fetal growth and development... final

8/13/2019 Fetal Growth and Development... Final

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INTRODUCTION

Understanding of the fetaldevelopment is a constructive step

towards achieving a positive

pregnancy outcome.

It provides prospective parents with

opportunity to make conscious

decisions about their health and

lifestyle.


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OBJECTIVES

Explain the overview of fetalgrowth and development

Describe the developmental

changes that take place in the

following systems:Cardiovascular system


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OBJECTIVES CONTD

Respiratory system

Urogenital system

Endocrine system

Digestive system


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OVERVIEW OF FETAL GROWTH &

DEVELOPMENT

FETUS- This name is used during the

period from the beginning of the

9thweek after fertilization to term

(end of 38thweek - 40thweek).


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OVERVIEW CONTD

By the beginning of the 9thfertilization, the human embryo

has developed into a recognizable

human being and most of the

body structures have commenced

development.


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OVERVIEW CONTD

The fetal period is mainly

concerned with differentiation and

growth of tissues and organs

which have already appeared.


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OVERVIEW CONTD

The fetus is less vulnerable

than the embryo, to the harmfuland deforming effects of

teratogenic agents.


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OVERVIEW CONTD

Tissues grow by cell proliferation,cell enlargement and accretion

(building up) of extracellular

material.

On average, the baby at termweighs 3400 grams (3.4 kg) and is

500mm long.


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DEVELOPMENTAL CHANGES IN THE

SYSTEMS

The cardiovascular system Is the first to function in the

embryo.

The heart and the vascular

system commences development

in the 3rdweekBy 4th week a primitive heart is

visible and is beginning to


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DEVELOPMENTAL CHANGES CONTD

Beating starts at around 22 daysbut can not be heard until after 16-

20 weeks.

Blood is pumped around the

vessels from the 4thweek .


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The red cel l form at ion There are three phases of red blood

cell formation.

York sac period :- from 3rd13thweek

Hepatic /liver period:- from weeks 5-

36

Born marrow period:- from week 12

throughout life.


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The red blood cells known as

erythrocytesproduced by the

York sac and the liver contain fetal

hemoglobin.


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Fetal hemoglobin (HbF) has amuch greater affinity for oxygen

and is found in greater

concentrations (18 -20g/dl atterm).

This enhances the transfer of

oxygen across the placental site.


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Fetal erythrocytes have a life spanof 90 days which is shorter than

the adult erythrocytes which is

around 120 days.

This short life span contributes toneonatal physiological jaundice.


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The respiratory system Development of the respiratory

system begins in the 4thweek.

The lungs originate from the bud

growing out of the pharynx, which sub

divides to form the branching structure

of the brachial tree.


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Lung development occurs onseveral levels and continues after

birth until about 8 years of age

when the full number ofbronchioles and alveoli will have

developed.


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At 20 weeks development of typeII alveolar commences.

These cells are necessary for theproduction of surfactant alipoprotein that reduces the

surface tension in the alveoli andassist gaseous exchange.


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The amount of surfactant increasesuntil the lungs are mature at 3034

weeks.

Babies born before 24 weeks

gestation have a reduced chance of

survival due to immaturity of the

capillary system in the lungs and the

lack of surfactant.


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By 3rdmonth there is somemovement of the thorax and more

definite diaphragmatic movements

from the 6thmonth.

This does not constitute breathingas gaseous exchange is via the

placenta.


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The urogenital systemThis is divided into the

urinary/renal system and

genital/reproductive system.

Both develop from theintermediate mesoderm.


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The kidneys develop from the 4thweek and produce small amounts

of urine from the 9thweek.

They become more functional

around 15thweek when moreurine is produced.


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The sex of the fetus is determinedat fertilization. The gonadsdevelop in the 5thweek.

In the two sexes genitaldevelopment is the similar and is

referred as ind if feren t s tate o fsexual development.


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Differentiation occurs from 7th

week, but female gonad

development occurs slowly and

the ovaries may not be identifiable

until the 10th

week.


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External genitalia in both sexes

develop in the 9thweek, but males

and females are not

distinguishable until 12thweek.


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The Endocrine systemThe adrenal glands develop from

the 6thweek, and grow to 10-20

times larger than the adult

adrenals.

Their size regresses during the

first year of life.


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They produce the precursor s for

placental formation of oestriols

They influence maturation of the

liver, the lungs and the epitheliumof the digestive tract.


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It is also thought that they play a

part in the initiation of labour (the

exact mechanism not fullyestablished).


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The digestive systemThe primitive gut develops from

the endodemal layer in the 4th

week of life.

It starts as a straight tube and

proceeds on several levels:foregut, midgut and hindgut.


