Embryology Flashcards
Foregut definition
Oesophagus to proximal half 2nd part duodenum
Foregut arterial supply
Celiac trunk
Foregut innervation
T5-T9
Midgut definition
Distal half 2nd part duodenum to proximal 2/3 transverse colon
Midgut innervation
T10/T11
Foregut innervation
T12/L1
Ladd’s Bands
Feature of intestinal malrotation - fix the caecum in the right upper quadrant
Meckels Diverticulum
diverticula of the small intestine that is formed as a remnant of the omphalomesenteric duct AKA vitelline duct or yolk stalk. It is present in 2% of the population.
Müllerian Agenesis (Rokitansky-Küster-Hauser syndrome)
Failure of the Müllerian duct to develop results in absent uterus and variable degrees of upper vaginal hypoplasia
Implicated in 15% cases primary amenorrhoea
Karyotype 46XX
Normal FSH/LH/E2 profile
Prevalence 1 in 5000
CAIS AKA Testicular Feminisation Syndrome
Genotype 46XY
Normal FSH/LH
Low E2
Absent uterus
During formation of the mid, fore and hind guts the initial gut tube undegoes rotation. Which of the following is correct regarding rotation of the midgut during this process?
The midgut undergoes a 270 degree anticlockwise rotation on itself.
Pharyngeal Arch 1
Muscle = muscles of mastication
Nerve = trigeminal nerve (V2 + V3)
Artery = external carotid; maxillary
Skeletal = maxilla
Pharyngeal Arch 2
Muscle = muscles of facial expression
Skeletal = stapes
Nerve = facial nerve
Artery = stapedial
Pharyngeal Arch 3
Muscle = stylopharyngeus
Skeletal = inferior parathyroids; hyoid
Artery = common carotid; external carotid
Nerve = glossopharyngeal nerve
Pharyngeal Arch 4
Muscle = cricothyroid
Skeletal = thyroid cartilage
Nerve = vagus; superior laryngeal
Artery = subclavian
Pharyngeal Arch 6
Muscle = intrinsic muscles of larynx except cricothyroid
Skeletal = cricoid cartilage
Nerve = vagus; recurrent laryngeal
Artery = pulmonary artery; ductus arteriosus
Which structure is the primary mechanism for shunting blood away from the fetal pulmonary circulation?
Foramen Vale
Fetal-maternal blood circulation
Blood enters RA and then passes through foramen ovale directly into LA and into aorta. Some blood goes from RA into RV and into pulmonary artery, but this passes through DA straight into aorta to bypass pulmonary circulation.
From what germ layer does GI tract initially develop?
Endoderm
GI Tract Germ Layers
Endoderm = mucosal epithelium & glands & submucosal glands
Mesoderm = lamina propria, muscularis externa, adventitia/serosa and submucosal connective
tissue/blood vessels
Neural crest ectoderm = neurons and nerves of submucosal and myenteric plexus
Endoderm
Stomach
Intestines/colon (mucosal layers)
Liver
Pancreas
Bladder
Lungs
Mesoderm
Muscle (smooth and striated)
Bone
Cartilage
Genitourinary system
Lymphatic system
Intermediate mesoderm
Kidneys
Gonads
Paraxial Mesoderm
Cartilage
Skeletal muscle
Dermis
Lateral plate mesoderm
Circulatory system (heart)
Spleen
Gut wall
Ectoderm
Epidermis
Hair
Lens
Cornea
Tooth enamel
Neural Crest Ectoderm
Dentin of teeth
Peripheral nervous system
Adrenal medulla
Neural Tube Ectoderm
Brain
Spinal cord
Pituitaries
Retina
Ductus Arteriosus Closure
Increase in arterial PO2
Decrease in blood pressure within the ductus lumen due to the postnatal decrease in pulmonary vascular resistance.
Decrease in PGE2 due to the loss of placental PGE2 production
Decrease in the number of PGE2 receptors in the ductus wall
Increased bradykinin
- Closes 1-2 days after birth
Closure of a patent ductus arteriosus in a term infant should be via?
- Surgical closure (prostaglandin infusion to keep patent until surgery)
Closure of a patent ductus arteriosus in a pre term infant should be via?
-NSAIDs (typically indomethacin)
How many days after fertilisation does implantation typically occur?
7-9 days
Which of the following structures develops into the definitive adult kidney?
Metanephros (The pronephros and mesonephros mostly regress)
Somites are derived from which germ layer?
Paraxial Mesoderm
Form: dermis, bone (ribs), skeletal muscle, cartilage.
Oocytogenesis
completes either at Birth or shortly before (3rd Trimester)
Ootidogenesis
comprises both meiotic divisions. The 1st Meiotic division halts until puberty. The 2nd meiotic stage only completes at fertilisation
Oogenesis
is the process of Ovum formation from Oogonia. It is the female form of gametogensis.
