A & P II - Chapter 28 - Fertilization

fertilization

-sperm's chromosomes combine with oocyte in fallopian tube

through week 8 =

-embryo

week 9 through birth =

-fetus

sperm penetration and fertilization (4)

1. approach

2. acrosomal reaction

3. binding

4. fusion of membranes

approach (sperm penetration and fertilization)

-aided by enzymes, sperm weaves through corona radiata

-digests connection between granulosa cells -> causing them to seperate

acrosomal reaction (sperm penetration and fertilization)

-when triggered by calcium influx, enzymes from sperm are released that digest holes in zona pellucida

binding (sperm penetration and fertilization)

-after path has been cleared in zona pellucida -> single sperm forcibly swims toward oocyte plasma membrane

fusion of membranes (sperm penetration and fertilization)

-oocyte and sperm membranes fuse

-cytoplasmic content of sperm (from head, which has 23 chromosomes) enter oocyte

monospermy

-only one sperm fertilizes

things that block polyspermy (2)

1. oocyte membrane block

2. zona (cortical) reaction

oocyte membrane block (things that block polyspermy)

-sheds sperm binding receptors (so it can't attach)

zona reaction (things that block polyspermy)

-causes hardening of zona pellucida -> detaching any other sperm

-activates oocyte to prepare for meiosis II

completion of meiosis II (3)

1. sperm penetration triggers completion of meiosis II in oocyte -> ovum + second polar body

2. mom and dads chromosomes combine -> diploid (46 chromosome zygote)

3. begins to undergo cleavage (rapid growth) -> triggered by unison of chromosomes

zygote to blastocyst implantation

1. cleavage

2. blastocyst formation

3. implantation

cleavage (zygote to blastocyst implantation)

-occurs while zygote moves toward uterus, rapid cell divisions

-produces: cells with high surface-to-volume ratio that enhances uptake of nutrients and oxygen + disposal of wastes

morula

-zygote becomes after 72hrs

-solid ball of 16 cells

blastocyst formation/blastula (zygote to blastocyst implantation)

-~day 4-5, ~100 cells = blastocyst/blastula

-composed of trophoblast cells(wall of the ball) and inner cell mass

trophoblast cells

-participate in childs placenta formation

-release human chorionic gonadotropin (hCG) -> prevent shedding of endometrium

blastocoel

-fluid-filled hallow part of a blastula

inner cell mass

-cluster of 20-30 rounded cells -> will form embryo and extraembryonic membranes; amnion, chorion, and yolk sac

implantation (zygote to blastocyst implantation)

-begins 6-7 days after ovulation

-trophoblast cells adhere to mother's endometrium

hCG

-prompts surge of progesterone and estrogen -> keeps endometrium built up

-what pregnancy tests detect

how many zygotes do not implant

-2/3

what makes estrogen and progesterone that prevents the endometrium from shedding (3)

1. secreted first by corpus luteum

2. hCG (via trophoblast cells)

-prompts corpus luteum to stay alive and keep secreted

-promotes placental development

3. placenta continues hCG

gastrulation

-differentiation occurs

-triggered via implantation

-blastocyst begins being converted into gastrula

extraembryonic membranes (3)

1. chorion (outer)

2. yolk sac (middle yellow)

3. amnion (middle blue)

germ layers (3)

-primitive tissues from which all body systems are derived

1. ectoderm

2. endoderm

3. mesoderm

ectoderm

-becomes nervous system

endoderm

-becomes epithelial linings of organs

mesoderm

-muscle and CT

amnion

-membrane that closely coves the embryo when first formed

-fills with the amniotic fluid -> causes it to expand (like a balloon)

