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USMLE Reproductive > Embryology > Flashcards

Embryology Flashcards

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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
When does the neural tube close by?
Week 4
26
When does organogenesis roughly occur?
Weeks 3-8 (embryonic period)
27
What period is especially susceptible to teratogens?
Weeks 3-8
28
During what week does the heart begin to beat?
Week 4 | 4 weeks = 4 limbs, 4 heart chambers
29
When do the upper and lower limb buds begin to form?
Week 4
30
During what week do fetal movements start?
Week 6
31
During what week do the genitalia begin to have male/female characteristics
Week 8
32
The presence of what structure indicates that gastrulation has begun?
Primitive streak
33
What structures are derived from the endoderm?
- Digestive system - Liver - Pancreas - Lungs (inner layers) - lower 1/3 of vagina (urogenital sinus) - Eustachian tube - Thymus - Thyroid follicular and parafollicular C cells - Parathyroid
34
What structures are derived from the mesoderm?
- Circulatory system - Lungs (epithelial layers) - Tracheal cartilage - Skeletal system - Connective tissue - Muscular system - Dura mater - Upper 2/3s of vagina
35
What structures are derived from the ectoderm?
- Skin - Hair - Nails - Nervous system
36
What structures are derived from the surface ectoderm?
- 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
37
What is a craniopharyngioma?
Benign Rathke's pouch tumour with cholesterol crystals, calcifications
38
What structures are derived from the neural tube?
- Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland) - Retina - Spinal cord
39
What structures are derived from the neural crest?
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
40
What is the only post-natal derivative of of the notochord?
- Nucleus pulposus of the intervertebral disc
41
Mesodermal defects are what?
VACTERL association - Vertebral defects - Anal atresia - Cardiac defects - Tracheo-esophageal fistula - Renal defects - Limb defects (bone and muscle)
42
Define agenesis
Absent organ due to absent primordial tissue
43
Define aplasia
Absent organ despite presence of primodial tissue
44
Define hypoplasia
Incomplete organ development; primordial tissue present
45
Define disruption
Secondary breakdown of previously normal tissue or structure (e.g amniotic band syndrome)
46
Define deformation
Extrinsic mechanical distortion (e.g congenital torticollis), occurs after embryonic period
47
Define malformation
Intrinsic developmental defect; occurs during embryonic period (wks 3-8 of development)
48
Define sequence
Abnormalities result from a single primary embryological event (e.g oligohydramnios -> Potter sequence)
49
Define a field defect
Disturbance of tissues that develop in a contigous physical space (holoprosencephaly)
50
What is the inner layer of the chorionic villi called?
Cytotrophoblast
51
What is the purpose of the cytotrophoblast?
Makes cells
52
What is the outer layer of the chorionic villi called?
Syncytiotrophoblast
53
What is the function of the syncytiotrophoblast?
- Synthesises and secretes hormones e.g hCG (structurally similar to LH - stimulates corpus luteum to secrete progesterone during first trimester)
54
What does the syncytiotrophoblast lack which decreases chance of attack from maternal immune system?
MHC I
55
What is the decidua basalis derived from?
Mother's endometrium (maternal blood in lacunae)
56
What is the amniotic fluid composed of?
Fetal urine (mainly) and fetal lung liquid
57
What are possible causes of polyhydramnios?
- Idiopathic - Fetal malformations (esophageal/duodenal atresia, anencephaly) - Diabetes in mother - Fetal anemia - Multiple gestations
58
Oligohydramnios (too little amniotic fluid) is associated with what other conditions?
- Placental insufficiency - Bilateral renal agenesis - Posterior urethral valves (males) - May cause Potter sequence
59
What is the most common type of monozygotic (identical) twin?
Monochorionic diamniotic (~75%)
60
What is the chorion?
Outermost layer of the embryo
61
Dizygotic vs monozygotic twins - what is more common?
``` Dizygotic = 66% Monozygotic = 33% ```
62
What are the different types of monozygotic twins?
- Dichorionic diamniotic (25%) - Monochorionic diamniotic (75%) - Monochorionic monoamniotic (rare) - Conjoined monochorionic monoamniotic
63
When does splitting occur in Dichorionic diamniotic monozygotic twins?
between 0-4 days from fertilisation | - at the 2 cell stage
64
When does splitting occur in monochorionic diamniotic twins?
4-8 days (most common) | - At the morula stage (before blastocyst formation)
65
When does splitting occur in monochorionic monoamniotic twins?
8-12 days - At the stage of the blastocyst (before embryonic disc forms) At > 13 days twins will be conjoined
66
In what type of twins can twin-twin transfusion syndrome occur?
Monochorionic twin gestations
67
Describe twin-twin transfusion syndrome
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
Where do the umbilical arteries come from?
