Week 1 Topics
Twins
Dizygotic: fraternal; 2 ova and 2 sperm (double ovulation)
- Two (or more) eggs = different chromosomal make ups
- 2 placenta, 2 chorions, 2 amnions (placentas may sometimes look like one)
- Can be same or different sex
Monozygotic: identical; developed from a single fertilization ovum at different stages of
early development
- Single fertilized ovum, monozygotic; random event
- One egg is fertilized, then splits = same DNA
- Develop from single ovum
- Same sex and genotype
o Twins increase with parity (having giving birth to a viable infant)
o Incidence of multiple preg. in US is approx. 1.5% of all births-- one-third of these are
monozygotic, the other two-thirds are dizygotic.
o greater risk for congenital abnormalities, conjoining, and TTTS (twins to twin transfusion
syndrome)
Twin to Twin Transfusion Syndrome:
- occurs when twins have a common placenta and membranes resulting in unequal
circulation; one twin receives little circulation while the other most of circulation;
outcome is usually poor for both twins
Fetal Circulation
KEY POINTS:
o High resistance in the lungs makes blood go away from them.
o Low resistance in the placenta makes blood travel towards it.
o The pattern of fetal circulation allows cephalocaudal (head-to-toe) development in the
fetus
o Veins carry oxygenated blood toward the body
o Arteries carry deoxygenated blood away from the body
o Umbilical cord has 2 arteries, 1 vein
Lungs and liver are nonfunctional, so circulation bypasses these organs through special fetal circulatory
structures
Blood returns from placenta through umbilical artery majority of blood bypasses liver through ductus
venosus goes to inferior vena cava
Blood enters right atrium from inferior vena cava crosses opening called foramen ovale to get from
right atrium to left atrium; this enables O2 rich blood from placenta to bypass lungs and be circulated to
body
,Mostly deoxygenated blood that enters right atrium from superior vena cava passes through tricuspid
valve right ventricle pulmonary artery passes through ductus arteriosus descending aorta
flows into 2 fetal arteries back to placenta where it becomes oxygenated
3 Adaptations:
1) Ductus Venosus
- Oxygenated blood travels from placenta through umbilical vein and joins up with the
inferior vena cava and then dumps into the R atrium
- Connects umbilical vein to inferior vena cava
- Allows oxygenated blood from the umbilical vein to bypass the liver
2) Foramen Ovale
- High pressure in the lungs and right atrium pushes blood from right atrium to left atrium
3) Ductus Arteriosus
- Connects pulmonary artery to aorta
- Pulmonary artery has very high pressures due to high resistance in the lungs blood
travels from high pressure to low pressure
Placenta
FUNCTIONS:
Fetal respiration
Nutrition
Excretion
Endocrine function
STRUCTURE:
- Half mom, half fetus
Maternal Portion:
- Consists of decidua basalis and its circulation
- Red, fleshlike, Dirty Duncan
Cotyledons: sections of the placenta
Sections missing or separated = impaired fetal circulation
Sections left in uterus after delivery = mom keeps bleeding until missing sections
come out
Fetal Portion:
- Consists of chorionic villi and their circulation
, - Surface is covered by amnion, shiny grey appearance, Shiny Schultz
Placenta is a barrier to large particles
o Bacteria CAN NOT cross placenta
o Viruses (small particles) CAN cross the placenta
FORMATION
- The placenta develops at the site where the developing embryo attaches to the uterine
wall
- Placental development and circulation do not occur until the third week of embryonic
development
- Once the placenta is established, it will take over hormone production at 11 weeks
- The corpus luteum functions to secrete hormones
o No hormones produced = SAB, miscarriage
Hormones
- 2 types pf placental hormones: steroid or protein
3 Protein Hormones
1) hCG (human chorionic gonadotropin) - comes from placenta, pregnancy test!
- Present in the blood 10 days after fertilization
- Stimulates progesterone and estrogen production by the corpus luteum to maintain the
pregnancy until the placenta is developed sufficiently to assume that function
2) HCS/hPL - effect breasts, produce breast milk
- Increases protein and glucose
- Monitor DM pts may need more insulin
- Antagonist of insulin, increases amount of circulating free fatty acids for maternal
metabolic needs, decreases maternal metabolism of glucose to favor fetal growth
3) Relaxin - relaxes cartilage in pelvis and all the smooth muscle to allow baby to pass
through and come out
- Inhibits uterine activity, diminishes strength of uterine contx, aids in softening of cervix
Steroid Hormones
1) Estrogen
- Breast development, puberty changes, maturation
- Stimulates uterine development to provide a suitable environment for the fetus
Twins
Dizygotic: fraternal; 2 ova and 2 sperm (double ovulation)
- Two (or more) eggs = different chromosomal make ups
- 2 placenta, 2 chorions, 2 amnions (placentas may sometimes look like one)
- Can be same or different sex
Monozygotic: identical; developed from a single fertilization ovum at different stages of
early development
- Single fertilized ovum, monozygotic; random event
- One egg is fertilized, then splits = same DNA
- Develop from single ovum
- Same sex and genotype
o Twins increase with parity (having giving birth to a viable infant)
o Incidence of multiple preg. in US is approx. 1.5% of all births-- one-third of these are
monozygotic, the other two-thirds are dizygotic.
