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Part 1 MFSRH 2024 > Embryology > Flashcards

Embryology Flashcards

1
Q

How many oocytes does a female 20 week foetus have

A

6-7 million

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2
Q

How many oocytes does a female have at birth?

A

1-2 million

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3
Q

How many oocytes does a female have at puberty?

A

300,000

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4
Q

When after fertilisation does the morula appear?

A

Day 4

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5
Q

When after fertilisation does the blastocyst appear?

A

Day 5

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6
Q

From what do the primordial germ cells arise?

A

Wall of the yolk sac in the 2nd week of development

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7
Q

What do primordial germ cells form in females?

A

Oogonia

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8
Q

What do primordial germ cells form in males?

A

Spermatogonia

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9
Q

When do the primordial germ cells migrate to occupy the gonadal ridges?

A

Week 6 of development

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10
Q

What happens to oogonia in the fetal period?

A

Oogonia proliferate by mitosis and differentiate into primary oocytes, however, these oocytes are then suspended in prophase I (I, i.e. the first meiotic division) from birth until puberty

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11
Q

At what stage of meiosis are oogonia suspended in from birth until puberty?

A

Prophase I

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12
Q

What causes the arrest in meiosis experienced by the primary oocytes during the foetal period?

A

Oocyte maturation inhibitor (OMI) - a peptide produced by the follicular cells surrounding a primary oocyte

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13
Q

What are the layers of the follicle that surround the primary oocyte?

A

1) Theca interna - the inner vascular and secretory layer

2) Theca externa - the outer fibrous layer

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14
Q

Where do the spermatogonia lie dormant in males, and until when do they remain dormant?

A

Spermatogonia remain dormant in the seminiferous tubules in the testes until puberty

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15
Q

How soon after ovulation does fertilisation take place?

A

12-24 hours after ovulation

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16
Q

What the summarised stages of fertilisation?

A

1) Sperm activation and penetration of the corona radiata
2) Attachment and penetration of the zona pellucida
3) Fusion of the oocyte and sperm cell membranes
4) Completion of meiosis of the oocyte and formation of the pronuclei
5) Formation of the zygote

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17
Q

What process do sperm need to undergo to be capable of penetrating the ovum?

A

Capacitation

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18
Q

What happens during capacitation?

A

Loss of glycoprotein and cholesterol from the acrosomal membrane by secretions from the cervix and uterine tube

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19
Q

How do sperm penetrate the corona radiata?

A

By the acrosomal reaction, releasing hyaluronidase

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20
Q

How do sperm penetrate the zona pellucida?

A

Also by release of the acrosomal enzymes - esterases, acrosin and neuraminidase

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21
Q

What is the zona reaction?

A

When the sperm binds with the zona pellucida

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22
Q

What is the point of the zona reaction?

A

It changes the physical properties of the zona pellucida to prevent attachment/penetration of any further sperm

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23
Q

What causes the zona reaction?

A

The release of lysosomal enzymes from the cortical granules into the privitelline space

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24
Q

When does the oocyte resume its second meiotic division?

A

Soon after entry of the spermatozoa

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25
Q

How do you know that the second meiotic division has occurred?

A

The 2nd polar body is visible down the microscope

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26
Q

What is the zygote?

A

The zygote is the product of complete fertilisation/ It occurs when the male and female pronuclei have met, their membranes broken down and their chromosomes mixed to create a single cell - this single cell is the zygote

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27
Q

What are the components of the blastocyst at day 5?

A 
Trophoblast = outer cell layer, from which foetal component of placenta will form
Embryoblast = inner cell mass, from which embryo will form
Blastocele = cavity inside the blastocyst
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28
Q

How many days after fertilisation does implantation occur?

A

Approx. 6

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29
Q

When does the trophoblast differentiate, and what does it differentiate into?

A

Week 2
Cytotrophoblast = inner, single layer of cells
Syncytiotrophoblast = outer layer. = more invasive but has not yet invaded the endometrial blood vessels
Decidualisation if the uterine stroma forms the maternal component of the placenta (separate reaction)

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30
Q

When does the embryoblast/inner cells mass of the blastocyst differentiate, and what into?

A

Also week 2

2 layers - the epiblast and the hypoblast. These form the bilaminar disc

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31
Q

Where does the amniotic cavity form?

A

In the epiblast layer, developing at approx. 8 weeks. The amniotic cavity is filled with amniotic fluid.

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32
Q

What does the hypoblast (of the bilaminar disc) develop into?

A

The exocoelomic membrane is derived from the hypoblast and forms the primary yolk sac.

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33
Q

What is the state of the trophoblast by day 12?

