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Embryology Flashcards

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1
Q

When does MSK embryology begin?

A

Near the end of the 4th week
Due to activation f mesenchymal cells in somatic lateral mesoderm
On day 24 Upper limb bud appears
Lower limb bud appears 1-2 days later

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2
Q

What is proimo-distal patterning?

A

Genes that are expressed in different regions which ultimately decides what skeletal element is formed
Allows for the different bones to be formed in their correct place
HOX expression results from a combination of SHH, FGF and WNT-7a expression

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3
Q

How do limb buds elongate?

A

By the proliferation of mesenchyme

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4
Q

Where to the limb buds appear?

A

Upper limb - opposite cuadal cervical segments

Lower limb - opposite lumber/sacral segments

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5
Q

What is the AER (apical ectodermal ridge)?

A

A thickening of the ectoderm at the apex of each limb bud
A multilayered epithelial structure that exerts influence on the mesenchyme
This mesenchyme is undifferentiated and rapidly proliferating cells

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6
Q

What do the cells proximal to the AER differentiate into?

A

Mesenchymal cells proximal to it differentiate into blood vessels, cartilage and bone models

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7
Q

How do hand and foot plates form?

A

Distal ends of the limb buds flatten into paddle like plates for hands, flipper like for feet
By end of 6th week he mesenchymal tissue condeses to form digital rays
7th week for foot plates

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8
Q

How do the limbs develop?

A

Cartilagionous precurosrs develop through chondrification within mesoderm in 6th week
Primary ossification centres appear in weeks 8-12 in response to growth factors
Endochondrial ossification occurs for all limb bones except for the clavicle

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9
Q

What ossification occurs for limb bones? (except clavicle)

A

Endochondrial ossification

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10
Q

What ossification occurs for the clavicle?

A

Membranous ossification

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11
Q

How do the upper limbs rotate?

A

Upper limbs rotate 90 degrees laterally

Brings extensors to the lateral and posterior surfaces

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12
Q

How do the lower limbs rotate?

A

Lower limb rotates 90 degrees medially, brings extensors to anterior surface

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13
Q

How are dermatomes formed?

A

During the 5th week, peripheral nerves grow from developing nerve plexi
Grow into mesochyme of limbs

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14
Q

What are the possible birth defects of limbs?

A 
Amelia
Meromelia
Phocomelia
Micromelia
Polydactyly
Syndactyly
Congenital clubfoot
Cingenital dysplasia of hip
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15
Q

What is Amelia?

A

Amelia is total absence of a limb

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16
Q

What is meromelia?

A

Partial absence of a limb

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17
Q

What is phocomelia?

A

Some long bones absent in limb

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18
Q

What is micromelia?

A

All parts of limb are present, by smaller than normal

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19
Q

What is polydactyly?

A

Where more than 5 digits are on hands or feet
Extra digit is incompletely formed and lacks muscular development
May be genetic or teratogenic

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20
Q

What is syndactyly?

A

Webbing of the hand or foot

Fiarly common

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21
Q

What are the types of syndactyly?

A

Cutaneous - simple webbing between digits, common and more frequent in feet

Osseous - fusion of bones
Due to notches between digital rays fail to develop

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22
Q

What is congenital clubfoot?

A

(AKA talipes equinovarus)
Sole of fot turned to arus side (medially) and inverted
Relatively common

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23
Q

What are the causes of clubfoot?

A

Multifactoral (genetic + environment)

Abnormal postioning or restricter movement of foetus’ lower limb in utero

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24
Q

What are the types of developmental dysplasia of the hip?

