Chapter 12: Conception and Fetal Development Flashcards
How long do the ovum and sperm remain viable?
- ovum – fertile for about 24 hours after ovulation
- if not fertilized, will degenerate and be reabsorbed
- sperm – viable in female reproductive tract for 2 - 3 days
What are the 3 stages of development following fertilization?
- morula/blastocyte: solid ball of cells surrounded by zona pellucida
- trophoblast: beginning of placenta
- embryoblast: beginning of embryo
What are the chorionic villi?
finger-like projections that extend into the endometrium of the uterus that create a rudimentary blood supply
Differentiate between the embryo and fetus?
– embryo: day 15 - week 8 after conception
* most critical time for development
* period of structure formation
* most vulnerable to teratogens (substances/exposure that cause abnormal development) – like thalidamide and alcohol
– fetus: week 9 - end of pregnancy
* period of refinement (structure and function)
* less vulnerable to teratogens
What is amniotic fluid?
- initially comes from maternal circulation
- fetus swallows fluid – circulates through lungs, kidneys make urine, fetus urinates, and process starts over
- important for fetus because amniotic fluid serves numerous functions
What is the yolk sac?
- forms after chorionic villi
- responsible for O2 and CO2 exchange in early fetal development
- incorporated into embryo by week 5/6
- becomes primative digestive system
How many vessels comprise the umbilical cord? What is the approximate size of the umbilical cord? What is Wharton’s jelly?
- 2 arteries, 1 vein
- 2 cm in diameter; about 55 cm long
- Wharton’s jelly: surrounds vessels to prevent compression
What forms the placenta? What are the functions of the placenta? What is important to note about the placenta?
- placenta forms from trophoblast; starts forming at implantation
- functions:
1. exchange of waste and nutrients
2. respiratory/gas exchange organ
3. early functioning as an endocrine gland – produces 4 hormones to maintain pregnancy (hcG) - the placenta is a diffusion membrane, not a filter (so viruses and toxicants may pass through)
Describe the flow of blood from fetus to placenta.
- deoxygenated blood leaves the fetus through the umbilical arteries
- deoxygenated blood enters placenta where it is oxygenated
- oxygenated blood leaves placenta through umbilical vein
- oxygenated blood enters fetus via umbilical cord
What is viability in terms of fetal maturation?
basically survivability; capability of the fetus to survive outside of the uterus; fetuses are considered viable if they can make it to about 23 weeks
What is different between fetal blood and maternal blood?
fetal blood carries 20 - 30% more O2 than maternal blood – hemoglobin concentration is 50% higher in fetuses
What is the normal range for fetal HR?
110 - 160; higher the more pre-term
How does fetal cardiac output differ from adult cardiac output?
fetal CO is greater than adult CO
What 2 things are stored by the liver for fetuses?
- glycogen stored up to be used as a source of energy for newborn
- iron stored – can last a newborn up to 5 months after birth
What is important to note about fetal kidneys?
they do not regulate acid-base balance in utero, but need to do so immediately after birth
