Embryology Flashcards
What occurs during Week 3?
1) Gastrulation
2) Neurulation
3) Somite formation
What occurs between weeks 4-8?
Organogenetic period
What occurs week 9 onwards?
Organ maturation
What does the cloaca divide to form?
> The GI tract
> Anteriorly the urogenital sinus
What does the mesonephric duct drain into?
The urogenital sinus
What does the urogenital sinus form?
> Urinary bladder
> The caudal end forms the urethra
Types of kidney in week 5 embryo?
> Pronephros
> Mesonephros
> Metanephros (Uteric bud and metanephric mesoderm)
Where is the pronephros?
The cervical region
Where is the mesonephros?
The thoracolumbar region
Where is the metanephros?
Pelvic region
When does the genital (gonadal) ridge formation occur?
Week 5-6
What does the genital (gondola) ridge form from?
The mesonephros forms a long ovoid structure in association with thoracic and upper lumbar vertebrae.
Where do the germ cells migrate from?
From the yolk sac, via dorsal mesentery, and embed into primitive sex cords
If germ cells do not migrate what will occur?
No gonads
Epithelium of the mesonephros invaginate to form what? What does this become?
A tube, this tube becomes the para-mesonephric duct
What does the mesonephric duct (The Wolffian duct) develop into, in a male?
Mesonephric duct develops into epididymis, vas deferens, seminal vesicle
What does the paramesonephric duct (The Mullerian duct) develop into in males?
Paramesonephric duct degenerates
What does the urogenital sinus form in males?
Urogenital sinus forms bladder, urethra; and prostate
What is another name for the mesonephric duct?
The Wolffian duct
What is another name for the paramesonephric duct?
The Mullerian duct
What does the mesonephric duct (The Wolffian duct) develop into, in a female?
Mesonephric duct degenerates
What does the paramesonephric duct (The Mullerian duct) develop into in females?
Paramesonephric duct forms fallopian tube, uterus, cervix part of vagina
What does the urogenital sinus form in females?
Urogenital sinus forms bladder and lower part of vagina
How does the indifferent gonad know whether to develop into a testes or an ovary?
SRY encodes for a protein called TDF (testis determining factor)
TDF makes the indifferent gonad develop into a testis
Other than allowing the development of the testes what does SRY encode for?
Sertoli cells
What is the role of the Sertoli cells (male)?
Sertoli cells recreate Mullerian inhibiting substance (MIS):
1) Paramesonephric duct degenerates. Therefore no development of fallopian tube, uterus, cervix part of vagina.
2) MIS transforms mesenchymal cells between cords to form Leydig cells –> Testosterone –> External genitalia
What is the role of the Leydig cells?
By 8 weeks gestation, Leydig cells produce testosterone which stimulate the differentiation of male external genital development and mesonephric ducts
Where do the seminal vesicles (male) develop from?
Outgrowth from caudal end of mesonephric duct
Where does the prostate develop from?
Outgrowth(s) from urethra, from urogenital sinus
Why does a female not develop testes?
They do not have the SRY of TDF regions
How many follicle at birth?
Around 2 million primordial follicles
After puberty, hormonal influences stimulation of how many follicles per month?
12-15 follicles per 28 day cycle
Only one follicle (normally) reaches maturity and ovulation
In females, what does the absence of testosterone lead to?
Degeneration of mesonephros and mesonephric duct
The paramesonephric ducts develop to give rise to female genital tract
What does the cranial end of paramesonephric duct become in females?
The ovaries
What does the caudal end of paramesonephric duct become in females?
Become uterus and superior part of the vagina
What does the inferior part of the vagina develop from?
The urogenital sinus
Where do the gonads initially form?
Within the lumber region
At week 7 where are the gonads/testes located?
Level of T10
At week 7 where are the gonads/ovaries located?
Level of T10
At week 12 where are the gonads/ovaries located?
Broad ligament
At week 12 where are the gonads/testes located?
Level of deep inguinal ring (remains until 7th month)
When do the testes enter the scrotum?
Just prior to birth 39 weeks
What happens to the gonads/ovaries before birth?
Round ligament drawn through inguinal canal to attach to labrum majorum
For the descent of the gonads in males what needs to be present?
The formation of the larger inguinal canal in males
For the descent of the gonads in females what needs to be present?
In the female – the presence of the round ligament and its passage through the inguinal canal
What is cryptorchidism?
Absence of testes in scrotum (cryptorchidism)
Types of cryptorchidism?
1) Undescended
2) Ectopic
3) Retractile testes
4) Absent testes
Complications of cryptorchidism?
1) Infertility
2) Malignant transformation (Germ cell tumours)
3) Testicular torsion
How is cryptorchidism managed?
Orchiopexy
In Cryptorchidism where can the testes be located?
1) Abdomen
2) Inguinal canal
3) Internal inguinal ring
4) External inguinal ring
5) Prescrotal (prepubic) region
Remnants of the mesonephric duct - cranial excretory tubule in the mesovarium?
Epoophoron
Remnants of the mesonephric duct - caudal excretory tubule in the mesovarium?
Paroophoron
Remnants of the mesonephric duct - small caudal portion in the wall of the uterus of vagina?
Gartner’s cyst
Types of anomalies of the female reproductive tract?
1) Complete duplication
2) Separate uterus
3) Bicornuate uterus (Partially separated, deep)
4) Arcuate uterus (Partially separated, shallow)
What is the ratio of babies being born with birth defects?
1 in 46 babies (2.2% of babies)
Within England and Wales which birth defect has a higher incidence than other European countries?
Spina bifida - 1 in 1000 babies
What are the most common birth anomalies?
Congenital heart defects
> 1 in 1000 babies
> Can require major surgery
> 6% babies will die before their 1st birthday
What is a teratogen?
1) A class of drug used for inflammatory conditions
2) Drug or other substance which can result in birth defect
3) Fetal anomaly associated with short or absent limbs
4) A congential ovarian cyst which can contain any type human tissue
What can a teratogen lead to?
May lead to structural or functional abnormality or even in utero death:
1) Death
2) Learning difficulties
3) Sensory deficient
4) Structural abnormalities
5) Cancer
6) IUGR or growth defects
7) Neurodevelopmental / behavioural dysfunction
8) Developmental delay
Teratogens within the 1st trimester?
> Structural defects when organogenesis is occurring
> Greatest risk between week 3 and 11.
When exposed to teratogens after which week are functional or growth defects more likely to occur?
After 12 weeks of gestation
What increases the risk of Fetal Alcohol syndrome?
Binge drinking = When an individual drinks five or more units of alcohol on one occasion
Regular binge drinking, around conception and in early pregnancy, is particularly harmful.
What is the classic triad for congenital rubella syndrome?
1) Sensorineural deafness
2) Eye abnormalities—especially retinopathy, cataract and microphthalmia
3) Congenital heart disease—especially pulmonary artery stenosis and patent ductus arteriosus.
What does Varicella lead to?
> Limb hypoplasia
Skin scarring
Eye defects
In which trimester does Varicella pose the highest risk?
Greatest risk 2nd trimester
When do cardiac defects occur during pregnancy?
Very early in pregnancy
What does warfarin use in pregnancy increase the risk of?
Cardiac defects
What can cause cardiac defects?
> Drugs e.g. Warfarin
Infections
Genetic
Who requires preconception counselling to reduce risk of anomalies?
> Epilepsy > Diabetes > Woman on anticoagulants > Woman with congenital anomalies > Antihypertensives
Why do we advise folic acid use?
To reduce the risk of a neural tube defect
