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USMLE Reproductive > Embryology > Flashcards

Embryology Flashcards

1
Q

What is the function of the sonic hedgehog (SHH) gene?

A

Anterior-posterior axis patterning, CNS development

  • SHH protein establishes L and R brain and midline and formation of forebrain
  • Also influences limb development in the anterior to posterior plane (ant=thumb, post=pinky)
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2
Q

Where is the SHH gene located?

A

Zone of polarizing activity at the base of limb buds

- Influences apical ectodermal ridge

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3
Q

What is the function of the Wnt-7 gene?

A
  • Dorsal-ventral axis patterning, limb development (flexors/extensors)
  • Wn7a is key for dorsal development, activates LMX-1 gene and ‘dorsalises’ one side of the mesoderm to give for example the back of the hand
  • Repression of Wnt-7 gives rise to ventral side
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4
Q

Where is the Wnt-7 located?

A

Apical ectodermal ridge at distal end of each limb

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5
Q

What does a mutation in the SHH gene lead to?

A

Holoprosencephaly

- Wholeforebrain, single lobed brain also facial abnormalities (cyclopia, cleft lip)

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6
Q

What is the function of the fibroblast growth facor (FGF)?

A

Limb lengthening (via mitosis of the mesoderm)

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7
Q

Where is the FGF gene located?

A

Apical ectodermal ridge

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8
Q

What is the function of the Homeobox genes?

A

Segmental organisation in cranial-caudal direction, transcription factor coding
- gene is located in multiple locations

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9
Q

What drug used by a mother may cause increased HOX gene expression in the fetus?

A

Isotretinoin (for acne, skin cancer)

- Birth defects

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10
Q

When does hCG secretion begin?

A

Within 1 week of fertilisation - day 6

- Implantation of blastocyst

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11
Q

What embryological tissue sits behind the apical ectodermal ridge?

A

Mesoderm

  • Also influences ectodermal ridge
  • Progress zone forms in mesoderm w. growing cells
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12
Q

A mutation in the HOX genes will lead to what?

A

Abnormal limb formations

  • Polydactyly (extra fingers/toes)
  • Syndactyly (fused fingers/toes)
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13
Q

What is the developing embryo called after the 2 cell stage?

A

Morula

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14
Q

What is the next structure called after the morula?

A

Blastula/blastocyst

- Blastula contains fluid cavity called blastocoel

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15
Q

What are the outer cells of the blastocyst called?

A

Trophoblast

- One side is different from the other (polarised)

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16
Q

What cells produce the blastocoel?

A

Trophoblasts

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17
Q

When does the bilaminar disc form?

A

Within week 2

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18
Q

What structures are formed from the bilaminar disc in week 2?

A
  • Epiblast

- Hypoblast

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19
Q

When does gastrulation (formation of trilaminar embryonic disc) occur?

A

Within week 3

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20
Q

What are the 3 structures formed from gastrulation/trilaminar disc?

A
  • Endoderm
  • Mesoderm
  • Ectoderm
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21
Q

What cells create the primitive streak?

A

epiblast cells invaginate

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22
Q

What does the notochord arise from?

A

Midline mesoderm

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23
Q

What becomes the neural plate (neuroectoderm)?

A

Ectoderm overlying the notochord (notochord induces ectoderm to become neural plate)

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24
Q

What is the neural tube formed by?

A

Neuroectoderm

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25
Q

When does the neural tube close by?

A

Week 4

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26
Q

When does organogenesis roughly occur?

A

Weeks 3-8 (embryonic period)

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27
Q

What period is especially susceptible to teratogens?

A

Weeks 3-8

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28
Q

During what week does the heart begin to beat?

A

Week 4

4 weeks = 4 limbs, 4 heart chambers

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29
Q

When do the upper and lower limb buds begin to form?

A

Week 4

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30
Q

During what week do fetal movements start?

A

Week 6

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31
Q

During what week do the genitalia begin to have male/female characteristics

A

Week 8

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32
Q

The presence of what structure indicates that gastrulation has begun?

A

Primitive streak

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33
Q

What structures are derived from the endoderm?

A
  • Digestive system
  • Liver
  • Pancreas
  • Lungs (inner layers)
  • lower 1/3 of vagina (urogenital sinus)
  • Eustachian tube
  • Thymus
  • Thyroid follicular and parafollicular C cells
  • Parathyroid
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34
Q

What structures are derived from the mesoderm?

