Questions and Answers - Recent questions and answers in Medical

Answered: what is Defects of the Tricuspid Valve

Mon, 18 Dec 2017 20:14:14 +0000

a) Tricuspid Atresia. This anomaly consists of complete absence of right atrioventricular orifice. In this condition there is atrophy of the right ventricle, hypertrophy of the left ventricle, and intense cyanosis. Survival is only possible if this anomaly is associated with ASD and a patent ductus arteriosus.
b) Ebstein's Anomaly. In this malformation the tricuspid valve is displaced downward into the right ventricle and the valve cusp are attached to the ventricular wall. The dysfunctional
valve allows the blood to regurgitate ii) Transposition of the Great
into the right atrium. Arteries
In about 5 of 10,000 live born in-iv) Defects of the Mitral Valve fants, the conotruncal septa develop
In mitral atresia the valve cusps but the aorticopulmonary septum fails
are completely fused to each other, to persue a spiral course. This pro-
The left ventricle js poorly developed duces transposition of great vessels, in
and an ASD is always present. which blood from left ventricle passes
into the pulmonary trunk, whereas blood from the right ventricle passes

Answered: defined Defects of the Pulmonary Valve

Mon, 18 Dec 2017 20:13:23 +0000

a) Pulmonary Stenosis. This
anomaly also has two forms: (i) pulmo-
nary valvular stenosis, and (ii) infundibular stenosis. In the pulmonary valvular stenosis the cups of the pulmonary valve are partially fused together to form a dome which has a central perforation. The infundibular stenosis is caused by an underdevelopment of the infundibulum (conus arteriosus) of the right ventricle. Depending on the degree of obstruction to blood flow, pulmonary stenosis is accompanied by a variable degree of hypertrophy of the right ventricle.
b) Pulmonary Atresia. In this malformation there is no orifice at the level of pulmonary valve. Consequently, the blood from right side of the heart passes to the left through a patent foramen ovale. In addition, a patent ductus arteriosus allows the blood to pass from the arch of aorta to the pulmonary trunk (which conveys this blood to the lungs). ..,

Answered: What is Valvular Anomalies

Mon, 18 Dec 2017 20:12:47 +0000

The congenital malformations of the cardiac valves generally take the form of stenosis (narrowing) or atresia (complete lack of lumen).
i) Defects of the Aortic Valve
a) Aortic Stenosis. This anomaly may present in two forms: (i) aortic valvular stenosis, and (ii) subaortic stenosis. In the aortic valvular stenosis the edges of the cusps of the aortic valve are fused with each other for a variable extent. Thus, the valve takes the form of a dome with a narrow opening. In the subaortic stenosis, a band of fibrous tissue is present just inferior to the aortic valve, which causes narrowing of this valve. This band results from persistence of mesenchymal tissue that normally degenerates as the valve forms. Both varieties of aortic stenosis result in the hypertrophy of the left ventricle.
b) Aortic Atresia. This condition results from complete fusion of the cusps of the aortic valve. This anomaly is accompanied by underdevelopment of aorta, left ventricle and left atrium. The blood reaches the aorta from the pulmonary trunk through a patent duc-tus arteriosus (the ductus arteriosus is a connection between pulmonary trunk and aorta that normally closes soon after birth; it is discussed in detail later).

Answered: defined Persistent Atrioventricular Canal

Mon, 18 Dec 2017 20:11:23 +0000

The basic defect in this cardiac anomaly is a failure of fusion of the superior and inferior endocardial cushions. This malformation is seen in about 20% of the cases of Down syndrome; otherwise it is relatively uncommon cardiac anomaly. The failure of fusion of the endocardial cushions leads to a variety of secondary cardiac defects which include: (i) ASD consisting of osteum primum defect, (ii) membranous variety of VSD and (iii) malformations of the atrioventricular valves.

Answered: defined Ventricular Septal Defects (VSD)

Mon, 18 Dec 2017 20:10:37 +0000

Ventricular septal defects are the most common of all congenital cardiac malformations. In 50% of cases VSD occurs as an isolated defect and in the remaining 50% it is part of a more complex malformation. Incidence
of isolated VSD has been reported to be 10 to 12 per 10,000 live births. Ventricular septal defects are found most frequently in the membranous part of the septum (membranous VSD). However, much less commonly, the muscular part of the septum may have a defect, constituting a muscular VSD. Small ventricular septal defects allow some shunting of blood but are of little clinical significance. Large defects allow large volumes of blood to shunt from the left to the right ventricle. This causes enlargement of the right ventricle and produces pulmonary hypertension due to excessive blood flow into the pulmonary artery. Clinical features include dyspnea (difficulty in breathing) and cardiac failure early in infancy. Large VSDs shorten life if surgery is not performed.

Answered: What is Common Atrium

Mon, 18 Dec 2017 20:10:01 +0000

This is a rare anomaly characterized by complete absence of the interatrial septum. It results from failure of development of the septum primum and septum secundum. Because the heart consists of three chambers (of which two are ventricles), the condition is also called cor triloculare biventriculare. This is a very serious cardiac anomaly and is associated with a high mortality rate.

Answered: defined Endocardial Cushion Defect with Osteum Primum Defect

Mon, 18 Dec 2017 20:09:31 +0000

This type of ASD is much less common than the osteum secundum defect. In this anomaly there is deficiency of endocardial cushion tissue, so that the endocardial cushions partially fuse with each other and the septum intermedium is poorly formed. The septum primum does not fuse with the septum intermedium and there is a patent osteum primum.

