Lesson 3 Flashcards
- series of progressive changes in an individual from it’s beginning to maturity
- specialization occurs as a hierarchy of developmental “decisions”
Development
- the theory that involves a tiny human in a sperm
Humoculus
- Many eggs release a chemical molecule that attracts sperm of the same species to the egg
Contact and Recognition Between Egg and Sperm
- Thin membrane above the egg plasma membrane
vitelline envelope
- Fertilization cone forms where the sperm contacts the vitelline membrane
- Sperm head drawn in and fuses with egg plasma membrane
- Important changes in the egg surface block entrance to any additional sperm
Prevention of Polyspermy
- the entry of more than one sperm
Polyspermy
- used to block out other sperm
Fast block
- the name for a fertilized egg
Zygote
- embryo divides repeatedly
Cleavage
- large cytoplasmic mass gets converted into small maneuverable cells
- No cell growth occurs, only subdivision until cells reach regular somatic cell size
Blastomeres
- Zygote has been divided into many hundreds or thousands of cells
Blastula
Cleavage Types
Holoblastic
Meroblastic
- Cleavage extends entire length of egg
– Egg does not contain a lot of yolk, so cleavage occurs throughout egg
Holoblastic
- cells divide at the top of the yolk
- too much yolk, can’t divide
Meroblastic
Egg Types and Cleavage
Isolecithal
Mesolecithal
Telocithal
– Very little yolk, evenly distibuted
– Use Holoblastic cleavage
Isolecithal
– Moderate yolk
– Use Holoblastic
Mesolecithal
– Have an abundance of yolk
– Use Meroblastic cleavage
Telocithal
- cleavage creates a cluster of cells called the blastula
- During the blastula stage, the first germ layer forms
– Cells are arranged around a fluid-filled cavity called the blastocoel
Blastulation
- Results in the formation of a second germ layer
- Involves an invagination of one side of blastula
– Forms a new internal cavity called the gastrocoel - creates an opening into the cavity: Blastopore
Gastrulation
2 layers of the gastrula
Ectoderm and Endoderm
- ## The only opening into embryonic gut
Blastopore
- Some animals retain the blind gut
- the opening does not fully extend to other side
Flatworms, sea anemones
- in which the opening extends and produces a second opening, the anus
Complete gut
- Animals with two germ layers
Diploblastic
- animals with 3 germ layers (most animals add a 3rd germ layer)
Triploblastic
- Forms between the endoderm and the ectoderm
- arises from endoderm
Mesoderm
- germ layer that deals with the epithelium and nervous system
Ectoderm
- germ layer that deals with epithelial lining of the digestive and respiratory
tract, liver, pancreas,
Endoderm
- Muscular system, reproductive system, bone, kidneys, blood
Mesoderm
- Body cavity surrounded by mesoderm
Coelom
– The method by which the coelom forms is an inherited character
• Important in grouping organisms based on developmental characters
– Upon completion
• Body has 3 tissue layers and 2 cavities
- coelom formation
- Animals Without a Coelom are called
Acoelomates
- Two major groups of triploblastic animals
Protostomes and Dueterostomes
- blastopore develops into an anus first, and the second opening becomes a mouth
Deuterostome embryos
- blastopore becomes a mouth first, then the second opening becomes an anus
Protosome embryos
- Coelom Formation - mesoderm movement
enterocoely and schizocoely
- Mesoderm sides push outward and expand into a pouch-like coelomic compartment
• Pouch-like compartment pinches off and forms a mesoderm bound space
surrounding the gut
• Occurs in Deuterostomes
Enterocoely
- Endodermal cells move to blastopore and develop into mesoderm
• Mesoderm separates or splits to form cavity (coelom)
• Occurs in Protostome
Schizocoely
- mesoderm fills the blastocoel
Acoelomate plan
- mesoderm lines one side of the blastocoel
- pseudocoelomate plan
- band of mesoderm surrounds the gut and spits open
Schizocoelous plan
- mesodermal pouches surround the gut
Enterocoelous plan
- mesodermal pouches surround the gut
Enterocoelous plan
– All vertebrate embryos share chordate hallmarks
The Common Vertebrate Heritage
•Dorsal neural tube
•Notochord
• Pharyngeal gill pouches with aortic arches
• Ventral heart
• Postanal tail
Common vertebrate heritage
- embryos develop within the amnion
Amniote
- Fluid-filled sac that encloses the embryo
– Provides an aqueous environment in which the embryo floats
– Protection from mechanical shock - contains 4 extraembryonic membranes including the amnion
Amniotic egg
- responsible for storing yolk
Yolk sac
• Storage of metabolic wastes during
development
• Respiratory surface for gas exchange
Allantois
• Lies beneath the eggshell
• Encloses the embryo and other extraembryonic membrane
Chorion
–Need for oxygen increases
–Allantois and chorion fuse to form a
respiratory surface, the chorioallantoic
membrane
Happens when the embryo is growing
– Most mammalian embryos do not develop within
an egg shell
- Develop within the mother’s body
- Most retained in the mother’s body
Mammalian Placenta
• Primitive mammals that lay eggs
• Large yolky eggs resembling bird eggs
•Duck-billed platypus and spiny anteater
Monotremes
– Embryos born at an early stage of development and
– Continue development in abdominal pouch of mother
Marsupials
– Represent 94% of the class Mammalia
– Evolution of the placenta
• Required reconstruction of extraembryonic membranes
• Modification of oviduct
– Expanded region formed a uterus
Placental Mammals
- Remains unchanged
- Surrounds embryo
- Secretes fluid in which embryo floats
Amnion
- Contains no yolk
- Source of stem cells that give rise to blood and lymphoid cells
- Stem cells migrate into the developing embryo
Yolk sac
- Contains no yolk
- Source of stem cells that give rise to blood and lymphoid cells
- Stem cells migrate into the developing embryo
Yolk sac
- Not needed to store wastes
- Contributes to the formation of the umbilical cord
Allantois
- Not needed to store wastes
- Contributes to the formation of the umbilical cord
Allantois
- forms most of the placenta
Chorion
