The document describes fetal development and circulation. It is divided into three periods: the ovular period lasting 2 weeks, the embryonic period from 3-10 weeks, and the fetal period from 8 weeks until birth. Fetal growth involves cellular hyperplasia, hyperplasia and hypertrophy. Nutrition is initially from histotrophic transfer and then hematotrophic transfer via the placenta. The fetal circulatory system differs from adults due to shunts like the ductus venosus, foramen ovale, and ductus arteriosus that allow blood to bypass the lungs. At birth, these shunts close and the lungs/heart assume the placenta's gas exchange and nutrient roles.

2. • Three periods are distinguished in the prenatal
development of the fetus.
• (1) Ovular period or germinal period—which lasts for
first 2 weeks following ovulation.
• 2) Embryonic period—begins at 3rd week following
ovulation and extends upto 10 weeks of gestation
• (3) Fetal period begins after 8th week following
conception and ends in delivery.

3. • Normal fetal growth is characterized by
• cellular hyperplasia followed by
• hyperplasia and hypertrophy
• and lastly by hypertrophy alone.

6. • (1) Absorption: In the early post fertilization period, the
nutrition is stored in the deutoplasm within the cytoplasm and
the very little extra nutrition needed is supplied from the tubal
and uterine secretion.
• (2) Histotrophic transfer: Following nidation and before
the establishment of the utero-placental circulation,the
nutrition is derived from the eroded decidua by diffusion and
later on from the stagnant maternal blood in the trophoblastic
lacunae.
• (3) Hematotrophic: With the establishment of the fetal
circulation, nutrition is obtained by active and passive transfer

7. • first in the yolk sac by 14th day.
• By 10th week, the liver
• extend to the spleen and bone marrow and
• near term, the bone marrow becomes the major site of
red cell production

8. • During the first half, the hemoglobin is of fetal type (α-2,
γ-2)
• But from 24 weeks onwards, adult type of hemoglobin (α-
2, β-2) appears and at term about 75–80% of the total
hemoglobin is of fetal type HbF.
• The fetal hemoglobin has got a greater affinity to
oxygen due to lower binding of 2, 3-
diphosphoglycerate compared to adult hemoglobin.
•
• Total fetoplacental blood volume at term is estimated
to be 125 mL/kg body weight of the fetus.

9. • URINARY SYSTEM: By the end of the first trimester, the
nephrons become active and secrete urine.
• Near term, the urine production rises to 650
mL/day.
• GASTROINTESTINAL TRACT: As early as 10–
12 week, the fetus swallows amniotic fluid.
• The meconium appears from 20th week

10. • At 16th week, lanugo (downy thin colorless hairs) appears
but near term almost completely disappears.
• Sebaceous glands appear at 20th week and the sweat
glands somewhat later.
• Vernix caseosa — the secretion of the sebaceous glands
mixed with the exfoliated epidermal cells is abundantly
present smearing the skin.
• The horny layer of the epidermis is absent before 20th
week which favors transudation from the fetal capillaries
into the liquor amnii.

11. • In the early months, the lungs are solid.
• At 28th week, alveoli expand and are lined by cuboidal
epithelium.
• At 24th week, lung surfactant related to
phospholipids—phosphatidylcholine (lecithin) and
phosphatidylglycerol appear.
• Surfactant is secreted by type-II alveolar cells.
• A lecithin: sphingomyelin (L:S) ratio of 2:1 in the
liquor amnii signifies full maturity of the fetal lung.
• Fetal cortisol is the natural trigger for augmented
surfactant synthesis.

12. Foetal circulation consequently differs from the adult one
predominantly due to the presence of 3 major vascular
shunts:
• Ductus venosus: between the umbilical vein and
IVC
• Foramen ovale: between the right and left atrium
• Ductus arteriosus: between the pulmonary
artery and descending aorta

14. • Pair of umbilical
arteries carry
deoxygenated blood &
wastes to placenta.
• Umbilical vein carries
oxygenated blood and
nutrients from the
placenta.

