Week 1 - Development BV + Paediatric

What are the 3 stages of embryology?

> Germinal period

> Embryonic period

> Foetal period

when does conception begin?

> when a sperm fertilises an egg to create a zygote

what is the name of the ball of cells when a zygote starts to divide?

- morula

> (the zygote divides into morula as it travels down the fallopian tube )

What does the morula separate into

- two distinct groups of cells

- outer cell mass + inner cell mass --> embryoblast which goes on to become a baby

How many cells does the embryo consist of around day 5 or 6 after fertilisation?

> ~100 cells and is known as a 'blastocyst'

> this goes on to implant into uterine wall around day 6-10

what period are the first 2 weeks referred to as ?

The Germinal period

What is the period from 2-8 weeks after fertilisation referred to as?

> embryonic period

> at this point foetus highly vulnerable to developmental errors

From what day of gestation is the first evidence of the eye being formed?

> 22 days of gestation in human embryo

What can happen at this early stage of development (22 days)?

> Abnormalities can lead to anopthalmos (no eye)

> & micropthalmos (an underdeveloped eye)

what is the structure of a blastocyst?

> outer cell mass (trophoblast) on the outside

> inner cell mass --> embryoblast (part that becomes baby)

What happens at around day 14 to the embryoblast?

> embryoblast starts to differentiate into 2 distinct structures :

> epiblast + hypoblast

> 2 layered disc

Describe the gastrulation process

> cells from epiblast migrate downwards through opening/ridge known as primitive streak

> process of 'gastrulation' dislodges the hypoblast downwards + ends up with creation of 3 distinct layers

2 layers---> 3 layers

what is the structure of the primitive streak?

> Ridge at top

> cells from top layer go through ridge and fold in on themselves to create 3rd layer

describe the 4 steps of gastrulation

> cells of inner cell mass begin to differentiate as amnion forms

> gastrula develops when cells begin to migrate inward, forming an indentation

> cells continue to push inward, forming ends-derm

> cells remaining on outer surface of gastrula are ectoderm

> mesoderm formed, as additional cells migrate inward between endoderm and ectoderm

what does the ectoderm become ?

> outer layer of skin

> hair

> lining of nose + mouth

> nervous system

> brain

> eyes

what does the endoderm become?

> digestive tract

> respiratory tract

> liver

> pancreas

What does the mesoderm become?

> Muscles + skeleton

> gonads

>kidneys

> heart

> blood vessels

what happens at day 16

> Trilaminar germ disc with ectoderm, mesoderm and endoderm forms

- entirety of baby formed from these 3 layers

Describe neural tube formation

> ectoderm begins to fold in on itself + when two edges meet they pinch off to form a tube with a separate layer above it

> neural tube destined to become brain + spinal cord

> initially tube has an opening at each end

what is the role of the notochord in neural tube formation?

> located in mesoderm and sets off process to form neural tube

> cells above notochord form wavy bumpy areas

> flat sheet of cells become m shape , tip of cells join and tube pinches off, cells at top rejoin together

describe the closure of the neural tube

> neural ectoderm rolling up to form a tube (will become brain)

> at anterior end of neural tube 2 small regions called 'eye fields'

> small bulges in eye fields begin to protrude + extend (whilst rest of tube seals)

--> called optic grooves

> rest of tube continues to develop into primitive brain

what can failure of the neural tube to close result in?

> conditions such as spina bifida (gap in spine)

> or anencephaly

what is the neural tube surrounded by?

> a layer of ectoderm, and as neural tube closes its encased by ectoderm

what happens to the optic grooves when they extend?

> they become optic vesicles

(beginning of eye)

- optic vesicles start to extend and grow

what happens around day 27/28?

- optic vesicles make contact with surface ectoderm surrounding them

- this triggers it to thicken and form lens placode

- this folding inward beigins formation of 2-layered optic cup

region at top --> primitive brain - extensions become our eyes

what happens to the lens placode after?

> starts to migrate inwards, eventually pinching off (creating double layer of cells) + sitting in mouth of optic cup

what does the hyaloid artery do?

