Ebook Langman''s medical embryology (12/E): Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Ebook Langman''s medical embryology (12/E): Part 2
Ebook Langman''s medical embryology (12/E): Part 2
ESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2o satisfy its nutritional requirements by diffusion alone. Progenitor heart cells lie in the epiblast, immediately adjacent to the cranial end of the primitive streak. From there, they migrate through the streak and into the splanchnic layer of lateral plate mesoderm where they form a horseshoe-shap Ebook Langman''s medical embryology (12/E): Part 2ed cluster of cells called the primary heart field (PHF) cranial to the neural folds (Fig. 13.1). As the progenitor heart cellsmigrate and form the PHEbook Langman''s medical embryology (12/E): Part 2
F during days 16 to 18. they are specified on both sides from lateral to medial to become the atria, left ventricle. and most of the right ventricle (ESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2his process and the signaling pathway it is dependent upon (Fig. 13.2) is essential for normal heart development.The remainder of the heart, including part of the right ventricle and outflow tract (conus cordis and truncus arteriosus), is derived from the secondary heart field (SHF).This field of ce Ebook Langman''s medical embryology (12/E): Part 2lls appears slightly later (days 20 to 21) thanFigure 13.1 A. Dorsal view of a late presomite embryo (approximately 18 days) after removal of the amniEbook Langman''s medical embryology (12/E): Part 2
on. Progenitor heart cells have migrated and formed the horseshoe-shaped primary heart field (PHF) located in the splanchnic layer of lateral plate meESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2ght ventricle.The remainder of the right ventricle and the outflow tract consisting of conus cordis and truncus arteriosus are formed by the secondary heart field (SHF). B. Transverse section through a similar-staged embryo to show the position of PHF cells in the splanchnic mesoderm layer, c. Cepha Ebook Langman''s medical embryology (12/E): Part 2locaudal section through a similar-staged embryo showing the position of the pericardial cavity and PHF.162Chapter 13 Cardiovascular System 163OropharEbook Langman''s medical embryology (12/E): Part 2
yngealthose in the PHE resides in splanchnic meso* derm ventral to the posterior pharynx, and is responsible for lengthening the outflow tract (see FiESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2the left contribute to the right. This laterality is determined by the same signaling pathway that establishes laterality for the entire embryo (Fig. 13.2) and explains the spiraling nature of the pulmonary artery and aorta and ensures that the aorta exits from the left ventricle and the pulmonary a Ebook Langman''s medical embryology (12/E): Part 2rtery from the right ventricle.Once cells establish the PHE they are induced by the underlying pharyngeal endoderm to form cardiac myoblasts and bloodEbook Langman''s medical embryology (12/E): Part 2
islands that will form blood cells and vessels by the process of vasculogenesis (Chapter 6. p. 75). With time, the islands unite and form a horseshoeESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2r it later develops into the pericardial cavity (Fig. 13.1Ổ.C).In addition to the cardiogenic region, other blood islands appear bilaterally, parallel, and close to the midline of the embryonic shield. These islands form a pair of longitudinal vessels, the dorsal aortae.Figure 13.2 Dorsal view of a Ebook Langman''s medical embryology (12/E): Part 2drawing of a 16-day embryo showing the laterality pathway.The pathway r$ expressed in Literal place mesoderm on the left side and involves a number ofEbook Langman''s medical embryology (12/E): Part 2
signaling molecules, including serotonin (SHT), which result in expression of the transcription factor PfTX2, the master gene for left stdechess-ThisESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2nsible for this patterning have not been completely determined. Disruption of the pathway on tlie left results in lateralty abnormalities, includng many heart defects.Figure I 3.3 Drawing showing the SHF that lies in splanchnic mesoderm at the posterior of the phar-ynx.The SHF provides cells that le Ebook Langman''s medical embryology (12/E): Part 2ngthen the outflow region of the heart, which Includes part of the right ventricle and the outflow tract (conus cordis and truncus arteriosus). NeuralEbook Langman''s medical embryology (12/E): Part 2
