The Common Integument

The Common Integument

Overview

  • Lecturer: Dr. Cristian Martonos (previous lecturer: Dr. Cristian Dezdrobitu)

Learning Objectives

  • Define the common integument.
  • Describe the role of the skin.
  • Describe the types of hair (what it is, development of hair).
  • Describe the footpads (where they have the best development).
  • Define the nails, claws, and hoofs (differences in species).
  • Define the horns (the importance of the cornual process and frontal sinus).

Common Integument Definition

  • Term: COMMON INTEGUMENT = ordinary skin with its covering of hair, variety of skin glands, and specialized parts such as claws, hoofs, and horns.

Role of the Skin

  • Covers the body and protects it against injury.
  • Temperature control.
  • Enables the animal to respond to various external stimuli.

Layers of the Skin

  • Epidermis (outer layer)
  • Dermis (inner layer)
  • Subcutis, hypodermis, or superficial fascia (loose connective tissue beneath the dermis)
  • Key structures:
    • Sebaceous gland
    • Arrector pili muscle
    • Sweat gland
    • Hair follicle
    • Arterial networks

Hair

  • Diagnostic of the class.
  • Thick haircoat is spread over the body in most species.
  • Exceptions: mouth, other openings, and surfaces of the feet.
  • Domestic pig: sparse covering.
Types of Hair

  • Straight, stiff guard hairs:

    • Provide a "topcoat".

  • Fine, wavy wool hairs:

    • Provide an "undercoat".

  • Stout tactile hairs:

    • Restricted distribution.
    • Associated with touch receptors.

  • Diagram of hair structure:

    • (A) Guard hair with thick medulla.
    • (B) Guard hair with thick cortex and thin medulla.
    • (C) Wool hair; the cortex is absent.
    • 1, Cuticle; 2, cortex; 3, medulla.
Responsible for the color
  • Melanin
  • Pigment is produced in melanocytes.
  • Albinism: congenital absence of pigmentation.
    • Results in white hair, feathers, scales, and skin, and pink eyes.
Guard Hairs
  • Lie close against the skin and sweep uniformly in broad tracts.
  • Give the coat a smooth appearance, disturbed only by whorls and crests.
  • Promote runoff of rain, preventing chilling.
  • Disturbed coat pattern may impair the ability to withstand severe weather.
  • Each hair grows from a tiny pit or follicle to protrude above the surface of the skin.
  • Follicle develops from an ectodermal bud.
  • Distal end of the bud forms a bulbous enlargement, indented by a mesenchymal (dermal) papilla to form a primitive hair follicle.
Development of Hair
  • (A) Ectodermal bud growing into mesenchyme.
  • (B) Differentiation of the bud; indications of glands appear.
  • (C) Hair follicle with accessory structures.
  • Key structures:
    • 1, Primitive hair follicle
    • 2, Dermal papilla
    • 3, Bud of sweat gland
    • 4, Bud of sebaceous gland
    • 5, Bulb (hair matrix) of hair
    • 6, Hair follicle
    • 7, Root of hair
    • 8, Arrector pili muscle
    • 9, Sebaceous gland
    • 10, Sweat gland
  • In the adult, many glands open independently, not into hair follicles.
Guard Hair Variations
  • Stiff, sparsely scattered bristles of pigs.
  • Coarse hair of the mane and tail of horses.
  • Long tail hairs of cattle.
  • Fetlock tufts of horses.
  • Feathering of the tail and limbs of certain breeds of dogs.
  • Hormone-dependent.
  • Evident in humans.
Hair Life Cycle
  • Hairs have restricted lives and are discarded sooner or later.
  • Hair shedding in humans is continuous, involving only a few hairs at a time.
  • Most other species shed many hairs at a time in a seasonal fashion.
Shedding in Domesticated Animals
  • Recurrent pattern with peaks in the spring and fall.
  • Spring shedding lasts about 5 weeks in dogs.
  • More obvious in animals not regularly groomed to remove dead hair.
  • Cats also molt most heavily in spring, with less substantial loss through the summer and fall, followed by attaining of prime condition in winter.
Wool Hairs
  • Provide the soft undercoat.
  • Thin.
  • Wavy.
  • Shorter and more numerous than the guard hair.
  • Concealed between the guard hair.
Follicle Structure
  • In many species, including mature dogs and cats, several hairs share a single follicle opening.
  • The central (primary) hair is longest and of the guard type.
  • The surrounding (secondary) hairs are shorter and softer.
  • They provide the undercoat and may be designated wool hairs because they have little medulla.
  • Diagram:
    • (A) Simple follicle present shortly after birth.
    • (B) Follicle present during the first few months after birth.
    • (C) Complex adult follicle; the primary hair is surrounded by several secondary hairs.
Tactile Hair
  • Substantially thicker.
  • Generally protrude beyond the neighboring guard hairs.
  • Reach deep into the subcutis or even the superficial muscles.
  • Characterized by the presence of a venous sinus filled with blood and located between inner and outer layers of the dermal sheath.
  • Nerve endings responsive contained within the dermal sheath.
  • Topography:
    • Face.
    • Principally on the upper lip and about the eyes.
    • Species-variable fashion on the lower lip, the chin, and elsewhere on the head.
  • Functionality:
    • Nerve endings responsive to mechanical stimulation.
    • The stimulus provided by disturbance of the hair is amplified by wave motion in the blood.
  • Development:
    • Follicles of tactile hairs appear early in development, before those of the coat hairs.

