Full embryology video      
 

Full embryology video

EMBRYOLOGY VIDEO TEXT

Go to Full embryology video with embedded individual videos

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STORY OF LIFE

The human embryo begins its story at the formation of the zygote at fertilisation. This is a single cell structure that grows and grows and grows until it becomes a whole organism. This occurs at birth. The human embryo is peculiar because there are debates as to what its nature is. Is the human embryo human or  is it subhuman? If it is human the killing of the human embryo then become murder. If it is not human then what is it? At what stage does it become human? There are several theories and the theories are as follows. We have the conception theory which is the absolutist theory and this is the most widely accepted. It is strange though that it is the latest model of understanding of the human embryo having only been used in the19th century because of the discovery of the human egg by von Baer.  Before this several models were followed including the ones used by the Jews and the Roman Catholic Church which states that the embryo become only human only when it reaches the fetal stage at which time it would have acquired its appendages  so that it is recognisable as human, that is, it will have  a head; it will have limbs. But before then, it was not considered  human. This is because the human egg was not recognised as an entity involved in fertilisation until the discovery by von Baer in the 19th century. The advantage of the theory of conception is that it has science behind it. Since the very first process of life begins at fertilisation which is the same point of conception and there is no other process, which separates new life from maternal life except this one. It is therefore difficult to expect scientists to believe that life begins before this.

Strangely though it is even the scientist themselves, by that I mean investigative scientists who refuse to accept the theory of conception. Most other people who may be shack scientists or who may have little knowledge of biology support this theory enthusiatically.

 

The next theory is the Morula theory. This theory has the least of support. It is found mostly amongst modern reproductive biotechnologists  who have discovered that maternal transcription of DNA which controls the early embryo behaviour continues until  sometimes 4 cell or even morula stage of the embryo when the actual zygotic or  embryo transcripts of the embryo genome begins.

When they latter begins the proteins produce for the physiology of the embryo are strictly derived from the transcriptional processes of the DNA of the embryo itself. In that case the embryo now becomes independent and fully human.

 

The brain wave theory suggests that it is only when the brain wave appears,  at which point it is assumed that the embryo has now developed a functional brain, that  is the time the embryo becomes human.

 

The Soul theory says it is only when the embryo acquires a soul, that it becomes human. Most Islamic theologians will suggest that this date will be 40 days after fertilisation.

 

The Primitive Streak theory. This theory  suggest that the organ primitive streak appears about  14 days after fertilisation. The primitive streak is unique because it brings organisation to a previously unorganised embryo. Before the formation of the primitive streak the embryo does not have head, tail or limbs, but just a  ball of cells. But after the appearance of the primitive streak it now has presumptive regions.

 

The Nervous System theory which is the next theory suggest that an embryo cannot be said to be fully human until it develops a nervous system. This theory  relies heavily on the fact that without a nervous system the embryo cannot feel pain. If there is no pain then there can be no actual life. In that case the embryo is considered to be a plant; it has the status of a plant because plants don't have no pain.

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Child delivery video

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Caesarean section  video

 

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Ovulation and early cleavage video

The secondary oocyte with a single polar body is released from a mature Graafian follicle. It is taken up by the fimbriae of particular fallopian tube and migrates  to the ampulla of the  tube. There it meets numerous sperm cells already released for fertilisation or it may wait for not more than 3 days for the sperm to arrive. The sperm cells attempt to penetrate the egg but only one succeeds. Male and female pronuclei then fuse to cause fertilisation. Cleavage begins with the zygote forming first cleavage division leading to two daughter cells, from 2 cells it goes to 4 and then 8 and then 16, at which point it is called morula. It proceeds to 32 cell and then 64 cells after which cavitation occurs and the embryo becomes the blastocyst with 2 population of cells- the inner cell mass and the outer cell mass. Further development leads to the inner cell mass  which develops into the actual embryo to become the germ disc initially with only one germ layer called the ectoderm but later joined by the endoderm derived from the same ectoderm.

 

 

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Implantation cleavage video

When the embryo enters the uterus after its journey through the fallopian tube, it seeks a place to stick to. It is assumed the place to be selected must be sticky so that the embryo does not fall off as a result of gravity. The embryo then begins to grow. This is the first time there is a physical contact with maternal tissue and it is recognised in physiology as the moment of maternal recognition of pregnancy. Shortly after this the woman becomes aware she is carrying a baby because of release of hormones, must especially human chorionic gonodotropins (hcg) which will then influence the physiology of the woman. Fetal membranes are formed as amnion, chorion  and later the placenta. They help to provide the interphase between  mother and child and also the much needed blood supply and nutriment for the growth of developing child.

