Answers-1, BIO 3220, Integumentary


1. Discuss the various functions of skin and its derivatives.
Protection and support – guards the body from harmful environmental elements, including solar radiation, weather, invading parasites, diseases
Sensory – several touch senses each of which is associated with a different type of receptor, embedded at a different level in the skin; some are sensitive to a light touch, others respond to pressure, others to temperature and yet others signal pain
Respiratory exchange – small animals with low metabolic rate diffuse gas directly across a moist body surface; ex. earthworms
Thermoregulation – skin prevents heat loss; also allows for rapid cooling during exercise through perspiration (sweating) and the vasodilation (widening) of blood vessels
Locomotion – skin and its derivatives, such as feathers of bird, scales of a snake, webbed feet of ducks, etc. aid in locomotion
Water balance – its continuous, tightly connected surface, lightly coated with oily sebum maintains a distinct fluid environment within our bodies from that environment encountered outside of our bodies
Protective coloring, behavior – skin/plumage can affect mating or act as camouflage
Vitamin D synthesis – skin synthesizes vitamin D with use of ultraviolet light from the substance ergosterol

2. Review the embryonic derivation of epidermis and dermis.
Epidermis – ectodermal derivation; Dermis – dermatome, lateral and ventral somatic mesoderm

3. Examine the overall structure of epidermis. What is keratin; its purpose? What are photophores? Identify the derivation of feathers, claws, scales, and glands.
The overall structure of epidermis is a stratum germinativum, the active mitotic layer, covered by a superficial layer which varies according to class.
Keratin, a tetrapod feature, is a tough, insoluble protein substance that is the chief structural constituent of hair, nails, horns, and hooves.
Photophores are light-producing organs found especially in marine fishes that emit light from specialized structures or derives light from symbiotic luminescent bacteria.
Feathers, claws, scales, and glands are derivatives of the epidermis.

4. Examine the structural make-up of the dermis. What potential makes the dermis unique?
The structural make-up of the dermis includes collagen, mucopolysaccharides, elastic fibers, smooth muscle, fat, blood and lymph vessels, follicles, and gland bases. Bone potential makes the dermis unique.

5. Name the three hard tissues in the body. Review their embryonic origin and briefly describe the phylogeny.
Enamel – calcium phosphate, calcium hydroxide present; permanent external tissue made from ectoderm
Dentin(e) – formed from mesoderm; similar to bone in make-up; about 25% organic fibers
Bone – derived from mesoderm; organic fibers, calcium crystals, usually has cells present
Phylogenetically speaking, bone is a primitive tissue.

6. Describe chromatophores. Contrast them between homeotherms and poikilotherms.
Chromatophores – irregularly shaped, pigment-containing cells often used for camouflage
Homeotherms – have melanophores which are a type of chromatophore that brings about a short term color changes by an active redistribution of pigment; pigment is injected into epidermis
Poikilotherms – have iridophores, xanthophores, and erythrophores; types of chromatophores in which the pigment remains in the dermis

7. Describe the epidermis of fish. Name the abundant glands.
The epidermis of fish is made up of epithelial cells, arranged one above the other. These cells are constantly shed and replaced with new ones. Inter-spaced between the epithelial cells are glands which produce mucoid secretions that form the very important protective covering, we know as the slime coat. These mucous glands help to clean and protect the skin, and decrease resistance when swimming. Club glands, granular glands, poison glands and multicellular light organs may also by present. There is no keratin present. Photophores may invade the dermis and serve as lures, warning, and recognition.

8. Describe the armor shields (4 layers) of ostracoderms and placoderms. Define denticle.
Armour shows four layers in section: dentine on the surface, capped with enamel-like tissues covered projections called denticles; a middle layer of spongy bone riddled with blood vessels and sensory pits; and a lamellar basal layer with few vascular channels.
Denticle – placoid scale of cartilaginous fish; also called dermal denticle

9. Compare cosmoid, ganoid, placoid, and modern scales. Relate scales phylogenetically to teeth and bones.
Cosmoid scales – cosmine is modified thick dentin layer, found in extinct sarcopterygians
Ganoid scales – ganoine is modified enamel layer; found in gars
Placoid scales – ancestor to teeth; denticle points decrease friction while swimming; found in chondrichthyes
Phylogenetically speaking, scales gave rise to teeth and bones.

10. Describe the two types of modern telocast scales.
Cycloid and ctenoid scales consist of two main regions, a surface “bony” layer, composed of an organic framework impregnated largely with calcium based salts, and a deeper fibrous layer composed mainly of collagen.
Ctenoid scales have a variously developed spiny posterior margin (the word “ctenoid” comes from the Greek “cteno”, meaning comb, and refers to the comb-like ctenii on the margin of the scale).
Cycloid scales have a smooth posterior margin lacking ctenii. The word “cycloid” comes from the Greek “cyclo”, meaning circle.

11. Name three major differences between fish and amphibian skin.
Amphibian skin has no scales, multicellular glands, and stratum corneum.

12. Explain the purpose of the stratum corneum in tetrapods.
The stratum corneum prevents against abrasion and dessication.

13. Describe the epidermis, epidermal glands, and dermis of amphibians.
The epidermis is thin and includes the stratum corneum with keratin and mucous and granular glands that sometimes secrete alkaloid material. The dermis is firmly attached and may have chromatophores.

