Integumentary System: Structure Function and Derivatives

Integumentary system and the derivatives in Amphibia, Birds and Mammals are discussed below:

Integumentary system in Amphibia:

Derivatives of Integuments in Class Amphibia are of the Epidermal glands such as Mucous gland and Poison gland.

1. Mucous Glands

• Structure: Small, tubular glands scattered throughout the skin.
• Function: Produce mucus to keep the skin moist, which is crucial for respiration and protection against pathogens.
• Examples: Common in frogs and salamanders, aiding in cutaneous respiration.

2. Granular (Poison) Glands

• Structure: Larger than mucous glands, often with a more complex structure.
• Function: Secrete toxic or irritating substances as a defence mechanism against predators.
• Examples: Parotid glands in toads secrete bufotoxins.

Derivatives of Integuments in Birds:

1. Epidermal Scales

• Structure: Overlapping plates of keratin.
• Function: Protects the skin on the legs and feet from injury and dehydration.
• Examples: Found on the legs and feet of chickens, ducks, and other birds.

2. Claw

• Structure: Keratinous sheath covering the distal phalanges.
• Function: Used for perching, climbing, hunting, and defence.
• Examples: Talons of eagles, claws of chickens.

3. Beak (Bill)

• Structure: Keratinized structure covering the upper and lower jaws.
• Function: Essential for feeding, grooming, manipulating objects, killing prey, and mating displays.
• Examples: Curved beaks of parrots, sharp beaks of hawks, flat beaks of ducks.

4. Feathers

Types:

1. Contour Feathers: Cover the body and give the bird its shape.
2. Flight Feathers: Located on the wings and tail; crucial for flight.
3. Down Feathers: Found under contour feathers; provide insulation.
4. Semiplume: Intermediate between down and contour feathers; provide insulation and smooth body contours.
5. Filoplume: Hair-like; involved in sensory function.
6. Bristles: Stiff, hair-like; often found around the mouth, eyes, and nostrils for protection and sensory functions.

Structure: Composed of a central shaft (rachis) with barbs and barbules forming a flat vane.

Feather Structure: 

A typical feather have consists of :- 1.Axis/Main stem & 2.Vane/Vexillum

1. Axis: Axis is divided into:– 1.Calamus & 2.Rachis

(I). Calamus: Proximal lower portion.

1. Hollow, tubular and semi transparent.
2. Base of the calamus is inserted into a pit or epidermal follicle of the skin.
3. At the lower end of the quill has a small opening called inferior umbilicus.
4. Superior umbilicus present at junction of the quill and rachis on the ventral surface.

(II). Rachis/Shaft: Distal upper portion of the axis.

1. The rachis or the shaft forms the longitudinal axis of the vane.
2. Longitudinal furrow (umbilical groove bear along the inner/ventral surface of rachis of its length)

2. Vane The expanded membranous part of the feathers is called the vane /the vexillum.

1. It is divided into two unequal lateral halves.
2. Vane is formed by a series of the numerous parallel and closely spaced, delicate, thread structures, the barbs. 
3. Barbs are present at both side.
4. Each barb gives rise to a double row of many extremely delicate, oblique filaments called the barbules.
5. Barbules: Distal Proximal barbules.
6. The lower edge of the distal barbules is produced into minute hooklets, hamuli or barbicles.

• Function: Insulation, flight, waterproofing, camouflage, and display.
• Examples: Peacock tail feathers (display), duck feathers (waterproofing), eagle feathers (flight).

Derivatives of Integuments in Mammals:

1. Horn

• Structure: Keratinized sheath covering a bony core.
• Function: Used for defence, fighting, and mating displays.
• Examples: Cattle (cows), goats, and sheep.

Different Types of Horns:

(I). True Horns

• Structure: Bony core covered by a keratinized sheath.
• Characteristics: Permanent, grow throughout the animal’s life, and are not shed.
• Examples:Cattles, goats, sheep etc.

(II). Antlers

• Structure: Entirely bone, covered by a layer of skin (velvet) when growing.
• Characteristics: Shed and regrown annually, typically branched, found mostly in males.
• Examples:Deer, Moose etc.

(III). Pronghorns

• Structure: Bony core covered by a keratinous sheath.
• Characteristics: Sheath is shed and regrow annually, branched with a single prong.
• Examples: Pronghorn (Antilocapra americana)

(IV). Giraffe Ossicones

• Structure: Ossified cartilage covered with skin and hair.
• Characteristics: Permanent and unbranched; present in both males and females.
• Examples:Giraffe, Okapi

(V). Rhino Horns

• Structure: Composed entirely of keratin, without a bony core.
• Characteristics: Continuously growing, not attached to the skull.
• Examples: White Rhino, Black Rhino

2. Claw

• Structure: Curved, keratinized structure covering the distal phalanges.
• Function: Used for gripping, climbing, hunting, and defence.
• Examples: Cats, dogs, and bears.

3. Nail

• Structure: Flat, keratinized plates at the tips of fingers and toes.
• Function: Protects the digits and enhances the ability to grasp objects.
• Examples: Humans, primates.

4. Hair

• Structure: Keratinized filament originating from follicles in the dermis.

Structure of Typical Hair:

(I) Hair Shaft

• Cuticle: Outermost layer; composed of overlapping, flat, keratinized cells.
• Cortex: Middle layer; contains densely packed keratin and pigment granules, giving hair its strength and colour.
• Medulla: Innermost core; may be absent in fine hair, composed of loosely packed cells and air spaces.

(II) Hair Root

• Hair Follicle: Tubular invagination of the epidermis surrounding the hair root.
• Hair Bulb: Enlarged base of the hair root; contains the dermal papilla and the matrix where hair growth begins.
• Dermal Papilla: Cone-shaped elevation at the base of the hair bulb; contains blood vessels that nourish the hair.
• Matrix: Mitotically active cells surrounding the dermal papilla; responsible for producing new hair cells.

(III) Associated Structures

• Sebaceous Glands: Produce sebum, which lubricates and waterproofs the hair and skin.
• Arrector Pili Muscle: Small muscle attached to the hair follicle; contracts to make the hair stand up (goosebumps).

Functions of Hair

• (I) Protection: Shields the skin from UV radiation and physical damage.Prevents the entry of foreign particles into body openings (e.g., eyelashes and nostril hair).
• (II) Insulation: Traps a layer of air close to the skin, reducing heat loss and helping to maintain body temperature.
• (III) Sensory Function: Hair follicles are associated with nerve endings, allowing the detection of slight movements and vibrations, aiding in sensory perception.

Examples: Fur in dogs, wool in sheep, and human hair.

5. Hoof

• Structure: Thick, keratinized structure covering the toes.
• Function: Supports weight, aids in movement, and protects the toes.
• Examples: Horses, cows, and deer.

6. Epidermal Scales

• Structure: Overlapping, keratinized plates.
• Function: Protects against abrasion and water loss.
• Examples: Found on the tails and feet of rodents and armadillos.

Dentition in Mammals