ty bsc embryo 1 introduction

7/21/2019 TY BSc Embryo 1 Introduction

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General Embryology1 Introduction: 4• Defnition and scope

• Theories o preormation,pangenesis, epigenesis, axial

gradient and germ plasm



Defnitions

• Embryology -The branch of biology that deals with the formation,early growth, and development of living organisms.

• The embryonic structure or development of an

orgnisms• Embryogenesis- development of embryo from

fertilized eggs.

• Animal pole- unfertilized egg is a large cell, it has

pigmented upper surface.• Vegetal pole- unfertilized egg is a large cell, it has lower

region, characterised by an accumulation of yolkgranules.



Defnitions

• Cleavage- are mitotic divisions of fertilized egg orzygote, in which cells do not grow between eachdivision, and so with successive cleavages the cells

become smaller.

• Blastula- after about 12 division cycles, the embryois known as blastula , consists of many small cellssurrounding a fluid filled cavity blastocoel above the

germ layer.• Germ layers- changes have occurred within the

cells and they interacted with each other so that somefuture tissue types have become partly specified.



Defnitions•

Mesoderm- is present in the blastula as an euatorial band. It gives rise to muscle, cartilage, bone, and otherinternal organs like heart, blood and kidney.

It also gives rise to a rod like notochord, runs from head

to tail.n either sides of notochord are segmented blocks of

mesoderm called somites, which gives rise to the musclesand vertebral column and dermis of skin.

• Endoderm- It gives rise to the gut, lungs and liver. Vegetal region gives rise to endoderm.

• Ectoderm- the animal region will give rise toectoderm. !hich forms both epidermis and the nervous

system.



Defnitions

• Gastrulation-there is a dramatic rearrangement ofcells, the endoderm and mesoderm move inside. "ndthe basic body plan of the tadpole is established.

• !eurulation- shortly after gastrulation, theectoderm above the notochord folds to form a neuraltube, which gives rise to brain and spinal cord.

• "rganogenesis- process during which specialized

cells such as muscle, cartilage and neuronsdifferentiated.



Germ cell

spermatozoon and ovum

1. #permatozoon#- a haploid male se$ cell, which is capable t

fertilize ova and transfer the characters from father to offspring

2. "vum%- haploid female se$ cell, secondary oocytearrested at metaphase in the second meiotic division andtransfer the characters from mother to offspring.

• Capacitation： In female reproductive tract, the sperm

were enabled to bind to the zona pellucida receptors,removal of glycoproteins &decapacitation factor' whichcover the sperms.

$efinitions



• %ertilization& The process in

which thespermatozoonpenetrates into theovum to form fertilized ovum.In the ampulla of

oviduct

Defnitions



1. (leavage ： early division of fertilized egg

2. )lastomere： daughter cells from cleavage

*. +orula： 12 to 1- cell stage, enclosed in the

zona pellucida, like morus. )lastocyst： about 1 blastmeres,

blastocoele、 inner cell mass and trophoblast.

Defnitions



Scope of embryologyA. Scientic signicance:-

1.Ontogenetic development;- it helps inunderstanding the development o individual and also

general concept o ontogenetic development.

2.!ylogenetic relations!ip:- comparative study o

development o organisms belonging to dierent groupshelps in assigning the p!ylogenetic relations!ip and

systematic position o dierent animal and plant groups.

".Evolutionary signicance:- study in

developmental biology helps to explain the occurrenceof vestigial structures.

4. !t explains the various phenomena pertaining to gro"th,

di#erentiations and regenerations.



Scope of embryology

$. Medical significance#-'( )n malformation&- abnormalities in

structure or function of an organ or part may ariseduring development. These may be caused due to

genetic defects, effect of drugs, viruses,hormones etc. The type of abnormality produceddepends more on the stages of development on whichthe effective agent acts.

*( Malignant tumours#- These are abnormal

forms of tissue development( The nature andcontrol of malignancy relates to the understanding

of normal processes of growth and differentiation.



Scope of embryology

$. Medical significance#-+(Ageing#- ageing process is one of the aspect of

development. It re/uires proper understanding of cell,tissue and organismal growth throughout the life span.

