Embryology Flashcards
what makes up the female reproductive system?
what makes up the male reproductive system?
what is shown here?
Blastocyst
Blastocyst – outer layer of cells that goes to form the placenta and membranes
Inner ball of cells that goes to form the embryo proper
The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast
Ectoderm ___, Mesoderm in ______, endoderm ______
Amniotic cavity _______ and yolk sac _______
Neural tube = ______________
Paraxial mesoderm = _______
Intermediate mesoderm = _____________
Lateral mesoderm = ____________
top
middle
bottom
above
below
brain and spinal cord
somite’s
forms urogenital systems
forms the bodies cavities
Intermediate plate mesoderm forms the ________ system
urogenital
timeline of events:
Weeks 1 & 2 – ________ formed
Week 3 – ________ (splits into 3 germ layers), neurulation (neural tube forms), _______ formation (paraxial mesoderm)
Weeks 4 – 8 - __________ period
Week 9 onwards – _________ of organ systems
blastocyst
gastrulation
somite
organogenetic
maturation
But…..Reproductive system Organogenesis:
- _________ beyond 8 weeks
- Extends beyond _________ period
Extends
post-natal
- Reproductive and urinary systems have close ___________ links
- Urinary system forms _________ for reproductive (part) system
embryological
template
Urinary system development - recap:
- 3 sets of kidneys develop
- _________ – cervical region – vestigial
- _________ – thoracolumbar region – briefly functional
- ________ – pelvic region – functional
- Each acts as template for subsequent stage
Pronephros
Mesonephros
Metanephros
Pronephros, Mesonephros and Metanephros develop from what?
intermediate plate mesoderm
pictures show the week 5 embryo:
The ___________ that goes to start developing the reproductive system
Mesonephric ducts drain into the ______
Mesonephros is no longer ________ as part of the urinary system so is refunctioned to form the ______
mesonephros
cloaca
function
gonads
At about _ weeks mesonephros forms a long ovoid structure in association with thoracic and upper lumbar vertebrae
_______ part of mesonephric ridge becomes thickened to form a ___________ ridge
_______ ridge forms the substance of the ______
6
Medial
genital/gonadal
Gonadal
gonads
(Anteromedial part of the mesonephros (in blue in bottom right) thickens to form genital ridge)
Need cells that can undergo meiosis so they need to be undifferentiated and you wont find them in these 3 germ layers so need to import them form the _____ ____
Germ cells migrate into Genital ridge = ________ _______
- Week 6 - ____ cells migrate from yolk sac, via dorsal mesentery, and embed into primitive sex cords (formed from mesenchyme of genital ridges)
- This structure is known as the _________ gonad (why?) – no difference between male and female at this stage
- No migration of germ cells - no ________
yolk sac
Indifferent Gonad
Germ
indifferent
gonads
what is the Paramesonephric duct?
Epithelium of the mesonephros invaginates to form a tube
This tube becomes the para-mesonephric duct
Paramesonpheric duct:
Develops lateral to developing gonads and __________ duct
Funnel shaped cranial end opens into __________ cavity
Caudally, cross ventral to __________ ducts
This projects into dorsal wall of _________ sinus
mesonephric
peritoneal
mesonephric
urogenital
what are the 3 main strucutres which go on to form the reproductive sytem in males and females?
- Indifferent gonad (with primordial sex cells that have moved in from the yolk sac)
- Mesonephric duct (Wolffian duct)
- Paramesonephric duct (Mullerian duct)
in males:
- Gonad forms _______
- Mesonephric duct develops into _______________________________
- Paramesonephric duct ____________
- Urogenital sinus forms ______________________
testis
epididymis, vas deferens, seminal vesicle,
degenerates
bladder, urethra; and prostate
In females:
- Gonad forms the ______
- Mesonephric duct ____________
- Paramesonephric duct forms ______________________
- Urogenital sinus forms ______________________
ovary
degenerates
fallopian tube, uterus, cervix part of vagina
bladder and lower part of vagina
How does the indifferent gonad know whether to develop into a testis or an ovary? (Only difference is chromosomes)
what is the proccess in men? fill in the blanks in the picture
study this histology
Sertoli cells have much lighter nucleus
Leydig cells in-between seminiferous tubules
what is the process of testis development?
sex cords, medulla and cortex
Wk 6 priWk 5 – primary mordial germ cells incorporated into primary sex cords
Wk 7 – TDF stimulates primary sex cords - extend into medulla - seminiferous cords - tubules
Seminiferous cords branch, ends anastomose - rete testis of medulla
Surface epithelium (mesothelium) lost when thick capsule forms (tunica albuginea of adult testis)
Mesenchyme between cords gives rise to Interstitial cells of Leydig
By week 8, Leydig cells produce testosterone and other hormones which stimulate masculine differentiation of mesonephric ducts and external genitalia
In males, paramesonephric duct degenerates
Testis – post natal development
what photo of the testis is prepubertal and which is postpubertal?