 

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Embryo growth video

Growth of the embryo is quite rapid. Between the 4th and 8 week of gestation there is massive proliferation and differentiation of cells to form various organ systems. At the end of the 8th week  almost all the primordia of various organs and systems in the body are already formed. Process for formation of this organ system is called organogenesis. In the early fetal period there is repid growth of fetus until the late fetal period which  is characterised by increased in fetal weight. From the 26th weeks after fertilisation to one month after childbirth it is called the perinatal period. Perinatology  is the branch of medicine that deals with the study of the fetus in the perinatal period. Perinatal medicine therefore combines some bits of obstetrics and pediatrics.

During the perinatal period, amniotic fluid can be obtained from the amniotic cavity by the process called amniocentesis and the fluid is subjected to various analysis for  diagnosis of various disorders. For example amniotic cells can be cultured and chromosomal stages can be done to detect disorders like Down's syndrome, Turner's syndrome, hemophilia. Alpha fetoproteins can be detected in the amniotic fluid and therefore it is known to increase in the condition like spina bifida cystica. Intrauterine blood transfusion can be performed during perinatal period and ultrasound or  ulttrasonography can be employed to detect such conditions as like anencephaly, fetal ascites, spina bifida, intrauterine growth retardation etc. Estimation of gestational age or fetal age is done by the following- information on last menstrual period (LMP), fertilisation age- measurement of height such as crown rump length, measurement of biparietal diameter, somite count etc.

 

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Embryo folding video

Shortly  after the formation of the intraembryonic mesoderm, the embryo folds laterally and anteroposteriorly in order to reduce the size of the gut formed from the yolk sac. And also to place the intraembryonic mesoderm ventrally.

Embryo folding. The flat trilaminar embryonic disc progressively increases in size and undergoes folding to be transformed into cylindrical structure. Embryo  folding takes place in two planes- longitudinal folding and transverse folding. These folding take place in a vertical direct during longitudinal fold and the head fold and the tail fold are formed. As the head fold forms part of yolk sac is incorporated into the embryo from the primitive foregut. This primitive  foregut is formed separated from the stomatodaeum by the oropharyngeal membrane, the cardiogenic area together with the primitive heart tubes and the septum transversum. They come to lie ventral to the primitive foregut with the septum transversum lying caudal to the primitive heart. The septum transversum takes part in the formation of the diaphragm. As the tail fold forms part of the  secondary yolk sac is incorporated into the embryo as the  primitive hind gut. This primitive hind gut is separated from the cloaca by the cloacal membrane. During transverse folding part of secondary yolk sac is also incorporated into the embryo as the primitive hind gut. This primitive hind gut is separated from the cloaca by the cloacal membrane during transverse folding. Part of the secondary yolk sac is also incorporated into the embryo as the primitive midgut. And as this  midgut forms it becomes attached to the dorsal aspect of the embryo by the dorsal mesentery. As a result a result of transverse and longitudinal folding the embryo becomes attached ventrally with the main part of the secondary yolk sac.  The yolk sac and the connecting stalk-all are formed and they lie close and ventral. Together they take part in the formation of the umbilical cord.

 

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Germ layers development video

 

The embryo initially forms two germ layers- the ectoderm and the endoderm. This embryo is therefore called the bilaminar embryo. Later a third germ layer is added, called the mesoderm. The process for the adding of the 3rd germ layer is gastrulation. This process leads to the formation of the organization of the embryo so that the embryo now has folds. It is organizable to head, tail or  limb buds. The primitive streak helps in the formation of this third germ layer. Cells that are coming from the ectoderm insinuate themselves between the ectoderm and the endoderm around the primitive streak. They migrate rapidly around the whole of the embryo and assist the process of organization forming the mesoderm.

 

 

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Somites development video

Somites reach  up to 42-44 in number when they are fully developed. They are formed from paraxial mesoderm  and are divided into dermatome, sclerotome and myotome. Dermatomes migrate into the skin to form the mesoderm of the skin, mainly the dermis.

