Human Embryology Flashcards
Why is embryology studied?
- history of prenatal origin
- understand birth defects
- to understand adult anatomy
- understand adult illness’s and origins
What are the embryological periods?
1st, 2nd, 3rd trimesters and pre-embryonic period
What is the embryonic period? (organogenesis)
beginning of 4th week to end of 8th week
What are the 3 germ layers and what do they give rise to
Ectoderm, Mesoderm, Endoderm
give rise to specific tissues and organs
what is the period of the foetus?
beginning of 3rd month to birth
What is gametogenesis?
process of production of male and female gametes from the primordial germ cells (PGC) via meiotic cell divisions
What are male and female gametogenesis called?
male - spermatogenesis
female - oogenesis
What are the principal goals of gametogenesis?
reduces chromosomal number of gametes from 46 (paired) to 23 (unpaired)
enhance genetic variability
starts at puberty in males and from fetal life in females
What do chromosomal abnormalities lead to?
birth defects, spontaneous abortions, fertility
What is fertilisation?
process of male and female gametes fuse to form a zygote
restores diploid number of chromosomes
what is capacitation?
a sperm conditioning process within the female reproductive tract in preparation for fertilisation - only capacitated sperm can pass corona cells
what is acrosome reaction?
release of enzymes needed to penetrate the zona pellucida (layer of ovum)
what is the cortical reaction?
the oocyte releases lysosomal enzymes from cortical granules making the plasma membrane impenetrable to other sperm
what is the zona reaction?
structure and composition of the zona pellucida is altered preventing polyspermy
what causes male infertility?
how can it be treated?
quality and quantity of spermatozoa
assisted reproductive technology (ART)
what causes female infertility?
multiple physiological and anatomical factors
what is and when does cleavage happen
within week of fertilisation
rapid repeated mitotic cell division of zygote to produce blastomeres
what is the purpose of cleavage?
form multicellular embryo (morula) from the single large zygote
what is the process of compaction
inner (embryoblast) and outer (trophoblast) cell masses forming and polarity being established
what is the blastocyst (inner mass) (2nd week)
the fully developed morula wi/ fluid filled cavity
what is the bilaminar embryonic germ disc?
a cluster of embryonic cells
inner cell mass (hypoblast) becomes embryo
outer cell mass (epiblast) becomes placenta and other fetal membranes
defines dorsal-ventral axis
Stem cell definition
undifferentiated cell that can form specialised cell types
can be either embryonic (pluripotent) or adult stem cell (multipotent)
Pluripotent cell definition
can form all mature cell types in body (other than placental & extraembryonic cells)
Multipotent cell definition
can form more than one closely related mature cell type in body
Totipotent cell definition
can form all differentiated cells types in body
what is the primitive streak?
transient thickening longitudinal midline structure forms on day 15 in the bilaminar embryonic germ disc
what is gastulation?
process of epiblastic cell movements (ingression or invagination) through the primitive streak the leads to formation of the trilaminar germ disc
what is the principle goal of gastrulation
establish all major body axes, (cranio-caudal, medio-lateral, dorso-vental, left-right)
clinical implications of errors of gastrulation
caudal dyslasia (caudal regression syndrome), caudal or sacral agenesis
dextrocardia (right side heart)
heart/septal defects
atrial/ventricular isomerism’s/inversions
what does the ectodermal germ layer give rise to?
organs and structures that maintain contact with the outside world eg, skin, teeth, ear, nose, mouth
what does the mesodermal germ layer (paraxial) give rise to?
cranial connective tissue
somitomeres (somites) develop with neural tube (segments of spine) can be counted according to age of embryo
what are the 3 parts of the mesodermal germ layer?
paraxial mesoderm
intermediate mesoderm
lateral plate mesoderm
what does the mesodermal germ layer (intermediate) give rise to?
urogenital system - primordial germ cells, gametes, gonads
what does the mesodermal layer (lateral plate) give rise to?
splits in 2 - parietal = cavity walls
visceral - wall of gut tube
dermis of skin, limbs, bones, connective tissue, muscle
what does the endodermal germ layer give rise to?
epithelial lining of GI tract
what is morphogenesis?
shape forming of embryo controlled by cell behaviours (shape, size, position, number)
interference with this process can result in birth defects
what is dysmorphogenesis
abnormal foetal development (outside the norm of form and function)
birth defect definition
structural, behavioural, functional, metabolic disorder present at birth
can be caused by malformations and deformations
what is malformation
primary morphologic defects in a organ or body part (results from disturbed developmental events or process during formation of structure)
what is deformation
secondary morphological defects causes by prolonged mechanical force being applied eg clubfeet due to compression in amniotic cavity
what is disruption
morphological alterations of already formed structures due to destructive processes
Malformation syndrome - down syndrome cause and effects
missing chromosome
flat face, small nose
reduced muscle
eye slants
hyper flexibility
Malformation syndrome - alcohol foetal syndrome effects
small eye openings
smooth philtrum
thin upper lip
brain damage
what is teratology?
the study of birth defects
a teratogen causes a birth defect
what determines the capacity of a teratogen
genotype of conceptus & maternal genome
Development stage at the time of exposure to teratogens
dose and duration of exposure
mechanism & actions of teratogen
what is pathogenesis
abnormal development that leads to dysmorphogenesis
can involve cell death, decreased proliferation
what can abnormal development cause?
death, malformation, growth retardation, functional disorders
congenital malformations statistics
birth defects - 25% of infant deaths (leading cause)
3% infants have structural anomalies
birth defect frequency’s are non-discrimatory (similar levels globally)
40-45% of defect have unknown cause
genetic factors account for 28% birth defects
what can minor anomalies help detect
major anomalies in infants as they are common in those that already show minors
