ch28 pregnancy and human dvlpmnt

pregnancy

events that occur from fertilization until infant is born

gestation period

time from the past menstrual period until birth (~280 days)

zygote

fertilized egg

conceptus

developing offspring

conceptus: embryo

conceptus from fertilization through week 8

conceptus: fetus

conceptus from week 9 through birth

oocyte viable for

12 to 24 hours after ovulation

sperm is viable for

24 to 48 hours

time for fertilization to occur

2 days before ovulation, 1 day after ovulation

fate of ejaculated sperm: most do not make it to egg because…

some leak out of vag immediately

some are destroyed by acidic vaginal environment

some fial to make it through cervix

some are dispersed into uterine cavity or destroyed by phagocytes

capacitation

functional changes in sperm traveling in female reproductive tract

capacitation: MUSTs

motility must be enhanced

cell membranes must become fragile enough to release hydrolytic enzymes

• secretions of female track weakens acrosome membrane

must occur before sperm can penetrate the oocyte

process of sperm activatation: stage 1 Approach

aided by enzymes on surface, a sperm cell weaves its way past granulosa cells of the corona radiata

process of sperm activatation: stage 2 acrosomal reaction

binding of the sperm receptors in zona pellucida causes Ca2+ levels within the sperm to rise, triggering acrosomal reaction.

acrosomal enzymes from many sperm digest holes through the zona Pellucida, clearing a path to the oocyte membrane

process of sperm activatation: stage 3 Binding

the sperms membrane binds to the oocytes sperm binding receptors

process of sperm activatation: stage 4 fusion

sperm and oocyte plasna membrane fuse. sperm contents enter the oocyte

process of sperm activatation: stage 5, blocks the polyspermy

oocyte sperm binding membrane receptors are shed. Ca2+ levels in the oocyte’s cytoplasma rise, triggering the cortical reaction (exocytosis of cortial granules).

as result, zonda pellucida hardens and the zona pellucida’s sperm-binding receptors are clipped off

fertilization: general

combining of materal and paternal chromosomes to produce diploid zygot

fertilization: step 1

after sperm penetrates secondary oocyte, oocyte completes meiosis II, forming the ovum and second polar body

fertilization: step 2

sperm and ovum nuclei swell, forming pronuclei

fertilization: step 3

the DNA in each pronucleus replicates.

pronuclei approach each other and a mitotic spindle forms between them

fertilization: step 4

chromosomes of pronuclei intermix. fertilization is accomplished and the cell, now called a zygote, is ready for first cleavage division

early embryonic development: significant events

cleavage, blastocyte formation, implantaiton

cleavage: genera;

occurs while zygote moves toward uterus

cleavage: Day 1 and 2

zygote (1 cell) → 2, 4, 8 cell stage

each cell is a BLASTOMERE

cleavage: Day 3

16 or more cells → Morula

solid ball of blastomeres

blastocyte formation: general

day 4

fluid filled hollow sphere composed of trophoblast and embryoblast

blastocyst formation: trophoblast

displays immunosuppressive factors

participate in placenta formation

blastocyst formation: embryoblast

(inner cell mass)

becomes the embryonic disc

• will form embryonic and extraembryonic parts

implantation: general

blastocyst floats in uterus for 2-3 days

implantation begins 6-7 days after ovulationi

implantation: trophoblast adheres

to a site with the proper receptors and chemical signals

-inflammatory like receponse occurs in endometrium

implantation: trophoblast proliferates..

proliferates and forms 2 distinct layers

-Cytotrophoblast → inner layer of cells

-Syncytiotrophoblast → cells in the outer layer fuse together into a multinucleate mass, burrows and digests the endometrium

implantation: implanted blastocyst is COVERED by…

endometrial cellsi

implantation: Implantation is completed by…

the 12th day after ovulation

preg hormones: Human chorionic gonadotropin (hCG) GENERAL

early secretion is by trophoblast cells

later secretion is by chorion (fetal part of placenta)

preg hormones: Human chorionic gonadotropin (hCG) FUNCTION

prompts corpus luteum to continue secretion of progesterone and estrogen

hCG levels rise until end of second month

later declines as the placenta begins to secrete progesterone and estrogen

Placenta: general

temporary organ that originates from both embryonic and maternal tissues

placenta: function

provides nutritive, respiratory, excretory and endocrine functions to the developing embryo/fetus

placentation: general

formation of placenta

contains both: embryonic and maternal tissues

placentation: maternal tissues

decidua basalis

stratum functionalis btwn chorionic villi and stratum basalis of endometrium develops blood-filled lacunae

placentation: embryonic tissues

chorion

formed by extraembryonic mesoderm cells (develop from embryoblasts) and trophoblast

chorionic villi emerge from chorion, invade endometrium

• allows the transfer of nutrients from maternal blood to fetal blood

placentation: Chorionic villi

extends into blood filled lacunae (intervillous spaces)

vascularized by umbilical arteries and veins

immersed in maternal blood

placentation: maternal and embryonic blood suppleies

do not intermix

placentation: embryonic placental barriers include…

1. membrane of the chorionic villi

2. endothelium of embryonic capillaries

placenta is formed and functional by…

end of month 3

• provides nutritive, respiratory, excretory and endocrine functions

embryonic development: flow

blastocyst → gastrulation → organogenesis

embryonic development: general

during implantation, inner cell mass of blastocyst subdivides into two layers → epiblast and hypoblast