,(Control of reproduction and development#- theinsight knowledge of reproduction has helped incontrolling reproduction and development ofhumans and their livestoc . This is being achieved by the

use of hormones, sperm storage at low temperature and embryo transfer. It has led to the development of

techni/ue called test tube baby . .roduction of/ransgenic animal0 1eproductive cloning(



• To study effects of gene products0 biochemical

pathways0 alternative &compensatory' pathways, and

developmental pathways

• To recreate human diseases in animals to establish

models to test the beneficial effects of drugs or gene

therapy . to study the regulation of gene associated with

the development of the tissue

• to study the function of specific gene involved in the

tissue development and the phenotype of those genes in

the tissue• to study regulation of genes involved in the oncogenesis

• The effects of substances or chemical substance in the

therapy of cancer

.roduction of /ransgenic animal



Cloning

• 1eproductive cloning- The entire animal isproduced from a single cell by ase$ual reproduction.This would allow for the creation of a human being

who is genetically identical to another.• Therapeutic cloning- )roader use of the term

0cloning. oes not create a new geneticallyidentical individual. 3esearch includes therapy for

human mitochondria disease and others that couldreplace damaged or diseased tissues without the riskof re4ecting another5s tissue. (ould create new skintissue for burn patients.



/heories

'( .reformation /heory &-•. The utch scientist 6wammerdam &1*7-8' proposed

that the se2 cells &ovum9sperm' contain preformedembryo or a more or less perfect miniature of the adult.

•.

In case of the man this miniature organism was calledhomunculus.

•. evelopment process involves the growth and unfolding ofthe miniature into the adult.

•. This theory was supported by +alpighi&128-1:', ;aller&178-:*' and 6pallanzani &172:-::'.

•. This group of scientist who believed that miniature organism was present in the egg were called ovists.



/heories

'( .reformation /heory &- contiunued•. "ccording to these ovists every ovum in the ovary

of female contained a tiny , miniature of theadult, which by proper stimulus from the seminal

fluid, developed into the adult.

•. 6ome ovist advocated e$treme form of preformationtheory, which they named encasement or

emboitment theory.•. It holds that the minatures of successive generations

of individual organism pre-e$isted one inside theother in the germ cells of mother.



/heories

'( .reformation /heory &- contiunued•. Another group of scientist belived that the

preformed miniature organism is present in thehead of sperm. These were called spermists. Theydescribed sperm as seeds and egg as the soil in

which seed was planted.

•. 3artsoeer &1<-172<' gave an illustrated

diagram of man5s sperm with homunculus.



/heories

*( Epigenestic /heory &-•. Casper %riedrich wolf &17<:' in volume entitled

0Theoria Generationis” described that in chicegg, there is no preformed miniature chic .

•. ;e advocated that the future embryonic regions ofan egg are formed of granules or vesicles.

•. uring development, these gradually organise intorudiments which can be called the germinal layers.

•. The method of progressive development fromsimpler to more comple2 organization through the

utilization of building units is called epigenesis.



/heories

*( Epigenestic /heory :%•. The theory of epigenesis is accepted even today but in

different form.

•.

!ith great advances in the fields of cytology andgenetics, it is known that the genetic constitutionof an organism is fi2ed by heredity in the fertilizedegg from which the organism develops in specific lines.



/heories+( Germplasm theory of 4eismann&-

•.

This theory was proposed by 4eismann in 188* can beconsider as ma4or landmark in developmental biology because

he was the first to distinguish germplasm as a separate

entity from somatoplasm.

•. "ccording to him, the germplasm is a self perpetuatingcellular entity which continues its e$istence though ages.

•. The child inherits characters of the parents through the se2

cells of the parents and not from other part of the body.

•. Germ cells ac/uire the characters from pre-e2isting germ

cells(

•. in each new generation, a temporary soma of body is built

around the germplasm that described from the parents.



/heories*( Germplasm theory of 4eismann :%&ont

•. "ccording to !eismann, embryo remains already organizedin the chromosomes of the nucleus and during early

development these characters are unpacked in an orderly

manner.

•. ;e recognized units of heredity as determinants and

these are segregated during the early cell division of the

embryo making these divisions differential.

