Neural tube defects and prevention - Spina bifida

Question 1

State enviromental factors that can lead to spina bifida

Answer 1

• Alcohol
• Vitamin deficiency (folate)
• Anticonvulsant drugs
• Increased maternal age, obesity, Diabetes

Question 2

State genetic risk factors for spina bifida

Answer 2

• prior pregnancy with spina bifida increaes risk
• Family history increases risk
• More common in caucasians
• Female fetuses are slightly more susceptible

Question 3

Why does folate help prevent against against spina bifida?

Answer 3

Folates may be related to NTD risk through their roles in nucleotide synthesis. In fact, in embryos, the rapidly dividing cells of the developing neural tube require the synthesis of large amounts of nucleotides in order to facilitate DNA replication. Barber et al. proposed the hypothesis that if neuroepithelial cells do not have an adequate internal supply of nucleotides, cellular replication will slow down and the development of the neural folds will be retarded

Question 4

How do women stay healthy during pregnancy?

Answer 4

• Avoid smoking - known to cause low weight babies
• Avoid Teratogenic substances
  
  • Alcohol, Cocaine and many others can lead to physical and mental defects.

Question 5

What are the vitamins and minerals recommended for mothers who are pregnant?

Answer 5

Folate (leafy green vegetables, fortified breakfast cereals)

Vitamin D

Vitamin C

Iron

Calcium

Do not take vitamin A supplements.

Question 6

What are the main hormones required for a normal pregnancy

Answer 6

Human Chorionic Gonadotropin

Estrogen

Progesterone

Human Chorionic Somatomammotropin

Question 7

What is the corpus leutum

Answer 7

The corpus luteum is actually a “temporary” gland structure that arises after ovulation has occued. It secretes the hormones estrogen and progesterone, preparing the body for the possibility of conception. These are the hormones that help further build up the lining of the uterus (to form a nice “bed” for the egg to implant itself into) and help maintain that lining.

If conception does not take place, the corpus luteum begins to break down. This leads to a drop in progesterone and estrogen, and this, in turn, triggers menstruation. The reproductive cycle starts over again.

Question 8

Human chorionic gonadotropin is secreted by which type of trophoblast?

Answer 8

Syncitiotrophoblast

It’s excretion can be measured aroud day8-9, reaches a maximum at around 10-12 weeks.

Question 9

What is the primary function of human chorionic gonadotropin?

Answer 9

• Prevents degradation of the corpus luteum, which would normally occur at the end of monthly female cycle
• HCG causes the corpus luteum to produce even more progesterone and estrogen
• Progestorne and estrogen both have roles in maintaining the uterus lining,

Question 10

Progesterone and Estrogen are also produced by the placenta. State functions of each aside from those mentioned regarding maininting endometrial wall.

Answer 10

Progesterone:

• Decreases the contractility of the uterus, minimising chance of spontaneous abortion
• Role in embryonic clevage
• Helps prepae breasts for lactation

Estrogen:

• causes enlargment of uterus
• enlargement of breasts and growth of breast ductal structure
• Enlargement of the female genatalia
• Relax pelvic ligaments, symphysis pubis becomes elastic - allowing easier passage of baby through uterus

Question 11

Relaxin is also produced by the Corpus luteum and the placenta. What is it’s role?

Answer 11

• Also increases elasticity of the ligaments fof the symphysis pubis (although it appears minimally in humans, estrogen does this mainly)

Question 12

Describe cardivascular changes in pregnancy

Answer 12

• Increased cardiac output by 40% over first few weeks then remains constant
• Position of the heart pushed upwards
• Cardiac hypertrophy to accomodate change in blood volume

Question 13

Describe respiratory changes that occur during pregnancy

Answer 13

• Increased tidal volume (increased air inspired and expired during one breath)
• Respiratory rate stays same

Question 14

Describe the physical abdominal changes

Answer 14

• Uterus grows up hiher into the abdominal cavity and almost takes up entire cavity near end of pregnancy
• Pushes maternal intestines, liver and stomach superiorly, e;evates the diaphragm and widens the thoracic cavity
• In pelvic cavity. ureters and and urinary bladder are compressed (hence needing to urinate more frequently)

Question 15

How are neural tube defects diagnosed?

Answer 15

• Ultrasound
• Checking levels of Alpha-feto protein

Question 16

Define spina bifida and how it is caused

Answer 16

Spina bifida is a birth defect where there is incomplete closing of the backbone and membranes around the spinal cord. It caused by posterior neuropore failing to close properly

Question 17

There are 3 main classes of spina bifida. State them

Answer 17

Spina Bifida Occulta

Spina bifida cystica-meningocele

Spina bifida cystica-myelomeningcoele

Question 18

Describe spina bifida occulta

Answer 18

• Mildest form
• portion of spinal cord does not fuse completely
• Skin at the site of lesion may be normal, or may have hair growing, or there may be dimples or birthmarks
• Not associated with an increase in AFP unlike other spina bifida
• Typically asymptomatic

Question 19

Describe meningocele

Answer 19

• also known as meningeal cyst
• least common form of SB
• failure in closure of neural tube folding resulting in herniation of the meninges
• The vertebra aso has also not closed properly
• A sac protrudes out containing CSF, but not the spinal cord itself

Question 20

Describe myelomeningocele

Answer 20

• ANother type of spina bifida
• often results in most severe complications
• Unfused spinal column allows the meninges and spinal cord to portrude through the gap, as well as the CSF in a protruding sac