At puberty the seminiferous tubules become canalised and the Leydig cells make more testosterone
Reproductive system development doesn’t fully complete until puberty
Seminal vesicles - Outgrowth from caudal end of ___________ duct
Prostate - Outgrowth(s) from _______ (from urogenital sinus)
Male external genitalia formed under the influence of __________
mesonephric
urethra
testosterone
__________ duct disappears in females, opposite to males
Mesonephric
Development of the gonad:
Indifferent stage
In the presence of TDF (No SRY region on chromosome so no tests determining factor) = gonad develops into a ______
In its absence gonad develops into an ______ (by default)
testis
ovary
In a female foetus (XX chromosome):
No ___ region
No ___
By default the ________ gonad develops into an _____
SRY
TDF
indifferent
ovary
Development of the ovary:
Primary sex cords _________ (leaving the primordial germ cells)
By 10 weeks secondary sex cords develop from surface __________
__________ germ cells become incorporated into them
Primordial germ cells then bud off with single surrounding layer of cortical cord cells to form primordial ________ (from ~16 weeks)
Active _______ of these early primordial follicles to form additional follicles
By _th month all follicles have formed
Oocytes enter _______ and arrested in prophase 1st meiotic division
Some follicular atresia by birth
degenerate
epithelium
Primordial
follicles
mitosis
7
meiosis
Postnatal ovarian development:
~2 million primordial follicles at birth
Many follicles become atretic before puberty
After puberty, ________ influences stimulate 12-15 follicles, per 28 day cycle, to develop
Only ___ follicle (normally) reaches maturity and ovulation (unsure how selection is made for one)
Continues until the _________
hormonal
one
menopause
Ovary – post natal development
what is A, B and C?
Childs ovary has millions of follicle
Where do the tubular components of the female reproductive system come from?
Absence of testosterone causes degeneration of mesonephros and mesonephric duct
Paramesonephric ducts develop to give rise to female genital tract
Origin of female genital tract:
Cranial (open funnel) end of paramesonephric duct becomes associated with ______
Caudal end of paramesonephric duct (uterovaginal primordium) becomes ______ and _____________________
Inferior part of vagina from ________ _____
(Mesonephric duct degenerates)
ovary
uterus
superior part of vagina
urogenital sinus
Descent of the gonads:
Gonads initially form in lumbar region, so positional changes occur as development takes place
what is the descent process of the testis?
- Week 7 – Level of T10 (Diaphragm undescended)
- Week 12 – Level of deep inguinal ring (remains until 7th month)
- Enters scrotum just prior to birth (39 weeks)
Descent due to the gubernaculum – fibrous cord
Gubernaculum contracts near birth and pulls the testes down
Descent of the gonads:
Gonads initially form in lumbar region, so positional changes occur as development takes place
what is the descent process of the ovaries?
- Week 7 – Level of T10
- Week 12 – Broad ligament
- Round ligament drawn through inguinal canal to attach to labrum majorum
In females:
Once in the pelvis the gubernaculum stop contracting and degenerates and forms a fibrous cord and its remanents form the _______ ligament and the rest of the gubernaculum forms the ______ ligament
Ovary doesn’t pass through inguinal canal so ______ so less prone to developing inguinal _______
ovarian
round
narrow
hernias
The following aspects are linked to the descent of the gonads:
- Formation of the larger _______ _____ in males
- In the female – the presence of the ______ ligament and its passage through the _______ ____
inguinal canal
round
inguinal canal
when do things go wrong?
- Undescended testis
- Remnants – eg: gartner’s cysts (embryologic remnants of the caudal end of the mesonephric (Wolffian) duct)
- Anomalies of the paramesonephric duct in female
what is Cryptorchidism?
a condition in which one or both of the testes fail to descend from the abdomen into the scrotum
When testes don’t descent as they should and they are not in the scrotum at birth
By 8th month they should of entered into scrotum
Want to find it in one of its location along its path
Parents notice absence of testes in scrotum (cryptorchidism): when?
- Undescended
- Ectopic
- Retractile testes
- Absent testes
What are some complications of undescended testis?
- Infertility
- Malignant transformation (germ cell tumours)
- Testicular torsion
what is the mangement of undescended testss?
Orchiopexy (a surgery to move an undescended (cryptorchid) testicle into the scrotum and permanently fix it there)
Remnants of mesonephric duct - what problems may it cause?
May form cysts
These swelling or cysts can have an impact on fertility and the womb
- Anomalies of the paramesonephric duct
Forms the fallopian tube, uterus and vagina in females
May not fuse completely or duplicate
Can get two vaginas
Can cause difficult pregnancy
Summary:
Mesoderm = _________ gonad
Mesonephric duct
SRY region of Y chromosome = ______ development = mesonephric duct becomes _______ _________. Also Mullerian Inhibiting Substance = ___________ duct degenerates
No SRY = gonad becomes _____, paramesonephric duct becomes ______________________________
Indifferent
testis
vas/ductus deferens
paramesonephric
ovary
fallopian tube, uterus, cervix and vagina
