1. Human Development and Aging Chapter 29 The Fetal Circulation

2. Lecture Overview and Objectives
Why does the fetus need a ‘different’ circulatory pattern from the newborn?
What are the anatomical differences in the fetal vs. the newborn circulation?
How do these anatomical differences better meet the physiological needs of the fetus?
When and how does the fetal circulation change after birth?

3. Overview of Fetal Circulation
Breathing and eating/digestion are carried out by the mother for the fetus.
Gases and nutrients are exchanged with the fetus through the placenta.
Besides the umbilical vessels, the major differences in fetal circulation arise because:
The fetal lungs are collapsed since the fetus is not breathing air
There is nothing to digest or process since the fetus is not eating
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

4. Pathway of Blood Through Mature Heart
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Systemic
circulation
Pulmonary circulation

5. Modifications in Fetal Pulmonary Circulation1 2
Figure from: Martini, & Ober, Visual Anatomy & Physiology, Pearson Science, 2012
1. Foramen ovale – allows blood returning to right atrium to bypass right ventricle and pass directly into left atrium (then to lt. ventricle, then aorta)
2. Ductus arteriosus – allows blood from right ventricle and pulmonary trunk to bypass the pulmonary arteries and pass directly into the aorta

6. Modifications in Fetal Digestive Circulation1
Figure from: Shier et. al., Hole’s Human Anatomy & Physiology, McGraw-Hill, 2010
1. Ductus venosus – allows about 50% of blood returning to fetus through the umbilical vein to bypass the liver and empty directly into the inferior vena cava (then back to rt. atrium of heart)

7. Changes in Fetal Circulation After Birth
Foramen Ovale -> Fossa ovalis
Ductus Arteriosus -> Ligamentum arteriosum
Ductus Venosus -> Ligamentum venosum
Umbilical vein -> Ligamentum teres
Umbilical arteries -> Medial umbilical ligaments (and superior vesical arteries to urinary bladder)
Figure adapted from: Tortora, Principles of Anatomy & Physiology, Wiley Press, 2002

8. Summary
Fetal circulation differs from the postpartum circulation to accommodate the interaction of the fetus and mother through the placenta.
There are four bypasses (shunts) in the fetus for this purpose:
1) Placental Circulation - 2 umbilical arteries and 1 vein
2) Ductus Arteriosus
3) Foramen Ovale
4) Ductus Venosus Major bypass of the liver
Subsequent to the newborn’s first breath and clamping of the umbilical cord, these bypasses within the fetal circulation are eliminated to adjust to life outside the uterus.
Bypass of pulmonary circulation

9. Summary of Fetal Circulatory Changes
Structure
Anatomy/Location
Function
Associated System (Shunt) in Fetus
What happens after birth
Umbilical Arteries (2 arteries)
Arise from fetal internal iliac arteries and enter umbilical cord
Bring deoxygenated, nutrient-poor blood to placenta
Placental
Vessels close and become medial umbilical ligaments & superior vesical arteries
Umbilical Vein (1 vein)
Arises from placenta and enters the ductus venosus (see below)
Brings oxygenated, nutrient-rich blood from placenta to fetus
Vessel closes and becomes the ligamentum teres
Foramen Ovale
Oval flap of tissue in interatrial septum
Bypass of right ventricle; blood flows from right atrium directly to left atrium
Respiratory
Flap closes and becomes fossa ovalis
Ductus Arteriosus
Vessel connecting pulmonary trunk and aorta
Allows most blood from right vetnicle to bypass the pulmonary circulation
Vessel closes and becomes ligamentum arteriosum
Ductus Venosus
Vessel connecting umbilical vein directly to inferior vena cava
Allows about 50% of O2/nutrient-rich blood to bypass liver
Digestive
Vessel closes and becomes ligamentum venosum

10. Presentation & Supporting Materials Are Available Online…
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11. Figure from: Shier et. al
Figure from: Shier et. al., Hole’s Human Anatomy & Physiology, McGraw-Hill, 2010

12. Figure from: Shier et. al
Figure from: Shier et. al., Hole’s Human Anatomy & Physiology, McGraw-Hill, 2010

13. Congenital Cardiovascular Problems
Right-to-left shunt
Left-to-right shunt -> Pulmonary hypertension, pulmonary edema, and cardiac enlargement
(Congenital = Present at Birth)
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

14. Congenital Cardiovascular Problems
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001