Chapter 29 - Human Development and Aging Flashcards
The study of prenatal development
Embryology
Examines changes in form and function from fertilized egg through old age
Developmental biology
3 primary germ layers of an embryo
ectoderm, mesoderm, endoderm
an individual becomes an embryo when it is _ days old
16
events leading up to the stage of an embryo
embryogenesis
what stage is the first 16 days after fertilization
pre-embryonic stage
fertilized egg at 16 days old
embryo
the egg must be fertilized within _ - _ _ of ovulation, if it is to survive
12-24 hours
how long after the sperm reaches the uterine tube does it take to fertilize the egg
10 hours
where do the sperm generally meet the egg during ovulation
distal uterine tube
How long are sperm viable for after ejaculation
6 days
when sperm encounters an egg, it undergoes what
acrosomal reaction
exocytosis of the acrosome, releasing enzymes needed to penetrate the egg
acrosomal reaction
what two things do sperm need to clear out of the way for the one sperm to penetrate the egg
granulosa cells and zona pellucida
what are the two acrosomal enzymes
hyaluronidase and acrosin
this digests hyaluronic acid that binds granulosa cells together
hyaluronidase
a protease similar to trypsin
acrosin
combines the haploid set of sperm chromosomes with the haploid set of egg chromosomes producing a diploid set
*must know for test
fertilization
fertilization by two or more sperm which would produce a doomed fertilized egg
polyspermy
two mechanisms to prevent polyspermy
fast block and slow block
binding of sperm to the egg opens na+ channels in egg membrane
fast block
involves secretory vesicles, cortical granules, just below membrane
stimulates cortical reaction, in which cortical granules release secretion beneath zona pellucida
sperm penetration releases an inflow of ca+
slow block
two eggs ovulated and both are fertilized by separate sperm forming two zygotes
implant separately in uterine wall and each have own placenta
no more genetically similar than any other siblings
2/3 of twins
dizygotic twins
one egg is fertilized but embryoblast later divides into 2
genetically identical
monozygotic twins
this begins meiosis II before ovulation but completes it only if fertilized
secondary oocyte
sperm and egg swell and become _______
pronuclei
what is a fertilized egg called
zygote
pregnancy is divided into 3 month intervals called…
trimester
during this trimester conceptus is most vulnerable to stress, drugs and nutritional deficiencies
first trimester
during this trimester organs complete most of their development
fetus looks human
second trimester
during this trimester, fetus grows rapidly and organs achieve enough cellular differentiation to support life
third trimester
the first 16 days of development culminating in the existence of an embryo
pre embryonic stage
the 3 major processes of the pre embryonic stage
cleavage, implantation, embryogenesis
mitotic divisions that occur in first 3 days while conceptus migrates down uterine tube
cleavage
what’s it called when the zygote splits in to two daughter cells
blastomeres
how long does it take for conceptus to arrive in uterus
72 hours after ovulation
a solid ball of 16 cells - resembles mulberry
occurs during cleavage process of pre embryonic stage
morula stage
how long does the morula lie free in the uterine cavity
4-5 days
when the zona pellucida disintegrates and releases conceptus - it’s called…
*know for test
blastocyst
a hollow sphere
*know for test
blastocyst
outer layer of squamous cells
destined to form placenta and nourish the embryo
trophoblast
what is the embryoblast and what does it become
*know for test
the inner cell mass of a blastocyst
it becomes the embryo
*know migration of conceptus photo for test
slide 29-16
during implantation ______ attaches to uterine wall 6 days after ovulation
usually on the fundus or posterior wall of uterus
blastocyst
the process of attachment of blastocyst to uterine wall
implantation
trophoblasts on attachment side separate into ___ layers
2
what are the layers of the trophoblast called once it separates
and where are they located
superficial layer - in contact with endometrium
deep layer - close to embryoblast
What hormone does trophoblast secrete
human chorionic gonadotropin (HCG)
trophoblast develops into membrane called….
chorion
HCG stimulates corpus luteum and it secretes (2) hormones
estrogen and progesterone
arrangement of blastomeres into 3 primary germ layers in embryoblast
embryogenesis
what are the names of the 3 primary germ layers of an embryoblast
ectoderm, mesoderm, endoderm
multiplying epiblast cells migrate medially into primitive groove
gastrulation
gastrulation replaces the original hypoblast with layer called
endoderm
migrating epiblast cells form a 3rd layer btwn first two. this layer is called…
mesoderm
the remaining epiblast layer is called…
ectoderm
this is a more loosely organized tissue which differentiates into a loose fetal connective tissue, called mesenchyme
the mesoderm
this gives rise to muscle, bone, and blood
mesoderm
what is complete once the 3 primary germ layers are formed
embryogenesis
once embryogenesis is complete, an individual is considered a….
embryo
this begins when all 3 primary germ layers are present (usually day 16)
embryonic stage
this is the embryo’s primary source of nutrition. after the first 2 weeks are complete, it forms over the next 6 weeks
the placenta
germ layers differentiate into organs and organ systems
organogenesis
organs are present at how many weeks
at 8 weeks when the embryo becomes a fetus
formation of organs from primary germ layers:
what derivatives from the ectoderm
epidermis, nervous system, lens and cornea, internal ear
formation of organs from primary germ layers:
derivatives of mesoderm
skeleton, muscle, cartilage, blood, lymphoid tissue, gonads and ducts, kidneys and ureters
formation of organs from primary germ layers:
derivatives of endoderm
gut and respirator epithelium and glands, bladder and urethra
what are the accessory organs that develop with embryo
placenta, umbilical cord and 4 embryonic membranes