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- (=ontogeny) - fertilization->birth hatching
- single, fertilized cell becomes millions.
- Develops basic structural organization of an individual.
- Birth to sexual maturity
- Growth in Size
- Acquisition of learned skills
- Acquisition of secondary sexual characteristics
- abrupt body of change
- undergoes division, or cleavage
- Cell types differentiate into three major germ layers:
- Ectoderm, Mesoderm, Endoderm
Zygote passes through stages
solid ball of cells
Division continues to form a hollow ball of cells
hollow ball of cells with invagination at one end
will become living embryo
will form membranes that nourish the embryo
Egg types differ
- in yolk amount and cleavage pattern, which depends on amount of yolk:
- (=complete) cleavage (bowfin, Amia)
- Different sized cells result from different amounts of yolk in each.
- Little or no yolk at the animal pole; more yolk toward the vegetal pole
- direction and order stereotyped
- First cleavage may not be complete prior to the second starting.
- Cleavages continue at increasing pace
- Blastula hollow ball of cells does not change mass greatly but many additional cells (=blastomeres) present.
- egg of a teleost.
- Cleavage forms a blastodisc (=blastoderm)
- Most of vegetal pole with most yolk does not divide; becomes periblast, a layer of cytoplasm adhering to undivided yolk mass.
- patterns differ
- Monotremes have discoidal cleavage
- have no morula stage.
- Cells spread inside zona pellucida and form protoderm.
- mammals pass from a morula to a blastocyst.
- Inner cell mass cells become embryo.
- Outer cells become trophoblast that forms membranes.
- Little yolk present.
- Gastrulation - blastula invaginates at vegetal pole.
- Blastopore=new opening
- Gastrocoel=new opening.
- This process initiates germ layer formation.
- Formation of endodermal tube of early gut.
- Space within gut=archenteron (=gastrocoel)
- Outer layer=ectoderm
- Layer that moves between=mesoderm, with three regions:
- Epimere, Mesomere, Hypomere.
- Mesodermal outpocketings
- Endoderm forms gut lining.
- early development through neurulation
- Holoblastic cleavage
- Mesolecithal egg
Differentiation in a teleost fish
- Meroblastic cleavage pattern
- Macrolecithal egg type.
Amphibian gastrulation and neurulation
- Holoblastic cleavage
- Mesolecithal egg type
- Cells move along surface (epiboly)
- Turn inward at blastopore at dorsal lip
- Form and enlarge gastrocoel
- Coelom forms by splitting of mesoderm
- 3-5=early cleavages
- 13-16 neurula
- 17 tail bud forms
- 18 Muscular twitches begin
- 19 heartbeat starts
- 20 functional early gills develop and blood circulates through the caudal fin
- 24 operculum appears
- 37 hindlimbs and then forelimbs appear
- Macrolecithal egg type
- Discoidal cleavage
- Primitive streak serves as does dorsal lip of blastopore.
- Cells move inward and differentiate into different germ tissues
- Separate stream of cells moves anteriorly to form notochord.
Later stage of bird gastrulation and neurulation
- Beginning of formation of tissues that will give rise to organs.
- Cells more toward locations from which they will differentiate into organs.
- Egg=little yolk
- Shows complex pattern of cell movement as does a bird.
- Primitive streak location where cells move into center of embryo
Structures from three germ layers divided according to colors of layers and structures formed.
Categories of connective tissues
Correlate tissue type with location within an organism and the function it performs
Correlates with function it performs within organism, so consider how structure and function relate to predict what kind of tissues occur in each location.
- Important to understand stresses on body regions.
- Allows us to determine (epiphyses open in growing animals)
- May allows us to determine (epiphyses open in growing animals)
- May allow determination of bone injury, pathology or illness.
- Bone status can permit health determination of individual or population.
- also called woven bone illustrates fast-growing bones.
- ex. alligator
- deposited in layers with different orientations, arranged as is plywood, and is therefore, stronger.
- ex. turtles
- a specialized form of lamellar bone.
- Organic salts arranged in regular and highly ordered.
series of concentric rings of bone cells and matrix around central canal for passage of blood and lymph vessels and nerves.
surrounds bone - carries nerves and blood vessels into bone shaft.
