ANSC 3600 Exam 3

What are the goals for the follicular phase?

Allow follicle to reach mature stage

Display estrus

What stages are part of the follicular phase?

Proestrus and estrus

What occurs during proestrus?

CL is killed,
Increased estrogen
Pushing follicle growth

What occurs during estrus?

Only period of receptivity to male

Peak estrogen

How often does the surge center “surge”?

Every 21 days (estrus)

What kind of feedback does estrogen have on the surge center?

When a dominant follicle is present, estrogen has positive feedback

When a dominant follicle is not present, estrogen has negative feedback

When does the tonic center start working?

From birth (never stops)

What is the main hormone in the tonic center?

Progesterone

Describe the activity level of the tonic center from birth to post-puberty onset.

Active at birth but slow release

Activity increases during puberty onset and during each follicular phase after puberty onset

What is Inhibin?

The follicle selection hormone

How does inhibin react with estrogen?

When inhibin is high, estrogen decreases

What type of nuclei are present in the tonic center?

Arcuate nucleus and Ventromedial nucleus

What does the tonic center do?

Stimulate basal LH needed for androgen synthesis in theca cells

Increases release of FSH needed for aromatization of androgen to estrogen in granulosa cells

What nuclei are present in the surge center?

Preoptic, suprachiasmatic, and anterior hypothalamic area nuclei

What are hormone levels like from the surge center during the luteal phase?

High P4 and low E2

Surge center is not active

Where are FSH and LH stored?

Gonadotrope cells

What are hormones like in the surge center during the follicular phase?

Low P4, high E2

What kind of feedback does the surge center receive during the follicular phase?

Positive feedback

What structure doesn’t have E2 receptors?

The hypothalamus

How much LH does the surge center release?

100-150 ng/mL

How much GnRH does the surge center release?

20-100+ pg/mL

Does follicle growth continue throughout the entire estrous cycle?

Yes

What dictates follicle growth?

Amount of FSH and LH in the blood

From smallest to largest what is the order of follicle size?

Cow, mare, sow

Sow, cow, mare

What stages of follicles have the most E2?

Large and pre-ovulatory follicles

What happens to follicles during the luteal phase?

Follicle growth still occurs, follicles just can’t reach dominance

What processes of follicle growth still occur during pregnancy?

Selection, growth, and recruitment

What occurs during the recruitment phase?

Small portion of primary follicles are selected and initiate growth

What are the 2 take-aways about how recruitment works?

Follicles will secrete AMH to inhibit follicles around them from being recruited

Oocyte orchestrates follicle progression

How many follicles typically start growing in cattle?

20

What occurs during the dominance phase?

Surviving follicle(s) continue to grow and increase E2 levels

Start to synthesize and secrete inhibin, decreasing FSH

What occurs during the selection phase?

LH starts to increase due to follicles secreting inhibin

FSH starts to decrease, inhibiting other follicles from growing

What is atresia?

Hormone controlled apoptosis

How does atresia work in monotocous species?

All but one follicle regresses

How does atresia work in polyocous species?

Utilizes E2/inhibin ratio to determine how many follicles survive

When does atresia occur?

Before a follicle can reach dominance

What environment is needed for a dominant follicle to form?

Low P4

What stage is inhibin released?

During selection

What type of receptors do dominant follicles have a lot of?

LH receptors

What stages can atresia occur?

During selection and dominance

Not during dominance pre-ovulatory

When is the first identifiable follicle wave in cattle?

During metestrus

What happens during mid-diestrus in cattle?

Second follicle wave is identifiable, but no dominant follicle will form

CL is present = high P4 = limited follicle growth → follicles regress and become atretic

What is occurring during the third follicle wave?

CL is regressing = P4 is decreasing

LH and FSH increase

Dominant follicle forms producing more E2

Mating and Ovulation

What is the ideal number of follicle waves?

3

During what periods of anestrus do follicle waves continue?

Prior to puberty

During pregnancy

During other periods of anestrus (lactational anestrus, illness caused, etc.)

What is the max number of oocytes ovulated for a cow?

136

Functions of FSH

Stimulate follicles to grow

Stimulates E2 production by granulosa cells

Functions of LH

Stimulates steroid production by theca interna cells

Initiates ovulation and lutenization

What cells help produce estradiol?

Theca and granulosa cells aromatize cholesterol to produce estradiol

Effect of estradiol in the hypothalamus?

Fires surge center

Effect of estradiol in the reproductive tract?

Tone myometrial layer; influence endometrium secretions (prep tract for sperm)

Effect of estradiol in the brain (behavior)?

Receptivity to male (estrus)

How is estradiol distributed throughout the body?

Diffuse through basement membrane to capillaries and bind to receptors

Lordosis “AKA”

Standing heat

What do leukocytes (immune cells) do in the reproductive tract?

Attack sperm

Protect from foreign material coming in with sperm

What does the oocyte have to pass through in order to ovulate?

Granulosa → basement membrane → theca interna and externa → intracellular connective tissue → tunica albuginea → peritoneum/surface epithelium

What is Hypermia?

Increased blood flow in ovary/follicle

What events are caused by LH surge?

