Development of Blood Vessels, Fetal Circulation PDF

EMBRYOLOGY. DEVELOPMENT OF THE MAJOR BLOOD VESSELS. BLOOD SUPPLY OF THE FETUS Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]  LEARNING OUTCOMES – Continua...

EMBRYOLOGY. DEVELOPMENT OF THE MAJOR BLOOD VESSELS. BLOOD SUPPLY OF THE FETUS Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]  LEARNING OUTCOMES – Continuation of the topic ‘Development of the heart’ EMBR.07 - Cardiovascular and Lymphatic system development EMBR.07.01 - Be able to explain the sequential formation of hemangioblasts, blood islands, endothelial lined tubes a EMBR.07.02 - Be able to explain the similarities between the heart tubes, dorsal aorta and the vitelline veins EMBR.07.03 - Be able to explain how lateral folding modifies the developing heart tube, dorsal aorta, and vitelline veins EMBR.07.04 - Be able to explain the components of the heart tube and there derivatives EMBR.07.05 -Be able to explain cardiac looping and clinical correlations EMBR.07.06 - Be able to explain the development of the atrioventricular canals EMBR.07.07 - Be able to explain the septation and further modification of the primitive atria and their clinical correlations EMBR.07.08 - Be able to explain the importance of the right-left blood shunt EMBR.07.09 - Be able to explain the septation and further modification of the primitive ventricles and their clinical correlations EMBR.07.10 - Be able to explain the formation and modification of Sinus Venosus and Truncus Arteriosus and their clinical correlations EMBR.07.11 - Be able to explain the difference between the membranous ventricular septum and the conotruncal septum EMBR.07.12 - Explain the veins of the sinus venosus- umbilical, vitelline, and cardinal EMBR.07.13 - Be able to explain the tributaries of the posterior cardinal vein and how they are modified EMBR.07.14 - Be able to explain the tributaries of the anterior cardinal vein and how they are modified EMBR.07.15 - Be able to explain how the common cardinal veins are modified EMBR.07.16 - Be able to explain how the truncus arteriosus is modified EMBR.07.17 - Be able to explain the formation and modification of fetal circulation and its shunts EMBR.07.18 - Be able to explain the development of the lymphatic system  OVERVIEW Blood vessels develop from mesenchymal cells derived from mesoderm. These are formed by two processes: vasculogenesis and angiogenesis. 1. Vasculogenesis: process of formation of new vessels by coalescence (assembly) of angioblasts (specialised mesenchymal cells). 2. Angiogenesis: process of formation of new vessels by budding and branching from preexisting vessels.  OVERVIEW Major blood vessels of the vascular system of the body, i.e., dorsal aortae and cardinal vessels are formed by vasculogenesis, and remaining vessels are formed by angiogenesis. Both the processes of vasculogenesis and angiogenesis are patterned, and guided by vascular endothelial growth factor (VEGF) and other growth factors.  DEVELOPMENT OF ARTERIAL SYSTEM Arteries of body develop from two main sources: pharyngeal (aortic) arch arteries, dorsal aorta. Aortic arches give rise to the arteries of head and neck region. Dorsal aorta gives rise to the arteries of rest of the body.  PHARYNGEAL ARCH ARTERIES AND THEIR DERIVATIVES 1. First arteries to appear in a developing embryo are the right and left primitive aortae. 2. These become continuous with two primitive heart tubes. Each primitive aorta is divided into three parts: a) Part lying ventral to foregut is called ventral aorta. b) Part lying dorsal to gut is called dorsal aorta. c) Arched portion connecting the ventral and dorsal aortae lies in the first pharyngeal arch. It forms first aortic arch artery.  PHARYNGEAL ARCH ARTERIES AND THEIR DERIVATIVES After fusion of two primitive heart tubes, the two ventral aortae partially fuse to form aortic sac. Unfused parts of ventral aortae form right and left horns of the aortic sac.  PHARYNGEAL (AORTIC) ARCH ARTERIES Aortic arches are blood vessels that run in between the pharyngeal pouches and form the major head and neck arteries. The arches develop in craniocaudal order. As the pharyngeal arches develop during 4th and 5th weeks, each arch is supplied by an artery – pharyngeal arch artery derived from the aortic sac (i.e., aortic sac contributes a branch to each new arch as it forms). Aortic sac gives rise to six pairs of aortic arch arteries. Fifth either never developing or also obliterating without giving rise to a vessel. Five aortic arch arteries are numbered as I, II, III, IV, and VI. Aortic arch arteries are embedded in the mesenchyme of the pharyngeal arches.  