Embryology Flashcards
What is the origin of the greater omentum
Dorsal mesentery
What is the origin of the lesser omentum
Ventral mesentery
The ventral mesentery develops into which two ligaments
Hepatogastric
Hepatoduodenal
The median umbilical fold is the remnant of what
Also known as the median umbilical ligament, it is the remnants of the the urachus extending from the apex of the bladder to the umbilicus
The 2 medial umbilical folds of the anterior abdominal wall are remnants of which structures
Umbilical arteries
What is the course of the umbilical arteries
From the iliac arteries to the umbilicus
Where does the the diaphragm develop from
The septum transversum
Explain the nerve supply of the diaphragm
Supplied by C3, 4 and 5 (phrenic nerve) - as the lungs expand during development the diaphragm is forced inferiorly, which drags the nerve supply
Supplied by the upper cervical ventral rami despite being at the base of the thorax in the adult
What are the embryological components of the diaphragm
Septum transverse
Pleuroperitoneal membrane
Dorsal mesentery of the oesophagus
Ingrowth from the body wall
The septum transversum becomes which structure in the adult
Central tendon
The crurs of the diaphragm develop from which structure
The dorsal mesentery of the oesophagus
How does the oesophageal hiatus of the diaphragm develop
Fibres from the right crus cross over the midline, creating a loop around the oesophagus
There are 3 hiatus in the diaphragm - at which levels are these found and what structures will pass through them
T8 - right phrenic nerve, IVC
T10 - oesophagus, left gastric artery and vein, vagal trunks
T12 - thoracic aorta, thoracic duct, azygos and hemiazygos veins
Incomplete development of the diaphragm leads to what condition and how does this present
Congenital diaphragmatic hernia
Midgut structures can pass through into the thorax - leading to pulmonary hypoplasia (often left sided)
2 types - Morgani and Bochladek
Morgani hernias - more often contain bowel, less commonly cause lung hypoplasia
The gut tube is developed from which layer of the trilaminar disc at week 3 of development
Endoderm
From which layer of the trilaminar disc is the urogenital system developed
Mesoderm
Which structures does the vitellien duct connect
The forgut to the yolk sac
Which structures have an ectodermal origin
Central and peripheral nervous system, epidermis and sensory epithelium
Which structures develop from the mesoderm
Muscle, bones, connective tissue, blood, blood vessels, serous membranes, urogenital system
What develops from the endoderm
The gute tube and villous structures derived from it (GI, respiratory, reproductive)
How does the thorax and abdomen become 2 separate cavities
Septum transversem grows from the anterior body wall to meet the gut tube, 2 pleuroperitoneal membranes grow from the posterior abdominal wall to meet the septum transversum
Which structures develop from the foregut
Pharynx
oesophageal - also gives respiratory diverticulum which develop into lung buds and trachea
Stomach
Duodenum
Pharyngeal pouch derivatives
Liver, pancreas, gallbladder and associated ducts
What is the origin fo the blood supply of the foregut
Coeliac axis
What structures develop from the midgut
Duodenum - distal to the duodenal papillae - 2nd, 3rd, 4th part
Jejunum
Ileum
Caecum
Appendix
Ascending colon
Right 2/3 of transverse colon
What is the blood supply of the midgut
Superior mesenteric artery
Which structures develop from the hindgut
Left 1/3 of the transverse colon
Descending colon
Sigmoid colon
Rectum
Part of the urogenital sinus
What is the blood supply of the hindgut
Inferior mesenteric artery
What is the relationship of the dorsal mesentery and the gut tube
Suspends the gut tube from the posterior abdominal wall
What arises from the dorsal mesenteries
Dorsal mesogastrium
Dorsal mesoduodenum
The mesentery - connected to the ileum and jejunum
Dorsal mesocolon - forms the transverse and sigmoid mesocolon
Which structures develop from the dorsal mesogastrium
Gastrosplenic, gastrophrenic, linorenal ligaments and the greater omentum
What is the ventral mesentery derived from
Septum transversum
The growth of which organ divides the ventral mesentery
Liver
What is the ventral mesentery divided into
Lesser omentum - posteriorly
Falciform ligament - anteriorly
Atresia of the abdominal organs arises when what physiological process does not occur
Recannualisation of the gut tube in weeks 6 and 7
The respiratory diverticulum develop from the ventral wall of which organ
Oesophagus
What is the function of the trachea-oesophageal septum
Partions off the oesophagus from the respiratory diverticulum ( respiratory primordium)
Describe the rotation of the stomach
In weeks 7 and 8 the stomach rotates 90 degrees on its longitudinal axis, bringing the lesser curvature to the right and the greater curvature to the left
After the initial longitudinal rotation of the stomach how does else does it move to its final position
Following 90 degrees of rotation along its longitudinal axis the stomach then moves, so that the cranial region moves left and inferior, whereas the caudal aspect moves right and superiorly
How does the omental bursa develop
Dorsal mesogastrium is pulled to the right, creating a space behind the stomach
How does the duodenum become a secondarily retroperitoneal organ
The rotation of the stomach causes the duodenum to bend into a c shape, and displaces it to the right so that it lies against the posterior body wall where it adheres and loses its mesentery
Where do the liver and gallbladder develop from
They arise from as a ventral outgrowth from the caudal foregut- the hepatic diverticulum (liver bud)
Explain how the bare area of the liver develops
When the septum transversum forms the central tendon of the diaphragm, the diaphragm remains in contact with the liver, meaning it has a bare area not covered by peritoneum. The surrounding peritoneum forms the coronary ligament around the bare area.
