Applied embryology Flashcards
1
Q
What are the pre requisites for conception?
A
Need to have function gametes
Viable sperm and mature egg
2
Q
For natural conception to occur we require three components:
A
An egg, a sperm and the anatomical structures that allow them to meet.
3
Q
How long can a sperm survive?
A
5 days
4
Q
How long can the oocyte survive?
A
24 hours
5
Q
Where does sperm go?
A
Travels up fallopian tube to reach the egg
6
Q
What does the sperm unite with?
A
The egg and unites with nucleus
7
Q
What are the 6 steps in fertilisation?
A
8
Q
What are the steps in the first 5 days of ealry embryo development?
A
Day 1 – Formation of pronuclei
Day 2 – First cell division
Day 3 – Cell division continues
Day 4 –Formation of Morula
Day5 - Blastocyst forms
9
Q
What is the pronuclei stage?
A
2 nuclei, then carries on with cell division
10
Q
What are the stages in implanatation up to day 5?
A
11
Q
Where does the early embryo go?
A
Enters the uterine cavity in morula phase which converts to blastocyst on day 5.
12
Q
What are the plantation steps?
A
Hatching
Apposition
Adhesion
Invasion
13
Q
What is hatching?
A
Trophoectoderm cells produce protease to dissolve the zona in preparation for implantation
14
Q
What. is appoisiton?
A
First connection between blastocyst and endometrium, apposes to microvilli like structure called pinopodes expressed on receptive endometrium
15
Q
What is adhesion?
A
Trophoblast of the blastocyst adheres to the epithelial layer of maternal endometrium, embryonic tissue starts to actively secrete hCG
16
Q
What is invasion?
A
Trphoblast proliferation, differentiation, crossing of the epithelial basement membrane and invasion of endometrial stroma to form the placenta. Uterine spiral arteries remodelled by the invasive trophoblast.
17
Q
Think about the drawing steps of implanatation?
A
18
Q
Study this image on apposition and adherence?
A
19
Q
What are the stages of invasion?
A
20
Q
Pre-requisite for trophoblast inasion and placentation
A
Involves transformation of stromal cells of maternal endometrium every month under the effect of hormone progesterone.
21
Q
What are the changes of decidulisation prior to invasion?
A
Stromal cell differentiation (elongated fibroblast like cells) converted into decidual( rounded epithelial cells).
Angiogenesis - new vessel formation, increase vascular permeability
Increased macrophages, lymphocytes and decidual leukocytes(uterine natural killer cells) for maternal immune tolerance
22
Q
What are the stages of placental formation?
A
23
Q
What are the stages of placentation?
A
Invading trophoblast form primary chorionic villi
With infiltration of extra-embryonic mesoderm these become secondary villi
When capillaries form they become tertiary villi
Invasion of cytotrophoblast remodels spiral arteries to increase blood flow
24
Q
What is the mature placenta formed of?
A
Several components: Chorionic villi, The intervillous space, Placental Septae and Cotyledons (subunits of the placenta)
25
What are the functions of the mature placenta?
Acts as an immunological barrier
Gas exchange
Nutrient exchange
Waste excretion
Endocrine functions
26
What is embryogenesis??
First eight weeks of embryo development post fertilisation.
27
What happens on day 5?
Fertilised egg forms blastocyst on day 5 with two organised cell groups- inner cell mass(embryoblast) and trophoblast which develop to form the baby and placenta respectively
28
What is the embryoblast development?
Week 2-3- formation of bilaminar disc and development of amniotic sac, yolk sac, extraembryonic mesoderm and chorionic cavity
Week 3-4- differentiation of bilaminar disc into trilaminar structure- three germ layers ( endoderm, medoderm and ectoderm) through process of gastrulation and neural tube formation
Week 5-8 - organogenesis.
29
What happens beyond the end of week eight?
The embryonic period ends and the fetal period begins
30
How does blastocyst development occur?
Pluripotent cells: bilaminar disc consisting of Epiblast and hypoblast.
Epiblast undergoes gastrulation to form the three germ layers - ectoderm, mesoderm and endoderm
Hypoblast forms extraembryonic mesoderm
Blastocele
Inner layer cytotrophoblast forms chorionic villi
31
What does the inner cell mass differentiate into?
bilaminar epiblast (columnar epithelial cells) and the hypoblast (cuboidal epithelial cells). Hypoblast is the layer facing the blastocoel, while the epiblast is on the other side
32
What are the 2 cavities formed after differentiation into the bilaminar epiblast?
Two cavities form, yolk sac on the side of the hypoblast and amniotic cavity on the side of epiblast
33
34
What does the cervical mucus do?
