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Hello! Welcome to my channel
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Today we are going to talk about the
Embryology of the Cardiovascular System
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First part
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in this video we are going to touch the referred topics
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to the formation of the heart,
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your partition
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and the origin of its driving system.
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All these topics, based on the book of Embryology
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Langman 14th Edition
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We start!
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As the embryo grows
during the third week
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It reaches a size that
no longer allows the simple diffusion mechanism
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distribute oxygen and nutrients
to all your cells
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or may dispose of waste products.
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The initial development of the heart
and the circulatory system
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is an embryonic adaptation
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allowing rapid growth of the embryo
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by constituting an effective mechanism
for the distribution of nutrients.
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Progenitor heart cells
are located in the epiblast,
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adjacent to the cranial end of the primitive line.
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From there they migrate along the line and inland
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of the visceral layer of the mesoderm of the lateral plate,
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where they form a horseshoe-shaped cell group
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which is called the primary cardiogenic field (CPC).
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These cells form certain regions of the atria
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and the entire left ventricle.
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The right ventricle and the outflow tract
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(which are the arterial cone and arterial trunk)
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derive from the secondary cardiogenic field (CCS)
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which also provides cells for integration
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of the atria and the caudal end of the heart.
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Once the cells establish
the Primary Cardiogenic Field
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are induced by the underlying pharyngeal endoderm
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to form cardiac myoblasts and blood islets,
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that will give rise to blood cells and vessels
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through the vasculogenesis process
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With the passage of time the islets unite
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and they form a horseshoe tube
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lined by endothelium and surrounded by myoblasts.
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This region is known as the cardiogenic region
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and intraembryonic coelom
which is located on it
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then becomes the Pericardial Cavity
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CARDIAC TUBE
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Initially, the central portion of the cardiogenic region
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is located in a previous region
to the oropharyngeal membrane
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already the neural plate
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However, with the closure of the neural tube
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and the formation of brain vesicles,
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the Central Nervous System
grows cranially so quickly
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that extends over the central cardiogenic region
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and the future
Pericardial cavity
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As a consequence of brain growth
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and the cephalic folding of the embryo,
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the Oropharyngeal Membrane
suffers traction in the ventral direction
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while the Heart and Pericardial Cavity
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they are located first at the cervical level
and finally at the thoracic level
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As the embryo grows
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and it folds in the cephalocaudal direction,
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it also does it laterally
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Consequently, the medial and caudal regions
of the two cardiac primordia
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they fuse except at their most caudal end.
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Simultaneously
the central horseshoe-shaped region dilates
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to form the future exit tract
and the ventricular regions
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Thus the heart becomes
in a continuous dilated tube
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consisting of an internal endothelial lining
and an external myocardial layer
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At its caudal pole it receives venous drainage
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and it starts pumping blood from
the first aortic arch
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towards the dorsal aorta at its cranial pole
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The developing heart tube bulges more and more
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in the direction of the pericardial cavity
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However, at the beginning it remains united
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to the dorsal region of the pericardial cavity
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by means of a fold of mesodermal tissue
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which is called the dorsal mesocardium
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derived from the Secondary Cardiogenic Field.
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As development continues,
the mid region of the dorsal mesocardium
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degenerates and gives rise to the transverse pericardial sinus,
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connecting both sides of the pericardial cavity
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The heart is then suspended in that cavity
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through the blood vessels
at its cranial and caudal ends
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As these events occur,
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the myocardium thickens and secretes
an extracellular matrix layer
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rich in hyaluronic acid
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called cardiac jelly
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Furthermore, the formation of the proepicardial organ
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occurs in mesenchymal cells located on the caudal border of the dorsal mesocardium
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The cells of this structure proliferate
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and migrate over the surface of the myocardium to form the epicardial layer of the heart
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Thus, the heart tube is made up of three layers
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1- The Endocardium
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which forms the endothelial lining
inner heart
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2- The Myocardium
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what constitutes the muscular wall
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3- The Epicardium or Visceral Pericardium
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covering the outside of the tube
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The outer layer is responsible for the formation
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of the coronary arteries
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and the endothelial layer forms the smooth muscle layer
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Now we go with the FORMATION OF THE CARDIAC HAND
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The heart tube continues to increase in size
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while adding CCS cells
at its cranial end
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This growth process is essential
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for normal integration of the right ventricle,
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the region of the outflow tract
and for the folding process
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As the exit tract continues to lengthen,
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the heart tube begins to curve on day 23
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The cephalic portion of the tube performs this action
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ventrally, caudally, and to the right,
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in both the atrial or caudal portion
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moves dorsally, cranially
and to the left
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This folding is what causes the cardiac loop
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His training is completed on day 28
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While the heart loop is forming
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localized expansions are observed at
the entire length of the tube.
