Lecture 7 Flashcards
Describe characteristics of the amphibian integument that were important in the transition from an aquatic to a terrestrial environment
The amphibian integument displays characteristics associated with the transition from a completely aquatic environment to a terrestrial environment.
• Development of a true stratum corneum
• Highly vascularized dermis for gas exchange
• Numerous integumentary glands:
• Unicellular mucous glands (of Leydig) in larval salamanders
• Multicellular mucous glands
• Multicellular granular (poisonous) glands
Stratum corneum:
• Beginning with amphibians, the stratum corneum become keratinized.
• The cells making up the outer layers of the epidermis are derived from the stratum basale and are specialized for synthesizing keratin, a
protein derivative of eleidin.
Dermis:
• The dermis is a significant respiratory organ among amphibians and, in some, is the only respiratory organ.
• The dermis is well supplied with blood vessels which serve as the major gas exchange organ for respiration.
List types of glands associated with the amphibian integument
Integumentary glands:
• Unicellular glands of Leydig are mucous glands found in certain larval salamanders.
• Multicellular mucous glands are common in the amphibian integument and serve to secrete a water-retaining layer of mucous on the surface of the epidermis.
• Multicellular granular (poison) glands are found in most amphibians and are especially well developed in toads (parotid glands) and in the poison dart frogs, some of which are brightly patterned members of
the family Dendrobatidae.
Compare the reptilian integument with the amphibian integument with emphasis on adaptations for terrestriality
Development of the stratum corneum:
• The stratum corneum first appeared in amphibians, but it became extremely well-developed in reptiles.
• A well-developed stratum corneum reduces water loss and also the necessity for many epidermal glands.
• A major derivative of the stratum corneum in reptiles are epidermal scales.
• Epidermal scales are actually folds in the stratum corneum rather than individual entities.
• For a reptile to grow, the epidermis must be shed (molted), and it is shed in a continuous sheet, demonstrating that the scales are part of a continuum.
Describe the epidermal scales and compare with dermal scales
Epidermal scales:
• Epidermal scales are epidermal derivatives, unlike the scales associated with dermal armor, which are dermal derivatives and closely associated with bone.
• Epidermal scales are interconnected by thin bridges of epidermis, resulting in the periodical shedding of an entire continuous layer of epidermal scales to allow for the growth of the animal.
• Thickening and hardening of the cornified epidermis results in the formation of cornified scales called scutes.
• In crocodilians and turtles, scutes form a pattern of flat plates.
• In snakes and lizards overlapping scales are commonly present.
• In snakes, the scutes on the ventral surface are large and aid in locomotion.
Dermal scales:
• In turtles, highly developed dermal scales contribute to the formation of the carapace and plastron.
• The dermal scales are overlapped and strengthened by epidermal scales.
• Some lizards have dermal scales called osteoderms.
• Both crocodilians and Sphenodon possess gastralia:
- Gastralia are dermal bones developed on the ventral surface of these animals.
• Crocodilians also have well-developed dermal plates along the back.
List major characteristics of the avian integument and compare with reptilian integument
• Birds have a relatively thin skin with a well-developed stratum corneum.
• Integumentary glands are reduced:
• Uropygial glands are found at the base of the tail.
• These are simple, branched alveolar glands that secrete an oily material.
• Birds use their beaks to collect this material and spread it over their
feathers (preening) to keep the feathers soft and water-proof.
• Modified oil glands are associated with external ear openings.
• Feathers are epidermal derivatives and are the hallmark of the avian
integument. Feathers are represented by several types:
• Contour feathers
• Down feathers
• Filoplumes
Describe general structure of a contour feather
Consists of a shaft:
- Base is the calamus.
- Longer, distal part is the rachis.
Barbs:
- Extend out from the rachis.
- Equipped with hooks and barbules which interconnect with adjacent barbs.
Vane:
- The wide, flattened surface composed of the rachis and barbs.
Contour feathers develop in tracts called pterylae.
• Featherless zones that separate the tracts are called apterylae.
• Contour feathers in the forearm and hand are remiges.
• Contour feathers in the tail are retrices.
• Flight feathers are set into the bones of the wing.
• Contour feathers elsewhere are attached to the skin.
List and compare feather types in birds
Down feathers: • Are also referred to as plumules • Usually evenly distributed • May be ancestral to contour feathers • Have a short calamus • Lack hooks on the barbs and are therefore more efficient for trapping air • Very soft and fluffy
Filoplumes:
• Have a threadlike shaft
• A filoplume with a stiff rachis is called a bristle.
