Lectures 5-7 Flashcards
Microlecithal egg:
SMall amt. yolk
Mesolecithal egg:
Moderate amt. yolk
Macrolecithal egg:
Large amt. yolk
Isolecithal egg:
yolk evenly distributed throughout egg.
Telolecithal egg:
Yolk is concentrated at one end of the egg
Why micro/meso/macrolecithal eggs?
micro: Depend on external source of nutrients…mammals
Meso: enough energy for tadpole and to metamorphosis
Macro: enough yolk to provide adult-like form
Developmental steps for frog embryo
1: passes through animal-vegetal axis- 2 daughters
2: passes through animal-vegetal axis perpendicular to first cut-4 daughters
3: perpendicular to the 1st 2 cuts- 8 cells [unequal-macro/micromeres]
4: cuts continue to 32-64 cells
5: cells separate from internal cavity [blastocoel]-animal pole side
6: after blastulation, gatrulation begins: layerings form rearranged hollow ball
7: neurulation: formation of neural tube-CNS
How does neurulation compare in frog to vertebrate?
Looks similar: pretty much the same
Vegetal pole
Side of egg w/ concentrated yolk
Animal pole
OPPO end of egg w/o yolk
Meroblastic or discoidal cleavage
not cleaving through a ball of yolk like frog—birds have macrolecithal eggs there is only room for blastodisc cleavage.
Discoidal cleavage Avians:
1: furrow in cytoplasm of disc @ animal pole
2: 1st cleavage plane is not into yolk.
3: 2nd cleavage is perpendicular to the 1st.-4 equal sized blastomeres
4: 3rd cleavage lie parallel on either side of 1st–8 blastomeres.
5: 4th cleavage-circular furrow forms periphery of the 1st 3 -16 blastomeres.
6: yolk creates subgerminal space
7: 16-32 stage cleavage parallel blastodisc-multiple layers of blastomeres.
8: several hundred cell-stage=blastoderm
9: 2 cell layers[upper/lower] Separate making cavity in middle DELAMINIATION
10: could be considered blastocoel or gastrocoel
Mammalian developmental steps:
1: 1st cleavage is holoblastic.
2: first several cleavages similar to amphibian egg [equal and perpendicular to each other]
3: after 4th cleavage, it becomes unequal
4: after 4.5 days, 8 larger inner cells and 99 outer cells
Inner cells=
Inner cell mass
Outer cells=
Trophoblast layer
Trophoblast:
Trophoblast attaches to the lining of the uterus and forms 2 tissues:
1-cytotrophoblast: chorion
2-Syncytiotrophoblast: erodes into the uterus
BECOMES the PLACENTA
Inner cell mass
Becomes the embryo proper: amnion, yolk sac, and allantoic stalk
Advantages to development in aquatic environment:
CO2 and O2 readily diffuses, readily excrete nitrogenous wastes, dessication is reduced risk.
disadvantages to development in terrestrial environment:
- Difficult to keep membrane moist
- can’t dilute ammonia waste product
- nutrition may not be readily available in terrestrial.
Four extra embryonic membranes:
Amnion
Chorion
Yolk sac
Allantois
Chorion
Involved in the formation of the placenta
Amnion
Creates fluid-filled environment for protecting embryo from dessication
Yolk sac
Preliminary site for the formation of blood cells and germ cells
Allantois
Forms the umbilical cord connecting embryo to placenta
Functions of the vertebrate integument:
Protection Coloration Sensory reception Excretion Gas exchange Water regulation Temperature regulation Food storage Nourishment Locomotion
Anatomy of the protochordate integument
Simple epithelium on simple gelatinous connective, no dermis, no glands……
Vertebrate has stratified squamous epidermis rests on basement membrane
Vertebrate integument
Stratified squamous epithelium on basement membrane which is dense irregular connective
Most constant feature in epidermis:
Collagen
Describe glands
Presence or absence of excretory duct, number of cells, type of secretion, mode of secretion, and shape
Exocrine glands
Empty contents into a body cavity or onto a surface.
Endocrine glands
Empty contents into bloodstream- ECF
Glands in fishes
Unicellular and multicellular mucous
Enamel vs. Dentine
Enamel: dead. Secreted by ameloblasts. Hardest substance in body.
Dentine: Secreted by odontoblasts. Organized in a matrix. LIVING. Blood vessels and innervation.
Scale of fishes EVO.
Enamel->cosmine->enameloid-> ganoin->thin fibrous tissue on top of compact bone.
Less layers through EVO.
Changes that occurred in early terrestrial vertebrates integument changes for possible terrestrial
Early fish became scaled no body armor b/c it was heavier-no buoyancy.