Tori (Pads)

  • Torus: A bulging or rounded projection or swelling.
  • In connection with the common integument, denotes a pad.
  • Includes the thick epidermal covering, the dermis, and the subcutaneous cushion, or Pulvinus.
  • Structure:
    • Naked, densely cornified epidermis.
    • Dermis is unremarkable.
    • Thick, resilient subcutis.
    • Admixture of collagenous and elastic fibers interspersed with adipose tissue (fat).
  • Footpads are the digital cushions on which animals walk.
Footpads
  • Bear footpads: forelimb and hindlimb digital pads, metacarpal pad, metatarsal pad, carpal pads, tarsal pad fused with the metatarsal pad
  • Canine and Feline footpads: forelimbs and hindlimbs digital pads, metacarpal pad, metatarsal pad, carpal pad, carpal gland and associated tactile hairs
Footpads in Ruminants, Pigs, and Horses
  • Ruminants and pigs:
    • Only digital pads called bulb, located in the hoof.
  • Horse:
    • Only digital pads called frog, located in the hoof.
    • Functional and in contact with the ground.
Palmar Surface

*Pig:
*Bulb (digital pad) of hoof
*Sole of hoof
*Wall of hoof
*Hoof of accessory digit
*Rudimentary hoof of dewclaw

*Cow:
*Bulb (digital pad) of hoof
*Sole of hoof
*Wall of hoof
*Hoof of accessory digit
*Rudimentary hoof of dewclaw

Horse Limb
  • Left forelimb and left hindlimb.
    • Chestnuts above carpus and below hock.
    • Ergots.
    • Bulbs of the heels.
    • Frog.

Nails, Claws, and Hoofs

  • Similar structures enclosing the distal phalanx appear strikingly different.
  • Local modifications of skin.
  • Serve primarily to protect the underlying tissues.
  • Used for:
    • Scratching.
    • Digging.
    • Weapon.
    • Grab the food
Equine Hoof

  • Reduces concussion on foot impact.

  • Presents three parts:

    • Wall
    • Sole
    • Associated pad (horny structure; it corresponds with the digital bulb of primates and the digital pad of carnivores).

  • The Wall:

    • Strongly curved.
    • The sides are sharply inflected to form the so-called bars.

  • Space between the bars is occupied by the frog, the part of the footpad that makes contact with the ground.

  • The sole horn that fills the ground surface between wall and frog meets the wall at a junction known as the white line (zona alba).

  • Great guidelines:

    • The 1/3-2/3 principle: should have approximately one-third of the shoe ahead of the tip of the frog, and wo-thirds behind.
    • Hoo and pastern must be aligned;
    • A plum line dropped through the long axis (the can on bone or third met ca pal) should bisect just before the end of the hoe;

  • Periople:

    • Band of soft horn.
    • Lies over the external surface of the wall near its junction with the skin.
    • It descends with the wall and dries to a protective glossy layer.
    • Widens at the back of the hoof, where it covers the bulbs of the heels and part of the frog.

Claws in Carnivores

  • Compared with a nail that has been laterally compressed.
  • Characteristics:
    • Sharp dorsal border.
    • Epidermis is minimally productive.
    • The dermis that covers the unguicular process fuses with the periosteum.
    • Longitudinal interdigitations between dermal and epidermal laminae strongly bond the claw to the dorsal border of the bone.
Carnivore Claw
  • (D) Longitudinal section and (E) palmar surface of canine claw.
  • Key structures:
    • Wall of claw
    • "Sole" of claw
    • Digital pad
    • Unguicular process

Horns

  • Horns of domestic ruminants:
    • Have osseous bases provided by the cornual processes of the frontal bones.
    • Are permanent and grow continuously after their first appearance soon after birth.
  • Clinical importance when dehorning an adult animal frontal sinus extending into horn
    • 1. Caudal frontal sinus extending into horn;
    • 2. cornual process of frontal bone

Practice Questions

  • The cornual process in cattle is invaded by the frontal sinus.
  • Using the attached image, name the structure numbered with 4: E. Digital pad
  • Which one of the following statements is correct statement regarding wavy wool hairs? E. Provide an ‘undercoat’