Lecture 14: Typical Development

What are the stages of birth

conception

germinal stage

embryonic stage

fetal stage

birth

When does fertilization occur

when a single sperm penetrates the outer layer of an egg (ovum)

What is created during fertilization and what does it begin

single-cell zygote, which begins the process of mitosis

How many chromosomes does the zygote contain

23 pairs (46 total)

23 from each parent

How many pairs are autosomes vs sex chromosomes

22 pairs of autosomes

1 pair of sex chromosomes

What are the autosome chromosomes responsible for

determining most individual traits

Biological sex presentation female v. male

XX= female

XY= male

What do chromosomes carry

genetic info

What are genes

segments of DNA that code for specific proteins

-functional units of herdity

What are the proteins responsible for

regulating cell activities

growth

development

heredity

What are the 3 functions of chromosomes

facilitate cell division

preserve genetic stability

telomere function

How do chromosomes facilitate cell division

during mitosis (somatic cell division) and meiosis (formation of gametes) chromosomes ensure accurate distribution of genetic material

How do chromosomes preserve genetic stability

maintain the integrity of genetic material across generations

How do chromosomes contribute to telomere function

telomeres prevent chromosomes from deteriorating or fusing with one another, preserving cell stability

aneuplodiy

abnormal number of chromosomes

Causes of aneuploidy

nondisjunction: failure of chromosomes to separeate during meiosis or mitosis

genetic mutations: maternal age may be a RF

types of aneuplodiy

monosomy

trisomy

tetrasomy

pentasomy

nullisomy

What is monosomy? Can they survive?

one chromosome is missing from a pair

-usually not viable for life if occurs on an autosome

-some sex monosomies are viable

Turner syndrome

one X chromosome

What is Trisomy? What does severity depend on

extra copy of a chromosome

-severity depends on the specific chromosome that is affected

Trisomy 21

down syndrome

When is trisomy less likely to be viable

when larger chromosomes are involved

Tetrasomy/Pentasomy

conditions where there are two or more extra copies of a single chromosome

How prevalent is tetrasomy/pentasomy? Survive? Example?

rare and usually not viable

-tetrasomy X (48, XXXX)

-fewer than 1000 ppl in US have tetrasomy

nullisomy? survive?

entire pair of homologous chromosomes is missing

-non-viable

deletions

port of the chromosome is missing/deleted

duplications

portion of the chromosome is duplicated, resulting in extra genetic material

translocations

portion of one chromosome is transferred to another chromosome

inversions

port of the chromosome has broken off, turned upside down, and reattached

-genetic material is inverted

rings

portion of a chromosome has broken off and formed a circle or ring

-can happen with or without loss of genetic material

What are the effects of chromosomal abnormalities

may not have any s/s

incompatible with life

developmental delays

physical malformations

reporductive issues

Why might someone not have any s/s with chromosomal abnormalities

redundancy in genetic material

region of the DNA is not used

What may happen if a chromosomal abnormality is not compatible with life

miscarriage/spontaneous abortion

termination of pregnancy

What might the physical malformations be with a chromosomal abnormality

structural abnormalities in organs, skeleton or facial features

-heart is commonly affected

When is the germinal stage? What happens?

weeks 1 and 2

-zygote development

-blastocyte formation

-inplantation

How long after fertilization does the zygote begin mitosis

within hours

When does blastocyte formation occur? What are the 2 parts of a blastocyte

by day 5

-inner cell mass: develops into embryo

-trophoblast: forms placenta

When does implatation occur

day 6-10 blastocyte attaches to endometrium

What is the embyronic disk developed from? What are the 2 layers

inner cell mass (which will become the embyro)

