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149 Cards in this Set

  • Front
  • Back
Define fertilization
fertilization: when a sperm
and an egg fuse to become a zygote
What is formed when a zygote divides mitotically?
Daughter cells called blastomeres, Mitotic cell division proceeds and cell type differentiation emerges
What is gastrulation?
the process of cell movements by which a developing embryo forms distinct germ layers from the embryonic disc that later grow into particular organs
What stage of development is an emybro in in weeks 1-2?
preembryo development; developing organism between between fertilization and complete implantation; implantation is initiated at approximately 7 days after fertilization (can be initiated as late as 10
days after fertilization); implantation is complete
by end of 2nd week
What stage is an embryo in in weeks 3-8?
Embryo development: prenatal
stage between completion of implantation at end
of 2nd week through 8th week after fertilization
What occurs during weeks 9-birth?
Fetus development: prenatal
stage between 9th week after fertilization until birth
Biological age since conception
Average time
of 38 weeks (266 days) from
fertilization/conception to birth and is divided into 3 trimesters each around 3 months long
Gestational age
the period of development of
offspring during pregnancy
Gestational age definition in clinical medicine
duration since day 1 of last menstrual period
which is approximately 2 weeks longer than
duration since conception
Gestational age in clinical medicine
average gestational age of a term birth is 40 weeks (280
days)
Definition of Pregnancy
Conception
Clinical medicine definition
Day 1 of last menstrual period, which is on average two weeks before conception
General Public definition
1-2 days after a missed menstrual period or when the pregnancy test is positive, which is on average two weeks after conception( when hCG is detectable)
Presumptive signs of pregnancy
-missed menstrual period with coitus in the past month
-nausea in the morning
-increase in size and tenderness of breasts
-darkening of areola around nipples
Probable signs of pregnancy
-increase in size of abdomen
-missed consecutive menstrual cycles
-increase in frequency of urination
-positive hegar's sign: uterine cervix becomes softer by 6th week of pregnancy
-positive pregnancy test
Positive signs of pregnancy
• Detection of fetal heartbeat
• Feeling the fetal movement
• Visualization of fetus by ultrasound or
fetoscopy
Where is hCG produced?
blastocyst and placenta of embryo and fetus
What are some properties of hCG?
-has similar activity as LH
-detection in blood and urine indicates pregnancy
-hCG is often not detectable by urine and blood tests until 15 days after conception
-can have false positive or false negative tests
How is the morula created? By what day is the morula completed? (how many days after fertilization)
Zygote undergoes several mitotic divisions after fertilization; this is a ball of 16-32 cells, completed by 3rd day after fertilization
Does the preembryo divide as it passes down the oviduct to the uterotubal junction?
yes
How does the developing preembryo move?
beating of oviductal cilia in uterine direction
When does the preembryo enter the uterus?
3-4 days
What is the preembryo called when it enters the uterus?
mass of cells called the blastocyst
What is the blastocyst
ball made of single outer layer of cells (trophoblast) just inside the zona pellucida surrounding a fluid filled cavity called the blastocoel
What is the Inner cell mass and where is it found?
clump of cells near one end of blastocyst underneath the trophoblast layer
What does the inner cell mass give rise to?
Gives rise to the embryo and is the source of embryonic stem cells
Where does conception occur?
ampullary isthmic protion of oviduct
When does implantation occur?
approximately 7 days after conception
What does implantation require?
A uterus that has been primed with appropriate amounts of estradiol and progesterone
What does the corpus luteum do?
secretes modest levels of estrogen and high levels of progesterone which primes the uterus and makes the endometrium more vascular, secretory, and ready for implantation
What enzyme causes the zona pellucida surrounding the blastocyst to dissolve? Where is this enzyme secreted? What activates this enzyme?
-enzyme is protease
-secreted by the uterus
-activated by progesterone
How long does a non-implanted blastocyst rest freely in the uterine cavity?
2-3 days
Approximately what day does the uterus secrete protease enzyme to dissolve the zona pellucida?
