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Questions and Answers
What is one of the primary functions of the integumentary system?
Which layer of skin is considered avascular?
What is the primary function of keratinocytes in the epidermis?
Which cells are responsible for producing the pigment melanin?
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What type of connective tissue primarily composes the dermis?
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Where are Merkel cells primarily located?
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How often does the human epidermis renew itself?
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What role do dermal papillae play in the integumentary system?
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What is the primary function of the stratum corneum in the skin?
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Which structures are involved in the formation of hair?
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What are cutaneous pouches found in sheep primarily composed of?
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What is a characteristic of ergots compared to chestnuts in equines?
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What is the main purpose of the root hair plexus surrounding hair follicles?
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Which hair type is considered a guard hair?
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In which locations do cutaneous pouches occur in sheep?
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What is a primary component of the hair structure?
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What is the primary function of the arrector pili muscles?
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Which phase of the hair cycle is characterized by hair growth?
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Dogs have two types of melanin. Which of the following is one of them?
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Which type of hair is known as tactile or sinus hair?
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What is the major role of sebaceous glands?
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Where do eccrine sweat glands commonly empty their secretion?
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What is the main difference between apocrine and eccrine sweat glands in dogs?
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Which statement about horse sweat is accurate?
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What is the primary function of claws in animals?
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Which of the following structures is NOT part of the hoof?
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Where are anal sacs located on cats and dogs?
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What is the role of the laminae in the hoof?
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What significant change in claws occurs in cats?
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Which type of corium is involved in laminitis in horses?
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What is the function of the frog in the hoof?
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What does the white line in a hoof signify?
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What is the primary characteristic of the stratum lucidum layer?
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Which layer of the dermis is responsible for providing the majority of the skin's structural support?
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What type of cells produce melanin in the skin?
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What structure is primarily used for temperature sensing in the papillary layer of the dermis?
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Which layer of the epidermis is characterized by spiky-shaped keratinocytes held together by desmosomes?
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Which type of connective tissue is primarily found in the hypodermis?
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What happens to keratinocytes in the stratum granulosum of the epidermis?
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What is the function of melanin in the skin?
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Study Notes
Integumentary System
- Integument is the largest organ in the body.
- Skin, claws, hooves, horns, hair, and glands are all integumentary structures.
- Integument protects underlying structures, prevents desiccation and infection, maintains body temperature, excretes waste, receives sensory information, and synthesizes vitamin D
- The integument is classified into two layers, separated by a basement membrane:
- Epidermis - outermost layer, composed of keratinized stratified squamous epithelium
- Dermis - (aka corium) inner layer, composed of fibroelastic connective tissue
- Thicker skin is found on the center of the back, between shoulder blades, and paw pads.
- Thinner skin is found on the eyes and scrotum.
- The hypodermis (aka subcutaneous layer) is located below the dermis and composed primarily of adipose tissue.
Epidermis
- Composed of keratinocytes, melanocytes, Langerhans cells, and Merkel cells.
- Keratinocytes produce keratin, the main structural protein of the epidermis.
- Keratinization is the process of keratinocyte maturation, where cells fill with keratohyalin granules and lose organelles, eventually giving rise to the stratum corneum.
- Melanocytes produce melanin, a pigment that protects keratinocytes from UV radiation.
- Langerhans cells are macrophages that contribute to the immune response in the epidermis.
- Merkel cells are located at the epidermal-dermal junction and are involved in touch sensation.
Layers of the Epidermis (deep to superficial)
- Stratum germinativum (basale): single layer of keratinocytes attached to the basement membrane, contains Merkel cells and melanocytes.
- Stratum spinosum: composed of multiple layers of keratinocytes held together by desmosomes, contains Langerhans cells.
- Stratum granulosum: composed of flattened keratinocytes that begin to fill with keratohyalin and lamellated granules.
- Stratum lucidum: translucent layer of flattened dead cells found only in thick skin.
- Stratum corneum: outermost layer, composed of keratinized, dead keratinocytes that slough off as dandruff.
Dermis
- Composed of dense irregular connective tissue with collagen, elastic, and reticular fibers.
- Contains hair follicles, nerve endings, glands, smooth muscle, blood vessels, and lymphatic channels.
- Divided into two layers:
- Papillary layer: thin, superficial layer of loose connective tissue, containing dermal papillae, Meissner's corpuscles, and temperature-sensing nerve endings.
- Reticular layer: thick, deep layer, composed of dense irregular connective tissue, containing parallel fibrous bundles that form tension lines.
Hypodermis
- Composed of loose areolar tissue, containing adipose cells, blood and lymphatic vessels, nerves, and Pacinian corpuscles.
- Acts as a shock absorber and insulator.
Pigmentation
- Melanin granules produce pigmentation, and more granules equal darker skin.
- Melanocyte-stimulating hormone (MSH) controls melanin dispersion and is produced by the hypophysis.
- Melanin protects keratinocytes from UV radiation.
Paw Pads
- Thick padding composed of fat, providing insulation, shock absorption, and protection.
- Outer layer is the toughest skin on the body, containing all 5 epidermal layers with a thickened stratum corneum.
- Microscopic conical papillae cover the pad surface.
- Exocrine sweat glands and lamellar corpuscles are present.
Planum Nasale
- The "nose print" area of the nose in certain animals, such as pigs, is a special integumentary feature.
Ergots & Chestnuts
- Dark, horny structures found on the legs of equines.
- Chestnuts are located on the inside of the leg, at the carpus and tarsus, and are considered vestigial carpal and tarsal pads.
