Nature and Function of the Integument

• The outer covering of the body of vertebrates

• Commonly referred to as SKIN– Includes the mucous membrane lining of

the mouth, eyelids, nostrils and the openings of rectum and urogenital organs.

– Forms the interface between organisms and the external environment.

• It consists of two layers:– An outer epidermis – Inner dermis

• Between then epidermis and dermis lies the basement membrane (basal lamina and reticular lamina)

– Basement membrane – underlying support where epithelial cells are rested. It demarcates the underlying connective tissue from epithelium.

– Basal Lamina - Membrane proteins of the epithelial cells are anchored in the basal lamina. The major 2 glycoproteins - LAMININ and Type IV COLLAGEN

– Reticular Lamina - Reticular fibers embedded in ground substance that connect the basal lamina with the underlying CT. It is synthesized by cells of the

– The basal lamina acts as a selectively permeable filter between epidermis and dermis connective tissue.

• It consists of two layers:– An outer epidermis – Inner dermis

• Between then epidermis and dermis lies the basement membrane (basal lamina and reticular lamina)

– Basement membrane – underlying support where epithelial cells are rested. It demarcates the underlying connective tissue from epithelium.

– Basal Lamina - Membrane proteins of the epithelial cells are anchored in the basal lamina. The major 2 glycoproteins - LAMININ and Type IV COLLAGEN

– Reticular Lamina - Reticular fibers embedded in ground substance that connect the basal lamina with the underlying CT. It is synthesized by cells of the

– The basal lamina acts as a selectively permeable filter between epidermis and dermis connective tissue.

• Under the dermis lies a subcutaneous tissue or hypodermis that is made up of very loose connective and adipose tissue

• Varies in different regions of the body, in different individuals, different ages and different groups of vertebrates

• Under the dermis lies a subcutaneous tissue or hypodermis that is made up of very loose connective and adipose tissue

• Varies in different regions of the body, in different individuals, different ages and different groups of vertebrates

Hypodermis

Structure of skin

Dermis

Dermal-epidermal junction

Epidermis

Epithelial tissue•stratifiedsquamous(keratinized)

Basementmembrane•glue-like layer

Connective tissue•dense, fibrousconnective tissue•blood vessel, nerves, etc.

Areolar & adipose tissue•superficial fascia•subcutaneous tissue

Functions of the Skin• Keeps water and other substances in a

controlled passage.• Protective barrier from mechanical, chemical,

bacterial, UV and thermal damages, and dessication (keratinocytes, glycolipids, melanocytes, wandering cells, cutaneous (skin) receptors).

• Cutaneous receptors: touch, pressure, temperature & pain

• Controls body temperature (heat loss or heat retention) Insulation & cushions underlying organs.

• Excretion of urea & uric acid through sweat.• Synthesizes vitamin D (conversion of

cholesterol Vit D

• Keeps water and other substances in a controlled passage.

• Protective barrier from mechanical, chemical, bacterial, UV and thermal damages, and dessication (keratinocytes, glycolipids, melanocytes, wandering cells, cutaneous (skin) receptors).

• Cutaneous receptors: touch, pressure, temperature & pain

• Controls body temperature (heat loss or heat retention) Insulation & cushions underlying organs.

• Excretion of urea & uric acid through sweat.• Synthesizes vitamin D (conversion of

cholesterol Vit D

Embryonic Origin and Development

• Epidermis – arises from ectoderm– S. germinativum – attached to

basement membrane, it actively cell divides to replenish the outer periderm.

– Epidermis differentiates into stratified layer with mucous or keratin coat on the outer surface (prevents dessication)

• Epidermis – arises from ectoderm– S. germinativum – attached to

basement membrane, it actively cell divides to replenish the outer periderm.

– Epidermis differentiates into stratified layer with mucous or keratin coat on the outer surface (prevents dessication)

• Dermis origin varies…– Dermatome – principal origin, from the

outer wall of dermomyotome of somites.– Connective tissue layer of the

dermis – from dermatome that settles under the epidermis. Some species may have stratum compactum that have diffuse, irregular collagen bundles.

• Hypodermis – beneath the dermis– Forms the fascia composed of loose

connective tissue and adipose tissue.

