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Membranes. -many body structures and surfaces are covered with membranes -superficial sheet of epithelial cells + underlying connective layer. -cover & protect. -four types:. 1. serous. 2. mucous. 3. cutaneous. 4. synovial. 1. Serous membranes.

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-many body structures and surfaces are covered with membranes

-superficial sheet of epithelial cells + underlying connective layer

-cover & protect

-four types:

1. serous

2. mucous

3. cutaneous

4. synovial


1. Serous membranes

-line the subdivisions of the abdominopelvic cavity and thoracic cavity

-covers, protects and moistens/lubricates

-comprised of an epithelial layer (simple squamous epithelium) called a mesothelium + underlying loose areolar connective tissue

-the mesothelium secretes a watery fluid = serous fluid (separates and lubricates the movement of organs)

-divided into two separate layers: 1)outer parietal layer - lines the cavity

2) inner visceral layer - covers organs

-serous membrane lining the pleural cavity (lungs) = pleura

- serous membrane lining the pericardial cavity (heart) = pericardium

- serous membrane lining the peritoneal cavity (abdomen) = peritoneum


2. Mucous membranes

-line cavities that directly communicate with the exterior environment

e.g. respiratory, urinary, reproductive, digestive

-covers, protects and moistens/lubricates

-epithelial layer (simple squamous, simple cuboidal, simple columnar) is kept

moist through production of mucus by glands, other glandular secretions or

exposure to fluids (e.g. urine)

-in areas of physical stress = stratified epithelial tissue rather than simple

-connective tissue layer is loose areolar tissue = lamina propria

--supports embedded blood vessels and nerves


3. Synovial membranes

-extensive areas of areolar connective tissue covered by incomplete layers of simple squamous or cuboidal epithelial cells

-lines & lubricates the synovial joint cavity - to permit easy movement of bones

-the epithelium differs from others: 1) there is no basal lamina

2) incomplete cellular layer - gaps between cells

3) derived from macrophages and from the surrounding connective tissue

-some cells within this membrane are phagocytic to remove pathogens

-others are secretory - secrete a watery synovial fluid for lubrication


4. Cutaneous membrane (skin)

-covers the surface of the body

-epithelial layer (keratinized stratified squamous)

-underlying areolar tissue reinforced with dense connective tissue


Integumentary System (Skin)

  • skin covers the entire body surface

  • -including the anterior surface of the eye!

  • -covers ~ 22 square feet

  • -about 16% of total body weight

  • skin turns in at the mouth, nasal cavity, anus and urethral and vaginal

  • openings – meets the mucous membranes lining these cavities

  • comprised of all four tissues:

  • 1. epithelium – lines the surface

  • 2. connective – provides strength & resiliency

  • 3. muscle – smooth muscle controls blood vessel diameter

  • and controls movement of hairs

  • 4. nervous – provides sensation and controls SM



1. physical protection: protection from microbes, abrasion, heat

2. chemical protection – keratin - dryness of the epidermis; salt of sweat

3. regulation of water exchange: by sweating

4. regulation of body temperature: thermoregulation

-by sweating & adjusting blood flow through the dermis

5. excretion of wastes -by sweating

6. nutrition – synthesis of vitamin D precursor

-activated in skin, converted to calcitrol in liver

7. sensation: touch, pressure, vibration, pain & thermal

8. immune defense: Langerhans cells of the epidermis


-two major components:

1. cutaneous membrane = skin (epidermis, dermis)

2. accessory structures = hair, nails, exocrine glands



-stratified squamous epithelium - 5 layers maximum

-four types of cells:

1. keratinocytes – make up the majority of the epidermis

-epithelial cells that synthesize the protein keratin

2. melanocytes – cells for the synthesis of the light absorbing pigment melanin

3. Merkel cells – neurons that detect pressure

4. Langerhans cells – immune responses


Epidermis: layers

- stratum germinativum:

-inner most/deepest layer of the epidermis

-also called stratum basale becauseit attaches firmly to the basal lamina or basement membrane found between

the epithelium and connective tissues of the dermis

- contain basal stem cells that differentiate into the keratinocytes and melanocytes of the epidermis

-Merkel cells are found in hairless regions

-pressure and touch receptors of the skin


Epidermis: layers

- stratum spinosum:

