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 b iology
some authorities assert that the fertilized egg or the two-cell stage is an
embryo
other authorities (including this textbook) say that an individual becomes and __ when it is 16 days old and consists of 3 primary germ layers
embryo
germ layers of an embryo
endoderm (inner), mesoderm(middle) , and ectoderm(outer)
the first 16 days after fertilization
preembryonic stage
process that migrating sperm must undergo to make it possible to penetrate an egg
capacitation
combines the haploid set of sperm chromosomes with the haploid set of egg chromosomes producing a diploid set
fertilization
fertilization by two or more sperm which would produce a doomed fertilized egg
polyspermy
two mechanisms to prevent polysmery
fast block and slow block
binding of the sperm to the egg opens Na+ channels in egg membrane
fast block
involves secretory vesicles, cortical granules, just below membrane; releases an inflow of Ca2+
slow block
when sperm encounters an egg, it undergoes an __ reaction-excytosis of the acrosome, releasing the enzymes needed to penetrate the egg
acrosomal
__ of many sperm are released to clear a path for the one that will penetrate the egg
enzymes
two acrosomal enzymes
hyaluronidase and acrosin
digests the hyaluronic acid that binds granulosa cells together
hyaluronidase (acrosomal enzyme)
protease similar to trypsin
acrosin (acrosomal enzyme)
from fertilization of egg through 12 weeks- more than half of embryos die due to chromosomal defects
first trimester
weeks 13 through 24, organs complete, fetus looks kinda human
second trimester
week 25 to birth- fetus grows rapidly and can survive outside of womb
third trimester
at 35 weeks and 5.5 pounds, fetus is considered
mature