-becomes the amnionic sac

-F: provides a protective environment for developing embryo

yolk sac

-sac that hangs from ventral surface of embryo

-forms part of digestive tube

-source of earliest blood cells and blood vessels

-provides food until placenta forms

allantois

-small outpocketing at caudal end of yolk sac

-structural base/makes umbilical cord

chorion

-forms child's portion of placenta

-encloses all other membranes

chorionic villi

-villi that sprout from the chorion to provide max contact exchange with maternal blood

placenta

-circular organ in the uterus

-F: nourishing and maintaining the fetus through the umbilical cord

-originates from both child and mother

embryonic portion of placenta

-chorion

mother's portion of placenta

-includes decidua basalis: endometrium located between chorionic villi (near rear end of fetus)

when is placenta fully formed and functional

-by the end of month 3

placenta provides _____________________

nutritive, respiratory, excretory, endocrine functions

placenta connects to ________________

umbilical cord

umbilical cord

-conduit between the developing embryo/fetus and the placenta

where do first blood cells arise from

-the yolk sac

vascular modifications in prenatal development (2)

1. umbilical arteries (2)

2. umbilical vein (1)

-in relation to babies heart

umbilical arteries

-spent blood to mom

umbilical vein

-fresh blood to baby

vascular shunts (3)

1. ductus venosus

2. foramen ovale

3. ductus arteriosus

ductus venosus

-"short cut"

-bypasses the liver

-umbilical vein -> ductus venosus -> inferior vena cave

foramen ovale

-opening in interatrial septum

-bypasses pulmonary circuit

ductus arteriosus

-bypasses pulmonary circuit

-pulmonary trunk -> ductus arteriosus -> aorta

average pregnancy =

-40 weeks

which trimester does the baby grow the most

-the 3rd trimester

anatomical effects of pregnancy on mother

-reproductive become engorged with blood

-breasts enlarge

-gain 28lbs

-lordosis

physiological effects of pregnancy on mother: GI

-morning sickness -> elevated hCG, estrogen, and progesterone

physiological effects of pregnancy on mother: urinary

-increased urine production

-frequency and urgency (bladder is compressed)

-stress incontinence

physiological effects of pregnancy on mother: relaxin

-hormone that relaxes various parts of mothers body (softens/loosen cervix/birth canal + ligaments around pelvis)

preeclampsia

-complication of pregnancy

-can result in deterioration of placenta and insufficient placental blood supply -> fetus could be starved of oxygen

-affects 1 in 10

parturition

-culmination of pregnancy' giving birth

labor

-series of muscular events that expel infant from uterus

initiation of labor (2)

1. in last few weeks, estrogen reaches its highest level within mothers' blood

2. fetal oxytocin causes placenta to produce prostaglandins

prostaglandins

-initiates contractions

oxytocin

-makes contractions more frequent and vigorous

protoxin

-man made oxytocin

-F: induction of labor

regular contractions

-uterus contracts to deliver baby

-only happens in labor

braxton hicks contractions

-"practice contractions"

-occur weeks before birth

episiotomy

-if baby is not coming out

-for emergencies

-cut mother from vulva to anus

stages of labor (3)

1. dilation stage

2. expulsion stage

3. placental stage

dilation stage

-time of the onset of labor until the cervix is completely dilated to 10cm

-longest stage of labor: 6-12hrs

-mild contractions

expulsion stage

-lasts from full dilation to delivery

-strong contractions every 2-3 min, each ~1 min long

-urge to push increases

crowning

-occurs when largest dimension of head distends vulva

vertex position

-preferred

-head 1st presentation

-allows breathing prior to complete delivery

-skull dilates cervix

breech position

-butt 1st presentation

-delivery is more difficult

-C-section is usually required

placental stage

-delivery of afterbirth (placenta and membranes)

-occurs within 30 min of giving birth

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

dystocia

-abnormally slow labor

-due to narrow pelvis or other blockage

-labor is abnormally difficult

APGAR

-0-2 points each

-score of 8-10 = healthy baby

what does APGAR stand for

A: Activity (muscle tone)

P: Pulse

G: Grimace (reflex)

A: Appearance (skin color)

R: Respiration

lactation

-caused by prolactin via pituitary gland

-towards end of pregnancy -> hypothalamus is stimulated to release PRH (prolactin releasing hormone)

advantages of breast milk for infant (3)

1. fats and iron are better absorbed

2. easily metabolized

3. encourages bacterial colonization of infant's gut

colostrum

-"super milk"

-first days after birth, yellow color milk

-due to elevated hormones

-has a ton of fat and protein