Lecture notes
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Concise lecture notes from the embryology strand of the IMS module taught in the first year of the MBChB course at the University of Leeds!
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E MBRYOLOGYINTRODUCTION
Dating of pregnancy
Menstrual age – clinicians
o Dates pregnancy from the woman’s last menstrual period
o Three equal trimesters
Fertilisation age – Embryologists
o Age of the embryo from when the oocyte was fertilised by sperm
o Early development (cell division, pre-embryonic) period (ED)
o Embryonic (organogenesis) period (E)
o Foetal period (F)
Genetic causes:
Monogenic- caused by a defective gene on a chromosome
Chromosomal- numerical issue, having too many chromosomes
o E.g. Trisomy 21 (Downs syndrome) Pair 21 has an extra chromosome
Environmental problems: teratogens
Infectious: Toxoplasmosis, Other (hepatitis B, Syphilis), Rubella (German measles), Cytomegalovirus (CMV), Herpes
o Diseases can cross the placenta and cause birth defects
Chemical – Alcohol, Thalidimide/drugs
Physical – Radiation (Chernobyl)
Maternal diseases - Diabetes
Deficiency- Folic acid
Description Symptoms
Toxoplasmosis Parasite Inflammation of retina and eye/
Caused by: cat faeces and undercooked/raw meat micropthalmia – eye doesn’t form
Usually asymptomatic properly
Hearing loss
Enlarged Liver & Spleen
Hydrocephaly
Microcephaly
Rubella Infection passes over placenta in first 3 months of Cloudy Cornea
pregnancy, when foetus is at most risk for Intellectual disability
congenital malformations Microcephaly
Can be protected by having an MMR vaccine Heart Defects
Cytomegalovirus Virus that crosses the placenta Inflammation of the retina
Infection via bodily fluids Enlarged spleen or liver
Asymptomatic Mineral deposits on the brain
Microcephaly
Psychomotor retardation
Herpes virus Herpes Simplex and Herpes Zoster Segmental skinloss/ scarring
Varicella zoster virus – Chickenpox Limb hypoplasia/paresis
o Most dangerous in between 13-20 weeks or Microcephaly
just before birth to two days postpartum Visual defects
Zika Transmitted by mosquitoes, bodily fluids Microcephaly
Fever, rash, joint pain, red eyes,
Cognitive disabilities
Radiation Cell death or chromosome changes Microcephaly
, CNS is most sensitive foetus is most sensitive in Mental and cognitive disabilities
first trimester Haemopoietic malignancies and
leukaemia
Diabetes Cellular structure defects Spina bifida
Changes in cellular physiology Renal agenesis
Macrosomia – can’t regulate glucose
levels properly, poor homeostasis
Folic acid Dietary deficiency Malformations in the central nervous
deficiency Needed for first part of CNS development formation
Spina Bifida
Anencephaly
Thalidomide
Prescribed for morning sickness
But caused shortened/ absent limbs
It is now used to treat leprosy and HIV
Foetal alcohol syndrome
Clear relationship between alcohol consumption & congenital abnormalities
Associated with: prenatal and postnatal growth retardation, intellectual disability, impaired motor ability and
coordination
Characteristics: small eye openings, thin upper lip, smooth philtrum
Gametogenesis: Mitosis: diploid cells, meiosis: haploid cells
Fertilisation
Fusion of male and female gametes to form zygote
Capacitation of sperm, acrosome reaction, formation of zygote,
fusion of pronuclei
Fertilisation usually takes place at the ampulla of the uterine tube
Fimbriae sweep oocyte (egg) into the uterine tube
Sperm undergo capacitation in female reproductive tract
Cortical reaction occurs post-fertilisation and prevent polyspermy
Acrosome reaction
Capacitated sperm pass through corona radiate
Acrosome releases enzymes that allow sperm to penetrate zona pellucida
Sperm penetration initiates cortical reaction
Zona pellucida becomes impenetrable
Cleavage
After fertilisation zygote cells divide
No change in size of zygote, blastomeres get smaller
Formation of morula
Forms after 8 cell divisions
16- 32 cells
Morula is important, differentiation of cells starts to occur
Embyroblasts form the inner cell mass- from the embryo foetus
Trophoblats form the outer cell mass, form support structures such as the placenta
Formation of blastocyst
Formation of fluid cavity, ball of cells accumulates fluid by osmosis
Composed of embryoblasts and trophoblasts
Embryoblasts form compact
mass, trophoblast form thin
layer
Blastocysts hatching and initiating
implantation (days 5-6)
Sagittal Coronal
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