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Embryology (IMS)
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Introduction to Medical Sciences TOPIC 9 - Embryology
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Medic_Summaries (IMS) Topic 9Embryology
Embryology: formation from unicellular to multicellular
- Week 8: body outline
- Week 20: half-way through, looks fully developed
- Week 40: birth, full-term
Embryology gives a logical framework for adult anatomy. It gives a better understanding of
pathology (eg. gonads originate on posterior abdominal wall, therefore testicular cancer can
metastasise up lymph nodes located near posterior abdominal wall). Congenital malformations/
anomalies and pathologies can be derived (eg. foramen ovale does not close fully at birth, leaving
an opening between the atria of the heart).
Dating of pregnancy:
- Menstrual age: dates pregnancy from woman’s last period
- Three equal trimesters
- 0-40 weeks
- Fertilisation age: embryologists use, not equal periods
- 0-3 weeks: early development (ED) - cell division, pre-embryonic
- 3-8 weeks: embryonic period (E) - organogenesis
- 8-38 weeks: foetal period (F) - two week difference due to ovulation
Human birth defects: 1/44 births in the UK
- Genetic: mitosis/meiosis
- Environmental: teratogens
- 61% diagnosed prenatally (27% at birth, 3% after one week, 6% after one month)
- 50% of teratogens are unknown
- 25% of cases and multifactorial (many causes)
- Major environmental factors (eg. Grenoble nuclear plant)
Genetic causes: mitosis/meiosis
- Monogenic: defective gene on autosome (INHERITED)
- Chromosomal: numerical/structural; chromosome separation/misalignment of genetic
material (eg. Trisomy 21)
Environmental causes: teratogens
- Infections (TORCH): Toxoplasmosis, Other (eg. HepB), Rubella, Cytomegalovirus, Herpes
- Chemical: pharmaceutical (Thalidomide) or recreational (alcohol)
- Physical: radiation
- Maternal disease: diabetes
- Deficiency: folic acid
Sensitivity to environmental factors changes throughout embryo development.
Most risk at 5 WEEKS (organogenesis): congenital malformations
- CNS
- Ears
- Eyes (at risk for longest period of time during development)
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 9
Toxoplasmosis: parasite, cat faeces, undercooked/raw meat
- Usually asymptomatic
- Inflammation of retina/eye
- Hearing loss
- Enlarged spleen
- Hydrocephaly: water on the brain (enlarged)
- Microcephaly: brain does not form properly (small head)
Rubella: German measles
- Infection passes over placenta in first three months of pregnancy
- MMR vaccination
- Cloudy cornea
- Intellectual disability
- Microcephaly
Cytomegalovirus: virus crosses placenta
- Infection via bodily fluids
- Asymptomatic
- CT scan (brain should be GREY) shows white matter (calcified deposits)
- Inflammation of retina
- Enlarged spleen/liver
- Mineral deposits in brain
- Microcephaly
- Psychomotor retardation
Herpes virus: herpes simplex
- 1/2 of herpes zoster
- Varicella/chicken pox/shingles
- Herpes zoster most dangerous WEEK 13-20 and just before birth to two days postpartum
- Segmental skin loss/scarring
- Microcephaly
- Limb hypoplasia (shortened)/paresis (not developed)
- Herpes can migrate up uterus to foetus and cause effect (RARE)
- Most common transmission is birth of child, passing through cervix
Zika virus: mosquito/bodily fluids (transmission)
- Fever, rash, joint pain
- Red eyes
- Microcephaly
- Severe cognitive disabilities
Thalidomide:
- 1950s developed in West Germany and prescribed for morning sickness
- Shortened/absent limbs
- Now treats leprosy and HIV/AIDS symptoms
Radiation: cell death/chromosome changes
- CNS is most sensitive and during first trimester
- Microcephaly
- Mental/cognitive disability
- Haemopoietic malignancies/leukaemia
Diabetes Mellitus: macrosomia (enlarged baby caused by poor homeostasis of nutrients)
- Cellular structural defects
- Changes in cellular physiology
- Ventricular septal defects
- Spina bifida (CNS defect)
- Renal agenesis
2 Adapted from Lectures at the University of Leeds Medical School
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