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The auricular portion constitutes a common atrium
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and later it will be incorporated into the pericardial cavity
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The atrioventricular junction does not expand
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and gives rise to the atrioventricular duct,
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connecting the common atrium with
the early embryonic ventricle.
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The arterial bulb is narrow,
except in its proximal third
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This region will give rise to the portion
trabeculate of the right ventricle
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The middle region where the arterial cone is,
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will constitute the outflow tracts of the two ventricles
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The distal portion of the bulb located in the arterial trunk
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will form the roots and proximal segments
of the aorta and pulmonary artery.
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The junction between the ventricle and the arterial bulb
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remains narrow and is called
primary interventricular foramen
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Thus, the heart tube is organized by region
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following its cranio-caudal axis in this way:
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1- Trunk Region
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2- Right Ventricle
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3- Left Ventricle
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4 - Atrial Region
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When the folding is complete
smooth-walled heart tube
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begins to develop primitive trabeculae
in two well-defined areas
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just proximal and distal
to the primary interventricular foramen
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The bulb retains its smooth walls
for some time
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The Primitive Ventricle that now has trabeculae, is called the Primitive Left Ventricle
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Similarly, the proximal third
trabeculate of the heart bulb
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Primitive Right Ventricle is named.
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The truncated cone region of the heart tube
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that initially on the right side
of the pericardial cavity,
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moves gradually
until reaching a more medial position
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This change of position is a consequence
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of the formation of two dilations
transverse in the atrium,
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protruding on either side of the heart bulb
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DEVELOPMENT OF THE VENOUS SINUS
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In the middle of the fourth week
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the venous sinus receives venous blood
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coming from the antlers of the
right and left breasts.
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Each pole receives blood from three important veins:
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1- The yolk or omphalomesenteric vein,
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2- The umbilical vein
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3- The common cardinal vein
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At the beginning, communication
between the sinus and the atrium is wide
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Despite this, in a short time the entrance to the breast
scrolls to the right
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This displacement is due above all
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in the presence of short circuits
left-right blood
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that are observed in the venous system
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during the fourth and fifth week of development
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With obliteration of the right umbilical vein
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and the left yolk vein during the fifth week
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the horn of the left sinus of the venous sinus
quickly loses its importance
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When at 10 weeks it is obliterated
the left common cardinal vein
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the only thing left of the left breast shaft
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is the oblique vein of the left atrium
and the coronary sinus
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As a consequence of short circuits
left-right blood
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the horn and veins of the right breast
increase its dimensions
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considerably
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The right pole, which now constitutes
the only communication
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between the original venous sinus and the atrium,
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joins the right atrium
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to give rise to the smooth portion
from the wall of that cavity
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Your site of entry, the Sinoauricular Orifice
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it is flanked by a valve fold
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Right and left Venous Valves
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In your dorsocranial region
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valves fuse and conform
a ridge known as Septo Espurio
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At the beginning the valves are big,
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but when the horn of the right breast
is incorporated into the wall of the atrium,
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the Left Venous Valve and Spurious Septum
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merge with the developing Atrial Septum
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The upper portion of the right venous valve
completely disappears
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and its lower segment grows
to form two structures:
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1- The Inferior Vena Cava Valve
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2- The Coronary Sinus Valve
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Terminal Ridge creates the dividing line
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between the original trabeculated portion
of the right atrium and its smooth wall
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that originates from the Right Sinus Pole
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TRAINING OF THE CARDIAC SEPARATORS
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The main partitions of the heart
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form between days 27 and 37 of development,
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when the embryo length increases by 5 mm
a 16 - 17 mm approximately
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A mechanism by which a partition can be formed
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involves the active growth of two masses
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approaching each other until merging,
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so that they divide the cavity
in two independent ducts
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these masses are called
Endocardial Pads or Bearings
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Such a partition
can also be formed by active growth
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single tissue mass
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that expands until it reaches
the opposite side of the cavity
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These endocardial prominences
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develop in the regions
atrioventricular and truncus
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and on these sites they facilitate training
of the atrial and ventricular septa
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what are the ducts
and the atrioventricular valves
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and the aortic and pulmonary ducts
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SEPARATE IN THE COMMON HEADSET
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At the end of the fourth week,
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a crescent-shaped ridge
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grows from the roof of the common atrium
towards its cavity
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This ridge is the first portion
of the septum primum
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The two ends of this partition expand
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towards the endocardial pads
in the atrioventricular canal
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The hole that persists
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between the lower edge of the septum primum
and the endocardial pads
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is the Ostium Primum
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Next, extensions of the upper and lower endocardial pads
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they grow along the edge of the septum primum,
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thereby closing the ostium primum
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However before the closing ends
