Ch. 29 - Development Flashcards
When is embryological development?
first 8 weeks after fertilization
- all principal adult organs are present
When is fetal development?
from 9 weeks until birth
- placenta is functioning by end of third month
What is fertilization?
haploid sperm + secondary oocyte merge; results in zygote with a single diploid nucleus
What is sperm capacitation?
series of functional changes sperm must go through to fertilize the egg
- rapid beating of flagella
- removal of cholesterol, prot, glycoproteins from plasma membrane near acrosome
What are the 2 layers sperm must penetrate to fertilize an oocyte?
- corona radiata
- zona pellucida
- SP3 = sperm receptor in zona pellucida
What does sperm entry trigger in the oocyte?
to complete meiosis II; oocyte divides into a larger ovum and a polar body that degenerates
What is the difference between fraternal and identical twins?
F - dizygotic; independent release of 2 oocytes fertilized by 2 separate sperm
I - monozygotic; developed from a single fertilized ovum
What are cleavage and blastomeres?
C - rapid mitotic cell divisons of zygote
B - progressively smaller cells produced by cleavage
When does the cell mass (morula) become a blastocyst?
when morula enters uterine cavity by day 5
What does the blastocyst give rise to?
- embryoblast (inner cell mass); will develop into embryo
2. trophoblast (outer cell mass); will develop into chorion
What is implantation?
attachment of blastocyst to endometrium approx 6 days after fertilization
- trophoblast secretes hCG to maintain corpus luteum
What does human chorionic gonadotropin do?
hCG allows for sustained secretion of estrogen and progesterone, preventing menstruation
SUMMARY: what are the 5 events in the first week of development?
- fertilization (12-24h after ovulation)
- cleavage (30h after fertilization)
- morula (3-4 days after fertilization)
- blastocyst (4.5-5 days after fertilization)
- implantation (6 days after fertilization)
What are the 2 layers the trophoblast divides into?
- syncytiotrophoblast (outermost)
2. cytotrophoblast (inner layer)
What does the embryoblast differentiate into?
- hypoblast (primitive endoderm)
2. epiblast (primitive ectoderm)
What is the amnion?
membrane that develops from the epiblast
What is the function of amniotic fluid?
absorbs shock, regulates body temp, prevents adhesions with surrounding structures
What is the function of the yolk sac?
- supply nutrients to embryo for next 1-2 weeks
- conains primordial germ cells that become spermatogonia/oogonia
- source of blood cells
What is the chorion and what forms it?
embryonic contribution to placenta; extraembryonic mesoderm and trophoblast
What is the function of the chorion?
- secretes hCG
- suppresses maternal immune response against fetus
What is induction?
one tissue stimulates the development of an adjacent unspecialized tissue into a specialized one
During week 3, what does the bilaminar embryonic disc become?
trilaminar embryonic disc: ectoderm, mesoderm, endoderm
What will the endoderm become?
lining of GI, resp, outer urinary & reproductive tracts
What will the mesoderm become?
muscle, bone, CT, CVS, inner urinary & reproductive system
What will the ectoderm become?
skin epidermis, nervous system
What is the notochordal process?
when mesoderm cells migrate towards head and form notochord (solid cylinder)
How does induction occur during days 22-24?
notochord secretes substances that cause nearby unspecialized mesoderm cells to become vertebral bodies (become nucleus pulposus)
Describe neurulation
- notochord induces thickening of ectoderm to form neural plate
- plate folds inward and forms neural groove
- raised edges of neural plate are called neural folds
- folds fuse into neural tube
- develop in brain and SC
What is spina bifida?
abnormality in neural tube closure; meninges and SC can protrude from vert column
What is anencephaly?
failure of cranial bones to surround brain tissue, leading to degeneration
What are the components of the placenta?
- fetal portion: chorionic villi of chorion
2. maternal portion: decidua basalis (endometrium)
What are functions of placenta?
- allows nutrient/waste exchange between mother and fetus
- produces hormones needed to sustain pregnancy
- act as barrier to most microorganisms
Describe blood supply between placenta to embryo
- 2 umbilical arteries (carry de-O2 fetal blood to placenta)
- 1 umbilical vein (carry O2 blood to fetus)
How does the fetus’ proportions change shape from week 9 to birth?
head changes proportion; now smaller than rest of body
What are 3 main causes for abnormal development?
