this presentation discuss about oogensis

1. TOPIC:
Oogenesis
Females produce their lifetime supply of gametes.

2. OVUM
unfertilized gamete, primary oocyte, secondary oocyte, ovum.
People may use ovum and egg interchangeably,
but in the other cases the egg
may actually fertilized and undergoing EMBRYONIC growth.
The ovum is a single cell but
it is also associated with the non-cellular
material produced by the female reproductive tract.

3. The three main modes of reproduction strategies:
1.OVIPARY/OVIPAROUS
animals expel the ova from the body.
And development occurs externally using the resources
within the egg fertilization may be external
most fish, and internal bird and reptiles.
Level of parental care ranges from none
intense. Few insects exhibit parental care where
most birds guard eggs and feed young.

4. 2. VIVIPARY/VIVIPAROUS
animals use internal fertilization, and young develop
within the female body. In early development
the young derive significant resources from mother.
Placenta mammals are most examples of vivipary
but also occurs in species of fish
snakes, skinks. The female reproductive tract produces
nutrients for offspring, which can be simple.

5. 3. OVOVIVIPARY/ OVOVIVIPAROUS
animals demonstrate feature both ovipary and vivipary
they use internal fertilization, followed by extensive
internal development of embryos, while in uterus
embryos device their nutrition from the yolk
rather than the mother when mature, the
eggs hatch within the mother. The strategy is
common in fish, sharks, reptiles, many invertebrates.

6. surprisingly, reproductive mode varies widely within texa
species are able to switch between modes
brine shrimp, for example can be ovoviviparous
and release free-living young (naupali) or oviparous
laying gastrulae encrusted in a shell (cysts)
the skink lerista has both oviparous and
viviparous population. Among condrichthians(sharks and rays)

7. Some species of skates lay fertilized eggs
that are float in the ocean current
some sharks are ovoviviparous, others are viviparous
the several sharks species the ovoviviparous embryo
thrives on the nutrients from the egg.
But then at some point begins to feed
life history strategy that is difficult categorize

8. Female reproductive tract includes:
Ovary- composed of the ova-producing Oogonia
as well as surrounding somatic cells that
provides structural and nutritive support for oogenesis
most species oogenesis progresses through the primary
oocyte stage. early in life of female
but finally steps of process are delayed
the oocytes from the surrounding somatic cells proliferate.

9. To form follicle that encapsulates the oocytes.
The follicle cells or granulosa cells, secrete
the extracellular matrix components that form acellular
layer between the oocyte and follicle cells
called zona pellucida. The entire follicle is
surrounded by basolateral membrane is known theca
they communicate with the oocytes by paracrine

10. Factors and direct cell-to-cell contacts
prior to ovulation, a subset of follicles
is stimulated to mature (folliculogenesis).the oocytes
must first increase in cytoplasmic volume, although
the increase in cell size occurs by
multiple mechanisms.Vertebrate oocytes grow by accepting
biosynthetic precursor a different pattern occurs in

11. many invertebrates fruit flies oocyte absorb cytoplasm
Surrounding nurse cells, derived from oogonia that
fail to differentiate into oocytes,when follicle
ruptures the ovum escapes the ovary and
moves into the COELOM. In some species,
ova are retained with in the COELOM.
Example some insects accumulate eggs until the

13. abdomen burst, killing the female. Commonly the
ovum crosses a short stretch of coelom
and enters the opening of the oviduct
called the FALLOPIAN TUBE in mammals.
The ovum passes through the oviduct into
uterus. Those species that use internal fertilization
retain the ova in oviduct or uterus

14. the uterus may be a simple passage
Or maybe strong muscular tissue that uses
smooth muscle contractions to expel ova, fertilized
eggs, or young through the gonopore: the
vagina in those species with dedicated reproductive
pore, or a CLOACA if the reproductive
and excretory systems have a common pore.

