Embryology Notes - PowerPoint Presentation

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Embryology NotesSlide2

Embryology

Development of a

multicellular

animal begins with

fertilization

:

fusion

of sperm with egg forming zygote

Zygote

immediately begins to develop – triggered by contact between cell membranesSlide3

Fertilization Process

Sperm cell comes into contact with jelly coat surrounding egg cell –

Zona

pellucida

Acrosome

(vesicle in head of sperm) releases enzymes that act on jelly coat and membrane of egg

Sperm forms a tube that pushes through jelly coat

Sperm

pronucleus

moves into egg cell

Egg’s membrane becomes impermeable to other sperm –

cortical reaction

Development is initiatedSlide4
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Embryological Development

Zygote begins rapid series of mitotic divisions immediately after fertilization –

cleavage

During

early cleavage, nuclei cycle rapidly between DNA replication (S phase) and mitosis – forms a solid ball of cells called a

morulaSlide6

MorulaSlide7

Newly formed cells (

blastomeres

) begin to pump Na+ into center of

morula

Results in the diffusion of water which creates a fluid-filled cavity –

blastocoel

Embryo is now a

blastulaSlide8

Gastrulation

An indentation forms on one side of the blastula –

blastopore

Blastula cells migrate in a continuous sheet through

blastopore

–

gastrulation

Forms three embryonic tissue layers –

gastrula

Ectoderm

– forms skin and nervous system

Endoderm

– lines digestive tract and forms associated organs (liver and pancreas)

Mesoderm

– forms most organs and tissues (kidney, heart, muscles, inner layer of skin)

Blastocoel

disappears as a new cavity forms –

archenteron

– will become the cavity of digestive tract and

blastopore

becomes anusSlide9
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Organogenesis

Ectoderm, endoderm, and mesoderm, rearrange themselves into organs

Nervous system – derived from ectoderm

Soon after

gastrulation

, ectoderm is divided into 2 components: epidermis and neural plate

Sheet of

ectodermal

cells lying along midline of embryo dorsal to newly formed digestive tract and developing notochord bends inward –

neurulation

Forms long groove extending the length of embryo

Folds that border groove move toward each other and fuse, converting groove into long tube beneath surface of back

Neural tube becomes detached from epidermis and differentiates into spinal cord and brainSlide12
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There are some differences between the early stages of embryological development in protostomes and deuterostomes

Development of coelom from mesoderm follows a different pattern

Blastopore becomes the mouth in protostomes and becomes the anus in deuterostomes

Protostomes – mollusks, annelids, and arthropods

Deuterostomes – echinoderms and chordatesSlide14
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Post Embryonic Development

Degree of development at birth varies between species

Some are self sufficient – fish, reptiles, amphibians

Some need limited amount of care (chicks, ducks)

Some are helpless and totally dependent (humans, mammals, many birds)Slide16

All organisms undergo major developmental changes after birth

Growth usually begins slowly, becomes rapid for a time and then slows or stops

Growth does not occur at same rate or same time in all parts of bodySlide17

Larval Development and Metamorphosis

Larval stages – many animals go through stages that bear little resemblance to adult

Metamorphosis

– developmental changes that convert immature animal into adult form

Involves extensive cell division and differentiation

Stage 1 – egg Stage 2 – larva

Stage 3 – pupa

After larval development, enter an inactive stage (pupa)

Enclosed in a case or cocoon, old larval tissues are destroyed and new tissues and organs develop from small groups of cells –

imaginal discs

Stage 4 - adult

Complete metamorphosis

– all stages including pupal stage

Incomplete metamorphosis

– has a nymph stageSlide18

Larva Pupa Emerging Adult AdultSlide19

Aging and Death

Development does not end with mature adult – continues until death

Aging

– complex of developmental changes through time that ultimately leads to deterioration and death

Factors contributing to aging:

Replacement of damaged tissue by connective tissue – becomes a burden on other cells

Changing hormonal balance – may disturb function of variety of tissues

Cells tend to accumulate metabolic wastes as they get olderSlide20

Mechanisms of Development

The developmental fate of cells is based on two general principles:

1. The cytoplasmic makeup is not the same throughout the unfertilized egg (differences in concentration of proteins and mRNAs)

Helps to establish polarity (animal/vegetal poles)

Local differences influence the expression of genes

In many species, first few divisions result in

totipotent

cells – retain zygote’s potential to form all parts of the animal

Determination

– results in progressive reduction of potency – occurs when cytoplasmic environment affects gene expression (cells begin to “remember” what they are supposed to be)Slide21

2.

Cell to cell interactions create more differences during morphogenesis

Cell interactions may elicit changes in gene expression that occur only among neighboring cells

May be accomplished by the transmission of chemical signals or by membrane interactions if cells are in physical contactSlide22

Induction

The ability of one group of cells to influence the development of an adjacent group of cells

Interactions between neighboring cells are crucial during and after

gastrulation

in the origin of most

organs

Resulting effect is to switch on sets of genes that cause cells to differentiate into specific tissuesSlide23

Differentiation

Cells begin to specialize in structure and function – cell has alterations to cellular structure and has

tissue-specific proteins

Cells become experts at making certain

proteins

All

cells of an organism have

genomic equivalence

(have the same genes)

Genes

that are not used are turned off (usually permanently)Slide24

Conclusion:

Nuclei change in some way as they prepare for differentiation

This change in not always irreversible implying that the nucleus of a differentiated cell has all the genes required for making all other parts of organism

Cells of body differ in structure and function because they express different parts of the common genome