> emerges beneath optic vesicle + a fissure (choroidal fissure) opens up to allow it to enter the eye

> this supplies the developing lens with nutrients

how are the neural retina and RPE formed ?

> from folding - invagination of optic cup

> resulting in 2 layers of tissue which are not physically attached

> this explains how its possible to get retinal detachment in some people

what occurs by week 6 of the eye forming?

- choroidal fissure begins to close, sealing hyaloid vessel + primitive vitreous into eye

- only place fissure doesn't completely close is at anterior end , where hole forms the pupil

What does failure of the choroidal fissure to close result in?

- abnormality called a coloboma

what does surface ectoderm (where lens placed originated) become?

> becomes cornea, conjunctiva and eyelids

> same ivagination process as formation of lens, without pinching off

what happens to retina + hyaloid artery?

> retina (now in several layers) will continue to develop and specialise

> hyaloid artery eventually degenerates and disappears leaving optically clear media

why are mesenchymal cells important?

> able to turn into anything

> help develop iris, sclera + cornea etc

> help develop extra ocular muscles , cranial nerves

how long do eyelids remain fused closed until?

> 28 weeks of pregnancy to protect developing cornea

formation of eye

> in 5th-7th weeks of gestation hollow lens starts to fill with fibres and by day 45 lens is solid

> small dense collections of tissue formed from mesoderm and neural crest cells (mesenchyme) appear between 26-29 days and become extra ocular muscles

> cranial nerves (3,4 and 6) grow from primitive brain into these tissues around days 31-33

> cornea forms from surface ectoderm + neural crest cells,+ 5 distinct layers visible by week 8

> sclera + choroid formed from mesenchyme start to condense into two layers surrounding primitive retina

what is the axial length, diameter of crystalline lens and optical power of cornea in a newborn eye?

> axial length ~16.5mm increasing to ~21mm by 3 years and 24mm in adulthood

> crystalline lens grows from ~6mm in diameter at birth to ~9.3mm by 16 years old

> At birth optical power of cornea 50D, which is greater than that of an adult

what are the stages of childhood?

- Prenatal (conception to birth)

- Neonatal (newborns) --> 0 to 8 weeks

- infancy : 8 weeks to 12 months

- Toddlers : 12 to 36 months

- preschool - 3 years starting to school

- key stage 1 -4/5 years to 7/8 years

- key stage 2 - 7/8 years onward

When is full term pregnancy considered and premature?

> 37-40 weeks, dated from mothers last period

> babies born before 37 weeks considered premature

> babies born very prematurely and/or with extremely low birth weight tend to be disadvantages in terms of IQ, motor performance, visual-motor integration and academic ability

statistics of premature babies

- 1/3 children born before 32 weeks have SEN

> prevalence of cerebral palsy as high as 15% in babies born between 24-27 weeks of pregnancy

> very premature babies at risk of retinopathy of prematurity and higher prevalence of strabismus (~10-30%), reduced VA (~40%) and reduced stereocauity (-36%)

What is the role of a health visitor

> baby assigned health visitor + red book which charts their development + vaccination history

> undergo no of assessments in first few weeks to screen them for developmental or congenital disorders

what is the supervision aimed to do ?

> supervision aimed to monitor growth, assessments in hearing + language, checking dentition, nutrition, offering help to parents

> goal to lower rates of child mortality, disability and morbidity, promote optimum growth + development to help children maximise their potential

what areas can we divide developmental milestones into ?

- physical

- cognitive

- social/emotional

The newborn (0-8 weeks)

> normal birth weight varies from ~2500g TO 4500g

> spend a lot of time sleeping

> start to recognise own parents - mothers voice

> like looking at faces

> responds to sounds

> demonstrate anticipatory behaviours (rooting)

- at this age minimal difference between typically developing baby and a baby with learning disability

what are early reflexes of newborns?

> primitive reflexes provide newborn with actions to aid their survival

- e.g sucking to find food)

> help brain to develop neural pathways for coordinated movement later in development

- eventually replaced with voluntary movement

what are the names of the early reflexes?

