RDA Flashcards
How man Carnegie Stages of Human Development are there?
1-23
What percentage of identifiable structures of the adult body have appeared by Carnegie stage 23?
90 percent
What is PF?
Post-fertilisation
Approx. 2 weeks less than gestational age, GA
What is oxygen tension in the fetus and placenta in the first trimester?
Before week 3= 3%
By week 10 PF= 8%
What happens in the 3rd week of pregnancy?
Formation of trilaminar disc (mesoderm), CNS and somites
Blood vessel initiation
Initiation of placental villi
(3mm)
What happens in the 4th week of pregnancy?
Closure of neural tube Heart, face, arm initiated Umbilical cord elaboration of placental villi (4mm)
What happens in the 5th week of pregnancy?
Face and limbs continue
5-8mm
What happens in the 6th week of pregnancy?
Face, ears, hands, feet, liver, bladder, gut, pancreas
10-14mm
What happens in the 7th week of pregnancy?
Face, ears, fingers, toes
17-22mm
What happens in the 8th week of pregnancy?
Lungs, liver, kidneys
Placental elaboration continues, development of villi
Placental endocrinology becomes dominant
Cytotrophoblast plugs in spiral arteries lost over next 2 weeks
(28-30mm)
How much does a fetus weigh by the end of week 12?
50g
How much does a fetus weigh by the end of week 28?
1050g
How much does a fetus weigh by the end of week 40?
2100g
When does most growth in the fetus occur?
Mostly 2nd and 3d trimester
Before 2nd= 50g, after 3rd= 2100g
How can you see changes in the first 4 weeks PF?
Microscopy
What size is a blastocyst at 9 days?
0.1cm
Early stage of implantation
What size is an embryo at 5-6 weeks?
1cm
Can see yolk sac (very red area= liver)
What size is a 3 month old fetus?
7cm
What is the conceptus?
Everything produced from fertilised egg
When is the embryonic genome activated?
Between Day 2 and 3
Between 4 and 8 cells
When do you call a fertilised egg an embryo?
After week 1
Expanded blastocyst has hatched
How do cells proliferate in the embryo?
Changes in response to GFs
Changes in receptor expression
May be due to changes in cell survival
All paracrine or autocrine regulation (embryo doesn’t have blood vessels so can’t have endocrine processes)
How do chemo-attractants cause movement in embryos?
Local production
Paracrine effects
What are cognate receptors expressed on?
Target cells