Embryology Flashcards
Urogenital ridge (that developed from intermediate mesoderm) differentiated into:
1) genital ridge > testes and ovaries
2) paramesonephric(mullarian) duct & mesonephric Wolffian duct.
3) nephrogenic cords> kidneys
Urogenital sinus gives rise to
Divides into 3 parts
Upper: Bladder except trigon
Pelvic: (in female: Urethra, Bartholin gland, paraurethral (skene’s) glands
In male: membraneous and prostatic urethra, bulbourethral (Cowper’s) gland, prostate
Phallic: vestibule in female and lower part of penile urethra in male
Distal 2/3 vagina
paramesonephric(mullarian) duct gives rise to
Uterus
Fallopian tubes
Upper 1/3 of vagina
mesonephric Wolffian duct gives rise to
Ureters and trigon of bladder in both fe/males In male: Vas deferens Seminal vesicles Epididymis Ejaculatory duct
paramesonephric(mullarian) ducts which fuse in female at 10 wks, error in fusion can result in:
1) bicornuate uterus
2) unicornuate uterus
3) uterine didelphys (double uterus)
paramesonephric(mullerian) ducts after fusion the septal resorption occurs at 20 wks, error in septal resorption can result in:
1) septate uterus (complete or partial)
2) arcuate uterus
Error in organogenesis of paramesonephric(mullarian) ducts seen in:
1) mullaerian agenesis (MRKH)
Mayer rokitansky kuster hauser syndrome
Is there any associated anomalies with mullarian defects ?
15-20% mullarian Duct anomalies associated with renal anomalies.
And 14-50 % associated with spinal anomalies.
Remember that No breast abnormality cause the ovary usually fully developed so estrogen and Breast development wouldn’t be affected
The primordial germ cells are large eosinophilic cells derived from
endoderm in the wall of the yolk sac
The primary oocytes, reaching a peak, when? What is the peak?
number of 600,000 (95% prediction interval: 70,000- 5,000,000) at 18 to 22 weeks of gestation.
Oogenesis: primordial germ cells by mitosis(meiotic process actually begins at 10 to 12 weeks’ gestation)diploid oogonia(46 ch) by mitosis > primary oocytes (haploid 23ch) undergoing meiosis1 in prophase 1 (arrested till ovulation)
Meiosis is preceded by interphase I during which DNA replication occurs, thus transforming the diploid oogonia with a DNA content of 2N to an oocyte with a DNA content of 4N.
Meiosis is defined in two stages.
The first, known as the reduction division (meiosis I) initiates in the fetal ovary but is then arrested and completed at the time of ovulation.
Embryologically, ovary develops from three major cellular sources.
First, primordial germ cells, which arise from the endoderm of the yolk sac, deferentiate into the primary oogonia. Coelomic epithelial cells develop into granulosa cells, which surround the oocytes. Third, mesenchymal cells from the gonadal ridge become the ovarian stroma.
Primordial germ cells can be seen in the yolk sac as early as the third week of gestation. These cells begin their migration into the gonadal ridge during the sixth week of gestation and generate primary sex cords. The ovary and testes are indistinguishable by histologic criteria until approximately 10 to 11 weeks of fetal life. After the primordial cells reach the gonad, they continue to multiply through successive mitotic divisions. Starting at 12 weeks’ gestation, a subset of oogonia will enter meiosis to become primary oocytes. Primary oocytes are surrounded by a single layer of flattened granulosa cells, creating a primordial follicle.
The maximal number of oogonia is achieved at the
20th week of gestation, at which time 6 to 7 million oogonia are present in the ovary.
Approximately 1 to 2 million oogonia are present at birth.
Fewer than 400,000 are present at the initiation of puberty, of which fewer than 500 are destined to ovulate.
What is the clinical significance of primitive pit ?
It’s connection btw amnionic and yolk sac ( Gut later) by neuroenteric canal can progress to neuroenteric cyst as congenital anomaly
Summary of the events in 1st week of embryology
- fertilization: typically after 12-24 hrs after ovulation in ampulla to form the zygote continue mitosis to form morula and blastocyst.
- implantation: occurs in 5-7 days after fertilization occurs during blastocyst where the inner layer of cytotrophoblast (dividing) and outer layer of syncytiotrophoblast (invading).
Summary of the events of Second week of embryo development
- Bilaminar layer: epiblast- hypoblast and precordal plate
- amnion begins to form
- yolk sac begins to form: 1ry and 2ry
- implantation continues
Summary of events in 3rd week of embryonic development
- formation of primitive streak
- Gastrulation : formarion of three embryonic tissue layers
- formation of the notochord
- initial development of the neural tube
- intial formation of the heart
- formation of the chorionic villi
Summary of events in 4th week of embryonic development
- body folding occurs : cranio-caudal fold, lateral folding.
- ## formation of body cavities for organ developement.
OEIS complex refers to
combination of defects consisting of omphalocele, extrophy of the cloaca, imperforate anus, and spinal defects.