A
  • Circulatory system
  • Lungs (epithelial layers)
  • Tracheal cartilage
  • Skeletal system
  • Connective tissue
  • Muscular system
  • Dura mater
  • Upper 2/3s of vagina
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35
Q

What structures are derived from the ectoderm?

A
  • Skin
  • Hair
  • Nails
  • Nervous system
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36
Q

What structures are derived from the surface ectoderm?

A
  • Epidermis
  • Adenohypophysis (from Rathke’s pouch)
  • Lens of eye
  • Epithelial linings of oral cavity
  • Sensory organs of ear
  • olfacotry epithelium
  • Anal canal below pectinate line
  • Parotid, sweat, mammary glands
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37
Q

What is a craniopharyngioma?

A

Benign Rathke’s pouch tumour with cholesterol crystals, calcifications

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38
Q

What structures are derived from the neural tube?

A
  • Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland)
  • Retina
  • Spinal cord
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39
Q

What structures are derived from the neural crest?

A

ELMO PASSES

  • Enterochromaffin cells
  • Leptomeninges (arachnoid, pia)
  • Melanocytes
  • Odontoblasts (teeth)
  • PNS ganglia (cranial, dorsal root, autonomic)
  • Adrenal medulla
  • Schwann cells
  • Spiral membrane (aorticopulmonary membrane)
  • Endocardial cushions (also derived partially from mesoderm)
  • Skull bones
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40
Q

What is the only post-natal derivative of of the notochord?

A
  • Nucleus pulposus of the intervertebral disc
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41
Q

Mesodermal defects are what?

A

VACTERL association

  • Vertebral defects
  • Anal atresia
  • Cardiac defects
  • Tracheo-esophageal fistula
  • Renal defects
  • Limb defects (bone and muscle)
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42
Q

Define agenesis

A

Absent organ due to absent primordial tissue

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43
Q

Define aplasia

A

Absent organ despite presence of primodial tissue

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44
Q

Define hypoplasia

A

Incomplete organ development; primordial tissue present

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45
Q

Define disruption

A

Secondary breakdown of previously normal tissue or structure (e.g amniotic band syndrome)

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46
Q

Define deformation

A

Extrinsic mechanical distortion (e.g congenital torticollis), occurs after embryonic period

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47
Q

Define malformation

A

Intrinsic developmental defect; occurs during embryonic period (wks 3-8 of development)

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48
Q

Define sequence

A

Abnormalities result from a single primary embryological event (e.g oligohydramnios -> Potter sequence)

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49
Q

Define a field defect

A

Disturbance of tissues that develop in a contigous physical space (holoprosencephaly)

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50
Q

What is the inner layer of the chorionic villi called?

A

Cytotrophoblast

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51
Q

What is the purpose of the cytotrophoblast?

A

Makes cells

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52
Q

What is the outer layer of the chorionic villi called?

A

Syncytiotrophoblast

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53
Q

What is the function of the syncytiotrophoblast?

A
  • Synthesises and secretes hormones e.g hCG (structurally similar to LH - stimulates corpus luteum to secrete progesterone during first trimester)
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54
Q

What does the syncytiotrophoblast lack which decreases chance of attack from maternal immune system?

A

MHC I

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55
Q

What is the decidua basalis derived from?

A

Mother’s endometrium (maternal blood in lacunae)

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56
Q

What is the amniotic fluid composed of?

A

Fetal urine (mainly) and fetal lung liquid

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57
Q

What are possible causes of polyhydramnios?

A
  • Idiopathic
  • Fetal malformations (esophageal/duodenal atresia, anencephaly)
  • Diabetes in mother
  • Fetal anemia
  • Multiple gestations
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58
Q

Oligohydramnios (too little amniotic fluid) is associated with what other conditions?

A
  • Placental insufficiency
  • Bilateral renal agenesis
  • Posterior urethral valves (males)
  • May cause Potter sequence
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59
Q

What is the most common type of monozygotic (identical) twin?

A

Monochorionic diamniotic (~75%)

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60
Q

What is the chorion?

A

Outermost layer of the embryo

61
Q

Dizygotic vs monozygotic twins - what is more common?

