2-Gametogenesis

Teratogens

Agents that can cause fetal abnormalities

Teratogens Examples

Cytomegalovirus

X-rays

Thalidomide, Warfarin, ACE inhibitors

Maternal Diabetes and Obesity

Germinal Stage of Embryonic Development

0-2 weeks of embryonic development

Embryo loss can happen due to chromosomal abnormalities

Embryonic Stage of Embryonic Development

3-8 weeks of embryonic development

Teratogen sensitivity is highest

Organs form

Fetal Stage of Embryonic Development

9 weeks to birth

Teratogen sensitivity is lowest

Sex organs, CNS, and organ systems form

Malformation

Primary poor formation of tissue (e.g., congenital heart defect)

Disruption

Secondary disruption of previously normal organ, breakdown of normal tissue (e.g., amniotic bands)

Deformation

Extrinsic disturbance of development by biomechanical forces, unusual forces on normal tissue (e.g., uterine constraint)

Dysplasia

Abnormal organization of cells in tissue (e.g., hip dysplasia)

Syndrome

Constellation of developmental abnormalities that are pathologically related (e.g., Turner syndrome)

Mitosis

1 parent cell becomes 2 identical daughter cells

Includes prophase, metaphase, anaphase, telophase

Meiosis

Diploid cell becomes 4 haploid cells, division happens twice

Primordial Germ Cell = Diploid Cell

Primordial Germ Cell

Diploid cell that becomes spermatocytes and primary oocytes (gametes)

Induce gonadal formation!

What happens if PGCs (primordial germ cells) fail to migrate?

Causes lack of testes/ovaries differentiation

Spermatogenesis Phases

Starts at puberty, regulated by LH

Includes:

• Spermatogonia

• Primary Spermatocyte

• Secondary Spermatocyte

• Spermatids

• Spermatozoa

Spermatogonia

Stem cells for sperm, derived from PGCs

Primary Spermatocyte

46 chromosomes, 4N DNA, first meiotic division occurs here

Secondary Spermatocyte

23 chromosomes, 2x DNA, second meiotic division happens here

Spermatids

23 chromosomes, 1N DNA

Spermatozoa

Associated with Sertoli Cells, 23 chromosomes, 1N DNA

Not fertilization-capable until cap removal and flagella activation

Spermiogenesis

Spermatid to Spermatozoa

4 phases to make sperm motile and fertilization-ready

Oogenesis and Phases

Process of oogonia becoming mature oocytes

1. Oogonia

2. Primary Oocytes

3. Follicular cells surround oocytes

Oogonia

Cells from mitotic division of PGCs

Primary Oocytes

Arrested in Prophase I of Meiosis I (P1 of M1)

Follicle Development Phases

1. Primordial Follicle

2. Primary Follicle

3. Secondary Follicle

4. Mature Graafian Follicle

Primordial Follicle

Made when you’re a baby, arrested until puberty

Primary oocyte covered in flat follicular cells

Primary Follicle

Responds to FSH and grows

Secondary/Antral Follicle

Primary oocyte with no further growth

Mature/Graafian Follicle

One follicle becomes secondary oocyte, completes 1st meiotic division, polar body released into zona pellucida

Ovulation (trigger and steps)

Triggered by LH surge

Causes primary oocyte to complete meiosis I

Secondary oocyte arrested in M2 of MII

Completes MII if fertilized, otherwise degenerates

Stimulates prostaglandins and hyaluronan to increase V, P, and viscosity

Theca cells contract to rupture follicle and ovary surface

Oocyte expelled with corona radiata

Corpus Luteum

Can become corpus albicans as a remnant

If pregnant, hCG maintains corpus luteum for progesterone production, regresses around 4th month of pregnancy

Menstrual Cycle Ovarian Cycle

Phases:

• Follicular Phase

• LH Triggered Ovulation (day 14)

• Luteal Phase (corpus luteum)

  • If pregnancy, this continues.

  • hCG (synctiotrophoblast) keeps CL functioning (progesterone production)

  • Menstruation stops

  • Cleavage of zygote and blastogenesis

  • Corpus luteum of pregnancy begins regression around 4^th month

Menstrual Cycle Uterine Cycle

Phases:

• Menstrual Phase (sloughing off)

• Proliferative Phase (follicular, thinning of cervical mucosa)

  • LH triggers ovulation and progesterone (luteinization)

• Secretory Phase (luteal)

  • Corpus Luteum

Fertilization Phase I

Corona Radiata Penetration:

• Sperm penetrates follicular cells, acrosomal reaction via hyaluronidase

Fertilization Phase II

Zona Pellucida Penetration:

• Cortical vesicles secrete protease, making ZP impermeable to other sperm

Fertilization Phase III

Fusion of sperm and oocyte plasma membranes, oocyte completes second meiotic division, forms diploid zygote

Trisomy 21

Down syndrome

Caused by meiotic nondisjunction

Growth and mental delay, craniofacial abnormalities, cardiac defects

Trisomy 18

Edward syndrome

Mental delay, syndactyly, renal abnormalities

Death likely by 2 months

Trisomy 13

Patau syndrome

Mental delay, holoprosencephaly, cleft lip/palate

Death likely by 1 month

Klinefelter Syndrome

47, XXY

Male infertility caused by nondisjunction of XX chromosomes

Turner Syndrome

45, X,

Female with webbed neck & short stature

Caused by paternal nondisjunction

The only monosomy you can live with

Cri-du-chat

Partial deletion of short arm of chromosome 5

Cat-like cry

Deletion 4q Syndrome

Partial deletion of long arm of chromosome 4

Cleft palate and limb abnormalities

Angelman Syndrome

Maternal chromosome 15 microdeletion

Lack of speech, puppet-walk, laughter

Moms are angels, girls are more fun

Prader-Willi Syndrome

Paternal chromosome 15 microdeletion

Obesity, undescended testes

Dads have willies, guys are fat

Oogenesis and Follicular Development Concurrency

Oogenesis and follicular development occur concurrently during a woman's reproductive years. Oogenesis, the process of producing mature oocytes (egg cells), is intrinsically linked to the folliculogenesis process, which involves the growth and development of ovarian follicles. These follicles surround and nourish the developing oocyte.