DERIVATIVES OF AORTIC ARCH ARTERIES The greater part of the first and second arch arteries disappear Fifth pair appears to disappear DERIVATIVES OF AORTIC ARCH ARTERIES DERIVATIVES OF AORTIC ARCH ARTERIES  DEVELOPMENT OF OTHER ARTERIES OF THE BODY These develop from primitive dorsal aortae.  DEVELOPMENT OF OTHER ARTERIES OF THE BODY Primitive dorsal aorta gives off three sets of branches: 1. Dorsolateral (somatic intersegmental) branches form arteries of upper and lower limbs, intercostal lumbar, and lateral sacral arteries. 2. Lateral splanchnic branches form phrenic, suprarenal, renal, and gonadal vessels. 3. Ventral splanchnic branches form vitelline (celiac, superior, and inferior mesenteric) and umbilical arteries. The arteries for bronchi and esophagus also arise from ventral splanchnic branches. BRANCHING PATTERN OF DORSAL AORTA AND ITS ANASTOMOSES SOURCE OF DEVELOPMENT OF MAIN ARTERIES  DEVELOPMENT OF VENOUS SYSTEM In the 5th week of intrauterine life (IUL), three pairs of major primitive veins are seen in the developing embryo. 1. Vitelline veins, which return poorly oxygenated blood from yolk sac. 2. Umbilical veins, which carry well-oxygenated blood from placenta. 3. Common cardinal veins, which return poorly oxygenated blood from the body of the embryo. Cardinal = important N.B. Common cardinal vein on each side is formed by the union of anterior and posterior cardinal veins.  DEVELOPMENT OF VENOUS SYSTEM Veins of developing embryo can be grouped as visceral and somatic veins. Visceral veins 1. Vitelline or omphalomesenteric veins - for draining yolk sac. 2. Umbilical veins - for placenta. Somatic veins These are cardinal veins for draining body wall: 1. Anterior cardinal veins (right and left) 2. Posterior cardinal veins (right and left) 3. Common cardinal veins or ducts of Cuvier (right and left) Anterior and posterior cardinal veins join to form common cardinal veins. Anterior cardinal veins drain: – cranial half of embryo – upper limb buds Posterior cardinal veins drain – caudal half of embryo – lower limb buds. DEVELOPMENT OF VENOUS SYSTEM. FLOWCHART  DEVELOPMENT OF VENOUS SYSTEM Visceral and somatic veins finally drain into the sinus venosus. These visceral and somatic veins later in adult form – portal veins – caval veins – azygous veins  FETAL CIRCULATION. OVERVIEW Fetal circulation is different from that of adult circulation in the following three ways: 1. Blood in the fetus is oxygenated by placenta and not by the lungs. 2. During fetal life, the lungs are collapsed; hence, the resistance to blood flow through the lung is much higher. As a result, only minimal amount of blood passes through the lungs to supply oxygen and nutrients to the lungs. 3. Portal circulation is of little significance.  FETAL CIRCULATION. OVERVIEW In the placenta, maternal blood does not directly mix with fetal blood; it is separated from it by the placental barrier. Oxygen and nutrients are exchanged across this barrier. Oxygenated blood from the placenta flows through the single umbilical vein to the fetus. Less oxygenated blood from the aorta flows through the common iliac arteries, internal iliac arteries and the two umbilical arteries to the placenta for oxygenation. Fetal shunts maintain the highest possible oxygen concentration for the brain and other organs.  BASIC PATHWAY OF THE FETAL CIRCULATION Deoxygented blood Oxygenated blood: placenta  umbilical vein  ductus venosus  inferior vena cava Mixed blood (high oxygen concentration): inferior vena cava  right atrium  foramen ovale  left atrium  left ventricle Mixed blood (low oxygen concentration): descending aorta  common iliac arteries  internal iliac arteries  umbilical arteries  placenta.  FETAL SHUNTS Blood in umbilical vein has a Po2 of ≈ 30 mm Hg and is ≈ 80% saturated with O2. Umbilical arteries have low O2 saturation. 3 important shunts: 1. Ductus venosus / Arantius’ duct – shunt between the umbilical vein and the inferior vena cava, bypassing the liver. 2. Foramen ovale - shunt between the right and left atria, bypassing the pulmonary circulation. 