Practical 2: CNS, Limb, GI, renal and GU Flashcards
When does neuralation begin?
beginning of 3rd week (same time as gastrulation)
What are the primary brain vesicles and what do they give rise to?
Prosencephalon:
- Telencephalon –> cerebral hemispheres
- Diencephalon –> thalamus, hypothalamus, epithalamus
mesencephalon –> midbrain
rhombencephalon:
- Metencephalon –> Pons + cerebellum
- myelencephalon –> Medulla oblongata
When do the anterior (cranial) and posterior (caudal) neuropores close?
Anterior: day 25
posterior: day 28
What are the primary brain vesicles?
They are 3 dilatations of the neural tube’s cranial end
in which week do the cerebral hemispheres begin to develop?
5th week
What are NCCs and why are they important? What structures do they give rise to?
Arise from the neuroectoderm
Migrate to different areas + form: OUTFLOW TRACTS, adrenal medulla, sympathetic NS, Schwann cells, pharyngeal arches (cranial nerves and FACIAL SKELETON…), smooth muscle, osteoblasts/clasts…etc
What is exencephaly? what is its incidence? What is its prognosis?
Failure of closure of the anterior neuropore –> brain outside skull
1/5000 births
Poor prognosis
What is the detection rate of anencephaly on the fetal anomaly scan?
90%
What may have caused hydrocephalus?
Chiarii II malformation spina bifida (myelomenignocele) --> tethering of the spinal cord pulling the brain down and herniate
What is a meningocele?
The meninges protrude out the spinal canal and is filled w/ CSF
What is a myelomeningocele?
Where the meninges an spinal nerves/neural tissue protrude through the defect
What is the detection rate of myelomeningocele on fetal anomaly screening?
90%
what factors increase the risk of NTDs?
Maternal DM, folate deficiency, previous NTD, ^ age, teratogens (anti-epileptics), obesity, PYREXIA
What is the problem w/ folic acid suppliments?
to be most effective need to be given from 1mth before pregnancy –> 50% of pregnancies are unplanned
what % of NTDs are prevented by folic acid supplimentation?
50-70%
What marker is raised in NTDs and can be detected prenatally in maternal serum/amniotic fluid?
AFP
What is cranioschisis?
failure of skull vault to form –> causes anaencephaly
When do limb buds appear?
end of week 4
What are the limb buds made from?
mesenchyme core and outer ectoderm
What does the mesenchyme core of the limb buds form?
Connective tissue + bones
What is the apical ectodermal ridge?
The ectoderm at the tip of the limb bud that thickens
What is the importance of the apical ectodermal ridge of the limb bud?
induces underlying mesenchyme to proliferate but remain undifferntiated (= progress zone)
What happens to the cells that become increasingly distal to the apical ectodermal ridge?
Begin to differentiate
What group of factors play a crucial role in maintaining proximal-distal outgrowth of the limbs?
What expresses them?
FGF (e.g. FGF 4+8)
Apical ectodermal ridge
What occurs at week 6 of limb development?
Hand/foot plates appear
How do the digits of the handplates and footplates form?
Apoptosis of mesenchyme
what group of genes are essential for cranio-caudal patterning of the limb? what kinds of abnormalities result if cranio-caudal patterning is disrupted?
HOX genes (SHH + ZPA)
polydactyly and cleft hand/foot
What protein group is involved in normal dorsal-ventral patterning of the limb?
WNT proteins (e.g. WNT 7)
give an example of a condition where dorsal-ventral patterning of the limb is disturbed?
back to front limbs
What is the incidence of limb defects? Are upper or lower limbs more affected?
6/10,000 live births
upper>lower
What is amelia?
Absence of a limb
What is phocomelia? What is it associated with?
A form of meromelia where hands/feet attached to trunk
Thalidomide
what is ectrodactyly?
middle finger lost
What is syndactyly?
failure of apoptosis of mesenchyme (fusion of one or more digits)
How does Cleft hand/foot appear?
Problem with the apical ectodermal ridge
what environmental factors cause limb defects?
thalidomide, warfarin, valproic acid…
what intrauterine factors may affect limb development?
oligohydramnios, multiple pregnancy
What is chondrodystrophy? Whta is the pattern of inheritance
skeletal dysplasia due to abnormal cartilage development
A.R.
