Anatomy and Physiology Chapter 29 - Embryonic and Fetal Development, Parturition, and Post-Parturition

embryonic development and 4 things about it

occurs during week 4/5 and is part of the 1st trimester

• chorionic villi develop to form fetal portion of the placenta > increase surface area to gather nutrients

• narrowing of yolk and body stalk

• extra-embryonic membranes bulge into uterus (the chorion does this)

  • embryo moves away from placenta

  • yolk and body stalk fuse to form umbilical cord

3 regions of the endometrium during embryonic development

1. decidua basalis: contact with chorionic villi

2. decidua capsularis: contact with chorion

3. decidua parietalis: rest of endometrium lining uterus

what structures give rise to the umbilical cord

the body and yolk stalk

• amnion expands outward

• fetus connected to placenta by umbilical cord

  • allantois and remnants of yolk stalk

fetal circulation

utilizes the umbilical cord

• ruptured maternal vessels supply O2 and nutrients

• oxygenated blood uses umbilical vein

• deoxygenated blood uses umbilical arteries and drops it off a chorionic villi

5 placental functions

1. nutrient/gas exchange

2. hCG (human chorionic gonadotropin): similar to LH and maintains the corpus luteum to keep producing progesterone

3. hPlacental lactogen and prolactin: stimulate mammary glands to develop and produce colostrum/milk

4. relaxin: loosens connective tissues (e.g. pubic symphysis)

5. progesterone and estrogen: produced after the 1st trimester and slow increase of estrogen leads to labor

placenta previa

partial or complete where it forms over the cervix, causing damage to placenta and interfere with blood supply

what happens during each trimester

• 1st trimester:

  • organogenesis: heart development (18-22 days)

  • lots of growth (maternal nutrition important)

  • growth of maternal breast tissue

• 2nd trimester:

  • placenta makes progesterone and decrease in hCG

  • organs and systems start to function

  • movement may be felt

• 3rd trimester:

  • gaining weight and volume

  • vernix coating: waxy fatty coating from sebaceous glands to protect from amniotic fluid

  • cells in lungs produce surfactant to reduce surface tension of water

4 maternal changes

1. increase in respiration rate (more O2 dump, excess CO2)

2. increase blood volume (lots of blood in placenta)

3. increase caloric intake (~300 extra calories/day in last 2 trimesters)

4. increase GFR (urine production due to increase blood volume and fetal waste)

role of progesterone and estrogen in initiation of parturition

• progesterone inhibits smooth muscle contraction (dominant through most of pregnancy)

• estrogens increase over time

  • begins to increase oxytocin release

  • pressure on cervix also increases oxytocin release

    • release of prostaglandins for contraction

    • results in positive feedback cycle

*relaxin loosens connective tissue for birthing

*fetus can release oxytocin in addition to stretching the myometrium can cause parturition

3 stages of labor

1. dilation stage

   1. cervix dilates

   2. loss of cervical mucus plug (bloody show)

   3. rupture of amniotic sac (water breaks)

   4. contractions ~30 seconds long 10-30 minutes apart

      1. increase in frequency over time

      2. may last 8 or more hours

      3. typically shorter each birth

2. expulsion stage

   1. max cervical dilation

   2. contractions ~60 seconds long 2-3 minutes apart

   3. ~2 hours (shorter with subsequent births)

   4. baby passes through birth canal and is delivered

3. placental stage

   1. within 1 hour of delivery

   2. uterine contractions tear connection of endometrium and placenta

   3. loss of blood

   4. placenta detaches and is expelled

3 things about premature birth

• risk factors: multiples, smoking, high stress, previous premature birth, short interpregnancy interval

• most fetuses born at 25-27 weeks don’t survive

  • survivors often at risk of development disorders

• fetuses born 28-36 weeks generally have high survival

  • low chance of lasting effects

3 things about c-section

• 1-2 hour surgery

• low horizontal incision in abdominal wall

• uterus is opened and amnichorionic membrane ruptured

  • baby and placenta removed

apgar score

quick evaluation of neonate 1-5 minutes post partum; color, pulse rate, reflex, muscle tone, and breathing are scored from 0-2 to add up to 8-10 for healthy

4 stages of postnatal development

1. neonate: birth to 1 month

2. infancy: 1 month to 2 years

3. childhood: 2 years to adolescence

4. adolescence: occurs from 9-14 in boys and 8-14 in girls

role of hormones in adolescence

• GnRH: has pulsitile frequency change and is a dependent process; secretion of kisspeptin (activated by leptin from adipose tissue) stimulates this

• gonadotropins: LH and FSH increase rapidly

• development of secondary sex characteristics: gamete production or follicular development

3 physiological changes at birth

1. lungs filled with fluid and collapsed (inhalation to inflate and clear)

2. pressure changes due to lung expansion changes cardiovascular circulation (ductus arteriosus and foramen ovale close)

3. meconium (bile secretions, mucus, and epithelial cells from gestation that are excreted during first few days)

colostrum vs. breast milk

colostrum:

• produced during first 2-5 days after birth

• thick, yellowish fluid

• rich in IgA and immune cells

• small volume, high concentration

• provides early immunity

breast milk:

• produced after colostrum

• thinner, white/bluish fluid

• higher in fats, lactose, and calories

• larger volume for infant growth

• provides long term nutrition and hydration