Development of Fetal Circulation PDF

Last edited: 9/18/2021 17. DEVELOPMENT OF FETAL CIRCULATION Embryology | Development of Fetal Circulation Medical Editor: Sohani Kashi Puranic OUTLINE Consequence...

Last edited: 9/18/2021 17. DEVELOPMENT OF FETAL CIRCULATION Embryology | Development of Fetal Circulation Medical Editor: Sohani Kashi Puranic OUTLINE Consequence  As the whole pulmonary circuit undergoes I) OVERVIEW vasoconstriction, II) BEFORE BIRTH III) AFTER BIRTH IV) PECULIARITIES OF FETAL CIRCULATION V) CHANGES FROM FETUS TO ADULT o Because of this, Right side of heart (right VI) ANOMALIES Atrium & ventricle) needs to generate high VII) SUMMARY pressure to pump blood into the high- VIII) APPENDIX pressure pulmonary circuit IX) REVIEW QUESTIONS X) REFERENCES I) OVERVIEW The circulation in fetuses is slightly different compared to Pressures in heart: that seen in adults Right side > Left side Placenta is the organ responsible for gas exchange Various remnants are present in adults, which represent fetal structures of the fetal circulation II) BEFORE BIRTH (A) CONDITION OF LUNGS In utero, that is before birth, the lungs are still developing (B) HYPOXIC VASOCONSTRICTION (1) Consequence of Hypoxia Figure 1. Hypoxic Vasoconstriction Due to hypoxia in the lungs, the pulmonary vasculature undergoes vasoconstriction (C) STRUCTURES & PATHWAY (1) Placenta REMEMBER Plays a role in exchange of gases The placenta is connected with the fetus through Effect of Hypoxia on: Umbilical cord Systemic Vessels- Vasodilation Functions of Placenta Pulmonary Vessels- Vasoconstriction Exchange of gases  Occurs by simple diffusion  O2 delivery to fetus is by placental blood flow (2) Reason for Vasoconstriction in Hypoxia Exchange of nutrients & electrolytes The pulmonary capillaries near hypoxic alveoli undergo vasoconstriction  Occurs rapidly  Increases as pregnancy advances Transmission of maternal antibodies  IgG By this, alveoli with more O2 concentration will receive  Provides PASSIVE I MMUNITY to fetus better blood supply for effective ventilation Hormone production (3) Hypoxic Vasoconstriction in Fetus  Progesterone Condition in Fetus  Estriol  hCG (human Chorionic Gonadotropin)  Pulmonary circuit vasoconstriction normally occurs  Somatomammotropin/ hPL (human Placental around hypoxic alveoli Lactogen)  In Fetus- all alveoli have ↓O2 concentration  This results in intense vasoconstriction throughout Protection the pulmonary circulation  Protects fetus from damaging agents  However, many drugs & viruses pass through placenta easily DEVELOPMENT OF FETAL CIRCULATION EMBRYOLOGY: Note #1. 1 of 8  (3) Umbilical Vein to IVC Ductus Venosus  It is a structure that shunts blood from (Left) Umbilical Vein DIRECTLY into IVC Sphincter Mechanism of Ductus Venosus Regulates blood flow from Umbilical Vein During uterine contraction: Figure 2. Placenta (2) Umbilical Cord Components Hepatic Sinusoids (a) Blood Vessels  Umbilical vein also drains into the sinusoids of the liver (i) 2 Umbilical Arteries  These drain into the Hepatic portion of IVC (ii) 1 Umbilical Vein (left)  Carries Oxygenated blood  85% O2 SATURATION (4) Right Atrium of Heart (b) Wharton’s Jelly o Mucopolysaccharide  Rich in proteoglycans  Provides insulation  Protects the blood vessels Figure 3. Structure of Umbilical Cord Figure 5. Openings in Right Atrium (c) Remnant of vitelline duct Openings (a) IVC (Inferior Vena Cava) Receives blood from: (i) Ductus Venosus (ii) Liver sinusoids Drains into Right Atrium (b) SVC (Superior Vena Cava) Figure 4. Umbilical Cord Receives blood from head, neck & upper extremities Termination of Umbilical Vein Drains into Right Atrium Derived from Right Common Cardinal Vein  Umbilical vein ultimately pours its Pathways from Right Atrium oxygenated blood from placenta into  Blood from the right atrium can go to the following IVC (Inferior Vena structures: Cava) (a) Left Atrium  There are 2 pathways for the (b) Right Ventricle blood from Umbilical vein to IVC Figure 4. Umbilical Vein & Ductus Venosus 2 of 8 EMBRYOLOGY: Note #17. DEVELOPMENT OF FETAL CIRCULATION  (5) Left Atrium of Heart 70% of the blood from Right Atrium goes to Left Atrium The connection between the Right & Left atria is Foramen Ovale Foramen Ovale Figure 7. Formation of