A&p Ii: Chapter 28

Front 1

DEFINITIONS OF TERMS

Back 1

A. PREGNANCY: state of mother lasting from conception to birth
B. CONCEPTUS: developing offspring
1. PREEMBRYO: conception through two weeks
2. EMBRYO: third week through eighth week
3. FETUS: ninth week to birth (PARTURITION)
C. INFANT: conceptus after parturition NEONATE for first 4 weeks.
D. GESTATION: development of conceptus in utero: 280dd (40wks).

Front 2

FERTILIZATION (CONCEPTION) (begin preembryonic period)

Back 2

A. SECONDARY OOCYTE with zona pellucida and corona radiata released during ovulation
into uterine tube

B. SPERM released into vagina during sexual intercourse (coitus)
1. travel by flagellum movement and by uterine contractions
2. encounters secondary oocyte in uterine tube
3. takes approximately 1HR to move thru female repro. tract

C. CAPACITATION OF SPERM COMPLETES
1. sperm mobility enhanced by seminal vessicle prostaglandins sperm viability
(capability of fertilizing egg) increases as acidic female environment weakens
acrosomal membrane.

ACROSOMAL REACTION: acrosomal membrane breaks & enzymes released
to break down corona radiata & zona pellucida around secondary oocyte

Front 3

FERTILIZATION (CONCEPTION) (begin preembryonic period) II

Back 3

D. SPERM PENETRATES SECONDARY OOCYTE MEMBRANE
1. acrosomal enzymes from several sperm weaken barrier around secondary oocyte.
Later sperm have easier time trying to penetrate egg.

2. SYNGAMY: once one sperm penetrates membrane of egg,
MEMBRANE CHANGES PREVENT ENTRANCE OF ANY MORE SPERM
Prevents POLYSPERMY
3. secondary oocyte completes meiosis II

4. MALE AND FEMALE PRONUCLEI: nuclei of sperm and ovum swell and migrate
towards each other

5. Pronuclei fuse to form ZYGOTE (one diploid [2n] cell) which immediately
undergoes rapid MITOTIC divisions (cleavage)

a. MONOZYGOTIC TWINS: (from one zygote) identical twins share same
amniotic sac, placenta. During early MITOTIC divisions, some cells break
apart from group, and now two identical cell clusters develop

b. DIZYGOTIC TWINS: (from two zygotes) "fraternal twins" separate amniotic
sacs, placenta.

Front 4

PREEMBRYONIC PERIOD AND DEVELOPMENT

Back 4

A. zygote and later divisions move to uterus thru uterine tube

B. CLEAVAGE: rapid mitotic divisions without growth -> more identical cells

1. FIRST CLEAVAGE: within 36 hr of fertilization
2. 4-CELL STAGE: 12 hr later
3. 8-CELL STAGE: 12 hr later
4. 16-CELL STAGE: 12 hr later: MORULA - a solid ball of cells
5. BLASTOCYST FORMATION:
a. morula enters uterine cavity, continues to divide
b. zona pellucida disintegrates DIFFERENTIATION of cells begins
c. BLASTOCYST CAVITY = cavity inside ball of cells
d. TROPHOBLAST = 1 layer of flat cells forming wall of ball of cells
1) forms the CHORION: fetal part of placenta

2) 8dd post fert., secretes Human Chorionic Gonadotropin (hCG) - a
hormone tested for by pregnancy tests (detectable at 3wks gestation)

a) hCG stimulates corpus luteum to stay active, producing
progesterone to maintain endometrium until placenta forms
and produces progesterone

b) levels peak at 8wks post fert, then decline to a low level
throughout gestation

e. INNER CELL MASS (ICM) = clump of cells at one end of blastocyst.
Becomes the EMBRYO and extraembryonic membranes.

