Chapter 12: Conception and Fetal Development

Question 1

How long do the ovum and sperm remain viable?

Answer 1

• 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

Question 2

What are the 3 stages of development following fertilization?

Answer 2

1. morula/blastocyte: solid ball of cells surrounded by zona pellucida
2. trophoblast: beginning of placenta
3. embryoblast: beginning of embryo

Question 3

What are the chorionic villi?

Answer 3

finger-like projections that extend into the endometrium of the uterus that create a rudimentary blood supply

Question 4

Differentiate between the embryo and fetus?

Answer 4

– 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

Question 5

What is amniotic fluid?

Answer 5

• 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

Question 6

What is the yolk sac?

Answer 6

• 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

Question 7

How many vessels comprise the umbilical cord? What is the approximate size of the umbilical cord? What is Wharton’s jelly?

Answer 7

• 2 arteries, 1 vein
• 2 cm in diameter; about 55 cm long
• Wharton’s jelly: surrounds vessels to prevent compression

Question 8

What forms the placenta? What are the functions of the placenta? What is important to note about the placenta?

Answer 8

• 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)

Question 9

Describe the flow of blood from fetus to placenta.

Answer 9

• 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

Question 10

What is viability in terms of fetal maturation?

Answer 10

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

Question 11

What is different between fetal blood and maternal blood?

Answer 11

fetal blood carries 20 - 30% more O2 than maternal blood – hemoglobin concentration is 50% higher in fetuses

Question 12

What is the normal range for fetal HR?

Answer 12

110 - 160; higher the more pre-term

Question 13

How does fetal cardiac output differ from adult cardiac output?

Answer 13

fetal CO is greater than adult CO

Question 14

What 2 things are stored by the liver for fetuses?

Answer 14

• 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

Question 15

What is important to note about fetal kidneys?

Answer 15

they do not regulate acid-base balance in utero, but need to do so immediately after birth

Question 16

What is the only immunoglobulin that can cross the placenta? What does it do for the fetus?

Answer 16

• IgG
• provides passive acquired immunity to the fetus

Question 17

Which immunoglobulin does the baby receive from breast milk?

Answer 17

IgA

Question 18

Differentiate between dizygotic twins and monozygotic twins.

Answer 18

• dizygotic: two sepearate eggs fertilized at the same time, resulting in fraternal twins
  – rate increases with maternal obesity and cessation of oral contraceptives (rebound FSH levels)
• monozygotic: one fertilized egg that divides, resulting in identical twins

Question 19

How do conjoined twins arise?

Answer 19

cleavage is incomplete and later