o greater risk for congenital abnormalities, conjoining, and TTTS (twins to twin transfusion
syndrome)
Twin to Twin Transfusion Syndrome:
- occurs when twins have a common placenta and membranes resulting in unequal
circulation; one twin receives little circulation while the other most of circulation;
outcome is usually poor for both twins
Fetal Circulation
KEY POINTS:
o High resistance in the lungs makes blood go away from them.
o Low resistance in the placenta makes blood travel towards it.
o The pattern of fetal circulation allows cephalocaudal (head-to-toe) development in the
fetus
o Veins carry oxygenated blood toward the body
o Arteries carry deoxygenated blood away from the body
o Umbilical cord has 2 arteries, 1 vein
Lungs and liver are nonfunctional, so circulation bypasses these organs through special fetal circulatory
structures
Blood returns from placenta through umbilical artery majority of blood bypasses liver through ductus
venosus goes to inferior vena cava
Blood enters right atrium from inferior vena cava crosses opening called foramen ovale to get from
right atrium to left atrium; this enables O2 rich blood from placenta to bypass lungs and be circulated to
body
,Mostly deoxygenated blood that enters right atrium from superior vena cava passes through tricuspid
valve right ventricle pulmonary artery passes through ductus arteriosus descending aorta
flows into 2 fetal arteries back to placenta where it becomes oxygenated
3 Adaptations:
1) Ductus Venosus
- Oxygenated blood travels from placenta through umbilical vein and joins up with the
inferior vena cava and then dumps into the R atrium
- Connects umbilical vein to inferior vena cava
- Allows oxygenated blood from the umbilical vein to bypass the liver
2) Foramen Ovale
- High pressure in the lungs and right atrium pushes blood from right atrium to left atrium
3) Ductus Arteriosus
- Connects pulmonary artery to aorta
- Pulmonary artery has very high pressures due to high resistance in the lungs blood
travels from high pressure to low pressure
Placenta
FUNCTIONS:
Fetal respiration
Nutrition
Excretion
Endocrine function
STRUCTURE:
- Half mom, half fetus
Maternal Portion:
- Consists of decidua basalis and its circulation
- Red, fleshlike, Dirty Duncan
Cotyledons: sections of the placenta
Sections missing or separated = impaired fetal circulation
Sections left in uterus after delivery = mom keeps bleeding until missing sections
come out
Fetal Portion:
- Consists of chorionic villi and their circulation
, - Surface is covered by amnion, shiny grey appearance, Shiny Schultz
Placenta is a barrier to large particles
o Bacteria CAN NOT cross placenta
o Viruses (small particles) CAN cross the placenta
FORMATION
- The placenta develops at the site where the developing embryo attaches to the uterine
wall
- Placental development and circulation do not occur until the third week of embryonic
development
- Once the placenta is established, it will take over hormone production at 11 weeks
- The corpus luteum functions to secrete hormones
o No hormones produced = SAB, miscarriage
Hormones
- 2 types pf placental hormones: steroid or protein
3 Protein Hormones
1) hCG (human chorionic gonadotropin) - comes from placenta, pregnancy test!
- Present in the blood 10 days after fertilization
- Stimulates progesterone and estrogen production by the corpus luteum to maintain the
pregnancy until the placenta is developed sufficiently to assume that function
2) HCS/hPL - effect breasts, produce breast milk
- Increases protein and glucose
- Monitor DM pts may need more insulin
- Antagonist of insulin, increases amount of circulating free fatty acids for maternal
metabolic needs, decreases maternal metabolism of glucose to favor fetal growth
3) Relaxin - relaxes cartilage in pelvis and all the smooth muscle to allow baby to pass
through and come out
- Inhibits uterine activity, diminishes strength of uterine contx, aids in softening of cervix
Steroid Hormones
1) Estrogen
- Breast development, puberty changes, maturation
- Stimulates uterine development to provide a suitable environment for the fetus