A

Abnormal development of acetabulum
Accounts for 15%
Common after breech births
Genralised joint laxity

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25
What is the effect of development dysplasia of the hip?
Increased risk of dislocation
26
With which system does the reproductive system share embryological links?
Urinary system
27
What are the three types of kidneys that develop?
Pronephros (cervical region) Mesonepros (thoracolumbar region) Metanepros (pelvic region)
28
What happens to each type of kidney?
Pronephros degenerated Mesonephros goes on to form reproductive system Metanepros forms kidneys
29
When does the gonadal ridge form?
weeks 5-6
30
How does the genital ridge form?
The mseonephris forms a long ovoid structure, associated with thoracib/lumbar vertebrae Medial part of this ridge thickens forming the genital ridge
31
How is the indifferent gonad formed?
When germ cells from the yolk sac migrate towards the genital ridge Migrate via dorsal mesentery Embed into Primartive sex cords
32
Why are they called indifferent gonads?
Because at this point it is impossible to tell which gonad they will become
33
What cells becomes the paramesonephric duct?
Epithelium invaginates to form a tube, which becomes the paramesonephric duct
34
Where does the paramesonephric ducts open into and develop?
Paramesonephricdevelops laterally to developing gonads Cranial end opens into peritoneal cavity Caudal end crosses centrally to mesonephric ducts into dorsal wall of urogenital sinus
35
What do the primordial reproductive structures form in males?
Gonad forms testis Mesonephric duct into epipidymis, vas defernes + seminal vesicle Paramesonephric duct degenerates Urogenital sinus forms ballder, prostate and urethra
36
What do the primordial reproductive structures form in females?
Gonad forms ovary Mesoneprhic duct degenerates Paramesonephric duct forms fallopian tube, uterus, cervix part of vagina Urogenital sinus forms bladder and lower part of vagina
37
What part of the X chromosome causes the changes in development?
SRY encoding form TDF (testis determining factor) | Expressed by cells within sex cords
38
What do the sertoli cells develop from?
Primordial supporting cells in promitive sex cords
39
What do the leydig cells develp from?
Mesenchymal cells between the primitive sex cords
40
How do the tesits develop?
Wk 5 - primary sex cords, medulla and cortex formed Wk 6 - primordial germ cells incorporated wk 7 - Seminiferous form + ends anastomose to make rete testis Surface epithelium lost when capsule forms Leydig cells form Wk 8 - leydig cells produce tesosterone
41
How do the seminiferous tubules develop?
TDF stimulates sex cords to eleongate forming seminiferous tubules Extend into medulla
42
What forms the seminal vesicles?
Outgrowth from caudal end of mesoneprhic duct
43
What forms the prostate?
Outgrowths from the urethra (urogenital sinus)
44
How does the ovary develop?
Primary sex cords degenerate leaving germ cells at 10 wks secondary sex cords develop from epithelium incoroprating the germ cells into them Germ cells bud off, surrounded by layer of cortical cord cells Active mitosis of these primordial follicles to form additional follicles 7th month all have formed Arrested in phrophase 1 until puberty
45
What brings rise to the female reproductive tract?
Paramesonephric ducts | The abscence of tesosterone causes mesonperos/duct to degenerate
46
How does the female genital tract develop?
Cranial end of paramesonephric duct becomes associated with ovary (catches) Caudal end becomes uterus + superior part of vagina Inferior part formed from urogenital sinus Mesonephric duct degenerates
47
How do the gonads descend?
Both in week 7-10 descend to T10 In testis week 12 they are level of deep inguinal ring and remains until 7th month Enters scrotum just prior to birth
48
How do the ovaries descend?
Both in week 7-10 descend to T10 Ovary at week 12 the muscle degenerates to form broad liagment, which is drawn through inguinal canal to attach to labrum majorum
49
What is cryptorchidism?
``` Absence of testes in scrotum: Undescended testes Ectopic Retraticle testes Absent testes ```
50
What are the complications of the undescended testis?
Infertility if left Malignant transformation Testicular torsion
51
What tissue forms the genital system (and urinary) in the developing embryo?
Intermediate plate mesoderm
52
What does the gubernaculum form in females?
Round ligament | Ovarian ligament
53
What are the common birth defects in relation to th reproductive system?
Cryotirchidism Remants of mesonephric duct (gartners cysts) Anomalies of female reproductive tract
54