Day 6
What happens when zona pellucida completely dissolves?
the inner cell mass end of the blastocyst attaches to the uterine wall and penetrates the endometrium, approximately 7 days after fertilization
What two layers does the trophoblast differentiate into?
outer syncytiotrophoblast and inner cytotrophoblast
What does the syncytiotrophoblast secrete?
secretes proteases that break down cells of the uterine endometrium
What makes implantation complete?
cells of uterine stroma demonstrate a deciduoma response and multiply rapidly and form a cap over blastocyst
What does the syncytiotrophoblast penetrate?
penetrates epithelium and then stroma
What does the Blastocyst penetrate?
penetrates further into stroma and amniotic cavity appears and blastocoel becomes yolk sac cavity
What is the deciduoma response?
uterine tissue grows around and over blastocyst and implantation is complete
What enzyme causes the zona pellucida surrounding the blastocyst to dissolve? Where is this enzyme secreted? What activates this enzyme?
-enzyme is protease
-secreted by the uterus
-activated by progesterone
How long does a non-implanted blastocyst rest freely in the uterine cavity?
2-3 days
Approximately what day does the uterus secrete protease enzyme to dissolve the zona pellucida?
Day 6
What happens when zona pellucida completely dissolves?
the inner cell mass end of the blastocyst attaches to the uterine wall and penetrates the endometrium, approximately 7 days after fertilization
What two layers does the trophoblast differentiate into?
outer syncytiotrophoblast and inner cytotrophoblast
What does the syncytiotrophoblast secrete?
secretes proteases that break down cells of the uterine endometrium
What makes implantation complete?
cells of uterine stroma demonstrate a deciduoma response and multiply rapidly and form a cap over blastocyst
What does the syncytiotrophoblast penetrate?
penetrates epithelium and then stroma
What does the Blastocyst penetrate?
penetrates further into stroma and amniotic cavity appears and blastocoel becomes yolk sac cavity
What is the deciduoma response?
uterine tissue grows around and over blastocyst and implantation is complete
What is the syncytiotrophoblast full of after implantation?
sinusoids full of maternal blood
Preembryo Sequence Day 0 - Day 15
• Day 0: conception with zygote formation
• Day 1: two blastomere cells
• Day 3: morula (16-32 cells)
• Day 4: early blastocyst
• Day 5: late blastocyst
• Day 6: blastocyst attaches to endometrium
• Day 7: implantation begins (may begin on day 10)
• Day 8: amniotic cavity & embryonic disc form
• Day 9: uterine sinusoids develop
• Day 10: implantation complete
• Day 15: first missed menses/positive pregnancy
test
Are the fetal cells geneticall different than those of mother?
-Yes, half of the chromosomes come from the father of the fetus
-However, the common histocompatibility molecules found on most nucleated cells are NOT found on placental cells; this may be part of the reason why implantations are not routinely rejected by the mother's tissue
What does the inner cell mass differentiate into after implantation?
differentiates into a bilaminar embryonic disc consisting of the epiblast and hypblast
What does the hypoblast, epiblast, and trophoblast contribute to?
all contribute to the development of extraembryonic membranes which sustain embryo during intrauterine development
What gives rise to the ectoderm, mesoderm, and endoderm?
epiblast
Some facts determined by research at Yale School of Medicine
• The maternal immune system has the ability to
express immune tolerance toward the implanting
trophoblast and the subsequent development of
the embryo and fetus.
• The maternal immune system can also work to
promote implantation and maintain pregnancy.
• While the innate immune system can
protect against infections it can also
contribute to the fetal-maternal immune
adjustment and the establishment of an
adequate microenvironment that will
promote cell growth and inhibit harmful inflammatory immune reactions.
What are Th1 and Th2?
Local Th1 and Th2 are necessary for a successful implantation
During implantation _________, is critical for appropriate tissue remodeling of maternal decidua tissue and invasion of developing embryo.
apoptosis
What are the roles of macrophages?
• Macrophages actively clear apoptotic cells
in the placental bed around developing
embryo & fetus.
• Macrophages are also an important source
of cytokines and growth factors and it is
postulated that these cells contribute to
maintaining the appropriate balance of Th-1
and Th-2 cytokines in the placental bed.