• Dermis origin varies…– Dermatome – principal origin, from the

outer wall of dermomyotome of somites.– Connective tissue layer of the

dermis – from dermatome that settles under the epidermis. Some species may have stratum compactum that have diffuse, irregular collagen bundles.

• Hypodermis – beneath the dermis– Forms the fascia composed of loose

connective tissue and adipose tissue.

Layers of the Skin

Layers…….• Skin is composed of

three primary layers: 1. epidermis which

provides waterproofing and serves as a barrier to infection;

2. dermis which serves as a location for the appendages of skin; and the

3. hypodermis (subcutaneous adipose layer), which is called the basement membrane.

• Skin is composed of three primary layers: 1. epidermis which

provides waterproofing and serves as a barrier to infection;

2. dermis which serves as a location for the appendages of skin; and the

3. hypodermis (subcutaneous adipose layer), which is called the basement membrane.

Epidermis

• The epidermis is composed of epithelial cells derived from the ectoderm.

• Serves as the interface between the organisms and the environment

• In aquatic vertebrates, covered by a thin coat of mucus and contains unicellular glands.

• In terrestrial vertebrates, covered by a layer of dead, water resistant cornified cells, the stratum corneum and contains multicellular glands.

• The epidermis is composed of epithelial cells derived from the ectoderm.

• Serves as the interface between the organisms and the environment

• In aquatic vertebrates, covered by a thin coat of mucus and contains unicellular glands.

• In terrestrial vertebrates, covered by a layer of dead, water resistant cornified cells, the stratum corneum and contains multicellular glands.

EpidermisEpidermis•Made up of stratified squamous layer of epithelial cells.Layers:1.Stratum corneum- outermost; composed of dead cells; keratinized

- keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out, making skin a natural barrier to infection.

2. Stratum lucidum- translucent layer, composed of flat, dead and non-nucleated cells.

3. Stratum granulosum- composed of keratohyaline granules

4. Stratum spinosum- prickle cell layer; composed of Langerhans cells.

5. Stratum germinativum (basale)- inner layer, composed of actively dividing cells

Epidermal cells

• The main type of cells which make up the epidermis are :– Keratinocytes- 90% of epidermal cells;

produce keratin.– Melanocytes- 8 % of epidermal cells;

produce melanin – Langerhans cells- capable of trapping

antigen in the skin.– Merkel cells- make contact with the

ending of a sensory neuron.

Dermis• The dermis lies below the epidermis

and contains a number of structures including blood vessels, nerves, hair follicles, smooth muscle, glands and lymphatic tissue.

• It consists of loose connective tissue otherwise called areolar connective tissue - collagen, elastin and reticular fibers are present.

• Provides tensile strength, and physiologic support for the interfacing epidermis

• Has an ancient and persistent potential to form bone

Hypodermis or Subcutaneous tissue

– Deep to dermis, abundant adipose tissue

– Considered not part of the skin but as anchorage to underlying organs

– “Shock absorber” & insulates the deep tissues from extreme temperature changes outside the body.

– Accounts for “curves” of the woman than man.

– Deep to dermis, abundant adipose tissue

– Considered not part of the skin but as anchorage to underlying organs

– “Shock absorber” & insulates the deep tissues from extreme temperature changes outside the body.

– Accounts for “curves” of the woman than man.

Subcutaneous Layer• The hypodermis is not part of the skin, and

lies below the dermis.• Its purpose is to attach the skin to

underlying bone and muscle as well as supplying it with blood vessels and nerves.

• It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat).

• Fat serves as padding and insulation for the body.

• The hypodermis is not part of the skin, and lies below the dermis.

• Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves.

• It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat).

• Fat serves as padding and insulation for the body.

Chromatophores (Pigment)

• Provides concealing coloration to the integument

• Occurs in certain cells in a form of small granules contained in chromatophores (pigment-bearing cells)– Greatest amount of color is exhibited when

pigment granules are dispersed throughout the cell.

– Less amount of color is exhibited when pigment granules are concentrated about the nucleus.

