Transcript fetal growth development

Fetal and Neonatal Physiology
Fetal & Neonatal physiology
•Goals
Fetal development
Functioning of the child immediately after
birth
Growth and development through the early
year of life
Fetal growth and functional development of
organs system
Growth and Functional Development of Fetus

At 12 weeks, fetus is
about 10 cm long

At 20 weeks, 25 cm

At term, about 50 cm
Relative Size of Human Conceptus
Relative Uterus Size During Pregnancy
Function of the Placenta
Development of the Organ Systems
Within 1 month, gross characteristics of all the
organs have begun to develop

During the next 2 -3 months, details of the organs
are established

Beyond 4 months, organs of the fetus are grossly
the same as those of the neonate

However, cellular development in each organ is far
from complete

Development of the Organ Systems


Circulatory system

Beating of the heart begins (4tth week)

Contracting of the heart- 65 beats/min

Increases to 140 beats/min before birth
Formation of Blood Cells
3 week-nucleated RBCs
 rd

In york sac & mesothelial layers of the placenta
4 to 5th week- nucleated RBCs
 th

fetal mesenchymal & endothelium of fetal blood vessels
6 week-RBCs-liver
 th
3 month-spleen & other lymphoid tissue
 rd
Development of the Organ Systems
3 month onwards
 rd


Principle source RBCs & most of WBC - bone marrow

Lymphocytes & plasma cells- lymphoid tissue
Respiratory System

No respiratory activity during fetal life

No air to breath in amniotic fluid

Lungs are completely deflated

Inhibition !
Prevents filling of the lungs with fluids and debris from
meconium excreted by fetus’s git into the amniotic fluid

Development of the Organ Systems

Nervous system


3rd to 4th month

Spinal cord and brain stem reflexes are present

Cerebral cortex is immature

Myelinization of major tracts completed 1 yr of postnatal life
Gastrointestinal

by midpregnancy

Fetus ingests and absorbs large quantities of amniotic fluid

Last 2-3 months - function approaches that of normal neonate

Formation of meconium during the last 2-3 months
Development of the Organ Systems

Kidneys

2nd trimester- urine excretion
Accounts 70-80 % of amniotic fluid

Oligohydramnios

Reduced formation of amniotic fluids


Abnormal kidney development

Severe impairment of kidney function
Renal control systems

regulation of fetal e.c.f volume & electrolyte balances, esp
acid base balance are almost non-existent until late fetal life


Do not reach full development until a few months after birth
Development of the Organ Systems


Fetal Metabolism

Glucose is the sole source of energy

Special problems about Ca, PO4, Fe and Vit metabolism
Metabolism of Calcium and Phosphate

12th-40th accumulates


Period of rapid

ossification of fetal bones

Weight gain of the fetus
Accumulation of iron

3rd weeks onwards

Stored in the form of Hb

Used for RBCs formation
Development of the Organ Systems

Vitamin utilization and storage
B vitamins (B12 & folic acid)
Formation of RBC & nervous tissues
Overall growth of fetus
Vit C
Intracellular substrate formation
Bone matrix
Fibers of connective tissue
Vitamins D
Is needed for normal bone growth
Is stored in the liver
Development of the Organ
Systems
•Vit E
•Normal development of embryo
•Its absence
•Early stage abortion in animal studies
•Vit K
•Formation of Factor VII, prothrombin, other blood
coagulation factors
Development of the Organ Systems
Adjustments of the Infant to Extrauterine Life


onset of breathing
Birth creates
Loss of placental connection

Loss of means of metabolic support


Adjustment: beginning of breathing

Cause of breathing at birth


Breathing begins within seconds (less than a min)
Sudden exposure to the exterior world

Slightly asphyxiated state incident to birth process

Sensory impulses – sudden cooled skin
Additional stimuli-hypoxia & hypercapnia which stimulates
respiratory centre

Adjustments of the Infant to Extrauterine Life
Delayed or abnormal breathing at birth (danger of
hypoxia)



Hypoxia frequently occurs because of

Compression of the umbilical cord

Premature separation of placenta

Excessive contraction of the uterus

Excessive anaesthesia of the mother
Degree of hypoxia that an infant can tolerate

Failure to breath 4m-death in adults
>8-10 permanent/serious brain impairment including death
in neonates