Female gametogensis
(1) oogonia –> growth/maturation –> primary oocyte + 1st polar body –> meiosis 1 –> secondary oocyte + 2nd polar body –> meiosis 2 –> ootid –> differentiation –> ovum
Male gametogensis
(1) spermatogonia –> growth/maturation –> primary spermatocyte –> meiosis 1 –> two secondary spermatocytes –> meiosis 2 -> four spermatids –> differentiation –> four spermatozoa
Placental blood flow
- Oxygenated blood returns to the fetus via single umbilical vein.
- Ductus venosus shunts oxygenated blood from the placenta to the heart.
- This oxygenated blood enters RA and is shunted straight to LA via Forman ovale.
- Some blood goes from RA to RV, and is shunted to aorta by ductus arteriosus.
- Ductus arteriosus connects pulmonary aorta and aorta.
- Deoxygenated fetal blood arrives at the placenta via two umbilical arteries.
- No direct mixing of fetal and maternal blood at placenta.
- At term, placenta received around 90% of uterine blood flow.
- ## At the umbilical vein, the pressure is 20 mmHg.
Classification of cells during oogenesis
Oogonium = diploid; 2 DNA pairs; 46 chromatids
Primary oocyte = diploid; 4 DNA pairs; 2 x 46 chromatids
secondary oocyte = haploid; 2 DNA pairs; 46 chromatids
ootid = haploid; 1 DNA pair; 23 chromatids
ovum = haploid; 1 DNA pair; 23 chromatids
At what age does meconium first appear in the fetal terminal ilium?
10-16 weeks
Approximately how many oocytes are present in the ovaries at birth?
20 week fetus = 6-7 millions
Birth = 1-2 million
Puberty = 400,000
Only around 400 follicles will go onto release ova at ovulation during a women reproductive life. >99% of follicles will breakdown in a process called atresia. <1% will undergo ovulation as ova.
Which type of sperm cell fuses with an oocyte during fertilisation?
Spermatozoa
From what does the blastocyst hatch?
Zona pellucida
The placenta develops from which structure?
Trophoblast (outer layer of blastocyst)
Layers of blastocyst: trophoblast - blastocyst cavity (blastocele) - inner cell mass
How many days after fertilisation does the blastocyst hatch from the zone pellucida?
6 days (5-7)
How many days after fertilisation does the morula form?
4 (morula proceeds the blastocyst)
What hormones are secreted by corpus luteum?
Progesterone (high levels)
Estradiol (moderate levels)
Inhibin A (moderate levels)
In the menstrual cycle if fertilisation doesn’t occur the corpus luteum stops secreting progesterone and degenerates into a corpus albicans.
If fertilisation occurs hCG signals the corpus to continue progesterone production and it is then termed the corpus luteum graviditatis
What is the embryological origin of Gartner’s duct?
Mesonephric duct
- The mesonephric duct forms the ureter and collecting system and in the female can form the epoophoron, appendix vesiculosa and Gartner’s duct.
The intraembryonic coelom forms within which structure?
Lateral plate mesoderm
What is the best indicator of gestational age on a dating scan in the first trimester?
Crown rump length
Biparietal diameter is appropriate after 14 weeks.
A 40-year-old woman is noted to have an elevation of alphafetoprotein. Which is the most likely pathology diagnosed by ultrasound scan?
Spina bifida
Alphafetoprotein is a glycoprotein synthesised by three fetal structures: the gut, liver and yolk sac. It is may be elevated in a defect of the anterior abdominal wall and the neural tube.
A teenage girl has a cyst in the canal of Nuck.
In which part of her anatomy will this be found?
Inguinal canal
The canal of Nuck is the female equivalent to a patent processus vaginalis in the male and presents as a swelling which can extend into the labia majora
In the development of the oocyte, when does the second meiotic division complete?
The answer is at entry of the spermatozoa. The primary oocyte resumes meiotic maturation in response to a surge in luteinising hormone. This results in a polar body and the secondary oocyte.
Implantation of the embryo occurs at which stage?
Blastocyst
Within 24 hours of fertilisation, the zygote undergoes cleavage. It then further subdivides into blastomeres. By the third day, the embryo contains 12 cells. By the fourth day, it is comprised of 16–32 cells and is called a morula. On day 5, the blastocyst hatches from the zona pellucida and implants into the endometrium.
The yolk sac rapidly degenerates before birth.
Occasionally it may persist to develop into which condition?
Meckel’s diverticulum
The inferior one-third of the anal canal originates from which structure?
Ectoderm of the proctodeum
The superior part of the anal canal originates from which structure?
The endoderm of the hind gut develops into the superior part of the anal canal.
At what gestational age do fetal breathing movements commence?
12 weeks
Meconium is found in the fetal gut from what gestational age?
14 weeks
How many turns does the midgut go through in its embryological formation?
Three 90 degree turns
What proportion of primordial follicles undergo atresia to create a primary follicle?