A 
Dizygotic = 66%
Monozygotic = 33%
62
Q

What are the different types of monozygotic twins?

A
  • Dichorionic diamniotic (25%)
  • Monochorionic diamniotic (75%)
  • Monochorionic monoamniotic (rare)
  • Conjoined monochorionic monoamniotic
63
Q

When does splitting occur in Dichorionic diamniotic monozygotic twins?

A

between 0-4 days from fertilisation

- at the 2 cell stage

64
Q

When does splitting occur in monochorionic diamniotic twins?

A

4-8 days (most common)

- At the morula stage (before blastocyst formation)

65
Q

When does splitting occur in monochorionic monoamniotic twins?

A

8-12 days
- At the stage of the blastocyst (before embryonic disc forms)

At > 13 days twins will be conjoined

66
Q

In what type of twins can twin-twin transfusion syndrome occur?

A

Monochorionic twin gestations

67
Q

Describe twin-twin transfusion syndrome

A

Unbalanced vascular connections between twins in shared placenta -> net blood flow from one twin to another

  • Donor twin will have hypovolemia and oligohydramnios (stuck twin appearence)
  • Recipient twin will have hypervolemia and polyhydramnios
68
Q

Where do the umbilical arteries come from?

A

Fetal umbilical arteries

- Return deoxygenated blood to placenta

69
Q

Where does the umbilical vein carrying oxygenated blood from the mother to the fetus drain?

A

Into the IVC via the liver or ductus venosus

70
Q

What is contained inside the amnion?

A

Wharton jelly

  • 2 umbilical arteries (deoxygenated)
  • Umbilical vein
  • Alantois
71
Q

What does the allantois derive from?

A

Hindgut

72
Q

What does the urachus derive from?

A

The allantois (which is derived from the hindgut and extends into the urogenital sinus and becomes the urachus)

73
Q

What are the complications of the urachus failing to involute?

A
  • Infection, malignancy (adenocarcinoma)
  • Patent urachus
  • Urachal cyst
  • Vesicouracal diverticulum
74
Q

What is a patent urachus due to?

A

Total failure of urachus to obliterate

- Urine discharge from umbilicus

75
Q

What is a urachal cyst due to? and what can it result in?

A

Partial failure of urachus to obliterate

  • Fluid filled cavity lined with uroepithelium between umbilicus and bladder
  • May become infected and present as painful mass below umbilicus
76
Q

What is a vesicourachal diverticulum?

A

Slight failure of urachus to obliterate

- Outpouching of bladder

77
Q

What is the obliterated urachus represented by?

A

Median umbilical ligament - covered by median umbilical fold of the peritoneum

78
Q

What is the function of the vitelline duct?

A

Connects yolk sac to midgut lumen

79
Q

When does the vitelline duct obliterate?

A

Week 7 of development

80
Q

What does a patent vitelline duct result in?

A

Meconium discharge from umbilicus

81
Q

What does a vitelline cyst increase the risk of?

A

Volvulus

82
Q

What part of the SI is outpouched in Meckel diverticulum?

A

There is a slight failure of the vitelline duct to obliterate
- Ileum outpouches (true diverticulum)

83
Q

How can Meckel diverticulum present?

A
  • Usually asymptomatic
  • May have heterotopic [abnormal tissue] gastric and/or pancreatic tissue
  • Melena
  • Hematochezia
  • Abdo pain
84
Q

What are the 3 layers of the pharyngeal apparatus?

A

Outside to inside (CAP)

  • Pharngeal cleft
  • Pharyngeal arches
  • Pharyngeal pouches
85
Q

What are the layers of the pharyngeal apparatus derived from?

A
  • Clefts = Ectoderm
  • Arches = Mesoderm + Neural crest
  • Pouches = Endoderm
86
Q

What is the vitelline duct also known as?

A

Omphalomesenteric duct

87
Q

What are the pharyngeal clefts, arches and pouches also known as?

A

Branchial clefts, arches, pouches

88
Q

What does the 1st pharyngeal cleft develop into?

A

External auditory meatus

89
Q

What do the 2nd through 4th clefts form?

A

Temporary cervical sinuses

90
Q

What are the temporary cervical sinuses (2nd - 4th clefts) obliterated by?

