Lecture 4 - Integument Support & Movement

Integument

The body covering system.

Includes:

• Skin

• Hair

• Associated glands

• Modified structures (claws, nails, hooves, horns, antlers)

Skin

Mammalian skin is thicker and more complex than in other vertebrates.

• Layers (outside → in): epidermis, dermis (thicker), hypodermis.

Hair

• Hair is derived from epidermal tissue.

• Thought to evolve from reptilian scales.

• Made of keratin.

• Each hair is made of 3 layers:

  • Medulla - core

  • Cortex - contains pigment

  • Cuticle - overlapping scales

Hair movement

Each hair follicle has a muscle attached to it, the erector muscle.

• When it contracts, hair stands up.

• This contraction is called piloerection. It acts as an insulator and warning signal.

Underfur

The bottom layer consisting of wool hairs.

• They tend to be shorter, flattened, curly, and denser than the top layer.

• Its principal function is thermal insulation and thus thermoregulation.

Guard hair

Outer layer consisting of longer, coarser, and straighter hair.

• The visible layer.

• Provides water resistance, pigmentation, and protection.

Awn hair

Found between underfur and guard hair. Not present in all mammals.

Hair cycles

• Humans shed and replace hair continually.

• Most mammals molt twice a year

Coloration

Seasonal color changes:

• Brown in summer

• White in winter (leukemism)

Specialized hairs

• Vibrissae: sensory hairs.

• Quills: modified hairs for defense.

The 4 epidermal glands

1. Eccrine sweat glands - produce watery sweat. Found in hairless areas (footpads).

2. Apocrine sweat glands - for communication, not cooling. Aid in chemical communication, warning, defense, and attraction.

3. Sebaceous glands - secrete sebum, a lubricant for waterproofing and hydrating. Can also inhibit growth of microorganisms (bacteria).

4. Mammary glands - produce milk.

Basic structure of claws, nails, and hooves

1. Unguis: hard outer layer. Keratin fibers arranged perpendicular to growth. Grows outward from the nail matrix.

2. Subunguis: soft, flaky layer. Keratin fibers run parallel to growth. Thickens as it moves across the nail bed.

Abscission layer

Every so often, the growth of claws stops and restarts, similar to hair.

3 types of horn like structures

1. Antlers

2. True horns

3. Other horn-like structures (giraffes, rhinos, and pronghorns)

Antlers

Found in the family Cervidae; deer, elk, moose, caribou.

• Usually only males have antlers (except in caribou).

• Grow from pedicels on the frontal lobes.

• Are covered during growth with velvet (vascularized skin) that sheds after breeding season (blood is cut off, it dies, and is rubbed away).

True horns

Found in the family Bovidae; cattle, goats, sheep, bison, antelope.

• Permanent, unbranched, and composed of a bony core and keratin sheath.

• Grow continuously and are never lost.

• Found in all males and many females.

Ossicones

Giraffe “horns”.

• Short, permanent, and unbranched.

• Covered in skin and hair.

• Do not project from the frontal lobes, but lie over the frontal and parietal bones.

• Found in both sexes.

What are the 3 major components of the basic skeletal structure?

1. Skull

2. Axial skeleton

3. Appendicular skeleton

Axial skeleton

The central axis of the body.

Includes: skull, vertebrae, rib cage, and sternum.

Appendicular skeleton

Includes the limbs and the girdles that attach them to the body.

There are two types of girdles:

1. Pectoral girdle (forelimbs)

2. Pelvic girdle (hindlimbs)

Pectoral girdle

Attaches the forelimbs to the body.

Consist of the scapula (shoulder blade) and clavicle (collarbone).

Pelvic girdle

Attaches the hindlimbs to the body.

Includes the ilium, ischium, and pubis. Together this is called the innominate bone.

Forearm bones

• Humerus - upper arm.

• Radius + ulna - forearm

• Carpals - wrist

• Metacarpals - palm

• Phalanges - digits

Hindlimb bones

Femur - thigh

Patella - knee cap

Tibia + fibula - lower leg

Tarsal - ankle

Metatarsals - foot

Phalanges - toes

Foot posture types

1. Plantigrade - entire foot contacts the ground.

2. Digitigrade - walk on digits (cats + dogs).

3. Unguligrade - walk on top of hooves (horses + deer).

Types of locomotion

1. Cursorial - running.

2. Graviportal - adapted for large body size; legs directly under body.

3. Saltatorial - jumping and hopping; elongated hindlimbs.

4. Fossorial - digging.

5. Arboreal - climbing, swinging.

6. Aerial - gliding, true flight.

7. Aquatic - swimming.