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a process of programmed cell death (apoptosis)
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which ends up producing perforations
in the upper region of the septum primum
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The coalescence of these areas gives rise
to the Ostium Secundum
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which ensures the free passage of blood
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from the right primitive atrium to the left
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When the right atrial cavity expands
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as a consequence of
incorporation of the horn of the venous sinus
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a new fold appears
crescent shaped
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This new fold is the Septum Secundum
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Its anterior end extends downward
in the direction of the septum
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in the atrioventricular canal
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When the left venous valve and spurious septum
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merge with the right side of the septum secundum
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the free concave edge of this last structure
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begins to overlap the ostium secundum
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The opening left by the septum secundum
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it is called foramen ovale
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When the upper portion of the septum primum gradually disappears
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the remaining portion becomes
at the valve of the foramen ovale
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The pathway between
the two atrial cavities
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is made up of an elongated oblique cleft
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laying the blood from the right atrium
flows to the left side
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AURICULOVENTRICULAR SEPARATION
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Finishing the fourth week,
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four endocardial pads appear
atrioventricular
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two sides,
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one on the dorsal or upper edge
atrioventricular duct
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and one on the lower or ventral edge
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With the end of the 5th week,
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dorsal and ventral pads project
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to a greater extent towards the cavity and fuse,
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giving rise to a complete division of the duct
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in left and right atrioventricular orifices
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SEPARATION OF THE ARTERIAL TRUNK AND THE ARTERIAL CONE
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During the fifth week of life,
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Flank walls appear on the trunk,
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facing each other on opposite walls
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These flanges are called
of arterial trunk ridges
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and they are located in the upper right region of the wall
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and in the lower left region of the wall
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the first one is called
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Upper right ridge of arterial trunk
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and the second
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Lower Left Crest of arterial trunk
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The upper right ridge of the trunk
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grows distally and to the left,
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in both the lower left
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grows distally and clockwise
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In this way
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as they lengthen in the direction of the aortic sac
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the ridges spiral,
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what gives rise to position
of the aortic and pulmonary arteries
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After its complete merger,
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the ridges give rise to the aortopulmonary septum,
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which results in the position of the aorta and the lung
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When these ridges appear on the trunk,
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similar ridges develop along
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of the right dorsal walls
and left ventral of the arterial cone
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Trunk cone ridges
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now grow towards each other and distally
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to join the septum of the trunk
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When the two frustoconal ridges merge,
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the septum divides the cone into an anterolateral canal
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for the right ventricular outflow tract
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and one posteromedial
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for the left ventricular outflow tract
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And the last partition that we are going to talk about is
in the ventricles
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By the end of the fourth week,
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the two Primitive Ventricles
start to expand
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This is accomplished by
continuous growth of the myocardium
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in the outer region
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and the continuous generation of
diverticula and trabeculae in the internal
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The medial walls of the expanding ventricles
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gradually add and merge
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to constitute the muscular portion
interventricular septum
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The interventricular foramen,
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located above the muscular portion
interventricular septum
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will obliterate
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once it is completed
cone septum formation
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In the septum formation
membranous ventricle
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intervene the muscular septum
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and the growths of the truncal ridges
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and the endocardial pads
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Tissue growth
of the anterior endocardial pad
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along the top
of the interventricular muscular septum
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close the hole
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And the complete closure of the ventricular foramen
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gives rise to the membranous portion
interventricular septum
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And the last topic of this video
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is the CARDIAC CONDUCTION SYSTEM
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Initially all myocardial cells
in the heart tube
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have pacemaker activity
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and the heart begins to beat
around 21 days of gestation
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Soon after, the cardiac pacemaker
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is restricted to
left caudal region of heart tube
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Later, the venous sinus assumes this function.
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and while it is incorporated into the right atrium,
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pacemaker tissue is arranged
near the superior vena cava drainage hole
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This is how the Sinoauricular Node (SA) is formed
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The Auriculoventricular (AV) Node
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begins its formation from a group of cells
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distributed around the atrioventricular duct,
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which coalesce to constitute the AV node
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Except for nerve fibers
sympathetic and parasympathetic
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that end at the Sinoauricular Node (SA),
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the rest of the cells
of the cardiac conduction system
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derived from cardiac myocytes that differ
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in Node Cells,
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the Beam Branches and the Purkinje Fibers.
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And well up to here with the end of the video,
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Hope it has fit
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Greetings and Success in your exams!
