MCB 135E Physiology of Development GSI: Jason Lowry Discussion

General Information 1.Discussions: Mon 4-5 pm in 106 Moffitt 2.Office Hours: Wed 1:30-2:30 in 434 Barker 3.

Introduction –Class Overview –Syllabus –Discussion Topics Growth and Development Male and Female Reproductive Systems Fertilization Process Implantation

Terminology Physiology –Study of Function Development –Functional Changes with Age –Fertilization  Death –Follows a predictable timetable with critical events Growth –Change in Size –Index used to measure development

Concepts Divisions of Life-Span (Intro. Table 1) –Pre-Natal –Post-Natal Life Periods of Development (Intro. Table 2) –Starts with fertilization and proceeds in a continuous and orderly sequence throughout the pre-natal and post-natal periods

Gametogenesis Terminology –Gamete – Either the Mature Sperm or Ovum –Zygote – Formed by the union of the mature Sperm with mature Ovum –Gametogenesis – Development of Male (Spermatogenesis) and Female (Oogenesis) sex cells

Spermatogenesis Formation of Spermatozoa (Sperm) Occurs in seminiferous tubules Involves two distinct maturational processes –Spermatocytogenesis 1 st Stage of sperm formation Spermatogonium  Spermatids Involves mitosis initially and then meiosis –Spermiogenesis Spermatids  Spermatozoa

Male Reproductive Endocrinology

Oogenesis

Fertilization Terminology –Fertilization the formation, maturation, and union of the Ovum and Sperm (Zygote) Roles of Ovum –Contribute the maternal complement of genes –Reject all sperms but one –Provide food reserve until the embryo begins to feed upon exogenous material Roles of Sperm –Reach and penetrate the egg –Activate the egg to nuclear and cytoplasmic division necessary to embryonic development –Contribute the paternal complement of genes

Terminology Capacitation – Changes that occur between sperm and ovum to allow only one sperm to successfully penetrate the ovum (Increase fertilizing capacity) Cleavage – Mitotic division of the zygote into a morula Morula – Ball of cells that will form blastula that will implant in uterus

Stages of Fertilization Penetration –Random contact between sperm and egg –Sperm propel past corona cells and attach to zona pelucida –One sperm-One Egg Activation –Completion of Meiosis of ovum – forms female pronucleus –Sperm Changes – Sperm travels toward center of egg, head swells, becomes male pronucleus –Rearrangement in egg – biochemical changes necessary prior to nuclear fusion Nuclear Fusion –Union of two pronuclei –Loss of nuclear envelope, contribution of chromosomes to first mitotic cleavage

Results of Fertilization Reassociation of male and female sets of chromosomes to full diploid number –Physical basis for inheritance and variation Determination of sex Activation of ovum into cleavage

Terminology Implantation – Process of preparation of the uterine zone for blastocyst embedding and the active penetration of this zone by the blastocyst Nidation – Latin for nest (alternate name for implantation) Blastocyst – Approximately 60 cells stage where morula has become fluid filled –Of the cells, about 5 clump together to form inner cell mass (ICM) that projects into blastocele

Uterine Preparation Estrogen –Involved in proliferation of uterus (hypertrophy) –3-5 Days post-ovulation E dominates and is thought to play a role in transport of ovum Progesterone –Increased Vascularization (hypervascularization) –5-7 days post-ovulation, P increases and counters the effect of E thus relaxing uterine contractions hCG –Prevents corpus luteum regression –Similar to LH –Maintains E+P during early embryonic development

Implantation Events Days 1-8 –Fertilized egg begins to divide by cleavage into smaller blastomeres –Blastomere increase follows a double synchronous sequence initially, but later becomes asynchronous –Later stage cleavage forms a ball of cells or morula –Fluid begins accumulating in morula and a conversion occurs to the blastula (blastocyst) –Blastocyst attaches to uterine stroma –Outer layer of cells begin to proliferate and invade stroma of uterus

Implantation Events Days 8-16 –Blastocyst lodged in uterine stroma –Trophoblast (outer cells) invades uterine stroma and begins to form placenta –Blastocele becomes chorionic cavity –Inner cell mass begins to proliferate and form germ disc and primitive entoderm –Complex sequence of chemical and physical interactions occur between ovum and mother Only about 50% of fertilized eggs successfully implant