Biology 453 Exam 1: Lecture 5

Front 1

Typical Amniote Keratinized Features

Back 1

# Stratum Corneum

* alpha keratin only
* thickness varies, thickest on palms of hands & soles of feet

# Keratinized/Horny Scales or Scutes

* rare
* examples - rodent & marsupial tails, armadillo outer "shells"; pangolin's "scales"
* alpha keratin only

# Claws

* inherited from ancestral amniotes
* Nails, Hooves similar design & homologous origin from amniote claws

Front 2

Horns: Typical Design, Growth

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* Typical Design
o keratin sheath over bone core
o ever-growing through out life of mammal
o in both sexes, but male forms are larger
o may curl or spiral, but never branched
* Growth
o a process of the frontal bone is covered with modified skin (corium)
o corium produces keratin (similar to the claw), which forms the outer shell of the horn.
o In young ruminants the "horn bud" (corium) can be identified in the skin as a small firm nodule.
o At this time the bud can be easily removed surgically or be destroyed by chemicals or electricity.
o If the bud is not destroyed at a young age it will combine with the periosteum of the rapidly growing bone & form the horn.
o The base of the horn has a rich blood and nerve supply.
* Typical Species - found in sheep, cows, afriican antelope...

Front 3

Pronghorn and Rhino Horn

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# Pronghorn - similar to other horns, but keratin sheath is shed annually (new keratin sheath in place before shedding occurs)
# Rhino Horn - no bone core, keratin grows above rostrum, thick hairs matted together with a sticky matrix

Front 4

Pigment & Skin Color in Humans: what causes difference b/t black and white skin

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* new genetic discovery of gene that controls activity of melanosomes
* same number of melanophores per mm3 across all races
* black skin
o higher rate of activity of melanophores
o pigment is well dispersed in epidermal cells
* white skin
o less active melanophores
o pigment concentrated above cell nuclei only

Front 5

Hair: Composition, Development, Evolutionary Origin - homologous with amniote epidermal scales?

Back 5

# Composition - alpha keratin
# Early Development

* dermal papilla causes overlying ectoderm to sink in
* this produces a solid cord of epidermis deep in skin
* unique development pattern
* hairs develop between scales, if epidermal scales are present

# Hypothesized Evolutionary Origin

* no fossil evidence of hair/fur yet found with synapsid fossils (mammalian ancestors), but suspected presence
* possible sequence of events:
o tactile bristles in hinge zones between scales of synapsid ancestors
o evolved by enlarging into more important & longer tactile hairs
o finally acquired functions of skin protection & endothermy
o hair is thus NOT a homolog of amniote epidermal scales

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Hair Design: 3 layers

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* Cuticle
o outer most layer, thin, made of overlapping "scales"
o pollen feeding bats use enlarged cuticle scales to trap pollen
* Cortex
o middle layer, many cells packed with keratin & pigments
* Medulla
o inner most layer, may contain pigment granules
o mostly hollow
+ large air spaces reduce weight of hair
+ large air spaces improves insulation

Front 7

Differences in Hair Color in Humans

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* black/browns - lots of melanin
* red; melanin + iron-based trichosiderin
* blond - much less melanin used
* white - no melanin; larger air spaces within hair shafts

Front 8

Hair Curliness caused by?

Back 8

curliness is genetically controlled & specified by the arrangement of disulfide bridges along the keratin strands

* curly - disulfide bridges cross-link keratin molecules at different levels
* straight - disulfide bridges cross-link keratin molecules at same level
* rollers - create weak, temporary curls by altering arrangement of the hydrogen bonds along keratin
* permament waves - break original disulfide bridges & then reform them

Front 9

Hair Distribution

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# most species - over most of body, or between scales
# exceptions: fur ~ absent in whales, elephants, humans & a few others

* these species have large body sizes that helps them retains heat
* &/or these species use more body fat for insulation

Front 10

Guard Hairs (or Terminal Hair in Humans)

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* thick - larger cortex region with round shafts make hair straight
* disulfide cross-brdges along keratin helix are at same level, keeping keratin fibrils straight
* more durable; protect skin & underlying hairs
* analog to contour feathers of a bird
* porcupine quills are highly modified guard hairs - thick & stiff

Front 11

Underfur (or Vellus in Humans)

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* larger medulla cavity may be oval or flat in cross section
* disulfide cross-brdges along keratin helix are at different levels so keratin fibrils "bend"
* shorter, softer, often wavy or curly hairs
* underfur is an analog of bird down (both insulate)
* thickest in marine species such as fur seal, sea lion, walrus
* in humans vellus increases with age & terminal hairs are lost

