Embryo: GI, Urinary, Pituitary Flashcards
What are the cranial and caudal limits of the GI tract?
Cranial limit = oropharyngeal membrane
Caudal limit = cloacal membrane
Vitteline Duct
Temporary connection during lateral folding
Endoderm is incorporated as midgut through vitteline duct.
Omphaloenteric Duct
Another name for vitteline duct
How is endoderm incorporated into GI tract?
epithelial lining and glands of the GI tract
How is mesoderm incorporated into GI tract?
Splanchnic (visceral) mesoderm: smooth muscle and connective tissue of GI tract
During folding mesoderm forms peritoneal around gut tube
Intraperitoneal vs. Retroperitoneal
Intraperitoneal = organs that are completely enclosed in mesentery and connected to wall via mesentery
Retroperitoneal = organ that lies against posterior body wall and is covered with peritoneum on anterior surface only
Peritoneum definition
serous membrane lining abdominal cavity and organs (we have parietal peritoneum and visceral peritoneum)
Parietal Peritoneum (definition and what is it derived form?)
Lines body wall
Derived from somatic mesoderm
Visceral Peritoneum (definition and what is it derived form?)
Lines organs
Derived from splanchnic mesoderm
Mesentery: definition
Mesentery = double layer folds of peritoneum that suspend organs from body wall and hold them to either ventral or dorsal wall
(We have a dorsal mesentery and a ventral mesentery)
Dorsal Mesentery (definition and what is it derived form?)
Holds midgut to posterior body wall. Runs entire length of gut tube.
Derived from splanchnic mesoderm
Ventral Mesentery (definition and what is it derived form?)
Associated with foregut.
Mesoderm of septum transversum that is between the liver and the foregut and the liver of the ventral abdominal wall.
Derived from splanchnic mesoderm
What can mesentery contain?
reminder: mesentery is a double-layer of peritoneum that suspends an organ from the body wall
can contain connective tissue, fat, blood vessels, lymphatics, nerves
Both dorsal mesentery and ventral mesentery are derived from ____.
Splanchnic mesoderm
Think: Mesentery means they are in contact with organs. Therefore from splanchnic.
Dorsal Mesentery Divisions
- Dorsal Mesogastrium (or greater omentum)
- Mesoduodenum
- Mesentery Proper
- Dorsal Mesocolon
Dorsal Mesogastrium
aka Greater Omentum
Dorsal mesentery division of the STOMACH
Greater Omentum
aka Dorsal Mesogastrium
Dorsal mesentery division of the STOMACH
Mesoduodenum
Dorsal mesentery division of DUODENUM
Mesentery Proper
Dorsal mesentery division of JEJUNA and ILEAL LOOPS
aka holds small intestine to posterior wall
Dorsal Mesocolon
Dorsal mesentery division of the COLON
Ventral Mesentery (definition and what is it derived form?)
Derived from septum transversum
Exists only in region of terminal esophagus, stomach and upper part of duodenum (ie FOREGUT)
Septum Transversum gives rise to _______
Mesodermal tissue that gives rise to central tendon of diaphragm and connective tissue in the liver
The liver grows into mesenchyme of septum transversum and divides _____ into ____&____
The liver grows into mesenchyme of septum transversum and divides the ventral mesentery into
LESSER OMENTUM and FALCIFORM LIGAMENT
Lesser Omentum (what is it and how is it formed?)
Extends from lower portion of esophagus, stomach and upper portion of duodenum to liver
formed from liver growing into mesenchyme of septum transversum and dividing ventral mesentery (into lesser omentum and falciform ligament)
Falciform Ligament (what is it and how is it formed?)
Extends from liver to ventral body wall
formed from liver growing into mesenchyme of septum transversum and dividing ventral mesenchyme (into lesser omentum and falciform ligament)
Round ligament of the liver
aka Ligamentum teres hepatis
free inferior margin of falciform ligament
contains obliterated umbilical vein
Ligamentum Teres Hepatis
aka Round ligament of the liver
free inferior margin of falciform ligament
contains obliterated umbilical vein
Hepatoduodenual Ligament
Free margin of lesser omentum connecting duodenum and liver
Contains the portal triad (bile duct, portal vein, hepatic artery)
Portal triad (what is it and where is it found?)
BILE DUCT, PORTAL VEIN, HEPATIC ARTERY
Contained within hepatoduodenual ligament (free margin of lesser omentum)
How is the ectoderm incorporated into GI tract? Think derivation
Enteric system (brain of the gut)
Enteric system is derived from neural crest cells (ectoderm)
What is the enteric system? Where is it derived from?
