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Questions and Answers
What is the primary purpose of keratinization in the epidermis?
What is the primary purpose of keratinization in the epidermis?
What layer of the dermis primarily consists of dense irregular connective tissue?
What layer of the dermis primarily consists of dense irregular connective tissue?
Which feature of foot/paw pads assists in protection against abrasion?
Which feature of foot/paw pads assists in protection against abrasion?
What characterizes the planum nasale in dogs?
What characterizes the planum nasale in dogs?
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What are ergots a vestige of?
What are ergots a vestige of?
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Functional sweat glands in foot/paw pads serve what purpose?
Functional sweat glands in foot/paw pads serve what purpose?
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What is the purpose of the cutaneous pouches found in sheep?
What is the purpose of the cutaneous pouches found in sheep?
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What ensures structural strength in the dermis?
What ensures structural strength in the dermis?
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What is the primary function of the keratinocytes in the epidermis?
What is the primary function of the keratinocytes in the epidermis?
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Which layer of the skin is primarily responsible for mechanical shock absorption?
Which layer of the skin is primarily responsible for mechanical shock absorption?
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What role do Langerhans cells play in the epidermis?
What role do Langerhans cells play in the epidermis?
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Which layer of the epidermis is where new cells are produced?
Which layer of the epidermis is where new cells are produced?
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What is the function of the stratum granulosum layer of the epidermis?
What is the function of the stratum granulosum layer of the epidermis?
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Which type of cells are responsible for pigmentation in the skin?
Which type of cells are responsible for pigmentation in the skin?
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Which component is NOT part of the integumentary system?
Which component is NOT part of the integumentary system?
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What is the outermost layer of the skin called?
What is the outermost layer of the skin called?
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What is the primary function of the arrector pili muscle in relation to hair?
What is the primary function of the arrector pili muscle in relation to hair?
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Which phase of the hair growth cycle is characterized as the active growth phase?
Which phase of the hair growth cycle is characterized as the active growth phase?
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What is contained within the anal sacs of animals?
What is contained within the anal sacs of animals?
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Which type of skin gland is primarily responsible for producing thick and oily sebum?
Which type of skin gland is primarily responsible for producing thick and oily sebum?
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What is the main function of tactile hairs in mammals?
What is the main function of tactile hairs in mammals?
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What happens during the telogen phase of the hair growth cycle?
What happens during the telogen phase of the hair growth cycle?
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Which type of gland in the skin is functional in domestic equids but less so in ruminants?
Which type of gland in the skin is functional in domestic equids but less so in ruminants?
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What is the primary contribution of a catagen phase in hair growth?
What is the primary contribution of a catagen phase in hair growth?
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What role does the tail gland play in mammals?
What role does the tail gland play in mammals?
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What is a potential consequence of clogged sebaceous follicles?
What is a potential consequence of clogged sebaceous follicles?
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Study Notes
Integumentary System
- Covers and protects underlying structures
- Prevents drying out
- Assists in maintaining normal body temperature
- Excretes water, salt, and organic wastes
- Acts as a sensory organ
- Involved in Vitamin D synthesis and nutrient storage
Integument Structure
- Composed of all four tissue types
- Includes hair, horns, hooves, claws, and skin-related glands
- Outer layer is composed of dead cells
- Keratinization occurs as cells die, providing protective and regulatory functions
Layers of the Integument
Epidermis
- Made of keratinized stratified squamous epithelium
Dermis (Corium)
- Composed of dense fibroelastic connective tissue
Hypodermis (Subcutaneous Layer/Subcutis)
- Primarily adipose tissue for thermal insulation and mechanical shock absorption
- Contains pressure receptors known as Pacinian corpuscles, allowing skin to move freely over underlying muscle and bone
- Contains larger blood vessels and nerves
Epidermis: Cells & Their Functions
Keratinocytes
- Majority of epidermal cells
- Produce keratin, a tough, fibrous, waterproof protein
- Provides skin with resiliency and strength
Melanocytes