• Provides concealing coloration to the integument

• Occurs in certain cells in a form of small granules contained in chromatophores (pigment-bearing cells)– Greatest amount of color is exhibited when

pigment granules are dispersed throughout the cell.

– Less amount of color is exhibited when pigment granules are concentrated about the nucleus.

• Various colors maybe produced by combinations of different chromatophores and by different degrees of dispersion of pigment granules.

• Skin color also depends on the background color of the stratum germinativum

• Some vertebrates have the ability to change color(metachrosis/metachromatosis), controlled by the endocrine and the nervous system

• Various colors maybe produced by combinations of different chromatophores and by different degrees of dispersion of pigment granules.

• Skin color also depends on the background color of the stratum germinativum

• Some vertebrates have the ability to change color(metachrosis/metachromatosis), controlled by the endocrine and the nervous system

Types of Chromatophores1. Melanophores• Pigment cell that ranges from yellow, brown to

black.• Chiefly found in S. basale• Melanin protects the chromosomes of mitotically

active basal cells against light-induced damage.• Pigmentation is not just under the control of light.

Hormones produced by the pituitary and the adrenal glands also affect pigmentation. Diseases of these two endocrine organs often result in changes of pigmentation of the skin.

• Although melanocytes are also ectodermal in origin, they are derived exclusively from the neural crest of the embryo, from where they migrate to all other parts of the body.

• Basal cells phagocytize the pigment as it accumulates them especially when skin is exposed to sun.

• FRECKLES OR MOLES – seen where melanin is concentrated in one spot.

1. Melanophores• Pigment cell that ranges from yellow, brown to

black.• Chiefly found in S. basale• Melanin protects the chromosomes of mitotically

active basal cells against light-induced damage.• Pigmentation is not just under the control of light.

Hormones produced by the pituitary and the adrenal glands also affect pigmentation. Diseases of these two endocrine organs often result in changes of pigmentation of the skin.

• Although melanocytes are also ectodermal in origin, they are derived exclusively from the neural crest of the embryo, from where they migrate to all other parts of the body.

• Basal cells phagocytize the pigment as it accumulates them especially when skin is exposed to sun.

• FRECKLES OR MOLES – seen where melanin is concentrated in one spot.

• 2. Lipophores– Carotenoids (yellow, orange, red

pigments)– Xanthophores – yellow– Erythrophores – red

• 3. Iridophores or Guanophores– Causes iridiscence in vertebrates (fishes)– Contains guanin (purine) crystals

B. Glandular epithelium

• From S. germinativum (epidermis)• Exocrine glands – have ducts directly

empties onto epithelium.Types of glands as to composition:• Unicellular G.

– Single-celled mucus-secreting glands• Multicellular G.

– Growth of s. germinativum (epidermis) into dermal region

• From S. germinativum (epidermis)• Exocrine glands – have ducts directly

empties onto epithelium.Types of glands as to composition:• Unicellular G.

– Single-celled mucus-secreting glands• Multicellular G.

– Growth of s. germinativum (epidermis) into dermal region

Types of Unicellular gland (basis: shape)

• 1. Club cells– Elongated, binucleated (amphibians)– Secretes mucus– May contain chemicals that stimulates alarm or fear– Secreted by individuals (in captivity) as warning to

others• 2. Granular cells

– Secretes mucus in skin (lampreys & other fishes)• 3. Goblet cells

– Narrow apical end, wide base (osteichthyes & chondricthyes)

– Secretes mucus• 4. Sacciform cells

– Secrete large, membrane-bound toxic products to repel enemies

• 1. Club cells– Elongated, binucleated (amphibians)– Secretes mucus– May contain chemicals that stimulates alarm or fear– Secreted by individuals (in captivity) as warning to

others• 2. Granular cells

– Secretes mucus in skin (lampreys & other fishes)• 3. Goblet cells

– Narrow apical end, wide base (osteichthyes & chondricthyes)

– Secretes mucus• 4. Sacciform cells

– Secrete large, membrane-bound toxic products to repel enemies

Types of multicellular glands:

1. Tubular GlandsTypes Characteristics Examples

1. Simple Tubular

-short, blind tubes located in the dermis and extend to the surface

-thumb pads (anurans)-ceruminous glands

2. Simple Coiled

-long, narrow tube, coiled distal end located in the dermis-openings are referred to as pores of the skin