A

The syncytiotrophoblast have formed lacunae which are responsible for derive ng nutritional support from the endometrium.

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34
Q

What is the state of the trophoblast by day 13?

A

The cytotrophoblast forms primary chronionic villi - finger like protrusions into the lacunae of the syncytiotrophoblast.

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35
Q

When does the primary yolk sac become the secondary yolk sac?

A

Day 13

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36
Q

What is the extra-embryonic mesoderm?

A

A connecting stalk between the embryo and cytotrophoblast. It is the forerunner of the umbilical cord.

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37
Q

What is the state of the trophoblast by day 14?

A

The syncytiotrophoblast begins to produce Beta-hCG to maintain the corpus luteum so that the corpus luteum can maintain the thickness of the endometrium.

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38
Q

What is the name of the process by which three germ layers are formed?

A

Gastrulation

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39
Q

What are the names of the three germ layers?

A

Epiblast —> 1) Ectoderm
From the ectoderm you also get the 2) Mesoderm
Hypoblast —> 3) Endoderm

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40
Q

When do the three germ layers develop?

A

3rd week

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41
Q

What forms from the ectoderm?

A

1) Surface ectoderm - epidermis, tooth enamel, lens, internal ear
2) Neural tube - CNS; retina; posterior pituitary
3) Neural crest - facial bones, adrenal medulla, cranial and sensory ganglia

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42
Q

What forms from the mesoderm?

A

1) Paraxial mesoderm - skeletal muscles of trunk and limbs, skeleton (except skull), dermis, connective tissue
2) Intermediate mesoderm - urogenital system
3) Lateral plate mesoderm - smooth muscles and connective tissue, viscera

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43
Q

What forms from the endoderm?

A

Gut tube and liver

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44
Q

After the development of the 3rd germ layer - i.e. the mesoderm - at what points do the ectoderm and endoderm remain in contact?

A

1) Prochordal plate - at the cephalic end of the disc —> becoming the buccopharyngeal membrane
2) Cloachal plate - at the caudal end of the disc —> becoming the cloachal membrane

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45
Q

What is the primitive streak?

A

A groove like depression in the bilaminar disk that forms at the caudal end in week 2, before it begins the deepen and extend in week 3 at the three germ layers develop

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46
Q

Where is the primitive node?

A

At the cephalic end of the primitive streak

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47
Q

What develops from the cells of the primitive node?

A

The notochordal plate, which then folds to form the notochord, which then underlies the future neural tube to ultimately form the nuceli pulposi (centres) of the intervertebral discs of the vertebral column

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48
Q

What is the name of the process that forms the brain and spinal cord?

A

Neurulation

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49
Q

What are the stages of neurulation?

A

Day 19 - neural plate formed from ectoderm, rounded up to form neural folds
Day 20 - neural plate deepens to form the neural groove, from which you get the neural tube

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50
Q

Where do neural crests form?

A

At the edge of the neural tube where the neuro-ectoderm is continues with the surface ectoderm

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51
Q

What is the connection between the yolk sac and the gut?

A

Vitello-intestinal (vitelline) duct.

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52
Q

Which develops first, the urinary system or the genital system?

A

Urinary BEFORE genital

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53
Q

Where do the urogenital ridges develop?

A

In the mesoderm, either side of the aorta

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54
Q

What are the different parts of the urogenital ridges?

A

Nephrogenic cord - develops into urinary system

Gonadal ridge - develops into genital system

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55
Q

What forms from endoderm?

A 
Stomach
Intestines (mucosal layers)
Colon (mucosal layers)
Liver
Pancreas
Bladder
Epithelial parts of trachea
Lungs
Pharynx
Thyroid
Parathyroid
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56
Q

What forms from intermediate meosderm?

A

Kidneys

Gonads

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57
Q

What forms from paraxial mesoderm?

A

Cartilage
Skeletal muscle
Dermis

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58
Q

What forms from lateral plate mesoderm?

A

Circulatory system (inc heart) and
Spleen
Gut wall

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59
Q

What forms from neural crest of ectoderm?

A 
Peripheral nervous system
Adrenal medulla
Melanocytes
Facial cartilage
Dentin of teeth
60
Q

What forms from neural tube of ectoderm?

A 
Brain
Spinal cord
Posterior pituitary
Motor neurons
Retina.
Anterior pituitary
61
Q

What is the incidence of Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome?

A

1/5000

62
Q

What are the 2 conditions that cause a congenital absence of the uterus?

A

1) Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome

2) CAIS AKA Testicular Feminisation Syndrome

63
Q

How do you differentiate between Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome and CAIS AKA Testicular Feminisation Syndrome?

