Ch. 3 fetal development Flashcards
how many chromosomes are in each body cell. how are they broken down
46
22 pairs of autosomes and 1 pair of sex chromosomes
Teratogens
things in medicine that cause damage to growing cells
Mitosis
cell division for replacing dead cells and growing. makes cells with 46 chromosomes
the diploid number of chromosomes
46 in a body cell
spermatogenesis
process of mitosis in the sperm
oogenesis
mitosis in the ovum
Meiosis
cell division where reproductive cells under go 2 divisions reducing the number of chromosomes to 23
the haploid number of chromosomes
23, sex cells
when does meiosis happen in the sperm
before it reaches the fallopian tube
when does meiosis happen in the ovum
when it is fertalized
Gametogenesis
the formation of gametes by meiosis
How many sperm are made by one spermatocyte
4
Where does fertilization occur
the outer third of the Fallopian tube near the ovary
How long does an ovum survive
24 hrs after ovulation
What in the female effects gender
pH and estrogen
When does the male embryo differentiate
6-7 weeks
When does testosterone secretion begin in reproduction
8 weeks
what is needed for female gonads to form
presence of estrogen and absence of testosterone
When do female gonads develop ovaries
6-8 weeks
Recessive disorder
alteration of defect in one gene
Dominant disorder
defect in both genes
if only one gene is normal what are the chances of developing a disorder
50%
How is a zygote formed
when a sperm and egg combine
what happens when a zygote is transported through the fallopian tube
rapid mitosis or cleavage but, the size doesn’t change just the number of cells
cleavage
begins with 2 cells that divide into 4 then 8 to make blastomere
Morula
the solid ball formed by cleavage
morula
enters uterus on third day and hangs out for 2-4 days before forming a cavity with 2 layers
Blastocyst
the inner layer of a morula, solid mass, turns into embryo and embryonic membrane
Trophoblast
outer layer that becomes the embryonic membrane, the chorion
Where does the zygote usually implant
in the upper part of the posterior uterine wall
Decidua
the endometrium after the zygote implants
Decidua basalis
area under the blastocyst that becomes the maternal placenta
What happens after implantation
the cells differentiate and develop special functions
What appears after implantation
chorion
amnion
yolk sac
primary germ layers
chorion
- what does it develop from
- what does it do
- what is it
- the trophoblast
- envelops the amnion, embryo and yolk sac and form the embryonic or fetal portion of the placenta
- thick membrane with villi
amnion
- what is it
- what does it do
- what does it from
- second membrane that meets the inside of the chorion
- covers and protects the embryo
- boundaries of the amniotic cavity
amniotic sac
the chorion and amnion together
describe amniotic fluid
clear
mild odor
contains bits of vernix and lanugo
vernix
fetal skin covering
lanugo
fetal hair on the skin
how much amniotic fluid
- 10 weeks
- 20 weeks
- 37 week
- 30 mL
- 350 mL
- 1000 mL
How much amniotic fluid per day does a fetus swallow
400 mL
Functions of amniotic fluid
- maintain termperture
- prevents sac from sticking to skin
- allows symmetrical growth
- allows fetal movement
- acts as protection
When does the yolk sac form and where
9th day
in the blastocyst
when does the yolk sac function and what does it do
about 6 weeks until liver takes over
initiates RBC production
What happens when the yolk sac finishes its job
umbilical cord covers it and it degenerates
what happens after implantation
the zygote in the blastocyst stage turns its embryonic disk into primary germ layers
What are the primary germ layers
ectoderm
mesoderm
endoderm
what does the ectoderm become
- outer skin
- oil glands
- hair follicles
- nails and hair
- external sense organs
- mucous membranes of mouth and anus
What does the mesoderm become
- true skin
- skeleton
- bone and cartilage
- connective tissue
- muscles
- blood and vessels
- kidneys
- gonads
what does the endoderm become
- lining of throat
- lining of GI tract
- lining of bladder and urethra
time period for embryo
2-8 weeks
time period for fetus
9 weeks - birth
What happens the second week
ectoderm, endoderm and amnion begin to develop
what develops week 3
single tubular heart
neural tube
primitive spine and brain
what develops in week 4
esophagus and trachea stomach neural tube closes forebrain limb buds ears and eyes begin
what develops in week 6
auditory canal eyes obvious heart has chambers nasal cavity upper lip
what develops in week 8
human appearance purposeful movement tail disappears sex organs start of most structures
what develops in week 17
genitalia visable leg movement visable feel movement bones ossified eye movement sucks and swallows fluid ova no true skin of fat
week 25
