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Ebook Langman’s medical embryology (12th edition): Part 2

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Nội dung chi tiết: Ebook Langman’s medical embryology (12th edition): Part 2

Ebook Langman’s medical embryology (12th edition): 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 (12th edition): 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 (12th edition): Part 2

ed 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 PH

Ebook Langman’s medical embryology (12th edition): 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 (12th edition): 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 (12th edition): Part 2

lls 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 amni

Ebook Langman’s medical embryology (12th edition): 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 me

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 (12th edition): 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. Cephal Ebook Langman’s medical embryology (12th edition): Part 2

ocaudal section through a similar-staged embryo showing the position of the pericardial cavity and PHF.162Chapter 13 Cardiovascular System i 63Orophar

Ebook Langman’s medical embryology (12th edition): Part 2

yngealCloacal membranethose in the PHE resides in splanchnic mesoderm ventral to the posterior pharynx, and is responsible for lengthening the outflow

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 (12th edition): Part 2 and those on the 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 t Ebook Langman’s medical embryology (12th edition): Part 2

he pulmonary artery from the right ventricle.Once cells establish the PHE they are induced by the underlying pharyngeal endoderm to form cardiac myobl

Ebook Langman’s medical embryology (12th edition): Part 2

asts and blood islands that will form blood cells and vessels by the process of vasculogenesis (Chapter 6. p. 75). With time, the islands unite and fo

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 (12th edition): Part 2dy) cavity over it later develops into the pericardial cavity (Fig. 13.15, C).In addition to the cardiogenic region, other blood islands appear bilate

rally, parallel, and close to the midline of the embryonic shield. These islands form a pair of longitudinal vessels, the dorsal aortae.Figure 13.2 Do Ebook Langman’s medical embryology (12th edition): Part 2

rsal viewofadrawirigofa 16-day embryo showing the laterality pathway.Tbe pathway 1$ expressed in lateral place mesoderm on the left side and rwolves a

Ebook Langman’s medical embryology (12th edition): Part 2

number of signaling molecules, including serotonin (5HT). which result in expression of the transcnpoon factor PÍTX2, the master gene for left sidedn

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 (12th edition): Part 2es response for this patterning have not been completely determined. Disruption of the pathway on tfve left results in laterafity abnormalities, induc

ing many heart defects.Figure I 3.3 Drawing showing the SHF that lies in splanchnic mesoderm at the posterior of the pharynx.The SHF provides cells th Ebook Langman’s medical embryology (12th edition): Part 2

at lengthen the outflow region of the heart, which includes part of the right ventricle and the outflow tract (conus cordis and truncus arteriosus). N

Ebook Langman’s medical embryology (12th edition): Part 2

eural crest cells, migrating from cranial neural folds to the heart through pharyngeal arches in this region, regulate the SHF by controlling FGF conc

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 (12th edition): Part 2I Systcms-Bascd EmbryologyClinical CorrelatesLaterality and Heart DefectsEstablishing laterality during gastrulation (see Chapter 5, p. 55-56) is esse

ntial for normal heart development because it specifics cells contributing to and patterning the right and left sides of the heart.The process require Ebook Langman’s medical embryology (12th edition): Part 2

s a signaling cascade that includes serotonin (5HT) as a key molecule in initiating the pathway (Fig. 13.2). 5HT is concentrated on the left side of t

Ebook Langman’s medical embryology (12th edition): Part 2

he embryo, in part because of a high concentration of its degrading enzyme, monoamine oxidase (MAO), on the right side near the primitive node. Nodal

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 (12th edition): Part 2ness.The right side is also specified, but signals responsible for this event have not been as well established.Cardiac progenitor cells are also spec

ified 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 Ebook Langman’s medical embryology (12th edition): Part 2

to 18) is critical for heart development and experimental studies showthat disruption of the laterality pathway causes many different types of heart

Ebook Langman’s medical embryology (12th edition): Part 2

defects, including dextrocardia (right-sided heart), ventricular septal defects (VSDs). atrial septal defects (ASDs), double outlet right ventricle (D

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 (12th edition): Part 2tenosis, and others. Laterality defects of the heart, such as atrial and ventricular isomerisms (both atria or both ventricles have similar characteri

stics instead of the normal left-right differences) and inversions (the characteristics of the aưia or ventricles arc reversed), also occur because of Ebook Langman’s medical embryology (12th edition): Part 2

disruptions in specifying left and right sidedness in the progenitor heart cells.The importance of laterality in normal heart development may explain

Ebook Langman’s medical embryology (12th edition): Part 2

the apparent role of antidepressants of the selective serotonin reuptake inhibitor (SSRIs) class that have been linked to an increase in heart defect

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 (12th edition): Part 2N OF THE HEARTTUBEInitially, the central portion of the cardiogenic area is anterior to the oropharyngeal membrane and the neural plale (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 o Ebook Langman’s medical embryology (12th edition): Part 2

ver the central cardiogenic region and the future pericardial cavity (Fig. 13.4). As a result of growth of the brain and cephalic folding of the embry

Ebook Langman’s medical embryology (12th edition): Part 2

o, the oropharynge.il membrane is pulled forward, while the heart and pericardial cavity move first to the cervical region and finally to the thorax (

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 (12th edition): Part 2c tube merge except at their caudalmost ends (Fig. 13.6). Simultaneously, the central part of the horseshoe-shaped cube expands to form the future out

flow tract and ventricular regions. Thus, the heart becomes a continuous expanded tube consisting of an inner endothelial lining and an outer myocardi Ebook Langman’s medical embryology (12th edition): Part 2

al layer (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 it

Ebook Langman’s medical embryology (12th edition): Part 2

s cranial pole (Figs. 13.6 and 13.7).The developing heart tube bulges more and more into the pericardial cavity. Initially, however, the tube remains

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 (12th edition): Part 2dium is ever formed. With further development, the dorsal niesocardium disappears. creating the transverse pericardial sinus, which connects both side

s of the pericardial cavity. The heart is now suspended in the cavity by blood vessels at its cranial and caudal poles (Fig. 13.7).During these events Ebook Langman’s medical embryology (12th edition): Part 2

, the myocardium thickens and secretes a thick layer of extracellular matrix, rich in hyaluronic acid, which separates it from the endothelium (Figs.

Ebook Langman’s medical embryology (12th edition): Part 2

l3.5Q.In addition,mesothelial cells on the surface of the septum transversum form the proepicardium near lhe sinus venous at its caudal end and migrat

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