What is critical in determining the success or failure of implantation of pregnancy?
the appropriate balance between pro-inflammatory and anti-inflammatory cytokines
What does RANTES (regulated upon activation, normal T cell expressed and secreted) promote at the site of implantation?
promotes trophoblast cell survival and modulates the balance of T reg/T effector lymphocytes in favor of maternal tolerance
What do the toll like receptors of the trophoblast do?
allows the placenta to recognize and respond to any microorganism that may endanger the fetus
What is derived from the ectoderm?
• Nervous system
• Epidermis of skin, hair, nails, and tooth enamel
What is derived from the mesoderm?
• Skeleton
• Notochord that develops into vertebral
column
• Muscles
• Heart & circulatory system
• Kidneys
• Gonads
• Deep layers of skin
What is derived from the endoderm?
• Digestive tube and the liver, gall bladder, and pancreas that bud off the gut tube
• Respiratory tube including the lungs
What are the 4 extraembryonic membranes?
• Yolk sac (mainly vestigial in humans)
• Allantois (mainly vestigial in humans)
• Amnion
-4th membrane is the chorion
What three extraembryonic membranes are derived from the inner cell mass?
-Yolk Sac
-Allantois
-Amnion
What extraembryonic membrane is derived from the cyotrophoblast?
chorion
What are some properties of the yolk sac?
• Endoderm-lined membrane that surrounds the blastocoel (yolk sac cavity)
• Vestigial & non-functional in humans but is very important in birds that lay eggs
• Degenerates early in embryonic
What are some properties of the amnion?
• Grows over forming embryo
• Amniotic cavity becomes filled with amniotic fluid
• Amniotic fluid supports and protects the fetus against mechanical shock and
provides water and other materials to fetus
What are some properties of the amniotic fluid during week 8, 20, 38, and 40?
week 8 = 5-10 ml
week 20 = 250 ml
week 38 = 1000-1500 ml
week 40 = 500-1000 ml
What is the maximm rate of amniotic fluid absorption and secretion?
300-600 ml per hour
What are some properties of the chorion?
• Derived from the cytotrophoblast and
surrounds the embryo after 1 month of development
• Chorion eventually fuses with amnion
• Chorion forms an important component of the placenta
What are some of the roles of the placenta?
• Placenta serves as a nutrient, respiratory, and
excretory organ for fetus
• Through placenta fetus receives oxygen, glucose,
growth factors, and other nutrients and eliminates
carbon dioxide and other waste products
Can molecules larger than 500 molecular weight pass through the chorionic villi to enter the fetal blood vessels?
No, however, late in pregnancy, large protein maternal antibodies are actively pumped into fetal circulation by placental cells
Why is the placenta considered hemochorial?
The chorionic villi are directly bathed by sinusoid pools of maternal blood
When do fingerlike projections of the cytotrophoblast extend through the synctiotrophoblast and toward the vascular uterine stroma?
Around day 14
How do the contents of maternal blood reach the fetus? What happens in the opposite direction?
• Contents of maternal blood (e.g., glucose and oxygen) diffuse from uterine sinusoids
through the thin wall of each chorionic villus and into the fetal vessel within each villus
and travel to the fetus via the umbilical vein
• In the opposite direction, the fetal waste products (e.g., CO2) leave the fetal blood
via the umbilical arteries and diffuse across villi into mother’s blood to be excreted
What percentage of the inner uterine wall is covered by the placenta at week 4? week 20? week 40?
• Week 4: 20% of inner uterine wall covered by placenta
• Week 20: 50% of inner uterine wall covered by placenta which weighs 200
gm, while fetus weighs 500 grams
• Week 40: placenta weight is 700 gms and has 285 liters of blood that pass through it each day
What does the stratum functionalis of endometrium transform into as fetus and placenta grow?
decidua of the pregnant uterus
What is the decidua basilis?
Maternal part of placenta
What is the Decidua capsularis?
result of deciduoma response with overgrowth of endometrium
What is the Decidua parentalis?
endometrium not directly connected to the fetus; technically, the fetus resides within the uterine wall, not the uterine cavity
What does the umbilical cord do?
• Connects fetus with the placenta
What is the umbilical cord derived from?
• Derived from body stalk that is structure connecting embryo and chorion
What is the average diamater and length of the umbilical cord?