 

 

 

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Development of Intraembryonic celom

The lateral plate mesoderm begins to develop spaces within it. And these spaces coalesce to form the intraembryonic coelom. The intraembryonic coelom surrounds the cardiogenic area which forms the pericardium and other coelomic cavities within the body wall. Intraembryonic coelom divides the  lateral mesoderm into 2 parts.The one that continues with the extraembryonic mesoderm surrounding  the amnion is called the somatic intraembryonic coelom; the one that continues with the extraembryonic mesoderm surrounding the primary yolk sac is called splanchnic extraembryonic mesoderm. The somatic intraembryonic mesoderm together with overlying ectoderm is called somatopleuric mesoderm and this forms the body wall.

The splanchnic intraembronic mesoderm and the underlying endoderm form the splanchnopleuric mesoderm and they are responsible for the covering of the walls of the gastrointestinal tract. The intraembryonic coelom forms  three main body cavities-1. pleural cavity, 2 peritoneal cavity 3 pericardial cavity.

 

 

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Face development video

There are 3 processes involved in the development of the face. And they are the frontonasal process, the maxillary process and the mandibular process. The frontonasal process becomes the forehead and the nose. Maxillary process forms face below the eye. The mandibular process  forms the face below the mouth. As the development of the face continues, the buccal cavity is being formed. The brain also expands.

At the presomite stage the face consist of only a bulging forehead superiorly and a developing pericardium inferiorly.  Laterally we can see the mandibular process. Stomodeal membrane covers the opening into the mouth. Later the membrane breaks down so that there is a communication between the mouth and the developing pharynx.  As development continues the mandibular processes on the right and left form the maxillary process. As the mandibular processes continues their development they will now fuse at the mid line forming the lower jaw together with the lower lip.

Superior to the mandibular process and the stomatodaeum but medial to the maxillary process is the olfactory placode. This placode will develop into a frontonasal process. The process consist of two main structures - the medial and lateral nasal folds. The area between the medial and lateral nasal folds is will therefore developing into olfactory system.

As development continues, the lateral nasal fold fuses with developing maxilla forming the nasooptic furrow, which enters into the developing eye placed above the frontal process (i.e. frontonasal process). The  medial and lateral nasal folds will meet and fuse forming a space between them  which becomes the anterior nares. This will be the opening into the nose. The right and left medial folds then come together reducing the space between them. This  space is going to become the nasal septum internally. The maxilla also fuses with the medial nasal fold and the right and left maxilla processes will meet the frontonasal process at the midline so that the two  will form the upper lip; while the maxilla alone will form the upper jaw.  

Maxillary and mandibular processes now contribute to the formation of the cheeks.  The transverse groove separates the bridge of the nose  from the developing  forebrain which then becomes the forehead.  The mesenchyme of the nose forms ossification centers for the ossification of the  two nasal bones.  Finally the muscles developed from the 2nd pharyngeal arch will invade the face region and the auricle to form the muscles of facial expression which maintain their nerve supply from the facial (VII) nerve.

 

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Development of pharynx video

The key to the understanding of the anatomy of the head and neck region lies in the understanding of the development that takes place in the pharynx  and these include the development of arches, the pouches and the clefts. Almost all the features in the head and neck region lies in the development from pharynx in a model similar to the gill clefts of fishes. Even the nerve supply to these primordial structures are derived from the head region even if they later migrate to neck or other regions. Most of the major organs are preformed in the pouches, , (or pharyngeal pouches). The original head does not contain these structures. It has only the brain and the  developing eye.

 

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Development of pharyngeal arches video

Pharyngeal arches are responsible for the formation of the structures derived from mesenchyme of the head and neck region. Their development leads to increase separation of the space between the stomatodaeum which is the primitive mouth and the pericardium containing the developing heart. Also they are placed lateral to the developing brain. The lateral plate mesoderm is responsible for the formation of the pharyngeal mesoderm and this mesoderm will differentiate into the following - cartilage and muscle. Cartilaginous elements later ossify to become bones, while the muscles are derived from in situ differentiation of arch mesoderm or mesenchyme. Other structures  which are associated with the arches invade the developing mesoderm of the arches.

The premandibular mesenchyme leads to the formation of extraocular muscles and they include the

superior medial,and inferior recti, with the oblique inferior oblique and levator palpebrae superioris.

The maxillomandibular mesenchyme leads to  two muscles-

lateral rectus

superior oblique

The nerve to the maxillomandibular mesenchyme includes the trochlear nerve and the abducens.

