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Reproductive Physiology - Y3 > embryology > Flashcards

embryology Flashcards

1
Q

journey of an egg

A

Sperm can survive for 5 days (travels cervic, uterine cnal, fallopian tube)

The oocyte can survive for 24 hours

step 1 - egg leaves ovary and enters fallopian tube
step 2 - sperm enters egg and united with nucleus
step 3 - fertilised egg divides
step 4 - cells attach to uterus

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2
Q

fertilisation

A

1 - sperm makes contact with egg
2 - acromosome reacts with zona pellucida
3 - acrosome reacts with periviterlline space
4- plasma membrane of sperm and egg fuse
5 - sperm nucleus enters egg

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3
Q

early embryo development

A

Day 1 – Formation of pronuclei (two nuclei in fertilised egg one to egg and one to sperm)

Day 2 – First cell division

Day 3 – Cell division continues (rapid increase number –> ball of cells (morula))

Day 4 –Formation of Morula

Day5 - Blastocyst forms

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4
Q

implantation process

A

Early embryo enters the uterine cavity in morula phase which converts to blastocyst on day 5.

Hatching- trophoectoderm cells produce protease to dissolve the zona in preparation for implantation

Apposition- first connection between blastocyst and endometrium, apposes to microvilli like structure called pinopodes expressed on receptive endometrium

Adhesion- trophoblast of the blastocyst adheres to the epithelial layer of maternal endometrium, embryonic tissue starts to actively secrete hCG

Invasion- 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.

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5
Q

hatching of the blastocyst

A

hatching of the embryo from sona pellucida 5th day after fertilisation

inability to hatch results in infertlity and premature hatching can result in abnormal implantation in the uterine tube

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6
Q

decidulisation change prior to invasion

A

Pre-requisite for trophoblast inasion and placentation -involves transformation of stromal cells of maternal endometrium every month under the effect of hormone progesterone.

Changes-
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

These changes transform the endometrium into a vascular receptive tissue for blastocyst invasion.

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7
Q

invasions of thropoblast

A

placenta isnt the mothers property mainly composed of the fetus

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8
Q

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

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9
Q

mature placenta components

A

Chorionic villi
The intervillous space
Placental Septae
Cotyledons (subunits of the
placenta)

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10
Q

functions of the placenta

A

Acts as an immunological barrier
Gas exchange
Nutrient exchange Waste excretion
Endocrine functions

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11
Q

embryogenesis

A

embryogenesis is the first eight weeks of embryo development post fertilisation.

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

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12
Q

embryoblast development

A

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.

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13
Q

blastocyst cell group

A

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

Blastocoele

Inner layer cytotrophoblast forms chorionic villi

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14
Q

inner cell mass differentiation

A

The inner cell mass differentiates 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

Two cavities form, yolk sac on the side of the hypoblast and amniotic cavity on the side of epiblast

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15
Q

epiblast differentiation / gastrulation

A

Epiblast differentiates into the three germ layers- ectoderm , mesoderm and endoderm in a process called gastrulation (D13 to 16 of embryo development)

Gastrulation starts with a groove appearing in the caudal end of epiblast called primitive streak

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

The newly formed trilaminar disc with three layers is called gastrula and forms the different organ systems

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16
Q

ectoderm purpose

A

Epidermis, central nervous system, peripheral nervous system, hair, nails, neuroendocrine organs (adrenal medulla, pituitary gland), enamel of teeth

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17
Q

mesoderm purpose

A

Dermis, musculoskeletal structures, cardiovascular system, kidneys, ureters, trigone of the bladder, gonads (not germ cells), adrenal cortex, visceral and parietal linings (pleura, pericardium, peritoneum),

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18
Q

endoderm purpose

A

Lining of the gastrointestinal tract, the parenchyma of the liver, pancreas, thyroid, parathyroid, tonsils and thymus, the bladder (excluding the trigone) and urethra

19
Q

mesoderm subdivisions

A

Paraxial Mesoderm

Intermediate Mesoderm

Lateral Plate Mesoderm

20
Q

whaT does intermediate mesoderm allow to develop

A

kidneys ureters and gonads

21
Q

multiple pregnancy

A

Dizygotic- Two or more eggs fertilising and implanting, non-identical

Monozygotic- One embryo Splitting
Timing of embryo splitting determines the nature of pregnancy
identicle twins

non-identical is more common

Risk of multiple pregnancy in natural conception 1-2%

Fertility treatments have increased the rates of multiple pregnancy, target to keep <10%. Strategies to reduce- One at a time.