Acts as a barrier to entry into the uterus and varies in its consistency throughout the menstrual cycle. Of the millions, if not 10s or 100s of millions of sperm deposited in the vaginal only hundreds will ascend to the fallopian tubes. There chemical signals will attract them to the egg. The egg itself is released into the peritoneal cavity and collected by the fallopian tube where it is normally fertilised by a single sperm.
35
What does the epiblast differentiate into?
The three germ layers- ectoderm , mesoderm and endoderm in a process called gastrulation (D13 to 16 of embryo development
36
What does gastrulation start with?
A groove appearing in the caudal end of epiblast called primitive streak
37
What do epiblast cells migrate into?
The hypoblast layer displacing them- forming the endoderm
•Further epiblast cells migrate through primitive streak between the epiblast and the hypoblast/endoderm to form the mesoderm
Remaining epiblast becomes the ectoderm
38
At cranial end primitive streak expans to make what?
Primitive node, then primtivie pit
Continues to caudal end of streak to make primitive groov
39
What does the ectoderm form?
•Epidermis, central nervous system, peripheral nervous system, hair, nails, neuroendocrine organs (adrenal medulla, pituitary gland), enamel of teeth
40
What does the mesoderm form?
•Dermis, musculoskeletal structures, cardiovascular system, kidneys, ureters, trigone of the bladder, gonads (not germ cells), adrenal cortex, visceral and parietal linings (pleura, pericardium, peritoneum),
41
What does the endoderm form??
•Lining of the gastrointestinal tract, the parenchyma of the liver, pancreas, thyroid, parathyroid, tonsils and thymus, the bladder (excluding the trigone) and urethra
42
What does the mesoderm subdivide into?
Paraxial Mesoderm
Intermediate Mesoderm
Lateral Plate Mesoderm
43
Why do multiple pregnancies occur?
Dizygotic- Two or more eggs fertilising and implanting, non-identical
Monozygotic- One embryo Splitting
Timing of embryo splitting determines the
nature of pregnancy (see next slide)
Identical twins
44
Is identical or non identitcal twins more common?
Non identitcal
45
What have fertility treatments done?
Increased the rates of multiple pregnancy, target to keep \<10%. Strategies to reduce- One at a time.
46
What are the monozygotic twin types?
47
What are the types of identical monozygotic twins?
48
What does the splitting of monozygotic look like?
49
What does splitting of the dizygotic look like?
50
What is the mesoderm subdivided into?
Paraxial Mesoderm
Intermediate Mesoderm
Lateral Plate Mesoderm
51
What does the intermediate mesoderm do?
Forms kidney, ureter and gonads
52
Part of urinary system (Kidney and ureter) and reproductive system develop from what?
The urogenital ridge in the intermediate mesoderm, therefore same origin
53
Urogenital ridge differentiates into what\>
Gonadal ridge medially which gives rise to gonad and nephrogenic cord laterally which forms the kidney and ureter
54
When does the urinary system develop?
Develops ahead of the reproductive system from 4th week of embryo development
55
What is the urinary system comprised of?
•Kidney, ureter, bladder and urethra.
56
Kidney and ureter develop from?
three overlapping systems in nephrogenic cord portion of the urogenital ridge - pronephros, mesonephros and metanephros
57
Where do the kidneys develop?
Develop in the pelvis and then ascends into the abdomen with the final position taken by 12th week.
58
What are the bladder and urethra formed from?
Urogenital sinus (part of cloaca) which also give rise to parts of female and male reproductive tract.
59
What are the 3 stages of development?
The pronephros (non-functional)
The mesonephros (functional but transient)
The metanephros (final kidney)
60
Metanephric mesenchyme forms what?
Kidney
61
Ureteric duct forms whaat?
Ureter
62
The nephric duct drains into what?
The cloaca which is a common temporary outlet for digestive, urinary and genital tract in embryonic life.
63
What are the different renal anomalies?
64
The caudal end of the enfolded yolk sac is known as what?
The cloaca. Its covered by the cloacal membrane which is formed by fusion of ectoderm and endoderm
65
The cloaca is divided by the urorectal septum to form what?
The urogenital sinus
The anal canal
66
The urogenital sinus will form what?
The bladder and urethra
67
The Mesonephric duct below the ureteric bud is incorporated into what?
the bladder as the trigone
68
What does the indifferentiated gonad develop?
In the gonadal ridge
69
The gonadal ridge is closely related to what?
Mesonephros
70
What are the primodial cells migrate from?
to the gonads from endoderm lining of yolk sac via hindgut around 6 weeks of gestation
71
Epithelium of gonadal ridge forms what?
Primitive sex cords
72
Combination of germ cells and primitive sex cord forms what?
The indifferent gonad which is capable of developing into a testis or ovary
73
What does the Y chromosome contain?
SRY gene
74
What does SRY produce?
