ANATOMY OF INTEGUMENTARY SYSTEM

ANATOMY OF INTEGUMENTARY SYSTEM

Posted by tania anvar

 Integumentary system

In = inward; tegere = to cover

Dermatology - medical speciality that deals with the diagnosis and treatment of integumentary system disorders.

Structure of the skin

             

Synonyms of skin

•                    integument
•           cutaneous membrane

   

- ·    Largest organ in the body in both surface area and weight.

•             In adults, skin covers an area of about 2 square meters.
•             weighs 4.5 – 5 kg.
•       over most of the body it is 1-2 mm thick.

       *0.5 mm on the eyelids.

       * 4 mm on the heels.

                                                   Epidermis

Structurally 2 main parts   {     Dermis

  

1.   Epidermis – superficial – thin – epithelial tissue.

2.   Dermis     –       deep     – thick – connective tissue

{                        Areolar tissue

Hypodermis     Adipose tissue

• ·      also known as subcutaneous / subQ layer
• ·      not part of skin
• ·      serves as a storage depot for fat
• ·      contains large blood vessels that supply skin
• ·      contain nerve endings – Pacinian/Lamellated corpuscles – that are sensitive to pressure

Epidermis – stratified squamous epithelium

·      Contains 4 principal types of cells

    1.   keratinocytes

    2.   melanocytes

    3.   Langerhans cells

    4. merkel cells

    

  

Keratinocytes	4-5 layered	Keratin -      protection  Lamellar granules
Melanocytes	Develop from ectoderm of embryo	Melanin - Skin colour -Absorb UV
Langerhans cells	Migrate from bone marrow	Immunity
Merkel cells	contacts with flattened process of sensory neuron – merkel /tactile disc	Touch sensation

4 strata / layers of epidermis

Thin skin	Thick skin
1.    Stratum basale	1. Stratum basale
2.   stratum spinosum	2. stratum spinosum
3.   stratum granulosum	3. stratum granulosum
4.   stratum corneum - thin	4.  stratum lucidum
	5. stratum corneum - thick

Stratum basale/ germina tivum	Single row cuboidal/ columnar keratinocytes deepest layer	Stem cells Nucleus Organelles *Tono filament	Melano cytes Merkel cells
Stratum spinosum Spine- thorn	8-10 layers polyhedral	Nucleus Organelles Tono filaments	Melanocytes Langerhans cells
Stratum granulosum	3-5 layers flattened	Apoptosis ^Keratohyalin	Keratin +Lamellar granules
Stratum lucidum Lucid - clear	3-5 layered Flattened clear dead keratinocytes	Thick skin of finger tips, soles, palms	Keratin Thickened plasma membranes
Stratum corneum Corn - horn	25-30 layered Flattened  dead keratinocytes	Cells are continuously shed and replaced by cells from deep strata	Keratin Lamellar granules

* Tonofilaments

•         composed of a protein that form keratin 

• attach to          

                                    bind cells of S.basale to 

         a. desmosomes   {                          each other                                                            & to cells of adjacent 

                                                           S.spinosum              

      

b. hemidesmosomes – bind keratinocytes to basement membrane positioned between epidermis and dermis

^keratohyalin

• ·      converts tonofilaments into keratin

      + Lamellar granules – water repellant sealent

   -    lipid rich secretion

•      decrease water entry and loss.
•       inhibits the entry of foreign materials.

Callus – abnormal thickening of stratum corneum due to constant exposure of skin to friction

Keratinization

Ø as the cells move from one epidermal layer to other, they accumulate more and more keratin

Ø whole process- cells form in S.basale →rise to surface → become keratinized →slough off

                                                  ↓

Ø takes 4 weeks in  an average epidermis of 0.1 mm thickness.

Dandruff - an excessive amount of keratinized cells shed from the skin of the scalp.

Psoriasis – premature shedding of keratinocytes; keratinocytes divide and move more quickly than normal as early as 7-10 days.

Dermis  

                      fibroblasts with macrophages

           a.Cells   {

      {                   adipocytes   

                                                          collagen

         b.Tissue – connective tissue  {

                                                          elastic fibres

Leather – dried and treated dermis of animals

Based on tissue structure, dermis divided into

1.   papillary region

2.   reticular region

papillary region       ↓ superficial	Areolar connective tissue	·      Thin collagen ·      Fine elastic fibres	*Dermal papillae ·      capillary loops ·      free nerve endings ·      meissners corpuscles
reticular region     ↓ deep	Dense irregular connective tissue	·      Bundles of collagen ·      Coarse elastic fibres ·      fibroblasts	Between fibres ·      adipose cells ·      hair follicles ·      nerves ·      sebaceous glands ·      sudoriferous glands

* Dermal papillae – strong finger like structure that project into the undersurface of epidermis.

