Principles of Embryology Flashcards
What is embryology?
Involves the study of EMBRYONIC PERIOD (8 weeks)
Timing of embryological development?
Conceptus (embryo) - fertilisation to the end of week 3
Embryo - week 4 to 8
…together known as embryogenesis
Foetus - week 9 to birth (period is about allowing foetus to develop so it can survive outside of the womb)
Phases of embryogensis?
Gametogenesis Fertilisation Cleavage Gastrulation Morphognesis Organogenesis
Describe gametogenesis
Development and formation of male and female GERM CELLS:
Oogenesis - process by which mature oocytes (eggs) are produced. Oocytes contain much more than sperm to kickstart embryo development
Spermatogenesis - begins are puberty and is process by which spermatozoa are produced (sperm)
Describe fertilisation
Process by which male and female gametes fuse resulting in the formation of the ZYGOTE
Describe cleavage
Once the zygote has reached a two-cell stage, it undergoes RAPID CELL DIVISION - during first 4-5 days of development - and forms BLASTOMERES (forms a loosely arranged clump with quite a bit of space and with each division, blastomeres become smaller and maximise contact with each other, due to limited space) - process is called COMPACTION
Cells continue to divide, forming a MORULA (cluster of 16 cells) which then undergoes COMPACTION (cells develop close associations with one another), to form a BLASTOCYST
Under ZONA PELLUCIDA of the blastocyst, lining the space, is a layer of cells under which are more loosely arranged cells (supporting cell contributing to placenta formation)
Where are embryonic stem cells normally obtained from?
BLASTOCYST
What is the zona pellucida?
Glycoprotein layer surrounding the plasma membrane of oocytes
Describe gastrulation
Formation of the GERM LAYERS: Ectoderm Mesoderm Endoderm ...give rise to different tissue types
BODY AXES ESTABLISHED, e.g: tail and head, right and left
Describe morphogenesis
Formation of the body plan - embryo develops 3D shape and things are brought into the correct spacial locations
Involves EMBRYONIC FOLDING
Describe organogenesis
PRIMORDIA of all ORGAN SYSTEMS
What is the foetal period?
Characterised by the MATURATION of tissues and organs and RAPID GROWTH of the body
What does the foetal period involve?
Many processes occur for the foetus by the placenta, e.g: removal of water; foetal tissues must mature and become functional. Period involves:
Growth and weight gain
Tissues maturing and becoming functional
Overt sexual differentiation
Bone is laid down, connections made in the CNS (continues past the foetal period
What are the foetal anatomical relationships?
Adult human: Foetal equivalent:
Anterior Ventral
Posterior Dorsal (spinal cord and CNS
tissue)
Superior Cranial (head-end)
Inferior Caudal (tail-end)
Transverse section is horizontal
Parasagittal plane - any plane parallel/lateral to the sagittal plane (cuts down median/midline section)
Coronal (frontal) section separates the foetus into ventral and dorsal
Terms are different as foetus is curled up
Primary processes underlying development?
Cell division - increases cell numbers
Apoptosis - programmed cell death
…both used in formation of hands (areas between fingers undergo apoptosis)
Differentiation - specialisation of cells to adopt new functions; involves a change in appearance and structure
Cell attachment - physical or functional linkages between cells, creating coherent assemblies (tissues)
Induction - ability of one cell type to cause another to differentiate; this can occur directly or from a distance
Cell migration - movement of cells from one location to another
Secondary processes underlying development?
Axis formation/polarity - during gastrulation. Cells must known where they are in relation to one another and with the embryo, as a whole; involves determination of which way is up, down, etc
Folding/rotation - during morphogenesis. Gives the embryo its 3D form and develops the entire embryo/structures within; allows formation of complex organ structures, e.g: heart and gut
Changes in mass/dimension - involves:
Expansion - which includes hypertrophy (increase in dimension with no increase in cell number) and hyperplasia (increase in cell number with an increase in dimension)
Compaction - which includes decrease in cell mass with a decrease in dimension and an increase in cell number with an increase in dimension
Methods of controlling development?
Genetic - involves gene expression (tightly regulated in time and space)
Epigenetic - preferential expression of either maternal or paternal copy of a gene
Environmental - e.g: teratogen (drug/substance capable of interfering with foetal development, potentially causing birth defects)
Examples of epigenetic condition?
Angelman syndrome - caused by deletion on MATERNAL chromosome 15, causing:
Mental retardation
Poor motor development
Prader-Willi syndrome - caused by deletion on PATERNAL chromosome 15, causing:
Mental retardation
Obesity
Hypogonadism