The mandibular arch gives rise to muscles of mastication-

The mandibular cartilage forms the Meckel's cartilage, the quadrate cartilage, the mental ossicles,  the anterior ligament of malleus and the sphenomandibular ligaments.

The nerve to the mandibular arch is the mandibular nerve is a branch  of the trigeminal (V) nerve

The hyoid arch is the 2nd arch. It gives rise to muscles of facial expression. The nerve supply to the hyoid arch is the facial nerve.

The third arch gives rise to stylopharyngeus. The nerve supply to the stylopharyngeus is the glossopharyngeal nerve.

The 4th pharyngeal arch give rise to the cricothyroid. The nerve supply to the cricothyroid is the superior laryngeal branch of X of the vagus nerve.

The 6th arch gives rise to the intrinsic muscles of larynx. The 6th arch is the

recurrent laryngeal branch of vagus nerve.

The caudal arches gives rise to the muscles of pharynx such as

superior constrictor

middle constrictor and

inferior constrictor

 of pharynx. Nerve supply to the caudal arches are from cranial accessory through the vagus nerve.

The development of the the tongue is close  to the development of the arches.

 

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Development of pharyngeal pouches video

 

The pouches  (pharyngeal pouches) are endodermal in origin. They initially communicate with  the pharynx but later this communication narrows and then they form pouches which have dorsal and ventral recesses. The  tongue does not allow the formation of ventral recess in the first pouch. On each side of the dorsal  recesses of the 1st and 2nd pouch there is an expansion of the pouches to form a tubotympanic recess with a single narrow pharyngeal opening.

The ventral recess of the 2nd pouch between the palate and the tongue  forms the palatine tonsils.

The right and left ventral recess of the 3rd pouch  form the thymus gland.. The dorsal recess of the 3rd pouch forms  the parathyroid  or parathyroid 3 or inferior parathyroid gland.

The dorsal recess of the 4th pouch forms superior parathyroid gland or parathyroid 4.

The last pouch which is called the ultimobranchial body forms the pouch and releases cells which are called C cells invade the thyroid gland and produce calcitonin in the adult.

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Development of heart video

At the 3rd week of gestation the heart develops from fused endothelial tubes forming the bulbus, ventricles and atria. The atria begin to rise above the ventricles. The truncus arteriosus is formed leading to the formation of the aortic sac above the bulbus cordis.

 

 

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Heart interior development video

The single chambered heart soon gives rise to the formation of the endocardial cushion with still a wide communication between atria and ventricles. Septum primum is formed at the roof of the right atrium which approaches the cushion and forms the ostium primum between it and the cushion. It then becomes detached from the top with the formation of the ostium secundum behind it and obliteration of ostium primum as it joins the endocardial cushion.. The ostium secundum then becomes the foramen ovale at the mature 6 weeks heart. With formation of the atrioventricular valves between the atria and ventricles becomes 4 chambered with only the foramen ovale as opening between the atria.

 

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Fetal circulation video

 

Blood in the fetus flows from the post hepatic inferior vena cava to enter the right atrium. It is separated from the blood coming from head and neck region which pass into the right atrium by the intervenous tubercle so that blood from the SVC goes straight into the right ventricle and the other goes through the foramen ovale to the left atrium. The right ventricular blood then enters the pulmonary trunk to be shunted via the patent ductus arteriosus to the aorta from where it is passed to the rest of the body and the placenta. Blood which enter the left atrium is immediately passed into the left ventricle and from there to the ascending aorta and then systemic circulation. This fetal circulation is designed to shunt blood from the right to left so that blood is diverted from the immature lungs to the placenta through systemic circulation where it is oxygenated via the umbilical arteries and then umbilical veins.

 

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Arterial arches development video

 

There are 6 aortic arches, the 5th is transient. The aortic sac develops from the  truncus arteriosus and is connected to all the aortic arches. Then the development shapens the arches and they form the aortic sac superiorly.  The right dorsal aorta of the 4th arch moves upwards and the left dorsal aorta moves downwards and forms the final configuration of the arterial arches.

Arteries in the embryo take origin from the aortic sac which originally was connected to a paired dorsal aortae. They arrive segmentally to supply the pharyngeal arches at 1st, 2nd, 3rd, 4th, 5th and 6th aortic arches. The 5th aortic arch disappears and the 5th pharyngeal arch. Again the 1st, and 2nd arches are obliterated at their ventral aspects. The 3rd arch is incorporated into the common carotid artery. The 4th aortic arch together with...