99%
What is the genetic origin in most cases (90%) of a complete molar pregnancy?
diploid as a result of an empty ovum being fertilised by one sperm which replicates
The majority of complete moles are homozygous and arise from an anuclear empty ovum that has been fertilised by a haploid 23X sperm (monospermy), which then replicates its own chromosomes resulting in a 46XX karyotype.
When in embryological development should the neural tube be closing?
4-5 weeks (days 22-28)
The primitive streak is a structure that forms in the blastula during the early stages of embryonic development.
By which day of embryonic development does the primitive streak usually appear?
Day 15
In the fetus, oxygenated blood from the placenta returns directly to the inferior vena cava, bypassing the liver.
Which structure carries the oxygenated blood?
Ductus venosus
The fetal umbilical vein joins the leftt branch of the portal vein in the porta hepatis and is conveyed directly to the inferior vena cava by the ductus venosus.
What does the ductus venosus become after birth?
After birth, the ductus venosus clots and becomes the ligamentum venosum. The clotted umbilical vein becomes the lingamentum teres.
What does the umbilical vein become after birth?
The clotted umbilical vein becomes the lingamentum teres.
Which structure constitutes the fetal component of the placenta?
Villous chorion
At about 8 weeks’ gestation the chorionic villi associated with the decidua basalis become the villous chorion, which is the fetal part of the placenta.
Which structure constitutes the maternal component of the placenta?
The decidua basalis is the part of the decidua deep to the conceptus that forms the maternal component of the placenta.
A post-mortem examination on a baby stillborn at 24 weeks reveals “incomplete closure of the lateral folds leaving a defect through which abdominal viscera protrude”
What is the diagnosis
Gastroschisis
Nägele’s rule refers to the length of a normal human pregnancy. What is the definition?
The calculation of the due date is the first day of the LMP + 9 months + 7 days (The expected date of delivery of a fetus is 266 days, or 38 weeks, after fertilisation.)
- Nagale’s rule involves counting back 3 months from the first day of the LMP, and adding 1 year and 7 days.
Between 6 and 8 weeks’ gestation, there is a physiological hernia within the umbilical cord containing a loop of gut.
Which is the main artery supplying the herniated gut?
Superior mesenteric artery
In 1–2% of newborn babies, only one umbilical artery is found in the cord.
With which condition is this abnormality associated?
Cardiac abnormalities
Sharing of the placenta and fetal membranes depends on the stage at which a single zygote divides.
If a zygote divides between day 4-8 before the formation of the bilaminar disc, what type of twins are formed?
Monochorionic diamniotic
How do different twins develop?
DCDA twins occur if splitting is by day 3.
MCDA twins are formed when separation occurs at day 4-8.
MCMA twins occur if splitting is between day 9-12 and conjoined twins occur after day 12.
What is eventration of the diaphragm?
Failure of the muscular tissue from the body wall to extend into the pleuroperitoneal membrane
What is omphalocele?
Persistence of herniation of abdominal contents into the proximal part of the umbilical cord, covered by cord epithelium
What is an umbilical hernia?
The umbilicus has not closed so intestines herniate through the skin-covered defect
With regard to MRI scanning what is the SI unit measure of magnetic flux?
Weber
Ideal GBS management:
- 3g Benzylpenicillin should be administered as soon as possible after the onset of labour and 1.5g 4 hourly until delivery.
- If penicillin allergic the alternative depends on severity of reaction. Provided a woman has not had severe allergy to penicillin, a cephalosporin should be used Cefuroxime.
If there is any evidence of severe allergy to penicillin, vancomycin should be used.
Staphylococcus + Streptococcus are which kinds of bacteria?
Gram positive Cocci
Rubella blood results interpretation:
IgM rise is typically seen with acute infection. IgG is produced in response to infection but is produced later than IgM. IgG is also produced in response to vaccination.
If IgG and IgM are negative the patient is susceptible to Rubella infection.
If IgG +ve and IgM -ve the patient should be considered immune.
If IgM +ve this suggests acute infection or false positive IgM (not uncommon)
Abdominal pressures during laparoscopy:
Intra-abdominal pressure 20-25 mmHg for gas insufflation prior to primary trocar.
Distension pressure 12-15 mmHg once trocar insertion complete
RCOG guidelines for anaemia in pregnancy:
- Cell salvage is recommended for women in whom an intraoperative blood loss of more than 1500 ml is anticipated
- If haemoglobin < 10.5 g/dl in the antenatal period, consider haematinic deficiency once haemoglobinopathies have been excluded. Oral iron is 1st line treatment for iron deficiency.
What is the approximate risk of HIV transmission during a single episode of receptive vaginal unprotected sexual intercourse with a known HIV positive person?
0.1%
Which gene most likely to be mutated in congenital adrenal hyperplasia?
CYP21A
90% of CAH cases are due to 21 Hydroxylase deficiency caused by a defective CYP21A gene.
