Embryology - PowerPoint PPT Presentation

1 / 24
About This Presentation
Title:

Embryology

Description:

3. Roux's experiment (using amphibian eggs) 1888 ... e. In certain species, especially amphibian eggs, a structure called the gray ... – PowerPoint PPT presentation

Number of Views:243
Avg rating:3.0/5.0
Slides: 25
Provided by: cob133
Category:

less

Transcript and Presenter's Notes

Title: Embryology


1
Embryology
2
Embryology the study of the development of an
organism from the time an egg is fertilized until
the time when all major organ systems are formed
A. Historical Aspect
1. Preformation this was a concept held during
the 17th and early 18th century which stated that
sex cells (gametes) contained a completely
formed, but greatly miniaturized human inside
them. This miniaturized person was termed a
homunculus
2. By the mid-18th century, another view began to
become popular known as epigenesis. This concept
stated that the egg contained material from which
the embryo was built and directed the formation
of the individual by some unknown creative
principal.
3
3. Rouxs experiment (using amphibian eggs) 1888
4. Drieschs experiment (using echinoderm eggs)
1892
4
V. Steps in Embryonic Development
A. Definitions
1. Gamete sex cell
2. Sperm male gamete
  • motile, flagellated
  • usually much smaller than the female gamete
  • haploid (contains only one set of chromosomes for
    that species) 1n

5
(No Transcript)
6
3. Egg or ovum female gamete
a) non-motile b) up to 1,000 times larger
than a sperm cell
c) haploid 1n also d) within the egg are
most of the enzymes, proteins, and other
information needed for development for the new
embryo
7
4. Fertilization union of sperm and egg
(fertilization is also called syngamy)
  • the result of fertilization is a diploid zygote
  • diploid having two complete sets of chromosomes
    resulting from syngamy
  • zygote the cell produced from the union of egg
    and sperm that will divide mitotically, forming a
    new organism

8
B. First Step Fertilization (syngamy)
  • Sperm must penetrate the gel coat surrounding the
    egg
  • 2. Enzymes called lysins, located in an
    organelle in the head of the sperm called the
    acrosome, dissolves the gel coat membrane around
    the egg

9
C. Second Step Egg Activation
1. Egg activation begins when the acrosomal
membrane of one sperm fuses with the egg membrane
2. Early changes to the egg ensures that only one
sperm will fertilize that egg
  • the first sperm that unites with the egg membrane
    is surrounded by the microvilli located on the
    membrane, which wraps around the penetrating
    sperm
  • the nucleus of this one sperm is drawn into the
    center of the egg (contains the DNA)
  • within milliseconds of the initial penetration of
    this sperm, ionic changes occur in the egg
    membrane making the membrane unresponsive to any
    other sperm
  • a protective barrier called the fertilization
    membrane prevents any other sperm from entering

10
e. In certain species, especially amphibian eggs,
a structure called the gray crescent forms on the
side opposite of the site where the sperm
initially penetrated
11
D. Third Step Metabolic and Nuclear Events
  • Very little mRNA synthesis occurs within the
    early zygote. Almost all of the mRNA directing
    early development and division was stored within
    the egg itself. This original mRNA is called
    maternal mRNA since it was formed by the mothers
    cells. (This is the main reason an egg cell is so
    much larger than a sperm cell)
  • The maternal mRNA directs protein synthesis early
    on in embryonic development
  • 3. The DNA only has to be concerned about
    replicating, not transcribing, and rapid
    replication occurs (mitotic divisions)
  • 4. Egg regions
  • a) animal pole area of the egg that
    contains less yolk, more mitochondria, more
    ribosomes and is more metabolically active