Meissners corpuscles – corpuscles of touch

Combination of collagen and elastic fibres in reticular region provides skin with

        #strength

       #extensibility – ability to stretch

         #elasticity

Striae – extreme stretching may produce small tears in the dermis

Epidermal ridges

Ø  downward projections of the epidermis into the dermis between the dermal papillae of the papillary region

·      

    *The surfaces of the palms, fingers, soles, and toes have a series of ridges and grooves.

• ·     They appear either as straight lines or as a pattern of loops and whorls, as on the tips of the digits.
• ·  These are produced during the third month of fetal development 

^increase the surface area of the epidermis

^ thus increase the grip of the hand or foot by increasing friction.

    Ø The epidermal ridge pattern is in part genetically determined and is unique for each individual.

Fingerprints (or footprints)

    Ø  Because the ducts of sweat glands open on the tops of the epidermal ridges as sweat pores,  

• ·      The sweat and ridges form fingerprints (or footprints) on touching a smooth object.

The study of the pattern of epidermal ridges is called dermatoglyphics

The Structural Basis of Skin Color

·      Three pigments that impart colors to skin.

1.   Melanin,

2.   hemoglobin, and

3.   carotene 

* The amount of melanin causes the skin’s color to vary   from pale yellow to reddish-brown to black.

^    number of melanocytes is about the same in all people

                                                       pheomelanin (yellow to red)

Two forms of melanin,  }

                                         eumelanin (brown to black)

Melanocytes, the melanin-producing cells, are most plentiful in the epidermis of the

         a. penis,

         b. nipples of the breasts,

         c. areolae

         d.  face, and limbs.

         e.  They are also present in mucous membranes.

In an organelle called a melanosome

                                     ↓

Melanocytes synthesize melanin from the amino acid tyrosine

                                     ↓

In the presence of an enzyme called tyrosinase.

      * Exposure to ultraviolet (UV) light increases the enzymatic activity within melanosomes and thus increases melanin production.

     * Melanin absorbs UV radiation

Exposing the skin to a small amount of UV light is actually necessary for the skin to begin the process of vitamin D synthesis. However, repeatedly exposing the skin to a large amount of UV light may cause skin cancer.

1.Freckles    - melanin accumulates in patches ·      genetically predisposed, ·      reddish or brown ·      tend to be more visible in the summer than the winter.

2.Age (liver) spots - accumulations of melanin as a person ages ·      These flat blemishes have nothing to do with the liver. ·      darker than freckles ·      range in color from light brown to black. ·      do not fade away during the winter months ·      are more common in adults over 40.

3. a nevus or a mole - A round, flat, or raised area that represents a benign localized overgrowth of melanocytes ·      usually develops in childhood or adolescence

4. Albinism - is the inherited inability of an individual to produce melanin. ·      Most have melanocytes that are unable to synthesize tyrosinase. ·      Melanin is missing from their hair, eyes, and skin. ·      This results in problems with vision and a tendency of the skin to burn easily on overexposure to sunlight

5. Vitiligo  - the partial or complete loss of melanocytes from patches of skin ·      produces irregular white spots. ·      The loss of melanocytes may be related to an immune system malfunction in which antibodies attack the melanocytes.

* Dark-skinned individuals have large amounts of melanin in the epidermis, so their skin color ranges from yellow to reddish-brown to black.

* Light-skinned individuals have little melanin in the epidermis. Thus, the epidermis appears translucent, and skin color ranges from pink to red depending on the oxygen content of the blood moving through capillaries in the dermis.

HEMOGLOBIN

·      The red color is due to hemoglobin

·       the oxygen-carrying pigment in red blood cells.

CAROTENE

·      *is a yellow-orange pigment that gives egg yolks and carrots their color.

·      *This precursor of vitamin A, which is used to synthesize pigments needed for vision,

·      is stored in the

•  stratum corneum and
•  fatty areas of the dermis and subcutaneous layer

-  in response to excessive dietary intake.

SKIN COLOR AS A DIAGNOSTIC CLUE

1.Cyanotic - When blood is not picking up an adequate amount of oxygen from the lungs, as in someone who has stopped breathing, the mucous membranes, nail beds, and skin appear bluish or cyanotic

2. Jaundice - is due to a buildup of the yellow pigment bilirubin in the skin. Ø This condition gives a yellowish appearance to the skin and the whites of the eyes, and usually indicates liver disease.

