HONORS ANATOMY & PHYSIOLOGY

THE REPRODUCTIVE SYSTEMPART 3

The Menstrual Cycle&

Pregnancy

Female Reproductive Cycle

2 parts:1. Ovarian Cycle

1. series of events in ovaries occurring during & after maturation of oocyte

2. Uterine (Endometrial) Cycle1. concurrent with ovarian cycle2. series of changes in endometrium to repare

it for implantation of fertilized egg

Hormonal Regulation

Hypothalamus secretes GnRH (gonadotropin-releasing hormone) that controls both the ovarian & uterine cycles

GnRH stimulates release of FSH & LH from anterior pituitary

FSH LH

initiates follicle growth

stimulates: follicles to release

E granulosa cells to

turn androgens E

stimulates : further development

of follicles release of E from

follicles release of androgens

from theca cells @ midcycle LH surge

triggers ovulation corpus luteum E, P,

relaxin, inhibin

Effects on Ovaries

Estrogens

3 of 6 different estrogens are present in significant amts:

1. ß estradiol2. Estrone3. Estrial

most abundant in non-pregnant female made from cholesterol in ovaries

Functions of Estrogens

1. promote development &maintenance of female reproductive structures, 2◦ sex characteristics

2. increase protein anabolism working synergistically with hGH

3. lowers cholesterol (1 reason females <50 yo have lower risk of CAD)

4. moderate levels inhibit release of GnRH, FSH, LH (negative feedback loop)

Progesterone

secreted by corpus luteumwith E prepares endometrium for

implantation & breasts for lactation

Relaxin

produced by corpus luteuminhibits contractions of myometriumduring pregnancy, placenta secretes more

relaxin…@ end of pregnancy it increases flexibility of pubic symphysis & may help dilate cx

Inhibin

secreted by granulosa cells of growing follicles & by corpus luteum after ovulation

action: inhibits secretion of FSH & to lesser extent LH

Hormones of the Menstrual Cycle

Phases of the Menstrual Cycle

1. Menstrual Phase2. Preovulatory Phase

in ovaries called follicular phase in uterus: proliferative phase

3. Ovulation4. Postovulatory Phase

in ovaries called luteal phase in uterus: secretory phase

Menstrual Phase

aka menstruation, menses~1st 5 d of cycle (d 1 of flow = day 1 of cycle)Ovaries:

FSH causes several primordial follicles to develop 1◦ follicles 2◦ follicles

Uterus: declining E & P levels prostaglandins

constriction of uterine spiral arterioles O deprived tissue death & shedding 50 – 150 mL of blood, tissue fluid, mucus, epithelial cells (entire stratum functionalis sloughs off)

Preovulatory Phase

time between end of menses ovulationmost variable length in time (reason cycles

vary in length)Ovaries:

follicles secrete E & inhibin d 16 one 2◦ follicle in 1 of the 2 ovaries becomes

the dominant follicle (secretes more E & inhibin decreases FSH)

dominant follicle (Graafian) enlarges until ovulation:~2cm

Preovulatory Phase (Proliferative)

Uterus: E stimulates repair of endometrium

producing new stratum functionalis new endometrial glands form endometrium thickens from ~4 to 10 mm

Ovulation

d 14 in 28 d cycle2◦ oocyte surrounded by zona pellucida &

corona radiatahigher levels of E @ end of preovulatory

phase have + effect on cells that secrete LH & GnRH: their increase leads to ovulation

OTC test for LH surge used to predict ovulation

Mittleschmerz

pain noted @ time of ovulationcaused by small amt of blood that leaks into

pelvic cavity from ruptured follicle

Postovulatory Phase (Luteal)

time between ovulation & onset of next mensesMost constant part of cycle = 14 days (d15 – 28)Ovary:

under influence of LH, granulosa cells transformed corpus luteum cellswhich secrete E, P, relaxin, inhibin

if oocyte not fertilized: corpus luteum lasts 2 wks corpus albicans

+ fertilization: corpus luteum persists until “rescued” by hCG (human chorionic gonadotropin) which is made by chorion of embryo @ ~ 8d after fertilization

Postovulatory Phase (Secretory)

Uterus: P & E made by corpus luteum promote:

growth & coiling of endometrial glands vascularization of superficial endometrium thickening of endometrium (12 – 18 mm) these changes peak 1 wk after ovulation if no fertilization levels of P & E decline

which eventually causes menstruation

Homeostatic Imbalances

Dysmenorrhea painful menses

Amenorrhea absence of menses #1 reason = pregnancy

Endometriosis disorder in which endometrium grows

outside uterus +/- painful can cause infertility due to scarring

Embryonic Period

Fertilization: Nuclei from sperm merges with nuclei from

2◦ oocyte forming a diploid nucleus Fallopian tube normal site of fertilization

w/in 12 -24 hrs after ovulation sperm can remain viable up to 48 hrs after

deposition in vagina

Fertilization

sperm must penetrate 2 layers:1. corona radiata

granulosa cells that surround 2◦ oocyte2. zona pellucida

clear glycoprotein layer between corona radiata & oocyte’s plasma membrane

Fertilization

ZP3: 1 of glycoproteins acts as sperm receptor

acrosomal reaction: occurs when ZP3 binds to specific membrane protein on sperm head plasma membrane release of contents of acrosome