Damage-thalamus, inferior colliculi, brain stem

Areas associated with motor functions of the body
Expansion of the Lungs at Birth
• At birth
– Alveoli walls are collapsed
due to surface tension of
the viscid fluid that fills
them
• >25mmHg –ve
inspiratory pressure
– opposes surface tension
– opens them
• Fortunately
– Ist inspiratory pressure
60mmHg –ve intrapleural
pressure
Respiratory Distress Syndrome

Deficient surfactant secretion

Respiratory epithelium

type 2 alveolar epithelia cells

Respiratory distress syndrome

Hyaline membrane disease
•Production of surfactant begins at 23 – 24 wks of gestation and
reaches maturation after 35 wks of gestation
•Decreased surfactant production in preterm babies decreases the
compliance
•risk for respiratory distress syndrome
•bronchopulmonary dysplasia and
•pulmonary hypertension
Circulatory Readjustments at Birth
Circulatory Readjustments at Birth
Circulatory Readjustments at Birth
Changes in the Fetal Circulation at Birth
Primary changes in pulmonary and systemic
vascular resistances at birth

Hypoxia causes tonic constrictions in lung blood
vessels in fetal life

Pulmonary arterial pressure, right ventricular
pressure and right atrial pressure are all reduced


Closure of the foramen ovale

2 to 4 mm Hg pressure in the left atrium
Changes in the Fetal Circulation at Birth

Closure of ductus arteriosus
Failure of closure, role of prostaglandins

Indomethacin, blocking the synthesis of
prostaglandins


Closure of ductus venosus
Nutrition of the neonate

Plasma glucose levels: 30-40 mg/dL

Infant’s body fluid turnover is 7 times that of an
adult

Special Functional Problems in the Neonate
Instability of various hormonal and neurogenic
control systems


Respiratory system (40 times/min)

Tidal volume: 16 ml

Functional residual capacity is one half that of adult

Excessive cyclical variations
Special Functional Problems in the Neonate

Circulation, Blood volume: 300 ml

Cardiac output: 500 ml/min

Arterial pressure: at the first day, 70 / 50 mmHg

Several months after birth: 90/60 mm Hg

Blood characteristics: 4 million RBC/mm3
Neonate jaundice and erythroblastosis fetalis

Special Functional Problems in the Neonate
Special Functional Problems in the Neonate
Fluid balance, acid-base balance and renal
function


Liver function
Digestion, absorption and metabolism of energy
foods and nutrition

Secretion of pancreatic amylase is deficient

Less fat absorption in the GI tract

Low and unstable glucose concentration

Synthesizing and storing new proteins

Special Functional Problems in the Neonate:
Body Temperature
Special Functional Problems in the Neonate

Metabolic rate and body temperature
The normal metabolic rate of the neonate in relation to
body weight is about twice that of the adult


Nutritional needs during the early weeks of life
Need for calcium and Vit D

Necessity for iron in the diet

Vit C deficiencey in infants

Orange or similar juice supplementation during
infancy


Immunity & allergy
Endocrine Problems in the Neonate
Normally, the endocrine system of the infant is highly
developed at birth

Mother receiving androgenic hormone and
masculinisation of the female newborn


Sex hormones from placenta and through milk
Untreated diabetic mother – low plasma glucose
concentrations

Type II Diabetes mellitus (stimulation of fetal growth
and increased birth weight)


Type I Diabetes mellitus – high mortality rate
Endocrine Problems in the Neonate
Hypofunctional adrenal cortex – agenesis of the
adrenal gland


Hyperthyroidism in the mother

Hypothyroidism in the mother – cretin dwarfism
Special Problems of Prematurity
Instability of the homeostatic control systems
in the premature infant


Instability of acid-base balance
Low blood protein because of immature liver
development & hypoproteinemic edema


Inability of the infant to regulate calcium levels

Variability of blood glucose levels

Instability of body temperature

Temperature tends to approach the surroundings
Special Problems of Prematurity
Danger of Blindness Caused by Excess Oxygen
Therapy in the Premature Infant


Respiratory distress and hypoxia
Excessive oxygen therapy in treating premature
infants may lead to blindness

Too much oxygen stops the growth of new blood
vessels in the retina


Growth of great mass of vessels

Retrolental fibroplasia

Breathing air with 40% O2 would be physiologic
Growth & Development of the Child