Human Embryology Flashcards
What are the 2 was of discussing embryological periods?
- Trimesters: 1st , 2nd, 3rd
2. Pre-embryonic (conception), embryonic and fetal
What weeks are each of the trimesters?
1st= 0-12 2nd= 12-25 3rd= 25-38
What are the week s of the periods pre-embryonic, embryonic and fetal?
Pre-embryonic= conception Embryonic= 0-8 Fetal= 8-38
What is gametogensis?
Production of male and female sex cells from the primordial germ cells via meiosis in gonads
What are primordial germ cells?
Specialised germ cells that give rise to the germ line and formed a generation earlier when the parents were embryos
Define stem cell:
Undifferentiated cell that can form specialised cells
Define Pluripotent cell
embryonic stem cell that can form all cell types but placenta and extra embryonic. It can not from a whole organism
Define multipotent cell
Adult stem cell that can form more than one closely related mature cell type, not as varied as pluripotent cells
Define totipotent cell
ability to form all differentiated cell types, even placenta and extra embryonic membrane cells. It could form a whole organism.
What could errors in gametogenseis lead to?
Chromosomal abnormalities resulting in birth defects or spontaneous abortions
What could errors in speratogenesis lead to?
Spermatoza abnormalities that could lead to problems with male fertility
What can treat male and female infertility?
Assisted Reproductive technology
How often does twinning naturally occur?
3% of births
What are the 2 types of twins?
Monozygotic
Dizygotic
What are monozygotic twins?
Identical twins.
Formed by splitting of a single zygotes
How often to monozygotic twins occur naturally?
0.4% of births
What are dizygotic twins?
2 seperate oocytes are produced and fertilised
How often do dizygotic twins naturally occur?
1.2% of births
What is invitro fertilisation (IVF)?
Sperm and eggs are placed in alab dish and fertalised
What is gamete intrafallopian transfer (GIFT)?
sperm and eggs are injected into the uterine tube to fertalise
What is artificial insemination by donor (AID)?
Sperm is injected into the cervix, uterus or uterine tube
What is Zona Drilling (ZD)?
A microsurgical technique that facilitates sperm penetration into the egg with the use of enzymes or special solution. Fertilised egg is then implanted into the uterus
What is subzonal insemination (SI)?
A procedure where spermatozoa are injected into the perivitelline space that surround the egg membrane. The fertilised egg is later implanted into the uterus
What is intracytoplasmic sperm injection (ICSI)?
a procedure where a single sperm is directly injected into an egg. The fertilised egg is then implanted into the uterus
What occurs in week 1 following fertilisation?
Cleavage: rapid mitotic division, no growth, the cells just become smaller
What is parthenogenesis?
Process where an unfertalised egg develops into a new individual –> normally dies unless they’re jesus lol
What occurs during week 2 following fertilisation?
The epiblast and the hypoblast form. = bilaminal germ disk
What does the formation of the bilaminar embryonic sperm disk do?
establishes and defines the primitive dorsal-ventral axis of the embryo
Epiblast= dorsal
Hypoblast= ventral
What is placentation?
The formation and growth of the placenta in the uterus
What are 3 key features of the placenta?
- To transfer nutrients from the mother to the developing foetus
- Eliminate metabolic waste from the embryo
- Provide immunity and protect against infections
What are the 3 main types of placentations?
- Epithelial placentation
- Endothelial placentation
- Hemochonial placentation
What is Epithelial placentation?
In horses, whales and lower primates where the placenta has the thickest barrier as all the maternal tissue layers separate the materna; blood from the fetal chorion
What is endothelial placentation?
In cats and dogs. This is a placenta with a thinner barrier as only th maternal blood vessels endothelial cells separate the maternal blood from the fetal chorion
What is hemochonial placentation?
Higher primates, humans, mice and rate. This is a placenta with the thinnest barrier, the maternal blood directly bathes the fetal chorion.
What can abnormal placentation lead to?
Abortion
What causes ectopic pregnancy?
Implantation occurs outside the uterus
What is a hydatiform mole?
Complete of partial: pregnancy developing without a fetus or with a remnant of a fetus
what are dizygotic twins?
implant seperately, develop separate placenta, seperate amnion. seperate chorionic sac, sometimes the placentas are fused
what are the types of monozygotic twins?