• Bristles can be used to screen objects from nostrils, increase the effective gape of the mouth, and form eyelashes.
Compare homeotherms with poikilotherms
- Homeotherms are able to maintain a relative constant body temperature in spite of variations in the ambient temperature.
- Homeothermy requires a means of producing heat and a means of either retaining body heat or losing body heat, depending on the ambient temperature.
- Poikilotherms include fishes, amphibians, and reptiles which take on the surrounding ambient temperature.
- Poikilotherms are not “cold blooded,” because they, at times, may have a body temperature that is much higher than that of a homeotherm.
- Poikilotherms typically become sluggish if ambient temperatures drop below optimum operating levels.
- Poikilotherms can employ basking in the sun, body pressing against a warm surface, or shade-seeking in order to alter their body temperature.
Describe some of the anatomical modifications that make homeothermy possible
• Both feathers and hair (fur) can trap air.
• Air is an insulator.
- Trapped air can help retain body heat.
- Both feathers and hair can be elevated or flattened, causing more or less
air to be trapped.
- Raising or lowering hairs/feathers is accomplished via the autonomic
nervous system and bundles of smooth muscle fibers called the arectores
pilorum (hair) or arrectores plumarum (feather).
• Homeothermy requires a high metabolic rate.
• In mammals, homeothermy may also involve integumentary functions
such as control of sweating or its analogue, panting .
• Homeothermy may also involve sending more or less blood to the
integument
Describe general characteristics of mammalian integument and list categories of derivatives
The mammalian integument consists of a well-developed epidermis and dermis.
• New derivatives of the stratum corneum, hairs, are found in mammals and represent one of the distinguishing characteristics.
• Mammals are also characterized by the presence of mammary glands, which are epidermal derivatives.
• The mammalian dermis is usually quite thick.
• The dermis of many mammals, such as cattle forms tough leather when prepared chemically in a process called tanning.
• Epidermal scales have generally disappeared from the skin of mammals.
Describe general characteristics of mammalian integument
The mammalian integument consists of a well-developed epidermis and dermis.
• New derivatives of the stratum corneum, hairs, are found in mammals and represent one of the distinguishing characteristics.
• Mammals are also characterized by the presence of mammary glands, which are epidermal derivatives.
• The mammalian dermis is usually quite thick.
• The dermis of many mammals, such as cattle forms tough leather when prepared chemically in a process called tanning.
• Epidermal scales have generally disappeared from the skin of mammals.
List categories of mammalian derivatives
Mammalian integumentary derivatives:
• Glands:
• Sudoriferous glands
• Sebaceous glands
• Mammary glands
• Meibomian glands
• Glands of Zeiss (eyelids)
• Ceruminous glands (ears)
• Scent glands
• Hairs
• Claws, antlers, hoofs, nails
• ChromatophoresCompare thick skin with thin skin
- The skin covering the human body can be referred to as thick skin or thin skin.
- This designation refers to the complexity of the epidermis and not to the overall thickness of the skin:
- The thickest skin is found on the back, and it is referred to as thin skin.
- The thinnest skin is found on the eyelids, and it is referred to as thin skin.
- Thick skin, which may be thinner than some skin elsewhere on the body is only found on the palms of the hands and the soles of the feet.
List characteristics of the layers of thick skin epidermis
Layers of the stratified squamous epithelium in thick skin: (* = stratum malpighi)
• Stratum basale (germinativum) *
- Deepest layer
- Single layer of cells
- Held together by desmosomes
- Hemidesmosomes hold layer to basal lamina
- High mitotic activity:
- Mitotic activity produces stem cells differentiating keratinocytes.
• Stratum spinosum*
• Stratum granulosum:
- Represented by only a few cells in thin skin
• Stratum lucidum:
- Absent in thin skin
• Stratum corneum
- Most superficial
- Multilayered (5-50 layers)
- Thicker in thick skin
- Enucleated, flattened, dead keratinocytes
- Cytoplasm replaced by keratin
Describe general histology of the dermis
Dermis characteristics:
• Dense fibrous irregular connective tissue layer beneath epidermis
• Derived from embryonic mesoderm
• Induces development of epidermis and epidermal derivatives
• Supports epidermis
Two layers:
• Papillary layer (closest to epidermis):
• Loose CT
• Separated from epidermis by basal lamina
• Network of fine elastic fibers and abundant capillaries
• Reticular layer
• Dense irregular CT
• Includes fibrocytes, macrophages, and adipocytes