Acrosomal Reaction

acrosomal enzymes digest a path thru zona pellucida

lashing flagella of sperm pushes it forwardseveral sperm bind to ZP3 molecules but only

1st sperm to penetrate zona pellucida & reach plasma membrane of oocyte “wins”

once diploid nucleus formed its called a zygote

Cleavage of the Zygote

rapid M phase but no growth1st division begins ~24 hrs after fertilization

taking 6 hrs to complete, following divisions take less time

~2 d after fertilization = 4 cells~ 3 d after = 16 cellscells get progressively smaller, & are called

blastomeresmorula (mulberry) solid sphere of cells, still

surrounded by zona pellucida & still about size of original zygote

Blastocyst Formation

~ end of 4th d: # of cells in morula increase as it is still moving thru fallopian tube enter uterine cavity on d 4-5

glycoprotein secretions fromendometrial glands enter morula providing nourishment

@ ~ 32 cell size, fluid enters morula & collects between blastomeres forming fluid-filled cavity = blastocyst cavity (up to ~100 cells) & now called a blastocyst or blastula (still ~ same size as original zygote)

Blastocyst Forms Layers

2 distinct structures form:1. Inner cell mass

eventually becomes embryo2. Trophoblast

ultimately forms fetal portion of placenta 5th d: blastocyst digests hole thru zona

pellucida & squeezes out

Implantation

attachment of blastocyst to endometriumafter implantation endometrium becomes

modified & is called decidua

Trophoblast

develops into 2 layers (both part of chorion):1. Syncytiotrophoblast2. Cytotrophoblast

hCG is Produced

hCG: human chorionic gonadotropinProduced by trophoblast starting on d 6hCG causes endometrium to grow &

proliferatehCGprevents the menstrual cycle from

occuringreason female misses her menses when she is

pregnant

Inner Cell Mass

differentiates into a bilaminar disc1. Hypoblast2. Epiblast

Amnion

thin protective membranedevelops from cytotrophoblast

Gastrulation

@ end of cleavage stage, cells making up the blastula move

surface proteins help cells recognize each other & help sort cells

3 layers of gastrula formed: called the 3 germ layers

EndodermMesodermEctoderm

Extraembryonic Membranes

develop from the germ layers but are NOT part of the embryo (lost at birth)

lie outside embryo & provide protection & nourishment

4 components:1. chorion2. amnion3. allantois4. yolk sac

Placentation

formation of the placentasite of exchange of nutrients & wastes

between the mother & fetusalso functions as protective barrier &

produces several hormones to maintain pregnancy (hCG)

Week 2

implantation continues until complete emersion into endometrium

Weeks 3 - 4

development of nervous system & cardiovascular system evident

Weeks 5 - 8

embryo will develop all structure that an adult has by end of week 8

Embryonic Period Fetal Period

1st thru 8th wkcharacterized by

development of structures (organs)

begins @ 9th wk & goes until birth @ 38 wks (from fertilization)

characterized by growth & development of structures formed in embryonic period

Embryo/ Fetus

Maternal Changes in Pregnancy

uterus nearly fills abdominal cavityGI tract compressed may cause heartburn,

constipationpressure on bladder causes frequency &

urgencycompression of inferior vena cava may cause

varicose veins, &/or edema in legscompression on renal vessels may cause

elevated BP (renal hypertension)

Maternal Hormone Changes During Pregnancy

pregnancy maintained by hCG, E, & Prelaxin increases flexibility of pubic

symphysishCS (human chorionic somatomammotropin)

contributes to:breast developmentprotein anabolismcatabolism of glucose & fatty acids

Labor

process by which fetus is expelled from uterus

true labor involves dilation & thinning of cxfalse labor may have painful contractions but

there are no cervical changes

Positive Feedback Loop

Adjustments Infant Makes at Birth

Infant’s respiratory & cardiovascular systems undergo changes to enable them to become self-supporting

Maternal Breast Changes

hormonal changes, increased blood flow, & changes in breast tissue cause breast to feel heavy, swollen, or sore

breast tenderness commonly starts w/in 4 wksareolas enlarge & darkenColostrum the yellowish1st milk your baby gets

may leak out any time after 3rd mo contains Ig A antibodies, protein, fat-

soluble vitamins, minerals replaced by milk after 2 – 4 days baby

nursing

Breastfeeding is Best

Prolactin Oxytocin

made in anterior pituitary

release controlled by dopamine

action: activates mammary glands to make milk

several minutes of baby nursing stimulates release

made in hypothalamus & stored in posterior pituitary

baby nursing stimulates its release

action: milk let down

Lactation Hormones