Embryology Flashcards
1
Q
How many oocytes does a female 20 week foetus have
A
6-7 million
2
Q
How many oocytes does a female have at birth?
A
1-2 million
3
Q
How many oocytes does a female have at puberty?
A
300,000
4
Q
When after fertilisation does the morula appear?
A
Day 4
5
Q
When after fertilisation does the blastocyst appear?
A
Day 5
6
Q
From what do the primordial germ cells arise?
A
Wall of the yolk sac in the 2nd week of development
7
Q
What do primordial germ cells form in females?
A
Oogonia
8
Q
What do primordial germ cells form in males?
A
Spermatogonia
9
Q
When do the primordial germ cells migrate to occupy the gonadal ridges?
A
Week 6 of development
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
11
Q
At what stage of meiosis are oogonia suspended in from birth until puberty?
A
Prophase I
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
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
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
15
Q
How soon after ovulation does fertilisation take place?
A
12-24 hours after ovulation
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
17
Q
What process do sperm need to undergo to be capable of penetrating the ovum?
A
Capacitation
18
Q
What happens during capacitation?
A
Loss of glycoprotein and cholesterol from the acrosomal membrane by secretions from the cervix and uterine tube
19
Q
How do sperm penetrate the corona radiata?
A
By the acrosomal reaction, releasing hyaluronidase
20
Q
How do sperm penetrate the zona pellucida?
A
Also by release of the acrosomal enzymes - esterases, acrosin and neuraminidase
21
Q
What is the zona reaction?
A
When the sperm binds with the zona pellucida
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
23
Q
What causes the zona reaction?
A
The release of lysosomal enzymes from the cortical granules into the privitelline space
24
Q
When does the oocyte resume its second meiotic division?
A
Soon after entry of the spermatozoa
25
How do you know that the second meiotic division has occurred?
The 2nd polar body is visible down the microscope
26
What is the zygote?
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
27
What are the components of the blastocyst at day 5?
```
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
```
28
How many days after fertilisation does implantation occur?
Approx. 6
29
When does the trophoblast differentiate, and what does it differentiate into?
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)
30
When does the embryoblast/inner cells mass of the blastocyst differentiate, and what into?
Also week 2
| 2 layers - the epiblast and the hypoblast. These form the bilaminar disc
31
Where does the amniotic cavity form?
In the epiblast layer, developing at approx. 8 weeks. The amniotic cavity is filled with amniotic fluid.
32
What does the hypoblast (of the bilaminar disc) develop into?
The exocoelomic membrane is derived from the hypoblast and forms the primary yolk sac.
33
What is the state of the trophoblast by day 12?
The syncytiotrophoblast have formed lacunae which are responsible for derive ng nutritional support from the endometrium.
34
What is the state of the trophoblast by day 13?
The cytotrophoblast forms primary chronionic villi - finger like protrusions into the lacunae of the syncytiotrophoblast.
35
When does the primary yolk sac become the secondary yolk sac?
Day 13
36
What is the extra-embryonic mesoderm?
A connecting stalk between the embryo and cytotrophoblast. It is the forerunner of the umbilical cord.
37
What is the state of the trophoblast by day 14?
The syncytiotrophoblast begins to produce Beta-hCG to maintain the corpus luteum so that the corpus luteum can maintain the thickness of the endometrium.
38
What is the name of the process by which three germ layers are formed?
Gastrulation
39
What are the names of the three germ layers?
Epiblast ---> 1) Ectoderm
From the ectoderm you also get the 2) Mesoderm
Hypoblast ---> 3) Endoderm
40
When do the three germ layers develop?
3rd week
41
What forms from the ectoderm?
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
42
What forms from the mesoderm?
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
43
What forms from the endoderm?
Gut tube and liver
44
After the development of the 3rd germ layer - i.e. the mesoderm - at what points do the ectoderm and endoderm remain in contact?
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
45
What is the primitive streak?
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
46
Where is the primitive node?
At the cephalic end of the primitive streak
47
What develops from the cells of the primitive node?
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
48
What is the name of the process that forms the brain and spinal cord?
Neurulation
49
What are the stages of neurulation?
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
50
Where do neural crests form?
At the edge of the neural tube where the neuro-ectoderm is continues with the surface ectoderm
51
What is the connection between the yolk sac and the gut?
Vitello-intestinal (vitelline) duct.
52
Which develops first, the urinary system or the genital system?
Urinary BEFORE genital
53
Where do the urogenital ridges develop?
