Embryology + development conditions

Question 1

Fertilisation location

Answer 1

Usually occurs in distal (upper) portion of fallopian tube, ciliated cells help transport ovum

Question 2

Zygote

Answer 2

Fertilised ovum

Question 3

Acrosome

Answer 3

Digestive enzyme on outer layer of sperm which digests outer layer of ovum

Question 4

Prenatal development stages

Answer 4

Germinal period
Embryonic period
Foetal period

Question 5

Germinal period

Answer 5

First 2 weeks post fertilisation
Zygote divides to form 2 cells
Cells keep dividing
Cells held loosely together, single cells can break away and develop into another baby (identical twins)

Question 6

The morula

Answer 6

Day 3-5
12 or more cells produced from repeated cell division

Question 7

Neural tube formation- Neurulation

Answer 7

First event of organgenesis
Forms CNS
Ectoderm thickens, forming neural plate
Neural plate folds inwards forming neural groove, two prominent neural folds and crest
Day 22- neural crest come together and fuse
Results in neural tube which pinches off into the body
Anterior end becomes brain, rest becomes spinal cord
Closure of neural tube is reliant on adequate folic acid levels available during pregnancy
Failure of neural closure can result in spina bifida

Question 8

Genetic birth defects

Answer 8

Inherited, followed predicated mendelian ratios
E.g. polydactyly- extra fingers/toes
Albinism- lack of melanin

Question 9

Congenital birth defects

Answer 9

Developmental
More difficult to predict
May arise spontaneously because of dietary deficiency or because of teratogens (enviro factors)
In many cases no traceable cause
Large number are fatal and lead to miscarriage, mothers immune system screens off defect and attacks it

Question 10

Spina bifida

Answer 10

Failure of closure of neural tube (3-4 weeks)
Around day 22 overlying tissue and skin form over closed tube
If there’s a lack of folic acid or exposure to teratogens closure may not occur
Results in open neural tube (split spine)
Results in permanent disabilities often requiring patient to be confined to wheelchair

Question 11

Types of spina bifida

Answer 11

Spina bifida occulta
Meningocele
Myelomeningocele

Question 12

Occulta (hidden spin bifida)

Answer 12

Neural tube closes and meninges form around brain and spinal cord but one or more of posterior portions of vertebra fail to close fully
Bones of vertebral body don’t fuse, may predispose back P
Many asymptomatic and unaware of their condition, discovered through X-ray or MRI

Question 13

Meningocele

Answer 13

Neural tube closes but meninges frequently herniated through spaces between vetebra or portions of the skull
Can lead to cerebrospinal fluid accumulating in herniated meninges and forming fluid filled bubble-like cysts
Cysts can enlarge dramatically
Can occur at any point along neural tube and can affect both spine and skull
Skull- can lead to facial disfigurement which usually requires surgery to correct

Question 14

Myelomeningocele

Answer 14

Most serious and common form
Neural tube failed to close leading to exposure of neural tissue
Since spinal cord carries nerve impulses to major muscle groups, failure of neural tube closure in early embryonic development results in incomplete spina cord and usually paralysis
Although surgery can cover exposed neural tissue it currently cannot repair incomplete spinal cord

Question 15

Hydrocephalus

Answer 15

‘water on the brain’
Cerebrospinal fluid produces ependymal cells which line hollow ventricles of the brain
CSF leaves ventricles and drains around spinal cord through cerebral aqueduct
Occurs when fluid doesn’t drain fully through occluded cerebral aqueduct
Leads to CSF collecting in ventricles and expanding the brain
Since bones of foetal skull are unused head can expand
Mild- severe

Question 16

Anencephaly

Answer 16

Defined as absence of cranial vault, result of closer of neural tubes at top part
Initially brain will form, and meninges and major bones of skull will form around brain
If anterior portion of neural tubes does not fuse then brain cannot develop and skull and cranial vault are absent
Detected via ultrasound in early pregnancy
On delivery, baby often shows complete absence of cerebral neural tissue
Absence of large amount means most babies do not survive

Question 17

Common teratogens

Answer 17

Any environmental factor which can interfere with prenatal development and lead to birth defects
Ionising radiation, noxious chemicals, certain drugs
Exposure during embryonic stage is particularly harmful since currently major organ/systems are forming

Question 18

Cytomegalovirus

Answer 18

CMV transmitted by sexual contact and secretions, adult infections may be asymptomatic
About 1% of pregnancies are affected, only small % have clinical symptoms
Symptoms include hearing loss, cerebral palsy, microcephaly, intellectual disabilities

Question 19

Alcohol

Answer 19

Features of foetal alcohol syndrome occur in 30-40% of babies born to chronic alcoholics
50-70% of such babies may suffer from foetal alcohol effects
Clinical features- growth retardation, CNS problems, characteristic facial appearance (typically small head, flat facial profile)

Question 20

Thalidomide

Answer 20

Wonder drug of 1960s developed to treat morning sickness
Tested extensively on animals with no apparent congenital effects
Interferes with development of limb buds early on in pregnancy resulting in abnormally short arms and legs
Hands and feet often deformed
Inhibits growth of blood vessels