Exam 2

What are the stages of gonadotropin dependence in the follicular growth?

1. Gonadotropin independent

2. Gonadotropin responsive

3. Gonadotropin dependent

Gonadotropin independent

Initial development occurs
independent of gonadotropins. Species vary in how advanced follicles can grow independent of gonadotropins.

Gonadotropin responsive

follicles can respond to gonadotropins but gonadotropin stimulus is not required for follicle growth

Gonadotropin dependent

follicles have been stimulated to grow towards ovulation, removal of gonadotropins results in atresia

What are the stages of a follicular wave?

• Recruitment (cyclic)

• Selection

• Dominance

Follicular Wave Recruitment

• A group of small antral follicles initiate growth following release of previously dominant follicle and an increase in FSH

• Fate: selected for continued growth or become atretic, atresia.

Follicular wave selection

• From recruited pool, one follicle will be selected for continued growth

• At selection, conc. of FSH have decreased, in response to - feedback of estradiol and inhibin from group of recruited follicles.

• As selected follicle becomes dominant, it become dependent upon LH

Follicular wave Dominance:

Selected follicles become dominant follicles

• Dom. Follicle secretes lots of estradiol and inhibin which keeps FSH low

• Low FSH prevents recruitment of the next wave

How does ovulation occur?

What are the different types of reproductive cycles?

• Polyestrous

• Seasonally polyestrous

• Monoestrus

Reproductive Cyclicity: Polyestrus

• Cattle, swine, rodents, domestic cats

• Uniform and regular cycles throughout year

• pregnancy opportunities year-round

Reproductive Cyclicity: Seasonally polyestrous

• Sheep, goats, horses, deer, elk, wild cats

• Clusters of cycles only during certain season of year (can artificially manage using light during winter)

Short day breeders vs long-day breeders

• Short:

  • Sheep, goat, elk, deer

  • Start cycles when day length decreases

• Long-day breeder

  • horses, wild cats

  • start cycles when day length increases

Reproductive Cyclicity: Monoestrus

• dogs, wolves, fox, bear

• One cycle per year

• duration of estus: several days

• domestic canine: typically 3 cycles in two years

What are the phases of the estrous cycle and its associated hormones?

• Follicular phase

  • growing follicles + estrogen dominance

• Luteal Phase

  • corpus luteum + progesterone dominance

Follicle phase

• Proestrus

  • transition: progesterone to estrogen dominance

  • Formation of ovulatory follicles. Increase estrogen secretion (FSH/LH primary hormones)

• Estrus:

  • Estrogen drives behavioral estrus

  • Sexual receptivity + peak estrogen + LH surge + Ovulation

Luteal Phase

• Metestrus (period between ovulation and initial CL formation)

  • luteinization of ovulated follicle

  • Estrogen and progesterone are low

• Diestrus

  • CL fully functional with sustained progesterone (+LH)

  • Higher progesterone prepares uterus for pregnancy

  • non-pregnant → luteolysis (uterine PGF2a)

What are the difference between cow and human cycles?

Cow:

• begins and ends with estrus/ovulation

• follicular phase is short

• luteal phase dominates

• Starts with ovulation

Human:

• follicular and luteal phases are the same length

• ovulation occurs in the middle of the cycle

• cycle begins and ends with menses

What is the estrous cycle in a female dog like?

• Anestrus (5 months long)

• Proestrus (9 d)

• Estrus (9)

• Diestrus (2 months)

Estrous cycles in female cat

• In estrus = no mating

• Female in constant follicular phase

• induced ovulators, copulation needed to induce LH surge

  • (no true luteal phase)

• Estrus cycle: 17

• Estrus: 9 d

• Estrus to ovulation: 30-40 hrs

Define Anestrus. What are the different anestrus types?

• Definition: period without regular estrous cycles (temporary)

• Non-physiological

  • inadequate nutrition

  • stressful environment

  • pathologic conditions

• Types:

  • Gestational

  • Lactation

  • Seasonal

Gestational Anestrus

• Negative feed-back from progesterone

• end of gestation (species specific)

Lactation Anestrus

• Species-specific

• Negative feedback from suckling

Seasonal Anestrus

• Evolutionary: driven by environment/nutritional conditions

• Photoperiod and temperature

• short day breeders

• long day breeders

Oocyte pick up and transport to site of fertilization

1. Picking up the oocyte from the surface of the ovary or from the ovarian bursa by the fimbria

   • mesosalpinx contracts rhythmically during ovulation, causing the fimbria to slide over the surface of the ovary

2. Transport of the oocyte through the oviductal ampulla

   • Smooth muscle in the broad ligament move the oviduct and ovary to aid in the positioning of the fimbria over the ovary

What are the types of sperm transport to the site of fertilization?

• Swimming Movements

• Contraction of SM via prostaglandins (PGF2a PDE2)

• Movement of fluids

Sperm loss in the reproductive tract

• Retrograde Loss:

  • semen leak out of vaginal canal via contractions

  • • phagocytosis-

      • death of sperm within female repro

what are the Sperm Capacitation and fertilization processes?

Capacitation: change sperm undergo in the female reproductive tract that enables them to penetrate and fertilize an egg.

Fertilization: hyperactive motility → binding to zona pellucida → acrosome reaction → penetration of zona pellucida → sperm-oocyte membrane fusion → release of 2nd polar body → sperm engulfed → decondensation of sperm nucleus → formation of male pronucleus

What are the methods used to block polyspermy (fertilization of multiple sperm to one oocyte)?

Zona block: (cow, pig, rats/mice) Zona pellucida hardens (like hardening concrete), runner-up sperm that have no finished traversing the zona pellucida by the time of hardening are stopped in their tracks

Vitelline block: (rabbit, rats, mice) sperm receptors in the zona pellucida are destroyed. Therefore, any sperm that have not yet bound to the zona pellucida will no longer be able to bind or fertilize egg.

Cortical Reaction

cortical granuals released on outside of cell modifies extracellular barrier to block sperm

Explain the resumption of meiosis and pronucleus formation

Explain the physical changes in the embryo from zygote to the blastocyst stage

Zygote: single-cell embryo that eventually divides → cleavage (increase cell # w/out increases cells mass) → forms blastomeres → blastocyst is a bunch of cells clumped together to form two cell populations → inner cell mass (embryo proper) and trophoblast (chorion (outer placental layer))

What is the importance of compaction?

Compaction def: maximizes intercellular contact and results in the formation of the morula (tight junction)

Before: free movement of molecules across embryo

After: polarized cell, environment different on each side of tight junction. Cells forming inside and outside of tight junction will have different fates

How is the blastocyst formed?

• inner cell mass = fetus

• Trophectoderm= placenta

• Blastocoel cavity = cavitation

What is the embryo metabolism during preimplantation development?

The oocyte in the beginning uses glycolysis (energy source) and PPP → Polyol pathway provides other sources of energy → after fertilization, the zygote depends on tricarboxylic acids (pyruvate and lactate) as energy sources.

What is the maternal to embryonic transition? (genome activation)

As the cell goes from oocyte to blastocyst, it slowly goes from transcript origin of maternal to more of a transcript origin of embryonic.

What happens to the embryo after it hatches from the zona pellucida?

Result of several forces to degenerate zona. Blastocyst growth and fluid accumulation increases the pressure. Enzyme production by trophoblastic cells weakens zona, blastocyst contraction causes intermittent pressure pulses.

Post hatching: blastocyst is free floating in uterus. dependent on uterine environment for survival. Adequate luteal progesterone increases uterine secretions

ovulation cycle