-sweat glands

3. Simple branched

-divides at its distal ends into two or more branches

-sweat glands in the axilla

4. Compound tubular

-consist of a varying number of simple tubular glands

-mammary glands

TUBULAR GLANDS

2. Saccular (alveolar) glands

Types Characteristics Examples

1. Simple saccular

-only one expanded bulb or acinus at the end of the duct

Mucous and poison glands (amphibians)

2. Simple branched

-with several acini arranged along a single excretory duct-with single acinus divided by partitions into several smaller acini

Meibomian glands

Sebaceous or oil glands

3. Compound saccular

-composed of several simple saccular glands called lobules

Mammary glands

ALVEOLAR / SACCULAR GLANDS

Types as to methods of secretion:1. Merocrine glands- true glands; not

destroyed during secretion; sweatgland

Types of Glands as to Method of Secretion

-the apical portions of cells are pinched off and lost during the secretory process.  This results in a secretory product that contains a variety of molecular components including those of the membrane.  Mammary glands release their products in this manner.

2. Apocrine glands- part of the cell is destroyed that go with the secretion.

3. Holocrine glands- the entire cell goes with the secretion but a new cell is produced to replace it; sebaceous or oil glandholocrine, involves death of the cell.

 The secretory cell is released and as it breaks apart, the contents of the cell become the secretory product.

Copyright ©1999 The McGraw-Hill Companies.

Types of Glands as to type of secretion:

• 1. Mucous glands- secrete mucus– Example; unicellular gland of aquatic

vertebrates and some simple saccular glands of fishes and amphibians

2. Serous gland (sudoriferous glands)- secrete watery substance; e.g. sweat

glands3. Sebaceous gland (oil glands)- Secrete oily substance- E.g. uropygial glands of birds, ceruminous

glands and Meibomian glands of human

• 1. Mucous glands- secrete mucus– Example; unicellular gland of aquatic

vertebrates and some simple saccular glands of fishes and amphibians

2. Serous gland (sudoriferous glands)- secrete watery substance; e.g. sweat

glands3. Sebaceous gland (oil glands)- Secrete oily substance- E.g. uropygial glands of birds, ceruminous

glands and Meibomian glands of human

Serous glands

Exocrine duct

Serous Gland: PAROTID GLAND, HUMAN

Types of Scales1. Epidermal Scales

-formed from the stratum germinativum-characteristic of Terrestrial tetrapods

-usually shed and replaced from time to time-Ex: Scutes of turtles and snakes

2. Dermal Scales

-of mesenchymal origin

-Ex: Fishes’ scales

Epidermal scute, Turtle

Epidermal scute, Snake

Types of Dermal Scales: FishesTypes Characteristics Hardening material

1. Cosmoid -small, thick scales

-possessed only by Latimeria (lobe-finned fish)

-thick layer: cosmine

-thin layer: enamel

2. Placoid -consist of a basal plate embedded in the dermis with a caudally directed spine projecting to the epidermis

-spine contains a central pulp cavity for blood vessels, nerve endings, & lymph channels from the dermis

-plate and spine: dentine

-spine covering: enamel

3. Rhomboid/ Ganoid

-rhomboidal in shape

-composed of bones

-surface of the bone: ganoin

4. Ctenoid -bony layer is characterized by concentric ridges (growth increments)

-anterior portion embedded in the dermis

-allow increased flexibility of the body

– made up of cosmine (dentine-like) forming thick scales over-layered with thin enamel.