> palmar grasp reflex - marked repose from birth to 4 months + then diminishes

- poor/no response indicative of neurological abnormality (including cerebral palsy)

> stepping reflex : present from birth to 2-3 months

- preterm babies can demonstrate a dif pattern of walking

what are the physical milestones of an infant (2-3 months)

> start to support own head, raise head when lying on stomach

> open + close hands, bring hands to mouth

> swipe at dangling objects

what are the social milestones of an infant ,2-3months?

> use facial expressions

> cry when hungry/tired/wanting comfort

if no enjoyable eye contact noted by 8 weeks the baby should be referred for an assessment of vision

what are cognitive milestones for infants: 2-3 months

> focus on moving objects

> follow a person with their eyes

> turn towards a voice/sound

> enjoy looking at faces (25% of their time)

what are the physical milestones of a 3-6 month infant

> learns to roll , can grasp feet with hands

> can support own weight on legs (when held)

> grasp toys, shake toys

> start to sit up with support

cognitive milestones 3-6 months

> repeats sounds back to you and makes sounds like 'da', 'ba' or ga'

> recognise familiar faces

social/emotional milestones infant : 3-6 months

> laughs

> imitate facial expressions

physical milestones infant: 6-12 months

> start to sit unsupported

> get into crawling position - start to crawl/bum shuffle

> pull themselves up to stand , cruise around furniture

> bang two objects together , put objects into a container

cognitive milestones 6-12 months

> understand difference between animate and inanimate objects , enjoys games

> starts to make meaningful sounds like 'mama' or 'dada'

social/emotional 6-12 months

> may display separation anxiety

- avoidance of eye contact been linked to autism

physical milestones toddler: 1-3 years

> begin to walk independently , stand up from seated unaided

> climb stairs , push toys

cognitive milestone toddler : 1-3 years

> says single words (forming simple sentences by ~30 months)

> recognise parts of the body

> enjoy singing nursery rhymes

social/emotional milestones toddler: 1-3 years

> can start to evaluate opinions of others + modify their behaviour accordingly

physical milestones of 3-5 year olds

> often have a lot of energy

> can run, hop, kick and throw a ball

> safely manage stairs

> start to hold a pencil with a pincer grip

> dress themselves - do buttons and zips

> use scissors

cognitive milestones 3-5 years old

> able to follow instructions - asks "who, what, where" questions

> tells long stories, starts to understand o'clock

social/emotional milestones of 3-5 years

> starts to reflect on their own actions

> evaluate performance + react emotionally to success/failure, enjoys jokes

> often protective of younger siblings

> manages frustrations better

physical milestones key stage 1: 4-8 years old

> may develop skills in sports/music etc

> handwriting improving

> still lots of energy

cognitive milestones key stage : 4-8yrs

> sense of competitiveness

> very inquisitive

> fluent speech, reads simple stories

> solve puzzles

social emotional milestones key stage 1 : 4-8 yrs old

> friendships come and go

> may actively dislike opposite sex

> can understand other peoples thoughts + wishes - family important

what is Piagets theory of cognitive development ?

4 stages:

1) sensorimotor stage - 0-2 years

2) pre operational stage - 2 to 7 years

3) concrete operational stage - 7 to 11 years

4) formal operational stage - 12+ yrs

describe the sensorimotor stage

> child experiences world through their basic senses + motor responses

- how objects feel + what they can see/hear around them

> thought primarily based on action (e.g baby might accidentally knock a toy hanging from a mobile, then accidentally do it again, and eventually learns to purposefully make that particular action to make the toy move)

> object permanence develops - objects remain even when you cant see them

what is the pre operational stage ?

- language plays a key role --> child narrate own activities

- symbolic thinking develops - use of self imagery + symbols to represent objects (engage in imaginative)

decentration develops: child starts to consider multiple aspects at the same time , rather than one thing

theory of mind develops

concrete operational

> child can apply conservation - understand objects can change size or appearance but essentially remain the same

> can understand that one person can be a father , grandfather, and brother at the same time

> develop rational thinking

> can group objects

formal operational

> Child can now apply logical thinking and reasoning

> Able to think about hypothetical possibilities (generate hypotheses)

>Can understand ethics and moral reasoning

>Sophisticated thought processes

> can consider multiple perspectives

e.g can now devise long-term strategies to win at a board game by making predictions about possible future events