Heart & vascular system I. Dawei Dong

Transcription

1 Heart & vascular system I Dawei Dong

2 Lecture goal Learn the basics of heart and vascular development.

3 Development of Heart, Blood, and Blood Vessels LEARNING GOALS: 1. explain the early development of the cardiac tube from visceral mesoderm ahead of the neural plate which is then folded beneath the pharynx of the head fold. 2. outline the fusion of the cardiac tube to form the simple linear heart, the segmentation and the loop formation with sinus venosus, atrium, ventricle, bulbus cordis, and truncus arteriosus. 3. show how septum formation in the primitive heart allows separate pumping of blood into the aortic and the pulmonary trunk. 4. describe the heart inlet separation through the incorporation of the sinus venosus and the pulmonary veins into the atrium. 5. understand the developmental process by which the conus cordis and truncus arteriosus are adapted to give the aortic and pulmonary trunk, i.e., the heart outlet separation. 6. describe the three periods of blood cell formation related to the yolk sac, the liver and the bone marrow. 7. define the three circulatory arcs of the heart to/from the body tissues, the yolk sac (vitelline) and the allantois (umbilical), describe their functions, and understand developmental changes of the arterial and venous systems, in particular, the left and right symmetry breaking. 8. understand the changes of the circulation at birth.

4 Early development of the heart The cardiac tube folds under the gut tube The cardiac tube(6) is established in the early gastrula as regions of visceral mesoderm ahead of the embryo itself. As a result of the head fold, the developing heart(8) ends up beneath the pharynx. Modified from Sadler (2006) 1.Ectoderm 2.Mesoderm 3.Endoderm 4.Amniotic cavity 5.&11.Yolk sak 7.Extra-embryonic coelom 9.Allantoic bud 10.Primitive gud 12.Allantois

5 Early development of the heart and connects bilaterally with the dorsal aorta via the aortic arches * The heart is a U-shaped tube(2) from the cardiogenic field(1) at the anterior part of the embryo. * The dorsal aortae(3,8) form independently and then grow to meet the ventral aortae(9) in the aortic arches, while fuse caudally(6). The anterior of the cardiac tube fuses with the vitelline veins(4,5). The sides(7) of the U-tube then fuse to produce the bulbus cordis(10), ventricle(11) and the atrium(12) as simple linear pump. Modified from McGaedy et al (2006) 13.Pericardial cavity, 14.septum transversum, 15.primitive gut, 16.brain vesicles

6 Segmentation of the cardiac tube and loop formation At first, the sinus venosus(6) and the atrium(4) are not enclosed within the pericardium cavity(5), but because the cardiac tube outgrows the pericardial cavity, and because the tube is fixed in the pericardium at both ends, the tube becomes U-shaped with the loop of U pointing ventrally, i.e., the bulboventricular loop, which draws the atrium and the sinus venosus into the pericardial cavity. Modified from McGaedy et al (2006) Continued cardiac growth results in the atrium occupying a position dorsal to the bulbus cordis(2) and the ventricle(3) and it expands toward the truncus arteriosus(1), which connects to the dorsal aortae(9) through the aortic arches(8). 7.septum transversum,

7 * The septum primum(6) divides the common atrium(1) into right(14) and left(15) atria. * Initially the foramen primum(7) persists as an opening, but it eventually closes. * Before it closes completely, programmed cell death results in the foramen secundum(13). * A second membrane--septum secundum(16)) arises from the dorsal right atrium and extends toward the septum intermedium(8) (but does not reach the septum intermedium). * Resultant opening is the foramen ovale(19). * Septum intermedium(8) grows from endorcardial cushions to divide the atrioventricular canal to left(9) and right(10). * The interventricular septum(11) grows near the interventricular sulcus(12) to divide the ventricle(2) and the bulbus cordis(3) into left(18) and right(17) ventricles. 4.cranial&5.caudal vena cava,20.cavitations. Partitioning of the heart into four chambers Modified from McGaedy et al (2006)

8 Division of inlet to the heart Modified from Hyttel et al (2010) * The right sinus horn(1,5) is incorporated into the right atrium(7), and also forms part of cranial(10) and caudal(9) vena cava. * The pulmonary veins(2,6) are incorporated into the left atrium(8). * The septum primum(3) divides the common atrium into L and R atria. * Initially the foramen primum(4) persists as an opening, but it eventually closes. * Before it closes completely, programmed cell death results in the foramen secundum(12) * A second membrane--septum secundum(11) arises from the dorsal right atrium and extends toward the septum intermedium (but does not reach the septum intermedium) * Resultant opening is the foramen ovale(13).

