A&P 2: Unit 3 embryology and development

development

changes in anatomy & physiology from fertilization to maturity (1 cell to 75 trillion)

differentiation

creation of different types of cells from the original zygote (over 200 different cells)

trimesters

3

3 month time periods used to divide pregnancy

gestation period

38 weeks for humans (OB use 40)

fertilization

• Embryo (week 1-8) + Fetus (week 9-38) = Prenatal

• Fusion of 2 haploid (23 chromosomes) gametes  zygote with 46 chromosomes

• Takes place between isthmus and ampulla of the uterine tube 24 hours after ovulation

• Takes sperm cells about 30 minutes to reach the uterine tubes

oocyte activation

oocyte is about 2000 times larger than the sperm cell

1) Oocyte membrane changes by inactivating sperm receptors and hardening outer membrane to prevent more than 1 sperm cell from entering the oocyte, life will not withstand multiple fertizilations

2) Oocyte completes meiosis II and forms the last polar body

3) Activation of enzymes that cause a rapid increase in the cell’s metabolic rate

• a cell that is going to divide, divide and divide needs mechanisms and support to do so

• ends with a female pronucleus & a male pronucleus → amphimixs (conception = 46 chromosomes)

blastomeres

daughter cells after cleavage

morula

after 3 days of cell division, small ball of cells → day 4 it reaches uterus

blastocyst

after 5 days

hollow ball

blastocoele

hollow cavity

trophoblast

outer cells that bring in nutrients

inner cell mass

cluster of cells at one end, inside blastocyst → will form the embryo

ectopic pregnancy

6/1000

blastocyst implants not in uterus, not compatible with life

implantation

attachment of the blastocyst to the endometrium of the uterus

amniotic cavity

gradual separation between inner cell mass and trophoblast and fills with fluid

primitive streak

center line of the inner cell mass, cells start to move toward it

gastrulation

developing of the inner cell mass → to embryo

ectoderm

superficial cells that did not migrate into the inner cell mass

mesoderm

unorganized cells between ectoderm and endoderm (last of layer to form)

endoderm

cells that face the blastocoele (inside)

embryonic disc

after the three layers form, an oval disc appears – this will become the embryo

extraembryonic membrane

this forms from the rest of the blastocyst, surrounds the embryo

yolk sac

pouch that forms from outer edges of blastocoele, later an important site of blood cell formation

amnion

ectoderm & later mesoderm cells line amniotic cavity – will contain amniotic fluid that will surround & cushion developing embryo/fetus (about week 3)

allantois

an out pocketing of endoderm near yolk sac  will become urinary bladder

chorion

(week 2&3- heart starts to pump), blood vessels start to form from trophoblast, first step in the creation of the placenta

placentation

blood vessels form around the blastocyst, placenta develops → organ that permits exchange between mother and fetus

placental circulation

as fetus moves farther from placenta umbilical cord develops, contains umbilical arties and veins, end of first trimester

endocrine placenta secretes what

human chorionic gonadotropin

lactogen/ prolactin

relaxin

progesterone/ estrogen

human chorionic gonadotropin

acts like LH, promotes progesterone → keeps endometrial lining intact

lactogen/ prolactin

helps prepare mammary glands for milk production

relaxin

increases flexibility of pelvis, causes dilation of cervix, delays release of oxytocin

progesterone/ estrogen

secreted enough by the placenta by the 2nd & 3rd trimester to maintain endometrium

embryogenesis

formation of a viable embryo, establishes foundations for all major organ systems

head fold

projection that will form the head

tail fold

projection that will form the lower extremities

second trimester

Fetus will grow to about 1.5 pounds

Beginning of all major organ systems have formed

third trimester

Fetus grows to birth weight of about 7 pounds

All organ systems become functional

maternal systems

1) respiratory rate and tidal volume increase

2) maternal blood volume increases

3) vitamin and nutrient requirements increase 10-30%, 25-40 lbs

4) glomerular filtration rate increases by 50%

5) uterus tremendously increases in size

6) mammary glands increase in size and secretion activity begins

changes in the uterus

(progesterone from placenta calms contractions from uterine stretching)

1) estrogen levels rise toward end of pregnancy – increases contractions (now overrides progesterone)

2) oxytocin levels rise toward end of pregnancy – increases force and frequency of contractions

3) prostaglandin production – stimulate smooth muscle contractions

false labor

contractions are neither regular nor persistent (braxten-hicks)

true labor

biochemical changes start delivery sequence

labor contractions

contraction of myometrium triggered by oxytocin from fetal pituitary gland

stages in labor

dilation

expulsion

placental

dilation stage

fetus shifts toward cervical canal  gravity & uterine contractions, 8 hours or more, usually amniotic membrane ruptures “water breaks”, (chance for infection – labor will be induced if not started)

expulsion stage

cervix dilates to 10 cm, delivery begins, “pushing stage”, less than 2 hours

placental stage

ejection of placenta(“afterbirth”), needed to prevent hemorrhage

episiotomy

incision thru perineal musculature – expands opening & prevents tearing

cesarean section

incision is made in abdominal wall to remove infant (15-25%, is too high by most studies)

premature labor

28-36 weeks, fetus under 27 weeks usually do not make it

difficult deliveries

face up 6%, breech (legs & butt first) 3-4%, cord around neck, use of forceps & suction

multiple births

1:89

fraternal twins (dizygotic)

70%

2 eggs are fertilized

identical twins (monozygotic)

separation of blastomeres or inner cell mass

Siamese twins (conjoined)

splitting of blastomeres is not complete and infants are connected

triplets

1:7921

quads

1:704969