Produces testis determining factor / SRY protein
This protein acts on the indifferent gonad to promote the formation of the testis
75
What are the steps in development of the ovary?
The migrating germ cells enter the ovary
The primitive sex cords extend into the medulla but degenerate
Secondary sex cords (cortical cords) develop and surround the germ cells to form the ovarian primordial follicles
Ovarian follicle pool (determining female ovarian reserve established at 20 weeks of gestation in fetal life
76
What are the steps in development of the testis?
The migrating germ cells enter the testis
The primitive sex cords extend into medulla and form testis cords (medullary cords) which transform into future seminiferous tubules and rete testis
Sertoli cell are derived from surface epithelium under effect of AMH
Leydig cells are produced from intermediate mesoderm and produce testosterone from 8 week onwards
77
Where do gonads originate?
In the posterior abdominal wall
78
When do the testes reach the deep inguinal ring?
By 7 konths of pregnancy
79
What do undescended testicle also known as?
Cryptorchidism- requires early surgery for correction
80
What are the 2 sets of genital ducts?
Mesonephric duct next to the gonad
Paramesonephric duct laterally
81
The presence or absence of AMH determines what?
Which of mesonephric and paramesonephric duct develops and regresses
82
In the male the presence of AMH causes what?
paramesonephric ducts to regress and these do not form any part of the adult
83
What is AMH?
Anti Mullerian hormone
84
Mesonephric ducts , also called Wolffian ducts drain into?
Mesonephros into the cloaca
85
In both males and females the mesonephric duct forms what?
The trigone of the bladder
86
What does the rest of the mesonephric duct persist in males form when there is testosterone?
Rest of the duct only persists in the males under the effect of testosterone and forms the epididymis, vas deferens and seminal vesicles
87
What does the mesonpehric duct do in females?
The duct regresses and remnants might remain as epoophoron, paraophoron (small cystic structures lateral to ovary) and gartners duct cyst (benign lesions on the lateral vaginal wall)
88
What happens in the absence of AMH?
In the absence of AMH, the paramesonephric ducts continue to develop and the mesonephric ducts regress
89
What happens to the paramesonephric duct in females?
Paramesonephric ducts grow medially and fuse. The fused portions of the paramesonephric ducts canalises to form the uterus and upper 2/3 rd of vagina. The unfused portions give rise to the fallopian tubes
90
What does the urogenital sinus form?
Forms the lower 1/3rd of vagina
91
What does the paramesonephric duct fuse with?
With the urogenital sinus at the sinus tubercle and point of fusion forms the hymen
92
Explain the development of external genitalia?
On either side of the cloacal membrane folds develop – The urogenital folds
Anteriorly these fuse to form the genital tubercle
Lateral to this are the labioscrotal swellings
As the cloaca is split by the urorectal septum the anus is separated off
93
Explain how the male external genitalia form?
In the male the genital tubercle elongates to form the penis
The labioscrotal swelling folds fuse posteriorly
The urogenital folds fuse posterior to anteriorly to form the penile urethra (spongy urethra)
The glans penis will canulate at the tip to form the final part of the urethra
94
Explain how the female external genitalia form?
In the female the urogenital folds form the labia minora
The labioscrotal folds form the labia majora
The genital tubercle forms the clitoris
95
What are some penis male reporductive tract anomalies?
Micropenis (genital tubercle does not elongate fully), hypospadias (urethral development problem causing opening to be abnormally located)
96
What are some testicular anomalies of thr male reporductive tract?
Absence, undescended (cryptochordism)
97
What are some different male reproductive anomalies?
Penile
Testicular
* Absence of vas deferens (cystic fibrosis)
* Absence of seminal vesicles
98
How common are anomalies of the female reporductive tract?
4-7% of women
99
What is the classification system of female reproductive tract anomalies?
No one agreed classification system:
ASRM (AFS)
ESHRE/ESGE
100
What do female reporudctive tract anomalies have an association with?
Renal tract anomalies
101
What are the different uterine anomalies- Underdevelopment?
102
What are the different uterine anomalies- fusion defect?
103
What are the different uterine anomalies- resorption defect?
104
What are some other congenital anomalies?
Vaginal anomaly
Vaginal Septa- Can be longitudinal or transverse (1:80,000)
Imperforate Hymen (1:2000)
Vaginal Agenesis- Lower part does develop proper
Absent or underdeveloped uterus and vagina
MKRH Syndrome (Mayer–Rokitansky–Küster–Hauser) or Mullerian agenesis syndrome (1:4500)- Failure of the paramesonephrict ducts to develop normally
105
Congenital malformation characterized by what?
A failure of the Müllerian duct to develop, resulting in a missing uterus and variable degrees of vaginal hypoplasia of its upper portion
