chapter 28

Question 1

fertilization

Answer 1

the process in sexual reproduction that involves the union of sperm and egg to form a diploid zygote

Question 2

fertilization time window

Answer 2

an oocyte is viable for 24 hours at most after ovulation
sperm can survive at most 5 days in female reproductive tract

Question 3

how many days in a single month it is possible for fertilization and pregnancy to occut

Answer 3

2-3 days

Question 4

of the million sperm that reach the vagina only a fraction reach the uterus

Answer 4

millions lost immediately from vagina : mucus doesn’t automatically thicken
millions more lost by acidic environment of the vagina : 3.5-5 too acidic for sperm

Question 5

if sperm make it to the uterus

Answer 5

• phagocytes kill off many more
• only a few thousand survivors: reverse peristalsis push sperm to uterine tubes
• sperm have various receptors to ensure they travel in the right direction

Question 6

sperm capacitation

Answer 6

sperm are incapable of fertilizing the oocyte immediately after entering the vagina

Question 7

before fertilization can occur sperm must be capacitated

Answer 7

1. Motility is enhanced
2. Weakening of sperm cell membranes: increase likelihood of fertilization

Question 8

oocyte is surrounded by 2 protective structures

Answer 8

corona radiata
zona pellucida

Question 9

corona radiata

Answer 9

outer layer
protects and nourishes the oocyte after is has been ovulated
granulosa cells release chemicals like estrogen: let sperm find egg

Question 10

zona pellucida

Answer 10

inner layer
protects the secondary oocyte and is necessary for fertilization to occur

Question 11

sperm entry for fertilization at the zona pellucida

Answer 11

• acrosomal reaction occurs: release of digestive enzymes from the acrosome of the sperm
  sperm bind zona pellucida : Ca2+ levels rise in sperm causing acrosome to rupture and release digestive enzymes
  enzymes from acrosome digest holes in zona pellucida
  1000s of sperm must do this to weaken the zona pellucida
  first sperm to reach egg doesnt fertilize egg

Question 12

after acrosomal reaction

Answer 12

1. sperm binds to sperm binding receptors on oocyte: lock sperm and prevent movement
2. once bound the 2 membranes fuse together: sperm contents enter the oocyte

Question 13

polyspermy

Answer 13

the entry of more than one sperm into the oocyte
would result in termination of the oocyte due to incorrect chromosome #

Question 14

blocking polyspermy

Answer 14

1. oocyte membrane blocks: sperm binding receptors are shed from oocyte surface
   - sperm unable to bind to oocyte surface and fertilize egg
2. cortical reaction: oocyte releases Ca2+
   - causes zona pellucida to harden

Question 15

completion of meiosis 2 and fertilization

Answer 15

sperm nucleus travel toward oocyte nucleus
as it travels sperm nucleus swells to form male pronucleus
surge in Ca2+ from cortical reaction causes release of zinc from oocyte

Question 16

what does zinc cause

Answer 16

Completion of meiosis 2 forms 2nd polar body and ovum

Question 17

after meiosis 2

Answer 17

female pronucleus forms
larger nucleus means more likely they will meet and exchange chromosomes
two pronuclei membranes rupture and chromosomes are released

Question 18

pronuclei rupture

Answer 18

Maternal and paternal chromosomes combine to form a diploid zygote
this is fertilization
No pregnancy if chromosomes don’t combine

Question 19

twins

Answer 19

usually one oocyte is ovulated and fertilized to produce a single zygote and embryo
but the rules are not always followed
gestation is shorter being 32-35 weeks bc mom has no more space
preemie babies

Question 20

monozygotic twins

Answer 20

identical twins
occurs when a single oocyte is fertilized splits into 2 identical embryos
unknown why/ how zygote splits
twins usually share a placentra

Question 21

dizygotic twins

Answer 21

occurs when 2 oocytes are ovulated and both are fertilized
twins have their own placenta
not as many developmental issues as monozygotic twins
usually of mixed sex
this increases after age 40

Question 22

embryonic development

Answer 22

development begins after fertilization
zygote begins to divide mitotically
cleavage: rapid division of zygote
first mitotic division produces 2 identical blastomere cells
by 72 hours a morula is formed: contains abt 16 cells

