Diagram of the human feto-placental circulatory system.
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The fetal circulation is the circulatory system of a human fetus, often encompassing the entire fetoplacental circulation that also includes the umbilical cord and the blood vessels within the placenta that carry fetal blood.
The fetal circulation works differently from that of born humans, mainly because the lungs are not in use: the fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord.[1]
Contents
- 1 Placental role
- 2 Circuit
- 3 Blood pressure
- 4 Flow
- 5 At birth
- 6 References
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Placental role
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. Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen. The uterine arteries carry oxygenated blood to the placenta, and permeates the sponge-like material there. Oxygen then diffuses from the placenta to the chorionic villus, an alveolus-like structure, where it is then carried to the umbilical vein.
Circuit
Blood from the placenta is carried to the fetus by the umbilical vein. About half of this enters the fetal ductus venosus and is carried to the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of the heart. In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows through this hole directly into the left atrium from the right atrium, thus bypassing pulmonary circulation. The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the maternal circulation.[1]
Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid).[1]
Blood pressure
It is the fetal heart and not the mother's heart that builds up the fetal blood pressure to drive its blood through the fetal circulation.
Intracardiac pressure remains identical between the right and left ventricles of the human foetus [2] .
The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to ca 45 mmHg at 40 weeks of gestation.[3] The fetal pulse pressure is ca 20 mmHg at 20 weeks of gestation, increasing to ca 30 mmHg at 40 weeks of gestation.[3]
The blood pressure decreases when passing through the placenta. In the arteria umbilicalis, it is ca 50 mmHg. It falls to 30 mmHg in the capillaries in the villi. Subsequently, the pressure is 20 mm Hg in the umbilical vein, returning to the heart.[4]
Flow
The blood flow through the umbilical cord is approximately 35 mL/min at 20 weeks, and 240 mL/min at 40 weeks of gestation.[5] Adapted to the weight of the fetus, this corresponds to 115 mL/min/kg at 20 weeks and 64 mL/min/kg at 40 weeks.[5] It corresponds to 17% of the combined cardiac output of the fetus at 10 weeks, and 33% at 20 weeks of gestation.[5]
Endothelin and prostanoids cause vasoconstriction in placental arteries, while nitric oxide causes vasodilation.[5] On the other hand, there is no neural vascular regulation, and catecholamines have only little effect.[5]
At birth
At birth, when the infant breathes for the first time, there is a decrease in the resistance in the pulmonary vasculature, which causes the pressure in the left atrium to increase relative to the pressure in the right atrium. This leads to the closure of the foramen ovale, which is then referred to as the fossa ovalis. Additionally, the increase in the concentration of oxygen in the blood leads to a decrease in prostaglandins, causing closure of the ductus arteriosus. These closures prevent blood from bypassing pulmonary circulation, and therefore allow the neonate's blood to become oxygenated in the newly operational lungs.[6]
References
- ^ a b c Whitaker, Kent (2001). "Fetal Circulation". Comprehensive Perinatal and Pediatric Respiratory Care. Delmar Thomson Learning. pp. 18–20. ISBN 978-0-7668-1373-1. http://books.google.com/books?id=R3WK8XyAHYgC&pg=PA18.
- ^ Johnson, P.; D.J., Maxwell, M.J. Tynan, L.D. Allan (2000). "Dr.". Heart 84 (1): 59-63. doi:10.1136/heart.84.1.59. http://heart.bmj.com/content/84/1/59.full. Retrieved 09/04/12.
- ^ a b Struijk, P. C.; Mathews, V. J.; Loupas, T.; Stewart, P. A.; Clark, E. B.; Steegers, E. A. P.; Wladimiroff, J. W. (2008). "Blood pressure estimation in the human fetal descending aorta". Ultrasound in Obstetrics and Gynecology 32 (5): 673–81. doi:10.1002/uog.6137. PMID 18816497.
- ^ "Fetal and maternal blood circulation systems". Swiss Virtual Campus. http://www.embryology.ch/anglais/fplacenta/circulplac01.html. Retrieved June 29, 2011.
- ^ a b c d e Kiserud, Torvid; Acharya, Ganesh (2004). "The fetal circulation". Prenatal Diagnosis 24 (13): 1049–59. doi:10.1002/pd.1062. PMID 15614842.
- ^ Le, Tao; Bhushan, Vikas; Vasan, Neil (2010). First Aid for the USMLE Step 1: 2010 20th Anniversary Edition. USA: McGraw-Hill. p. 123. ISBN 978-0-07-163340-6.