- Produce melanin, a dark brown-black pigment
- Melanin is stored in membrane-bound granules called melanosomes
- Melanin is absorbed by keratinocytes, providing protection from UV exposure
Langerhans Cells
- Macrophages found only in the epidermis
- Originate in bone marrow and migrate to the skin
- Function to phagocytize microbes and stimulate other immune cells
Merkel Cells
- Form Merkel disks with sensory nerve endings at the epidermal-dermal junction
- Thought to aid in touch sensation
Epidermal Layers (Deepest to Most Superficial)
Stratum Germinativum (Stratum Basale)
- Attached to the epithelial basement membrane
- New cells are produced here and move up
Stratum Spinosum (Spiny Layer)
- Contains Langerhans cells
- Cell death and keratinization begin here
Stratum Granulosum (Granular Layer)
- Keratohyaline granules are synthesized here
Stratum Lucidum (Clear Layer)
- Contains keratinized clear cells, found only in very thick skin areas
Stratum Corneum (Horny Layer)
- Outermost and thickest layer
- Composed of cornified remnants of keratinocytes (dandruff)
Keratinization
- The process where keratinocytes produce keratin as they move up through the layers of the epidermis, eventually dying and forming a protective outer layer
- As older cells move up from the basal layer, they fill with keratohyaline and glycolipid granules
- Cells lose their nuclei, cytosol, and organelles, becoming dead sheets of keratin
- Dead cells and keratin slough off as dander/dandruff
Dermis
- Makes up the largest part of the skin
- Provides structural strength
- Composed of two layers:
Papillary Layer
- Loose connective tissue with fibers and ground substance
- Located just beneath the epidermis; forms dermal papillae
Reticular Layer
- Dense irregular connective tissue containing collagen, elastic, and reticular fibers
- Comprises 80% of the dermis; most fiber bundles run parallel to one another
- Orientation depends on the direction of stress placed on them
Special Features of Integument
Foot/Paw Pads
- Thick layers of fat and connective tissue
- Tough, thick outer epidermal surface
- Often pigmented
- Composed of all 5 epidermal layers
- Bear the weight of the animal
- Protection against abrasion
- Protection against thermal extremes
- Functional sweat glands that secrete onto the surface of the pad
Planum Nasale
- Top of the nose in dogs, cats, pigs, sheep, and goats
- Known as planum nasolabiale in horses and cattle
- Composed of only 3 epidermal layers in dogs
- Usually pigmented
- No glands in the epidermis or dermis in dogs
- Tubular glands present in ruminants and pigs
Ergots and Chestnuts
Ergots
- Dark brown, horny patches on the legs of horses and other equids
- Vestiges of the 2nd and 4th digits
Chestnuts
- Vestiges of carpal and tarsal pads of the 1st digit
Cutaneous Pouches of Sheep
- Infolding of skin forming pouches containing sebaceous (oil) glands
- Secretions used in marking territory, courtship, etc.
Functions of Hair/Fur
- Insulates by trapping layers of air
- Hairs erect when cold
- Coat color determined by melanin and pheomelanin
- Intra- and interspecies communication
- Erection of hair when aroused or frightened
- Degree of erection indicates implantation angle
Arrector Pili Muscle
- Smooth muscle attached to hair follicle
- Innervated by the sympathetic nervous system
- Mixed intermittently throughout the coat
Tactile hairs
- Sensitive to touch and pressure, and help organisms sense their environment
- Found in many mammals, especially as whiskers
- Very sensitive to the slightest bending or touch
Hair Growth Cycles
Anagen Phase
- Active growth phase
- Hair shaft lengthens
Telogen Phase
- Quiescent, resting phase
- Occurs when maximum length is achieved
- Hair stops growing and follicle shortens
Telogen Effluvium
- Loss of a large percentage of hair volume at one time
- Caused by metabolic stress or illness
Catagen Phase
- Transitional period between anagen and telogen phases
Skin Glands
Sebaceous Glands
- Located in the dermis (not in foot pads or nasal planum)
- Simple or compound acinar gland
- Holocrine secretion
- Empty into hair follicle
- Arrector pili muscle squeezes secretion out or empties directly onto the skin surface
- Thick and oily
- Composed of glycerides and free fatty acids
- Coats hair and traps moisture
- Keeps skin moist and supple
- Has some antibacterial and antifungal properties
- Can clog follicles, causing whiteheads that turn black (comedones or blackheads) which can become infected
Sweat (Sudoriferous) Glands
- Present in most domestic species but only functional in equids and to a lesser extent in ruminants
- Both merocrine secretion
Eccrine Glands
- Empty onto skin surface
- Simple, coiled tube in dermis connected to skin surface by a long duct
- Found in foot pads and deep layers of fat in dogs
Apocrine Glands
- Empty into hair follicles
- Single, coiled secretory/excretory duct
- Located in the external ear canal
Tail Glands
- Oily patch at the dorsal base of the tail in dogs and cats
- Contains sebaceous and apocrine glands
- Assists in communication and identification of individuals
- Sensitive to sex hormone levels
Anal Sacs
- Lined with sebaceous and apocrine glands
- Stores secretions produced
- Expressed during defecation or when the animal is frightened or excited
- Used in marking territory and attracting mates
Claws, Hooves, Horns & Antlers
Claws & Hooves
- Hard outer layer made of keratin
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Description
This quiz covers the essential functions and structures of the integumentary system, including the different layers such as the epidermis, dermis, and hypodermis. Test your understanding of the system's role in protection, temperature regulation, and sensory functions.