A

Proliferation of 2nd arch mesenchyme

91
Q

What is a pharyngeal cleft cyst due to?

A

Persistent cervical sinus (2nd-4th clefts)

92
Q

How can you differentiate between a pharyngeal cleft cyst from a thyroglossal duct cyst?

A
  • Pharyngeal cleft cyst - lateral neck mass anterior to sternocleidomastoid muscle which does move with swallowing
  • Thyroglossal duct cyst does move with swallowing
93
Q

What cartilage/bones are derived from the 1st pharyngeal arch?

A
  • Maxillary process (maxilla, zygomatic bone)

- Mandibular process (meckel cartilage, mandible, malleus and incus, spenomandibular ligament)

94
Q

What muscles are derived from the 1st pharyngeal arch?

A

Muscles of mastication
- Temporalis, masseter, lateral and medial pterygoids,

  • Mylohyoid
  • Ant belly of digastric
  • Tensor tympani
  • Ant 2/3s of tongue
  • Tensor veli palatini
95
Q

What nerve is derived from the 1st pharyngeal arch?

A

CN V3 (chew)

96
Q

What cartilage/bones are derived from the 2nd pharyngeal arch?

A

Reichert cartilage

  • Stapes
  • Styloid process
  • Lesser horn of hyoid
  • Stylohyoid ligament
97
Q

What muscles are derived from the 2nd pharyngeal arch?

A

Muscles of facial expression

  • Stapedius
  • Stylohyoid
  • Platysma
  • Posterior belly of digastric
98
Q

What nerve is derived from the 2nd pharyngeal arch?

A

CN VII (smile)

99
Q

What cartilage/bones are derived from the 3rd pharyngeal arch?

A

Greater horn of hyoid

100
Q

What muscle is derived from the 3rd pharyngeal arch?

A

Stylopharyngeus

101
Q

What nerve is derived from the 3rd pharyngeal arch?

A

CN IX (stylo-pharyngeus)

102
Q

What cartilage/bones are derived from the 4th and 6th pharyngeal arches?

A
  • Arytenoids
  • Cricoid
  • Corniculate
  • Cuneiform
  • Thyroid
    ACCCT
103
Q

What muscles are derived from the 4th pharyngeal arch?

A
  • Most pharyngeal constrictors
  • Cricothyroid
  • Levator veli palatini
104
Q

What muscles are derived from the 6th pharyngeal arch?

A

All intrinsic muscles of the larynx except cricothyroid

105
Q

What nerve is derived from the 4th arch?

A

CN X

- superior laryngeal branch

106
Q

What nerve is derived from the 6th arch?

A

CN X

- Recurrent/inferior laryngeal branch

107
Q

What forms the posterior 1/3 of the tongue?

A

Arches 3 and 4

108
Q

What are sensory and motor nerves derived from?

A

Not pharyngeal arch derivatives

  • Grow into the arches instead
  • Sensory - Neural crest
  • Motor - Neuroectoderm
109
Q

What structures are derived from the 1st pharyngeal pouch?

A
  • Middle ear cavity
  • Eustachian tube
  • Mastoid air cells
110
Q

What structure is derived from the 2nd pharyngeal pouch?

A

Epithelial lining of palatine tonsil

111
Q

What structure is derived from the 3rd pharyngeal pouch?

A
  • Dorsal wings -> inferior parathyroids
  • Ventral wings -> thymus

Structures from 3rd pouch end up below those of the 4th

112
Q

What structure is derived from the 4th pharyngeal pouch?

A
  • Dorsal wings -> Superior parathyroids
  • Ventral wings -> ultimopharyngeal body -> parafollicular (C) cells of thyroid

‘Para4licullar’

113
Q

What is cleft lip due to?

A

Failure of fusion of the maxillary and merged medial nasal processes (formation of primary palate)

114
Q

What is cleft palate due to?

A

Failure of fusion of the 2 lateral palatine shelves or failure of fusion of lateral palatine shelf with the nasal septum and/or primary palate (formation of secondary palate)

115
Q

What artery is derived from the first pharyngeal arch?

A

Portion of maxillary artery

116
Q

What artery is derived from the 3rd pharyngeal arch?

A
  • Common carotid

- Proximal internal carotid

117
Q

What arteries does the 4th arch give rise to?