Question 23

zygote

Answer 23

diploid cell resulting from the fusion of 2 haploid cells

Question 24

benefit of cleavage for embryonic development

Answer 24

allows for formation of different structures in the body: multicellular
allows for fixing of small mistakes

Question 25

morula cells continue to divide and forms

Answer 25

blastocyst

Question 26

blastocyst layers

Answer 26

external trophoblast internal embryoblast

Question 27

external trophoblast

Answer 27

- does not contribute cells to embryo - aids in embryo implantation - contributes to chorion formation/function - has immunosuppressive effects: stops mothers immune system from destroying egg

Question 28

internal embryoblast

Answer 28

- inner cell mass - will eventually form the embryo proper and extraembryonic membranes

Question 29

implantation of blastocyst in the endometrium

Answer 29

endometrium is receptive to implanting embryo due to high estrogen and progesterone trophoblast attaches to endometrium occurs high in the uterus to allow multiple opportunities for implantation

Question 30

once bound trophoblast

Answer 30

- releases digestive enzymes and growth factors on epithelium of endometrium

Question 31

digestive enzymes influence

Answer 31

- erosion of endometrium around blastocyst - blastocyst buries itself in the blood-rich lining - surrounding endometrial cells proliferate and cover the blastocyst

Question 32

growth factor influences

Answer 32

- endometrium thickens - The trophoblast proliferates and releases enzymes to facilitate implantation

Question 33

once implantation is complete

Answer 33

embryo release human chorionic gonadotropin (hCG)

Question 34

placenta

Answer 34

temporary organ originating from embryonic and maternal tissues

Question 35

hCG

Answer 35

maintains the corpus luteum (releases estrogen and progesterone) for abt 12 weeks and suppresses the female human immune system

Question 36

functions of placenta

Answer 36

maintains pregnancy exchange respiratory gases provides nutrients to embryo/fetus dispose of waste

Question 37

embryonic contribution to placenta

Answer 37

chorion: membrane that surrounds fetus chorion has chorionic villi blood vessels extend from chorionic villi form umbilical vein and arteries

Question 38

parental contribution to placenta

Answer 38

functional layer of endometrium develops blood filled lacunae endometrium that lies underneath embryo becomes decidua basalis endometrium that surrounds uterine cavity face of embryo forms: decidua capsularis

Question 39

function of decidua basalis

Answer 39

forms placenta with chorionic villi

Question 40

function of decidua capsularis

Answer 40

expands the accommodate growing fetus chorionic villi degenerate here as pregnancy progresses

Question 41

extraembryonic membranes

Answer 41

membranes formed during the first few weeks of development that support and nourish the developing embryo/fetus during gestation

Question 42

extraembryonic membranes include

Answer 42

amnion yolk sac allantois chorion

Question 43

amnion

Answer 43

layer that extends around the embryo filled w amniotic fluid

Question 44

functions of amniotic fluid

Answer 44

1. provides buoyancy and protection 2. maintains consistent temperature 3. prevents developing parts of embryo from fusing/sticking together 4. allows movement of embryo/fetus

Question 45

yolk sac

Answer 45

sac-like structure eventually forms digestive tube forms earliest blood cells forms precursor gametes

Question 46

allantois

Answer 46

helps form umbilical cord later in fetal developments allows for gas exchange, waste disposal and nutrient exchange

Question 47

chorion

Answer 47

allows exchange of gases, nutrients and waste encloses all other extraembryonic membranes

Question 48

gastrulation

Answer 48

early developmental process where the blastocyst is reorganized into a 3 layered embryo

Question 49

3 primary germ layers

Answer 49

endoderm ectoderm mesoderm

Question 50

process of gastrulation

Answer 50

begins with formation of primitive streak cells migrate and enter the primitive streak: these cells form the endoderm (inferior layer) other cells follow and push between cells of the upper and lower layers: these cells form the mesoderm mesodermal cells immediately beneath primative streak form notochord some cells remain at surface (ectoderm)

Question 51

notochord

Answer 51

first axial support of the embryo ensures embryo doesnt grow crooked

Question 52

primitive streak

Answer 52

a groove that will eventually form the long axis of the embryo