Front 5

IMPLANTATIONPREEMBRYONIC PERIOD AND DEVELOPMENT II

Back 5

C. IMPLANTATION
1. 6-7 dd past ovulation, endometrium ready for blastocyst, implantation is usually hi in
uterus

2. ICM-side implants toward endometrium

3. trophoblast secretes enzymes to erode endometrium and is now called the CHORION

4. endometrium grows over blastocyst, implantation completes in 7 dd

D. FORMATION OF PRIMARY GERM LAYERS (begins during preembryonic, continues
during embryonic period)

1. cells of ICM begin to become different from each other (DIFFERENTIATION)

2. AMNIOTIC CAVITY forms in ICM near chorion


3. EMBRYONIC DISC FORMS: ICM near blastocyst cavity flattens into two layers
a. ECTODERM: layer next to amniotic cavity (BLUE)
b. ENDODERM: layer next to blastocyst cavity (YELLOW)

4.layer develops between endo and ectoderm = MESODERM (RED)

5. three primary germ layers form all tissues:

a. ENDODERM: glands and epithelial linings of: digestive, respiratory,
urogenital tracts (also forms yolk sac and allantois)
b. ECTODERM: nervous tissue, epidermis (also forms amnion)
c. MESODERM: all other organs: blood, muscle, bones....

Front 6

EMBRYONIC PERIOD

Back 6

A. finish formation of embryonic disc (see above)

Front 7

AMNION

Back 7

develops from ectoderm
a. sac surrounding embryo, broken by umbilical cord

b. AMNIOTIC FLUID: filtrate of maternal blood, fetal urine
(AMNIOCENTESIS 4th mo on)

c. protects embryo from jarring, maintains temperature, allows movement

d. ruptures before birth (“water breaks”)

Front 8

CHORION

Back 8

developed from trophoblast
a. outermost membrane

b. CHORIONIC VILLI penetrate maternal tissue to form conceptus’ part of
PLACENTA

c. fuses with amnion as conceptus enlarges

Front 9

YOLK SAC

Back 9

develops from endoderm
a. hangs from "belly" - side of embryo

b. forms part of fetal digestive tract

c. SOME cells migrate to become gamete-producing cells

d. produces blood cells until week 6

Front 10

ALLANTOIS

Back 10

: formed from end of yolk sac

a. contributes to bladder, umbilical AA and V

b. remains as part of umbilical cord = WHARTON'S JELLY

Front 11

PLACENTA FORMATION BEGINS (continues thru fetal period)

Back 11

1. placenta= highly vascular temporary organ, expelled with extraembryonic
membranes = AFTERBIRTH

2. functions as support structure for conceptus
a. exchange of nutrients b. excretion
c. respiration d. storage of nutrients

3. maternal and embryonic tissue makes up placenta
a. fetal: chorion from trophoblast
*CHORIONIC VILLI extend into maternal tissue
* contain lots of blood vessels including those of the umbilical cord to
bring fetal blood in close proximity to maternal blood

b. maternal
1) DECIDUA BASALIS = stratum functionalis of endometrium around
the chorionic villi forms maternal part of placenta
2) DECIDUA CAPSULARIS = stratum functionalis around rest of
uterus and conceptus, not placental
3) DECIDUA PARIETALIS = stratum functionalis around uterus where
implantation did not take place, not placental

Front 12

PLACENTA FORMATION BEGINS (continues thru fetal period) II

Back 12

4. UMBILICAL CORD: attaches placenta to conceptus
a. allantois forms outer wall
b. Wharton's Jelly
c. umbilical aa (waste away from baby) and umbilical v (nutrients to baby)
d. scar at birth = umbilicus = navel

5. PLACENTA FORMS HORMONES
a. estrogen and progesterone:
1) maintain endometrium
2) prepare mammary glands for lactation
3) suppress GnRH, FSH, LH (no more ovulation)

b. hCG: maintain corpus luteum til placenta fully formed

c. relaxin: to relax pubic symphysis, pelvic ligaments

d. inhibin: to inhibit GnRH, LH, FSH no more ovulation

e. human Chorionic Somatomammotropin - hCS
(Human Placental Lactogen - HPL)
1) stimulate mammary gland development
2) changes mom's metabolism (glucose sparing)
3) fetal growth

f. Human Chorionic Thyrotropin (HCT): increases maternal metabolism

Front 13

ORGANOGENESIS

Back 13

organs and systems are forming from primary germ
layers. Looks "human" by end of week 8

Front 14

FETAL PERIOD

Back 14

A. rapid growth and maturation of all organs and tissues

B. QUICKENING: fetal movement beginning around 20 wks

C. VERNIX CASEOSA: cheesy mix of sebum and dead cells covering and protecting fetal skin

D. LANUGO: fetal hair covers body, keeps vernix caseosa in place

E. 28 WEEKS: fetus may survive with lots of aid

F. 38-40 WEEKS: full term

Front 15

CHANGES OCCURRING WITHIN MOTHER DURING GESTATION

Back 15

A. UTERUS
1. enlarges to fill pelvic cavity by 3 mo
2. encroaches on abdominal cavity and then thoracic cavity
3. at term, is 20X larger by weight than pre-gestation