bilayered blastocyst is known as embryonic disc

embryonic development: embryonic disc gives rise to…

1. three primary germ layers via gastrulation:

ectoderm, mesoderm, endoderm

function → undergo organogenesis to form all the body’s tissues and organs

2. extraembryonic membranes:

amnion, yolk sac, allantonis, chorion

function → protect and support the embryo

extraembryonic membranes: amnion

creates a sac filled with amniotic fluid

cushions and protects the embryo from mechanical shock

helps maintain a constant homeostatic temperature

allows freedom of movement

prevents parts from fusing together

extraembryonic membranes: yolk sac

produces early red blood cells and other cells that form the gut

extraembryonic membranes: Allantois

forms blood vessels within the umbilical cord → connecting the fetus to the placenta

extraembryonic membranes: Chorion

forms the embryonic part of the placenta through its chorionic villi

enables exchange of nutrients, oxygen and waste with the mother

gastrulation: general

occurs in week 3

embryonic disc becomes a gastrula → 3 layered embryo

gastrulation: epiblast cells

being to migrate into the groove to form 3 primary germ layers → primitive tissue from which all body organs derive:

• first cells to migrate form → endoderm

• following cells push laterally and form → mesoderm

• cells remaining on the embryo’s dorsal surface form → ectoderm

gastrulation: hypoblast cells form what?

yolk sac

what does gastrulation set the stage for?

organogenesis

organogenesis, germ layers: ectoderm

nervous system and skin epidermis

organogenesis, germ layers: endoderm

epithelial lining and glands of the digestive and respiratory

organogenesis, germ layers: mesoderm

forms all other tissues → all other organs

at eighth week all organ systems are recognizable…

end of embryonic period

pregnant body undergoes changes to support..

fetal development, increased demands, preparation for childbirth

pregnancy induced changes: anatomical changes

displacement of organs

enlargement of the uterus and breasts

pregnancy induced changes: physiological changes

systems like the cardiovascular, respiratory and renal systems adapt, increasing cardiac output, oxygen consumption and kidney filtration

pregnancy induced changes: metabolic changes

body’s processing carbohydrates, fats and proteins is altered

hormonal changes induce a state of insulin resistance to ensure energy is available for fetus

parturition: general

giving birth to babyl

labor: definition

series of events that expel the infants from uterus

initiation of labor: flow

fetal cortisol secretion → placenta estrogens increase → oxytocin receptors AND prostaglandin secretion → uterine contraction → cervical dilation → maternal stress → hypothalamus activation → oxytocin release → poweful uterine contractions

stages of labor

1. dilation stage

2. expulsion stage

3. placental stage

initation of labor: stage 1 fetal secretion of cortisol

fetal secretion (increase) of cortisol stimulates placenta to secrete MORE estrogen

prepares uterine myometrium for contraction by:

• increased production of oxytocin receptors

• increased production of prostaglandin receptors

induces placenta to produce prostaglandins

initation of labor: stage 2

prostaglandin triggers rhythmic expulsive contractions of uterus (weak)

initation of labor: stage 3

pressure from baby’s head dilates the cervix

initation of labor: stage 4

cervical dilation causes maternal emotional and physical stress that activates hypothalamus

initation of labor: stage 5

activated hypothalamus stimulates posterior pituitary releasing oxytocin

• oxytocin and prostaglandins → POWERFUL uterine muscle stimulants

initation of labor: stage 6

positive feedback cycle

what does the placenta secreting more estrogen (stimulated from fetal secretion of cortisol) do?

prepares uterine myometrium for contraction BY:

• increase production of OXYTOCIN RECEPTORS

• increased production of PROSTAGLANDIN RECEPTORS

induces placenta to produce PROSTAGLANDINS

more estrogen = decrease in progesterone action

labor stages, dilation: general

longest stage of labor - 6-12 hours

from initiation of labor to full dilation of cervix

labor stages, dilation: stage 1

inital weak contractions:

15-30 min apart, 10-30 sec long; becomes more vigorous and rapid

labor stages, dilation: stage 2

cervix effaces (thins) and dilates fully to 10cm

labor stages, dilation: stage 3

amnion ruptures, releasing amniotic fluid → “water breaking”

labor stages, dilation: stage 4

engagement occurs → head enters the true pelvis

stages of labor, expulsion

dilation to delivery

1. strong contractions, 2-3 min ab 1 min long

2. urge to push increases

3. crowing occurs when largest dimension of head distends vulva

   1. delivery of infant

stages of labor, placental

within 30 min after birth, strong contractions continue causing:

1. detachment of placenta

2. delivery of '“afterbirth” (placenta +membranes)

3. compression of uterine blood vesseles

• prevents continued uterine blood after bird (postpartum bleeding)

lactation: basic

production of milk by mammary glands

lactation: towards end of pregnancy

1. placental estrogens, progesterone, lactogen stimulates hypothalamus to release prolactin-releasing factors (PRFs)

2. PRFs stimulates anterior pituitary to release prolactin

3. prolactin stimulates milk production

lactation: colostrum

yellowish secretion rich in vit A, proteins, minerals and antibodies

released during first 2-3 days

followed by true milk production

lactation: after birth

suckling initates a positive feedback mechanism

oxytocin causes letdown reflex