introduction early embryology...the developing human – three phases early development embryonic...
TRANSCRIPT
Introduction&
Early Embryology
Human Structure & Development ANHB 2212
Semester 1 – 2010
Dr. Avinash [email protected]
© 2010 Avinash Bharadwaj
Welcome! The Promise :
An exciting unit! All possible help during the course of the unit
About the unit : All information on the unit website…
http://www.lab.anhb.uwa.edu.au/hsd212 … and on WebCTIt is meant to be read!
A few points and thoughts…
© 2010 Avinash Bharadwaj
Some Key Issues Progress from the ‘transition year’… Analytical, conceptual thinking Integrative unit.
Gross anatomy, histology, embryology Being an educated lay person Anything that is here in the unit…
…is here for a reason!
© 2010 Avinash Bharadwaj
UWA student email account must be active Check your email regularly Class List emails for important announcements No auto redirect to other accounts!
All mails to be sent from UWA student account.
Course Reader : first three chapters ‘must-read’especially if you have not done ANHB 1101.
Important!
© 2010 Avinash Bharadwaj
Embryology : Why and How
Embryology
Gross Form, Correlation
Errors in developmentStructuralMolecular
(Clinical aspects)
Real life aspects (“non medical”)
Evolutionary mirror
Cellular and Molecularphenomena
© 2010 Avinash Bharadwaj
Fertilisation Oöcyte at ovulation…
…Second meiotic divisionOne polar body
Site of fertilisation : Ampulla Sperm : Acrosomal reaction Zona pellucida Single sperm…
© 2010 Avinash Bharadwaj
Single sperm enters Meiosis complete (two polar bodies).
1
♀
♂
Female and male pronuclei2
First mitotic division begins.(Cleavage).Note mitotic spindle.
3Two smaller cells.Diploid
4
© 2010 Avinash Bharadwaj
Fertilisation
Completion of meiosis II Polar bodies (Also dealt with in Week 11)
Restoration of diploidy Initiation of cleavage Chromosomal sex determination Genetic and evolutionary implications
Paternal and maternal chromosomes Further mixing during next gametogenesis (crossing
over)
© 2010 Avinash Bharadwaj
Cleavage
Nuclear-cytoplasmic ratio …Reduction of cell size
Journey through the uterine tube
Zona pellucida…retained until implantation
Morula Cell compaction
© 2010 Avinash Bharadwaj
Blastocyst Inner cell mass Embryo foetus Trophoblast mainly for nutrition
Invasive nature Zona pellucida disappears Implantation
© 2010 Avinash Bharadwaj
Implantation
Embryo within the endometrium
© 2010 Avinash Bharadwaj
Embryo : Two layers – Epiblast and hypoblastAlso note : Amnion + Amniotic cavity.
Yolk sac.
A
Y
Embryo is “bilaminar”
Trophoblast
© 2010 Avinash Bharadwaj
A B
A
B
Cut edge of amnion
Primitive streak
Germ Layers…
Flat, bilaminar embryo Epiblast and hypoblast Epiblast endoderm, mesoderm, ectoderm
The beginning : Primitive streak.
© 2010 Avinash Bharadwaj
Endoderm
Endoderm replaceshypoblast!
Epiblast
HypoblastEndoderm
H HEndoderm
© 2010 Avinash Bharadwaj
Remaining epiblast ectoderm
Mesoderm
Endoderm
Mesoderm1
2
© 2010 Avinash Bharadwaj
Mesoderm spreads…
A small area at the head end…no mesoderm! (More about this later).
© 2010 Avinash Bharadwaj
Notochord & Neural Plate Notochord
Cells from the primitive node Axis Induction…
Neural plate Ectoderm Neural groove
© 2010 Avinash Bharadwaj
Neural Tube and Crest Plate groove tube “Lips” of the groove : crest Surface ectoderm continuous Crest buried dorsal to the tube.
Nervous system is ectodermal!
© 2010 Avinash Bharadwaj
Divisions of Mesoderm
Axis
ParaxialLateral plate Intermediate
© 2010 Avinash Bharadwaj
But we are not ‘flat’!
Ectoderm : Interface with the exterior Endoderm : Mainly concerned with
food intake Mesoderm : “everything in between”,
including coelomic cavity
“Folding” : a complex process
Key point at this stage :
© 2010 Avinash Bharadwaj
Fate of Germ Layers
Ectoderm Epidermis (not skin!), nervous system
Mesoderm Muscle, Connective tissues : “Form” of the body Some epithelial structures
Parts of urogenital systems Endothelium of heart and blood vessels “Serous membranes”
Endoderm Lining of the digestive system ++
© 2010 Avinash Bharadwaj
The Link with Histology – an Example
Mesoderm muscle (3 types), different types of connective tissue…
Each has specialised cells Cell differentiation : commitment to form
specialised cells Full differentiation implies structural and
functional specialisation Some undifferentiated cells persist even in
adult life.
© 2010 Avinash Bharadwaj
The Developing Human – Three Phases
Early development Embryonic phase – organogenesis
Most sensitive phase Potential for maldevelopment Effects of ‘teratogens’ Each system has its particular sensitive periods
The foetal period Mostly growth, but… Differentiation, Histogenesis and Functional
development continue
© 2010 Avinash Bharadwaj
Summary The beginning :
Fertilisation, cleavage, implantation
Concepts introduced in this lecture, to be developed in later weeks :
Three germ layers and their importance Embryology as the key to :
Anatomical form and relationships Developmental defects (elementary!) Immense variety of specialised cells