crest cells, migrating from cranial neural folds to the heart through pharyngeal arches in this region, regulate the SHF by controlling FGF concentraESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2tcms-Bascd EmbryologyClinical CorrelatesLaterality and Heart DefectsEstablishing laterality during gastrulation (see Chapter 5. p. 55-56) is essential for normal heart development because it specifics cells contributing to and patterning the right and left sides of the heart.The process requires a s Ebook Langman''s medical embryology (12/E): Part 2ignaling cascade that includes serotonin (5HT) as a key molecule in initiating the pathway (Fig. 13.2). 5HT is concentrated on the left side of the emEbook Langman''s medical embryology (12/E): Part 2
bryo, in part because of a high concentration of its degrading enzyme, monoamine oxidase (MAO), on the right side near the primitive node. Nodal and FESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2The right side is also specified, but signals responsible for this event have not been as well established.Cardiac progenitor cells are also specified at this time both for the parts of the heart they will form and their left-right sidedness by the laterality pathway. Thus, this period (days 16 to 1 Ebook Langman''s medical embryology (12/E): Part 28) is critical for heart development and experimental studies showthat disruption of the laterality pathway causes many different types of heart defecEbook Langman''s medical embryology (12/E): Part 2
ts, including dextrocardia (right-sided heart), ventricular septal defects (VSDs). atrial septal defects (ASDs). double outlet right ventricle (DORV; ESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2is, and others. Laterality defects of the heart, such as atrial and ventricular isomerisms (both atria or both ventricles have similar characteristics instead of the normal left-right differences) and inversions (the characteristics of the aưia or ventricles arc reversed), also occur because of disr Ebook Langman''s medical embryology (12/E): Part 2uptions in specifying left and right sidedness in the progenitor heart cells.The importance of laterality in normal heart development may explain theEbook Langman''s medical embryology (12/E): Part 2
apparent role of antidepressants of the selective serotonin reuptake inhibitor (SSRIs) class that have been linked to an increase in heart defects. ThESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2THE HEARTTUBEInitially, the central portion of the cardiogenic area is anterior to the oropharyngeal membrane and the neural plate (Fig. 13.4/1). With closure of the neural tube and formation of the brain vesicles, however, the central nervous system grows cranially so rapidly that it extends over t Ebook Langman''s medical embryology (12/E): Part 2he central cardiogenic region and the future pericardial cavity (Fig. 13.4). As a result of growth of the brain and cephalic folding of the embryo, thEbook Langman''s medical embryology (12/E): Part 2
e oropharyngeal membrane is pulled forward, while rhe heart and pericardial cavity move first to the cervical region and finally to the thorax (Fig. 1ESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2merge except at their caudalrnost ends (Fig. 13.6). Simultaneously, the central part of the horseshoe-shaped tube expands to form the future outflow tract and ventricular regions. Thus, the heart becomes a continuous expanded tube consisting of an inner endothelial lining and an outer myocardial lay Ebook Langman''s medical embryology (12/E): Part 2er (Fig. 13.5Q. It receives venous drainage at its caudal pole and begins to pump blood out of the first aortic arch into the dorsal aorta at its cranEbook Langman''s medical embryology (12/E): Part 2
ial pole (Figs. 13.6 and 13.7).The developing heart tube bulges more and more into the pericardial cavity. Initially, however, the tube remains attachESTABLISHMENT AND PATTERNING OFTHE PRIMARYHEART FIELDThe vascular system appears in the middle of the third week, when the embryo is no longer able to Ebook Langman''s medical embryology (12/E): Part 2s ever formed. With further development, the dorsal mesocardium disappears. creating the transverse pericardial sinus, which connects both sides of the pericardial cavity. The heart is now suspended in the cavity by blood vessels ar its cranial and caudal poles (Fig. 13.7).During these events, the m Ebook Langman''s medical embryology (12/E): Part 2yocardium thickens and secretes a thick layer of extracellular matrix, rich in hyaluronic acid, which separates it from the endothelium (Figs. l3.5Q.lEbook Langman''s medical embryology (12/E): Part 2
n addition, mesothelial cells on rhe surface of the septum transversum form the proepicardium near lhe sinus venous at its caudal end and migrate overGọi ngay
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