Ectodermal contribution to GI tract (derived from neural crest cells)
“Brain of the gut” - functions without innervation from the brain, it functions on it’s own.
Component of foregut
Pharynx Esophagus Stomach Proximal 1/2 duodenum (includes major duodenal papillae - pancreatic and bile duct papillae)
Components of midgut
Distal 1/2 duodenum Jejunum Ileum Secum Ascending Colon Proximal 2/3 Transverse Colon
Components of hindgut
Distal 1/3 Transverse Colon Descending Colon Sigmoid Colon Rectum Anus
Arterial Supply to GI tract?
Each gut region supplied by a major artery off of ABDOMINAL AORTA
- Foregut = CELIAC TRUNK ARTERY
- Midgut = SUPERIOR MESENTERIC ARTERY
- Hindgut = INFERIOR MESENTERIC ARTERY
Foregut derivatives
Pharynx, lower respiratory system, esophagus, stomach, proximal 1/2 duodenum (including pancreatic and bile duct papillae)
Associated organs: liver, gallbladder, pancreas, spleen (although spleen not digestive organ)
Esophagus & outgrowth
Immediately caudal to pharynx
Endodermal outgrowth week 4 = tracheobronchial diverticulum (aka respiratory diverticulum aka lung bud)
Tracheobronchial Diverticulum
(or respiratory diverticulum or lung bud)
Endodermal outgrowth from esophagus on ventral side of foregut
Becomes trachae, respiratory tree and lungs
Greater curvature / lesser curvature of stomach
Week 4
Stomach appears as fusiform dilation of foregut
As stomach enlarges, dorsal side expands faster = greater curvature of stomach
ventral side expands slower = lesser curvature
Stomach rotation: where do lesser/greater curvatures end?
90deg CLOCKWISE around longitudinal axis (anteroposterior axis) - as if looking SUPERIOR
ventral side (lesser curvature) = RIGHT
dorsal side (greater curvature) = LEFT
What are cardia and pylorus? Where do they go during stomach rotation?
Cardia = cephalic part of stomach Pylorus = caudal part of stomach
Both initially lie in midline. After growth and stomach rotation (alone anteroposterior axis):
- Cardia (cephalic) = slightly downward and left
- Pylorus (caudal) = up and to the right
What happens to dorsal mesogastrium during stomach rotation?
Carried to the left
This enlarges a space posterior to stomach (omental bursa aka lesser sac of peritoneum)
What is the omental bursa?
As a result of mesogastrium movement during rotation, space posterior to stomach is enlarged.
Space is called omental bursa or lesser sac of peritoneum.
Continuous with greater sac of peritoneum
What is the lesser sac of peritoneum?
As a result of mesogastrium movement during rotation, space posterior to stomach is enlarged.
Space is called omental bursa or lesser sac of peritoneum.
Continuous with greater sac of peritoneum
Spleen Premidorium
Mesodermal proliferation within dorsal mesogastrium
dorsal mesogastrium lengthens, portions between spleen and dorsal midline swing left, fusing with peritoneum of posterior abd. wall
INTRAPERITONEAL
Lienorenal ligament and gastrorenal ligament
Lienorenal ligament = connects spleen to body wall in left kidney region
Gastrolienal ligament - connects spleen to stomach
Greater Omentum definition
single, 4-layer sheet hangs from greater curvature of stomach
Greater Omentum formation
As stomach rotates, dorsal mesogastrium extends inferiorly, forms sac (space) lined by double-layers on either side.
Sac extends over transverse colon and small intestinal loops
Two sides of double layer of sac fuse, creating 1, 4-layered sheet off of greater curv. of stomach
In rotation, where does duodenum end?
Right side.
Think. Greater curv of stomach ends LEFT, where is pylorus? Duodenum comes from there.
Duodenum rotates because of rotation AND head of pancreas growth
What leads to duodenal swinging away fro midline? Where does it go?
Stomach rotation and head of pancreas growth.
Duodenum swings RIGHT (from midline)
Are the duodenum/pancrease retroperitoneal or intraperitoneal?
Duodenum and head of pancreas = RETROPERITONEAL (against dorsal body wall)
duodenal cap (near pylorus) = intraperitoneal
small portion of head of pancreas = intraperitoneal
Liver Primodrium (when and where?)
Week 3
appears at distal end of foregut as outgrowth of endodermal epithelium
= LIVER BUD (HEPATIC DIVERTICULUM)
What does the liver primodrium do?
As the liver bud (hepatic diverticulum) proliferates, it penetrates septum transversum which splits the ventral mesentery into falciform ligament and lesser omentum
What does the Common Bile Duct connect?