Answered: defined Osteum Secundum Defect

Mon, 18 Dec 2017 20:08:31 +0000

This is the most common type of ASD and is characterized by the presence of a large opening between the right and left atria. This condition can be the result of one of the following two developmental defects:
a) Excessive resorption of septum primum leading to the formation of a very large foramen secundum, which is not completely covered by a normally developed septum secundum.
b) Inadequate development of septum secundum, so that this septum is too short to cover the foramen secundum completely.

Answered: defined Atrial Septal Defects (ASD)

Mon, 18 Dec 2017 20:07:48 +0000

The atrial septal defects constitute a common variety of CHD. Incidence of ASD has been reported to be 6/1000 live births. Females are more frequently affected than males. Atrial septal defect has been found to be associated with most of the autosomal and sex chromosome aberrations and is a common accompaniment of trisomies including trisomy 18 and trisomy 21.
There are three clinically significant types of atrial septal defects:
i) Osteum secundum defect.
ii) Endocardia! cushion defect
with osteum primum defect.
iii) Complete failure of formation
of interatrial septum leading to a
common atrium.

Answered: What is Ectopia cordis.

Mon, 18 Dec 2017 20:07:07 +0000

In this anomaly the heart is partially or completely exposed on the surface of the thorax. This condition results from a faulty development of the sternum and
pericardium. This anomaly is incompatible with life and the infant usually dies during the first few days after birth due to infection and cardiac failure.

Answered: What is Dextrocardia.

Mon, 18 Dec 2017 19:11:19 +0000

When the heart lies on the right side of the thorax instead of the left, the condition is called dextrocardia. This condition occurs when the heart loop bends to the left instead of right (to understand this points, the reader is advised to refer back to the subject of formation of cardiac loop discussed under the topic of establishment of external form). Dextrocardia entails a transposition in which the heart and its vessels are reversed left to right as in a mirror image. This malformation may occur as an isolated anomaly or may be the part of a more generalized anomaly called situs inversus, in which there is transposition of all the thoracic and abdominal viscera. Isolated dextrocardia is usually associated with other serious cardiac defects.

Answered: Defined Anomalies of Position

Mon, 18 Dec 2017 19:10:40 +0000

This group consists mainly of two congenital cardiac anomalies (i) dextrocardia, and (ii) ectopia cordis.'

Answered: What is Congenital Anomalies of the Heart and Great Vessels

Mon, 18 Dec 2017 19:09:09 +0000

The congenital cardiovascular defects make up the largest category of the human congenital malformations, accounting for about 20% of all congenital anomalies observed in liveborn infants. The percentage in stillborns is much higher. The incidence of congenital heart defects (CHD) has been estimated to be 6 to 8 per 1000 births.
The cause of most cardiovascular malformations is not well understood. However, a few can be attributed to specific genetic or environmental factors. It has been estimated that about 4% of cardiovascular defects can be ascribed to single gene mutations, another 6% to chromosomal aberrations such as monosomies and trisomies, and 5% to exposure to specific .teratogens. The remaining 85% of the cardiovascular defects are caused by multifactorial inheritance, ie, by a
complex interplay between genetic and environmental factors.
The teratogens known to cause CHD are rubella virus, thalidomide, vitamin A, and alcohol, etc. There is evidence that maternal diabetes and hypertension also cause congenital cardiac defects.
Most of the congenital cardiovascular defects are well tolerated during intrauterine life because gaseous exchange is occurring in placenta and pulmonary circulation has not begun. After birth, however, the pulmonary circulation starts and the impact of congenital heart defects become evident. Some of these defects produce very little disability, others are incapacitating, while still others are incompatible with extrauterine life. The cyanosed child is also called a blue baby.
Those cardiovascular anomalies which cause shunting of oxygenated blood into the deoxygenated blood produce a clinical condition called cyanosis, which consists of a dark bluish or purplish discolouration of the skin and mucous membranes. The Cyonosis results from excessive concentration of reduced hemoglobin in the blood. A considerable number of congenital cardiovascular defects can be corrected surgically.
The number of reported congenital cardiac defects is very large. The cardiac anomalies of clinical significance can be grouped as under:
1) Anomalies of position.
2) Atrial septal defects (ASD).

Answered: Differentiation of the Cardiac Wall

Mon, 18 Dec 2017 19:08:31 +0000

As already described, the early heart tube consists , of endocardium, myocardium and epicardium.
The myocardium differentiates into an outer compact layer of muscle and an inner spongy layer, the loosely arranged trabeculae of which project into the heart cavity. The endocardium dips into the spaces between the trabeculae and lines them. Initially the spongy layer has a much greater thickness than the compact layer. However in later development the cardiac wall becomes mainly compact. The original trabeculae remains in the atria and auricles as musculi pectinati and in the ventricles as trabeculae carneae.
The musculature of the ventricles is more developed than that of the atria. However the thicker wall of the left ventricle is mainly acquired after birth as a result of the harder work performed by the left ventricle.
Initially the myocardium of the atria and ventricles is continuous with each other. However, development of connective tissue in the region of atrioventricular canal separates the atrial muscle from the ventricular muscle and only a small muscular link remains. This connecting muscular band differentiates to form the atrioventricular bundle. It is specialized to conduct the cardiac impulse from atria to ventricles. The sinuatrial node, the atrioventricular node, and the Purkinje fibers develop
as a local differentiation of cardiac muscle.