3. Erythema  - redness of the skin, Ø is caused by engorgement of capillaries in the dermis with blood due to skin injury, exposure to heat, infection, inflammation, or allergic reactions.

4. Pallor or paleness of the skin, may occur in conditions such as shock and anemia.

Tattooing is a permanent coloration of the skin in which a foreign pigment is deposited with a needle into the dermis.

Body piercing, the insertion of jewelry through an artificial opening,

Accessory Structures of the Skin

Hair, 

Skin glands         }     develop from the embryonic epidermis.

Nails

Hairs, or pili

Ø are present on most skin surfaces except

§  the palms,

§  palmar surfaces of the fingers,

§  the soles, and

§  plantar surfaces of the feet.

In adults, hair usually is most heavily distributed

§  across the scalp,

§  in the eyebrows,

§  in the axillae (armpits), and

§  around the external genitalia. 

Genetic and hormonal influences largely determine the thickness and the pattern of hair distribution.

* Hair on the head guards the scalp from injury and the sun’s rays.

*It also decreases heat loss from the scalp.

Anatomy of a Hair

Ø Each hair is composed of columns of dead, keratinized epidermal cells bonded together by extracellular proteins.

Parts Of A Hair

1. The shaft  - superficial portion of the hair,

Ø which projects above the surface of the skin

2. The root  - the portion of the hair deep to the shaft

Ø penetrates into the dermis, and sometimes into the subcutaneous layer. 

The shaft and root of the hair both consist of three concentric layers of cells:

                                                                    I.        inner medulla,

                    II.        cortex,

                  III.        cuticle 

Inner Medulla	which may be lacking in thinner hair	is composed of two or three rows of irregularly shaped cells	Pigment granules -        contain large amounts in dark hair, -        small amounts in gray hair -        lack of pigment granules and the presence of air bubbles in white hair.
Middle Cortex	forms the major part of the shaft	Consists of elongated cells.
Cuticle	the outermost layer,	consists of a single layer of thin, flat cells	that are the most heavily keratinized.

Hair Follicle

Ø Surrounding the root of the hair is the hair follicle

Ø
which is made up of

·      

     an external root sheath               together referred to as an

     an internal root sheath,      }       epithelial root sheath

external root sheath	downward continuation of the epidermis.
internal root sheath	produced by the matrix

The dense dermis surrounding the hair follicle - dermal root sheath.

BULB

Ø  Base of each hair follicle and its surrounding dermal root

sheath is an onion-shaped structure, the bulb (Figure 5.4c).

·      houses a nipple-shaped indentation, the papilla of the

hair,  which contains

-  areolar connective tissue and

-  many blood vessels that nourish the growing hair follicle.

·      also contains a germinal layer of cells called the hair matrix.

·      

   The hair matrix  cells arise from the stratum basale

·      Hence, hair matrix cells are responsible for the growth of existing hairs, and they produce new hairs when old hairs are shed.

Arrector Pili

·      a bundle of smooth muscle cells  associated with hairs

·      It extends from the superficial dermis of the skin to the dermal root sheath around the side of the hair follicle.

Goose Bumps” Or “Gooseflesh” ·      In its normal position, hair emerges at a less than 90° angle to the surface of the skin. ·      Under physiological or emotional stress, such as cold or fright, autonomic nerve endings stimulate the arrector pili muscles contract, which pulls the hair shafts perpendicular to the skin surface. 1. This action causes “goose bumps “or “gooseflesh” because the skin around the shaft forms slight elevations.

Hair Root Plexus

-        are dendrites of neurons Surrounding each hair follicle

·      which is sensitive to touch

·      generate nerve impulses if their hair shafts are moved.

Hair Growth

Each hair follicle goes through a growth cycle, which consists of

1.        growth stage,	Scalp hair  - for 2 -6  yrs
2.        regression stage,	for 2 to 3 weeks,
3.        a resting stage	for about 3 months.

·                                                                   Growth stage,  

                             ↓

1.Cells of the hair matrix divide.

·      As new cells from the hair matrix are added to the base of the hair root,

                              ↓

2.existing cells of the hair root are pushed upward and the hair grows longer.

·      While the cells of the hair are being pushed upward,

                                        ↓

      they become keratinized and die.