• At birth, cord is 0.3-1.0 inches diameter and 20-22
inches long and is covered with amniotic membrane
What are the structures that carry oxygenated and deoxygenated blood through the placenta?
What are the vessels within the cord cushioned with?
• Two umbilical arteries carry de-oxygenated fetal
blood to the placenta
• One umbilical vein carries oxygenated blood from
the placenta to the fetus
• Vessels within cord are cushioned by a gelatinous substance called Wharton’s jelly
What are dyzygotic fraternal twins? What is different in a spatially seperate implant versus a close together implant?
Dizygotic fraternal twins: two genetically distinct zygotes form & two embryos implant into uterus
• Implant spatially separate: two separate placentas, chorions, and amnions (Fig 10-7A)
• Implant close together: single placenta, fused chorions, and two amnions (Fig 10-7B)
What are monozygotic identical twins?
Monozygotic identical twins: develops when inner cell mass of blastocyst divides, producing two embryos with a single placenta and chorion,
but two amniotic sacs (Fig 10-8)
• In some cases, however, splitting of early morula
produces monozygotic twins with separate amnions, chorions, & separate or fused placentas
Do dizygotic twins vary by ethnicity, maternal age, parity, and fertility drugs? What are the differences between different ethnicities?
• Dizygotic twin frequency varies by ethnicity, heredity, maternal age, parity, and fertility drugs:
• Ethnic differences appear to be in part due to
ethnic variations in follicle-stimulating hormone
• 1/20 in a rural community of Yoruba in Nigeria
• 1/80 in black females
• 1/100 in white females
• 1/155 in Japan
For dyzygotic twins, is the herity of mother or father more important?
Mother
What are some facts about the rate of twinning?
• Rate of twinning is near 0% at puberty to a peak level at
around age 37 when FSH levels are highest
• Rate of twinning increases with parity: the more children a
woman has had the greater the likelihood her next pregnancy will be twins
• Increased fecundity and higher rate of dizygous twins
reported in women who conceive within one month after stopping oral contraceptives, but not during subsequent months; this appears to be due to the sudden release of pituitary gonadotropin in amounts greater than usual during the first spontaneous cycle after stopping oral contraceptives.
• Use of fertility enhancing drugs e.g., clomid increase the
rate dizygotic, trizygotic, etc. pregnancies
What is the frequency of monozygotic twins and is is dependent on ethnicity, age, herity, and parity?
1/250 worldwide, and is not dependent on ethnicity, age, herity, and parity
What are increased risk of monozygotic twins associated with?
• Delayed transport through the fallopian tube
• Women who have recently been on combination oral contraceptives because they
cause decreased tubal motility
• Minor trauma to blastocyst during assisted reproductive techniques
In monozygotic twinning, what happens if division occurs in first 72 hours?
If division occurs in first 72 hours after conception, before chorion and morula formation, two embryos with two chorions, two amnions, and one or two placentas will develop
In monozygotic twinning, what happens if division occurs between days 4-8 after conception?
If division occurs between days 4-8 after conception, after chorion and inner cell mass formation, two embryos with one chorion, two amnions, and one placenta will develop
In monozygotic twinning, what happens if division occurs after day 8?
If division occurs after day 8, after chorion and amnion have already formed, two embryos with a single chorion, amnion, and placenta will develop
In monozygotic twinning, what happens if division occurs even later, that is after the chorion, amnion, and embryonic disck have been formed?
If division occurs even later e.g., day 14, that is after the
chorion, amnion, and embryonic disk have been formed, cleavage is incomplete and conjoined twins are formed
When do the three germ layers form?
by the end of the second week
When do the major internal and external structures take shape?
week 3-8 post conception, very sensitive to disturbances that could result in death of congeital malformations
What happens during embryonic development week 3?
• Week 3 of development, the flat, trilaminar embryonic disc begins to curl under to form a
sausage-like shape (Fig 10-9)
• Ectoderm forms dermal layer & nervous system
• Endoderm lines the inner tube which forms gut/intestine
• Mesoderm is sandwiched in between these layers
• Neural tube develops along embryo back and develops spinal cord and brain from ectoderm
• A series of lumps (somites) form along either side of neural tube which develop into the vertebrae, ribs, and muscles in the back
What happens during embryonic development week 4?