 

 

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Development of veinS video

The cardinal, vitelline and the hepatocardiac veins develop  below the heart. They form series of longitudinal anastomoses which later come together to  form the definitive inferior vena cava.

The ductus venosus is also formed above the liver. It passes through the liver and is connected to the subcardinal anastomosis initially. The inferior vena cava. The inferior vena cava is  also becomes formed and its connected to the ductus venosus.

Veins are not segmental the way arteries are in the embryo. The original veins are the paired anterior and posterior cardinal veins which form the common cardinal  veins on both sides. They enter the sinus venosus. The right anterior cardinal vein forms the right internal jugular  vein and the brachiocephalic veins and also part of superior vena cava above the azygos vein. A cross anastomosis between the anterior cardinal veins form part of the brachiocepalic vein on the left. Posteriorly the subcardinal veins appear and they drain the mesonephric ridges. The body wall is drained by the supracardinal veins that appear later and the inferior vena cava  is formed from many veins. The initial ductus venosus is formed within the liver before the inferior vena cava.

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Development of Lung

The lungs develop from a single diverticulum forming the laryngotracheal tube which divides and subdivides until it becomes the actual lung.

 

 

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Development of gut video

The primitive gut is formed form the endodermal sac which is carved out of the receding yolk sac and the folding embryo. The portion before the yolk sac becomes the foregut guarded by an anterior intestinal portal and the portion behind the yolk sac becomes the midgut. The portion facing the yolk sac directly is the midgut. The esophagus is formed from the elongation of the tube between the pharynx and the stomach. and the foregut ends at the level of the bile duct. The stomach now rotates with its ventral mesogastrium so that its  lesser curvature, which  is continuous with the ventral mesogastrium now lies to the right and the dorsal mesogastrium carried to the left forming the omental bursa behind it.. The duodenum then comes to lie right of the stomach. The spleen is formed within  the rotating dorsal mesogastrium. The pancreas is formed by two diverticula for the gut tube. The largest is the dorsal pancreas while the smaller is the ventral pancreas. With the rotation of the stomach, the ventral pancreas is carried behind the stomach to meet the dorsal and the two fuse to form the definitive pancreas.

The ventral diverticulum of the pancreas also forms the gall bladder and common bile duct and later the liver. The liver develops from the junction of the yolk sac and foregut from primordium of cells which form the hepatic rudiment and grows into the septum transversum. It is initially surrounded by three veins, umbilical, vitelline and hepatocardiac veins. The hepatocardiac veins drain the liver directly  into the sinus venosus. But as soon as develop continues the liver allows the obliteration of many veins and finally forms within its substance the ductus venosus, which later becomes the inferior vena cava at birth.

The midgut herniates during the development of the gut and undergoes rotation and then returns back at about 3  months of intrauterine life due to the decrease in size of the kidneys and other intrabdominal organs.

 

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Development of Kidney

The kidneys are formed from three important preceeding stuctures. The first is the pronephros. It is not very clear whether this exists in the human embryo is it does clearly in those of lower animals. But if it does, it stays for just a short while and may occur in the intermediate mesoderm which is opposite the cranial somites. It gives way to the mesonephros which develops tubules and extends from the septum transversum to the third lumbar vertebrae. Its  long duct is then called the  or mesonephric duct or Wolffian duct. The next renal system is the metanephros which forms below the mesonephros at the sacral region. A ureteric bud then grows out of the caudal part of mesonephric duct and grows into the metanephros. It consolidates itself and becomes the definitive kidney complete with secretory and tubular parts.

 

 

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Development of gonads video

In the female  the ovary develops by the invasion of the germinal epithelium by primordial sex cells. The sex cords are then formed. The mesonephric duct degenerates but the Mullerian duct persists. And the Mullerian duct forms most of the ductal systems of the female reproductive system.

In the male at 6 weeks  the sex cells (primordial cell sex cells) begin to invade the germinal epithelium and also form sex cords. There is now a connection from the mesonephric duct to the tubules. These tubules form the seminiferous tubules while the Mullerian duct degenerates.