Umbilical Arteries This communication is called Foramen Ovale Placenta  Blood from Umbilical arteries drain into placenta, where CO2 is given out  O2 is taken up in the placenta, and oxygenated blood is delivered to fetus via Umbilical vein (8) Pathway from Right Ventricle Blood to right ventricle: i. Majority of Deoxygenated blood from SVC ii. 30% of Oxygenated blood from IVC Figure 6. Foramen Ovale Blood from right ventricle is pumped into Pulmonary (6) Right Ventricle of Heart Trunk The remaining 30% of blood from Right Atrium flows into From pulmonary trunk, it follows 2 pathways: Right Ventricle Ductus Arteriosus Why majority of blood flows into Left Atrium  It is a structure that connects Pulmonary Artery to Aorta Blood flows from High Pressure to Low Pressure  It shunts the deoxygenated blood Right side of heart: HIGH pressure  Due to hypoxic vasoconstriction Left side of heart: LOW pressure  Relatively lower than right side HENCE , MAJORITY OF B LOOD FROM RIGHT ATRIUM (HIGH P RESSURE ) FLOWS INTO LEFT ATRIUM (LOW PRESSURE ), Figure 8. Ductus Arteriosus & NOT RIGHT VENTRICLE Pulmonary Arteries (7) Pathway from Left Atrium  ↓↓↓ blood flows through Right & Left Pulmonary Blood from right atrium passes through Foramen Ovale to arteries reach the left atrium. From there, it goes to different  This blood reaches the developing lung structures, in the following order: Why majority of blood flows through Ductus Arteriosus Left Ventricle Ascending Aorta, Arch of Aorta Blood flows from Descending Aorta High Pressure to Low Pressure Common Iliac Artery Internal Iliac Artery Umbilical Artery Pulmonary Artery: HIGH pressure  Carries Oxygenated blood mixed with  Due to hypoxic vasoconstriction Deoxygenated blood  58% O2 SATURATION Aorta: LOW pressure  Relatively lower pressure in left side of heart & aorta HENCE , MAJORITY OF B LOOD FROM PULMONARY ARTERY (HIGH PRESSURE ) FLOWS INTO AORTA (LOW PRESSURE ), & NOT THROUGH BOTH PULMONARY ARTERIES TO LUNG DEVELOPMENT OF FETAL CIRCULATION EMBRYOLOGY: Note #1. 3 of 8 , Structures that shunt blood AWAY from Pulmonary Circulation: Foramen Ovale Ductus Arteriosus III) AFTER BIRTH (A) EVENTS RIGHT AFTER BIRTH (1) Umbilical Cord is cut Connection between Placenta & Fetus is broken Figure 10. No hypoxic vasoconstriction (B) CHANGES AFTER BIRTH (1) Closure of Foramen Ovale Pressure in left side of heart ↑ This is called the FUNCTIONAL closure of Foramen Ovale Figure 9. Umbilical Cord is cut after birth (2) Lungs Anatomical closure occurs by fusion of Septum secundum & Septum primum Baby cries right after birth  Allows for air to flush into lung  O2 floods into alveoli Consequence of no vasoconstriction o Because of this, pressure on Right side of heart (right Atrium & ventricle) ↓ OPPOSITE pressure gradient to that seen before birth Figure 11. Fossa Ovalis REMEMBER Closure of Foramen Ovale: Functional- Immediately after birth Pressures in heart: Anatomical- 1 year after birth Left side > Right side Figure 12. Pulmonary Circulation 4 of 8 EMBRYOLOGY: Note #17. DEVELOPMENT OF FETAL CIRCULATION  (2) Pulmonary Circulation Pathway for oxygenated blood: There is now ↑ blood flow through the pulmonary circuit Pulmonary Veins Pulmonary Arteries Left Atrium  Carry deoxygenated blood from right ventricle to (2) Left Side of Heart lungs Left Atrium Pulmonary Capillaries Left Ventricle  Supply alveoli which are now well-ventilated Aorta  Exchange of gases occurs at alveoli (3) Systemic Circulation Pulmonary Veins Oxygenated blood is supplied to different organs via the  Carry oxygenated blood from lungs to left atrium Aorta and its branches (3) Closure of Ductus Arteriosus At the tissues,  This means blood is deoxygenated Pathway for deoxygenated blood: Blood from lower extremities: Iliac Veins → IVC Blood from head, neck, upper extremities: SVC (4) Right Side of Heart Figure 13. Closure of Ductus Arteriosus IVC, SVC → Right Atrium Ductus Arteriosus closes due to: Right Ventricle O2 ↑ Pulmonary Trunk PGE2 ↓ 1 𝑂𝑂2 ∝ 𝑃𝑃𝑃𝑃𝑃𝑃2 Ductus Arteriosus is closed. Before closure, for a very short period, Bradykinin ↑ blood is shunted to Aorta. Hypoxia and ↑ PGE2 keep Ductus Arteriosus patent & open before birth (5) Pulmonary Circulation After birth, the DA remains open for Pulmonary Trunk a very short