•. In the first cell division, the determinants are distributed

into right and left sides of the future embryo and later

divisions into anterior and posterior parts and so on.

•. =ater, interaction between them enable epigenetic

development possible.



,( /heory of pangenesis• In 188 (harles arwin proposed >angenesis, a

developmental theory of heredity.• ;e suggested that all cells in an organism are

capable of shedding minute particles he calledgemmules,

• which are able to circulate throughout the body andfinally congregate in the gonads.

• These particles are then transmitted to the ne2tgeneration and are responsible for the

transmission of characteristics from parent tooffspring.

• If any cells of the parent undergo changes as a resultof environmental change, they will conse/uently

transmit modified gemmules to their offspring.

/heories



• 6oon after arwin?s pangenetic theory was published,

%rancis Galton designed a series of bloodtransfusion e$periments on differently pigmentedrabbits to test its validity .

• ;e found no evidence in support of the e$istence of

arwin?s gemmules and the concept of .angenesis was largely abandoned.• In this article, recent reports of successful induction of

heritable changes by blood transfusion are reviewed.• $etection of circulating nucleic acids and prions in

plant sap and animal blood is considered as freshevidence for the e$istence of gemmules.

• It is now apparent that a considerable revision of views onarwin?s >angenesis must occur before a new

comprehensive genetic theory can be achieved.

/heories,( /heory of pangenesis-cont



,( /heory of pangenesis-cont

• $arwin became aware, blending inheritance &including

his own theory of 0.anogenesis in which each organ

and tissue of an organism throws off tiny contributions

of itself that are collected in the #e2 organs anddetermine the configuration of the offspring'

• It could not account for the conservation of

variations, because differences between variant

offspring would be halved each generation, rapidly

reducing the original variation to the average of the

pre-e2isting characteristics.

/heories



• 3ippocrates &c. @c. *7< )(A', known as thefather of medicine,

• believed in the inheritance of ac/uiredcharacteristics and to account for this,

• ;e devised the hypothesis known as .angenesis.

• ;e postulated that all organs of the body of aparent gave off invisible 0seeds, which were like

miniaturized building components and weretransmitted during se2ual intercourse,reassembling themselves in the mother5s wombto form a baby .

/heories,( /heory of pangenesis-cont



• Boveri &1:1' introduced a gradient concept.• ;e postulated that the vegetal region of sea

urchin influences the morphogenesis of animalregion of the embryo and this influence

gradually decreases towards the animal pole.

• C( M(Child &1:' and others proposed BMetabolica2ial gradient theory 5 according to which there

e2ists a gradient of the o2idative metabolism inthe egg.

• )y using rate of reduction of vital dyes,particularly 6anus green as an indicator of the

rate of o2idative metabolism.

7( A2ial Gradient /heory/heories

/h i



• (hild demonstraed the difference in the rate of

general metabolism in ooplasm of animal and vegetal hemispheres of the oocytes and the cleaving egg of sea urchin and starfish.

• (hild proposed that there e$ists a gradual decrease in

the rate of o2idative metabolism in the ooplasm fromanimal pole to vegetal pole, which can be described asthe metabolic a2ial gradient along the animal-vegetala$is.

• (hild5s metabolic a2ial gradient theory was latermodified by 3orstadius &1:<<' and 1unnstrom &1:7'.They proposed the e2istence of a double gradient system to control the morphogenesis anddifferentiation during early development of seaurchin embryo.

7( A2ial Gradient /heory- cont/heories

h i



• The animal gradient is ma2imum at the animal pole and is

responsible for the formation of structure characteristics of

that region.

• 6imilarly vegetal gradient , which is most intense at the

vegetal pole, control processes like invagination, formation

of archenteron and mesenchyme.

• If the animal gradient is weaened or supressed, the

vegetal gradient become preponderant and the embryo is

vegetalized.

• If the vegetal gradient is weaened, the animal gradient

becomes preponderant and animal becomes animalized.

• " normal development results only when two gradients are

in control euilibrium.

/heories7( A2ial Gradient /heory -cont



'!an(s

ty bsc embryo 1 introduction

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