AMphibians became smoother skin-stratum Corneum [layers of dead keratin]
Keratinized stratum Corneum is adaptation to terrestrial life for defense to water loss in dry environment
Amphibian integument characteristics important in transition from aquatic to terrestrial environment:
- True stratum Corneum
- Vascularized dermis for gas exchange:dermis is resp. Organ.
- Numerous integumentary glands
TYpes of glands asso. W/ amphibian integument
- Leydig [unicellular]
- Multicellular mucus glands [water-retention]
- Multicellular poison glands -parotid glands are poison glands.
Keratin is made from
It is a protein derivative of eleidin
Reptile vs. amphibian integument
Reptiles stratum Corneum became more well-developed for reducing water-loss and epidermal glands or SCALES. Scales are folds in stratum Corneum.
Epidermal scales vs. dermal scales
Epidermal: scales are interconnected by thin bridges of epidermis-shedding happens. Allows for animal growth. Thickening-cornfield scales called cutes..
Dermal:Overlapped and strengthened by epidermal scales. Dermal scales: bone/ plates
Reptile vs. avian integument
Birds: thin skinned, well-developed stratum Corneum. Uropygial glands at base tail secrete oily material and spread for feathers to be soft and water-proof. Feathers are epidermal derivatives
Contour feather
Shaft base: calamus.
Shaft connected to feather part is rachis.
Barbs extend out from rachis.
Rachis and barbs make the vane
Feather types in birds:
Down feathers:plumules. Short calamus and no hooks on barbs =more efficient for trapping air.soft and fluffy. Ancestor to contour
Filoplumes: threadlike shaft. Stiff rachis= bristle-used to screen objects from nostrils, increase gape of mouth and form eyelashes
Homeotherms
Able to maintain relative constant body temp. In spite of variations in ambient temp.
Poikilotherms
Take on surrounding ambient temp. ( fish,amphibians, and reptiles)
What anatomical modifications made homeothermy possible?
- Feathers /hair trap air and can act as insulator.
- High metabolic rate
- Integument function-sweating, panting
- sending more or less blood to the integument
Which vertebrate groups are homeotherms?
Birds and mammals
General characteristics of mammalian integument:
- Well-developed epi/dermis
- hair
- mammary glands
- thick dermis
- dermis forms tough leather-tanning
- no epidermal scales
- glands
Mammalian integument derivatives:
Glands
Hairs
Claws,antlers,hoofs,nails
Chromatophores
Thick skin vs. thin skin
Designation depends on complexity of epidermis…
All skin is thin except skin on palms and soles of feet.
What is missing in thin skin in the epidermis?
Stratum lucidum
Also rare in stratum granulosum
Dermis histology
Dense fibrous irregular connective tissue
Hypodermics characteristics:
Loose connective tissue under dermis
Contains panniculus adiposus
2 layers of dermis
Papillary layer
Reticular layer
Papillary layer
- Loose connective tissue
- Separate from epidermis by basal lamina
- network of fine elastic fibers and abundant capillaries
Reticular layer
- Dense irregular Connective tissue
- fibrocytes, macrophages, and adipocytes
Sudoriferous glands
Long, hollow tubular glands- produce sweat [watery secretion]
Larger and connected to hair follicles
Apocrine and Merocrine sweat glands
Apocrine sudoriferous sweat glands
Asso. W/ hair follicles in axiliary and pubic region
Thicker secretions acted upon by bacteria
Merocrine sudoriferous sweat glands
Watery secretion for evaporative cooling and important for thermoregulatory system
Sebaceous glands
Holocrine glands
Asso. W/ hair follicles
Help keep hairs pliable and may provide a role in waterproofing the integument
Mammary glands
Histologically similar to sudoriferous glands
Apocrine and Merocrine secretions
Different nipples in placentals and ungulates
Claws, nails, hoofs, and horns
All similar- compressed layers of stratum Corneum
Keratin that makes this up has higher sulfur content-hard keratin.
Claws, nails, hoofs, and horns structure
Nail: ungus
Under nail: subungis
Where nail is grown from: stratum greminativum [matrix]
Nail plate can be flat, curved horseshoe shape in different animals
Ungulates
Walk on distal edge of nail
Have unguligrade stance
If you walk on your toes
Digitigrade stance [cats/dogs]
Walk on soles of feet
Plantigrade stance
Horns
Both genders;
Solid core of bone attached to frontal bone and covered w/ stratum Corneum;
Bone remains after death…Corneum doesn’t.
Antlers:
Usually only male[except reindeer];
Outgrowths of frontal bone;
Growing bone= highly vascularized skin-velvet.
Fall off after breeding season
MAjor defining characteristics of mammals:
Hair and mammary glands
