3 - Special Circulation: Fetal Flashcards
What are the major intracardiac and extracardiac features of the fetal circulation?
Intracardiac: Foramen Ovale
Extracardiac: Ductus Arteriosus, Ductus Venosus
Designed to deliver oxygenated blood to myocardium and brain
What is the rough pathway of blood in the fetal circulation, focusing on the key shunts?
- Blood enters from umbillical vein (motor)
- Goes toward liver, mostly bypassing via Ductus Venosus. Enters R Ventricle
3a. Enters R Atrium via Foramen Ovale Shunt
3b. Some goes toward Ductus Arteriosus, bypassing pulmonary circulation for Descending Aorta
- R Atrium receives some blood from lungs
- L. Ventricle moves blood out through aorta, back to placenata
What fetal blood vessel has the highest [O2]?
Umbilical vein
What do the following structures bypass (shunt function)?
Ductus Venosus (DV)
Foramen Ovale (FO) - What is the flap called?
Ducturs Arteriosus (DA)
DV - Bypass hepatic circulation
FO - Bypass R Ventricle, go to L Ventricle; Eustacian Valve
DA - Bypass pulmonary circulation
Why is it important the ascending aorta be given high oxygen blood in fetal circulation?
Heart and Brain need good blood supply
Where does maternal blood swap out nutrients/waste with fetal blood?
Where does fetal blood swap out nutrients/waste with maternal blood?
Does this blood mix?
Intervillous Space
Chorionic Villi
The blood does NOT mix
What does Combined Cardiac Output (CCO) measure?
(Combined Ventricular Output - CVO is the same thing)
Why is this important for fetal circulation?
What is the dedicated flow for L/R ventricle?
Sum of outputs of right and left ventricles
- -
The ventricles don’t pump in a series (mature), they pump in parallel–their inputs and outputs mix
L Ventricle - Mostly coronary/upper body
R Ventricle - Lower body, slightly larger output
Why is the pulmonary circuit resistance so high in fetal circulation?
How does systemic circulation compare?
- The collapsed lungs
- Hypoxic Vasoconstriction
**Result = Blood flow to lungs is low in fetus, minimal amount supports lung growth and development
Systemic circulation has lower resistance
Where does the fetal liver receive its blood supply?
Umbilical Vein, Portal Vein, Hepatic Artery
What vessels does the ductus arteriosus connect?
What substance is key to maintaining patency?
What does this bypass, and what does that depend on?
Pulmonary Arterial Trunk to Descending Aorta
Prostaglandin E2 (PGE2)
Bypass pulmonary circulation, depends on the resistance of the pulmonary vasculature
What are the major cardiopulmonary adjustments at birth?
Gas Exchange from placenta to lungs
Close right to left coronary shunts
Increas L Ventricular Output
Increase Systemic Resistance
Decrease Pulmonary Resistance
*Pulmonary Circulation now accepts entire cardiac output
What occurs to the systemic resistance upon closure of placental circulation?
Total peripheral resistance increases
(During fetal period, systemic resistance is low due to placental circulation)
What effect does the opening of pulmonary circulation at birth have?
Expansion of lungs and opening of pulmonary vessels decreases pulmonary vascular resistance
Increase in PO2 that occurs when breathing leads to pulmonary vasodilation
These reduce pulmonary vascular resistance
What occurs to the Ductus Venonus (DV) following birth?
Functionally closed within minutes of birth due to cessation of blood flow
Rapid increas in PO2 from breating maintains constriction of umbilical vessels
What is the fate of the foramen ovale following birth?
The pressure gradient of right and left ventricles flips, and the L Atrium Pressure Increase causes the foramen ovale to close