Answered: defined Atrioventricular Valves

Mon, 18 Dec 2017 19:07:15 +0000

As already described earlier, formation of the septum intermedium results in division of the atrioventricular canal into right and left atrioventricular orifices. Each orifice soon becomes surrounded by swellings produced by proliferation of mesenchyme under the endocardium of the atrioventricular canals. These swellings are excavated on their ventricular sides to form valvular cusps. The mesenchymal core of each cusp differentiates into dense fibrous connective tissue. Three cusps are formed at the right atrioventricular orifice and constitute the tricuspid valve.
Two valvular cusps are formed at the left atrioventricular orifice, constituting the bicuspid valve. The cusps remain connected to the ventricular wall by muscular strands. The proximal parts of these strands retain muscular tissue and become papillary muscles. However, the, distal parts of these strands, which are attached to valves cusps, undergo fibrous degeneration to form the chordae tendineae.

Answered: defined Semilunar valves

Mon, 18 Dec 2017 19:06:30 +0000

When formation of the aorticopulmonary septum has been completed, the semilunar valves begin to develop at the orifices of the aorta and pulmonary trunk. The primordium of each semilunar valve appears as three swellings of endocardial tissue at the orifices of both the aorta and pulmonary trunk. The swellings become hollowed out on their upper surfaces to form three thin-walled cusps of the semilunar valve. In addition to the local tissue, the neural crest cells also contribute to the formation of the semilunar valves.

Answered: Formation of Interventricular Septum

Mon, 18 Dec 2017 19:05:19 +0000

The partition that separates the right and left ventricles from each other is called interventricular septum (or just ventricular septum).
The interventricular septum is a composite septum which consists of two parts: (1) a thicker muscular part called septum musculare, and (2) a thin membranous part known as septurn membranaceum. Development of these two parts occurs from different sources.
Initially the primitive right and left ventricles do not have any partition between them. At the end of the 4th week the two primitive ventricles begins to grow rapidly. Consequently, the -medial walls of the expanding ventricles become apposed to produce a thick muscular ridge which is the primordium of the muscular interventricular septum. This septum grows further by the active proliferation of myoblasts in it. However, the growth of this septum stops; in the middle of the seventh week and there remains a crescentic. gap between the septum intermedium and concave free edge of the septum musculare. This gap, called interventricular foramen, permits communication between the right and left ventricles.
• Closure of the interventricular foramen occurs during the seventh week by the formation of the septumj membranaceum. This septum is formed mainly by tissue derived from the inferior endocardial cushion (which has by now joined the superior endocardial cushion to form the septum intermedium). Mostauthorities believe that the right and left bulbar ridges (developing in the conus cordis) also contribute tissue to the septum membranaceum. The newly formed tissue grows to give rise to a thin, membranous septum which fuses with the concave upper edge of the septum musculare and, thus, closes the interventricular foramen. Closure of this foramen 1 not only shuts off the communication between the right and left ventricles but also ensures that the right ventricular cavity communicates with the pulmonary trunk and the left ventricular cavity communicates with the aorta. In addition, the right atrioventricular opening now connects exclusively with the right ventricular cavity, and the left atrioventricular opening with the left ventricular cavity.

Answered: define Absorption of the Right Sinus Horn into the Right Atrium

Mon, 18 Dec 2017 19:03:18 +0000

As mentioned earlier, the right sinus horn enlarges considerably and receives venous blood through the superior and inferior vena cava. It opens into the posterior wall of the developing right atrium through the sinuatrial orifice. This orifice is a vertically oriented slit-like opening which is flanked on each side by a tissue flap;
lar tissue flaps are called right and left venous valves. Superior to the sinuatrial orifice the right and left venous valves join to form a ridge, which is called septum spurium.
Between the 6th and 8th week the right atrium increases rapidly in size and the right sinus horn, failing to keep pace, is gradually incorporated into the wall of the right atrium to from the smooth-walled part of the right atrium (this part of the right atrium is called sinus venarum, indicating that it is derived from sinus venosus). The sinus venarum forms the right posterior part of the atrium. Rest of the right atrium and the right auricle have a rough trabeculated appearance.
As the right sinus horn is taken
up into the right atrium, the right and left venous valves move away from each other. The left venous valve (along with the septum spurium) fuses with the septum secundum and is incorporated into the interatrial septum. The cranial part of the right venous valve disappears; however, the caudal part 'of this valve forms valve of the inferior vena cava and valve of the coronary sinus. Superior to the valve of the inferior vena cava a vertical ridge of tissue, called crista terminalis, delimits the sinus venarum from the trabeculated part of the right atrium (some authorities believe that the crista terminalis represents the cranial part of the right venous valve). i

Answered: denfine Formation of the Interatrial Septum

Mon, 18 Dec 2017 19:01:29 +0000

The common atrium is divided into right and left atria by the forjpation of the interatrial septum. This is a complex septum formed by the fusion of two embryonic septa called septum primum and septum secundum.
Before the details of the development of the interatrial septum are described, it is important to remember that during the embryonic and fetal life, oxygenated blood from the placenta is being returned to the right atrium (through the inferior vena cava). It is essential that major part of this blood should pass to the left atrium through the interatrial septum, so that it may enter the left ventricle through the atrioventricular orifice. From the left ventricle the oxygenated blood is pushed into the systemic circulation.
The above given description makes it dear that, throughout the intrauterine life, the interatrial septum is not a complete partition and in various stages of its development there is always an arrangement to allow the passage of blood from the right atrium to the left atrium. However, after birth the interatrial septum becomes a complete partition between the two atria.