A

Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome = normal hormone levels
CAIS AKA Testicular Feminisation Syndrome = low E2

64
Q

What is ootidogenesis?

A

The 2 meiotic divisions the primary oocytes undergo to become ootids

65
Q

What is oocytogenesis?

A

Growth and maturation of oogonium to primary oocytes

66
Q

What are Ladd’s bands?

A

When intestinal malrotation causes fibrous bands that fix the caecum in the right upper quadrant

67
Q

How is the foregut innervated?

A

T5-T9

68
Q

How is the midgut innervated?

A

T10-T11

69
Q

How is the hindgut innervated?

A

T12-L1

70
Q

What is the most important chemical for maintaining a patent DA during pregnancy?

A

PGE2

71
Q

Where is PGE2 produced in pregnancy?

A

Placenta

72
Q

When does meconium first appear in the terminal ileum?

A

10-16 weeks gestation

73
Q

What does the corpus luteum produce?

A

1) Progesterone
2) Estradiol
3) Inhibin A

74
Q

What is the maturation process for sperm?

A

Spermatocytogenesis - spermatagonium to primary spermatocytes

75
Q

What is spermatidogenesis?

A

When spermatocytes undergo 2 meiotic divisions to become spermatids

76
Q

What is spermiogenesis?

A

When spermatids differentiate into spermatazoa

77
Q

What is the life span of the corpus luteum?

A

14-16 days

78
Q

What is a Gartner’s duct?

A

A cystic structure found lateral to the vagina

It’s embryological origin is the mesonephric duct

79
Q

From what does the intraembryonic coelom form?

A

Lateral plate mesoderm

80
Q

What is the canal of Nuck associated with?

A

Round ligament

81
Q

At what stage does implantation occur?

A

7-9 days, i.e. when the embryo is a blastocyst

82
Q

What condition occurs is the yolk sac persists?

A

Meckel’s diverticulum

83
Q

From what structure do the kidneys and renal tract develop?

A

Metanephros

84
Q

From what germ layer do the autonomic ganglia develop from?

A

Neural crest

85
Q

A bicornate uterus results from a failure of fusion of what?

A

Paramesonephric ducts

86
Q

From what germ layer are the ureters derived?

A

Mesoderm

87
Q

From where do primordial germ cells originate?

A

Yolk sac

88
Q

From which embryological structure does the penis develop?

A

Genital tubercle

89
Q

What develops first, the urinary system or genital system?

A

Urinary system

90
Q

What are the components of the urinary system?

A

Pronephros - week 4 appearance, never functional
Mesonephros - week 4 appearance, functions between weeks 6-10
Metanephros - week 4 appearance, functions from week 12 as the permanent kidney

91
Q

What are the 2 parts of the metanephros?

A
  1. Ureteric bud
  2. Metanephric mesoderm
92
Q

What is derived from the ureteric bud?

A
  1. Collecting duct
  2. Minor and major calyx
  3. Renal pelvis
  4. Ureter
93
Q

What is derived from the metanephric mesoderm?

A
  1. Renal glomerulus
  2. Renal capsule
  3. PCT
  4. Loop of Henle
  5. DCT
94
Q

From what embryological structure are the bladder, urethra, urethral/paraurethral glands and vagina derived?

A

Urogenital sinus

95
Q

From what embryological structure are the labia minora and ventral aspect of the penis derived?

A

Urethral folds

96
Q

From what embryological structure are the labia majora and scrotum derived?

A

Genital swellings

97
Q

From what embryological structure are the ovarian and round ligament derived?

A

Gubernaculum

98
Q

As the kidney ascends from the pelvis, by how many degrees does it rotate?

A

90 degrees

99
Q

In whom, and on which side is renal agenesis more common?

A

In males, and on the L side

100
Q

What is renal agenesis caused by?

A

When the ureteric bud fails to induce the metanephric mesoderm

101
Q

When does duplication of the ureter occur?

A

It occurs as a result of early splitting from the ureteric bud

102
Q

Where is the SRY gene located?

A

The short arm of chromosome Y - Yp11

103
Q

From what does a Gartner’s cyst derived (found in the uterus/vagina)?

A

When the caudal part of the mesonephric ducts persists

104
Q

What is the time frame for the journey the testis make into the scrotum?

A

Week 12 - testis reach the inguinal canal
Week 28 - testis migrate through the inguinal canal
Week 33 - testis reach the scrotum

105
Q

What are the fascial layers of the testis, and from what are they derived?

A

Internal spermatic fascia - from transversalis fascia
Cremesteric fascia - from internal oblique
External spermatic fascia - from external oblique

106
Q

When does the primitive gut form?

A

Week 4

107
Q

What structures arise from the foregut?

