Download Egg Production or Oogenesis

Assisted Reproductive
Technology
Chapter 2
Central Points
 Sperm and eggs are formed in specialized organs
 Males and females have different reproductive
organs
 Infertility is a problem in some areas of the world
 Medical techniques can assist infertile individuals
 Legal cases will decide treatment of frozen embryos
2.1 How Are Sperm and Eggs Made?
 Eggs and sperm are human gametes
 Females
• Ovaries produce eggs by meiosis and secrete
estrogens
 Males
• Testes produce sperm by meiosis and secrete
androgens
Animation: Meiosis and Sexual
Reproduction (sperm formation)
2.2 Male Reproductive System
 Testes form in the abdominal cavity before birth
 Descend into the scrotum
 A duct system transports sperm out of the body
 Glands secrete fluids to maintain sperm viability
and motility
 Organ of copulation is the penis
Male Reproductive System
Male reproductive system
Sperm Production
 Sperm are produced by spermatogenesis in
the seminiferous tubules
 Move to epididymis for storage
 Muscles move sperm to the vas deferens
 Then move sperm to the urethra and out
Vasectomy
 Vas deferens is cut
 Sperm are absent
Spermatogenesis
 Occurs in seminiferous tubules, begins at
puberty, and continues throughout life
 Spermatogonia divide by mitosis
 Spermatocytes divide by meiosis to produce
spermatids (23 chromosomes)
 Spermatids form mature sperm with tails
Spermatogenesis
Animation: Spermatogenesis
2.3 Female Reproductive System
 Ovaries produce eggs by oogenesis
 Fertilization occurs in fallopian tubes
 Fertilized egg or zygote moves into the uterus
• Outer uterine layer: myometrium
• Inner uterine tissue: endometrium
 Cervix opens into the vagina
Female Reproductive System
Female reproductive system
Egg Production or Oogenesis (1)
 Occurs in the ovary
 Follicles consist of a developing egg
surrounded by an outer layer cells
 Oogonia divide by meiosis during embryonic
development and stop
 Oocytes remain arrested until ovulation
Egg Production or Oogenesis (2)
 Meiosis is not completed until after fertilization
 Lifetime supply of developing eggs at birth
 Sperm and egg nuclei fuse to form a diploid
zygote
Oogenesis
2.4 Infertility
Requirements for a successful conception:
 A healthy sperm and a healthy egg unite to form
a zygote
 Place for fertilization to occur (a fallopian tube)
 Place for the fetus to grow (a uterus)
Age and Infertility
Causes of Infertility in Women
Problems that Affect or Prevent Ovulation
 Hormone levels (most common cause of
infertility)
 Absent or damaged ovaries
 Premature menopause
Other Causes of Infertility in Females
 Secondary amenorrhea
 Fallopian tube blockage
Causes of Infertility in Males
 Low sperm count
 Low sperm motility
 Impotence including
erectile dysfunction
 Aspermia
Other Factors Influence Fertility
 Personal habits
 Environmental factors
 Age associated with decreased fertility and
increased risk of chromosomal abnormality
 Sexually transmitted diseases
 Social factors
2.5 Assisted Reproductive Technologies
(ART)
Three of the most common:
 Donation of gametes
 In vitro fertilization (IVF)
 Surrogacy
Donation of Gametes
 Measure hormone levels and may treat with
estrogen or testosterone
 If hormone treatments unsuccessful, gamete
donation from a sperm and/or egg donor
Sperm and Egg Donor Ads
Sperm Donation
 Widely used for almost 50 years
 Known or unknown donors
 Frozen in liquid nitrogen
 Sperm banks offer sperm from qualified donors
 Web sites offer ability to choose the traits of the
donors
Artificial Insemination
 Sperm is placed into the woman’s uterus at
ovulation
 Sperm donation or sperm from several
ejaculations can be pooled and concentrated
 Sperm can be retrieved from the epididymis or
the testis using microsurgery
Egg Donation
 Egg donation is more difficult
 Retrieval is time-dependent and involves
surgery
 Donor undergoes hormone treatment and
laparoscopy
 Freezing is difficult, and eggs are used for IVF
immediately after retrieval
In Vitro Fertilization (IVF)
Surrogacy
 Two types:
• Egg donor surrogacy
• Gestational surrogacy
 Surrogate may be relative, friend, or paid
stranger
New Ways to Make Babies