Following the growth stage is the regression stage,

·      when the cells of the hair matrix stop dividing,

                                     ↓

·      the hair follicle atrophies (shrinks), and

                                     ↓

·      the hair stops growing.

After the regression stage, the hair follicle enters a resting stage.

·      Following the resting stage, a new growth cycle begins.

·      The old hair root falls out or is pushed out of the hair follicle, and a new hair begins to grow in its place.

At any time, about 85% of scalp hairs are in the growth stage. Visible hair is dead, but until the hair is pushed out of its follicle by a new hair, portions of its root within the scalp are alive.

Chemotherapy is the treatment of disease, usually cancer, by means of chemical substances or drugs. ·      Chemotherapeutic agents interrupt the life cycle of rapidly dividing cancer cells. ·      Unfortunately, the drugs also affect other rapidly dividing cells in the body, such as the hair matrix cells of a hair. * It is for this reason that individuals undergoing chemotherapy experience hair loss. * Since about 15% of the hair matrix cells of scalp hairs are in the resting stage, these cells are not affected by chemotherapy. *Once chemotherapy is stopped, the hair matrix cells replace lost hair follicles and hair growth resumes.

·      Alopecia - the partial or complete lack of hair,

·      Hirsutism  - excessive body hair or body hair in areas that usually are not hairy in females or prepubertal males

Types of Hairs

·      Hair follicles develop at about 12 weeks after fertilization

·      Usually by the fifth month of development, the follicles produce very fine, nonpigmented, downy hairs called lanugo that cover the body of the fetus.

Terminal Hairs

·      Prior to birth, the lanugo of the eyebrows, eyelashes, and scalp are shed and

·      replaced by long, coarse, heavily pigmented hairs called terminal hairs.

Vellus Hairs

·      The lanugo of the rest of the body are replaced by vellus hairs commonly called “peach fuzz,”

·      which are short, fine, pale hairs that are barely visible to the naked eye.

In response to hormones (androgens) secreted at puberty,      *  terminal hairs replace vellus hairs in ·      the axillae (armpits) and pubic regions of boys and girls and ·       They replace vellus hairs on the face, limbs, and chests of boys, which leads to the formation of a mustache, a beard, hairy arms and legs, and a hairy chest.

*During adulthood, about 95% of body hair on males is terminal hair and 5% is vellus hair; 

^ on females, about 35% of body hair is terminal hair and 65% is vellus hair

Hair Color

The color of hair is due primarily to the amount and type of melanin in its keratinized cells.

Melanin is synthesized by

·      melanocytes scattered in the matrix of the bulb and

·      passes into cells of the cortex and medulla of the hair

Dark-colored hair	Contains mostly eumelanin (brown to black);
blond and red hair	Contain variants of pheomelanin (yellow to red).

Gray hair	progressive decline in melanin production	contains only a few melanin granules.
White hair	lack of melanin	the accumulation of air bubbles in the shaft.

Hair coloring is a process that adds or removes pigment

Skin Glands

•exocrine glands associated with skin

1.        •sebaceous (oil) glands
2.        •sudoriferous (sweat) glands,
3.        •ceruminous glands.
4.         •Mammary glands

Sebaceous Glands or oil glands

·      are simple, branched acinar (rounded) glands.

·      With few exceptions, they are connected to hair follicles

* The secreting portion of a sebaceous gland lies in the dermis and

* usually opens into the neck of a hair follicle.

*    In some locations, sebaceous glands open directly onto the surface of the skin. such as the

# lips,

#tarsal glands of the eyelids

#glans penis,

# labia minora, ,

 * Absent in the palms and soles,

 * are small in most areas of the trunk and limbs,

* but large in the skin of the

#face,

# neck,

# breasts,

# superior chest

·      During childhood, sebaceous glands are relatively small and inactive.

·      At puberty, androgens from the testes, ovaries, and adrenal glands stimulate sebaceous glands to grow in size and increase their production of sebum

*Sebaceous glands secrete an oily substance called sebum

            a mixture of

# triglycerides,

#cholesterol,

# proteins, and

# inorganic salts.

Functions of sebum

1. Sebum coats the surface of hairs and

2. helps keep them from drying and becoming brittle.

3. also prevents excessive evaporation of water from the skin,

4. keeps the skin soft and pliable, and

5. inhibits the growth of some (but not all) bacteria.