What is the pattern of inheritance in achondroplasia?
A.D.
What embryological structure does the primitive gut tube arise?
endoderm
How is the gut tube formed?
Folding of the embryo results in a portion of the endoderm lines yolk sac to form the primitive gut tube
Foregut, midgut and hingut
the midgut is continuous with the yolk sac
The foregut extends from the oropharyngeal membrane –> liver outgrowth
midgut: liver outgrowth –> 2/3 R transverse colon
hindgut: trasnverse colon –> cloacal membrane
Which genes are important in specifying the stomach? duodenum? hindgut?
Oesophagus/stomach: SOX-2
Duodenum: PDX 1
Hindgut: CDXA + CDXC
What are the 3 branches to the gut of the Ao?
coeliac trunk
superior mesenteric artery
inferior mesenteric artery
What is the difference between the dorsal and ventral mesentary?
dorsal mesentary extends from the lower oeseophagus –> cloacal hindgut
ventral mesentary: lower oesophagus –> upper duodenum
What happens if the cloacal membrane fails to perforate?
there will be no connection between the lower and upper anus
When does oesophageal atresia occur?
4th week of development (when respiratory bud forms on gut tube)
What is the incidence of oesophageal atresia?
1/2500-4000 births
How would a baby present w/ oesophageal atresia?
vomiting, coughing when feeding, cyanosis…etc
What are the complications of oesophageal atresia / tracheo-oesophageal fistula?
aspiration pneumonia
RFs for oesophageal atresia?
smoking, alcohol
how does the stomach come to lie in a lift sided position?
stomach rotates both:
1) longitudinal axis (90 degrees)
2) anteroposterior axis (due to differences in growth rates of the curvatures)
How does pyloric stenosis present?
projectile non-bilious vomiting
is pyloric stenosis more common in males or females?
males
What is physiological herniation of the midgut? Why does it occur?
in week 6 there is RAPID growth of liver + elongation of the intestinal loop –> abdo cavity TOO SMALL to contain the loops and so they herniate into the extraembryolic cavity
When do the midgut loops return to the abdomen?
week 10
What is the difference between omphalocele and gastroschisis?
Omphalocele –> intestines, liver + other organs outside the abdomen covered in amnion. Usually associated w/ other chromosomal abnormalities
gastroschisis –> not covered in amnion. Usually occurs in isolation. bigger risk of volvulus (as no amnion)
How does omphalocele occur?
Failure of the bowel to retract back into the abdo cavity (week 10)
How does gastroschisis occur?
abnormal closure of the body wall around the connecting stalk
What is the incidence of omphalocele?
2.5/10,000 births
What is the prognosis of omphalocele?
25% mortality rate
WHat is the incidence of gastroschisis?
2-3/10,000
What is interesting about the aetiology of gastroschisis?
incidence rates are increasing –> especially in women <20 (risk factor???)
If there are chromosomal/congenital abnormalities present is the child likely to have omphalocele or gastroschisis?
omphalocele
What is Hirschprung’s disease? How would the infant present?
aganglionic megacolon (most cases rectum)
absence of the prarasympathetic ganglia of the colon
abdo distension due to constipation
What does the urinary system develop from?
The rudimentary mesoderm
What are the 3 parts of the renal development? Which doesn’t function?
prosenephros (not functional / rudimentary), mesonephros and metenephros
When does the prosenephros disappear?
4th week
When does the mesonephros start to appear/develop?
4th week
What forms the definitive kidney? When does it start to develop?
metenephros
5th week
which structure does the ureteric bud give rise to?
Ureter, renal pelvis, major/minor calyces, collecting tubules
Are lobulated kidneys normal in a fetus?
Yes and may persist in adulthood
What is congenital polycystic kidneys associated with?
Problems w/ cilia (bardet biedal syndrome and meckel gruber syndrome)
How common is horseshoe kidney?
1/600 people
What are the complications of horseshow kidney?
Renal calculus / hydronephrosis
How do accessory ureters arise?
Early splitting of the ureteric bud
Why are accessory renal arteries common?
persistence of embryonic vessels that formed in the ascent of kidneys
What is crucial for sex determination of the fetus? what region is on it?
