embryology I: prenatal development

what are gametes

haploid (23 instead of 46 chromosomes) reproductive cells produced in gonads via meiosis

what are the gonads/gametes for female/male

female - ovaries / oocytes (eggs)

male - testes / sperm cells

ovulation

secondary oocyte (completed 1st meiotic division) released from one of the ovaries 14 days after menstural cycle has begun

how do cells divide during each meiotic division

not equally, resulting in a large cell (oocyte), and a small cell (the polar body)

what happens to the oocyte

it is swept out of ovary into uterine tube (fallopian tube) via finer-like projections into ampulla (widened region)

what happens to the polar body

it gets rid of extra genetic material from steps of meiosis and degrades over time

fertilization

in ampulla within uterine tube, the sperm and oocyte fuse to form a zygote (diploid fertilized egg)

where do the sperm go after ejaculation

• 20 million in vagina

• 1% in uterus

• 100-200 in ampulla

why do few sperm reach oocyte

poor motility and many killed by low pH of female reproductive tract

forces responsible for moving sperm through female reproductive tract

• sperm swimming ability (self-propelled by their flagella)

• oxytocin released during intercourse + prostaglandins in semen, stimulate muscular contractions in uterus and uterine tubes (enhancing sperm movement)

when can fertilization occur and why

• sexual intercourse must occur between 6 days before, and 1 day after ovulation

• sperm can be viable in female reproductive tract for up to 6 days, and oocyte can be fertilized for up to 24 hours after ovulation

parts of female reproductive tract

list prenatal period stages

from conception/fertilization until birth; germinal, embryonic, fetal periods

germinal period

• fertilization to 14 days (first 2 weeks)

• primitive germ layers form (will become body tissues)

embryonic period

• weeks 3-8

• major organ systems develop

• called an ‘embryo’

fetal period

• 9th week until brith (typically 38 weeks)

• organs systems (exist already) grow and become more mature

• called ‘fetus’