Embryogenesis Basic Processes

7/31/2019 Embryogenesis Basic Processes

1/18

EMBRYOGENESIS BASIC

PROCESSES


2/18

BASIC PROCESSES

How a single celled zygote isconverted in to multicellular humannew born baby?

By two processes

GROWTH

Quantitative changeDifferentiation Qualitative

change (Structural and functional)


3/18

GROWTH

DEF:Increase in bulk. A quantitativechange

TYPES

Multiplicative( increase in number)

Auxetic (Increase in size)

Accretionary (Increased accumulationof intercellular substance)

Appositional(Addition of new layers onpreviously formed ones)


4/18

Multiplicative Growth

Increase in number By succession of mitotic divisions

Average cell size remains same

Categories of body cells

1. No postnatal division Neurons

2. Continuous loss of cells Replenished by

mitosis of stem cells -Epidermis of skin,

Intestinal epithelium, blood cells

3. Mitosis under altered conditions- Liver cells


5/18

Auxetic Growth

Increase in size

By increase in cytoplasmic volume

Disturbed nuclear cytoplasmic ratio

1:4/6 Structural genes ineffective cytoplasmic

proteins not replaced degradation

Satellite cells

provide nutrition

Examples: Oocytes surrounded by follicular

cells, Large neurons surrounded by neuroglia


6/18

Accretionary/Interstitial Growth

Increased accumulation of intercellular

substance

Overall growth of structure

Increase in length

Eg. Connective tissueBone and

Cartilage


7/18

Appositional growth

Addition of new layers on previously

formed ones

It takes place at the edges

Responsible for contours

Seen in rigid materials Bone Addition

of lamellae


8/18

Cell Reproduction and Cell Growth

Growth of cells by synthesizing new

protoplasm Interphase (G1,S,G2)

Reproduction of individual cells of body

by mitotic cell divisions


9/18

Phases of growth

Lag period

Exponential period

Stationary period Declining growth

period


10/18

Stages of growth period in Man

Prenatal stage - 9 months of embryoniclife

Infantile stage - Birth to 10 months of age

Early childhood - 10 months to 5 years ofage

Juvenile stage - 5 years to 14 years or the

time of puberty

Adolescent and post adolescent stage -

14 years to 20 - 22 years


11/18

ISOMETRIC GROWTH


12/18

ALLOMETRIC GROWTH

Parts of same organism grow at

different rate


13/18

DIFFERENTIATION- DEFINITION

A processwhere groups

of cells

acquire specialcharacteristics

and are

assignedspecial

functions


14/18

Cell Potency

Definition: Potential to differentiate into differentcell types

Totipotent: Zygote

Pleuripotent: Inner cell mass Multipotent: Haematopoietic cells, Mesenchymal

cells

Oligopotent: Lymphoid or myeloid stem cells,Vascular stem cells

endothelium, smooth

muscle

Unipotent:Liver cell


15/18


16/18

DIFFERENTIATION -TYPES

Chemo diferentiation Molecular level -

invisible

Histo differentiation

Tissue level

Organo differentiation/organogenesis

Organ

Organ remodelling Functional differentiation


17/18

Organisers Any part of the embryo which exerts a

morphogenetic stimulus on an adjacent part or parts TYPES:

Primary organiser

Eg. Blastopore/primitive streak

Notochord and

secondary mesoderm

Secondary organiser

Eg.Notochord

Brain and spinal cord

Tertiary organiser

Eg. Neural tube - Somites


18/18

Mode of action of organiser

Evocation Liberation of chemicalsEvocator - a chemical substance emitted by an

organizer that evokes a specific morphogeneticresponse from competent embryonic tissue in contact

with it.

Induction embryonic region made todifferentiate Invaginating chordamesoderminteracting with surface ectoderm to formneurectoderm

Individuation- The action of organiser to bring

together different cell types to form an organ

Embryogenesis Basic Processes

Documents

Transcript of Embryogenesis Basic Processes