- 2 cell stage split: implant sep and placenta developes sep, sep amnion, sep chorionic sac
- earlt blastocyst stage split: common placenta and chorionic cavity, sep amniotic cavity
- Bilaminal germ disc stage split: have common placenta, chorionic and amnitic split
When does gastrulation occur?
3 weeks
What is gastrulation?
The bilaminar germ disk forms the trilaminal germ disk with the establishemnt of the 3 primary germ layers:
1. ectoderm
2. mesoderm
3. endoderm
Commenses with the primitive streak where the epiblastic cells forms the 3 layers.
Establishes the major body axis
what are the major body axis’?
cranio-caudal, medio lateral, dorso-ventral, Left/Right
What is a malformation that can occur during gastrylation?
Caudal Dysplasia
What makes up the trilaminar enbryonic germ disk?
mesoderm (maturing into the extraembryonic and the intraembryonic) , under it is the endoderm and then in the centre is the notocord plate which matures into the notocord
What organs does the ectoderm form?
Ones that contact the outside world e.g skin
neuroectoderm
sensory epithelium of the ear, nose and eye
enamel of teeth
oral and anal cavity epithelium
What does neuroectoderm formation lead to?
neural tube, neural crest cells and the pituitary gland
What 3 parts make up the mesoderm?
- Paraxial mesoderm
- Intermediate mesoderm
- lateral plate mesoderm
What is the paraxial mesoderm?
Contain neuromeres making head conective tissue
Contain somitomeres from the head downwards forming 42-44 paires of somites by the 5th week. This count can be used to age an embryo
What somite pairs are made by the paraxial mesoderm?
4 occipital, 8 cerviacal, 12 thoracic, 5 lumbar, 5 sacral and 8-10 coccygeal
What is the intermediate mesoderm?
contributes to the formation of the structures of the urogential system including gamtes and gonads
What is the lateral mesoderm?
Splits into
- Parietal layers: forms dermis of skin, bones, cartilage, muscles and connective tissue. Mesothelical/serous membranes secrete serous fluid
- Visceral layer: with the endoderm forms the wall of the gut tube. Forms the visceral layer of the serous membrane that surrounds organs. Blood cells and blood vessels
What are the derviatives of the endodermal germ layer?
GI tract- walls (SM and connective tissue form from the mesoderm)
Epithelial lining of the: respiratory tract, urinary bladder, urethra, trympanic cavity and the auditory tube
The parenchyma of the thyroid, parathyroids, liver and pancreas
What does parenchyma mean?
the functional tissue of an organ as distinguished from the connective and supporting tissue
What is morphogenesis?
A form shaping process in an embryo. Can have genetic mutations and teratogen exposure which can result in dysmorphogenesis and birth defects.
What cellular behaviour changes can occur in morphogenesis?
cell shape, size, position, number and adhesivity
what is normogenesis?
developing normally- in terms of a close range of the abstract norm in form and function
what words can be used to describe disorders as a result from not forming normally
Birth defects, congenital malformations and congenital anomaly
What are malformations?
Primary morphological defects in an organ or body part that result from disturbances of development events or processes directly involved in the formation of a particual structure
What can cause malformations?
Environment (tetratogens) and or/genetic factors acting individually or together
What are some examples of malformations
NTDs due to none closure of the neural folds
Syndactyly due to failure of the digits to separate fully
What are deformations?
Secondary morphological defects that are imposed upon and organ or body part due to mechanical forces over a prolonged period- an indirect affect.
What is an example of a deformation?
Club feet due to a compression in the amniotic cavity as a result of insufficient amniotic fluid. It is common in the skeletal system development. Result in morphological alterations of already formed structures.
Really good prognosis!! and low occurrence in contrast to many malformations
What is malformation syndrome?
When dysmorphogenesis occurs in a pattern of well characterised multiple primary malformations appearing together in a predictable fashion in one or more tissues due to a specific underlying singe or common cause.