Answered: What is Division of the Atrioventricular Canal

Mon, 18 Dec 2017 19:00:54 +0000

After the formation of the bulboventricular loop, the atrium opens into the primitive left ventricle by a narrow opening called atrioventricular canal. By the time atrium exhibits two sacculations (the future right and left atria), the atrioventricular canal becomes widened transversely and extends to the right. As a result, the two parts the common atrium, ie, the future right atrium and left atrium, become connected to the primitive right ventricle and left ventricle, respectively. Soon afterwards, the atrioventricular canal divides into right and left canals. This division takes place by the appearance of superior and inferior endocardial cushions (also called atrioventricular cushions). These cushions are small swellings formed by the proliferation of the endocardial tissue. As their name indicates, one of these cushions appears in the superior (ie, dorsal) wall, whereas the cither is formed in the inferior (ie, ventral) wall of lthe atrioventricular canal The superior and inferior endocardial cushions gradually grow toward each other. By the end of the 6th week, they meet and fuse to form a septum intermedium,
which divides the common atrioventricular canal into right and left atrioventricular canals

Answered: Division of the Atrioventricular Canal

Mon, 18 Dec 2017 02:35:13 +0000

Answered: define Partitioning of the Conotruncus

Mon, 18 Dec 2017 02:34:13 +0000

During the fifth week of development, proliferation of the endocardial tissue in the wall of the cbnus cordis results in the formation of ridges (swellings) in the right dorsal and left ventral wall of the conus cordis. These ridges, called bulbar ridges (also called conus swellings), grow toward each other to form a septum, called conal septum, which divides the conus cordis into two parts: (1) an anterolateral part, which forms the outflow tract of the right ventricle (called conus arteriosus or infundibulum), and (2) a posteromedial part which forms the outflow tract of the right ventricle (called aortic vestibule). Distally the conal septum joins the sep-
tum developing in the truncus arteriosus, whereas proximally the conal septum contributes tissue to the developing interventricular septum (vide infra).
When bulbar ridges are being formed in the conus cordis, similar ridges, called truncal ridges (also called truncus swellings) appear in the truncus arteriosus. These ridges pursue a spiral course in the truncus arteriosus. Fusion of the truncal ridges with each other produces a spiral aorticopulmonary septum, which divides the truncus arteriosus into two large arterial channels: ascending aorta and pulmonary trunk.
As mentioned earlier, the distal end of the conal septum joins the caudal end of the aorticopulmonary septum, so that the two septa behave as one continuous septum. This arrangement also ensures that the blood from the infundibulum passes into the pulmonary trunk, whereas the blood from the aortic vestibule passes into the ascending aorta.
Initially the ascending aorta and pulmonary trunk are fused to each other because the aorticopulmonary septum forms a common partition between these two subdivisions of the truncus arteriosus. However, as a result of programmed cell death, a split occurs in the aorticopulmonary septum. Consequently, these two great arteries become separate and independent vessels. It is to be noted that, due to the spiral course of the aorticopulmonary septum, the separated ascending

aorta and pulmonary trunk slightly intertwine, the latter crossing ventral to the ascending aorta.
Neural crest cells migrate through the pharyngeal arches to reach the developing bulbar ridges and truncus swellings. These cells contribute greatly to the formation of septa in the conus and truncus. Abnormalities in migration, proliferation, or differentiation of neural crest cells result in the production of many congenital heart defects (described later).

Answered: What is Absorption of the primitive pulmonary vein into the wall of the Left Atrium

Mon, 18 Dec 2017 02:33:37 +0000

As the right atrium grows in size by incorporating the right sinus horn, the left atrium also enlarges by absorbing the primitive pulmonary vein into its wall.
During the 4th week a pulmonary vein develops as an outgrowth of the posterior atrial wall, so that originally only one pulmonary vein opens into the posterior wall of the developing left atrium. The primitive pulmonary vein promptly divides into right and left branches, which bifurcate again to produce a total of four pulmonary veins. These veins grow toward the lungs and become connected to the veins developning
in the mesoderm surrounding the bronchial buds.
Due to rapid expansion of the left atrium during the 5th week, the pulmonary vein and its' branches are gradually absorbed into the wall of the left atrium. As mentioned above, initially pulmonary venous system opens into the left atrium through a single orifice, then transiently through two orifices, and finally through four orifices of the definitive pulmonary veins.
Most of the wall of the definitive left atrium is smooth because it is derived form the pulmonary veins and its branches. The trabeculated part of the primitive left atrium is displaced ventrally and to the left, where it becomes the left auricle.

Answered: What is Absorption of the Right Sinus Horn into the Right Atrium

Mon, 18 Dec 2017 02:33:02 +0000

Answered: What is Septum Secundum

Mon, 18 Dec 2017 02:32:26 +0000

At about the time when foramen secundum is being formed, another septum grows down from the atrial roof of the right side of the septum primum. This new septum, which is thick and muscular is called septum This is also a crescentic septum and, as it grows down, it gradually overlaps
the foramen secundum in the septum primum. The free concave edge of the septum secundum grows posteroinferiorly, but it halts before it reaches the septum intermedium, leaving a large opening near the floor of the right atrium; this opening is called foramen ovale.
The uppermost part of the septum primum (initially attached to the roof of the left atrium) gradually disappears. The remaining part of the septum primum (attached inferiorly to the septum intermedium) forms the flaplike valve of the foramen ovale. Throughout rest of the fetal development, the foramen ovale allows most of the blood entering the right atrium to pass into the left atrium. However, passage of blood in the opposite direction (ie, from the left to the right atrium) is prevented because the thin and membranous septum primum closes against the relatively thicker septum secundum.
After birth the right to left shunt of the Blood stop because the increased pressure of blood in the left atrium pushes -the flexible septum primum against the more rigid septum secundum. The two septa become fused to each other to form the definitive interatrial septum which becomes a complete partition between the atria. In about 20% of the people the septum primum and secundum do not become actually fused and there remains a narrow oblique cleft between the two atria. This condition, called probe patency of foramen ovale, is
quite harmless because it does "not allow intracardiac shunting of blood,
In the adult heart the lower edge of the septum secundum can be seen in the right atrium as limbus fossae ovalis. The depression below this (representing , the embryonic foramen ovale) is known as fossa ovalis.