Increased internal blood pressure in follicle (Hypermia) → breakdown of tissues forming follicle wall → contractions of ovarian smooth muscle

What does Hypermia cause?

Increase PGE2 and histamine (vasodilators)

Increase vasodilation, angiogenesis

Increase blood flow to ovary and pre-ovulatory follicle = antrum size increases (increased pressure)

What tissue holds the follicles and follicle wall together?

Collagenase

What does collagenase do?

Breaks down collagen in the follicle wall

What are the steps in wall breakdown?

Block enzyme in theca interna that converts P4 to T

Steroid synthesis stops at P4

Local P4 promotes synthesis of collagenase

Collagenase breaks down collagen in the follicle wall

Apex of follicle weakens and pushes out to form “stigma”

What happens when you block smooth muscle contraction with inhibitors?

Ovulation is blocked

What happens during wall contraction of the follicle?

Increase local PGF2 alpha production

Contraction of “myoid” components of ovary

What are lysosomes?

“Clean up crew”

Prepares follicle for lutenization

Rupture in granulosa

Enzymes in lysosomes disrupt connective tissue

What leads to ovulation?

Increased follicle pressure + weakened follicle wall

What is initiated by preovulatory LH surge?

Gap junction breakdown between granulosal cells and oocyte

• Allows egg to continue meiotic journey so it’s mature enough for fertilization

What does OMI stand for?

Oocyte Maturation Inhibitor

What does MPF stand for?

Maturation Promoting Factor

What is Spontaneous ovulation?

Cyclic changes based on predictable hormonal event

Ex: cow, ewe, mare, sow

Male presence not needed to ovulate

What is induced ovulation?

“Reflex” ovulatory

Ovulatory process starts due to copulation (stimulation of vagina/cervix)

Ex: cat, rabbit, llama

What hormone change occurs during induced ovulation?

LH amplitude increases with increased mating

• 50% cats ovulate with one mating

  • Increased mating increase % ovulating

4 phases of oocyte maturation:

Prenatal mitotic divisions

Nuclear arrest in dictyotene of prophase 1 (“prolonged diplotene”)

Cytoplasmic growth

Resumption of meiosis at ovulation

When do mitotic divisions occur?

Occur prior to birth

What is the last mitotic division?

Oogonia → primary oocyte

What occurs during prophase 1?

Each chromosome duplicates = sister chromatids

Crossing over can occur

What is the purpose of Meiosis II?

Gametes are formed

Which process involves identical daughter cells and which mixes maternal and paternal genes around?

Mitosis produces identical daughter cells

Meiosis shuffles maternal and paternal chromosomes around = genetic variation

What are the methods in meiosis that result in genetic variation?

Crossing over

Independent assortment

What is the equation for number of combinations in independent assortment?

2 to the power of n

n = # of chromosomes

What is the chiasmata? When does it occur?

Site of crossing over; exchange of genetic material between non-sister chromatids

Occurs during synapsis of prophase I

What does crossing over produce?

Recombinant chromosomes

• Chromosomes w/ DNA from maternal and paternal

What is formed in the primary oocyte?

The cytoplasm

What develops in the secondary oocyte?

Zona pellucida (grows to max size)

• aids in single sperm fertilization

What is the process of oocyte growth?

Primordial oocyte → primary oocyte → secondary oocyte → tertiary small antral → tertiary preovulatory → mature ovulated oocyte

What is the interval from ovulation to luteolysis?

The luteal phase

Stages of the luteal phase?

Metestrus (increasing P4, CL developing)

Diestrus (High P4, full CL)

Major events of the luteal phase?

Formation of CL

Synthesis and release of P4

Luteolysis (when no pregnancy)

What do granulosa cells become during the luteal phase?

Granulosa cells → large luteal cells

How were large luteal cells formed? What do they do?

Granulosa cells increased during lutenization (hypertrophy)

Produce bulk of P4, oxytocin, and relaxin

What do theca cells become in the luteal phase?

Theca cells → small luteal cells (mostly liquid droplets)

How were small luteal cells formed? What do they do?

Theca cells increase in number (hyperplasia)

More receptive to LH

Fine tune P4 secretion

What structure is present during metestrus?

Corpus hemorrhagicum (CH)

• temporary structure right after ovulation, similar to blood clot

What hormone has a minimum required amount to maintain a pregnancy but not a maximum amount?

P4

What is required for P4 synthesis?

Cholesterol substrate

Tonic LH stimulation

What is the role of LH stimulation during P4 synthesis?

LH increases amount of cholesterol moving into mitochondria to make P4

What happens to the CL during luteolysis?

Functionally killed

Tissue is still present

What kind of feedback does P4 have on the tonic center? What is that effect?

Has negative feedback on tonic center = negative feedback on GnRH/Pituitary

What tissues are targeted by P4? What are some of the effects?

Target: Alveolus of mammary gland

Effect (+ feedback): Puberty onset, prepare mammary glands for milk (not milk production)

Target: Uterine tissue

Effect (+ feedback): Increase uterine duct secretion

Effect (- feedback): Relax myometrial layer = better environment for embryo/gestation

Target: Hypothalamus

Effect: Negatively regulate GnRH from pituitary gland

What hormones from where signals for luteolysis?

PGF2 alpha from the uterus

Oxytocin from the CL