Ch 5 Conception & Fetal Devlopment

fertilization

• fusion of ova and sperm

• start of pregnancy

• occurs 2wks after last menstrual period

• sperm deterrents in uterus

sperm deterrents

• at cervix, inside, etc

  • only a few cells make it in fallopian tubes, even less to egg → 1 makes it in!

ovulation

• about 2 wks into menstural cycle

menstural cycle

• 30 days

implantation

• usually occurs in upper uterus

  • best resources!

• usually occurs 6-10 days after conception

• spotting common, can be confused w/ period

• pregnancy has not occured until sucessful implantation

upper uterus & implantation

• ideal place

• good fetal gas, nutrition, and waste exchange/elimination

  • bc of lots of big vessels!

• thick lining

  • prevents placenta from attaching too deeply

  • limits blood loss after birth

• typically placenta dysfxn w/ implantation elsewhere

amennorrhea

• typically from pregnancy hormones

implant site

where placenta forms

human development stages

• zygotic

• blastocyst

• embryonic

• fetal

zygotic stage

• fertilization of sperm+egg thru 2nd week

• some cell division

blastocyst stage

• zygote divides into solid ball of cells

  • attaches to uterus

• a cellular formation!

embryonic stage

• major organs & structures begin to emergy

• by end of 2nd wk → 8th wk

fetal stage

• 8th wk → birth

• diffentiation

• structures specialize

why gestational development knoweldge is important

• don’t know! lifestyle changes not made

  • ie: alcohol, drug use

• whats developed during preterm labor?

  • respiratory support needed?

• life viability

crown-rump length

• fetal length from head to butt

• CRL

3wk CRL

• 1.5mm

3wk nervous/sensory system

• flat neural plate begins to close to form neural tube

• neural tube still open at each end

3wk cardiorespiratory system

• heart consists of 2 parallel tubes that fuse into 1

• contractions of heart tube begin

• chorionic villi of early placenta connect w/ heart

3wk digestive system

• endoderm will become digestive tract

  • inner germ layer

3wk musculoskeletal system

• somites

  • paired, cube-shaped swellings

  • appear & form most of head & trunk skeleton

• muscle, bone, & cartilage develop from mesoderm

wk 3 integumentary system

• paired, cube-shaped swellings (somites)

• epidermis develops from ectoderm (outer germ layer)

• dermis & connective tissue form from mesoderm (middle germ layer)

4wk CRL

• 4mm

4wk nervous/sensory system

• nerual tube closed at each end

  • cranial end of neural tube makes brain

  • caudal end makes spinal cord

• eye development starts as outgrowth of forebrain

• nose development begins as 2 pits

• inner ears begin developing from hindbrain

4wk cardiorespiratory system

• heart begins partitioning into 4 chambers

  • starts beating!

• blood circulares thru embryonic vessels & chorionic villi

• tracheal development begins as bud on upper guts & branches to 2 bronchial buds

4wk digestive system

• development of primitive guts as embryo folds laterally

• stomach begins as widening of tube-shaped primitive gut

• liver, gallbladder, & biliary ducts begin as a bud from primitive gut

4wk genitourinary system

• primordial germ (reproductive) cells present on embyronic yolk sac

4wk musculoskeletal system

• upper limb buds are present and look like flippers

• lower limb buds appear

4wk integumentary system

• mammary ridges that develop into mammary glands appear

6wk CRL

• 13mm

6wk nervous/sensory system

• development of pituitary gland & cranial nerves

• head sharply flexed bc of reapid brain growth

• eyelid development beginning

• external ear development begins in neck reigon as 6 swellings

6wk cardiorespiratory system

• blood formation primarily in liver

• 3 R & 2 L lung lobes develop as outgrowths of R & L bronchi

• paritioning of heart into 4 chambers completed

6wk digestive system

• most intestines contained within the umbilical cord bc liver & kidneys occupy most of abd cavity

