han 202 - pregnancy n human development (ch 28+29)

pregnancy

• event that occur from fertilization until birth

  • divided into 3-month trimesters

gestation period

• time from last menstrual period until birth (abt 280 days)

  • avg 266 days from conception to childbirth

conceptus

• products of conception

  • pre-embryonic stage - from fertilization thru first 16 days

  • embryo - from day 16 to week 8

  • fetus - week 9 till birth

oocyte viability

• for 12-24 hrs

sperm viability

• for 24-48 hrs after ejaculation

fertilization

• when sperm’s chromosomes combine with secondary oocyte (immature egg) to form fertilized egg (zygote)

for fertilization to occur

• coitus (sex) must occur no more than

  • 2 days before ovulation

  • 24 hrs after ovulation

sperm propelled by

• whiplike tail movement of flagella

• endometrial cilia n forceful uterine contractions which disperse them throughout uterine cavity

sperm ejaculation

• leak out vagina immediately after deposition

• destroyed by acidic vaginal envi

• fail to make it thru cervical mucus

• dispersed in uterine cavity or destroyed by phagocytes

• few (100 - few thousand) reach uterine tubes

• total trip = 5 inches

sperm reach oocyte

• need to pass 2 layers

  • corona radiata

  • zona pellucida

• sperm must be capacitated before penetrating oocyte

  • secretions of female tract weaken acrosome membrane

capacitation

• sperm membrane become fragile so hydrolytic enzyme can be released

  • make sperm membrane more permeable to calcium

  • activate receptors for chemical attractants

sperm penetration

• acrosomal process forms n binds to receptors on oocyte’s plasma membrane

• sperm n oocyte membranes fuse

• nucleus pulled into oocyte cytoplasm

• only 1 sperm allowed to penetrate oocyte (monospermy)

when sperm enters oocyte

• waves of ca2+ released into oocyte cytoplasm which activates

  • oocyte to prep for 2nd meiotic division

  • cortical reaction

cortical reaction

• zonal inhibiting proteins r released

  • blocks other sperm from entering

polyspermy

• not desired

  • results in non-viable embryo

pre-embryonic stage

• first 16 days of development, cumulates in an embryo

• 3 major processes

  • cleavage

  • implantation

  • embryogenesis

cleavage

• rapid mitotic division of zygote without increase in size

• increases SA n # of cells

• easier for uptake in nutrients, o2, waste removal

zygote formation

• blastomere (36 hrs) - 2-8 cells

• morula (72 hrs) - 16+ cells

• blastocyte (4-5 days) - fluid filled hollow sphere ; reaches uterus

identical twins

• monozygotic - 1 placenta

• one egg/sperm = one zygote

• embryoblast divide into 2 within 2 weeks of fertilization

fraternal twins

• dizygotic - 2 placenta

• 2 eggs/sperm = 2 zygote

blastocyte

• trophoblast (outer layer) cells - single layer of flat cells

  • participate in placenta formation

• inner cell mass

  • becomes embryonic disc

ectopic pregnancy

• when egg implants itself outside uterus

• most common is implanting itself in fallopian tube

blastocyst

• floats for 2-3 days

• nourished by uterine secretions

• aborted if implantation fails

implantation

• begins 6-7 days after ovulation

  • trophoblast adheres to endometrium

  • secretes enzymes to irritate endometrium

human chorionic gonadotropin (hCG)

• secreted by trophoblast cells, later becomes chorion

• prompts corpus luteum to continue secretion of progesterone n estrogen

• hCG levels rise until the end of second month, then declines as placenta begin secrete progesterone n estrogen

  • hCG levels r used in pregnancy tests

placenta formation

• from embryonic n maternal tissues

  • embryonic tissue - chorion (develop from inner cell mass)

  • maternal tissue - decidua basalis

mom + baby blood supply

• lie close but don’t intermix

development of circulation

• first blood cells arise in yolk sac

• end of third week

  • embryo has system of paired vessels

  • can hear baby heartbeat

what carries o2 from placenta to baby

• blood vessel carrying o2 from placenta to baby is umbilical vein

unique vascular modifications

• umbilical arteries carry deoxygenated blood

• umbilical veins carry oxygenated vein

teratogens

• harmful substances that can cross placental barriers

• enters fetal blood n cause congenital abnormalities or death

extraembryonic membranes

• amnion

• yolk sac

• allantois

• chorion

• all formed within first 2-3 weeks of development

amnion

• forms amniotic sac

yolk sac

• forms part of digestive tube

allantois

• umbilical cord

chorion

• helps form placenta

embryogenesis

• gastrula → fetus = gastrulation

• implantation: blastocyte convert to gastrula

• inner cell mass become embryonic disc

• 3 primary germ layers n extraembryonic membranes develop (week 3)