12
b. vegetal pole contains more yolk (food) and
is less metabolically active
E. Fourth Step Cleavage and Egg Types
1. Definitions
  • cleavage cell divisions (the result of
    cytokinesis)
  • blastomeres the cells resulting from cell
    divisions

c) Yolk lipids, glycogen, proteins,
carbohydrates and other organic compounds used
for food
d) Synchrony term used for simultaneous
division of cells
13
2. Cleavage patterns
a) Holoblastic cleavage division of a cell that
divides it into two equal daughter cells,
uniformly across the whole ball of cells
b) Meroblastic cleavage egg cells with a lot of
yolk divide only at one end (not equal)
i) examples include bird eggs and reptilian eggs
14
c) spiral cleavage cleavage patterns occur at
obtuse angles to one another i) this type
is typical to lower invertebrates (determinant
development) d) radial cleavage cleavage
patterns oriented directly over other cells at
right angles to each other i) typical of
highest invertebrates and chordates
15
  • Determinant development zygotes, even by the
    four cell stages, have become specialized (lower
    invertebrates)
  •     f) Indeterminant development cells become
    specialized much later in the gastrula stage
  • i) unspecialized cells are called
    totipotential cells or undifferentiated cells
  • ii) undifferentiated cells are also
    called stem cells

16
3. Embryo development as a result of cleavages
  • The one cell (zygote) divides by mitosis to
    become two cells, two cells divide to become
    four, four to eight, and so forth
  • Soon a hollow fluid filled ball of cells forms
    called the blastula (the cavity within is called
    the blastocoel)

c) Some cells on the blastula begin to grow
inward (invaginate) which forms a double walled
structure called the gastrula (process is called
gastrulation) d) The opening created by this
invagination of cells is called the blastopore
and the new cavity is called the archenteron e)
The outer layer of cells will become the ectoderm
and the inner layer of cells will become the
endoderm
17
VI. Primary Germ Layers beginnings of
differentiation formed during gastrulation
A. There are three primary germ layers
1.Ectoderm (outer tissue)- origins of the
following tissues
  • nervous tissue including brain
  • epidermis, including skin, nails, hair, fur,
    teeth, etc.
  • sensory organs associated with the skin

2. Endoderm (inner tissue) origins of the
following tissues
a) gut tract lining
18
b) respiratory tract lining c) digestive glands
including pancreas and liver
3. Mesoderm (middle tissue) -origins of the
following tissues
  • connective tissues (bones, cartilage, blood,
    tendons, ligaments)
  • b) muscle tissue (smooth, striated, and
    cardiac)
  • c) notochord in chordates
  • d) dermis (inner layer of skin)
  • e) outer covering of internal organs
  • f) excretory organs
  • g) reproductive organs

19
(No Transcript)
20
Patterns of Development
  • Protostomes
  • Blastopore Mouth
  • Spiral-Determinate Cleavage
  • Ectodermal Skeleton
  • Deuterostomes
  • Blastopore Anus
  • Radial-Indeterminate Cleavage
  • Mesodermal Skeleton

21
Tissue Organization
  • Acellular
  • Single-celled, No tissues
  • Diploblastic
  • Body parts organized into layers that are derived
    embryologically from two tissue layers, Ectoderm
    and endoderm
  • Triploblastic
  • Body parts organized into layers that are derived
    embryologically from three tissue layers,
    Ectoderm, mesoderm, endoderm

22
VII. Vertebrate Embryology
A. Chordate characteristics during some stage
of the development or life of a chordate, it has
  • a hollow, dorsal nerve cord
  • a stiff, but flexible, rod-like structure used as
    support in their back called a notochord
  • post-anal tail
  • pharyngeal gills slits

23
B. Formation of a hollow tube (the neural tube)
in the back of vertebrates occurs after
gastrulationthis process is called neurulation.
It occurs by the invagination of the ectoderm
C. Avian and Reptilian Embrylogy
  • Both of these groups undergo meroblastic
    development
  • The egg in these groups is the true egg plus
    several protective membranes
  • vitelline membrane surrounds and protects the
    true egg
  • albumin egg white nutritional and consumed
    along with yolk during development

24
  • shell composed of calcium carbonate and is
    porous for the exchange of gases
  • yolk food reserve
  • amniotic sac encloses developing embryo in a
    fluid for protection
  • chorion sac found near the shell and aids in
    gas exchange
  • allantois waste sac, helps to accumulate uric
    acid wastes and break those toxic compounds into
    non-harmful products
Write a Comment
User Comments (0)
About PowerShow.com