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Human Development and AgingChapter 29

The Fetal Circulation

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?

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Overview of Fetal Circulation

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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:1.The fetal lungs are collapsed since the fetus is not breathing air

2.There is nothing to digest or process since the fetus is not eating

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Pathway of Blood Through Mature HeartFigure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Pulmonary circulation

Systemiccirculation

Modifications in Fetal Pulmonary Circulation

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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

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Modifications in Fetal Digestive Circulation

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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)

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

Changes in Fetal Circulation After Birth

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Figure adapted from: Tortora, Principles of Anatomy & Physiology, Wiley Press, 2002

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)

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.

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Bypass of pulmonary circulation

Summary of Fetal Circulatory Changes

Structure Anatomy/Location FunctionAssociated

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

Placental 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

Respiratory 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

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Presentation & Supporting Materials Are Available Online…

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The slides for this presentation, as well as supplementary materials to support this topic, are available online at:

http://www.gserianne.com/science/FetalCirculationCCM/

You may email questions to: gerianne@optonline.net

** Thank you! **