Found in: Elasmobranchs

Modifications of placoid scales: Shark teeth; dorsal fin spines

Found in :

Gars

Sturgeons

Paddlefish

Redfish

Bichirs

Teleost scales

-with comb-like or serrated edges along the rear margins

Teleost or Bony fish scales

-smooth rear margins

- Skin of most fishes is non-keratinized and covered by a mucus cuticle

Functions of the mucus cuticle in fishes1. Prevents penetration of bacteria

2. Contributes to the laminar flow of water across the surface3. Makes the fish slippery to predators

4. Includes chemicals that are repugnant or toxic to enemies

Epidermis of Fishes

-alive and active on the body surface

-no superficial layer of dead, keratinized cells

-contains two types of cells:

*Epidermal cells

-mitosis is not restricted to the basal layer

-make up the stratified epidermis*Specialized unicellular glands-connected through cell junctions containing numerous secretory vesicles that are released to the surface

-contributes to the mucous cuticle

• Skin of Fish

Skin epidermis, Dogfish

Fishes Epidermis Dermis

1. Hagfishes and lampreys

-composed of stacked layers of numerous epidermal cells containing large granular cells and elongated club cells

-organized into regular layers of fibrous connective tissue containing pigment cells-contains multicellular slime glands (Hagfishes)

2. Osteichthyes -include a basal layer of cells and stratified epidermal cells above-secretory and club cells occur contributing to the mucous cuticle-presence of larger sacciform cells

-subdivided into a superficial layer of loose connective tissue and a deep layer of dense fibrous tissue

3. Chondrichthyes

-numerous secretory cells and stratified epidermal cells-presence of chromatophore on the lower part

-composed of elastic and collagen fibers giving the skin strength and prevents it from wrinkling during swimming

• Placoid scale embedded in skin epidermis, Shark• Chromatophores in epidermis and pulp (arrow)

Lamprey skin epidermis (E), thinner dermis (D)Unicellular glands (arrow).

D

E

Guanophores – guanin (purine crystal); causes iridiscence in fishes

-specialized as a respiratory surface (Cutaneous respiration)

1. Epidermis

-divided into four layers:*stratum basale

*stratum spinosum

*stratum granulosum

*stratum corneum

-stratum corneum is thin allowing cutaneous respiration

-capillary beds reach into the lower part for cutaneous respiration

2. Dermis

-thinner

-composed of fibrous connective tissue divided into 2 layers:

*stratum spongiosum

*stratum compactum

-mucous and granular poison glands are located in the dermis

-chromatophores are located in the dermis but sometimes found in the epidermis

Epidermis

Stratum spongiosum

Stratum compactum

Epidermis

Dermis

Hypodermis

-more adapted to terrestrial existence than in Amphibians

-extensive keratinization

-fewer skin glands

1. Epidermis

-divided into three layers:

*stratum basale

*stratum granulosum

*stratum corneum

-epidermal scales are present :

*Scutes -large, plate-like scales*scales modified into crests, spines or horn-like processes

-dermal bones located under the epidermal scales are found in Crocodiles, some Lizards, and some Extinct Reptiles

2. Dermis

-composed of fibrous connective tissues

Molting or Ecdysis

-shedding of cornified layer of the skin

Stratum basale duplicates the deeper layers of granulosum and corneum forming new skin

A temporary layer filled with WBC (stratum intermedium) is formed between the old and new skin

WBC promote the separation and loss of the old superficial layer of the skin

Molting or Ecdysis -shedding of cornified layer of the skin

S. basale duplicates the deeper layers of granulosum and corneum forming new skin

• Molted skin, Boa snake

Osteoderms – in alligators

Skin glands in Reptiles

-restricted to certain areas of the body

-important in reproductive behavior and protection

*Femoral glands-found along the underside of the hindlimbs in the thigh region of lizards

*Scent glands

-open into the cloaca and on the margins of the lower jaw in crocodiles and some turtles

- Adapted to free movement over the muscles

-delicate except in exposed areas (legs and feet)

-covered and protected by feathers

1. Epidermis

-composed of statum basale, a transitional layer and stratum corneum

2. Dermis

-richly supplied with blood vessels, sensory nerves and smooth muscles

Brood patches

-highly vascularized dermis in the breast during brooding season

Skin glands in Aves:

1. Uropygial glands

-secretes lipid and protein products used in preening to make the feathers water repellent

2. Salt glands

-excrete excess salt

-modified reptilian scales

-formed from the beta keratin layer of the epidermis

• Long, slender shaft with few barbs at distal end

• Distributed over the body surface

• Shaft – embedded in skin– Chicken – plucked– Peacocks – unusual length

Filoplume, Peacock

Filoplumes are very small and have only a very few barbs at their tips.  They are believed to have a sensory function, helping birds keep their feathers in order.