-called the “spiny layer” because of histological appearance following chemical treatment

-keratinocytes of the stratum basale migrate into this layer

-several layers thick

-keratinocyotes interconnected by bundles of protein filaments called tonofibrils –connect neighbouring keratinocytes together

-act as cross braces providing strength

-cells can divide - division of cells within this layer increases thickness

-melanocytes are common

-Langerhans cells also found – in the more superficial layers of this layer

-initiate immune responses to pathogensand to cancer


Epidermis: layers

-stratum granulosum:

-made up of keratinocytes migrating up from the stratum spinosum

-cells synthesize large quantities of proteins (including keratin) – cytoplasm appears


-the granules = keratohyalin granules

-these granules surround the keratin filaments as they develop

-as keratin is made – keratinocytes become thinner and flatter

-the cells then die and dehydrate

-creates layers of interlocking keratin “sandwiches”


Epidermis: layers

stratum lucidum:

-covers the Str. Gran.

-flattened, densely packed cells filled with


-have a glassy appearance because they do not

stain well

-present only in the skin of fingertips, palms &




Epidermis: layers

- stratum corneum:

-cornu = horn

-makes up surface of both thick and thin skin

-15-30 layers of flattened, dead, interlocking cells

-large amounts of keratin are present – the tissue is said to be “cornified”

-covered in secretions from dermal glands to help moisturize the outer layer

-but keratin makes this layer water-resistant - very dry

– prevents growth of microorganisms

-most of this layer is also hydrophobic

-penetration is promoted by attachment to a lipid or dissolution in a lipid-based solution

-transdermal drug patches – drugs are in oils or lipid-soluble carriers

- moisturizing lotions – only penetrate few first layers of corneum

-takes 15-30 days to move from germinativum to corneum

-cells will remain in corneum for an additional 2 weeks before being shed



-two major components:

1. papillary layer

2. reticular layer

Papillary Layer

-about 1/5th thickness of dermis

-loose areolar connective tissue + elastic


-contains capillaries for blood supply

& sensory nerve endings

-dermal projections into the epidermis

= papillae (papilla – “nipple-shaped mound)

-some papillae contain Meissner’s

corpusclesfor touch

-also free nerve endings – project into the

epidermis - sensations of pain, warmth, itching

Reticular Layer (“little net”)

-dense irregular connective – interwoven

collagen bundles plus elastic fibers

-contains blood vessels, nerves,

hair follicles, sweat glands and

sebaceous/oil glands

-also contains lamellated corpuscles

(Pacinian corpuscles) that detect deep

touch and pressure


Fingerprints: epidermal ridges

-formed from the stratum germinativum

-extends down into the dermis

-formed by the connections between dermal papillae and the epithelium

-the contours of the skin follow these ridge patterns = fingerprints

-function to increase the SA of the skin and increase friction


Skin colour

  • dermal blood supply:

  • - hemoglobin bound to O2 – bright red in color

    • -gives pinkish cast to skin

    • -when hemoglobin lacks O2 – bluish colour

    • -this bluish skin colour = “cyanosis”

    • -the thin skin of the lips and transparency of the nail enables us to see the blood in the peripheral circulation = red lips and pink nails

  • -dermal blood supply comes from the larger blood vessels found in the subcutaneous layer (located under the dermis)

  • -these larger vessels branch to form a cutaneous plexus (plexus = network) - this supplies the reticular layer

  • vessels continue up and branch further into the papillary plexus - found in the dermal papillae

  • -blood is drained out of the papillae by tiny veins = venules

  • -these drain into the larger veins of the dermis -> which then drain into the SQ layer


Skin colour

2. pigmentation – two pigments: carotene and melanin

-carotene = orange, yellow colour

-derived from vitamin A

-can be converted back to vitamin A in the skin

- required for epithelial maintenance & the synthesis of visual pigment (rhodopsin)

-carotene accumulates in keratinocytes

-yellow color is very evident in the stratum corneum


-melanin = dark brown, black colour

-synthesized from the amino acid tyrosine

-melanin absorbs UV light and prevents damage to the keratinocytes of skin

-melanin production stimulated by UV light

-produced by the melanocytes of the epithelium

-forms in intracellular vesicles = melanosomes

-melanosomes are secreted out of the cells = melanin is transferred into


-Caucasians: transfer occurs to keratinocytes only in the Str. germ. and spinosum-Blacks: larger melanosomes

-transfer also occurs in the Str. granulosum

-darker pigmentation results

-more active melanocytes – NOT more in number!