15. • Facilitates gas and
nutrient exchange
between maternal and
fetal blood.
• The blood itself does not
mix.

16. The core concept behind fetal circulation is that fetal
hemoglobin has a higher affinity for oxygen than
does adult hemoglobin, which allows a diffusion of
oxygen from the mother's circulatory system to the
fetus.
The circulatory system of the mother is not
directly connected to that of the fetus, so the
placenta functions as the respiratory center for
the fetus as well as a site of filtration for plasma
nutrients and wastes.

17. • By the third month of
development, all major
blood vessels are
present and functioning.
• Fetus must have blood
flow to placenta.
• Resistance to blood
flow is high in lungs.

18. Exchange of gases
occurs in the
placenta.
Oxygenated blood is
carried by the
umbilical vein
towards the fetal
heart.

19. Blood from the ductus
venosus enters to the
inferior vena cava. Increase
levels of oxygenated blood
flows into the right atrium.
The ductus venosus directs
part of the blood flow
from the umbilical vein
away from the fetal liver
and directly to the inferior
vena cava.

20. • In adults, the increase
pressure of the right
atrium causes the
tricuspid valve to open
thus, draining the blood
into the right ventricle.
• However, in fetal
circulation most of the
blood in the right atrium is
directed by the foramen
ovale (opening between
the two atria) to the left
atrium.

21. The portion of the blood that drained into the
right ventricle passes to the pulmonary artery.

22. • As blood enters the pulmonary
artery (carries blood to the
lungs), an opening called
ductus arteriosus connects
the pulmonary artery and the
descending aorta.
• Hence, most of the blood will
bypass the non-functioning
fetal lungs and will be
distributed to the different
parts of the body.
• A small portion of the
oxygenated blood that enters
the lungs remains there for

23. The umbilical arteries then carry the non-
oxygenated blood away from the heart to the
placenta for oxygenation.

26. • Gas exchange function is transferred from
placenta to the lungs.
• Separation of systemic and pulmonary
circulations
• Increased metabolism to maintain body
temperature and hence increased cardiac
output.

28. FETAL CIRCULATION VIII: Conversion to post-natal*
Pulmonary
veinsVena cava Right
ATRIUM
Pulmonary
arteries
Right
VENTRICLE
Left
VENTRICLE
Aorta
LUNGS
SYSTEMIC
CAPILLARIES
HEART
Umbilical
arteries
Ductus arteriosus
IVC
OLef t
ATRIUM
Closure of Foramen ovale
DUCTUS VENOSUS
means that blood expelled from the
right ventricle has to go to the lungs
Closure of
Closure of
Stops use of umbilical
vessels, & converts all
vena cava blood to
deoxygenated
Forces venous blood (now all deoxygenated) into
the right ventricle for expulsion to the lungs
Closure of
Stops use of
umbilical vessels

29. S.No FETAL STRUCTURE ADULT STRUCTURE
1. FORAMEN OVALE FOSSA OVALIS
2. UMBILICAL VEIN LIGAMENTUM TERES
3. DUCTUS VENOSUS LIGAMENTUM VENOSUM
4. DUCTUS
ARTERIOSUM
LIGAMENTUM
ARTERIOSUM
5. UMBILICAL ARTERY
AND ABDOMINAL
LIGAMENT
MEDIAL UMBILICAL
ARTERY AND SUPERIOR
VESICULAR ARTERY

30. • Patent (open) ductus arteriosus and patent foramen
ovale each characterize about 8% of congenital
heart defects.
• Both cause a mixing of oxygen-rich and oxygen-
poor blood; blood reaching tissues not fully
oxygenated. Can cause cyanosis
• Surgical correction now available, ideally completed
around age two.
• Many of these defects go undetected until child is at
least school age.

31. THANK YOU