B. WEIGHT GAIN (around 30 pounds)
1. increased uterine size 4. increased blood volume
2. fetus 5. placenta
3. amniotic fluid 6. increased breast size

C. METABOLISM
1. increased urinary rate, RR, BP, HR, cardiac output, apatite
2. high blood calcium (to go to fetus)
3. glucose sparing (so fetus gets glucose)

D. POSTURE - LORDOSIS

Front 16

LABOR AND PARTURITION (BIRTH)

Back 16

A. PRE-LABOR
1. hi estrogen towards the end of gestation
a. stimulates myometrium to form more OXYTOCIN (OT) receptors
b. causes increased irritability of uterus producing weak contractions "FALSE
LABOR" or Braxton-Hicks contractions

2. fetal cells produce OT which stimulates placenta to release prostaglandins (PG)

3. OT and PG increase uterine contractions

4. hypothalamus is stimulated to produce more OT and post. pituitary releases more OT

Front 17

STAGES OF LABOR

Back 17

1. DILATION and TRUE LABOR
a. TRUE LABOR: rhythmic uterine contractions with increasing intensity due to
hi OT levels

b. AMNION BREAKS (along with highly thinned chorion and decidua
parietalis) amniotic fluid is released

c. ENGAGEMENT: fetal head enters true pelvis

d. EXTERNAL OS OF CERVIX DILATES: opens to allow passage of fetus

2. EXPULSION: “pushing stage” from end of complete cervical dilation to parturition

3. PLACENTAL STAGE
a. 10 -15 min. post parturition, placenta separates from uterine wall
b. forceful contractions of uterus expel placenta and embryonic membranes =
AFTERBIRTH

Front 18

CHANGES TO BABY AFTER PARTURITION

Back 18

A. LUNGS
1. fetal lungs are collapsed, may contain amniotic fluid (absorbed into blood at birth) 2. umbilical cord is cut, no maternal O2 to baby
3. CO2 increases in blood, stimulates respiratory center in brain
4. first breath is strong and deep to inflate collapsed lungs
5. first exhalation strong -> crying

B. CIRCULATION
1. remove bypasses to lungs, send blood to lungs:
a. FORAMEN OVALE: between atria closes -> FOSSA OVALIS
b. DUCTUS ARTERIOSUS: bypassing lungs -> LIGAMENTUM
ARTERIOSUM between aorta and pulmonary trunk
2. send blood to liver to be filtered
a. DUCTUS VENOSUS: bypassing liver -> LIGAMENTUM VENOSUM
3. no more blood to/from umbilical cord
a. UMBILICAL AA. -> ligaments attaching bladder to umbilicus
b. UMBILICAL V -> ROUND LIGAMENT OF LIVER

C. HEAD: gradually achieves a round shape
D. SENSITIVE: to changes in temperature, infections for approximately 4 weeks =
NEONATAL PERIOD

Front 19

. CHANGES TO MOTHER POST PARTURITION

Back 19

A. UTERUS
1. decreases in size = INVOLUTION
2. Placental detachment heals up
3. menstrual-type bleeding over several days to weeks to shed excess uterine tissue
3. Cervix returns to normal firmness
4. normal hormonal cycles resume


B. CIRCULATORY, ENDOCRINE AND URINARY
1. increased urination to remove excess blood volume
2. decrease in placental hormones may lead to “post-partum syndrome” or other emotional changes


C. MAMMARY GLANDS
1. increased progesterone and estrogen before birth allows PROLACTIN (PRL) to
become effective

2. PRL stimulates production of milk. Three day lag time before milk is produced.

3. COLOSTRUM: cloudy, yellow fluid hi in protein, vit. A, minerals and antibodies is
secreted until milk is produced

4. SUCKLING by the infant stimulates OT release which stimulates "MILK LET
DOWN" or release from the mammary glands as well as stimulating PRL. Thus, as
long as the baby suckles, there will be milk produced.

5. There is some evidence that lactation may prevent ovarian cycles (PRL inhibits
GnRH, LH and FSH, so no ovulation takes place). However, this is not a very
effective birth control mechanism.