-endoderm and ectoderm

When is gastrulation

weeks 3-8

What happens during gastrulation

inner cell mass reorganizes into 3 layers

-ectoderm

-mesoderm

-endoderm

What does the ectoderm become

nervous system (brain, SC, nerves)

epidermis

hair/nails

What does the mesoderm form

muscles

circulatory system

bones

kidneys

reproductive organs

connective tissue

What does the endoderm become

digestive system

respiratory system

liver pancreas

other internal organs

What does gastrulation establish

body-axis formation

-anterior-posterior

-dorsal-ventral

-left-right

What does gastrulation define and initiate

defines where each organ system will form and the spatial organization of the tissue

initiation of organogenesis

What forms during the embyronic stage? What does that become

neural plate and tube

-becomes the CNS

What is neurulation and when does it occur

formation of neural tube

weeks 3-4

What forms the neural plate and how does it become the neural tube

ectoderm forms neural plate which folds into neural tube

How is the PNS formed

neural crest cells migrate from the neural tube

When is the CNS most susceptible to major malformation/defects

between 3-4 weeks (neural tube foramtion)

-neural tube fails to close properly resulting in SC, brain and surrounding structure deficits (spina bifida

Causes/risks for neural tube deficits

genetics and chromosomal abnormalities

folic acid deficiency

materal factors: obesity, diabetes, increased maternal age, hyperthermia

certain medications (anticonvulsants, methotrexate)

When does brain region development begin

week 4

What are the brain regions developed

forebrain, midbrain, hindbrain

What develops within the forebrain

diencephalon becomes the thalamus, hypothalamus, 3rd ventricle

telencephalon becomes the cerebral hemispheres, basal ganglia, cerebral cortex, lateral ventricles

What does the midbrain become

midbrain, cerebral aqueduct

What does the hindbrain become

metencephalon- pons, upper medulla, cerebellum, 4th ventricle

myelencephalon- lower medulla

When does cardiac development occur

weeks 4-8

Explain heart development

heart begins to form as a simple tube

cardiac looping: heart tube folds and twists into an S shape

septation: partitioning divides heart into 4 chambers

heart spontaneously beats by day 23

What happens if there is disruption to cardiac development process

congenital heart defects

When is the fetal stage? What are the substages

weeks 9-birth

early fetal development: first trimester wks 9-12

second trimester wks 13-24

third trimester wks 25-40

What happens during early fetal development

expansion of brain structures

basic reflexes (sucking/grasping)

neuronal proliferation

What is neuronal proliferation? When is peak

rapid production of neurons

-peak occurs between 8 and 12 wks

What can disruptions in proliferations lead to

microcephaly (small brain)

megalocephaly (big brain_

What occurs during the second trimester

growth and movement

-fetus grows significantly

-movement of fetus can be felt by mother (around wk 16)

skin and hair

-lanugo (fine hair) and vernix caseosa (waxy coating) form to protect skin

sensory development

-hearing develops around wk 18

eyes are sensitive to light

When can spontaneous muscle contractions of the fetus occur

7 wks gestation

What is the significance of movement in the fetus

development of muscles and joints

When does viability occur

week 24

lungs and other systems are developed enough that the fetus may survive outside of the womb with intensive medical care

What are the neural organization processes that occur during the third trimester

synaptogenesis: formation of synapes, enables communication between neurons

pruning: excess neurons and synapses are eliminated, enhancing the efficiency of neural networks

circuit formation: neurons form organized circuits for sensory processing, motor control, and cognitive functions

When does myelination occur? explain process

third trimester- wk 28 to birth

-begins at SC and spreads to brainstem and CNs

-at birth essential structures for survival are myelinatied

-postnatal myelination continues in the cerebral cortex (especially in areas responsible for higher order cognitive function)

What happens in the third trimester

rapid weight gain- fat added for insulation and energy storage

lung maturation (weeks 34-36)- adequate levels of surfactant

week 36: fetus moves into a head down position

What happens if a baby is born before wk 34-26 in terms of lung maturation

high risk of Respiratory Distress Syndrome due to not having enough surfactant

What happens if the baby doesn't move into a head-down position

breech postion may require c-section and is associated with hip dysplagia

What are the maternal changes associated with birth

hormone release

-oxytocin: stimulates contractions

-relaxin: loosens pelvic ligaments

cervix thins (effacement) and opens (dilation) to prepare for labor

What is considered a full term birth

37 weeks 0 days- 41 weeks 6 days

Full term baby size

6-9 pounds

19-21 inches

Full term baby development features

lung development: fully developed with sufficient surfactant

organ function: all major organ systems are functioning

fat stores: subcutaneous fat, helps regulate body temp

motor systems: allow newborn to exhibit basic movements, reflexes, and responses critical for survival