• stomach nearing final form

• development of upper & lower jaws

6wk genitourinary system

• kidneys near bladder in pelvis

  • occupy much of abd cavity

• primordial germ cells incorporated into developing gonads

• male & female gonads identical in appearance

6wk musculoskeletal system

• arms paddle shaped, fibers webbed

  • feet & toes similar, but a few days later

• bones cartilaginous but skull ossification begins

6wk integumenary system

• mammary glands begin development

• tooth buds for primary teeth begin developing

8wk CRL

• 30mm CRL

8wk nervous/sensory system

• spinal cord stops at end of vertebral column

• taste buds begin developing

• eyelids fuse

• ears have final form, but are low set

8wk cardiorespiratory system

• heart partitioned into 4 chambers

• heartbeat detectable w/ ultrasound

• additional branching of bronchi

8wk digestive system

• stomach reached final form

• intestines remain in umbulical cord

• lips fused

8wk genitourinary system

• testes begin developing under Y chromosome influence

  • ovaries develop if absent

• external genitalia begin to differentiate, but still appear quite similar

8wk musculoskeletal system

• bones begin to ossify

• joints resemble those of adults

• fingers & toes still webbed but distinct by end of wk 8

8wk integumentary system

• auricles of ears low-set but beginning to assume final shape

10wk CRL

• 61mm

• weight - 14g

10wk nervous/sensory system

• head flexion still present, but straighter

• eyelids closed & fused

• top of external ear slightly below eye level

10wk cardiorespiratory system

• may be possible to detect heartbeat w/ doppler

• blood produced in spleen & lymphatic tissue

10wk digestive system

• intestines contained within abd cavity as growth of cavity catches up w/ system development

• digestive tract patent from mouth to anus

10wk genitourinary system

• kidneys in adult position

• male & female external genitalia have diff appearances, but still easily confused

10wk musculoskeletal system

• toes distinct

• soles face e/o

10wk integumentary system

• fingernails begin development

• tooth buds for permanent teeth being developing far behind primary teeth

12wk CRL

• 87mm

• weight - 45g

12wk nervous/sensory system

• surface of brain is smooth

  • no sulci (grooves) or gyri (bumps)

• nasal septum & palate complete development

12wk cardiorespiratory system

• heartbeat should be detected with doppler transducer

12wk digestive system

• suckling reflex present

• bile formed by liver

12wk gentiourinary system

• kidneys start producing urine

• male & female external genitalia can be distinguished by appearance

12wk musculoskeletal system

• limbs are long & thin

• involuntary muscles of viscera develop

12wk integumentary system

• downy lanugo begins developing at end of week

28wks nervous/sensory system

• major sulci & gyri are present

• eyelids no longer fused after 26wks

• responds to bitter substances on tongue

28wks cardiorespiratory system

• erythrocyte formation completely in bone marrow

• sufficient alveoli, surfactant, & capillary network to allow respiratory fxn

  • respiratory distress syndrome still common

• most born at this time survive w/ intensive care

28wks gentiourinary system

• testes descended through inguinal canal into scrotum by end of wk 26

28wks integumentary system

• skin slightly wrinkled by smoothing out as SQ tissue is deposited under it

28wks CRL

• 270mm

• weight - 1300g

32 wks nervous/sensory system

• maturation of parasympathetic nears that of sympathetic

  • fetal heart variability on electronic fetal monitor tracing

32 wks cardiorespiratory system

• surfactant production nears mature levels

• respiratory distress still possible

• fetal HR variability gradually increases toward full term

32 wks integumentary system

• skin smooth & pigmented

• large vessels visible underneath skin

• lanugo disappearing

32 wks CRL

• 300mm

• weight - 2100g

38 wks CRL

• 360mm

• weight - 3400g

38 wks nervous/sensory system

• sulci & gyri developed

• visual acuity ~ 20/600 at birth

38 wks cardiopulmonary system

• newborn infant has ~ 1/8-1/6 the amt of alveoli an adult has

• well-developed ability to exchage gas

teratogens

• smth that causes birth defects/abnormalities in a developing embryo/fetus

  • pregnancy problems

  • esp bad when pregnancy not known

• exposure thru envrionment/ingestion

• lots of meds

teratogen ex

• cigarette smoking

• BPA

• caffeine

• chickenpox

• cocaine

• coumarin anticoagulants

• cytomegalovirus

• ethanol (>1 drink/day)

• hyperthermia

• iodides

• ionizing radiation (>10 rads)