Narrow connection between the liver and foregut (DUODENUM)
Cystic Duct (what and where?)
Ventral outgrowth of common bile duct
connection between common bile duct and gallbladder
Dorsal pancreatic bud and ventral pancreatic bud
- what do they originate from?
- where do they grow from?
both originate from endodermal lining of duodenum
dorsal bud = grows from within the dorsal mesentery
ventral bud = outgrowth of the common bile duct
How do ventral and dorsal pancreatic buds come together? How are they arranged? What do they form?
As duodenum rotates, ventral pancreatic duct swings clockwise with it (because originates as outgrowth of common bile duct) until meets dorsal bud.
Ventral bud is behind and below dorsal bud.
Together = PANCREATIC DUCT
What do ventral pancreatic duct and dorsal pancreatic duct form respectively?
ventral pancreatic duct = ucinate process of the head, inferior portion of the head of pancreas
dorsal pancreatic duct = rest of head of pancreas, neck, body and tail
What are the midgut derivatives?
distal 1/2 duodenum (after pancreatic/bile papillae)
jejunum, ileum, cecum, appendix, ascending colon and proximal 2/3 transverse colon
What shape is the midgut?
U-shape around the superior mesenteric artery
Primary Intestinal Loop (what is it? how is it formed?)
Formed by rapid elongation of gut and mesenteries
Two parts: CEPHALIC LIMB & CAUDAL LIMB
formed around the superior mesenteric artery
Cephalic limb becomes…
Cephalic limb is a part of the primary intestinal loop
Becomes
- Distal 1/2 duodenum
- Jejunum
- Proximal Ileum
Caudal limb becomes…
Caudal limb is part of the primary intestinal loop
Becomes
- distal ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon
What is between the two limbs of the primary intestinal loop?
The Vitteline Duct is between the caudal limb and the cephalic limb of the primary intestinal loop
Vitteline duct is a temporary connection bteween the gut tube and the yolk sac
First midgut rotation
Week 6
90deg counterclockwise rotation around superior mesenteric artery
causes physiological umbilical herniation (weeks 6-10 where intestinal loops enter extra-embryonic cavity)
Second midgut rotation
Week 10
180deg counterclockwise rotation around the superior mesenteric artery
brings midgut back into normal *definitive) position
After 2nd midgut rotation, what are the definitive positions of all of the components?
Ascending and Descending Colons = secondarily retroperitoneal (because started off intraperitoneal)
Appendix, lower end of cecum, sigmoid colon = intraperitoneal because maintain their free mesenteries
What are the midgut mesenteries?
Transverse mesocolon and Mesentery proper
-Renamed because now in definitive position after midgut rotation
Transverse Mesocolon
From hepatic flexure of ascending colon to splenic flexure of descending colon
Fuses with posterior wall of greater omentum (maintains mobility) = INTRA PERITONEAL
Mesentery Proper
Mesentery of jejunoileal loops
Line of attachment extends from where duodenum because intraperitoneal to ileocecal junction
Describe the process of re-canalization and when it occurs in the gut tube
Recanalization = remaking a canal. Originally a tube, became occluded, then became tube again.
Wk 6: proliferation of endodermal lining occludes gut tube
Wk 9: gut tube re-canalization is complete
Meckel’s Diverticulum (Ileal Diverticulum)
Remnanet of vitteline duct persists in finger-like outpouching of ileum (40-60cm from ileocecal jxn)
May contain: pancreatic tissue/gastric mucosa that secrete acid causing ulcers/bleeding
Most common GI malformation in ~2% population
Omphalomesenteric fistula
less common persistence of vitteline duct
GI tract open to outside world
Omphalomesenteric vyst
less common persistence of vitteline duct
tissue and cyst remain within what was the vitteline duct
Omphalomesenteric ligament
less common persistence of vitteline duct
fibrous band
holds midgut to the abdominal wall
Hindgut derivatives
Distal 1/3 transverse colon descending colon sigmoid colon rectum superior portion of anal canal
Urorectal septum (what is it and where does it grow?)
partitions the cloaca
grows inferiorly towards the cloacal membrane (separates into urogenital membrane and anorectal membrane)
partitions the cloaca into ventral urogenital sinus and dorsal anorectal sinus
When does cloacal membrane rupture?
week 7
Which portions of the anal canal are endoderm/ectoderm?
Endoderm = superior 2/3
Ectoderm = inferio 1/3
Proctodeum definition
anal pit
Pectinate line
junction of endodermal and ectodermal regions
How does epithelium change through anal canal?
Endoderm is columnar
Ectoderm is stratified squamous
When does the urinary system begin formation?
