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