(haversian bone) offers density and strength along edges.
remodeled throughout life of individual
centrally located (within a long bone for example)
at angles and connect osteons
Two types of bone growth
- Endochondral - model performed in cartilage is replaced by invasion of bone cells.
- Dermal (=membranous) bone growth pattern.
- Mesenchymal cells converge
- produce osteoid tissue (bone matrix precursor)
- Blood vessels enter.
- Osteoblasts appear.
- Osteoid becomes enriched with calcium and becomes matrix.
- Matrix becomes denser.
- Osteoblasts mature and become osteocytes.
Formation of a new osteon
- Remodeling occurs throughout the life of bones
- Old osteons replaced by new ones.
- Old osteons eroded by osteoclasts.
- Osteoblasts along the channel perimeter form concentric rings of new bone around a central blood vessel.
- Blood clots and debris form callus between broken ends.
- Replaced by cartilage.
- Cartilage calcifies, blood vessels and osteoblasts enter.
- Osteoclasts remove debris.
- New matrix laid down as woven bone spicules which hold ends together.
- Increased density=healed bone.
Neural crest and embryonic placodes
- Only in bertebrates.
- Neural crest cells that break lose from surface epithelium prior to neural fold closing.
- Form specific cell clumps.
- Migrate and differentiate.
- Sink inward from ectoderm to form paired sensory structures.
- Lateral line placodes
- Octic placodes
- Dorsolateral placodes
- Epibranchial placodes
- Adenohypophyseal placode (contributes to pituitary)
- Optic placode
Neural cells differentiate into
- Spinal and cranial nerve ganglia
- Schwann cell insulating sheaths surrounding peripheral nerves.
- Chromaffin cells of adrenal medulla
- Pigment cells except for retina and CNS
- Hormone producing cells throughout body
- Cartilage and bone of lower jaw
- Most voluntary muscle connective tissues
- Dental odontoblasts that secrete inner core of tooth dentin.
Arise from embryonic germ layers, but not as egg envelopes that surround many types of eggs as they pass though the reproductive tract.
- have extraembryonic memberanes
- Reptiles, birds and mammals
- fishes and amphibians
- lay eggs in water or moist areas
- four estraembryonic membranes: Amnion, Chorion, Allanatois, Yolk sac
Extraembryonic membranes in amniotes
- Different placental types have evolved
- Determine how nutrients from mother are transferred to growing embryo.
- Main body cavity into which internal organs are suspended.
- Produced by splitting of hypomere.
- Coelomic fold grows down to meet transverse septum which grows upward. They join to form diaphragm and pleural cavities that separate lungs from abdominal organs.
fundamental body reorganization=adult body form
sexual maturity without metamorphosis
sexual maturity but somatic development slows, allowing persistence of juvenile characters.
change in timing and rate of growth of features
- An adult that retains juvenile features.
- Somatic growth ends early; adult has appearance of juvenile.
- Adult exhibits extended growth of features.
- Somatic growth ends late; features continue to grow.
Ontogeny recaptiulates phylogeny=biogenetic law
Von Baer's Law
- Development proceeds from the general to the specific
- Modification of Biogenetic law
- Embryos of ancestral and descendant forms resemble each other, but not necessarily the adults.
- Early stage embryos resemble each other more closely than do later stage or adults.
- Vertebrae replace notochord in mammalian embryos.
- Vertebrae develop around notochord.
- Arise from sclerotomes.
- Protect nerve cord.
- Provide origin sites for muscles that move column.
- master control genes that determine where parts of organism form.
- Control structural genes that build structures.
- Effect=greater further posteriorly and can add up to large changes downstream.
- Regulate development of front-to-back structures in body in different organisms, vertebrate or not.
- Can permit appearance of what is considered to be rapid evolutionary changes.
Mechanism by which Hox genes effect evolutionary change
- Changes in the number of Hox genes
- Changes in Hox gene expression over body regions.
- Chnages in downstream regulation of genes or function.
Limb formation in embryos
- Structures grow outward
- Other cell types migrate into limb bud.
- Take blood supply with them.
- Blood vessels=most variable system because many paths allow them to reach and drain tissues of the limb.
- Apical ectodermal ridge interacts with mesoderm to produce limb type mechanical barrier to this interaction can mimmic production of ancestral conditions.
- Extra toes in horses show that underlying developmental pattern of ancestor is still present.
- Panda's thumb=derived from a carpal bone that elongated and became larger.
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