Fetal umbilical arteries | - Return deoxygenated blood to placenta
69
Where does the umbilical vein carrying oxygenated blood from the mother to the fetus drain?
Into the IVC via the liver or ductus venosus
70
What is contained inside the amnion?
Wharton jelly - 2 umbilical arteries (deoxygenated) - Umbilical vein - Alantois
71
What does the allantois derive from?
Hindgut
72
What does the urachus derive from?
The allantois (which is derived from the hindgut and extends into the urogenital sinus and becomes the urachus)
73
What are the complications of the urachus failing to involute?
- Infection, malignancy (adenocarcinoma) - Patent urachus - Urachal cyst - Vesicouracal diverticulum
74
What is a patent urachus due to?
Total failure of urachus to obliterate | - Urine discharge from umbilicus
75
What is a urachal cyst due to? and what can it result in?
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
What is a vesicourachal diverticulum?
Slight failure of urachus to obliterate | - Outpouching of bladder
77
What is the obliterated urachus represented by?
Median umbilical ligament - covered by median umbilical fold of the peritoneum
78
What is the function of the vitelline duct?
Connects yolk sac to midgut lumen
79
When does the vitelline duct obliterate?
Week 7 of development
80
What does a patent vitelline duct result in?
Meconium discharge from umbilicus
81
What does a vitelline cyst increase the risk of?
Volvulus
82
What part of the SI is outpouched in Meckel diverticulum?
There is a slight failure of the vitelline duct to obliterate - Ileum outpouches (true diverticulum)
83
How can Meckel diverticulum present?
- Usually asymptomatic - May have heterotopic [abnormal tissue] gastric and/or pancreatic tissue - Melena - Hematochezia - Abdo pain
84
What are the 3 layers of the pharyngeal apparatus?
Outside to inside (CAP) - Pharngeal cleft - Pharyngeal arches - Pharyngeal pouches
85
What are the layers of the pharyngeal apparatus derived from?
- Clefts = Ectoderm - Arches = Mesoderm + Neural crest - Pouches = Endoderm
86
What is the vitelline duct also known as?
Omphalomesenteric duct
87
What are the pharyngeal clefts, arches and pouches also known as?
Branchial clefts, arches, pouches
88
What does the 1st pharyngeal cleft develop into?
External auditory meatus
89
What do the 2nd through 4th clefts form?
Temporary cervical sinuses
90
What are the temporary cervical sinuses (2nd - 4th clefts) obliterated by?
Proliferation of 2nd arch mesenchyme
91
What is a pharyngeal cleft cyst due to?
Persistent cervical sinus (2nd-4th clefts)
92
How can you differentiate between a pharyngeal cleft cyst from a thyroglossal duct cyst?
- Pharyngeal cleft cyst - lateral neck mass anterior to sternocleidomastoid muscle which does move with swallowing - Thyroglossal duct cyst does move with swallowing
93
What cartilage/bones are derived from the 1st pharyngeal arch?
- Maxillary process (maxilla, zygomatic bone) | - Mandibular process (meckel cartilage, mandible, malleus and incus, spenomandibular ligament)
94
What muscles are derived from the 1st pharyngeal arch?
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
What nerve is derived from the 1st pharyngeal arch?
CN V3 (chew)
96
What cartilage/bones are derived from the 2nd pharyngeal arch?
Reichert cartilage - Stapes - Styloid process - Lesser horn of hyoid - Stylohyoid ligament
97
What muscles are derived from the 2nd pharyngeal arch?
Muscles of facial expression - Stapedius - Stylohyoid - Platysma - Posterior belly of digastric
98
What nerve is derived from the 2nd pharyngeal arch?
CN VII (smile)
99
What cartilage/bones are derived from the 3rd pharyngeal arch?
Greater horn of hyoid
100
What muscle is derived from the 3rd pharyngeal arch?
Stylopharyngeus
101
What nerve is derived from the 3rd pharyngeal arch?
CN IX (stylo-pharyngeus)
102
What cartilage/bones are derived from the 4th and 6th pharyngeal arches?
- Arytenoids - Cricoid - Corniculate - Cuneiform - Thyroid ACCCT
103
What muscles are derived from the 4th pharyngeal arch?
- Most pharyngeal constrictors - Cricothyroid - Levator veli palatini
104
What muscles are derived from the 6th pharyngeal arch?
All intrinsic muscles of the larynx except cricothyroid
105
What nerve is derived from the 4th arch?
CN X | - superior laryngeal branch
106
What nerve is derived from the 6th arch?
CN X | - Recurrent/inferior laryngeal branch
107
What forms the posterior 1/3 of the tongue?
Arches 3 and 4
108
What are sensory and motor nerves derived from?
