1. Fetal and Neonatal Physiology

2. Fetal and Neonatal Physiology
Summary
Gestation period
fertilization to birth (38 weeks)
Prenatal period (before birth)
embryological development
first 2 months after fertilization (embryo)
all principal adult organs are present
fetal development
from 9 weeks until birth (fetus)
placenta is functioning by end of 3rd month
Neonatal period
first 42 days after birth

3. Fetal & Neonatal physiology
Discussion
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

4. 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

5. Relative Size of Human Conceptus

6. Relative Uterus Size During Pregnancy

7. 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

8. 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
3rd week-nucleated RBCs
In york sac & mesothelial layers of the placenta
4th to 5th week- nucleated RBCs
fetal mesenchymal & endothelium of fetal blood vessels
6th week-RBCs-liver
3rd month-spleen & other lymphoid tissue

9. Development of the Organ Systems
3rd month onwards
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

10. 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

11. Development of the Organ Systems
Kidneys
2nd trimester- urine excretion
Accounts % 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

12. 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
Most stored in the liver

13. 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

14. 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

15. Development of the Organ Systems

16. 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

17. 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

18. Expansion of the Lungs 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

19. Respiratory Distress Syndrome
Deficient surfactant secretion
Respiratory distress syndrome
Hyaline membrane disease
Production of surfactant begins at 23 – 24 wks of gestation and reaches maturation after 35 wks of gestation
Respiratory epithelium
type 2 alveolar epithelia cells
Decreased surfactant production in preterm babies decreases the compliance
risk for respiratory distress syndrome
Collapse tendency of alveoli and
pulmonary oedema development

20. Circulatory Readjustments at Birth Special anatomical structure of fetal circulation
During fetal life
Lungs are non functional
Liver is partial functional
It is not necessary the heart to pump blood thru either of them
Much blood pumped thru the placenta
oxygenation

21. CARDIOVASCULAR SYSTEM
Fetal Circulation
Nutrients for growth and development are delivered from the umbilical vein in the umbilical cord → placenta → fetal heart

22. Inferior vena cava (mixes with
Fetal Circulation
Oxygenated blood from mother
↓ (via umbilical vein)
by pass Liver
Ductus venosus ↓
Inferior vena cava (mixes with
deoxygenated blood)
Right atrium

23. ↓ (through Foramen ovale)
Right atrium
↓ (through Foramen ovale)
Left atrium ↓
Left ventricle
↓ (through Aorta)
Heart and Brain

24. Deoxygenated blood from lower half of fetal body ↓ Inferior vena cava
Right atrium
Right ventricle
Deoxygenated blood flowing through Superior vena cava

25. ↓ (through Ductus arteriosus)
Right ventricle ↓
Pulmonary artery
↓ (through Ductus arteriosus)
Descending aorta
Hypogastric arteries
Umbilical arteries
Placenta

26. Fetal Circulation
Source:

27. Differences in Fetal and Adult Circulation
1st difference:
Presence of shunts which allow oxygenated blood to bypass the right ventricle and pulmonary circulation, flow directly to the left ventricle, and for the aorta to supply the heart and brain
3 shunts:
- Ductus venosus
- Foramen ovale
- Ductus arteriosus

28. Differences in Fetal and Adult Circulation
2nd difference:
Ventricles of the fetal heart work in parallel compared to the adult heart which works in sequence.

29. Differences in Fetal and Adult Circulation
Fetal cardiac output per unit weight is 3 times higher than that of an adult at rest.
This compensated for low O2 content of fetal blood.
Is accomplished by ↑ heart rate and ↓ peripheral resistance

30. Changes After Birth
Clamped cord + fetal lung expansion = constricting and collapsing of umbilical vessels, ductus arteriosus, foramen ovale, ductus venosus
Fetal circulation changes to that of an adult

31. Changes After Birth: Closing of Shunts
Functional closure
Anatomical closure
Remnant
Ductus arteriosus
10 – 96 hrs after birth
2 – 3 wks after birth
Ligamentum arteriosum
Formamen ovale
Within several mins after birth
One year after birth
Fossa ovalis
Ductus venosus
3 – 7 days after birth
Ligamentum venosum
Umbilical arteries → Umbilical ligaments
Umbilical vein → Ligamentum teres

32. Changes After Birth Maintenance of ductus arteriosus depends on:
- difference in blood pressure bet. Pulmonary artery and aorta
- difference in O2 tension of blood passing through ductus. ↑ p O2 = stops flow. Mediated through prostaglandins.

33. Special Functional Problems in the Neonate
Instability of various hormonal and neurogenic control systems
Immature development of the organs
Control systems have not adjusted to the new way of life
Respiratory system
Circulation
Git
Renal etc

34. 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

35. 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
when oxygen therapy stops
Retrolental fibroplasia
Breathing air with 40% O2 would be physiologic

36. Growth & Development of the Child