Answered: What is Septum Primum

Mon, 18 Dec 2017 02:31:55 +0000

By the end of 4th week, a thin, sickle-shape membrane, called septum primum,grows from the roof of the common' atrium downwards into the lumen. The free edge of the septum .primum grows toward the septum intermedium formed by the fusion of the endocardia! cushions. The temporary gap between the septum intermedium and crescentic inferior border of the septum primum is called foramen primum (also called osteum primum). This foramen allows passage of blood form the right to' the left atrium. The osteum primum becomes progressively smaller and finally disappears as the inferior margin of the septum primum fuses with the septum intermedium. However, before the closure of the foramen primum, programmed cell death creates perforations in the upper central part of the septum primum. These perforations coalesce to form another opening called foramen secundum (also called osteum secundum). After the closure of the foramen primum, the foramen secundum allows the blood to be shunted from the right atrium to the left atrium.

Answered: define Formation of the Interatrial Septum

Mon, 18 Dec 2017 02:31:18 +0000

Answered: define Internal Specializations

Mon, 18 Dec 2017 02:30:20 +0000

At the end of the 4th week, the heart consists of undivided chambers. During the next two weeks, important development changes occur, which lead to the formation of the 4-chambered human heart. These changes can be summarized as under:
1) Division of the atrioventricular canal into two canals.
2) Formation of the interatrial septum.
3) Absorption of the right horn of sinus venosus into the wall of the right atrium.
4) Absorption of the primitive pulmonary vein into the wall of the left atrium.
5) Partitioning of the conotruncus.
6) Formation of the interventricular septum.
7) Histogenetic differentiation of the heart wall and formation of the cardiac valves.
It is important to keep in mind, ,once again, that these developmental events do-not necessarily take place in the sequence given above. The
following discussion would make it clear that there is considerable overlap in the timing of various developmental events that bring the internal structure of the heart to an adult-like condition.

Answered: what is Development of the Heart

Mon, 18 Dec 2017 02:28:52 +0000

the intraembryonic coelom during the third week splits this mesoderm into a splanchnic and a somatic layer. During the splitting process, the cardiogenic mesoderm becomes segregated in the splanchnic layer which is now called cardiogenic field. The intraembryonic coelom created in the cardiogenic area is called primitive pericardia! cavity.
The cardiogenic field is a horseshoe-shaped area which is located in the floor of the primitive pericardial cavity and overlies the endoderm of the embryonic disc. An inductive influence from the underlying embryonic endoderm appears to stimulate the formation of the cardiac primordium. This primordium appears in the form of a pair of endothelial tubes formed by the process of vasculogenesis in the mesoderm of the cardiogenic area. These tubes are called endocardia I heart tubes.
During the early 4th week\ the cephalic and lateral folding of the embryo brings the endocardial heart tubes in the thoracic region, where they meet along the midline and, by the day 22, bogin to fuse which each other to form a single heart tube (also called primary heart tube). The cranial end of the heart tube is the arterial end which is
connected to the two dorsal aorta by means of the first pair of aortic arches. The caudal end of the heart tube is the venous end which becomes connected to the vitelline, umbilical and common cardinal veins,:
As the heart tube forms, a series of constrictions (sulci) and dilatations appear along the heart tube. In the beginning, three divisions of the heart tube can be recognized. From the cranial to caudal direction, these divisions are: bulbus cordis, ventricle (also called primitive ventricle) and atrium (also called primitive atrium). The primitive atrium will give rise to parts of both (ie, right and left) atria, and the primitive ventricle will form most of the definitive left ventricle. The bulbus cordis and ventricle are separated from each other by the bulboventricular sulcus, whereas between the ventricle and atrium lies the atrioventicluar sulcus. Within the next 24 to 36 hours a fourth division becomes recognizable caudal to the atrium. This division, called sinus venosus, is formed by the confluence of the six veins (right and left vitelline, right and left umbilical and right and left common cardinal veins) which drain into the caudal end of the heart. The sinus venosus is a partially bifid chamber having two horns (called right and left sinus horns). Each sinus horn receives three veins (ie, vitelline, umbilical and common cardinal).
initially the primary heart tube consists only of endothelium. However, by day 22, a thick mass of splanchnic mesoderm invests the heart tube.

Answered: define Histogenesis of the Embryonic Blood Vessels

Mon, 18 Dec 2017 02:27:55 +0000

Formation of the embryonic blood vessels occurs during the third week of development by two methods: vasculogenesis and angiogenesis. The vasculogenesis entails formation of vessels from blood islands (which are clusters of mesenchyme-derived he-mangioblasts). It results in the establishment of primary vascular beds in the regions where blood vessels are required to be formed. The angiogenesis involves formation of additional vessels by budding and sprouting from existing blood vessels (which have developed as a result of vasculogenesis).