 

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Development of male reproductive system video

Male reproductive system

Primordial sex cells are formed in the yolk sac in the pre-somite embryo. They migrate from this position to the medial aspect of the mesonephric ridge. The epithelium of the mesonephric ridge then proliferates and forms its own ridge called the genital ridge. Two ducts are now recognised as the Wolffian or mesonephric duct and the paramesonephric duct (Mullerian ducts) bilaterally. The mesonephric duct is associated with the mesonephros and the developing kidney system. In the male, as soon as the sex cells arrive, the epithelium of the genital ridge form sex cords which becomes cut off from the surface epithelium and are linked to the mesonephric tubular system to form the primitive seminiferous tubules of the testis. This allows the mesonephric duct to be the main duct that differentiates into the definitive male reproductive system with the formation of the duct of epidydimis, the vas deferens, and ejaculatory duct. The Mullerian tubercle which is formed at the junction of the two ducts with the urogenital sinus in both sexes becomes the seminal colliculus of the prostate. The paramesonephric duct degenerates in the male but forms the ductal system in the female, but may also form vestigial structures in the male such as appendix of testis and epidydimis. The paradydimis and aberrant ductules are formed from the mesonephric tubules  which persists.

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Development of female reproductive system video

Primordial sex cells are formed in the yolk sac in the presomite embryo. They migrate from this position to the medial aspect of the mesonephric ridge. The epithelium of the mesonephric ridge then proliferates and forms its own ridge called the genital ridge. Two ducts are now recognised as the Wolffian or mesonephric duct and the paramesonephric duct (Mullerian ) ducts bilaterally. The mesonephric duct is associated with the mesonephros and the developing kidney system. In the female, as soon as the sex cells arrive, the epithelium of the genital ridge form sex cords which becomes cut off from the surface epithelium. They will form the primary follicles and begin meiosis shortly before birth. The paramesonephric duct becomes the main duct in the female reproductive system while the mesonephric or Wolffian duct degenerates. The longitudinal parts of the paramesonephric ducts now fuse to form the duct system of the female such as the uterus, the fallopian tubes and the cervix. Cervix is formed from the caudal part, the iuterine tubes from the cranial part and the intermediate part forms the uterus. Vaginal plate epithelium is insinuated between the Mullerian tubercle and the urogenital sinus. It divides and forms the vagina which later canalises. The mesonephric duct degenerates but forms some vestiges such as the epoophoron and paroophoron. The Gartner's duct formed by the caudal part of the mesonephric duct degenerates but may persist as aberrant ductules in the adult system.

 

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Development of external genitalia video

External genitalia in both male and female are formed from the genital tubercle, genital swelling and genital folds. The genital tubercle becomes the phallus. In the male it continues its development until it is fully grown and forms the penis with the  penile urethra opening at its tip (i.e. tip of penis). In the female it grows for a little while and stops further growth to allow the the urethra to develop outside its walls in the anterior wall of the vagina. In both it leads to the formation of similar phallic structures such as the corpora cavernosa and the corpus spongiosum. In the female the Mullerian tubercle becomes the hymen and moves to the surface. The genital fold then becomes the labia minora while the genital swellings become the labia majora. In the male, the genital tubercle becomes the penis, genital swelling the scrotum and the genital fold the penile urethra.

 

 

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Development of Limb

The development of the limb begins from the limb bud after organisation and influence of the primitive streak. The limb differentiates in situ most especially the mesenchyme which may be derived from the mesenchyme of the body wall  which is the somatopleuric mesenchyme. The muscles are not formed from myotomes but differentiate within the limb buds and followed by their nerve and blood supply. After then any where they migrate into they carry along their blood vessels and nerve and their migratory movement leads to fusion, extension and recombination of the nerve fibers and hence the formation of plexus in the limbs.

 

 

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Bone ossification video

Bones ossify in three ways. They may ossify in membrane and then they would be called membrane bones or ossify in cartilage, then thy would be cartilaginous bone. A third category stands alone and affect the clavicle and that is ossification in precartilage. Usually you have a primary ossification centre with many secondary ossification centres which then spread the wave of ossification around the entire bone until it is completed.

 

 

 

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Brain development video

The central nervous system begins as single tube with wide opens at the ends called anterior and posterior neuropores. But as development continues they form what are called flexures. Two are ventral while one is dorsal.  The ventral ones are the cervical (between spinal cord and medulla) and mesencephalic flexures (placed in the midbrain). The dorsal flexure is the pontine flexure. Three primary brain vesicles are now recognisable and they are the forebrain, midbrain and hindbrain. They undergo considerable distortion and flexures until they reach their level of maturity.

 

 

 

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CONGENITAL ANOMALIES

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