Weeks 4-5
Urinary system is developing at the same time as what other system?
reproductive system
Urinary and reproductive system are both derived from _____
intermediate mesoderm along posterior abdomen
Urogenital system is divided into two different systems ____ & ____. Are the two connected?
Urinary system and reproductive system
They are interconnected embryologically (both from intermediate mesoderm) and anatomically
Intermediate mesoderm swells to form _____
Urogenital ridge (bilaterally)
The urogenital ridge is a swelling of ___ that bulges out into the ____
swelling of intermediate mesoderm
bulges out into the intraembryonic coelomic cavity
The urogenital ridge differentiates into a medial ____ ridge and a lateral ____ ridge.
Medial ridge = genital ridge for reproductive system
Lateral ridge = nephrogenic cord/ridge for urinary system
What happens to the nephrogenic cord during folding?
Lateral body wall folds come together (WEEK 4), nephrogenic cord gets pushed being lateral plate mesoderm
making nephrogenic cord RETROPERITONEAL
3 kidney systems throughout development
Pronephros, mesonephros and metanephros
(in that order)
These develop sequentially cranial to caudal
When does pronephros begin? When does it end?
Begins at start of week 4, ends at end of week 4
What marks the beginning of pronephros?
7-10 solid cells groups in intermediate mesoderm of cervical region
Is the pronephros a functional system?
Not in humans
It has an inductive role - lays the foundation for mesonephric kidney development
When does mesonephros begin?
Early in week 4 (overlaps with pronephros degeneration)
Is mesonephros a functional system?
Functional through weeks 6- 10
Excretory units (nephrons) Collecting ducts (mesonephric ducts of wolffian ducts)
What region does this mesonephros appear in?
upper thoracic region to upper lumbar region (L3)
What first appears in mesonephric development?
Excretory tubules appear and rapidly lengthen to form S-shaped loop.
they acquire tuft of capillaries (glomerulus)
What surrounds the glomerulus?
Portion of the tubules called bowman’s capsule
How do mesonephric (wolffian) ducts first appear?
solid, longitudinal rods within intermediate mesoderm which grow caudally to fuse with cloaca
Do mesonephric ducts become incorporated into the bladder?
Yes.
They contribute to the posterior wall of the bladder
How do mesonephric ducts form from solid rods?
Rod cavitation (starts caudally and runs cranially) Forms a lumen which forms the mesonephric ducts
What happens when mesonephric ducts come in contact with the cloaca?
Induces an outpocketing called the ureteric bud
What is another name for ureteric bud?
Metanephric diverticulum
What is the uteric bud?
Outgrowth of mesonephric duct close to it’s entrance to the cloaca
When does metanephros begin? What marks their beginning?
Week 5
Marked by appearance of ureteric buds sprouting at each caudal end of metanephric ducts
There are two functional components of the metanephros: ___ & ____
Ureteric bud (collecting ducts of kidney)
Metanephric blastema (excretory unit of kidney)
What are the collecting portions of the kidney?
Collecting tubules, major and minor calyces, renal pelvic, ureter
What are the excretory portions of the kidney?
(Nephron)
Bowman’s capsule, proximal conv. tubule, loop of henle, distal conv. tubule
The ureteric bud forms the ____ portion of the kidney and the metanephric blastema forms the ____ portion of the kidney.
Ureteric bud forms collecting duct of kidney
Metanephric blastema forms the excretory duct of kidney
How are metanephric blastemas formed?
Ureteric bud grows into the intermediate mesoderm of sacral region - inducing mesoderm to form mesonephric blastemas.
They form a cap over the ureteric buds.
Ureteric buds form the _____ portion of the kidney which includes _____.
Collecting portion
Collecting tubules, major and minor calyces, renal pelvis, ureter
Metanephric blastema forms the ____ portion of the kidney which includes ____
Excretory portion
Bowman’s capsule, prox conv tubule, loop of henle, distal conv tubule
When does the definitive kidney become function?
Week 12
What are the definitive kidneys formed by?
metanephros
How is urine passed throughout the amnion?
Urine passed into amniotic cavity (mixes with amniotic fluid), urine swallowed by fetus and recycled through kidneys
What is the main function of the kidney in fetus?
fetal urine produces amniotic fluid
What in the fetus excretes waste?
Placenta
Nephron formation is reliant on _____ induction.
Reciprocal induction
What is reciprocal induction? Why is it important for nephron formation?
Inductive signaling from ureteric bud forms the nephrons
If ureteric bud is abnormal/missing - nephron won’t develop)
Where is the definitive kidney initially positioned?
pelvic region
How are the kidneys initially supplied?