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By the 5th

week, the foregut(oesophagus, stomach andduodenum) is visible.

The midgut (small intestines,caecum and appendix, ascending

colon and transverse colon)undertakes much of itsdevelopment in the 6thweek


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The hindgut (rectum, and anal

canal ) completes its development

in the 7thweek.


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The liver grows rapidly and from

the 5th-10thweek, fills much of the

abdominal cavity.

It is responsible for about 10% offetal weight by the 9thweek.


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Around 12 weeks the digestivetract is well formed and the lumen

is patent.

Most of the digestive juices are

present before birth and act on theswallowed substances to form

meconium.


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Meconium is normally retained inthe gut until after birth when it is

passed as the first stool of the

newborn.


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The nervous systemThe brain begins to develop from

around day 19 and three

structures the fore brain; midbrain

and hind brain are visible.


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By 5thweek, the major structures,the thalamus and the

hypothalamus are differentiated.

The neural tube is derived fromthe ectoderm.


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This ectoderm folds in wards by acomplicated process to form theneural tube which is then covered

over by the skin.

This process is occasionally

incomplete, leading to a conditioncalled open neural tube defect


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The development of the sensory

organs is associated with the

development of the head and

neck

which begin early in fetal life andcontinues until the cessation of

growth in the late teens.


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Eyes develop from around 22days and are complete by 20

weeks but the eyelids are fused

up until the 6thmonth.

The developing eyes are sensitiveto light.


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The inner ear which contains thestructures for hearing and balance

commences early in life and are

completed by 25thweek.

The fetus is able to hear externalsound.


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Motor output in the form ofmovement begins around 8

weeks.

These movements are not usually

felt until around 16 weeks and areusually referred to as quickening


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Integumentary, skeletal andmuscular systems

The epidermis is develops from a

single layer of ectoderm to which

other layers are added.


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By the end of the first month, athin outer layer of flattened cells

covers the embryo.

Further development continues

until the sixth month.


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From 18 weeks, the fetus iscovered with a white creamy

substance called vern ix caseosa.

This protects the skin from the

amniotic fluid and any frictionagainst itself.


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At 20 weeks, the fetus is coveredwith a fine downy (silky, velvety)hair called lanugo, at the same

time the head hair and eye browsbegin to form.

Lanugo is shed from 36 weeksand by term there is little left.


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Fingernails develop from about 10weeks but the toenails do not formuntil 18 weeks.

By term, the nails usually extendbeyond the fingertips.

Length of the nails is unreliableguide to maturity.


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The skeleton first appears ascartilage

At specific periods the cartilage is

replaced is replaced by the true

bone through a process ofossification.


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Nevertheless, the skull and thefacial bones develop from direct

ossification with no intermediate

cartilage stage.

Skeletal, cardiac and smoothmuscles are formed during the

fetal period and continues into

childhood. FACTORS NECESSARY FOR FETAL


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FACTORS NECESSARY FOR FETAL

DEVELOPMENT

Oxygen:

Necessary for all metabolic

processes

Nutrients:

Glucose: The primary source ofenergy for metabolism andgrowth


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FACTORS CONTD

Aminoacids,

vi tam ins ,m inerals, iron and

calc ium:

Necessary for metabolism and

growth.


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FACTORS CONTD

Insul in:Necessary for the metabolism of

glucose but this later is secreted

by the fetal pancreas.

FACTORS ADVERSELY AFFECTING


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FACTORS ADVERSELY AFFECTING

FETAL GROWTH & DEVELOPMENT

Placental insufficiency or impairedutero placenta blood flow

Maternal conditions such as

hypertension, chronic infections, andcardiac disease have detrimental

effect upon the efficiency of the

placenta to transmit nutrients fromthe mother to the fetus.


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FACTORS CONTD

Genetic factorsBabies born with abnormalities e.g

Downs syndrome and dwarf

syndromes are small forgestational age at birth.


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FACTORS CONTD

Alcohol and narcotic addiction

This causes fetal growth

retardation. Besides this, babiesborn to these mothers can also be

addicted and may have congenital

abnormalities.


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FACTORS CONTD

Infections and hyperpyrexia of

the mother

Many viruses such as Rubella and

HIV and other organisms can

pass through the placentalmembrane and adversely affect

fetal growth.


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FACTORS CONTD

Multiple pregnancy

Each placenta is usually reduced

in size and there is an increased

nutritional burden upon the mother

for each additional fetus.


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FACTORS CONTD

Maternal malnutrition

If the mother is lacking certain

necessary nutrients, the fetus will

also be deprived of them.

fetal growth and development... final

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