Acne is an inflammation of sebaceous glands that usually begins at puberty

sudoriferous glands	sweat glands
Sebum	Sweat / perspiration
triglycerides, cholesterol, proteins, inorganic salts.	ammonia, urea, uric acid, water, ions, glucose, lactic acid
Simple branched acinar glands	Simple coiled tubular glands

Sudoriferous Glands

There are three million to four million sweat glands, or sudoriferous glands  in the body.

·      The cells of these glands release sweat, or perspiration, into hair follicles or onto the skin surface through pores.

Sweat glands are divided into two main types,

·     1.  eccrine            }     based on their structure

·     2. apocrine,              and type of secretion.

	Eccrine sweat glands	Apocrine sweat glands
	much more common than apocrine sweat glands	have larger ducts and lumens than eccrine glands
Distribution	throughout the skin of most regions of the body, especially in the skin of the forehead, palms, and soles.	Mainly in the skin of the axilla ,groin, areolae of the breasts, bearded regions of the face in adult males
are not present,	in the margins of the lips, nail beds of the fingers and toes, eardrums.    glans penis, glans clitoris, labia minora
The secretory portion is located	mostly in the deep dermis (sometimes in the upper subQ  layer).	located in the lower dermis or upper subcutaneous layer,
The excretory duct projects through	ends as a pore at the surface of the epidermis	opens into hair follicles
sweat	-        Less viscous -        ammonia, urea, uric acid, water, ions, glucose, lactic acid	-        appears milky or     yellowish in color -        plus lipids and proteins -        odorless.
Start function	soon after birth,	do not    begin to function until puberty
functions	1. thermo regulatory sweating. -        sweat first forms on the forehead and scalp -        then extends to the rest of the body, forming last on the palms and soles.	are not active during    thermoregulatory sweating and, therefore, do not play a role in thermoregulation.
	2.a small role in eliminating wastes such as urea, uric acid, and ammonia from the body.	secrete sweat during sexual activities
	3.emotional sweating or a cold sweat. -        first occurs on the palms, soles, and axillae and -        then spreads to other areas of the body	active during emotional sweating

Body Odor - when apocrine sweat interacts with bacteria on the surface of the skin,

                              ↓

the bacteria metabolize its components,

                              ↓

causing apocrine sweat to have a musky odor that is often referred to as body odor.

Insensible Perspiration

-        Sweat that evaporates from the skin before it is perceived

as moisture

Sensible Perspiration

-        Sweat that is excreted in larger amounts and is seen as moisture on the skin 

Ceruminous Glands

ceruminous            glands	Modified sweat glands in the external ear
secretory portions	lie in the subcutaneous layer, deep to sebaceous  glands.
Their excretory         ducts	open either directly onto the surface of the external auditory canal (ear canal)     or into ducts of sebaceous glands.
Cerumen or earwax.	·      The combined secretion of the ceruminous and sebaceous glands is a yellowish material ·      produce a waxy lubricating secretion.
functions	Cerumen, together with hairs in the  external auditory canal,    ·      provides a sticky barrier that impedes the entrance of foreign bodies and insects.   ·      waterproofs the canal and   ·      prevents bacteria and fungi from       entering cells.

Impacted Cerumen         Some people produce an abnormally large amount of cerumen in the external auditory canal.         If it accumulates until it becomes impacted (firmly wedged),  → sound waves may be prevented from reaching the eardrum

Nails

        are

            ·      plates of tightly packed, hard, dead, keratinized epidermal cells

            ·      that form a clear, solid covering over the dorsal surfaces of the distal portions of the digits.

Each nail consists of

         1. A Nail Body,

         2. A Free Edge, And

         3. A Nail Root

Nail Body, (plate)	Free edge	Nail root
·      is the visible portion of the nail.	is the part of the nail body that may extend past the distal end of the digit.	is the portion of the nail that is buried in a fold of skin.
·      It is comparable to the stratum corneum of the epidermis of the skin, with the exception that its flattened, keratinized cells fill with a harder type of keratin and the cells are not shed.
Below the nail body is a region of epithelium and a deeper layer of dermis.
Most of the nail body appears pink because of blood flowing through the capillaries in the underlying dermis.	The free edge is white because there are no underlying capillaries.
The whitish, crescent-shaped area of the proximal end of the nail body is called the lunula	Beneath the free edge is a thickened region of stratum corneum called the hyponychium
It appears whitish because the vascular tissue underneath does not show through due to a thickened region of epithelium in the area.	which secures the nail to the fingertip.

Nail Bed

·      is the skin below the nail plate that extends from

the lunula to the hyponychium.

·      The epidermis of the nail bed lacks a stratum granulosum.

