Oogenesis, Folliculogenesis, and Egg Maturation

Animal Science Oogenesis

Ovary Two Major Functions

Oogenesis/Folliculogenesis and Steroidogenesis

Oogenesis

Produce fertilizable ova (pre-natally)

Steroidogenesis

Produce steroid hormones that maintain repro tract, facilitate migration of early embryo, and assist in successful implantation

Folliculogenesis

Growth of the ovarian follicle (contains the oocyte)

Female - XX Chromosome Pair (d35-36)

No SRY Protein → Ovaries develop → No AMH → Paramesonephric ducts become the oviducts, uterus, cervix, and part of vagina → Complete female repro tract

2 Prenatal Stages of Oocyte Maturation

1. Mitotic division (oogonia)

   1. Nuclear Arrest (Primordial follicles)

2 Postnatal phases of Oocyte maturation

3. Cytoplasmic growth

4. Resumption of meiosis

Day 150 - Meiotic Arrest

Resulting in a fixed number of primordial follicles (ovarian reserve)

Cortex

Contains ovarian structures (follicles and corpus lutea) and is where ovulation occurs

Medulla

Contains the lymphatics, nerves, and vasculature

Primordial Follicle

Single layer flattened follicular cells, fixed # at birth

Primary Follicle

Single layer granulosa cells

Secondary Follicle

>2 layers granulosa cells, no antrum, zona pellucida

Tertiary Follicles

Multiple layers granulosa cells, antrum

Theca externa

Connective tissue (Tissue support), blood vessels end

Theca interna

Bind LH → testosterone

Granulosa cells

Bind FSH → estrogen + follicle development

Zona pellucida

Separates oocyte from granulosa cells

______ days from activation to preovulatory

90

_____ from prenatal to preovulatory (large antral) size

42

______ days early antral to preovulatory (follicular wave)

10-13

Recruitment

A cohort of small antral follicles begin to grow and produce estrogen

Selection

One follicle selected to become dominant follicle (potentially ovulatory) from the cohort of previously recruited antral follicles

Dominance

Dominant follicle produces increasing amount if estrogen and inhibin

Dominant follicles exert ______ ______ on other antral follicles from the cohort

Inhibitory effects

GnRH - Hypothalamus

Causes release of gonadotropins

LH - Anterior Pituitary Gland

Estrogen production; Causes ovulation

FSH - Anterior Pituitary Gland

Estrogen production; Granulosa cell mitosis and follicular fluid production to form antrum

E2 - Ovarian Follicles

many - mating behavior

P4 - Ovarian Corpus Luteum

Pregnancy Maintenance

GnRH, LH, FSH critical roles in:

Steroidogenesis, growth, maturation, ovulation, and luteinization of the dominant follicle

FSH plays a major role in _____ ______ and stimulates granulosa cell mitosis and ______ _____ ______

Antrum Formation

Follicular Fluid Formation