• 2 mm long embryo with C shape at beginning of week 4 (Fig 10-9)
• Eyes began to form on head
• Inner ear development begins
• Pharyngeal arches develop in neck area which will develop into jaws, ear and other structure
• Heart forms and begins beating
• Tiny arm and leg buds develop
What happens during embryonic development week 5?
• Rapid growth of brain
• Arm buds flatten and hands
become paddle shaped (Fig 10-9)
• 1 cm in length by end of week
What happens during embryonic development week 6?
• Eyes become pigmented
• Exterior ears began to form (Fig 10-9)
• Head/brain continues to grow
• Leg bud becomes paddle shaped
• Hand rays indicate positions of digits
• Distinct tail is still present
What happens during embryonic development week 7?
• Toe rays form indicating position of digits (Fig 10-9)
• Rapid development of gut tube causes intestines to protrude into the umbilical
cord to produce an umbilical herniation
• Tail is diminished
What happens during embryonic development week 8?
• 1.25 inches long by the end of week 8
• Eyelids have grown to meet each other and fuse so eyes are closed
• Fingers and toes can be clearly seen, however, a thin sheet of webbing still exists
between each digit (Fig 10-9)
• Tail has disappeared
• Embryo now begins to look human
• Brain, spinal cord, and peripheral nerves are all developed
What happens during Fetal Period? (week 9-birth)
• Organ systems established in the embryonic period continue to develop and differentiate
• Period of rapid growth
What happens during week 12 (fetal period)
• fetal heart rate can be heard with a
stethoscope
• Fetus can react to stimuli and fetal movements begin, however mom can not
yet feel these movements
What happens during month 4-5 of gestation?
Mom may begin to feel fetus moving
What happens in week 13 of males?
testicles in mail
What happens in week 15?
Fingers
What happens at 4 months?
fetus starts to look like a baby
How many arteries and veins does the umbilical cord have?
2 arteries and 1 vein
What happens at 16 weeks in males?
Penis develops
What happens in week 21 of females?
Visible clitoris in between labia
What is apparent by the end of the 2nd trimester?
• Skin covered with protective layer of
fatty secretions called vernix caseosa
• Skin grows layer of downy hair (lanugo)
What happens at 6 months?
Fetus is covered with downy hair
What happens during the third trimester?
• 3rd trimester (months 7, 8, & 9)
• Fetus adds layers of fat and loses its wrinkled appearance
• Lungs mature
What is the limiting factor for survival of premature infants?
lung development
What is the youngest premature infant that has survived?
Biological gestation age of 21 weeks post conception (clinical medicine gestation age = 23 weeks); most born at this age do not survive
What nutrients does the fetus get from the mother's blood? How does it get to the fetus?
The fetus gets glucose, amino acids, fatty acids, vitamins, salds, and minerals via the umbilical vein
How is carbon dioxide and other waste products delivered to the placenta?
via umbilical arteries
When are fetal kidneys functional? How much urine is produced and where is it excreted?
Functional throughout the fetal period and produce about 450 ml of urine a day late in pregnancy which is excreted into the amniotic fluid. In late pregnancy, the fetus swallows about 500 ml of amniotic fluid each day
What allows for the transport of oxygenated blood to the fetus?
Placenta
How does blood travel in the heart of a fetus?
When blood enters the right side of the fetal heart, it travels up the pulmonary trunk and by passes the lungs by moving through the ductus arteriosis
to the aorta (Fig10-12)
• The blood is exchanged between the
right side and left side of heart through passage of blood through hole called foramen ovale between right & left
atria
• Blood is transported from the right ventricle directly to the aorta via the ductus arteriosis
• The ductus arteriosis and the foramen ovale both typically close at birth
What % of preembryos/embryos die within the first three weeks of life?
50%, conceptus is typically lost before the women knows that she is pregnant
What % of confirmed pregnancies are miscarried?
15-20%
What percentage of spontaneously aborted preembryos/embryos/fetuses are due to chormosomal abnormalities?
42%
How often to choromosomal abnormalities occur?
1/200 newborns
Of these infections that can harm embryos and fetus', which are viruses? Which are bacteria?