Answered: What is CARDIOVASCULAR SYSTEM

Mon, 18 Dec 2017 01:10:07 +0000

In the early stages of development the embryo obtains its nourishment from the surrounding tissues, which reaches the embryo by diffusion across the extraembryonic coelom and yolk sac. However, as the embryo increases in size, simple diffusion can not meet the increasing nutritional requirements of the rapidly growing embryo and the early development of a transport system becomes necessary. The primitive cardiovascular system, therefore, begins to develop during the 3rd week of development.The primitive CVS becomes functional in the 4th week as the developing heart begins to beat.
The two major components of the cardiovascular system are: (1) heart, and (2) blood vessels. The heart itself is a specialized blood vessel with
a large lumen and very thick muscular walls.

Answered: define Male Pseudohermaphroditism

Mon, 18 Dec 2017 01:07:49 +0000

Persons with this intersexual condition have a 46, XY chromosome complement. Consequently, their cells
are chromatin- negative, ie, their nuclei do not show the Barr body*. Male pseudohermaphroditism is produced by insufficient production of testosterone by the fetal testes. It has been proposed that mutations that affect the enzymes required for the synthesis of testosterone cause a deficiency or absence of this hormone. The resulting pseudohermaphroditism affects the development of all those structures that are dependent upon testosterone for their differentiation. The external genitalia develop into a female type, the testes do not descend and mesonephric ducts do not differentiate into male genital ducts. However, because Sertoli cells of testis produce MIS, the paramesonephric ducts degenerate and the uterus and the feminization is not reversed at the time of puberty because the blood testosterone level fails to rise and, hence, the person continues to resemble a female even in the adulthood.
Another variety of male pseudohermaphroditism is seen in persons suffering from androgen insensitivity syndrome (formerly called testicular feminization syndrome). Persons with this syndrome have the external appearance normal of females, although the chromosomal constitution is 46, XY and testes are present. The androgen insensitivity syndrome results from the absence of androgen receptors. The
The Barr body or nucleolar satellite represents the resting X chromosome and is seen in the cells of the females uterine tubes are absent.
testosterone produced by the fetal testes fail to induce the development of male genitalia because the target tissues (in the genital tubercle, urethral folds and labioscrotal swellings) do not respond and development proceeds as though androgens were absent.
The MIS produced by the fetal testes induces the regression of paramesonephric ducts and, hence, the uterus and uterine tubes are absent.
The vagina ends blindly in a pouch. The testes are usually present in the abdomen or inguinal canals but may descend into the labia majora. These abnormally located testes are liable to develop malignant tumors and, therefore, should be removed as soon as they are discovered. Androgen insensitivity syndrome is an X-linked recessive disorder caused by mutations in the gene encoding the androgenreceptors.

Answered: Define female pseudohermaphroditism ,

Mon, 18 Dec 2017 01:07:15 +0000

Female pseudohermaphrodites are genetic females who have ovaries but whose external genitalia are of a male type. The masculinization of the external genitalia occurs due to exposure to abnormally high levels of androgens. The commonest cause of female pseudohermaphroditism is congenital adrenal hyperplasia. This condition (also called adrerogenital syndrome) is characterized by the excessive production of androgens by the fetal suprarenal cortex. This results in masculinization of the external genitalia. Commonly there is enlargement of the clitoris, partial fusion of the labia majora, and a small persistent urogenital sinus. In some cases the masculinization may be so intense that the external genitalia are almost of a male type. Some cases of the female pseudohermaphroditism have been reported to be caused by the administration of androgenic agents to the pregnant women. Most of such cases have resulted from the use of certain virilizing progestins administered for the prevention of abortion.

Answered: What is Pseudohermaphroditism

Mon, 18 Dec 2017 01:06:37 +0000

A pseudohermaphrodite is defined as an individual who has the external genitalia of one sex but the gonads of the other sex. When the gonads of the affected person are histologically testes, the patient is called a male pseudohermaphrodite. On the other hand, when the gonads of the pseudohermaphrodite are histologically ovaries, the patient is called a female pseudohermaphrodite. Pseudohermaphroditism is always caused by sex hormone anomalies. Usually these anomalies are characterized by abnormal levels of sex hormones. Less

commonly, the basic defect may be an abnormality in the sex hormone receptors.

Answered: What is True Hermaphroditism

Mon, 18 Dec 2017 01:06:04 +0000

The gonads of the true hermaphrodites are usually streak-like, composite organs called ovotestes. An ovotestis has both ovarian and testicular tissue, suggesting the development of both cortex and medulla of the indifferent gonad. In true hermaphrodites the phenotype may be male or female but the external genitalia are ambiguous. In 70% of the cases of true hermaphroditism the genotype is 46 XX. About 20% of the cases are mosaics (46, XX / 46, XY; 45, X / 46, XY; or 46, XX / 47 XXY), and nearly 10% have 46, XY chromosome constitution.
It is easy to explain the presence of true hermaphroditism in mosaic individuals. In such persons the ovarian tissue develops from cells without a Y chromosome, whereas testicular tissue develops from cells with a Y chromosomes.
It is difficult to explain the presence of true hermaphroditism in individuals with 46, XX and 46, XY genetic constitution. It is thought that true hermaphrodites with a 46, XY genotype may also be mosaics. It has been proposed that one of the X chromosomes in some cells of these persons carries a fragment of the shot arm of the Y chromosome. These cells lead to the development of testicular tissue, whereas the normal cells cause the development of ovaries tissue. True hermaphrodites with a 46, XY genotype are the most difficult to explain. It has been suggested that in such individual some sells undergo mutation on the sex-determining region of the Y chromosome. This produces an effective mosaicism in which the mutated cells cause the development of ovaries tissue, while the normal cells lead to the formation of testicular tissue.