When in pelvic region, arterial blood supply from a pelvic branch off of the aorta
How are the kidneys supplied during their ascend?
receive blood supply from arteries off of aorta at continuously higher levels - these vessels do not stretch, the caudal ones degenerate as new cranial ones develop
Where can complications occur during kidney’s ascent? What complications?
Kidneys have to pass through “arterial fork” of umbilical arteries - complications can occur here.
Pelvic kidney or horseshoe kidney
What is pelvic kidney? What feature are they near?
Kidney remains in the pelvis near the common iliac artery
What is horseshoe kidney? Where does this occur?
As 2 kidneys try to push passed umbilical arteries they are so close together that their inferior poles fuse and they are caught on the root of inferior mesenteric artery
This occurs at the lower lumbar levels
When does the bladder develop?
Weeks 4-7
The urorectal septum divides the cloaca into ___ and ____
Urogenital sinus (anteriorly) and the anal canal (posteriorly)
What divides the cloaca into two regions? What are the regions?
Urorectal septum divides cloaca into urogenital sinus (anterior) and anal canal (posterior)
What are the three parts of the urogenital sinus?
Vesicle part, pelvic part, phallic part
What part of the urogenital sinus develops the bladder?
The vesicle part (the largest part)
How are the mesonephric ducts and ureteric buds incorporated into the bladder?
at posterior wall of bladder
ureteric bud becomes ureters into bladder wall and mesonephric ducts are carried inferiorly to level of pelvic urethra (below the neck of urethra)
What is the trigone of bladder?
Triangular region of incorporated mesonephric duct on posterior bladder wall
What do the 3 parts of the urogenital sinus become in a female?
vesicle part = bladder
pelvic part = urethra
phallic part = contributes to the vestibule of the vagina
What do the 3 parts of the urogenital sinus become in a male?
vesicle part = bladder
pelvic part = prostatic urethra and membraneous urethra
phallic part = penile (spongy) urethrapi
Pituitary gland is also called _____
hypophysis
Pituitary gland is seen in the ____ section of the head
sagittal
Pituitary gland is craddled in the ______ or _____
craddled in the sella turcica or hypophyseal fossa
What is the location of the pituitary gland relative to the optic chiasm?
pituitary gland is inferior to optic chiasm
What is the location of the pituitary gland relative to the hypothalamus?
pituitary gland is inferior to hypothalamus
What is the location of the pituitary gland relative to the sphenoid sinus?
pituitary gland is posterior and superior to the sphenoid sinus
What is a placode?
a thickening of layering
The pituitary gland develops from what two sources?
oropharyngeal ectoderm and neuroectoderm
both begin by developing placodes
What is Rathke’s pouch?
an outpocketing of stomedeum
invagination of oropharyngeal ectoderm that persists in development and eventually closes
Invagination of neuroectoderm in pituitary development leads to what
a solid mass forming infundibulum and posterior lobe
Neuroectoderm in pituitary gland development is an extension of what?
the diencephalon
What weeks can you clearly see anterior/posterior pituitary gland distinguishing?
Weeks 6-10
Rathke’s pouch originates from _____ and eventually looses it’s connection with the ____
oropharyngeal ectoderm; oral cavity
Rathke’s pouch gives rise to what 3 structures?
- Adenohypophysis (aka pars distalis)
- Pars Tuberalis
- Pars intermedia
Adenohypophysis aka ____
Pars distalis
Pars tuberalis grows in which direction and along what structure?
Pars tuberalis grows as a dorsal extension of anterior lobe superiorly along the stalk
Which portion of the anterior lobe develops alongside a nerve plexus? Which nerve plexus?
Pars tuberalis grows alongside the hypothalamohypophyseal system (nerve plexus)
Where is the pars intermedia located?
posterior to anterior lobe - between anterior and posterior pituitary lobes
What is the function of the pars intermedia?
unknown in humans
has an association with melanocyte stimulating hormone (MSH) producing cells
Which portion of the anterior lobe has a connection with melanocyte stimulating hormone producing cells?
Pars intermedia
Which portion of the anterior lobe grows along the stalk?
Pars tuberalis
Which portion of the anterior lobe is found between the anterior and posterior lobes?
Pars intermedia
What two structures do the posterior lobe give rise to?
stalk and pars nervosa (aka neurohypophysis)
Pars nervosa aka _____
neurohypophysis
Where are cell bodies/axon terminals located in the posterior lobe?
cell bodies located in hypothalamus
axons project through stalk
axon terminals located in pars nervosa
Why do we learn about anterior pituitary development in an embryology lecture?
pituitary gland functions in regulating and developing the reproductive system