Which structures connects the liver to the duodenum
Hepatic duct
Where does the pancreas develop from
The dorsal and ventral pancreatic buds from the endoderm of the duodenum
Which structures develop from the dorsal pancreatic bud
Upper head, body, and tail of pancreas
Which structures develop from the ventral pancreatic bud
Inferior head and ucinate process
what is the main pancreatic duct formed from
The dorsal and ventral pancreatic bud
What forms the accessory pancreatic duct
Proximal dorsal pancreatic bud
What is an annular pancreas
Where the dorsal and ventral pancreatic buds fuse around the duodenum in a circle
What divides the dorsal mesogastrium into two ligaments
Linorenal ligament
Gastrosplenic ligament
Describe the extent of the recesses of the omental bursa (lesser sac)
The lower recess of the omental bursa lies inside the greater omentum and does not extend beyond the level of the transverse colon
The upper recess extends up behind the livers left lobe
Describe physiological umbilical herniation
The midgut elongates to form abentral v shape loop of the gut, then the midgut/primary intestinal loop projects into the umbilical cord - this is to allow for the rapid growth of the abdominal organs which the abdominal cavity cannot accommodate - there is rapid growth of mesentery to allow for this
Describe the cranial limb of the midgut during umbilical herniation
Grows rapidly, developing into the distal duodenum, the jejunum and the ileum
Describe the caudal limb of the midgut during umbilical herniation
Minimal change other than for the growth of the caecal diverticulum - forms the lower, ileum, the ascending colon and the proximal 2/3 of the transverse colon
Describe the rotation of the midgut
While in the umbilical cord the midgut loop rotates 90 degrees anticlockwise around the axis of the SMA.
During the rotation the cranial loop of the midgut elongates and forms the jejunal and ileal loops and the expanding caecum forms a vermiform appendix
Passes back into the abdomen - and undergoes a further 180 degrees of anticlockwise rotation
Where is the caecal diverticulum initially found in the abdomen and describe it’s descent
Initially in the right upper quadrant, lying behind the right lobe of the liver, descends to the right iliac fossa - this gives rise to the ascending colon and the hepatic flexure on the right of the abdomen
Why are the ascending and descending colon secondary retroperitoneal
The dorsal mesenteries for the ascending and descending colon shorten and fold, bringing the sections of colon into contact with the posterior abdominal wall
Which parts of the colon retain their mesenteries
Appendix, caecum, sigmoid colon
Transverse mesocolon fuses with the posterior layer of the greater omentum (so the transverse colon remains intraperitoneal)
What is the blood supply of the hindgut
Inferior mesenteric artery
What does the hindgut form
The left 1/3 of the transverse colon, the descending colon, the sigmoid colon, the rectum, the superior part of the anal canal and the urinary bladder, +majority of the urethra
What is the cloaca
The terminal part of the gut tube
What does the anterior portion of the cloaca form compared to the posterior portion
Anterior - urogenital system
Posterior - anorectal canal
What is the relationship between the allantois and cloaca
The cloaca receives the allantois ventrally - this developed as an outgrowth from the caudal end of the yolk sac, it is seen as a short blind tube running into the connecting stalk
What causes the fibrosis of the allantois and what does it become
Enlargement of the bladder leads to fibrosis of the allantois, with it becoming the urachus
What causes the cloaca to partition and into what partitions
The urorectal septum grows into the cloaca from the angle between the allantois and hindugt - partitions the cloaca into the ventral primitive urogenital sinus and dorsally - the rectum
What does the urogenital sinus give rise to
The bladder, pelvic urethra
What occurs following fusion of the urogenital sinus with the cloacal membrane
Divides it into the ventral urogenital membrane and the dorsal anal membrane
It also divides the cloacal sphincter into the external anal sphincter posteriorly, and the superficial transverse perineal, bulbospongiosum, and ischiocavernous muscles anteriorly
What is the origin of the anal canal
The superior 2/3 - derived from the handout
Inferior 1/3 from the proctoderm
The border between the two is marked by the rectorate crus
How does an imperfonate anus occur
Where the anal breakdown does not breakdown - usually happens in week 8
What is Hirschsprung’s disease
The lack of normal development of colonic innervation - leads to a constricted aganglionic segment of the bowel with a distended segment proximally
What is exompthalmos
Failure of the intestines to return back to the abdomen, lies within the peritoneum and minion in the umbilical cord (viscera is covered by peritoneum)
What is gastroschisis
