Essentials Of Clinical Medicine 11

Front 1

Summarise the major events in the embryonic period

Back 1

- 24 hrs = embryo reaches 2-cell stage
- 3 days = morula reaches uterus
- 7 days = Blastocyst begins to implant
- 2.5 weeks = Notochord and neural plate are formed; tissue giving rise to the heart is differentiating; blood cells are formed in yolk sac and chorion
- 3.5 weeks = Neural tube forms; primordial ear and eye visibile; pharyngeal pouches forming; liver bud differentiation; respiratory system and thyroid gland begin to develop; heart tubes fuse, bend and begin to beat; blood vessels are laid down
- 4 weeks = Limb buds appear; 3 primary vesicles of the brain are formed
- 2 months = muscle differentiating; movement; gonads distinguishable; ossification of bones begins; differentiation of central cortex, principle blood vessels assume final position

Front 2

Summarise the major developmental events of the foetal period

Back 2

- Week 11 = loss of symmetry (heart, stomach, liver)
- 3 months = Sex can be determined by external inspection; notochord degenerates; lymph glands develop; respiratory movements
- 4 months = Facial expression; lobes of cerebellum differentiate; eye, ear and nose take on term appearance
- 3rd trimester = Neurons myelinated; rapid growth
- 266 days = birth (from conception)

Front 3

What are the 2 signalling centres of the embryo?

Back 3

1. Node = organiser
- Responsible for generating the body (triggers differentiation)
- Produces many proteins, plus Chordin and Noggin
2. Anterior visceral endoderm
- Formed before the node
- Combines with the node to produce the forebrain
- Does not produce Chordin and Noggin

Front 4

Describe the growth of the foetus

Back 4

- Growth in body length particularly fast in the 3rd, 4th and 5th months
- Slowdown in the growth of the head = in 3rd month 1/2 of CRL. By 5th month 1/3 CHL and by birth 1/4 CHL
- Increases of weight more striking in last 2 months of gestation (30-36 weeks)
- There is no increase in the amount of amniotic fluid or placenta size during this period

Front 5

How are key genes in development appropriately expressed?

Back 5

Transcription factors
- Interact with the basal apparatus
- Modify DNA structure (methylation)
- Control the activity of other DNA factors (multiple factors needed to regulate a single gene)

Modular proteins
- DNA-binding domain recognises cis-acting elements
- Transactivation domain = interacts with components of basal apparatus

Major families of transcription factors involved in development e.g. T-box, winged-helix, zinc finger

As genes are correctly expressed development of the embryo continued. Consequently, failure of gene expression or abnormal expression of a gene can give rise to congenital disease

Front 6

Why is fetal-maternal interaction so important?

Back 6

- Fetal-mother interactions support development
- Healthy development of foetus relates to the lifestyle, environment and nutrition of the mother
e.g. foetal alcohol syndrome
viral infection (rubella) at a critical stage of development
- Inadequate dietary folate intake can cause neural tube defects
- Prescription drugs can cause effects e.g. thalidomide can stop limb development
- Maternal endocrine function can effect thyroid development of child
- Interuterine enviroment has been shown to have a strong influence on later postnatal health - 'Barker Hypothesis'