A
  • Left: aortic arch

- Right: proximal right subclavian artery

118
Q

What arteries does the 6th arch give rise to?

A
  • Left: proximal pulmonary artery AND ductus arteriosus

- Right: proximal pulmonary artery

119
Q

What arch is affected in Treacher Collins syndrome?

A

1st arch

  • Failure of neural crest cell migration
  • Underdeveloped facial bones (small mandible, jaw, absent ears, retraction of tongue)
  • May lead to difficulty breathing
120
Q

What is the philtrum?

A

The groove which exists between the upper lip and nose

- If nasal prominances are not fused normally cleft lip may develop

121
Q

The release of Mullerian inhibitory factor (antimullerian inhibitory factor) from sertoli cells suppresses the development of what?

A

Paramesonephric ducts (becomes fallopian tubes, uterus, upper portion of vagina)

122
Q

What does the SRY gene on the Y chromosome produce?

A

Testis-determining factor -> testes development

123
Q

Androgens from Leydig cells stimulate the development of what?

A

Mesonephric (Wolffian) ducts

  • Male internal structures
  • SEED - Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens
124
Q

What is the female remnant of the Mesonephric (Wolffian) duct?

A

Gartner duct

125
Q

What is the male remnant of the paramesonephric (Mullerian) duct?

A

Appendix testis

126
Q

What is the lower portion of the vagina derived from?

A

Urogenital sinus

127
Q

Mullerian agenesis presents with what?

A
  • Primary amenorrhea
  • Fully developed secondary sexual characteristics (functional ovaries)
  • Fallopian tubes, uterus, upper portion of vagina do not form
128
Q

What are the types of gonads that are produced when there is an absence of Sertoli cells or Mullerian inhibitory factor?

A

Streak gonads (development of both male and female genitalia)

129
Q

What are the different types of uterine (Mullerian duct) anomalies?

A
  • Septate uterus
  • Bicornuate uterus
  • Uterus didelphys
130
Q

What is a septate uterus due to?

A

Incomplete resorption of the septum

131
Q

What is the septate uterus treated with?

A

Septoplasty

132
Q

What is a bicornuate uterus due to?

A

Incomplete fusion of paramesonphric (Mullerian) ducts

133
Q

What is a uterus didelphys due to?

A

Complete failure of fusion of paramesonphric (Mullerian) ducts

134
Q

What are the 2 types of abnormal openings of the urethra?

A

Hypospadias (Ventral/underside) (more common)

Epispadias (dorsal)

135
Q

What kind of uterine (MUllerian duct) anomalie contains a double uterus, cervix and vagina?

A

Didelphys

136
Q

What is hypospadias associated with?

A
  • Inguinal hernia
  • Cryptochordism
  • Chordee (up/down bend of penis)
  • 5-alpha reductase deficiency
137
Q

What is epispadias associated with?

A

Exstrophy of the bladder

138
Q

What is hypospadias due to?

A

Failure of urethral folds to fuse

139
Q

What is epispadias due to?

A

Faulty positioning of genital tubercle

140
Q

What is epispadias associated with?

A

Exstrophy of the bladder

141
Q

The genital tubercle becomes what?

A 
Men
- Glans
- Corpus cavernosum/spongiosum
Women 
- Clitoris 
- Vestibular bulbs
142
Q

The urogenital sinus becomes what in men?

A
  • Bulbourethral glands (of Cowper)

- Prostate gland

143
Q

The urogenital sinus becomes what in women?

A
  • Greater vestibular glands (of Bartholin)

- Urethral and paraurethral glands (of Skene)

144
Q

What do the urogenital folds become?

A

Men
- Ventral shaft of penis (penile urethra)
Women
- Labia minora

145
Q

What does the labiosacral swelling become?

A

Men
- Scrotum
Women
- Labia majora

146
Q

What is the female remnant of the gubernaculum (anchors testes in men)?

A
  • Ovarian ligament

- Round ligament of uterus

147
Q

What is the gubernaculum made of?

A

Band of fibrous tissue

148
Q

What is the processus vaginalis made of?

A

It is an evagination of the peritoneum

149
Q

What does the processus vaginalis form in men (obliterated in women)?

A

Tunica vaginalis

- Persistent patent processus vaginalis may result in hydrocele

USMLE Reproductive (14 decks)

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