Failure of the abdominal wall - the open abdominal wall leads to exposed viscera
Where does the spleen develop
Within the dorsal mesentery close to the posterior wall - the tail of the pancreas extends into the lenorenal ligament with the splenic vessels
What does the gastrosplenic ligament connect
The spleen to the stomach
Where does the allantois span
From the ventral region of the urogenital sinus to the umbilicus
What is the distal portion of the allantois Calle
Urachus
What does the urachus become in the adult
The median fold of the anterior abdominal wall
What does the lateral plate mesoderm become
The peritoneal cavity
What does the intermediate mesoderm become
The posterior abdominal and pelvic wall
What are the Wolffan ducts
The mesonephric ducts
What the three primitive kidney systems that are formed
Pronephros
Mesonephros
Metanephros
What becomes the definitive kidney
Metanephros
What forms the renal tissue
Metanephric blastema
Where does the ureteric bud extend from
Caudal mesonephric duct
What occurs for a bifid ureter to form
Abnormal branching of the ureteric bud
How does renal agenesis occur
Failure of the ureteric bud to branch at all within the metanephric blastema, will lead to kidneys not developing
The urorectal septum becomes what structure
Perineal body
What does the proximal part of the urogenital sinus become
Urinary bladder
What does the pelvic part of the urogenital sinus become
Prostatic and membranous urethra in men
Urethra and lower 2/3 of vagina
What do the mesonephric ducts become in men
The ejaculatory ducts
The mesonephric ducts and ureteric buds become incorporated into which structures
The urogenital sinus - primitive urinary bladder and urethra
What develops lateral to the mesonephric ducts
Paramesonephric ducts - they are an invagination from a cord of coelomic epithelial cells
What are the different origins of the reproductive organs in the different sexes
Female - paramesonephric
Male - mesonephric
Describe the development of the female reproductive tract
Absence of the Y chromosome and its SRY gene leads to female development from the paramesonephric ducts, the mesonephric ducts regress due to a lack of testosterone
What do the paramesonephric ducts give rise to
Oviducts
Ureterus
Cervix
Upper 1/3 of the vagina
How does the uterus and proximal vagina form
The 2 paramesonephric ducts meet in the midline and fuse with each other forming the sinovaginal bulb - this forms the proximal vagina, uterus and cervix
Why do the paramesonephric ducts need to stay separate cranially
To form the left and right uterine tubes with fibrillated ends
What happens if there is a failure of the fusion of the paramesonephric ducts
Double uterus and double vagina
Or just double uterus
How does a bicornate uterus form
Failure of fusion of the upper part of the paramesonpehric ducts
How does a unicornate uterus form
When one paramesonephric duct does not develop
What does the gubernaculum become in females
Round ligament of the uterus
What is suspended within the broad ligament of the uterus
Ovaries
Describe the initial development of male gonads
Presence of a Y chromosome and its SRY leads to the development from the mesonephric ducts and the degeneration of the paramesonephric ducts
What does the paramesonephric ducts persist as in a male
Appendix testes
Prostatic article
What do the mesonephric ducts give rise to
Efferent ducts
Rete testes
Epididymis
Seminal vesicles
Vas deferens
What happens to the gubernaculum in males
The gubernaculum shrinks to draw the testes that arise in the lumbar region down the posterior abdominal wall to the inguinal canal, then through the inguinal canal during month 8 and 9, sot they are in the scrotum at birth
What is the processes vaginalis derived from
Parietal peritoneum - taken with the testes on their descent from the abdomen
What does the genital tubercle become in males and females respectively
Males - body and glans of penis
Females - body and glans of clitoris
What do the urogenital folds become in males and females respectively
Males - ventral aspect of penis and the penile raphe
Females - labia minora
What do the genital swellings become in males and females respectively
Males - scrotum and scrotal raphe
Females - Labia majora, Mons Pubis
Describe the development of the penis
During week 8 the urogenital folds duse with the genital tubercle, growing and creating a temporary urethral groove in between
The urogenital folds will move towards each other to form the penile urethra - zipping up the penis in essence
How does the scrotum form
Labioscrotal swellings on either side of the urogenital folds fuse to form the scrotum
How does hypospadias occur and what happens
Failure of the urethral folds to form or extend along penis and fuse throughout the full length causes penile hypospadias
The urethra opens onto the ventral surface rather than at the glans
What forms the trigone of the bladder
Mesonephric ducts
What forms the heart tube