15. The yolk provides building blocks and metabolic precursor
most animals with the exception of placental
mammals, provide each ovum with a source
of nutrients in the form of YOLKS,
a complex mixture of proteins and lipids.
Most of the macromolecules in yolk are
produced outside the oocyte, then sequestered by
the oocyte early in oogenesis. Triglyceride from

16. the extracellular fluid passes from the blood
between the follicle cells to the oocyte,
where taken up and stored within vesicles.
Vitellin is the most abundant, it is
produced in the oocyte from vitellogenin, a
bulky and complex phospholipoglycoprotein that is produced
by the insect fat body, the vertebrate liver.

18. VITELLOGENESIS
animals in initiate vitellogenesis in response to
external cues, such as environmental condition or
developmental program . The pathways begins centrally within
the brain, trigerring a hormonal cascade that
causes biosynthetic tissues to produce and secrete
vitellogenesis. This protein passes the follicular cells
and taken up by the oocytes stored.

19. Then converted to vitellin. Invertebrates and vertebrates
differ in the specific hormones and target
tissues but the general features are similar.
Suites of hormones mediate vitellogenesis . External signals
of various forms stimulate the central nervous
system to release vitellogenic factors. vitellogenesis begins
shortly after the animal consumes blood meal.

20. INSECT EGGS ARE SURROUNDED BY A CHORION
In The Silk Moth , The Ova Develop
In Four Ovaries (Ovarioles), Each Of Which
Contains In Excess Of 100 Follicle
Arrange In The Series. The Follicle That
Is Closet To The Genopore Undergoes Oogenesis
at late stages of oogenesis, a single
ovariole possesses each of development stages of

21. separated by about 2.5 hours of development.
These stages are divided into three groups:
1. PREVITELLOGENESIS
2. VITELLOGENESIS
3. CHORIOGENESIS

22. Ecdysone controls the early development of ovarioles
as well as the previtellogenic stages. During
prevetellogesis, the follicles have not yet begun
to produce yolk. The oocyte the begins
to accumulate yolk proteins marketing onset of
the vetellogenic period. The yolk proteins from
the fat body are transferred from the

23. Hemolymph to the oocyte across the follicle
cells. The follicular cells also produce eggs-specific
proteins that are secreted and taken up
by the oocyte. Early stages of development
ecdysone controls the production of yolk proteins.
After vitellogenesis has begun, a reduction in
20HE levels causes the follicle cells to

24. Begin chorion formation(choriogenis). The follicular cells
produce and secrete more than 100 types
of proteins to construct the chorion. The
ovum moves into the oviduct, where it fertilized.
Sperm cross this impermeable shell through a
tunnel called the MICROPYLE. The fertilized eggs
are then laid.

25. EGGS STRUCTURE DIFFERS IN AQUATIC AND
TERRESTRIAL VERTEBRATES
most fish and amphibians produce eggs that
are simple in structure. The ovum is
physically connected to yolk. As the ovum
passes down the reproductive tract, it receives
a viscious coating from reproductive tract secretions
the gelatinous eggs are released from the
animal into the water unfertilized. amphibians and fish

26. The young leave the egg as aquatic
larvae and complete their reproductive maturation. The
constraint of this strategy is the need
for water at all development stages. Like
the insects they produced a hardened external
shell around the egg that provided support
and prevented dehydration. In constrast to the

27. Proteinacious chorion of insects, the eggshell of
reptiles and birds is composed of calcium
carbonates embedded in an organic matrix. The
bird eggshells has a thick layer of
calcium carbonate salts, giving it a brittle
but hard texture. Many reptiles produce eggshells
analogous to those in birds, but some reptiles

28. Since the eggshell in birds and reptiles
is impermeable, even to sperm, the animals also
needed to coevolve different mode of fertilization
the ovum in reptiles, birds, and monotremes
(egg-laying mammals) must be fertilized before the
eggshell is formed. Thus, fertilization is internal
and the eggshell forms in the oviduct

29. Around a fertilization ovum. EUTHERIAN(PLACENTAL) and
METATHERIAN(MARSUPIAL) mammals, of course, have dispensed
with eggshell and solve the challenges of
terrestrial life by rearing fertilized ova internally.
Reptiles, birds, and mammals are collectively AMNIOTES,
a name derived from one of the
four extraembryonic membranes.