Lab 43 - Gametogenesis and the female cycles

Vagina

External osCervical canalInternal os

Wall of uterusPerimetriumMyometriumEndometrium

Round ligament of uterus

Uterinetube

InfundibulumFimbriae

IsthmusAmpulla

Lumen (cavity)of uterus

Suspensoryligament of ovary Uterine (fallopian) tubeOvarian bloodvessels

MesosalpinxMesovarium

Broadligament

Mesometrium

Ovary

Ovarian ligamentBody of uterusUreterUterine blood vesselsIsthmusUterosacral ligamentLateral cervical(cardinal) ligamentLateral fornixCervix

(a)

Fundusof uterus

Ovaries

• Follicle

• Immature egg (oocyte) surrounded by

• Follicle cells (one cell layer thick)

• Granulosa cells (when more than one layer is present)

Follicles

• Several stages of development

• Primordial follicle: squamouslike follicle cells + oocyte

• Primary follicle: cuboidal or columnar follicle cells + oocyte

• Secondary follicle: two or more layers of granulosa cells + oocyte

• Late secondary follicle: contains fluid-filled space between granulosa cells; coalesces to form a central antrum

Ovaries

• Vesicular (Graafian) follicle

• Fluid-filled antrum forms; follicle bulges from ovary surface

• Ovulation

• Ejection of the oocyte from the ripening follicle

• Corpus luteum develops from ruptured follicle after ovulation

Figure 27.11a

Medulla

Tunicaalbuginea

Germinalepithelium

Cortex

Oocyte Granulosa cellsLate secondary follicle

Antrum

Primaryfollicles

Oocyte

Zonapellucida

Thecafolliculi

Ovulatedoocyte

Mesovarium andblood vessels

Vesicular(Graafian)follicle

Coronaradiata

Developingcorpus luteum

Corpus luteum

Ovarianligament

Degenerating corpusluteum (corpus albicans)

(a) Diagrammatic view of an ovary sectioned to reveal the follicles in its interior

Uterine Wall

• Three layers

1. Perimetrium: serous layer (visceral peritoneum)

2. Myometrium: interlacing layers of smooth muscle

3. Endometrium: mucosal lining

Figure 27.13b

Lumen of uterus

Uterine glands

Smooth muscle fibers

Straight artery

Radial artery

Arcuate arteryUterine artery

Endometrial vein

Capillaries

Venous sinusoids

Epithelium

Spiral (coiled) artery

Lamina propria ofconnective tissue

(b)

Figure 27.17

Meiotic events Follicle developmentin ovaryBefore birth

Infancy andchildhood(ovary inactive)

Primary oocyte

Primary oocyte (stillarrested in prophase I)

Vesicular (Graafian)follicle

Primary follicle

Primordial follicle

Primordial follicle

Oocyte

Ovulated secondaryoocyte

In absence offertilization, ruptured follicle becomes a corpus luteum andultimately degenerates.Degenating

corpus luteum

Secondary follicle

Primary oocyte(arrested in prophase I;present at birth)

Oogonium (stem cell)

Each month frompuberty to menopause

Meiosis I (completed by one primary oocyte each month in response to LH surge)

First polar body

Mitosis

Growth

Meiosis II of polarbody (may or may not occur)

Polar bodies(all polar bodiesdegenerate)

OvumSecondpolar body

Meiosis IIcompleted(only if spermpenetration occurs)

SpermOvulation

Secondary oocyte(arrested in metaphase II)

Follicle cells

Spindle

Ovarian Cycle

• Monthly series of events associated with the maturation of an egg

• Two consecutive phases (in a 28-day cycle)

• Follicular phase: period of follicle growth (days 1–14)

• Ovulation occurs midcycle

• Luteal phase: period of corpus luteum activity (days 14–28)

Follicular Phase

• Primordial follicle becomes primary follicle

1. The primordial follicle is activated

• Squamouslike cells become cuboidal

2. Follicle enlarges to become a primary (1) follicle

Figure 27.18 (1 of 7)