 Eponychium  or cuticle

·      is a narrow band of epidermis

·      thatextends from and adheres to the margin (lateral  border) of the nail wall.

·      It occupies the proximal border of the nail and

·      consists of stratum corneum.

Nail Matrix

      ·      The portion of the epithelium proximal to the nail root

      ·      The superficial nail matrix cells divide mitotically to produce new nail cells.

      ·      The growth rate of nails is determined by the rate of mitosis in matrix cells, which is influenced by factors such as

             -        age of  person,

             -        health, and

             -        nutritional status.

Nail growth

·      also varies according to

-        the season,

-        the time of day, and

-        environmental temperature.

·      The average growth in the length of fingernails is about 1 mm (0.04 in.) per week.

·      The growth rate is somewhat slower in toenails.

·      The longer the digit the faster the nail grows.

Functions Of Nail

1. They protect the distal end of the digits.

2. They provide support and counter pressure to the palmar surface of the fingers to enhance touch perception and manipulation.

3. They allow us to grasp and manipulate small objects, and they can be used to scratch and groom the body in various ways.

Functions of the Skin

1.Thermo regulation	a. by liberating sweat at its surface b. by adjusting the flow of blood in the dermis
2. Blood Reservoir	The dermis houses an extensive network of blood vessels
3. Protection	§  Keratin - protects underlying tissues from microbes, abrasion, heat, and chemicals,   §  keratinocytes  - resist invasion by microbes.   §  Lipids released by lamellar granules ·      inhibit evaporation of water from the skin surface, ·      thus guarding against dehydration; ·      they also retard entry of water across the skin surface during showers and swims. §  The oily sebum from the sebaceous glands keeps skin and hairs from drying out and contains bactericidal chemicals §  The acidic pH of perspiration  - retards the growth of some microbes. The pigment melanin  - helps shield against the damaging effects of ultraviolet light.
4. Cutaneous Sensations	are sensations that arise in the skin, including    ·      tactile sensations—touch, pressure, vibration, and tickling—as well as    ·      thermal sensations such as warmth and coolness.    ·      pain, usually is an indication of impending or actual tissue damage. ·      There is a wide variety of nerve endings and receptors distributed throughout the skin, including   §  the tactile discs of the epidermis,   §  the corpuscles of touch in the dermis, and hair root plexuses around each hair follicle.
5. Excretion and Absorption	Excretion ·      removing water and heat from the body, ·      excretion of small amounts of salts, carbon dioxide, ammonia and urea. Absorption   ·      fat-soluble vitamins (A, D, E, and K),   ·      certain drugs,   ·      the gases oxygen and carbon dioxide   ·      Toxic materials include * organic solvents such as acetone (in some nail polish removers) and * carbon tetrachloride(dry-cleaning fluid); * salts of heavy metals such as lead, mercury, and arsenic; and * the substances in poison ivy and poison oak.
6. Synthesis of Vitamin D	·      requires activation of a precursor molecule in the skin by ultraviolet (UV) rays in sunlight.                                ↓ ·      Enzymes in the liver and kidneys then modify the activated molecule,                               ↓ Finally producing calcitriol, the most active form of vitamin D. (Only a small amount of exposure to UV light (about 10 to 15 minutes at least twice a week) is required for vitamin D synthesis)

Two types of cells carry out protective functions that are immunological in nature.

Intraepidermal  macrophage

- alert the immune system to the presence of potentially harmful microbial invaders by recognizing and processing them,

Macrophages in the dermis

                                              - phagocytize bacteria and viruses that manage to bypass the intraepidermal macrophages of the epidermis.

Since topical (applied to the skin) steroids, such as cortisone, are lipidsoluble, ü They move easily into the papillary region of the dermis. ü Here, they exert their anti-inflammatory properties by inhibiting histamine production by mast cells Certain drugs that are absorbed by the skin may be administered by applying adhesive patches to the skin

Thermoregulation

In response to high environmental temperature or heat produced by exercise,        §  sweat production from eccrine sweat glands increases;    §  the evaporation of sweat from the skin surface helps lower body temperature.   §  blood vessels in the dermis of the skin dilate    §  consequently, more blood flows through the dermis,   §  which increases the amount of heat loss from the body

In response to low environmental temperature,   §  production of sweat from eccrine sweat glands is decreased,    §  which helps conserve heat.           §  Also, the blood vessels in the dermis of the skin constrict (become narrow),    §  which decreases blood flow through the skin        §  reduces heat loss from the body. And, skeletal muscle contractions generate body heat.