HIV
Chicken pox
syphilis
typhoid
herpes simplex
tuberculosis
rubella
parvovirus
Viruses:
• HIV, chickenpox, herpes simplex, mumps, rubella, parvovirus
Bacteria:
• Syphilis, tuberculosis, typhoid
During what weeks do teratogens, mutagens, and other agents damage the fetus?
What are some of these teratogens/mutagens?
• Main effects during 4-7th week gestation
• Mercury, lead, cadmium, arsenic, PCBs, DDT, benzene, and carbon tetrachloride
• Alcohol/fetal alcohol syndrome
• Tobacco
• Recreational intoxicants
• Some pharmaceuticals
By which week can an ultrasound detect fetal heart rate?
week 8
What is the purpose of an ultrasound?
Ultrasound is used to assess fetal anatomy and movement and placenta position
What are the purpose of multiple serum marker tests?
Multiple serum marker test from maternal blood: hCG (human chorionic gonadotropin), alpha fetoprotein, and estriol
levels can estimate likelihood that a fetus has Down’s syndrome, however this test is
not definitive
What is the purpose of an amniocentesis fetal evaluation?
• Recommended in women over 34 years, or women with family history of genetic disorders
• Procedure performed between 14th and 16th week of pregnancy (biological definition) or 16-18 weeks gestation (clinical medicine definition)
• Needle is inserted through abdominal and uterine walls into amniotic fluid with ultrasound guidance
• Cells and amniotic fluid can be evaluated for chromosomal abnormalities
What is the purpose of chorionic villus sampling (fetal evaluation)?
• Recommended in women over 34 years, or women with
family history of genetic disorders
• Procedure performed between 8th & 10th week of
pregnancy (biological definition) or 10th & 12th week
gestation (clinical medicine definition)
• Needle is inserted through vagina and cervix into uterine
cavity using ultrasound as a guide
• Chorionic cells removed from placenta & analyzed
• Higher risk of inducing miss-carriage than with
amniocentesis
• With CVS get results earlier than amniocentesis, which is
preferable if the pregnancy is going to be terminated
based on the test results
Is a 1st trimester abortion safe? What percentage of all induced abortions in the USA are in the 1st trimester?
• Relatively safe for mother
• 87% of all induced abortions in the USA are in the 1st trimester
What is considered an induced abortion?
Medical abortion from taking pill or surgical abortion that uses aspiration and instruments to empty contents of uterus
What is the embryonic period abortion induced by?
prostaglandins and mifepristone
What is Mifepristone?
Mifepristone = RU486 referred as the abortion pill acts by preventing progesterone action by blocking progesterone receptors
When can mifepristone be taken?
Mifepristone can be taken within first 35 days post-conception to induce a miscarriage and is sometimes taken with misoprostol (prostaglandin)
vaginal suppository that softens the cervix to facilitate the release of miscarriage out of cervix
What is the most frequently used method of abortion in 1st trimester? When is this procedure done?
vacuum aspiration, performed during 5th-11th week after conception
How does vacuum aspiration work?
• Vacurette tube is placed through cervix into uterus and is connected to a suction devise
• If material is not completely removed by suction, the endometrium is scraped with a
curette
When is dilation and curettage done? How does it work?
• Done in 8th - 14th week after
conception
• Cervix is typically dilated with
Laminaria which is a brown algae (Fig 15-6)
• The endometrium is scraped with a curette which is inserted through the cervix
How is an abortion typically induced during the 2nd trimester?
• Cervix is typically dilated with a small tube of Laminaria (brown algae) inserted into cervix which absorbs moisture and expands and dilates cervix
• Administration of intra-amniotic (Fig 15-7) saline, urea, glucose, or prostaglandin alone or in combination to terminate the pregnancy and induce delivery
What is induced abortion 2nd trimester dilation and evacuation? When is it performed?
• Performed after 12th week post conception
• Cervical dilation using Laminaria (brown algae)
• Uterine contents removed using suction, curettes, and forceps
What happens during induced abortion during late 2nd trimester/3rd trimester?
• Dilation and extraction referred to as “partial birth abortion” and has been typically performed in the late 2nd trimester and early 3rd trimester
• Ban on this procedure in certain areas of the world
When do the ovaries in a fetus develop?
Week 11