Theca folliculi

Primary oocyteZona pellucidaAntrum

Secondaryoocyte

Secondary oocyteCorona radiata

12

3 4

5

6

7

8 Primordialfollicles

1

Luteal Phase

• Ruptured follicle collapses

• Granulosa cells and internal thecal cells form corpus luteum

• Corpus luteum secretes progesterone and estrogen

Establishing the Ovarian Cycle

• During childhood, ovaries grow and secrete small amounts of estrogens that inhibit the hypothalamic release of GnRH

• As puberty nears, GnRH is released; FSH and LH are released by the pituitary, and act on the ovaries

• These events continue until an adult cyclic pattern is achieved and menarche occurs

Establishing the Ovarian Cycle

• At puberty

• Leptin from adipose tissue decreases the estrogen inhibition

• GnRH, FSH, and LH are released

• In about four years, an adult cyclic pattern is achieved and menarche occurs

Hormonal Interactions During a 28-Day Ovarian Cycle

• Day 1: GnRH release of FSH and LH

• FSH and LH growth of several follicles, and estrogen release

• estrogen levels

• Inhibit the release of FSH and LH

• Stimulate synthesis and storage of FSH and LH

• Enhance further estrogen output

Hormonal Interactions During a 28-Day Ovarian Cycle

• Functions of corpus luteum

• Produces inhibin, progesterone, and estrogen

• These hormones inhibit FSH and LH release

• Declining LH and FSH ends luteal activity and inhibits follicle development

Hormonal Interactions During a 28-Day Ovarian Cycle

• Days 26–28: corpus luteum degenerates and ovarian hormone levels drop sharply

• Ends the blockade of FSH and LH

• The cycle starts anew

Figure 27.19

Hypothalamus

Late follicular andluteal phases

1

1

2 2

2

3

4

5

5

6

8

8

7 Slightlyelevated estrogen and rising inhibin levels.

Positivefeedback exerted by large inestrogen output.

Mature follicleCorpus luteum

Ovulatedsecondaryoocyte

Rupturedfollicle

LH surgeProgesteroneEstrogenInhibin

Hypothalamus

Early and midfollicular phases

Travels viaportal blood

Granulosacells

Inhibin

Androgens

Convertandrogens toestrogens

Thecalcells

Anterior pituitary

GnRH

FSH LH

Figure 27.20a

(a) Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle.

FSH

LH

Figure 27.20b

(b) Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle.

Primaryfollicle

Secondaryfollicle

Vesicularfollicle

Ovulation

Corpusluteum Degenerating

corpus luteum

Follicularphase

Ovulation(Day 14)

Lutealphase

Uterine (Menstrual) Cycle

• Cyclic changes in endometrium in response to ovarian hormones

• Three phases

• Days 1–5: menstrual phase

• Days 6–14: proliferative (preovulatory) phase

• Days 15–28: secretory (postovulatory) phase (constant 14-day length)

Uterine Cycle

• Menstrual phase

• Ovarian hormones are at their lowest levels

• Gonadotropins are beginning to rise

• Stratum functionalis is shed and the menstrual flow occurs

Uterine Cycle

• Proliferative phase

• Estrogen levels prompt generation of new functional layer and increased synthesis of progesterone receptors in endometrium

• Glands enlarge and spiral arteries increase in number

Uterine Cycle

• Secretory phase

• Progesterone levels prompt

• Further development of endometrium

• Glandular secretion of glycogen

• Formation of the cervical mucus plug

Figure 27.20c

(c) Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a).

Progesterone

Estrogens

Figure 27.20d

(d) The three phases of the uterine cycle: • Menstrual: Shedding of the functional layer of the endometrium. • Proliferative: Rebuilding of the functional layer of the endometrium. • Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo.Both the menstrual and proliferative phases occur before ovulation, and together they correspond to the follicular phase of the ovarian cycle. Thesecretory phase corresponds in time to the luteal phase of the ovarian cycle.

Menstrualphase

Menstrualflow

Endometrialglands

Blood vessels

Functional layer

Basal layer

Proliferativephase

Secretoryphase

Days