period of time before it Pulmonary Arteries closes Pulmonary Capillaries  Gas exchange occurs at alveoli, where the deoxygenated blood is oxygenated IV) PECULIARITIES OF FETAL CIRCULATION (A) SHUNTING Blood is shunted along its course at 3 points: Ductus Venosus  To direct blood to IVC by bypassing liver, without losing O2 content Figure 14. Factors affecting patency of DA Foramen Ovale (C) STRUCTURES & PATHWAY  To equalize distribution to each half of heart, and (1) Pulmonary Circulation more oxygenated blood to upper half vital organs With air entering alveoli, and production of surfactant, the Ductus Arteriosus lungs are now functional Gas exchange occurs at alveoli where:  To direct blood to placenta for oxygenation by bypassing lungs [IB Singh]  This means blood is oxygenated DEVELOPMENT OF FETAL CIRCULATION EMBRYOLOGY: Note #1. 5 of 8  (B) MIXING VI) ANOMALIES During its course from placenta to the organs of the fetus, blood in the Umbilical vein gradually loses its high oxygen (A) PATENT FORAMEN OVALE content as it mixes with deoxygenated blood. [Langman] Foramen Ovale doesn’t close Places where mixing occurs: Table 1. Sites of mixing of Oxygenated & Deoxygenated Blood Oxygenated Deoxygenated Site Blood Blood Liver Umbilical Portal system vein IVC Umbilical Lower vein extremities Right Umbilical + Upper Atrium vein blood extremities from IVC From Right Left Atrium Atrium through From Lungs Foramen Ovale Figure 15. Patent Foramen Ovale [mayoclinic.org] Ductus Pulmonary Aorta Arteriosus Trunk (B) PATENT DUCTUS ARTERIOSUS Ductus Arteriosus doesn’t close (C) NICE TO KNOW IVC carries the most oxygenated blood in fetus More oxygenated blood is delivered to Upper Limbs Upper limbs > Lower Limbs V) CHANGES FROM FETUS TO ADULT Table 2. Postnatal occlusion of vessels/ structures & their remnants Structure Remnant Left Umbilical Vein Ligamentum Teres Hepatis Umbilical Arteries i. Proximal part i. Superior Vesical Artery ii. Distal part ii. Medial Umbilical Ligament Ductus Venosus Ligamentum Venosum Ductus Arteriosus Ligamentum Arteriosum Foramen Ovale Fossa Ovalis REMEMBER Remnant of: Figure 16. Patent Ductus Arteriosus UmbilicAL Arteries- MediAL Umbilical Ligaments [Netter’s Atlas] Allantois (Urachus)- Median Umbilical Ligament (C) PORTAL HYPERTENSION Ligamentum teres hepatis recanalizes 6 of 8 EMBRYOLOGY: Note #17. DEVELOPMENT OF FETAL CIRCULATION  VII) SUMMARY Figure 17. Development of Fetal Circulation VIII) APPENDIX Figure 18. Fetal Circulation & Transition to Post-natal Circulation [Netter’s Atlas] DEVELOPMENT OF FETAL CIRCULATION EMBRYOLOGY: Note #1. 7 of 8  IX) REVIEW QUESTIONS X) REFERENCES 1) Which is NOT essential for maintenance of fetal Cochard, L. R., & Netter, F. H. (2002). Netter's atlas of human circulation? embryology. Teterboro, N.J: Icon Learning Systems. Inderbir Singh, Pal GP. Human Embryology. 8th ed. India: Mac a) Foramen ovale Millan Publishers Limited; 2007. b) Ductus arteriosus Sadler TW. Langman's Medical Embryology. Philadelphia: c) Renal veins Wolters Kluwer; 2019. d) Inferior Vena Cava Le T. First Aid for the USMLE Step 1 2020. 30th anniversary edition: McGraw Hill; 2020. Marieb EN, Hoehn K. Anatomy & Physiology. Hoboken, NJ: Pearson; 2020. 2) Which structure carries the most oxygenated blood Boron WF, Boulpaep EL. Medical Physiology.; 2017. in fetus? a) Umbilical vein b) Renal vein c) Inferior vena cava d) Umbilical artery 3) What is the remnant of umbilical arteries? a) Ligamentum arteriosum b) Superior vesical artery c) Ligamentum teres hepatis d) Ligamentum venosum 4) What is the concentration of oxygen in Umbilical Artery? a) 15% b) 28% c) 58% d) 85% 5) Ductus arteriosus connects pulmonary artery to which of the following? a) Pulmonary vein b) Foramen ovale c) Subclavian artery d) Aorta 6) Before birth, blood is shunted: a) Away from pulmonary circulation b) Towards pulmonary circulation c) No shunts present d) Both a & b, according to respiration 7) What is the remnant of urachus? a) Medial umbilical ligament b) Lateral umbilical ligament c) Median umbilical ligament d) Ligamentum teres 8) Ductus arteriosus is sensitive to all EXCEPT: a) Prostaglandins b) Leukotrienes c) Oxygen d) Bradykinin CHECK YOUR ANSWERS 8 of 8 EMBRYOLOGY: Note #17. DEVELOPMENT OF FETAL CIRCULATION