Y chromosome
SRY gene (sex determining region)
What protein does the SRY gene transcribe?
testis determining factor
When do the gonads begin to develop? What do they appear as?
week 7
gonadal ridges (epithelium w/ underlying mesenchyme)
When do PGCs migrate into the primitive gonad? when do they invade?
Week 5
week 6
What do the genital ridges do after the arrival of the PGCs?
proliferate + form primitive sex cords = indifferent gonads
What happens if PGCs fail to reach the genital ridges?
Gonads fail to develop
teratoma?
What is the other name for the mesenephric and paramesenephric duct?
Wolffian
müllerian duct
In males what factors promote development of the mesonephric/wolffian duct and inhibits development of the paramesonephric duct?
SRY gene –> SOX9 which inhibits WTN4 (leydig cells produced)
Leydig cells produce testosterone by week 8 (stimulate proliferation of mesonephric duct
sertoli cells produce mullerian inhibiting substance (anti-mullerian hormone) –> causes mullerian duct to degenerate
In males, what do the mesenphric ducts give rise to?
epidydmis + vas deferens
What hormone + receptor is important in meseneprhic duct formation?
testosterone
What is hypospidiasis?
fusion of the urethral folds is incomplete –> abnormal opemings of the urethra along the inferior aspect of the penis
what is the incidence of hypospidiasis?
3-5/1000 births
Why is the epidemiology of hypospidiasis interesting?
incidence doubled past 15yrs as environmental oestrogens have increased
what is epispodiasis? Whta is its incidence?
urethral meatus found on dorsum of penis
1/30,000 births
What malformations are associated w/ epispodiasis?
exstrophy of the bladder and abnormal closure of the ventral abdo wall
What is congenital indirect inguinal hernia?
Connection between abdo cavity and processus vaginalis in the scrotal sac (doesn’t close after 1st yr birth –> hernia)
incomplete closure: hydrocele
In females, what factors promote development of the paramesonephric/mullerian ducts?
absence of SRY gene (no testosterone or anti-mullerian hormone)
WTN4 expressed (ovary determining) –> inhibits SOX-9 + upregulates DAX 1
what do the mullerian/paramesonephric ducts become?
uterine tubes, uterus, cervix, upper vagina
How might a didelphus (double uterus) and other uterine congenital abnormalities form?
abnormal / incomplete fusion of the paramesonephric ducts
What is cranioschisis?
Skull vault doesn’t form –> causes anancephaly due to necrosis of the caudal neural tissue
What is rachischisis?
Failure of posterior neuropore to close (necrosis of spinal cord tissue)
different to spina bifida where there is failure of vertebral arch formation or incomplete –> defect in posterior part of vertebral column at a certain level (usually lower lumbar region)
What maintains proximal-distal outgrowth of the limbs?
progress zone (of the mesenchyme under the AER)
What does the AER express to specify the underlying mesenchyme to become the progress zone?
FGF 4 + 8
Causes of NTD?
Obesity, low folate, Maternal DM, valproate (anti-epileptics), pyrexia, syndrome (T18)…ETC
What do the mesonephric duct give rise to?
Seminal vesicle, epididymus, vas deferens, ejaculatory duct
What does the paramesonephric duct give rise to?
fallopian tubes, uterus, cervix, upper vagina
What proteins are high level in male + female gonadal development?
Male: SOX-9
Female: WNT 4
what cells produce testosterone in males?
Leydig cells
When does sexual differentiation occur?
week 6-7 (before this - indifferent gonads containing both paramesonephric + mesonephric ducts)
In females what causes the wolffian duct to degenerate?
What causes mullerian ducts to persist?
No Y chromosome –> therefore no SRY gene –> so no production of testes/leydig cells –> no production of testosterone
Testosterone is needed for development of wolffian duct
No anti-mullarian hormone produced (as no testis) –> therefore mullarian/paramesonephric duct persists
What causes the development of the male external genetalia?
DHT: dihydro testosterone
What cells produce anti-mullerian hormone in males?
Sertoli cells
What is the role of testosterone in male sex differentiation?
proliferation of wolffian/mesonephric duct
