MCB 135EPhysiology of Development

GSI: Jason LowryDiscussion

General Information

1. Discussions:• Mon 4-5 pm in 106 Moffitt

2. Office Hours:• Wed 1:30-2:30 in 434 Barker

3. E-Mail: Jlowry@Berkeley.edu

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• 1st 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