14. List five ways reptile skin differs from amphibian skin.
Reptile skin has a thick stratum corneum, epidermal scales, horny surface structures, few glands, and some have bony dermal scales/plates.

15. Describe the epidermis, scales, scutes, glands, and dermis of reptiles. Include osteoderms, “shells,” and gastralia.
Epidermis is comprised of the stratum corneum with keratin, no mucous glands, and may have granular/scent glands, although small and very few.
Scales are small epidermal structures that characteristically form the external covering of reptiles. They overlap and are shed.
Scutes are horny, chitinous, or bony external plates or scales, as on the shell of a turtle, the underside of a snake or the rattle on a snake.
Reptiles have no mucous glands. Some have granular/scent glands, but they are small and few.
The dermis is thin and varies between species. In crocodiles, the dermis is an osteoderm, with bone in the dermal layer. In turtles, the dermis is a shell, carapace or plastron. Gastralia, or splints of bone in the ventral abdominal wall of crocodiles, is a dermal scale derivative.

16. List the general differences found in bird skin.
Bird skin is thin, only thick at foot and beak and includes feathers.

17. Describe the epidermis, scales, glands, and beak of birds.
The epidermis of birds is thin and includes horny scales at lower leg and toes that are not shed and uropygial glands located at the tail feathers that are used for waterproofing. The beak is an epidermal structure made of keratin. Feathers are also epidermal structures.

18. Explain how feathers evolved.
Most adult feathers have a backbone, or stem, called a rachis, from which the feather’s barbs branch. Each individual barb then branches again into the feather’s smallest unit, the barbule, which is composed of a single row of epithelial cells. Downy feathers, like those on a chick, lack rachides altogether and are made up of just barbs studded with barbules. The standing hypothesis among many paleontologists has long been that the scales on dinosaurs must have lengthened into rachides that then became notched to form barbs and barbules.

19. Distinguish the parts of contour feathers. Explain what preening does to these feathers.
The parts of a contour feather are the shaft – which includes the calamus or quill and rachis – and the vane – which includes barb and barbules with hooklets.
Preening is carefully and methodically combing through feathers – smoothing them, cleaning them, putting them back in place.

20. Contrast the structure and function of down feathers and contour feathers.
Contour feathers have a backbone, or stem, called a rachis, from which the feather’s barbs branch. Each individual barb then branches again into the feather’s smallest unit, the barbule, which is composed of a single row of epithelial cells. Downy feathers, like those on a chick, lack rachides altogether and are made up of just barbs studded with barbules.

21. Explain molt.
Molting is the normal process by which a bird replaces his feathers. Broken and disheveled feathers can not be repaired and so once a year or so, the bird will systematically drop feathers and replace them with new ones. Most birds molt annually, though there is some fluctuation between species. Frequency of molt can also be affected by age, seasonal changes, hours of daylight and breeding activity. Though there is some fluctuation between species, most birds drop a few feathers at a time and then grow replacement feathers using the same feather follicle.

22. Describe the dermis of birds.
The second and deeper layer of birds, the dermis, consists of cells which generate the epidermis. It contains numerous tiny blood and lymph vessels, nerve-fiber endings and usually fat. The dermis also initiates the production of special structures such as feathers and scales. It also contains arrector pilorum muscles which are autonomically innervated smooth muscles oriented obliquely in dermis, creating “gooseflesh”.

23. List four mammalian skin characteristics.
Hair, variety of glands, stratified cornified epidermis, thick dermis

24. Identify the layers of mammalian epidermis.
Stratum germinativum, stratum granulosum, stratum corneum

25. Name the stratum corneum derivatives in mammals.
Horny scales, claws, hooves, nails, armadillo shell, horns

26. Name and contrast three types of horns.
True horns – dermal bony core with horny cover; not shed; ex. antelope horn
Hair horns – derived from the epidermis; not shed; ex. male and female rhinos
Antlers and giraffe horns – composed entirely of bone with no actual horn substance; velvet is skin which is shed on antlers, but not giraffe horns

27. Discuss mammalian integumentary glands. Which are unique to mammals?
Sweat/Sudoriforous glands – glands in the skin that secrete perspiration; unique to mammals
Sebaceous glands – a cutaneous gland that secretes sebum (usually into a hair follicle) for lubricating hair and skin
Scent glands – specialized organs that produce secretions having odors with specific functions in animal behavior
Mammary glands – milk-secreting organ of female mammals; unique to mammals

28. Theorize the phylogenetic origin of hair.
Hair is commonly believed to be derived from reptilian scales, as were the feathers of birds, to help retain body heat, because hair is an excellent heat insulator.

29. Describe the structure of hair. Include shaft, root, cortex, cuticle, medulla, follicle, bulb and the arrector pili muscle.
Each strand of hair, or shaft consists of three layers. An innermost layer or medulla which is only present in large thick hairs. The middle layer known as the cortex which provides strength and both the color and the texture of hair. The outermost layer is known as the cuticle which is thin and colorless and serves as a protector of the cortex. Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the bulb, or dermal papilla. The dermal papilla is fed by the bloodstream which carries nourishment to produce new hair. The arrector pili muscle, originates in the dermis and inserts on the outer sheath of the hair follicle.

30. Name four types of hair.
Guard, underfur, vibrissae, quills

31. Describe the dermis of mammals.
Dermis is very thick and contains many glands, blood vessels, hair follicles, and arrector pili muscles.