In the mesoderm, either side of the aorta
54
What are the different parts of the urogenital ridges?
Nephrogenic cord - develops into urinary system
| Gonadal ridge - develops into genital system
55
What forms from endoderm?
```
Stomach
Intestines (mucosal layers)
Colon (mucosal layers)
Liver
Pancreas
Bladder
Epithelial parts of trachea
Lungs
Pharynx
Thyroid
Parathyroid
```
56
What forms from intermediate meosderm?
Kidneys
| Gonads
57
What forms from paraxial mesoderm?
Cartilage
Skeletal muscle
Dermis
58
What forms from lateral plate mesoderm?
Circulatory system (inc heart) and
Spleen
Gut wall
59
What forms from neural crest of ectoderm?
```
Peripheral nervous system
Adrenal medulla
Melanocytes
Facial cartilage
Dentin of teeth
```
60
What forms from neural tube of ectoderm?
```
Brain
Spinal cord
Posterior pituitary
Motor neurons
Retina.
Anterior pituitary
```
61
What is the incidence of Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome?
1/5000
62
What are the 2 conditions that cause a congenital absence of the uterus?
1) Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome
| 2) CAIS AKA Testicular Feminisation Syndrome
63
How do you differentiate between Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome and CAIS AKA Testicular Feminisation Syndrome?
Mullerian Agenesis AKA Rokitansky-Kuster-Hauser syndrome = normal hormone levels
CAIS AKA Testicular Feminisation Syndrome = low E2
64
What is ootidogenesis?
The 2 meiotic divisions the primary oocytes undergo to become ootids
65
What is oocytogenesis?
Growth and maturation of oogonium to primary oocytes
66
What are Ladd's bands?
When intestinal malrotation causes fibrous bands that fix the caecum in the right upper quadrant
67
How is the foregut innervated?
T5-T9
68
How is the midgut innervated?
T10-T11
69
How is the hindgut innervated?
T12-L1
70
What is the most important chemical for maintaining a patent DA during pregnancy?
PGE2
71
Where is PGE2 produced in pregnancy?
Placenta
72
When does meconium first appear in the terminal ileum?
10-16 weeks gestation
73
What does the corpus luteum produce?
1) Progesterone
2) Estradiol
3) Inhibin A
74
What is the maturation process for sperm?
Spermatocytogenesis - spermatagonium to primary spermatocytes
75
What is spermatidogenesis?
When spermatocytes undergo 2 meiotic divisions to become spermatids
76
What is spermiogenesis?
When spermatids differentiate into spermatazoa
77
What is the life span of the corpus luteum?
14-16 days
78
What is a Gartner's duct?
A cystic structure found lateral to the vagina
| It's embryological origin is the mesonephric duct
79
From what does the intraembryonic coelom form?
Lateral plate mesoderm
80
What is the canal of Nuck associated with?
Round ligament
81
At what stage does implantation occur?
7-9 days, i.e. when the embryo is a blastocyst
82
What condition occurs is the yolk sac persists?
Meckel's diverticulum
83
From what structure do the kidneys and renal tract develop?
Metanephros
84
From what germ layer do the autonomic ganglia develop from?
Neural crest
85
A bicornate uterus results from a failure of fusion of what?
Paramesonephric ducts
86
From what germ layer are the ureters derived?
Mesoderm
87
From where do primordial germ cells originate?
Yolk sac
88
From which embryological structure does the penis develop?
Genital tubercle
89
What develops first, the urinary system or genital system?
Urinary system
90
What are the components of the urinary system?
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
What are the 2 parts of the metanephros?
1. Ureteric bud
2. Metanephric mesoderm
92
What is derived from the ureteric bud?
1. Collecting duct
2. Minor and major calyx
3. Renal pelvis
4. Ureter
93
What is derived from the metanephric mesoderm?
1. Renal glomerulus
2. Renal capsule
3. PCT
4. Loop of Henle
5. DCT
94
From what embryological structure are the bladder, urethra, urethral/paraurethral glands and vagina derived?
Urogenital sinus
95
From what embryological structure are the labia minora and ventral aspect of the penis derived?
Urethral folds
96
From what embryological structure are the labia majora and scrotum derived?
Genital swellings
97
From what embryological structure are the ovarian and round ligament derived?
Gubernaculum
98
As the kidney ascends from the pelvis, by how many degrees does it rotate?
90 degrees
99
In whom, and on which side is renal agenesis more common?