Down feathers

-Smaller and lack the barbules and their accompanying hooklets so they are not zipped together and do not look as neat.

-They are soft and fluffy

-Provide most of the insulation to the avian body

Down feather or plumulae, Falcon

Semiplume, Falcon

Contour feather or Plumae• Arise from feather tracts or Pterylae• Long shaft: Calamus (hollow quill, embedded in skin) and

Rachis (solid part that bears the vane.• Vane (broad, flat portion-exposed)• Gives avian body outline or contour• Flight feathers or remiges – contour feather on the wings• Rectrices – feathers on the tail• Common in most birds except Penguins and Ostriches

Remiges, Falcon

Rectrices, Falcon

• Penguin feathers-with minute feathers for insulation but not for flight or swimming

• Each feather grows from a structure in the bird's skin roughly comparable to a hair follicle in humans. First the old feather falls away. As a new one grows, it starts to look like a plastic drinking straw. Within this tube, or sheath, the feather itself develops, its barbs crammed in a tight packed spiral. After the tip of the spiral splits, allowing the feather to unfold, fan-like, into its final shape.

EPIDERMIS in Humans

• The stratum basale- Deepest layer (closest to the dermis) consists of single layer of columnar or cuboidal cells resting on the basement membrane. - Basal cells (stem cells) of the epidermis, have active mitotic replenishing the cells in more superficial layers and eventually shed from the epidermis. - Renewal of the human epidermis: 3-4 weeks. 

• The stratum spinosum- Irregular polygonal Spinous cells are oftenly separated by narrow, translucent clefts that are spanned by spine-like cytoplasmatic extensions of the cells, which interconnect the cells of this layer. Spines of cells meet end-to-end or side-to-side and are attached to each other by desmosomes. EM shows membrane-bound lamellar granules in the cytoplasm of the spinous cells.

• The stratum granulosum- In thick skin, of a few layers of flattened cells; In thin skin, only one layer may be visible. - Keratinocytes cells contains numerous fine grains, keratohyaline granules as "free" accumulations in the cytoplasm of the cells. The cells release the contents of the lamellar granules. The lipids contained in the granules come to fill the entire interstitial space, which is important for the function of the epidermis as a barrier towards the external environment. 

• The stratum lucidum (thick skin)- Consists of several layers of flattened dead cells. Nuclei already begin to degenerate in the outer part of the stratum granulosum. In the stratum lucidum, faint nuclear outlines are visible in only a few of the cells.  

• The stratum corneum- Cells are completely filled with keratin filaments (horny cells) which are embedded in a dense matrix of proteins. - Individual cells are difficult to observe because (1) nuclei can no longer be identified, (2) the cells are very flat and (3) the space between the cells has been filled with lipids, which cement the cells together into a continuous membrane.- In the EM, the cell membranes appear thickened and interdigitate with those of neighbouring cells. Closest to the surface of the epidermis, the stratum corneum has a somewhat looser appearance. - Horny cells are constantly shed from this part of the stratum corneum.The protection of the body by the epidermis is essentially due to the functional features of the stratum corneum.

DERMIS• Thick layer of CT to which the epidermis is attached. • Its deepest part continues into the subcutaneous tissue without a

sharply defined boundary. Its thickness about 1-2 mm is a good estimate for "average" skin.

May be divided into two sublayers (again without a sharp boundary):• 1. Papillary layer consists of loose, comparatively cell-rich CT, which fills

the hollows at the deep surface (dermal papillae) of the epidermis. Capillaries are frequent. Collagen fibers appear finer than in the reticular layer.

• 2. Reticular layer appears denser and contains fewer cells. Thick collagen fibres (5-10 µm) often aggregate into bundles (up to 100 µm thick). The fibers form an interlacing network, usually, their main orientation will follow the "lines of greatest tension" in the skin (Kraissl lines). This is of some surgical importance since incisions parallel to these lines will heal faster and with less formation of scar tissue.

Epidermis - beaver tail

• Since the dermis may have a potential to form bones…

Hooves-homologous to fingernails in amniotes