Not pharyngeal arch derivatives - Grow into the arches instead - Sensory - Neural crest - Motor - Neuroectoderm
109
What structures are derived from the 1st pharyngeal pouch?
- Middle ear cavity - Eustachian tube - Mastoid air cells
110
What structure is derived from the 2nd pharyngeal pouch?
Epithelial lining of palatine tonsil
111
What structure is derived from the 3rd pharyngeal pouch?
- Dorsal wings -> inferior parathyroids - Ventral wings -> thymus Structures from 3rd pouch end up below those of the 4th
112
What structure is derived from the 4th pharyngeal pouch?
- Dorsal wings -> Superior parathyroids - Ventral wings -> ultimopharyngeal body -> parafollicular (C) cells of thyroid 'Para4licullar'
113
What is cleft lip due to?
Failure of fusion of the maxillary and merged medial nasal processes (formation of primary palate)
114
What is cleft palate due to?
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
What artery is derived from the first pharyngeal arch?
Portion of maxillary artery
116
What artery is derived from the 3rd pharyngeal arch?
- Common carotid | - Proximal internal carotid
117
What arteries does the 4th arch give rise to?
- Left: aortic arch | - Right: proximal right subclavian artery
118
What arteries does the 6th arch give rise to?
- Left: proximal pulmonary artery AND ductus arteriosus | - Right: proximal pulmonary artery
119
What arch is affected in Treacher Collins syndrome?
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
What is the philtrum?
The groove which exists between the upper lip and nose | - If nasal prominances are not fused normally cleft lip may develop
121
The release of Mullerian inhibitory factor (antimullerian inhibitory factor) from sertoli cells suppresses the development of what?
Paramesonephric ducts (becomes fallopian tubes, uterus, upper portion of vagina)
122
What does the SRY gene on the Y chromosome produce?
Testis-determining factor -> testes development
123
Androgens from Leydig cells stimulate the development of what?
Mesonephric (Wolffian) ducts - Male internal structures - SEED - Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens
124
What is the female remnant of the Mesonephric (Wolffian) duct?
Gartner duct
125
What is the male remnant of the paramesonephric (Mullerian) duct?
Appendix testis
126
What is the lower portion of the vagina derived from?
Urogenital sinus
127
Mullerian agenesis presents with what?
- Primary amenorrhea - Fully developed secondary sexual characteristics (functional ovaries) - Fallopian tubes, uterus, upper portion of vagina do not form
128
What are the types of gonads that are produced when there is an absence of Sertoli cells or Mullerian inhibitory factor?
Streak gonads (development of both male and female genitalia)
129
What are the different types of uterine (Mullerian duct) anomalies?
- Septate uterus - Bicornuate uterus - Uterus didelphys
130
What is a septate uterus due to?
Incomplete resorption of the septum
131
What is the septate uterus treated with?
Septoplasty
132
What is a bicornuate uterus due to?
Incomplete fusion of paramesonphric (Mullerian) ducts
133
What is a uterus didelphys due to?
Complete failure of fusion of paramesonphric (Mullerian) ducts
134
What are the 2 types of abnormal openings of the urethra?
Hypospadias (Ventral/underside) (more common) Epispadias (dorsal)
135
What kind of uterine (MUllerian duct) anomalie contains a double uterus, cervix and vagina?
Didelphys
136
What is hypospadias associated with?
- Inguinal hernia - Cryptochordism - Chordee (up/down bend of penis) - 5-alpha reductase deficiency
137
What is epispadias associated with?
Exstrophy of the bladder
138
What is hypospadias due to?
Failure of urethral folds to fuse
139
What is epispadias due to?
Faulty positioning of genital tubercle
140
What is epispadias associated with?
Exstrophy of the bladder
141
The genital tubercle becomes what?
``` Men - Glans - Corpus cavernosum/spongiosum Women - Clitoris - Vestibular bulbs ```
142
The urogenital sinus becomes what in men?
- Bulbourethral glands (of Cowper) | - Prostate gland
143
The urogenital sinus becomes what in women?
- Greater vestibular glands (of Bartholin) | - Urethral and paraurethral glands (of Skene)
144
What do the urogenital folds become?
Men - Ventral shaft of penis (penile urethra) Women - Labia minora
145
What does the labiosacral swelling become?
Men - Scrotum Women - Labia majora
146
What is the female remnant of the gubernaculum (anchors testes in men)?
- Ovarian ligament | - Round ligament of uterus
147
What is the gubernaculum made of?
Band of fibrous tissue
148
What is the processus vaginalis made of?
It is an evagination of the peritoneum
149
What does the processus vaginalis form in men (obliterated in women)?
Tunica vaginalis | - Persistent patent processus vaginalis may result in hydrocele

USMLE Reproductive (14 decks)

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