Paired endothelial tubes form to make the primitive heart tube
What are the 5 regions of the primitive heart tube
Sinus venosus
Atrium
Ventricle
Bulbus cordis
Truncus arteriosus
What does the sinus venosus become incorporated into
The atrium
What does the bulbs cordis become incorporated in
The ventricle
What forms the interventricular septum
Endotrachial cushions (ventral and dorsal) grow out and meet in the midline and an interventricular septum develops from the apex and grows up towards the endocardial cushions
The endocardial cushions divide the common atrioventricular orifice into what
Right (tricuspid) orifice
Left (mitral) orifice
What does the septum premium fuse with
The endocardial cushions
What is the foramen secundum
A hole in the septum primum
What overlaps the foramen secundum
The septum secundum
What does the septum secundum act like
A valve across the foramen secundum - allowing blood to go from the right side to the left side fo teh fetes
How does the foramen oval close at birth
The increased blood flow through the lung sand rise in left atrial pressure causes the septum primum to be pushed across and close the foramen ovale
How does the fossa ovalis form
The septum primum is pushed over the foramen ovale due to increased left atrial pressure. The septum primum and septum secundum fuse, obliterating the foramen ovale and leaving the fossa ovalis
What does the sinus venosus join
Joins the atria, becoming the two vena cava on the right and the 4 pulmonary veins on the left
Describe the folding of the heart tube
The 2 ‘ends’ fold toward each other and to the right, pushing the apex of the loop to the left and rotating slightly so that the RHS of the heart tends to be more anterior
What does the trunks arterioles initially form
6 pairs of arches - these curve around the distal pharynx to join the dorsal aortae which fuse distally into the descending aorta
Which arches disappear completely
First, second and fifth arches
What does the third arch form
The carotid artery
What does the fourth arch form
The subclavian on the right and the aortic arch on the left
What does the sixth arch form
Right and left pulmonary arteries
Common connection to the dorsal aorta disappears on the right, continues as the ductus arteriosus on the left - connecting with the aortic arch
Where is the recurrently larygneal nerve on the right
Hooked around the subclavian artery
Where is the recurrent laryngeal nerve on the left
Hooked around the 6th arch (ligamentum arteriosum)
How does an ASD occur
Either - the septum secundum is too short to cover the foramen secundum in the septum primum and when the septum primum and septum secundum are pressed together there is a gap- ostium secundum defect
Or failure of the septum primum to fuse with the endocardial cushions - ostium primum defect
How many pharyngeal pouches are there
4
From which pharyngeal pouch is the Eustachian tube, middle ear, mastoid and antrum formed
First
What does the second pharyngeal pouch form
Tonsillar fossa (palatine tonsil)
What does the third pharyngeal pouch form
Thymus
Inferior parathyroid
Which pharyngeal arch forms the superior parathyroid
fourth
How many branchial arches are there
6
What is derived from the first branchial arch
CN V (Trigeminal)
Incus and Malleus (Meckel’s Cartilage)
Muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, tensor palati
Sphenomandibular ligament and anterior ligament of malleus
What is derived from the second branchial arch
CN VII (Facial)
Stapes, styloid process, upper body of hyoid and lesser cornu of hyoid
Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius, stylopharynges
Stylohyoid ligament
What is derived from the third branchial arches
CN IX (Glossopharyngeal)
Lower part of body of hyoid, greater cornu of hyoid, stylopharyngess
What nerves are formed from the fourth to sixth branchial arches
CN X
including recurrent laryngeal and superior laryngeal
What is derived from the fourth - sixth branchial arches
CN X
Thyroid cartilage, arytenoid cartilage, corniculate cartilage, cuneiform cartilage
Muscle of the pharynx, larynx and palate
How does a cleft lip occur
On one or both sides of the philtre there is a failure of fusion of the maxillary and frontonasal processes
Where does the thyroid develop from
Develops as a diverticulum from the floor of embryonic pharynx just caudal to the tuberculum impar (site of developing tongue), site of origin remains as foramen caecum of Tongue’
What is the initial development of the spine
The neural groove appears on the dorsal surface of the embryo
Describe the development of the spine after the development of the neural groove
The neural groove becomes closed off, forming the neural canal which becomes separated from the ectodermal covering of the body. Anterior to the nerual canal is the notochord
The vertebral bodies develop around which structure
Notochord
The vertebra ossify from 3 primary centres one on each side of the arch and one in teh middle for the body