Wrinkles: reduction in the thickness of the dermis

-loss of collagen in the dermal reticular layer

-loss in dermal flexibility = wrinkles and sagging



Scars: from greek word schara (place of fire)

-damaged dermis is replaced with tissue of inferior quality and rich in collagen

-scars do not have sweat or oil glands and do not have hair

-redness of the scar is due to inflammation and is not permanent

- two common types:

1. hypertropic (red and raised, do not grow beyond boundaries of original


2. keloid – permanently growing scars

– can lead to benign tumors

- more common in darker skin, common on chest and shoulders

Stretch marks: extensive and quick distortion of the dermis damages it

-no recoil of skin after stretching

-leads to breaking of elastic and collagen fibers in the dermis

- replaced with new, poorly organized collagen

Retin-A (tretinoin) : increases blood flow to the dermis

-promotes dermal repair

-decreases wrinkles and stretch marks


Subcutaneous layer

-also referred to as the hypodermis or superficial fascia

-connects the skin to underlying muscles

or other organs

-made up of:

1. loose connective tissue

2. adipose tissue - “baby fat”

- also contains elastic fibers for flexibility

-fat content helps reduce heat loss

-fat distribution changes with age and gender:

-males – neck, upper arms, abdomen and lower back

-females – breasts, abdomen, buttocks, hips and thighs

-contains large arteries and veins – supply the dermal plexuses with blood

-the superficial layers of the hypdermis are the sites for drug injections - hypodermic


Accessory Structures

Hair follicles

Sweat glands

Sebaceous/Oil glands



Hair & Hair follicles

  • over all epidermal surfaces except soles of feet, palms of hand, sides of fingers and toes and portions of external genitalia

  • approx. 5 million hairs on the body

  • formed in hair follicles

  • Comprised of three major regions:

  • 1. Hair bulb – contains the living, hair

  • papilla

  • 2. Hair root – site of connection with

  • arrector pili (smooth muscle) and a

  • sebaceous gland

  • 3. Hair shaft – portion of the hair above the sebaceous gland

  • -portion of it is exposed above the skin


Hair structure

-hair papilla – found at the base of the hair within the hair bulb

-contains the stem cells of the hair = hair matrix

-also contains capillaries and sensory nerves for touch

-epithelial tissue surrounding the matrix make up the hair bulb

-hair root: projects up from the hair bulb

-surrounded and protected by a hair follicle

-site of attachment of arrector pili smooth muscle (pulls hair upright for better sensation)

-continues above the sebaceous gland as the hair shaft – also exposed above the surface of the skin


Hair Production

-hair production = specialized keratinization

-hair is produced from the hair matrix – epithelial layer similar to stratum basale (contains living cells of the hair - many are stem cells)

-keratinocytes differentiate within the matrix – cells immediately produce the keratin of hair

-keratin forms into an outer cortex and inner medulla

-cortex – hard keratin - stiffness

-medulla – soft keratin – flexible

-single layer of dead cells encloses the cortex of the hair = cuticle

-within the dermis – hair is enclosed in a protective follicle (made also by the hair matrix



-found in the dermis surrounding the hair

-often rooted in SQ layer

-wall is comprised of four layers:

1. internal root sheath: surrounds the root & deeper portion of


-produced by the cells of the hair matrix

2. external root sheath: runs continuously from the hair bulb to the skin surface to

enclose the hair

3. glassy membrane: thickened basement membrane between external root sheath and

the connective tissue sheath

4. connective tissue sheath


Exocrine Glands

  • secretions are discharged out onto the surface of the epithelium that lines

  • body cavities or out onto the skin

  • many exocrine glands secrete to the exterior via tubes called ducts

  • exocrine secretions:

  • 1. perspiration

  • 2. digestive enzymes

  • 3. milk

  • 4. mucous

  • 5. oil

Exocrine glands

Exocrine glands

  • you can classify exocrine glands many ways

  • one way – by the consistency of what they secrete

    • e.g. serous

  • another way – by their structure

    • e.g. multicellular

  • last way – by the mode of secretion

    • e.g. holocrine


  • exocrine gland types – consistency of secretion:

  • 1. serous - watery fluid that contains enzymes

  • e.g. saliva – parotid salivary gland

  • 2. mucous - glycoproteins called mucins that absorb water to form a

  • slippery mucus

  • e.g. sublingual salivary gland

  • 3. mixed - more than one type of gland cell

  • -produces different types of secretions - mucus and serous

  • e.g. submandibular salivary gland


  • exocrine gland structure:

  • Unicellular are single-celled glands

  • e.g. goblet cells

  • Multicellular glands

    • -two characteristics to classify:

      • shape of the secretory portion

      • branching pattern of the duct

    • -simplest multi-cellular gland is a secretory sheet

      • secrete into a compartment

      • e.g. gastric epithelium


Modes of Secretion: Exocrine glands

  • merocrine:

  • -contents are released through exocytosis


2. apocrine: loss of cytoplasm from the apical portion of the cell together with secretory product

e.g. milk secretion


3. holocrine: results in death of gland cell

-entire cell fills with secretory product and then bursts

e.g. sebaceous glands associated with hair follicles


Skin glands

1. Sweat/Sudoriferous – of the serous type

2. Oil/Sebaceous – of the mucus type

3. Wax/ Ceruminous

Sebaceous glands/Holocrine glands

-”sebace” = greasy

-secreting portion is within the dermis

-most open onto hair follicles

-glands located at the lips, glans penis, labia minora and eyelids - open

directly to the skin surface

-absent on palms and soles

-large in size and numbers on breast, face, neck and upper chest


  • sebaceous glands secrete an oily substance = sebum

  • acne = inflammation of a sebaceous gland due to the presence of bacteria

    • may cause a cyst or sac of connective tissue to form which destroys epithelial cells

    • known as cystic acne


Sudoriferous Glands

  • 3 to 4 million glands in the body

  • sudori = sweat, ferous = bearing

  • released by exocytosis into hair follicles or onto the skin surface

  • two main types:

  • 1. Merocrine sweat glands (eccrine)

    • simple, coiled tubular glands - serous

    • secretion through exocytosis

    • found throughout the skin, PLUS margins of lips, nail beds, glans penis and clitoris

    • most numerous in forehead, palms and soles

    • secretory portion is located in the reticular layer of dermis

    • ends as a pore in the skin

    • main function is to regulate body temperature through evaporation

    • also functions in waste elimination

    • thin, watery perspiration - about 600 ml per day

      • -water, sodium, chloride, urea, uric acid, ammonia, glucose, amino acids

      • -perspiration can be: a. insensible - evaporates before being perceived

      • b. sensible - larger amounts, can be seen and felt


  • Apocrine sweat glands

  • makes odorous secretion - secretions are slightly more viscous than merocrine

  • simple, coiled tubular glands – secretory portion in hypodermis

  • skin of axilla (armpit), groin, areolae, bearded region of face in males

  • released by a portion of the cell breaking off and disintegrating

  • secretory portion located in SQ layer - opens onto a hair follicle

  • same components as sweat + lipids and proteins

  • do not function until after puberty

Sudoriferous gland – merocrine/apocrine


  • Mammary glands

    • Large, complex apocrine sweat glands

  • Ceruminous glands

    • modified sweat glands

    • in ear canal

    • secretory portion is in the SQ layer, deep to sebaceous glands

    • secrete either directly into the ear canal or into the ducts of

    • the sebaceous glands

    • produce waxy cerumin - together with the hairs of the canal

    • provides protection

Nail anatomy

Nail Anatomy

  • Nail body:visible

    • free edge projects beyond digit

    • pink due to blood flow

    • proximal end is white crescent

    • called a lunula-thickened str. basale

  • hyponychium: secures the nail to the finger

  • Nail root:

    • -production of nail

    • -buried in a fold of skin

    • -deep to the root = nail matrix

  • Cuticle (eponychium)

    • -fold of stratum corneum

    • -adheres nail to the lateral borders of the nail wall

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