Front 12

Tetrapod Epidermal Glands:
Sebaceous (Oil): Composition, Secretion Method, Design, Functions

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* Chemical Composition - lipids, waxes, fatty acids, proteins, salts...
* Secretion Method - holocrine; sticky
* Design
o all multicellular, alveolar shape
o most empty into hair follicles
o in humans many go to surface directly
* Functions
o waterproofing & protect fur
o lubrication of skin, mouth, labia
o deter bacterial growth on skin
o synthesizes dehydrocholesterol, the precursor to vitamin D

Front 13

Tetrapod Epidermal Glands:
Sudoriferous Eccrine: Composition, Secretion Method, Design, Functions

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* Chemical Composition - 99% water, salts, some urea, ammonia & lactic acid; pH = 4-6
* Secretion Method - eccrine, watery, clear
* Design
o multicellular, narrow tubular, in dermis or hypodermis
o duct goes direct to top of epidermis
o numerous where underfur is absent; e.g. human palm (450/cm2)
o furred species have very localized & fewer sweat glands
o no glands in sirenia - manatees, cetaceans
* Functions
o "true" sweat - aids thermoregulation by releasing water onto skin for evaporative cooling
o some waste removal

Front 14

Tetrapod Epidermal Glands:
Sudoriferous Apocrine: Composition, Secretion Method, Design, Functions

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* Chemical Composition - water, salts, wastes, higher in fatty acids, protein
* Secretion Method - apocrine; sticky, milky white or yellow color
* Design
o multicellular, large tubular shape
o often deep in dermis or hypodermis
o often near hairs; ducts empty into hair follicle
o lumen of gland is large compared to eccrine glands
* Typical Locations - anal and genital regions
* Functions
o Do not aid thermoregulation
o Respond to stress and sexual activity by secreting sweat with a characteristic odor.
o scent/pheromone to attract mates, mark territories
o occassionally they can be defensive against predators (e.g. scent glands of skunks)

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Tetrapod Epidermal Glands: Sudoriferous Apocrine in Humans

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# located in armpits, around breasts, labia, groin
# glands become active at puberty
# in women their activity is linked to menstrual cycles
# glands also stimulated by stress, sexual arousal
# no conscious recognition of scent - pheremone

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Tetrapod Epidermal Glands: Mammary Glands: Composition, Secretion Method, Design, Function, Origin

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* Chemical Composition - milk
o water, lipid, protein, sugar, vitamins, immunoglobulins,....
* Secretion Method - apocrine
* Design
o multicellular, mixture of tubular & alveolar networks
o monotremes - secretion lapped off of hair tuft (no nipple)
o marsupials - nipples stored in depressions within skin
o placentals - larger glands, nipple variation
* Function - nutrition for newborn mammals
* Hypothetical 1st Function - delivering immunity to newborns - via immumoglobulins
* Evolutionary Origin - unknown; similar to both sudoriferous & sebaceous glands

Front 17

Tetrapod Dermis:
General Structure?

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* thicker than in all others vertebrates
* although thickness varies by body region (e.g. very thick palms, soles)

Front 18

Tetrapod Dermis: Osteoderms. Where are shells and accessory bones found

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# "Shells"

* rare - e.g. armadillos & fossil glyptodonts (relative of fossil armadillos)
* bony shell protects, skull, back, tail & may fuse with other bones of the skeleton

# "Accessory" Bones

* sesamoid bones in foot of ungulate
* become attachment points for important tendons & ligaments

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Tetrapod Osteoderms: Antlers: Exapmles, Design, Function, Origin?

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* Examples - "cervids" - deer, elk, moose, caribou, reindeer
* Design
o initial growth
+ males only except caribou & reindeer
+ dermal bone covered with soft vascular skin called velvet
+ velvet supplies all nutrients to the bone/antler as it grows
o maturation
+ complex branching patterns in mature antlers
+ When the annual growth is completed a band of connective tissue "tightens" around the base of the antler and cuts off the blood supply.
+ Velvet dies, so it is shed or scraped off, exposing the bone.
o loss - shed annually; bone has no blood supply once velvet is gone
o size - size increases annually as the individual matures (as long as health/diet are good)
+ old adults have antlers that decrease in size as their overall fitness declines
* Hypothesized Evolutionary Origin
o primitive cervids had canine tusks for fights - these may lead to injuries
o derived cervids have antlers that may have evolved as defense against tusks or as an improved defensive weapon against other predators
* Functions - sexual display to attract mates, ritual combat; defense