Answered: What is Abnormalities of Sex Differentiation

Mon, 18 Dec 2017 01:05:25 +0000

In a normal person the appearance of the external and internal genitalia is in accordance with the sex
chromosome complement of the individual. Errors in sex determination and differentiation lead to various degrees of intermediate sex or intersexuality. In some cases the errors of sex differentiation lead to hermaphroditism, which implies the presence of characteristics of both sexes in one individual; such an individual is called a hermaphrodite or intersex. The hermaphrodites are of two types (i) true hermaphrodites, and (ii) pseudohermaphrodites. This classification is based on the histological structure of the gonads.

Answered: Define Micropenis

Mon, 18 Dec 2017 01:03:07 +0000

A very small-sized penis is caused by the deficiency of androgens during development. Such deficiency may result from primary hypogonadism (testicular failure) or hypopituitarism.

Answered: What is Epispadias

Mon, 18 Dec 2017 01:02:31 +0000

This is a very rare malformation (incidence 1:30,000 male infants) in which the urethra opens on the dorsal surface of the penis. The embryological basis of this anomaly is unclear. It has been proposed that epispadias is caused by a caudal shift of the paired primordia of the genital tubercle, forcing the urethral groove to form on the dorsal surface of the penis. The epispadias is mostly associated1 with exstrophy of the urinary bladder.

Answered: What is Hypospadias

Mon, 18 Dec 2017 01:01:59 +0000

In this abnormality the external urethral orifice is present on the inferior aspect of the penis. It is a common anomaly (incidence: 1 in 300 male infants), and occurs due to the faulty fusion of the urethral folds. Various varieties of the hypospadias have been described, out which 80% belong to the following two types: (1) glandular hypospadias, in which the urethral opening is present on the ventral surface of the glans penis, and (2) penile hypospadias in which the external urethral meatus is present on the ventral (inferior) surface of the shaft of the penis. The uncommon varieties of hypospadias include penoscrotal hypospadias and perineal hypospadias. In the penoscrotal type the urethral opening is present at the junction of the penis and scrotum. In the perineal type of hypospadias the urethral folds and the labioscrotal swellings fail to fuse with
each other entirely. Consequently, a wide sagittal cleft is found along the entire length of the penis and scrotum.

Answered: What is Development of Male External Genitalia

Mon, 18 Dec 2017 00:14:49 +0000

Masculinization of the indifferent external genitalia occurs under the influence of androgens produced by the fetal testes. The genital tubercle enlarges and elongates rapidly to form the phallus, which is the primordium of penis. The elongating phallus pulls the urethral folds, so that the urethral groove comes to lie on ventral (ie, inferior) surface of the developing penis. A coronary sulcus around the distal part of the penis defines the glans. The urethral groove does not extend into the glans penis. The epithelial lining of the urethral groove becomes thickened to form the urethral plate. During the 7th and 8th weeks the urethral folds fuse in the median plane. The urethral groove is thus converted into an endoderm-lined canal, which lies within the penis and is known as spongy or penile urethra. Because the urethral groove does not extend to the tip of the penis, the penile urethra is initially blindended. The terminal part of the urethra is ectodermal in origin and is formed during the 4th month in the following manner. A sold cord of ectodermal cells grows inwards from the apex of the glans penis. This rod meets and fuses with the endodermal penile urethra. Complete canalization of the ectodermal cord occurs during the 5th month. This results in completion of the terminal part of the urethra and carries the external urethral meatus to the tip of the glans penis.
The genital (labioscrotal) swellings grow in a caudal direction and also move toward each other. Finally, they fuse in the midline to form the scrotum. Externally the line of fusion of the genital swellings persist as scrota/ raphe, whereas infernally the two halves of the scrotum are separated by the scrotal septum.

Answered: defined Development of Female External Genitalia

Mon, 18 Dec 2017 00:14:06 +0000

If the developing individual is a genetic female, the external genitalia differentiate into the female type. The stage of differentiation begins in the 9th week of development. It has been proposed that the estrogens produced by the placenta and fetal ovaries stimulate the development of the external genitalia in the female.
The genital tubercle grows for a short distance and bends inferiorly to form the clitoris. The urethral folds on each side of the urogenital orifice persist as labia minora. The genital swellings enlarge and become the labia ma-jora. The endoderm lined urethral groove forms the vestibule into which the urethra and vagina open.

Answered: what is Development of External Genitalia Indifferent stage

Mon, 18 Dec 2017 00:13:32 +0000

Early development of external genitalia is similar in males and females. From the 4th to the 7th week, the external genitalia are sexually un-differentiated. Distinguishing sexual characteristics begin to appear during the 9th week. However, the external genitaiia are not fully differentiated until the 12th week of development.
In the 4th week of development, a pair of swellings, called cloacal folds, develop on either side of the doacal membrane. Just cranial to the cloacal membrane these folds unite to form a midline swelling called genital tubercle.
During the 7th week the urorectal septum fuses with the cloacal membrane and divides the cloacal membrane into an anterior part called urogenital membrane, and a posterior part called anal membrane. The cloacal folds also become divided into two parts. That part of the cloacal fold flanking the urogenital membrane is now known as urethra! fold (also called urogenital fold), and the part flanking the anal membrane is now called anal fold. Very soon afterwards, a new pair of swellings develop on each side of the urethral folds, these swellings are called genital swellings (also called labioscrotal swellings).
By the end of 7th week the urogenital membrane disintegrates and disappears. As_a result, the phallic part of the urogenital sinus loses its floor and now opens into the amniotic cavity. The opening of the urogenital sinus is in the form of a cleft-like groove called urethral groove. This groove is lined by endoderm and bounded on each side by a urethral fold.

