, pressure, and slow vibrations

Lamellated (Pacinian) Corpuscles:

Lamellated (Pacinian) Corpuscles Pacinian Corpuscles These are found in the reticular region of the dermis and the subcutaneous layer and provide the sensation of deep pressure and rapid vibrations

Epidermal Wounds :

Epidermal Wounds Damage mostly in epidermis Abrasions and minor burns Basal cells of epidermis surrounding the wound break contact with basement membrane Cells enlarge and migrate as a sheet When they encounter other epidermal cells they stop migrating (contact inhibition) Epidermal growth factor stimulates basal stem cells to divide and replace new ones that have moved into wound

Epidermal Wound Healing:

Copyright 2009, John Wiley & Sons, Inc. 36 Epidermal Wound Healing

Deep Wound Healing:

Copyright 2009, John Wiley & Sons, Inc. 37 Deep Wound Healing

Stages of deep wound healing:

Stages of deep wound healing Inflammatory phase Migratory phase Granulation phase Maturation phase

Inflammatory phase :

Inflammatory phase Blood clot forms and loosely connects wound edges Increased blood flow to area brings phagocytes to kill bacteria (this causes redness, heat and swelling seen in inflammation) Stem cells develop into fibroblasts

Migratory Phase:

Migratory Phase Blood clot becomes a scab Epithelial cells in basal layer migrate under scab to fill in gap Fibroblasts synthesize collagen Damaged blood vessels begin to regrow

Proliferative phase:

Proliferative phase Epithelial cells undergo mitosis New tissue continues to grow under scabs

Maturation phase:

Maturation phase Scab falls off Epidemris restored to normal thickness Formation of a scar is called fibrosis Tissue appears different because collagen fibers are more densely arranged There are fewer melanocytes (thus this skin is more sensitive to UV in future) Fewer blood vessels

How are skin burns classified? :

How are skin burns classified? First degree: involves only the epidermis Characterized by erythrema and mild pain Second degree: involves entire epidermis and possible part of the dermis characterized by erythrema, edema, pain, formation of blisters (areas where epidermis is separated from dermis and filled with fluid)

Third degree burn:

Third degree burn Third-degree burn: involves epidermis, dermis and subcutaneous layers (even accessory organs) Characterized by marble-white to charred tissue that appears black with edema There is numbness due to damage to nerve endings These type of burns may require skin grafts for healing

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