skin wrinkled lean body eyes open VIABLE quickening has sleep schedule vernix careosa Lanugo brown fat forms surfactant fingernails resp. movement
week 29
assumes cephalic position
CNS functioning
spleen stops making blood
bone marrow makes blood
weed 36
head and abd equal
subcut fat
what is full term
39-40 weeks
what are the measurements full term
- length
- weight
- 48 to 52 cm (18-21 in)
- 3000 to 3600 g (6 lb to 7 lb 15 oz)
week 3
mesoderm and neural tube forms
primitive heart starts to pump
when does the placenta attach
12 weeks (end of first trimester)
abnormal attachment to uterine wall results in
placenta accreta or placenta previa
what is the age of viability
20 weeks
placenta
temporary organ for resp., nutrition and excretion, endocrine gland
when does the placenta form
when the chorionic villi of the embryo extends into the mother’s decidua basalis
where does the maternal part of the placenta come from
decidua basalis
what does the fetal side of the placenta come from
chorionic villi and chorionic blood vessels
what does the amnion do
covers the fetal side and umbilical cord giving them a gray shiny look
what does enlarged placenta signal
maternal diabetes
increased morbidity of fetus
what causes small placenta
stress
undernutrition
steriods
chronic hypoxia
how much does the placenta weigh at term
1/6 weight of baby
how does deoxygenated blood and waste leave the fetus
2 umbilical arteries that enter placenta through branch of main stem villus which comes from the intervillous space (lacuna)
how does oxygenated blood from mom get to baby
goes into the intervillous space from spiral arteries in the decidua
what hormones are made by the placenta
- progesterone
- estrogen
- human chorionic gonadotropin (hCG)
- human placental lactogen (hPL)
function of progesterone in pregnancy
- maintain implantation
- reduces contractions and prevents miscarraige
- prepares milk
- stimulates testosterone in male baby
function of estrogen in pregnancy
- stimulates uterine growth
- increases blood flow to uterus
- helps development of breast ducts for milk
effects of estrogen not directly related to pregnancy
- mask of pregnancy
- vascular changes to skin and membranes in nose and mouth
- increased saliva
function of Human chorionic gonadotropin
-makes corpus luteum to keep making estrogen and progesterone to sustain pregnancy
what do pregnancy test check for and how soon
hCG, 7-9 days after fertilization
Function of Human placental lactogen
-decrease insulin sensitivity and glucose utilization in mom so baby has what it needs to grow
what is in the umbilical cord
2 arteries and a vein
Wharton jelly
covers the vessels in the umbilical cord
how long is the cord
55cm (22 in)
ductus venosus
fetal circulatory shunt
sends some blood away from the liver as it goes to the placenta
foramen ovale
fetal circulatory shunt
diverts most blood from the right atrium to the left instead of going to lungs
ductus arteriousus
fetal circulatory shunt
diverts most blood from pulmonary artery to the aorta
why does the foramen ovale close after birth
pressure on the right side of the heart falls as the lungs fill
what causes the ductus arteriousus to constrict after birth
oxygen levels rise
when does the ductus venosus close after birth
when flow from the umbilical cord stops
when does the foramen ovale close
- functionally
- permanently
- 2 hr after birth
- 3 months
when does the ductus arteriousus close
- functionally
- permanently
- 15 hrs
- 3 weeks
when does the ductus venosus close
- functionally
- permanently
- when the cord is cut
- 1 week
what do the ductus arteriousus and ductus venosus become after they close permanently
ligaments
what can cause the foramen ovale to reopen
conditions that keep lungs from filling fully
what can cause the ductus arteriosus to remain open
conditions that lower blood oxygen levels
what causes wet lung in newborns
c-section or rapid delivery
when is the fetus most susceptible to external influences
first 3 months
what does pancreatic beta cells cause
impaired insulin secretion
what can happen in utero and increase risk for hypertension later in life
changes in vascular or renal structures or hormonal systems from malnourishment
what can impaired fetal liver growth late in gestation cause
impaired lipid metabolism and increased cholesterol level
what is used for assessment of fetal growth
- weight
- length
- placenta size
- head and abd size
monozygotic twins
identicle
physical differences in monozygotic twins are caused by
differences in blood supply from the placenta
monozygotic twins begin to develop when
end of first week after fertilization
what things to monozygotic twins share
- chorion
- placenta
- some vessels
what causes conjoined twins
embryonic disk not dividing completely
dizygotic twins
fraternal twins
what increases chances of dizygotic twins
genetics and older age