9 McGaedy et al (2006) Division of the outlet of the heart * Septum intermedium grows from endorcardial cushions to divide the atrioventricular canal. * Interventricular septum grows from the interventricular sulcus to divide the ventricule and the bulbus cordis into left and right ventricles. * Interventrical foramen is later closed by the membranous interventrical septum (developed from the endocardial cushion, in shuch a way that both ventricles open into the conus cordis. * Conus cordis and truncus arteriosus are divided by growing pair of cushions from their walls to form aorticopulmonary septum, rotating180, so that the aortic trunk (on the right at the top) is linked down to the left ventricle and the pulmonary trunk (on the left at the top) is linked down to the right ventricle.

10 Formation of blood cells THREE OVERLAPPING PERIODS OF BLOOD CELL FORMATION 1. MESOBLASTIC PERIOD FIRST BLOOD CELLS, 4MM EMBRYOS FORMED IN YOLK-SAC WALL 2. HEPATO-LIENAL PERIOD 10MM EMBRYOS FORMED IN LIVER IN SPLEEN LATER UNTIL BIRTH 3. MEDULLARY PERIOD THE ONLY LASTING ONE FROM EMBROY THROUGH ADAULT LIGE FORMS IN BONE MARROW

11 Developing vascular system THREE CIRCULATORY ARCS OF THE EMBRYONIC BLOOD SUPPLY 1. BODY CIRCULATION TRANSPORT OF O 2 /FOOD MATERIALS TO TISSUES TRANSPORT OF WASTE MATERIALS AWAY 2. VITELLINE CIRCULATION CARRIES MOBILISED FOOD MATERIALS FROM THE YOLK SAC LOST FUNCTION IN MAMMALS BECAUSE SAC EMPTY CARRIES FIRST BLOOD CELLS FROM YOLK SAC WALL 3. ALLANTOIC CIRCULATION IN MAMMALS TAKES OVER THE FUNCTIONS OF THE VITELLINE ARC IN BIRDS SUPPLIES FOOD MATERIALS FROM MATERNAL CIRCULATION RETAINS AVIAN FUNCTION OF REMOVAL OF WASTE AND GAS EXCHANGE

12 Developing vascular system Dorsal aorta Cardinal veins Mesonephros Aortic arches Vitelline vein Vitelline artery Allantoic artery Deoxygenated blood Mixed blood Oxygenated blood Yolk sac Allantoic vein placenta

13 Developing vascular system Modified from Hyttel et al (2010) 4. truncus brachiocephalicus, 7. left external carotid artery, 11: N. Vagus, 12: N. laryngeus recurrens. I-VI aortic arches corresponding to six branchial arches, III, IV, VI prominent, connecting ventral aorta(2) to dorsal aorta(1) right and left. III arches forms right and left(6) common carotid arteries. IV right forms the proximal right subclavian artery(5 ), the left retained as the aorta(3) connecting the left ventricle to the left dorsal aorta. VI proximal forms left(10) and right(10 ) pulmonary arteries, the distal right atrophies and the distal left forms the ductus arteriosus(9).

14 Developing vascular system Modified from Hyttel et al (2010) 4. truncus brachiocephalicus, 7. left external carotid artery, 11: N. Vagus, 12: N. laryngeus recurrens. dorsal aortae atrophy between the III and IV aortic arches. III arches forms right and left(6) common carotid arteries. cranial parts of dorsal aortae give rise to left(8) and right internal carotid arteries. caudal parts of dorsal aortae are mostly fused to a single caudal aorta and give rise to dorsal, lateral and ventral segmental arteries. a pair of dorsal segmental arteries, together with parts of the dorsal aortae form the left subclavian artery(10) and the rest of the right subclavian artery(10 ).

15 Developing vascular system The left vitelline vein and the right allantoic vein involute and disappear. The proxiaml left allantoic vein forms anastomosis with the proximal portion of the right vitelline vein and persists as the ductus venosus which shunts oxygenated blood from the placenta through the liver. The proximal right vitelline vein develops into the hepatocardiac portion of the caudal vena cava, connecting the ductus venosus and the heart. The distal portion of the right vitelline vein develops into the portal vein McGaedy et al (2006)

16 Changes in circulation at birth McGaedy et al (2006) The blood flow from the placenta to the fetus is stopped by the contraction of the ductus venosus and the left allantoic vein. The blood flow to the placenta is stopped by contraction of the allantoic arteries. Starting respiration starts stimulates the pulmonary blood circulation. As a result, the blood pressure in the left atrium increases which closes the foramen ovale. The ductus arteriosus closes reflexively, preventing deoxygenated blood in the pulmonary trunk from entering the aorta.

17 REFERENCES Hyttel S, Sinowatz F, Vejlsted M (2010) Domestic animal embryology. McGeady TA, Quinn PJ, Fitzpatrick ES, Ryan MT (2006) Veterinary embryology. Sadler TW (2006) Langman's medical embryology. WEB LEARNING AIDS