In males, and on the L side
100
What is renal agenesis caused by?
When the ureteric bud fails to induce the metanephric mesoderm
101
When does duplication of the ureter occur?
It occurs as a result of early splitting from the ureteric bud
102
Where is the SRY gene located?
The short arm of chromosome Y - Yp11
103
From what does a Gartner's cyst derived (found in the uterus/vagina)?
When the caudal part of the mesonephric ducts persists
104
What is the time frame for the journey the testis make into the scrotum?
Week 12 - testis reach the inguinal canal
Week 28 - testis migrate through the inguinal canal
Week 33 - testis reach the scrotum
105
What are the fascial layers of the testis, and from what are they derived?
Internal spermatic fascia - from transversalis fascia
Cremesteric fascia - from internal oblique
External spermatic fascia - from external oblique
106
When does the primitive gut form?
Week 4
107
What structures arise from the foregut?
```
Oesophagus
Trachea and lung buds
Stomach
Proximal duodenum
Liver, biliary tree, pancreas
```
108
What structures arise from the midgut?
Distal duodenum
Small intestine
Caecum and appendix
Ascending colon and two thirds of the transverse colon
109
What structures arise from the hindgut?
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
What does the pectinate line (also called the white line) denote?
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
What does the umbilical vein form after birth?
Ligamentum teres hepatis
112
What does the ductus venosus form after birth?
Ligamentum venosum
113
What develops from the vitelline vein?
Hepatic veins
Inferior part of IVC
Superior mesenteric vein
Portal vein
114
From what does the blastocyst hatch?
Zona pellucida
115
At what gestation does a conceptus become a fetus?
9 weeks
116
How many cells are there in a blastocyst?
70-100 cells
117
When does the buccopharyngeal membrane breakdown?
Week 4
118
When does the cloacal membrane breakdown?
Week 7
119
From when is the first heartbeat noted?
Day 21
120
When does embryo folding occur?
Days 21-24
121
From when are spontaneous limb movements first noticeable on USS?
Week 7
122
What is the maximum number of somites, and what is their rate of production?
Max 42-44 pairs
| Rate of 3 pairs/day
123
What are the layers of the decidua?
Basalis
Capsularis
Parietalis
124
What is the name for the changes in the endometrial glands as a result of progesterone?
Arias-Stella
125
What are the 2 units of the placenta?
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
What divides the placenta into lobules?
Placenta septa (inter-cotyledon septa), which arise from the decidua at 4 months gestation
127
What are the possible genotypes of partial molar pregnancies?
In order of decreasing frequency:
69XXY
69XXX
69XYY
128
From what are the body cavities - i.e. the peritoneal/pleural/pericardial - derived?
Coelomic cavity
129
What are the body cavities lined by?
Parietal layer of serous membrane - derived from somatic mesoderm
Visceral layer of serous membrane - derived from splanchnic mesoderm
130
What are the types of ossification?
Membranous ossification - development of flat bones
| Endochondral ossification - developmental of long bones
131
When does ossification start and end?
Weeks 6-25
132
The inner nucleus pulposus is derived from notochord, what is the outer nucleus pulposis derived from?
Sclerotomes
133
What are fontanelles?
Unossified mesenchyme
134
What does each myotome divide into?
Ventral hypomere - muscles of anterior wall
| Dorsal epimere - muscles of posterior wall
135
What muscle group does dorsal limb muscle mass give rise to?
Extensor group
136
What muscle group does ventral limb muscle mass give rise to?
Flexor group
137
What suspends the gut tube in the body of embryo?
Dorsal mesentery
138
When does gut herniation occur?
Herniates at week 6, and then returns at week 10
139
What is the rotation of the gut from herniation?
90 degrees anticlockwise as it herniates into the umbilical cord
Further 180 degrees anticlockwise when it returns to the abdomen
140
Which is associated with chromosomal abnormalities - omphalocele or gastroschisis?
Omphalocele
141
What does Meckel's diverticulum contain?
Gastric mucosa
| Pancreatic mucosa
142
What does the allantois become?
The urachus (which itself becomes the median umbilical ligament)
143
What is the bladder trigone formed from?
Mesonephric duct
144
From what is the bladder formed?
Urogential sinus
145
From what are Leydig cells derived?
Gonad mesenchymal cells
146
From what are granulosa cells derived?
Primitive sex cords
147
What is the severity of the ambiguity of gonads classified by?
Prader stages 1-5