A 
Oesophagus
Trachea and lung buds
Stomach 
Proximal duodenum
Liver, biliary tree, pancreas
108
Q

What structures arise from the midgut?

A

Distal duodenum
Small intestine
Caecum and appendix
Ascending colon and two thirds of the transverse colon

109
Q

What structures arise from the hindgut?

A

Distal third of the transverse, descending and sigmoid colon
Rectum and superior part of anal canal
Epithelium of urinary bladder and most of urethra

110
Q

What does the pectinate line (also called the white line) denote?

A

The junction between the endoderm of the hindgut and the ectoderm of the proctodeum, dividing the upper two thirds and the lower third of the anal canal

111
Q

What does the umbilical vein form after birth?

A

Ligamentum teres hepatis

112
Q

What does the ductus venosus form after birth?

A

Ligamentum venosum

113
Q

What develops from the vitelline vein?

A

Hepatic veins
Inferior part of IVC
Superior mesenteric vein
Portal vein

114
Q

From what does the blastocyst hatch?

A

Zona pellucida

115
Q

At what gestation does a conceptus become a fetus?

A

9 weeks

116
Q

How many cells are there in a blastocyst?

A

70-100 cells

117
Q

When does the buccopharyngeal membrane breakdown?

A

Week 4

118
Q

When does the cloacal membrane breakdown?

A

Week 7

119
Q

From when is the first heartbeat noted?

A

Day 21

120
Q

When does embryo folding occur?

A

Days 21-24

121
Q

From when are spontaneous limb movements first noticeable on USS?

A

Week 7

122
Q

What is the maximum number of somites, and what is their rate of production?

A

Max 42-44 pairs

Rate of 3 pairs/day

123
Q

What are the layers of the decidua?

A

Basalis
Capsularis
Parietalis

124
Q

What is the name for the changes in the endometrial glands as a result of progesterone?

A

Arias-Stella

125
Q

What are the 2 units of the placenta?

A
  1. Chorionic plate - is fetal in origin - consists of a) amnion; b) extra-embryonic mesenchyme; c) cytotrophoblast; d) syncytiotrophoblast
  2. Basal plate - has a fetal derived part (from the cytotrophoblast and syncytiotrophoblast) and a maternal derived part (from the decidua)
126
Q

What divides the placenta into lobules?

A

Placenta septa (inter-cotyledon septa), which arise from the decidua at 4 months gestation

127
Q

What are the possible genotypes of partial molar pregnancies?

A

In order of decreasing frequency:
69XXY
69XXX
69XYY

128
Q

From what are the body cavities - i.e. the peritoneal/pleural/pericardial - derived?

A

Coelomic cavity

129
Q

What are the body cavities lined by?

A

Parietal layer of serous membrane - derived from somatic mesoderm
Visceral layer of serous membrane - derived from splanchnic mesoderm

130
Q

What are the types of ossification?

A

Membranous ossification - development of flat bones

Endochondral ossification - developmental of long bones

131
Q

When does ossification start and end?

A

Weeks 6-25

132
Q

The inner nucleus pulposus is derived from notochord, what is the outer nucleus pulposis derived from?

A

Sclerotomes

133
Q

What are fontanelles?

A

Unossified mesenchyme

134
Q

What does each myotome divide into?

A

Ventral hypomere - muscles of anterior wall

Dorsal epimere - muscles of posterior wall

135
Q

What muscle group does dorsal limb muscle mass give rise to?

A

Extensor group

136
Q

What muscle group does ventral limb muscle mass give rise to?

A

Flexor group

137
Q

What suspends the gut tube in the body of embryo?

A

Dorsal mesentery

138
Q

When does gut herniation occur?

A

Herniates at week 6, and then returns at week 10

139
Q

What is the rotation of the gut from herniation?

A

90 degrees anticlockwise as it herniates into the umbilical cord
Further 180 degrees anticlockwise when it returns to the abdomen

140
Q

Which is associated with chromosomal abnormalities - omphalocele or gastroschisis?

A

Omphalocele

141
Q

What does Meckel’s diverticulum contain?

A

Gastric mucosa

Pancreatic mucosa

142
Q

What does the allantois become?

A

The urachus (which itself becomes the median umbilical ligament)

143
Q

What is the bladder trigone formed from?

A

Mesonephric duct

144
Q

From what is the bladder formed?

A

Urogential sinus

145
Q

From what are Leydig cells derived?

A

Gonad mesenchymal cells

146
Q

From what are granulosa cells derived?

A

Primitive sex cords

147
Q

What is the severity of the ambiguity of gonads classified by?

A

Prader stages 1-5

Part 1 MFSRH 2024 (20 decks)

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