Chapter 28--Fertilization

Fertilization

the sperm has reached the secondary oocyte

sperm’s chromosomes combine with oocyte, making the thing 46 chromosomes again in the fallopian tubes

Embryo

baby through week 8

fetus

baby week 9 through birth

Completion of Meiosis II

the sperm enters/penetrates the egg, triggering the completion of meiosis II in the oocyte

results in ovum and second polar body

zygote blastocyst implantation steps

cleavage, blastocyst formation, and implantation

cleavage

rapid cell divisions, occurs while zygote moved toward the uterus

produces cells with high surface-to-volume ratio that enhances nutrient absorption and waste secretions

Morula

72 hours after fertilization, becomes a solid ball of 16 cells

blastocyst formation

day 4-5, embryo (now 100 cells) reaches uterus

morula becomes blastula

Blastula

hollow sphere composed of trophoblast cells and inner cell mass

trophoblast cells

participate in placenta formation, creates fluid-filled hollow space of blastula

inner cell mass

cluster of 20-30 rounded cells, which will form embryo and extraembryonic membranes

Implantation

6-7 days after ovulation

trophoblast cells adhere to endometrium and release hCG, preventing shedding of endometrium

prompts surge of progesterone and estrogen, keeping corpus lutem alive

how many zygotes implant

blastula burrows into endometrium around day 5

estimated that 2/3 of zygotes dont implant

Gastrulation

differentiation occurs in trophoblast cells, triggered by implantation

Gastrula

invagination of blastula (pinches and folds inward), contains three germ layers

the germ layers

ectoderm—becomes nervous system

endoderm—becomes epithelial linings organs

mesoderm—becomes muscular and connective tissues

baby transformation pathway

secondary oocyte

zygote

morula

blastula

gastrula

extraembryonic membranes

chorion, yolk sac, and amnion

chorion

form’s child’s portion of placenta, encloses all other membranes

chorionic villi

villi that sprout from the chorion to provide maximum contact and exchange with maternal blood

yolk sac

sac that hangs from the belly button of the embryo

source of blood vessels/cells and nutrients until the placenta forms

allantois

structural basis for umbilical cord

amnion

a membrane that closely covers embryo when first formed

filled with amniotic fluid and becomes the amniotic sac

provides a protective environment for developing embryo

Placenta

circular organ in the uterus nourishing and maintaining fetus through the umbilical cord

temporary organ that originates from both embryonic and maternal tisssues

fully formed and functional by the end of month 3

provides nutritive, respiratory, excretory, and endocrine functions

connects to umbilical cords

embryonic placenta

chorion with chorionic villi

maternal placenta

decidua basalis

endometrium located between chorionic villi (near the rear end of fetus)

umbilical cord

a conduit between the developing embryo or fetus and the placenta

unique vascular modifications only seen during development

umbilical arteries

2

send blood back to mom

umbilical vein

1

fresh blood supply to baby

named in relation to child’s heart

differences in fetus’s circulatory system

ductus venosus

foramen ovalis

ductus artreiosus

ductus venosus

bypasses the liver because mom’s liver does the job

umbilical vein drains into ductus venosis, which empties into inferior vena cava

foramen ovalis

opening in interatrial septum bypasses pulmonary circulation

ductus arteriosus

bypasses pulmonary circulation

pulmonary trunk drains into it and then drains into the aorta

fetal development

0-12 weeks—first trimester

13-28 weeks—second trimester

29-40 weeks-third trimester

which trimester does baby gain the most weight/most rapid growth

third trimester

mom’s physiological changes

weight gain

gastrointestinal issues (morning sickness due to elevated hCG, estrogen, and progesterone) (heartburn and constipation)

frequent urgent, urination and stress incontinence (bladder compression)

more blood, more blood output, higher blood pressure

preeclampsia

can lead to fetus being starved of oxygen, may be due to immunological abnormalities, affects 10% of pregnancies

parturition

culmination of pregnancy, giving birth to baby (all hormonal and mechanical factors)

labor

series of events that expel infant from uterus

oxytocin

causes placenta to produce prostaglandins, a powerful myometrium

makes contractions more frequent

prostaglandins

initiates contractions

stages of labor

dilation, expulsion, and placental

dilation

time of the onset of true labor until the cervix is completely dilated (10cm)

longest stage (6-12 hours)

expulsion

from full dialation to delivery of infant

strong contractions every 2-3 minutes, each for about 1 minute long

urge to push increases

crowning indicated baby coming out

Vertex

head-first position, skull dialates cervix

breech

butt-first position

delivery is more difficult, or C-section

dystocia

shoulder is caught on pelvis

placental stage

delivery of afterbirth (placenta and membranes) within 30 minutes after biirth

strong contractions continue, causing detachment of placenta and compression of uterine blood vessels

APGAR

birth is a shock to baby, so physical status is assessed within 1-5 minutes

activity (muscle), pulse, grimace (reflexes), appearance (color), respiration (breathing/crying)

score of 8-10 means a healthy baby

lactation

caused by prolactin via pituitary gland

production of milk by mammary gland

breast feeding is better than formula