Possible embryologic mechanisms proposed for these findings of OEIS (omphalocele-exstrophy-imperforate anus-spinal defects) complex have included:
a single defect of early blastogenesis or a defect of mesodermal migration during the primitive streak period.
sex of embryo can be distinguished based on external genitaliaat which week
12 wks
Mesonephric (wolffian) duct develop to what? What is the rigger ?
needs to be induced to develop by testosterone from the Leydig cells of testes
forms male internal sexual organs (SEED): Seminal vesicles, Epididymis, Ejaculatory duct above penile urethra, vas deferens
Genital tubercle is a common Precursor of in female and male ?
Female: Estrogen Results in Development of Glans clitoris, Vestibular bulbs.
Male: Dihydrotestosterone Results in Development of Glans penis, Corpus cavernosum and spongiosum.
Where Fertilization happen? When ?
It occurs in the ampula of the fallopian tube approximately 12 hours after ovulation.
Following fertilization the —— meiotic division of the ovum is completed, leading to the production of
Following fertilization the second meiotic division of the ovum is completed, leading to the production of a haploid ovum and the second polar body.
Gastrulation is the phase in early embryonic development when the three germ layers , which week it happen ?
It occurs in the third week of intra-uterine life
The mesoderm is composed of which are…
the paraxial, intermediate, and lateral plate mesoderms
The paraxial mesoderms give rise to
the somites — rounded elevations of paraxial mesoderm that appear on either side of the neural tube under the surface ectoderm on the dorsal aspect of the embryo from the base of the skull to the tail region. The first pair appears on day 20 of intra-uterine life and they develop at a rate of three pairs per day to a maximum number of 42–44 pairs.
The neural plate may be seen by day – of intra- uterine life while the neural tube is seen by day – of intrauterine life.
The neural plate may be seen by day 18 of intra- uterine life while the neural tube is seen by day 22 of intrauterine life.
The cranial neuropore closes at day – while the caudal neuropore closes by day - of intra-uterine life. Failure of these closures leads to —- & —’
The cranial neuropore closes at day 24 while the caudal neuropore closes by day 26 of intra-uterine life. Failure of these closures leads to anencephaly and spina bifi da respectively.
The morula period begins at the — to —cell stage and ends when the blastocyst forms, which occurs when there are – to – blastomeres present.
The morula period begins at the 12- to 16-cell stage and ends when the blastocyst forms, which occurs when there are 50 to 60 blastomeres present.
As early as – to – days after fertilization, the 58-cell blastula differentiates into five embryo-producing cells—the inner cell mass. The remaining 53 outer cells, called the trophectoderm, are destined to form trophoblasts
As early as 4 to 5 days after fertilization, the 58-cell blastula differentiates into five embryo-producing cells—the inner cell mass (see Fig. 5-7). The remaining 53 outer cells, called the trophectoderm, are destined to form trophoblasts
Urogenital sinus connected to connecting stalk through
Allantois which is Endodermal in origin
Its Remnant in adult called median umbilical ligament or urachus
long narrow tube that joins the yolk sac to the midgut lumen of the developing fetus.
vitelline duct, also known as the vitellointestinal duct, the yolk stalk, the omphaloenteric duct, or the omphalomesenteric duct
failure to disappearance of vitelline duct in the baby after delivery lead to
Mickle’s diverticulum
What are the remnants of wolffian (mesonephric) duct in females ?
Paraophoron Epoophoron Garterner duct > cyst in vagina Ductulus aberrans Epidydemis appendix Paradidymis
Remnants of Müllerian duct in male
Degenerate by MIF from Sertoli cells
Remain only
- appendix testis
- prostatic utricle = utriculus masculinus
Ambiguous genitalia results form (emryologically)
MIF works locally that’s why it results from unilateral mullerian and testicular tissue contralateral
SRY (sex region on Y ch.) + EGF stimulate the secretion of
MIF from Sertoli cells
Origin of distal 2/3 of vagina
2 sinovaginal bulbs at posterior part of UGS (Endodermal in origin)
Genital tubercle from UGS develop to (in both fe/male)
Clitoris
Penile urethra
What are the embryological origin of urogenital ridge ?
from intermediate mesoderm
Genital fold give rise to (in both fe/male)
Labia minora
Penile urethra
Genital swelling (or labioscrotal fold) gives rise to
Labia majora
Scrotum
Fetal blood volume:
50 ml/kg
—- fusion (7–9 weeks gestation) occurs when the lower segments of the Müllerian ducts fuse. —– fusion (around 8 weeks gestation) occurs when the lower Müllerian system fuses with the ascending endodermal sinovaginal bulb and the lower third of the vagina is formed and canalises
Lateral fusion (7–9 weeks gestation) occurs when the lower segments of the Müllerian ducts fuse.Vertical fusion (around 8 weeks gestation) occurs when the lower Müllerian system fuses with the ascending endodermal sinovaginal bulb and the lower third of the vagina is formed and canalises
