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UPNS MISC Exam 2 SG #2 OB EXAM 2
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UPNSMISC
Exam 2
SG #2
OB EXAM 2
OB EXAM 2
Chapter 12 – Conception and Fetal Development
•
• Conception
o Union of a single egg and a single sperm
o Not an isolated event but part of a sequential process
• Embryo and Fetus
o Primary germ layers
▪ During the third week after conception, the embryonic disk differentiates into
three primary germ layers – all tissues and organs of the embryo develop
from these layers
▪ Ectoderm - the outermost layer of cells or tissue of an embryo in early
development, or the parts derived from this, which include the epidermis
and nerve tissue.
▪ Mesoderm – middle layer
▪ Endoderm - the innermost layer of cells or tissue of an embryo in
early development
o Embryo: lasts from day 15 until 8 weeks after conception
▪ Most critical time for development
o Two fetal membranes that surround the developing embryo
▪ Chorion – develops from the trophoblast and contains chorionic villi on
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MISC
Exam 2
SG #2
OB EXAM 2
its surface
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MISC
Exam 2
SG #2
OB EXAM 2
▪ Amnion – develops from the interior cells of the blastocyst
o Amniotic fluid
▪ Serves many functions
• Helps maintain constant body temp, source of oral fluid and a
repository for waste and helps maintain fluid and electrolyte
homeostasis
▪ Volume is important
• Oligohydramnios
• Polyhydramnios (hydramnios)
o Development of the embryo
▪ Yolk sac
• Aids in transferring maternal nutrients and oxygen for the first 5-6 weeks
▪ Umbilical cord
• Wharton’s jelly
• Vessels; 2 arteries and 1 vein
• Arteries – carry blood away from embryo and the one vein returns
blood to the embryo with nutrients
o Placenta
▪ Structure
• Complete by the twelfth week
• Structure is developed by day 17
▪ Functions
• Endocrine gland function
o 2 hormones that are produced = progesterone, estrogen,
HCS and HCG
▪ hCG – human chorionic gonoadotrpin – identifying a
pregnancy (basis for pregnancy tests)– this is going to
be detected first in maternal serum and we will
eventually see it in maternal urine – helps confirm the
pregnancy and also tells us where she is in her
pregnancy – can detect it 8 days after conception
o Which one is critical? – progesterone
o Multiple metabolic functions
o Adequate circulation necessary for placental function
• Human chorionic gonodotropin (HcG)
o Pre conception counseling might need to happen even before something is planning
on getting pregnant
o We need to talk about:
▪ Reducing teratogens
▪ Take folic acid !! <- this is imperative
▪ Take a pre natal vitamin
o 12 weeks – usually when spontaneous abortions occur
o Stage of the fetus lasts from 9 weeks until the pregnancy ends
o Fetal maturation
▪ Fetus lasts from 9 weeks (fetus is recognized as a human) until pregnancy ends
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MISC
Exam 2
SG #2
OB EXAM 2
▪ Viability: the capability of the fetus to survive outside the uterus – this number
is usually around 22-25 weeks gestation – between this time period is when
we can use technology to save the baby that’s born super early
o Fetal circulatory system –IMPORTANT
▪ First organ system that sets up = fetal circulatory system
▪ This is the first one because it supplies circulatory processes to the rest of
the developing fetus that allows everything else to happen
▪ This circulatory system is different from infant, child, and adult.
• All of these will close very soon for a new newborn.
▪ Ductus arteriosus – bypasses the lungs
▪ Ductus venosus – most blood passes through this to the inferior vena cava
▪ Foramen ovale – an opening into the left atrium
o Hematopoietic system
▪ Fetal hemoglobin
▪ Formation of blood occurs in the yolk sac
o Gastrointestinal system
o Hepatic system – develops in week 4
o Respiratory system – IMPORTANT
▪ Pulmonary surfactants – surface active phospholipids
• present in the amniotic fluid – we can measure the surface active
phospholipids and come up with a ratio that tells us about lung
maturity
• development begins in week 4 and continues through week 17 with
formation of larynx, trachea, bronchi, and lung beds
• 16-24 weeks the bronchi and terminal bronchioles enlarge and
vascular structures and primitive alveoli form
▪ L/S ratio: used to determine fetal lung maturity
• We call it the LS ratio. L to S is 2:1 = the lungs are considered to
be mature. If it’s less than this they’re considered to be
immature. 35 weeks of gestation is when we see this.
o Gastrointestinal system
▪ Fetus swallows amniotic fluid beginning in the fifth month
o Renal system
▪ Kidneys form in 5th week and begin to function 4 weeks later
▪ Urine is excreted into amniotic fluid
o Neurologic system – begins to develop 3rd week
▪ Folic acid helps prevent neural tube defects – needed by week 4
▪ Sensory awareness – fetus begins responding at 24 weeks, taste by the
5th month and they can see later on.
o Endocrine system
o Reproductive system
▪ Sex differentiation begins in the embryo during the seventh week
o Musculoskeletal system
o Integumentary system
o Immunologic system
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