-hypotonia

-spontaneous limb mvts

-physiologic flexion

brain development: approximately 1/3 adult size

-growth continues after birth

What limits fine motor control and coordinated voluntary movements in newborns

corticospinal tracts are not fully myelinated

anterior vs posterior fontanelles closing

anterior closes between 18mo-2yrs

posterior closes during first several months of life

cranisynostosis

sutures close before brain is done growing

-requires surgery

infant motor behaviors

general movements

reflexes

Describe the 2 distinct stages of general movements

-distinct and spontaneous general movements from before birth to 20 wks post term

writhing movements: begin during 1st trimester and continues until 5 wks post term

-variable sequence of neck, arm, trunk, leg

-wax and wane

-vary in intesnity, speed and ROM

-gradual onset and end

fidgety movements: begin 6-9 wks post term (after writhing movements gradually disappear)

-tiny movements of neck, trunk, limbs

-moving in all directions

-variable acceleration

Prechtl Qualitative Assessment of General Movements

baby is placed in supine and assessor watches spontaneous movements of baby

-uses a Gestault approach to determine whether the movements are normal or abnormal for the baby at their gestational age

-provides info about NS

-need to be trained and certified to perform

What can the prechtl qualitative assessment of general movements predict

cerebral palsy

primitive reflexes

present at birth

-obligatory movements, not voluntarily controlled

What does it mean that reflexes have different periods of integration

should no longer be present during mvt

-abn persistence of reflexes may interfere with normal mvt development

-anb persistence may indicate neurological impairment

premature birth categories

late pre-term: 34-36 wks

moderate pre-term: 32-34 wks

very pre-term: 28-32 wks (requires intensive medical care and have significant risk for complications)

extremely pre-term: 24-28 wks (long-term complications are very likely

Complications of pre-term birth

lung immaturity and low surfactant: respiratory distress syndomr and bronchopulmonary displasia d/t prolonged O2 therapy

patent ductus arteriosus: failure of ductus arteriosus to close

risk of hypotension and circulatory issues

intraventricular hemorrhage

long-term developmental disorders

delayed myelination and immature neural circuits

feeding difficulties due to inability to suck and swallow effectively

weakened immune system and highly susceptible to infections

limited fat stores and immature skin can increase risk for hypothermia

low birth weight categories

low birth weight: <5lb, 8oz

very low: <3lb, 5 oz

extremely low: <2lb, 3 oz

Risk factors of low birth weight

premature birth

intrauterine growth restriction

materal factors: poor maternal nutrition, smoking, alcohol, drug use, chronic health conditions (HTN, diabetes), infections (TORCH infections)

multiple pregnancies

What are TORCH infections

toxoplasmosis

other (syphilis)

Rubella

cytomegolovirus

herpes

What is considered a post term birth

>42 weeks gestation

Risks to baby for post-term birth

macrosomia: risk of trauma at birth from large baby

placental insufficiency: not delivering enough O2 or nutrients ot baby

meconium aspiration syndrome: first stool is inhaled, leading to difficulty breathing

oligohydramnios (low amnotic fluid): umbilical cord compression and fetal distress

still birth

Typical development is what?

predictable, sequential, but uneven

-mvts may be initially random or accidental

-timing of motor milestones vary

-culture and environment are important to consider

What are the things to consider the generality of during typical devleopemnt

cephalocaudal (head control first)

proximal to distal: trunk before fine motor control

reflexive to voluntary

0-2 months motor milestone

turns head side to side, briefly lifts head in tummy time

3-4 months motor milestone

good head control

pushes up on forearms, rolls

5-6 months motor milestone

rolls both ways, sits with support then independently

7-8 months motor milestones

sits well, move in and out of sitting, begins crawling

9-10 months motor milestone

crawls well, pulls to stand, cruises along furniture