Answered: define Imperforate hymen.

Mon, 18 Dec 2017 00:12:36 +0000

Normally the hymen becomes perforated in the perinatal period. However, sometimes the hymen fails to perforate. This condition usually remains undetected during the childhood. But when menstrual cycles begin a clinical condition called hematocolpos (meaning collection of blood in vagina) results. Surgical incision of the obstructing membrane relieves the condition

Answered: define Double vagina

Mon, 18 Dec 2017 00:11:34 +0000

Failure of fusion of the sinuvaginal bulbs results in the formation of a double vagina. This condition may exist in the form of two completely separate vaginae. More commonly, a membranous septum divides the vagina into two halves.

Answered: define Atresia of vagina.

Mon, 18 Dec 2017 00:11:01 +0000

Failure of canalization of the vaginal plate results in vaginal atresia. The vaginal lumen is absent in the lower two-thirds, where the vagina is represented by a bansverse septum. However, the opening of the cervix uteri is surrounded by a small vaginal pouch, indicating that the upper one-third of the vagina is derived from the paramesonephric ducts.

Answered: What is Uterus unicornls.

Mon, 18 Dec 2017 00:10:29 +0000

Sometimes one paramesonephric duct either fails to develop or degenerates and disappears, so that the uterus consists of only one hom with one uterine tube.

Answered: What is Uterus bicornis unicollis

Mon, 18 Dec 2017 00:09:58 +0000

In this anomaly the uterus consists of two horns, which open into a single cervical canal. Sometime one of the two uterine horns is underdeveloped and remains in rudimentary condition (due to atrophy of a paramesonephric duct). This condition is called uterus bicornis with a rudimentary horn. The rudimentary horn usually does not communicate with the cavity of the uterus. This leads to complications when puberty arrives and menstruation begins.

Answered: What is Uterus bicornis bicollis.

Mon, 18 Dec 2017 00:09:25 +0000

This malformation is also known as uterus didelphys or double uterus. Literally uterus bicornis bicollis means a uterus having two horns and two cervices. In this anomaly the uterus consists of two horns, each having its separate cervical canal. The condition is usually associated with a double vagina.

Answered: What is Uterus septus.

Mon, 18 Dec 2017 00:08:45 +0000

In this anomaly the cavity of the uterus is divided by a median septum. Usually such a septum extends from the fundus to the isthmic region of the uterus. However, sometimes the septum reaches the in-
ternal os, completely dividing the uterine cavity; this condition is called uterus bilocularis.

Define Uterus arcuatus

Sun, 17 Dec 2017 23:12:57 +0000

Define Uterus arcuatus

Questions and Answers - Recent questions and answers in Medical

Answered: what is Defects of the Tricuspid Valve

Answered: defined Defects of the Pulmonary Valve

Answered: What is Valvular Anomalies

Answered: defined Persistent Atrioventricular Canal

Answered: defined Ventricular Septal Defects (VSD)

Answered: What is Common Atrium

Answered: defined Endocardial Cushion Defect with Osteum Primum Defect

Answered: defined Osteum Secundum Defect

Answered: defined Atrial Septal Defects (ASD)

Answered: What is Ectopia cordis.

Answered: What is Dextrocardia.

Answered: Defined Anomalies of Position

Answered: What is Congenital Anomalies of the Heart and Great Vessels

Answered: Differentiation of the Cardiac Wall

Answered: defined Atrioventricular Valves

Answered: defined Semilunar valves

Answered: Formation of Interventricular Septum

Answered: define Absorption of the Right Sinus Horn into the Right Atrium

Answered: denfine Formation of the Interatrial Septum

Answered: What is Division of the Atrioventricular Canal

Answered: Division of the Atrioventricular Canal

Answered: define Partitioning of the Conotruncus

Answered: What is Absorption of the primitive pul­monary vein into the wall of the Left Atrium

Answered: What is Absorption of the Right Sinus Horn into the Right Atrium

Answered: What is Septum Secundum

Answered: What is Septum Primum

Answered: define Formation of the Interatrial Septum

Answered: define Internal Specializations

Answered: what is Development of the Heart

Answered: define Histogenesis of the Embryonic Blood Vessels

Answered: What is CARDIOVASCULAR SYSTEM

Answered: define Male Pseudohermaphroditism

Answered: Define female pseudohermaphrodi­tism ,

Answered: What is Pseudohermaphroditism

Answered: What is True Hermaphroditism

Answered: What is Abnormalities of Sex Differentiation

Answered: Define Micropenis

Answered: What is Epispadias

Answered: What is Hypospadias

Answered: What is Development of Male External Genitalia

Answered: defined Development of Female External Genitalia

Answered: what is Development of External Genitalia Indifferent stage

Answered: define Imperforate hymen.

Answered: define Double vagina

Answered: define Atresia of vagina.

Answered: What is Uterus unicornls.

Answered: What is Uterus bicornis unicollis

Answered: What is Uterus bicornis bicollis.

Answered: What is Uterus septus.

Define Uterus arcuatus

Answered: What is Absorption of the primitive pulmonary vein into the wall of the Left Atrium

Answered: Define female pseudohermaphroditism ,