- Ergots are smaller and less obvious, located on the fetlocks and are vestigial 2nd and 4th digits.
Cutaneous Pouches (Sheep)
- Infoldings of the skin found in sheep, containing fine hairs, sebaceous and oil glands.
- Secrete a fatty yellow substance that covers the skin.
- Locations: infraorbital pouches, interdigital pouches, and inguinal pouches.
Hair
- Provides insulation, camouflage, and protection.
- Most animals have fur (short, fine, falls out) instead of hair (long, keeps growing, needs to be cut).
- Hair is found in whales, pigs, and humans.
Hair Strands and Follicles
- Shaft: part of the hair above the skin.
- Root: part of the hair in the skin.
- Hair follicle: anchors the hair in the dermis.
- Hair bulb: deepest part of the follicle, containing the papilla.
- Papilla: mound of dermal cells at the base of the bulb, supplied by blood vessels.
- Matrix: rapidly dividing epithelial cells covering the papilla, responsible for hair growth.
- Root hair plexus: sensory endings surrounding the root, providing touch sensation.
- Internal epithelial root sheath: innermost layer.
- External epithelial root sheath: middle layer.
- Dermal or connective tissue root sheath: outermost layer.
Hair Follicles Continued
- Compound follicles: multiple hair strands emerge from a single epidermal orifice, each strand with its own follicle and bulb.
- Guard hair: long, primary hair.
- Satellite hairs: smaller secondary hairs surrounding the guard hair.
- Dogs typically have 3 compound follicles per pore.
Hair Formation
- Hair structure is composed of three concentric layers:
- Medulla: core.
- Cortex: surrounds the medulla, made of hard keratin.
- Cuticle: forms the hair surface.
Growth Cycles of Hair
- Anagen: hair growth phase.
- Telogen: hair has reached maximal growth and is resting.
- Catagen: transitional phase between anagen and telogen.
- Shedding and growth occur constantly, influenced by environmental, hormonal, and seasonal factors.
Hair Color
- Horses have one type of melanin, with coat colors based on melanin quantity.
- Dogs have two types of melanin:
- Pheomelanin: yellowish-reddish colors.
- Tyrosine melanin: brown-black colors.
- Agouti coloration: pigmentation accumulates at the tips of hair strands.
Types of Hair
- Primary/guard hairs: straight, thick, arched hairs.
- Secondary/wool-type hairs: softer and shorter than primary hairs.
- Tactile/sinus hairs: probers or feelers, also known as whiskers.
Arrector Pili Muscles
- Keep the hair erect, resulting in goosebumps in humans.
- Contract when frightened or cold, innervated by the sympathetic nervous system.
- Force sebum from the sebaceous glands to keep the skin moist and supple.
Sebaceous Glands
- Secretes sebum, a mixture of glycerides and free fatty acids.
- Keeps the skin lubricated, traps moisture, and has antibacterial and antifungal properties.
- Empties into hair follicles or directly onto the skin surface.
- Holocrine glands: cells rupture during secretion.
- Arrecter pili muscles compress the gland to secrete sebum.
Sweat Glands
- Also known as sudoriferous glands, present in most domestic species.
- Horses produce profuse sweat.
Eccrine Sweat Glands
- Simple coiled tube located in the dermis or hypodermis.
- Empties onto the skin surface via a duct.
- Found in dogs: deep layer of fat and in foot pad connective tissue.
Apocrine Sweat Glands
- Coiled tube located in the dermis or hypodermis.
- Empties into hair follicles.
- Found in dogs: located in the external ear canal.
Tail Glands
- Found in most cats and dogs, at the dorsal base of the tail.
- Contains coarse, oily hairs.
- Contain apocrine and sebaceous glands.
- Believed to assist in animal recognition.
Anal Sacs
- Located at 5 and 7 o'clock relative to the anus in cats and dogs.
- Produces foul smelling glandular fluid.
- Expressed when the animal is afraid or defecates.
- Assist in marking territory.
Claws and Dewclaws
- Claws: hard pigmented coverings on the distal digits, providing traction and protection.
- Only cats retract their claws, except cheetahs.
- Dewclaws: vestigial digits, sometimes containing bones.
The Hoof
- Also known as the "ungula," which covers the coffin bone.
- Consists of the wall, sole, and frog.
- Growth occurs from the coronary band.
- Corium: sensitive tissue attached to the periosteum of the coffin bone, providing a dermis-like function.
- Laminae: interdigitations between the corium and hoof wall, ensuring hoof stability.
Wall of the Hoof
- External convex portion, composed of the toe, quarters, and heel.
Sole of the Hoof
- Plantar surface, connected to the underside of the coffin bone by the corium.
- The "white line" is located at the junction of the sole and wall.
The Frog of the Hoof
- Triangular horny structure located between the heels on the underside of the hoof.
- Composed of leather-like tissue, providing shock absorption and foot support.
- The apex faces the toe, with a central sulcus or cleft.
The Five Types of Corium
- Laminar corium: located between the hoof wall and the 3rd phalynx, responsible for maintaining stability.
- Perioplic corium: located in the perioplic sulcus.
- Coronary corium: located in the coronary sulcus.
- Sole corium: located superior to the sole.
- Frog corium: located superior to the frog.
Horns
- Emerge from horn processes on the frontal bone of the skull.
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Description
Explore the largest organ of the body, the integument, and its various structures including skin, hair, and glands. This quiz covers the composition of the epidermis and dermis, their functions, and the role of the hypodermis. Gain a deeper understanding of how the integumentary system protects and maintains the body's integrity.
