Female Physiology Before Pregnancy and the Female Hormones

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FEMALE PHYSIOLOGY BEFORE PREGNANCY AND THE FEMALE HORMONES

FEMALE REPRODUCTIVE SYSTEM

Table 17-6: FUNCTIONS OF GRANULOSA CELLS1. Nourish oocyte

2. Secrete chemical messengers that influence the oocyte and the theca cells3. Secrete antral fluid4. Are the site of action for estrogen and FSH in the control of follicle

development during early and middle follicular phases.5. Express aromatase, which converts androgen (from theca cells) to estrogen6. Secrete inhibin, which inhibits FSH secretion _____ on the pituitary7. Are the site of action of LH induction of changes in the oocyte and follicle

culminating in ovulation and formation of the corpus luteum.

Ovarian Events in a Menstrual Cycle

SYSTEMATIC PLASMA HORMONE CONCENTRATION AND OVARIAN EVENTS DURING THE MENSTRUAL CYCLE

1. FSH and LH increase2. Multiple antral follicles begin to enlarge and secrete estrogen3. Plasma estrogen concentration begins to rise.4. One follicle becomes dominant and secretes large amount of estrogen5. Plasma estrogen level increases markedly6. FSH secretion and plasma FSH concentration decrease causing atresia of a

nondominant follicles.7. Increasing plasma estrogen exerts a “positive” feedback on gonadotropin

secretion8. LH surges is triggered.9. The egg completes its first meiotic division and cytoplasmic maturation while

the follicle secretes less estrogen accompanied by some progesterone.10.Ovulation occurs.

Effect of the LH Surge on Ovarian Function

1. The primary oocyte completes its first meiotic division and undergoescytoplasmic changes that prepare the ovum for implantation shouldfertilization occur. These LH effects on the oocyte are mediated bymessengers released from the granulose cells in response to LH.

2. Antrum size (fluid volume) and blood flow to the follicle increase markedly.

3. The granulose cells begin releasing progesterone and decrease the releaseof estrogen, which accounts for the midcycle decrease in plasma estrogenconcentration and the small rise in plasma progesterone just beforeovulation.

4. Enzymes and prostaglandins, synthesized by the granulose cells, break downthe follicular-ovarian membranes. These weakened membrane rupture,allowing the oocyte and its surrounding granulose cells to be carried out ontothe surface of the ovary.



5. The remaining granulose cells of the ruptured follicle (along with the thecacells of that follicle) are transformed into the corpus luteum, which begins torelease progesterone and estrogen.

POSTULATED MECHANISM OF OVULATION

Luteinizing hormone

Follicular steroid hormone(progesterone)

Proteolytic enzyme Follicular hyperemia and(Collagenase) prostaglandin secretion

Weakened follicle wall Plasma transudation into follicle

Degenerationt of stigma Follicle swelling

Follicle rupture

Evagination of ovum

11.The corpus luteum forms and begin to secrete large amounts of bothestrogen and progesterone

12.Plasma estrogen and progesterone increases13.FSH and LH secretion are inhibited and plasma concentration decreases.14.The corpus luteum begins to degenerate and decrease its hormone secretion15.Plasma estrogen and progesterone concentrations decrease.16.FSH and LH secretion begins to increases and a new cycle begins.

Table 17-4 Summary of Major Feedback Effects of Estrogen, Progesteroneand inhibin

1. Estrogen, in low plasma concentration, causes the anterior pituitary tosecrete less FSH and LH in response to GnRH and also may inhibit thehypothalamic neurons that secrete GnRH

Result: Negative feedback inhibition of FSH and LH secretion during the earlyand middle follicular phase.

2. Inhibin acts on the pituitary to inhibit the secretion of FSH

Result: Negative feedback inhibition of FSH secretion throughout the cycle.



3. Estrogen, when increasing dramatically, causes anterior pituitary cells tosecrete more LH (and FSH) in response to GnRH and also stimulate thehypothalamic neurons that secrete GnRH.

Result: Positive feedback stimulation of the LH surge which triggers ovulation.

4. High plasma concentration of progesterone in the presence of estrogen,inhibit the hypothalamic neurons that secrete GnRH.

Result: Negative feedback inhibition of FSH and LH secretion and preventionof LH surges during the luteal phase and pregnancy.

CONTROL OF ESTROGEN SYNTHESIS DURING THE EARLY AND MIDDLEFOLLICULAR PHASES

LH FSH

Ovarian follicle

Theca cells Granulosa cells

SynthesizeAndrogens Diffusion Convert androgens to estrogen

Hormonal Control of Ovarian Function During the Early and Middle FollicularPhases

Hypothalamus secretes GnRH

GnRH (In hypothalamo-pituitary portal vessels)

Anterior pituitary secretes FSH and LH

FSH LH

Ovaries

Granulosa Cells Theca Cells

Androgens

Influence oocytesInhibin Estrogen



Reproductive tract and other organs respondto estrogen

Hormonal Ovarian Control in the Late Follicular Phase

HypothalamusSecretes GnRH

Increased GnRH(In hypothalamic-pituitary portal vessels)

Anterior pituitary secretes LH

LH surge

Ovary Corpus Luteum(Begin)

Large amounts of estrogen Progesterone and estrogen

RELATIONSHIPS BETWEEN OVARIAN AND UTERINE CHANGES DURING THEMENSTRUAL CYCLE

SUMMARY OF THE MENSTRUAL CYCLEDAYS MAJOR EVENTS

1-5

Estrogen and progesterone are low because the previous

corpus luteum is regressing; therefore, (a) endometriallining sloughs(b) secretion of FSH and LH is

released from inhibition, and their plasma concentrationsincrease.

Therefore, several growing follicle are stimulated tomature.

7 A single follicle (usually) becomes dominant.7-12 Plasma estrogen increases because of secretion by the

dominant follicle. Therefore, Endometrium is stimulated toproliferate

7-12 LH and FSH decreases due to estrogen and inhibinnegative feedback. Therefore, degeneration (atresia) of nondominant follicles occur.

12-13 LH surge is induced by increasing plasma estrogen. Therefore, (a) Oocyte is induced to complete its firstmeiotic division and undergo cytoplasmic maturation.(b) Follicle is stimulated to secrete digestive enzymes andprostaglandin

14 Ovulation is mediated by follicular enzymes and



prostaglandins.15-25 Corpus luteum forms and, under the influenced of low but

adequate levels of LH, secretes estrogen andprogesterone, and so plasma concentrations of thesehormones increase.

Therefore, (a) Secretory endometrium develop(b) Secretion of FSH and LH are inhibited, lowering theirplasma concentrations. Therefore, no new follicledeveloped

15-28 Corpus luteum degenerates (if egg is not fertilized). Therefore, plasma estrogen and progesteroneconcentrations decrease.

Therefore, endometrium begins to slough at conclusion of day 28, and a new cycle begins.

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Female Physiology Before Pregnancy and the Female Hormones