embryonic disc subdivision

• into epiblast n hypoblast

gastrulation

• embryonic disc (2 layers) become 3-layered embryo

  • ectoderm, mesoderm, endoderm

• primitive streak (dorsal groove) appears

• notochord

  • mesodermal cells

  • form axial support

ectoderm germ layer

• external layer

• NS n skin epidermis

ectoderm specialization

• neurulation

  • first major event of organogenesis

  • give rise to brain n spinal cord

  • neural plates fold inward as neural groove n fuse into neural tube

  • neural crest cells

neural crest cells

• cranial

• spinal

• sympathetic ganglia

• adrenal medulla

endoderm

• epithelial linings of digestive, respiratory, urogenital systems

epithelia

• endoderm + ectoderm

mesoderm

• forms

  • notochord

  • somite

  • intermediate mesoderm

  • lateral plate mesoderm

    • somatic mesoderm

    • splanchnic mesoderm

notochord

• nucleus pulposus of intervertebral disc

somite

• sclerotome - vertebrae n ribs

• dermatome - dermis of dorsal body region

• myotome - trunk n limb musculature

intermediate mesoderm

• kidneys

• gonads

lateral plate mesoderm - somatic mesoderm

• parietal serosa

• dermis of ventral body region

• CT of limbs (bones, joints, ligaments)

lateral plate mesoderm - splanchnic mesoderm

• wall of digestive n respiratory tracts (except epithelial lining)

• visceral serosa

• heart

• blood vessels

anencephaly

• no brain produced

• nonviable for life

organogenesis

• formation of body organs n systems

• week 8:

  • all organ systems r present, but not fully functional

  • end of embryonic period - embryo become fetus

fetal development

• time of rapid growth of body structures established in the embryo

• occurs from week 9 thru birth

adjustments to pregnancy

• relaxin (placenta) causes pelvic ligaments n pubic symphysis to relax to ease birth passage

• reproductive organs become engorged with blood

• increase in lordosis

• uterus expands, occupying most of abdominal cavity

adjustments to pregnancy - GI tract

• morning sickness due to elevated estrogen n progesterone levels

adjustments to pregnancy - urinary system

• more urine made due to increased metabolism n fetal wastes

• stress incontinence

adjustments to pregnancy - respiratory system

• tidal volume increase

• dyspnea may occur later in pregnancy

adjustments to pregnancy - CV system

• blood volume increase 25-40%

• BP n pulse rise

• venous return from lower limbs may be impaired

initiation of labor

• last few weeks of preg

  • fetal secretion of cortisol stimulates placenta to secrete more estrogen

• surfactant protein A

  • from fetal lungs, causes cervix softening

• fetal oxytocin

  • placenta makes prostaglandins

• maternal emotional n physical stress

  • activates hypothalamus, cause oxytocin release → powerful uterine contraction

• pos feedback mechanism

more estrogen in preg

• causes production of oxytocin receptors

  • assists w smooth birth

• antagonizes calming effects of progesterone

  • braxton hicks contractions (weak irregular contractions) in uterus - false labor

parturition

• act of giving birth

  • expel infant from uterus

stages of labor

• dilation - longest stage (6-12+ hrs)

• expulsion - 30 mins

• placental - afterbirth - 30 mins later

dilation stage

• initial weak contractions

  • 15-30 mins apart, 10-30 secs long

  • gets more vigorous n rapid

• cervix dilates to 10cm

• amnion ruptures, releasing amniotic fluid - water breaking

• engagement occurs

  • head enters true pelvis

pelvis

• true pelvis - where baby exits

• false pelvis - made by iliac crest

  • baby go from false to true pelvis

early dilation

• baby head sideways to pass thru true pelvis

late dilation

• baby head rotate posteriorly once past true pelvis

expulsion stage

• contractions every 2-3 mins, 1 min long

• want to push (absence of local anesthesia)

• crowning occurs when largest dimension of head distends vulva

• 30-50 mins

• end: infant delivered

placental stage

• more strong contractions → placenta detaches

• delivery of afterbirth (placenta n membranes) occurs 30 mins after birth

• all placenta fragments must be removed to prevent postpartum bleeding

placenta previa

• placenta form low in uterus, adjacent to and/or covering cervix

placental abruption

• placenta separates from uterus wall before birth

first breath

• increase co2 → central acidosis → stimulates respiratory control centers to trigger first inspiration

  • surfactant in alveolar fluids help reduce surface tension

• respiratory rate - abt 45 breaths per min for first 2 weeks, then declines

  • premies usually put on respirators, lungs immature

neonatal period

• 4 week period immediately after birth

newborn’s physical status

• assessed 1 n 5 mins after birth using APGAR score

  • appearance - skin color

  • pulse rate

  • grimace - reflex response

  • activity - mm tone

  • respiration

• APGAR score

  • 0-3 - critically low

  • 4-6 - fairly low

  • 7-10 - normal/healthy

lactation

• make milk thru mammary glands

  • anterior pituitary release prolactin

• oxytocin causes letdown reflex → actual ejection of milk from mammary glands

colostrum

• yellowish secretion rich in vit A, protein, minerals, IgA antibodies

• released first 2-3 days