Embryology 1 Flashcards
How do we describe the regions in an embryo? How do we describe anatomical planes of cuttings?
Top = Cranial Tail = Caudal Front = Ventral Back = Dorsal
Cut the embryo into cranial and caudal sections = transverse
Cut the embryo into left and right sections = sagittal
Cut the embryo in dorsal and ventral sections = coronal section
What are the methods to date a pregnancy? How do they differ?
- Menstrual Age: Date using the date of the mother’s last mensural. The gestation period is 40 weeks. Not as accurate as it does not take into account when the egg was fertilised. Split into 3 equal trimesters.
- Fertilisation age: Starts the pregnancy period based on when the egg was fertilised. Therefore gestation period is 38 weeks as ion the first 2 weeks of the menstrual cycle, the egg had not been released. Used by embryologists. Split into 3 periods: 3 early development period; 5 week organogenesis period and 30 week foetal maturation period (up to week 38).
Give examples of causes of human birth defects
- Infectious agents
- Genetics - monogenic or chromosomal
- Chemical agents such as alcohol or thalidomide
- Physical agents such as radiation
- Maternal disease such as diabetes
- Maternal deficiencies such as folic acid
In what period is the foetus most vulnerable to human birth defects?
During the organogenesis period - i.e week 3-6. Before which the pregnancy is most likely to be terminated if there are defects. After which human birth defects are less likely as the foetus is just maturing.
Discuss the most common infectious agents that cause disease.
Hint: TORCH
T: Toxoplasmosis - Parasite found in raw meat and cat faeces. Usually asymptomatic but when it crosses the placenta, it can cause inflammation of the retina, hearing loss, enlarge liver/spleen, hydrocephaly and microcephaly.
O: Other e.g. Hepatitis B and Syphilis
R: Rubella - Can cross the placenta. Can lead to microcephaly, heart defects and cloudy cornea.
C: Cytomegalovirus - Virus that passes the placenta. Infection via bodily fluids. Usually asymptomatic. leads to inflammation of the retina, enlarged liver/spleen. Can cause mineral deposits on the brain and microcephaly.
H: Herpes - Can be passed during childbirth as usually the virus does not travel up the female reproductive system. This leads to scarring/skin loss. Also can cause microcephaly and visual defects.
Why are the brain and eye affected in a lot of these TORCH infections?
The eye and the CNS take the longest time to develop during the organogenesis period and so are very vulnerable to infections.
What is Thalidomide? What is its effect on developing foetuses?
A drug that was prescribed for morning sickness developed in Germany in the 1950s. It lead to shortened or absent limbs. It is currently be used to treat leprosy and HIV.
What is the Zika virus? What is its effect on developing foetuses?
A virus found prevalent in South America, it leads to fever, rash, joint pain and red eyes in adults. It is spread through a mosquito and bodily fluids. It can cross the blood brain barrier and lead to microcephaly and severe cognitive disabilities.
What is the effect of alcohol on a developing foetus?
It can lead to foetal alcohol syndrome. There is a clear relationship between alcohol consumption and congenital abnormalities. It is associated with prenatal and postnatal growth retardation; intellectual disability and impaired motor ability and coordination.
What is the effect of radiation on a developing embryo?
It can cause cells each and chromosomal changes. The embryo is most sensitive in the first trimester - the CNS is particularly sensitive. It can lead to microcephaly and mental/cognitive disabilities. It can also lead to haemopoietic malignancies and leukaemia.
What is the effect of maternal diabetes mellitus on a developing foetus?
It can lead to macrosomia - large babies. It can also cause ventricular septal defects and spinal bifida.
What is folic acid required for? As a result, what congenital malformations can it result in?
Folic acid is required for neuralation. Folic acid is required to build up in the mother before conception.. As a result, deficiencies can result in malformations in the CNS e.g. spina bifida and anencephaly.
What steps are required for fertilisation to occur?
- Capacitation of the sperm - as the sperm travels through the female reproductive system, secretions result in modifications in the sperm to prepare it for fertilisation.
- Acrosome reaction - The acrosome releases its degrative enzymes that break down the Zone pellucida.
- Formation of the zygote
- Fusion of pronuclei.
- Cortical reaction - The cortical granules of the egg are released to prevent polyspermy. (Zona reaction)
Day 1 - 4:Once fertilisation has occurred, what is the next step in the formation of an embryo?
The zygote rapidly divides in a process known as cleavage. Once there are 16-32 blastomeres in number, a morula is formed, The blastomeres get smaller when they replicate as they take up the same amount of space. This is due to zone pellucida still being present.
Day 4:What are the different components of the morula?
The inner cell mass are the embryoblasts and will go onto form the embryo. The outer cell mass are the trophoblasts and will go onto form the supportive structures.