• lead

• lithium

• methotrexate

• parovirus B19

• rubella

• syphyllis

• tetracycline

• thalidomide

• toxoplasmosis

• valproic acid

• varicella

cigarettes & teratogens

• cause vasoconstiction of placenta vessels

• cause BP issues in mom

• altered oxygenation to baby

ionizing radiation & teratogens

• >10 rads

• x-rays

  • esp early on ! affects bone growth

methotrexate & teratogens

• cause abortions

• typically an autoimmune drug

non-teratogenic agents

• spermicides

• acetaminophen

• prenatal vitamins

alcohol & teratogens

• affects CNS

chickenpox & teratogens

• rare but serious defect - congenital varicella syndrome

• can also cause neonatal varicella

BPA & teratogens

• in plastics sometimes

• potentially teratogenic in last trimester

caffeine & teratogens

• limit intake to 200mg/day

teratogens 10-14 days

• begin affecting embryo development

teratogens 3.5-4.5 wks

• exposure can cause neural tube defects

teratogens first 20wks

• chickenpox & congenital varicella syndrome

umbillical cord

• formed from amnion when placenta is forming at end of 2nd wk

  • connect thru placenta to fetus

• lifeline btwn mother & fetus

• covered in wharton’s jelly for protection

• 1 large vein, 2 small arteries

• like a phone cord

whartons jelly

• protects umbilical cord

  • from compression mainly

umbilical cord blood flow

• 1 large vein

  • carries oxygenated blood to fetus

• 2 small arteries

  • carries deoxygenated blood out

• reverse ppl (arteries big, veins small)

• flow soooo important

placenta

• interface btwn mother & fetus

  • super impressive!

• makes hormones to control mom physiology to supply fetus

  • mom - O2 & nutrients! → fetus

  • mom’s homeostasis has to be intact to fxn right

• removes waste from fetus → mom

placenta hormones

• needed for normal, healthy pregnancy

  • chorionic gonadotropin

  • prolactin

  • estrogen

  • progesterone

  • HCS

  • relaxin

amniotic sac

• amnion

  • inner layer

  • from ectoderm germ layer during early stages

  • expands to touch chorion w/ growth

• chorion

  • outer layer

• thin protective membrane that contains fluid

amniotic fluid

• increases as pregnancy progresses

  • made by mom’s body as it acknowledges pregnancy

  • fetus makes later on - GI/renal system

    • fetus eats & excretes

• prevents hit damage

• keeps baby bouyant

• maintains temp

• 1L full sized

• saltyyy..

umbilical vein

• carries oxygenated blood & nutrients to baby!

  • carries blood to baby’s heart

fetal circulation

• diff from newborns!

• 3 shunts

  • carry blood away from nonfxning areas in fetus

    • ie: lungs, liver

fetal circulation shunts

• ductus arteriosus

• foramen ovale

• ductus venosus

fetal circulation path

1. blood arrives via umbilical vein

2. ductus venosus shunts oxygenated blood from placenta away from semifxnal liver to heart

3. oxygenated blood from placenta enters R atrium via inferior vena cava

4. foramen ovale allows oxygenated blood in R atrium to reach L atrium

5. ductus arteriosus connects aorta w/ pulmonary artery further shunting blood away from lungs into aorta

6. mixed blood travels to head & body → back to placenta via aorta

   1. thru internal iliac arteries → umbilical arteries → mom

ductus arteriosus

• connects aorta w/ pulmonary artery

• shints blood away from lungs into aorta to circulation

foramen ovale

• allows oxygenated blood in R atrium to get to L atrium

  • R atrium more pressure

• like a doorway - opens & closes w/ R heart pressure

  • one way!

fetal lungs

• filled w/ fluid

• high pressure fluid system!

  • esp high in pulmonary trunk, RV, & RA

• RA fluid (bc of pressure) shunts thru foramen ovale

  • some blood still gets in reroute to aorta via ductus arteriosus !

• lungs still need a lil O2 to keep developing

ductus venosus

• shunts oxygenated vlood from placenta away from liver → heart (IVC)

fetal inferior vena cava

• carries deoxygenated blood from organs & tissues at bottom of the developing fetus

• mixes w/ ductus venosus oxygenated blood - partially oxygenated

  • superior vena cava blood comes in → even less oxygenated → heart RA

oligohydramnios

• bad

• abnormally low amt of amniotic fluid

  • <50% expected for gestational age/<400mL at term

• can be associated w/ congenital anomalies r/t kidney fxn

oligohydramnios factors

• poor placental blood flow

• low birth weight infants

• failure of fetal kidney development

• blocked urinary excretion

• poor fetal lung development

polyhydramnios

• bad

• abnormally high amt of amniotic fluid

  • may exceed 2000mL