22
Q

types of twins

A

Dichorionic diamniotic (separate placenta and amniotic sac)

monochorionic diamniotic (share placenta, separate amniotic sac)

monochorionic monoamniotic (share placenta and amniotic sac)

conjoined twins (as above, joined up organs)

23
Q

What three major units is mesoderm subdivided into

A

paraxial Mesoderm

Intermediate Mesoderm

Lateral Plate Mesoderm

24
Q

link between urinary system and gonads

A

Part of urinary system (Kidney and ureter) and reproductive system develop from the urogenital ridge in the intermediate mesoderm, therefore same origin

Urogenital ridge differentiates into gonadal ridge medially which gives rise to gonad and nephrogenic cord laterally which forms the kidney and ureter

Urinary system develops ahead of the reproductive system from 4th week of embryo development

25
Q

what is the urinary system comprised of

A

Kidney, ureter, bladder and urethra

26
Q

when do different parts of the urinary system develop

A

Kidney and ureter develop from three overlapping systems in nephrogenic cord portion of the urogenital ridge - pronephros, mesonephros and metanephros.

Kidney develop in the pelvis and then ascends into the abdomen with the final position taken by 12th week.

Bladder and urethra are formed from urogenital sinus (part of cloaca) which also give rise to parts of female and male reproductive tract.

27
Q

what are the three stages of development for the nephorgenic chord

A

The pronephros (non-functional)

The mesonephros (functional but transient)

The metanephros (final kidney)

Metanephric mesenchyme forms kidney and ureteric duct forms the ureter

The nephric duct drains into the cloaca which is a common temporary outlet for digestive, urinary and genital tract in embryonic life.

28
Q

whaT are common renal anomolies

A

renal agenesis
horseshoe kidney
pelvic kidney
duplex kindeys
duplex ureter and cloacal system

29
Q

describe development of the cloaca

A

The caudal end of the enfolded yolk sac is known as the cloaca. Its covered by the cloacal membrane which is formed by fusion of ectoderm and endoderm

The cloaca is divided by the urorectal septum to form

  • The urogenital sinus
  • The anal canal

The urogenital sinus will form the bladder and urethra

The Mesonephric duct below the ureteric bud is incorporated into the bladder as the trigone

30
Q

development of the gonadal ridge

A

The indifferent gonad develops in the gonadal ridge

The gonadal ridge is closely related to the mesonephros

Primordial germ cells do not originate in the gonadal ridge but migrate to the gonads from endoderm lining of yolk sac via hindgut around 6 weeks of gestation

Epithelium of gonadal ridge forms primitive sex cords

Combination of germ cells and primitive sex cord forms the indifferent gonad which is capable of developing into a testis or ovary

31
Q

gonad differentiation

A

The Y chromosome contains the SRY gene (sex-determining region Y)

SRY produces testis determining factor / SRY protein

This protein acts on the indifferent gonad to promote the formation of the testis

In rare cases, following a translocation error, a male can be born with a 46 XX Karyotype (1:20,000)

32
Q

development of ovary

A

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

33
Q

developent of testes

A

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

34
Q

tesTicular descent

A

The gonads originate in the posterior abdominal wall

The testes reach the deep inguinal ring by 7 months of pregnancy

By term 97% of male infants will have fully descended testes

Undescended testicle, also known as cryptorchidism requires early surgery for correction

35
Q

development of reproductive tract

A

There are two sets of genital ducts
Mesonephric duct next to the gonad
Paramesonephric duct laterally

The presence or absence of AMH determines which develops and which regresses

In the male the presence of AMH causes the paramesonephric ducts to regress and these do not form any part of the adult

36
Q

male reproductive tract

A

Mesonephric ducts , also called Wolffian ducts drain the mesonephros into the cloaca

In both males and females it forms the trigone part of the bladder

Rest of the duct only persists in the males under the effect of testosterone and forms the epididymis, vas deferens and seminal vesicles

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)

37
Q

female reproductive tract

A

In the absence of AMH, the paramesonephric ducts continue to develop and the mesonephric ducts regress

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

Urogenital sinus forms the lower 1/3rd of vagina

Paramesonephric ducts fuse with the urogenital sinus at the sinus tubercle and point of fusion forms the hymen

38
Q

DEVELOPMENT OF EXTERNAL GENITALIA

A

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

39
Q

MALE EXTERNAL GENITALIA

A

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

40
Q

FEMALE EXTERNAL GENITALIA

A

In the female the urogenital folds form the labia minora

The labioscrotal folds form the labia majora

The genital tubercle forms the clitoris

41
Q

MALE REPRODUCTIVE TRACT ANOMALIES

A

Penile- micropenis (genital tubercle does not elongate fully), hypospadias (urethral development problem causing opening to be abnormally located)
Testicular- Absence, undescended (cryptochordism)
Absence of vas deferens (cystic fibrosis)
Absence of seminal vesicles

42
Q

FFEMALE REPRODUCTIVE TRACT ANOMALIES

A

Anomalies of the female reproductive tract are common
4-7% of women

No one agreed classification system:
ASRM (AFS)
ESHRE/ESGE

There is an association with renal tract anomalies

43
Q

OTHER CONGENITAL ANOMALIES IN FEMALE

A

Vaginal anomaly

Vaginal Septa
	Can be longitudinal or transverse (1:80,000)

Imperforate Hymen (1:2000)

Vaginal Agenesis

   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

Reproductive Physiology - Y3 (12 decks)

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