What is dysmorphogenesis?
abnormal tissue formation
Name 2 malformation syndromes
- Down syndrome
2. Foetal Alcohol syndrome
Describe the characteristics of down syndrome (trisomy 21)
- Flat facial features with a small nose
- Reduced muscle tone (hypotonia)
- Upwards or downwards slant of the eye
- Enlarged tongue that tends to stick out
- Single deep crease across centre of palm
- Hyperflecibility (extension) of the joints
Describe the characteristics of foetal alcohol syndrome
- Short palpebral fissure length (opening between eye lids)
- Smooth philtrum (the cleft bit under your nose running to your lip)
- Thin upper lip
- Brain damage
What is a tetragen?
Agent or factor that causes malformations of an embryp
What are the factors that contribute to formation of birth defects after exposure to a tetragen?
- genotype of the conceptus (early embryo) and maternal genome
- Development stage at the time of exposure to tetratogens
- Dose and duration of exposure to a tetratogen
What is pathogenesis?
the manner of the development of the disease, resulting in dysmorphogenesis
What are some manifestations of abnormal development?
Death, malformation, growth retardation, functional disorders
What is the MSAFP plus test (maternal serum screening) and what is measured?
it looks for 4 markers
- Maternal Serum alpha-fetoproetin (AFP) a protein from the liver that increases steadily during pregnancy.
- hCG made by the placenta, peaking at 14 weeks.
- uE3 produced by the placenta
- Inhibin-A produced by the fetus and placenta
If AFP is high = NTDs
If hCG and inhibin-A high and uE3 low = Down Syndrome
Should be followed by other tests due to a high FP rate
What is ultrasonography and what can it detect?
Used to examine the fetus and can detect a variety of fetal abnormalities.
Can detect heart issues.
Used to look at nuchal region translucency, measuring the thickness of the clear area at the back of the neck- can be a sign of Down Syndrome
What conditions can the MSAFP plus test detect?
If AFP is high = NTDs
If hCG and inhibin-A high and uE3 low = Down Syndrome
What is amniocentesis?
Analysis of the amniotic fluid aspirated from the amniotic cavity between 14-16 weeks of gestulation
What is chorionic villus sampling?
Analysis of the chorionic tissue sample
What is the most sensitive stage of teratogenic insult?
Gastrulation
What cells are usually damaged by teratogens during gastrulation?
Ingressing epiblast cells whose fate has already been decided
What can high alcohol do to cells during gastrulation?
Kill cells of the anterior midline of them erm disc, leading to deficiency of midline in craniofacial structres and results in an abnormality called holoprosencephaly
What is hyper and hypotelonism?
Eyes to far or too close together
What does a child with holoprosencephaly look like?
Midline cleft lip, lack of nasal tissue, eyes too close together
What is claudal dysplasia?
due to mesodermal insufficiency in the caudal most region of the embryo, which contributes ot he formations of the lower limbs, urogential system and lumbosacral vertebrate.
This results in hypoplasia and fusion of the lower limbs, vertebral abnormalities, renal agensis, imperforate anus and abnormalities of the genital organs.
It is associated with maternal diabetes
What is situs inversus?
Transposition of the viscera in the thorax and abdomen (visceral organs are mirrored)
What are lateral sequences?
Patients with these conditions have bilateral situs inversus, either left or right sided. Issues with spleen and heart defects.
What do those with left sided bilaterality have?
Polysplenia (multiple spleens)
What do those with right sided bilaterality have?
Asplenia (no spleen) or hypoplastic spleen (malformed spleen)
What is sacroccygeal teratomas?
Conditions where remnants of the primitive streak persist in the sacrococcygeal region to form tumours, the most common type of tumour in newborns that contain tissue from all 3 germ layers
What is the leading cause of infant mortality?
Birth defects- 25% of deaths
How often are birth defects recognised in alive new borns and how much does this increase by as they get to age 5?
3% and then 3% again
What % of birth defects have unknown aetiology (cause)?
40-45%
What % of birth defects are due to genetics?
3-4%
What % of birth defects are due to multiple aetiology?
20-25%
What % of newborns have minor abnormalities?
15%
Of newborns with a minor abnormality, what is there chance of having a major malformation?
3%
What is chance of a newborn with 2-3+ minor abnormalities having a major malformation?
10% and 20% respectively