- genetic
- environmental (teratogens)
- unknown
What are some examples of teratogens?
alcohol, viruses, smoking, radiation
When does abnormal development usually occur?
usually week 3-8; different effects depending on time of exposure
What is a fetal ultrasonography?
screening tool (not diagnostic!)
- emits high-freq sound waves which are converted to an image called a sonogram
- usually taken ~week 10 and ~week 18
What can a fetal ultrasonography show?
can confirm pregnancy, determine fetal age, viability, growth, position, multiple, and maternal abnormalities
What can maternal blood screening detect? (quad screen)
test for abnormal levels of:
- alpha-fetoprotein produced by fetus
- human chorionic gonadotropin by placenta
- estriol by fetus/placenta
- inhibin A by placenta
What can abnormal levels (from quad screen) indicate?
neural tube defect, trisomy 18/21, or other chrom disorders
When are quad screens performed?
week 16-18
What is amniocentesis?
needle inserted through abdominal wall and uterus to remove ~10mL of amniotic fluid (containing fetal cells)
- done ~weeks 14-16
What can amniocentesis detect?
suspected genetic abnormalities
- fetal cells examined for gen disorders (e.g. down syndrome, sickle cell disease, hemophilia)
What is chorionic villi sampling?
needle through abdominal wall or through cervix to remove ~30mg of chorionic villi (contains same genome as fetal cells)
- done ~8 weeks
- higher chance of spontaneous abortion
What can chorionic villi sampling detect?
chromosomal analysis identifies same gen disorders as amniocentesis
What is the function of hCG in pregnancy?
- stimulates continued production of estrogens and progesterone by corpus luteum
- for continued attachment of embryo/fetus to endometrium
What is the function of estrogen/progesterone in pregnancy?
maintain lining of uterus and prep mammary glands
What secretes hCG? Estrogen/progesterone?
chorion; corpus luteum (then secreted by placenta after 3rd-4th month)
What is the function of relaxin in pregnancy?
- increases flexibility of pubic symphysis and ligaments around pelvis
- helps dilate uterine cervix during labour
What is the function of human chorionic somatomammotropin (hCS)
- helps prep mammary glands for lactation
- decreases glucose use in mother so more glucose is avail for fetus (increase FA use)
What is the function of corticotropin-releasing hormone (CRH) in pregnancy?
- establishes timing of birth (high levels = preemie delivery)
- increases secretion of cortisol which is important for lung dev and surfactant production
Describe the maternal CV changes to meet needs of fetus
- rise in CO by 20%-30% due to placenta
- maternal blood vol increases by 30%-50%
Describe the maternal resp changes
- increase in TV by 30%-40%
- total body O2 consumption increases by 10%-20%
Describe hormone changes that occur in labour
- decease in progesterone to contract myometrium and relax cervix
- increase in estrogen
How do estrogen levels rise during labour?
- placenta secretes CRH
- fetal ant pituitary secretes ACTH
- fetal adrenal glands secrete cortisol and DHEA
- placenta converts DHEA to estrogens
How does estrogen function during labour?
- increase number of OT receptors on uterine muscle fibers
- muscle fibers form gap junctions bt cells
- stimulate placenta to release prostaglandins (that dilate cervix)
What is false labour?
abdominal pain at irregular intervals that do not intensify
What is true labour?
- regular, painful, uterine contractions that increase in freq/intensity
- dilation of cervix
What are the 3 stages of true labour?
dilation, expulsion, placental
What occurs in the dilation stage?
- regular uterine contractions
- rupture of amniotic sac
- complete dilation of cervix (10 cm)
What occurs in the expulsion stage?
baby moves through birth canal
What occurs in the placental stage?
- placenta expelled after delivery by uterine contractions
- contractions constrict BV to reduce risk of hemorrhage
What are some changes in the CV system after birth? (infant)
- foramen ovale closes
- ductus arteriosus and umbilical arteries/vein close and become ligaments
What are some changes in the resp system after birth? (infant)
- surfactant is produced by end of 6th month
- umbilical cord is cut (no O2 in/CO2 out)
- increased CO2 levels in blood stimulate resp centre in medulla
- forceful inhalations and exhalations!
