Integumentary System Part 2 Study Notes

Special Features of the Integumentary System

Pigmentation

• Definition: Pigmentation or coloration of the skin results from the presence or absence of melanin granules in the extensions of melanocytes.

• Mechanism:

  • If there are no granules near the nucleus, pigmentation does not occur.

  • Pigmentation occurs when granules in cellular arms and surrounding tissues push towards the cell's exterior.

• Controls:

  • Controlled by hypothalamic signals from the pituitary gland located behind the eyes at the bridge of the nose.

  • Involves melanocyte stimulating hormone (MSH) that influences skin darkening due to sun exposure.

Melanocyte Activity

• Melanosome Transport:

  • Melanosomes are transported to the tips of cellular projections (long finger-like extensions of melanocytes).

  • Released into the intracellular space and absorbed by keratinocytes.

• Keratinocytes' Role:

  • Keratinocytes arrange melanin on the side of the cell with maximum sun exposure, thereby protecting from harmful ultraviolet rays.

Paw Pads (Toe Beans)

• Definition: Paw pads are tough, thick layers of fat and connective tissue with exocrine sweat glands and lamellar corpuscles.

• Structure:

  • Include all five epidermal layers due to their thickness; significantly, the stratum corneum layer is the thickest.

  • Contains conical papillae covering the entire pad, which are pigmented.

• Types of Pads:

  • Digital Pads: Located on the fingers of the animal.

  • Metacarpal Pads: Correspond to the palm.

  • Carpal Pad: Located on the wrist.

  • Dewclaw: Additional pad structure.

• Functionality:

  • Fat insulation allows animals to walk on various surfaces (hot, cold, rough).

  • Protective adaptation that eliminates the need for footwear in many cases, though extreme temperatures may still require protective gear.

Other Special Features of the Integumentary System

• Sensory Structures: Lamellar corpuscles sensitive to pressure, vibration, and touch.

Planum Nasal

• Definition: The planum nasal is the nose's surface in cats, pigs, sheep, and dogs; in cows and horses, it’s called the planum nasolabial (combined nose and lip area).

• Characteristics:

  • Typically darker pigmentation, aglandular except in sheep, pigs, and cows.

  • The surface of the nasal planum is moist due to glandular tissue in specific species.

• Epidermal Layers: Consist of three layers, with a particularly thin stratum corneum divided by deep grooves.

Ergots and Chestnuts

• Definition: Dark horny structures on equine species' legs, thought to be vestigial digit formations.

• Locations:

  • Chestnuts: Found at the inner segments of each leg, near the carpus and tarsus.

  • Ergots: Smaller structures often hidden within heavy coat hairs of the fetlock.

• Functional Evolution:

  • Chestnuts represent vestiges of the carpal and tarsal pads of the first digit; ergots reflect second and fourth digits.

• Trimming: Required as they can grow excessively long in various species.

Cutaneous Pouches in Sheep

• Definition: Infoldings of skin containing fine hair, e.g., infraorbital cutaneous pouch.

• Gland Presence: Sheep possess sebaceous and oil glands in specific areas (infraorbital, interdigital, inguinal) that secrete lanolin—historically known as infant fat, used in waterproofing and cosmetics.

Importance of Hair in Mammals

• Role: Essential for thermal regulation and camouflage, traps insulating air layers.

• Nuanced: Dense fur protects from environmental elements, while thinner hair on the abdomen reflects reduced protective need.

Hair Structure

• Parts of Hair:

  • Shaft: Visible portion above the skin.

  • Root: Beneath the skin, anchored by the hair follicle. The hair bulb's base contains the papilla and matrix (rapidly dividing cells).

• Growth Mechanism:

  • Hair grows as keratinized cells migrate upwards away from nourishment provided by the papilla.

Hair Follicle Anatomy

• Composition:

  • The hair is made of three layers: medulla (central), cortex (middle), cuticle (outer).

  • Hair follicle has three layers: internal epithelial root sheath, outer epithelial root sheath, and dermal connective tissue root sheath.

• Compound Follicles: Present in dogs, with multiple strands emerging from a single follicle.

Hair Growth Phases

• Anagen Phase: Active growing phase where hair length increases.

• Catagen Phase: Transitional phase marking hair follicle shortening.

• Telogen Phase: Resting phase prior to shedding, duration varies based on environmental conditions and species.

Hair Pigmentation

• Color Sources: Controlled by melanin concentration within the hair strand's cortex and medulla.

  • Types of melanin: pheomelanin (yellow/red hues) and eumelanin (dark hues).

• Aging Effect: Melanin production decreases with age, leading to graying due to air-filled medullar and cortical structures.

Types of Hair

• Primary Hairs: Thicker and longer; also known as guard hairs.

• Secondary Hairs: Softer and shorter than primary; important for insulation.

• Tactile Hairs: Whiskers or sinus hairs serving as sensory tools.

Erect Hair Response

• Mechanism: Contraction of erector pili muscles in response to stimuli (e.g., fear) causes hair to stand up.

• Example: Common behavior in cats when startled.

Glands of the Integumentary System

Sebaceous Glands

• Function: Produce oily sebum that lubricates skin and hair, helps moisture retention, and prevents infections.

• Distribution: Most of the body except certain areas (e.g., paw pads, planum nasal).

Sweat Glands

• Types:

  • Eccrine Glands: Secret sweat directly onto skin.

  • Apocrine Glands: Empty into hair follicles, including locations in dog ear canals.

  • Equine sweat glands are more specialized, with unique structural elements assisting with scent production.

Tail Glands**

• Location: Found at the dorsal base of the tail in many mammals, containing large apocrine and sebaceous glands.

• Purpose: Used for recognition and identification between individuals.

Tail Gland Conditions

• Stub Tail: Condition resulting from overactive tail glands leading to greasy fur and potential hair loss, scientifically termed tail gland hyperplasia (hyperplasia meaning overgrowth).

Anal Glands

• Location: Positioned at 5 o'clock and 7 o'clock around the anus, often expressed during defecation or when animals are startled.

• Contents: Lined with sebaceous and apocrine glands. The expression of these glands results in a characteristic odor often associated with stress or fear.

• Health Considerations: Can become impacted or cancerous, leading to excessive grooming or behavior changes in animals.