INTEGUMENT OF BIRDS & ITS DERIVATIVES

INTEGUMENT OF BIRDS & ITS DERIVATIVES

The integument of bird is dry, thin, loosely attached to body covered with epidermal derivatives. The main derivatives are feathers. Feathers are unique to all birds which are light, elastic, waterproof and most important for flight. They are differently colored and modified into many types in order to insulate the body (homeothermy).

V.S OF SKIN OF BIRD

Ø The skin of bird like any other vertebrate composed of 2 layers, stratified epithelium and dermis.

Ø The skin is very thin and loosely attached to achieve maximum freedom of movement of feathers during flight.

Ø Epidermis is in turn made up of 2 layers viz., Stratum corneum and stratum   germinativum or profoundum.

Ø Stratum corneum is multilayered, outer part of epidermis which is keratinized without any uni or multi cellular gland cell.

Ø Stratum germinativum is unilayered cuboidal or columnar epithelium resting on a basement membrane from which the top layers are constantly replaced.

Ø From the epidermal layer various modifications or derivatives are seen like feather covering the entire body, except hind limbs covered with scales, beak, claws, spurs, web etc., diversified and adapted to different habitats. All the derivatives are thought to evolve from epidermal scales.

Ø The epidermis including both layers evaginates to form feather germs from which calamus the basal part of feathers arising from feather follicles.

Ø The dermis has 2 layers viz., outer stratum laxum corii and inner stratum compactum corii.

Ø Stratum laxum  corii , has loose connective tissue, elastic fibers, blood capillaries, smooth muscle fibers without glands or chromatophores but has melanocytes forming a layer beneath the germinativum contain pigments which migrate to feathers and scales  imparting varied coloration.

Ø The skin glands are found exceptionally in the tail region called uropygial or preen glands which are very well developed in aquatic birds.

Ø The preen glands secretes oil or waxy secretion which used to coat on feathers and beak during preening.

Ø Stratum compactum is the inner most layer of the dermis which has collagen fibers and smooth muscle fibers arranged horizontally and compactly in between which  are found numerous fat cells or adepocytes which function both as storage and insulation an adaptation for homeothermy or warm bloodedness.

DERIVATIVES OF BIRD’S SKIN:

Pterylosis:  The arrangement or distribution of feathers on body is known as Pterylosis. The flightless birds (Ratitae) feathers are uniformly distributed, but in Carinatae, feathers are arranged in distinct patches or tracts called Pterylae which are separated by featherless interspaces called Apteria.

ARRANGEMENT OF FEATHER

TYPES:

There are usually 4 types of feathers:

                i.   Quill or Remex

               ii.   Contour or Pinnae

              iii.    Filoplumes or Hair or Pin feathers

              iv.    Down or Plumules

ü Quill or Remex feathers: are feathers present on tail or wing ( Rectrices & Remiges respectively)

ü A typical quill feather has 2 parts viz., a small proximal Calamus or quill and an upper distal portion the Vane.

ü Calamus is hallowed and its lower end has a small inferior umbilicus at the junction of calamus and rachis.

ü A small tuft of soft feather known as hypo rachis or after shaft arises near the superior umbilicus the upper opening of the calamus.

ü The calamus continues as shaft or rachis a solid opaque forming the longitudinal axis of the vane.

ü T he ventral umbilical groove is a narrow furrow running along the inner surface of the rachis throughout its length.

ü Vane is made of two unequal lateral halves with its distal end narrower than its proximal end.(outer web & inner web respectively)

ü Each lateral half of the vane consists of numerous narrow parallel and closely spaced thread called barbs with interlocking barbules.

ü Quill feather helpful in flight.

QUILL FEATHER

2. Contour or Pinnae: are feathers which form the general covering of the body.

ü It consists of two parts, a) central axis or vane b) calamus.

ü These are small feathers with barbs having poorly developed barbules so that the barbs can be easily isolated.

ü The calamus is hallowed and very a small compared to quill feathers made up of dry dermal pulp.

ü Both the halves of the vane are more or less equal.

ü Contour feathers provide a smooth surfacing to body to resist the friction while moving in air.

ü These feathers overlap completely covering the body and acting as insulator i.e., preventing heat loss, maintain homeothermy.

CONTOUR FEATHER

3. Filoplumes or Hair or Pin feathers:

ü Filoplumes are small delicate and hair like feathers found separately distributed all over the body.

ü It consists of a short calamus with inferior umbilicus at its proximal end.

ü The rachis is and thread like having a few barbs and barbules at its free tip.

ü The actual function of filoplumes is not known.

PIN FEATHER

4. Down feathers or Plumules:

ü Down feathers are very small soft and wooly feathers which differ from contour feathers by the absence of rachis.

ü The barbs are long flexible with small short rudimentary barbules appearing as a fluffy tuft from the top of the calamus.

ü The down feathers are seen covering only the newly hatched birds providing excellent insulation.

ü They are absent in adult birds completely replaced by contour feathers.

DOWN FEATHER