Circulatory system: Arteries and veins (TA A12.0, TH H3.09.02, GA 6.543/GA 7.641)
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Systemic circulation |
(Left heart) → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → (Right heart)
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Pulmonary circulation |
(Right heart) → Pulmonary arteries → (Lungs) → Pulmonary vein → (Left heart)
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Blood vessels |
- Endothelium
- Tunica intima
- Tunica media
- Tunica externa
- Vasa vasorum
- Vasa nervorum
- Rete mirabile
- Circulatory anastomosis
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Arteries |
- Nutrient artery
- Arteriole
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Veins |
- Vena comitans
- Superficial vein
- Deep vein
- Emissary veins
- Venous plexus
- Venule
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Lymphatic |
- Lymphatic vessel
- Lymph
- Lymph capillary
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anat(a:h/u/t/a/l,v:h/u/t/a/l)/phys/devp/cell/prot
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noco/syva/cong/lyvd/tumr, sysi/epon, injr
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proc, drug(C2s+n/3/4/5/7/8/9)
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Anatomy of torso, cardiovascular system: heart (TA A12.1, TH H3.09.01, GA 5.524)
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General |
Surface
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base · apex · grooves (coronary/atrioventricular, interatrial, anterior interventricula, posterior interventricular) · surfaces (sternocostal, diaphragmatic) · borders (right, left) · Openings of smallest cardiac veins
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Internal
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atria (interatrial septum, musculi pectinati, sulcus terminalis) · ventricles (interventricular septum, trabeculae carneae, chordae tendineae, papillary muscle) · valves · cusps · Atrioventricular septum
cardiac skeleton
Intervenous tubercle
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Chambers |
Right heart
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(venae cavae, coronary sinus) → right atrium (atrial appendage, fossa ovalis, limbus of fossa ovalis, crista terminalis, valve of inferior vena cava, valve of coronary sinus) → tricuspid valve → right ventricle (conus arteriosus, moderator band/septomarginal trabecula) → pulmonary valve → (pulmonary artery and pulmonary circulation)
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Left heart
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(pulmonary veins) → left atrium (atrial appendage) → mitral valve → left ventricle → aortic valve (aortic sinus) → (aorta and systemic circulation)
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Layers |
Endocardium
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Heart valves
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Myocardium
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Conduction system: Cardiac pacemaker · SA node · AV node · bundle of His · Purkinje fibers
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Pericardial cavity
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Pericardial sinus
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Pericardium
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fibrous pericardium (Sternopericardiac ligaments) · serous pericardium (epicardium/visceral layer) · Fold of the left vena cava
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noco/cong/tumr, sysi/epon, injr
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proc, drug (C1A/1B/1C/1D), blte
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Cardiovascular system, physiology: cardiovascular physiology
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Heart |
Volumes
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Stroke volume = End-diastolic volume – End-systolic volume
Cardiac output = Heart rate × Stroke volume
Afterload · Preload
Frank–Starling law of the heart · Cardiac function curve · Venous return curve
Aortic valve area calculation · Ejection fraction · Cardiac index
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Dimensions
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Fractional shortening = (End-diastolic dimension – End-systolic dimension) / End-diastolic dimension
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Interaction diagrams
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Cardiac cycle · Wiggers diagram · Pressure volume diagram
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Tropism
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Chronotropic (Heart rate) · Dromotropic (Conduction velocity) · Inotropic (Contractility) · Bathmotropic (Excitability) · Lusitropic (Relaxation)
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Conduction system /
Cardiac electrophysiology
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Cardiac action potential (Atrial action potential, Ventricular action potential) · Effective refractory period · Pacemaker potential · EKG (P wave, PR interval, QRS complex, QT interval, ST segment, T wave, U wave) · Hexaxial reference system
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Chamber pressure
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Central venous pressure/right atrial pressure → Right ventricular pressure → Pulmonary artery pressure → Pulmonary wedge pressure/left atrial pressure → Left ventricular pressure → Aortic pressure
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Other
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Ventricular remodeling
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Vascular system/
Hemodynamics |
Blood flow
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Compliance · Vascular resistance (Total peripheral resistance) · Pulse · Perfusion
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Blood pressure
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Pulse pressure (Systolic - Diastolic) · Mean arterial pressure
Jugular venous pressure
Portal venous pressure
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Regulation of BP
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Baroreflex · Kinin–kallikrein system · Renin–angiotensin system · Vasoconstrictors/Vasodilators · Autoregulation (Myogenic mechanism, Tubuloglomerular feedback, Cerebral autoregulation) · Paraganglia (Aortic body, Carotid body, Glomus cell)
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noco/cong/tumr, sysi/epon, injr
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proc, drug (C1A/1B/1C/1D), blte
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anat(a:h/u/t/a/l,v:h/u/t/a/l)/phys/devp/cell/prot
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noco/syva/cong/lyvd/tumr, sysi/epon, injr
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proc, drug(C2s+n/3/4/5/7/8/9)
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Prenatal development/Mammalian development of circulatory system (GA 5, TE E5.11)
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Heart development |
Tubular heart
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Truncus arteriosus · Bulbus cordis · Embryonic ventricle · Primitive atrium · Sinus venosus
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Septa/ostia
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Atrioventricular cushions/Septum intermedium · Primary interatrial foramen · Septum primum (Foramen secundum) · Septum secundum (Foramen ovale) · Aorticopulmonary septum
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Other
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Atrioventricular canal · Primary interventricular foramen
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Vasculogenesis,
angiogenesis,
and lymphangiogenesis |
Blood island of umbilical vesicle
Development of arteries
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Dorsal aorta · Aortic arches
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Development of veins
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Anterior cardinal vein · Posterior cardinal vein · Common cardinal veins
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Development of lymph vessels
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Lymph sacs
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Development of circulatory system
about teeth near children
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anuli: Anulus sanguineus perienameleus · lacunae: Lacuna sanguinea supraenamelea (Ductus sanguineus mesialis · Ductus sanguineus distalis · Ductus sanguineus lingualis · Ductus sanguineus palatinus · Ductus sanguineus buccalis · Ductus sanguineus labialis), Lacuna sanguinea apicalis, Lacuna sanguinea periodontalis, Lacuna sanguinea parodontalis, Lacuna sanguinea gingivalis
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Extraembryonic
hemangiogenesis |
Chorion · Connecting stalk · Yolk sac · Placenta
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Fetal circulation |
umbilical cord: Umbilical vein → Ductus venosus → Inferior vena cava → Heart → Pulmonary artery → Ductus arteriosus → Aorta → Umbilical artery
yolk sac: Vitelline veins · Vitelline arteries
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noco/cong/tumr, sysi/epon, injr
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proc, drug (C1A/1B/1C/1D), blte
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anat(a:h/u/t/a/l,v:h/u/t/a/l)/phys/devp/cell/prot
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noco/syva/cong/lyvd/tumr, sysi/epon, injr
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proc, drug(C2s+n/3/4/5/7/8/9)
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