3. Ductus arteriosus / ductus Botalli – shunt between the pulmonary trunk and the initial segment of the descending aorta, bypassing the pulmonary circulation and the aortic arch.  FETAL CIRCULATION In fetus (i.e., before birth), the highly oxygenated (80% saturated with O2), nutrient-rich blood from the placenta returns to the fetus by umbilical vein. Umbilical vein traverses through the umbilical cord, enters the abdomen through umbilicus, and passes to the liver through falciform ligament. In the liver, the umbilical vein joins the left branch of portal vein. Here, most of blood from umbilical vein (about 85%) bypasses the sinusoids of the liver by passing through ductus venosus – a channel that connects left branch of portal vein to the IVC. Only small amount of blood of umbilical vein (about 25%) enters the liver sinusoids and mixes with the blood from the portal circulation. IVC – inferior vena cava SVC – superior vena cava  FETAL CIRCULATION In the IVC, richly oxygenated blood mixes with the deoxygenated blood returning from the lower limbs. After a short course, the IVC opens into the right atrium. As this blood enters in the right atrium, it is guided by the valve of IVC toward foramen ovale. Most of blood from the IVC passes through foramen ovale into the left atrium. Only small amount of blood from the IVC remains in the right atrium. Here, it mixes with the deoxygenated blood from the SVC and passes to the right ventricle.  FETAL CIRCULATION Blood from the right ventricle passes through pulmonary trunk, and right and left pulmonary arteries. But due to high resistance in pulmonary tissue during fetal life, only a small amount of blood enters the pulmonary circulation. Most of blood passes into the aorta through the ductus arteriousus – a channel that connects the left pulmonary artery to arch of aorta.  FETAL CIRCULATION Left atrium receives mainly rich oxygenated blood from the right atrium through the foramen ovale. Only a small amount of deoxygenated blood enters the left atrium from the lungs through the pulmonary veins. Blood from the left atrium passes to the left ventricle. Blood from the left ventricle enters into the ascending aorta, which through its three large branches (brachiocephalic artery, left common carotid artery, and left subclavian artery) supply oxygenated blood to the head, neck, brain, and superior extremity.  FETAL CIRCULATION Since the coronary and carotid arteries are the first branches of the aorta, the heart musculature and brain are supplied by well- oxygenated blood. Arch of aorta receives poorly oxygenated blood from the pulmonary trunk through the DA. Then the blood is distributed by the aorta and common iliac arteries to the lower part of the body. Lower part of the body is thus supplied with relatively less oxygenated blood as compared with the upper part of the body.  FETAL CIRCULATION Two umbilical arteries arising from internal iliac branches of common iliac arteries pass through umbilicus and enter the placenta through the umbilical cord, where it is oxygenated. O2 saturation in umbilical arteries is about 58%. FLOWCHART: FETAL CIRCULATION CIRCULATORY CHANGES AT BIRTH Following birth, 3 shunts will close because of changes in the pressure gradients and in oxygen tensions. Umbilical vein closes and reduces blood flow into the right atrium. Ductus venosus also closes. Lung expansion reduces pulmonary resistance and results in increased flow to the lungs and increased venous return to the left atrium.  POSTNATAL CLOSURE OF SHUNTS Closure of the foramen ovale occurs as a result of the increase in left atrial pressure and reduction in right atrial pressure. Closure of the ductus venosus and ductus arteriosus occurs over the next several hours as a result of the contraction of smooth muscles in its wall and increased oxygen tension. Release of bradykinin and the immediate drop of prostaglandin E at birth also facilitate the closure of the ductus arteriosus. CIRCULATORY CHANGES AT BIRTH  FOLDS OF INTERNAL SURFACE OF THE ANTERIOR ABDOMINAL WALL 1. Median umbilical fold (plica umbilicalis mediana) – an unpaired fold formed by the median umbilical ligament (a remnant of the urachus) 2. Medial umbilical fold (plica umbilicalis medialis) – a paired fold formed by the medial umbilical ligament 3. Lateral umbilical fold (plica umbilicalis lateralis) – a paired fold formed by the inferior epigastric vessels. COMPARISON OF THE FETAL AND POSTNATAL CIRCULATION REFERENCES