What are some common anomalies of the female reproductive tract?
Complete duplication of uterus Septate uterus (has septum) Bicornate uterus Arcutate uterus
55
What is mesenchyme?
>Embryonic connective tissue >Same properties as connective tissue and develops in to bone, cartilage blood vessels etc >Once mesoderm merges with neural crest cells considered mesenchyme
56
What is special about the areas that become the future mouth and anus?
There is no mesoderm present
57
How is the neural tube formed?
Some of the ectoderm in the middle fold down to form neural tube >Goes on to form brain + spinal cord >Forms axis of embryo
58
How do neural crest cells develop?
Some cells at the crest separate to form neural crest cells >Migrate to form variety of structures Mix with mesoderm to form >neural crest cells
59
How do somites develop?
They are derived from paraxial mesoderm Form structures like axial skeleton and muscles 33 develop
60
What do the somites do?
In future head region: >Help cranial skeleton development >Bulbous somites at top form brain + two eyes >Folds embryo
61
What are the pharyngeal arches?
(AKA branchial arches because gills in a fish) >Series of arches that develop around future mouth and pharynx >Support primative pharynx
62
How many pharyngeal arches are there? (total + at end?)
6 in total formed | 5th Arch degenerates
63
What makes up a branchial arch?
``` Ectoderm makes outside >Forms clefts between atches Mesochyme forms cartilage and muscles Endoderm on inside >Forms pouches between arches ``` Clefts + pouches go on to form structures
64
What nerve arises from the 1st branchial arch?
CN V3 | >Mandibular branch of the trigeminal nerve
65
What nerve arises from the 2nd branchial arch?
CN VII | >Facial nerve
66
What nerve arises from the 3rd branchial arch?
CN IX | >Glossopharyngeal
67
What nerve arises from the 4th branchial arch?
CN X >Specifically superior laryngeal branch >Vagus
68
What nerve arises from the 6th branchial arch?
CN X >Specifically recurrent laryngeal branch >Vagus
69
How can you tell what arch forms what muscle?
All muscles innervated by nerves from branchial arches have migrated upwards >During migration take nerve with them >Same origin as nerve
70
What arch forms the facial muscles?
2nd brachial arch | >Supplied by facial
71
What arch forms the anterior belly of the diagastric muscle?
1st branchial arch | >Supplied by mandibular nerve of trigeminal
72
What arch forms the posterior belly of the diagastric muscle?
2nd brachial arch | >Supplied by facial
73
What cartilage arises from the 1st pharyngeal arch?
Mandible | Hammer/anvil of ear (Malleuls, incus)
74
What cartilage, bone and ligament arise from the 2nd pharyngeal arch?
Upper part of hyoid bone Styloid process Stylohyoid ligament
75
What bone arises from the 3rd pharyngeal arch?
Lower part of hyoid bone
76
What cartilage arises from the 4th pharyngeal arch?
Upper thyroid cartilage
77
What cartilage arises from the 6th pharyngeal arch?
Lower thyroid cartilage | Cricoid cartilage
78
What glands arise from the branchial arches?
Thyroid gland Parathyroid gland Part of the pituitary gland
79
What processes does the face develop from?
1 frontonasal process 2 Maxillary processes 2 mandibular processes Important for understanding how clefts form
80
What does the frontonasal process develop from?
Mesenchyme superior to future mouth
81
What do the maxillary processes develop from?
Mesoderm of 1st branchial arch
82
What do the mandibularprocesses develop from?
Mesoderm of 1st branchial arch
83
What are the steps in the face's development?
The two mandibular processes fuse in midline Ectoderm thickening of frontonasal placade >Splits frontnasal process into 3 >Lateral 2 parts from nostrils Medial nasal process grows further downwards and laterally forming philtrum
84
How does the palate develop?
Stage 1: Medial nasal process grows downwards and forms philtrum. >forms the primary palate Stage 2:From the maxillary processes, two palatine shelves grow inwards Stage 3: The palatine shelves meet in the midline to form the secondary palate. Now the oral cavity and nasal cavity are separate.
85
What are the three sections of the skull?
Cranial vault Base of skull Viscerocranium
86
How is the cranial vault formed?
Membranous bones -> formed by membranous ossification calcaria (ossify directly) Mesenchym dervied mesoderm that lies above the surface of developing brain Not fully formed at birth - soft sutures between to allow passage though birth canal
87
What condition occurs if cranial bones ossify at the wrong time?
craniossynostosis
88
How is the base of the skull formed?
Formed by endochondral ossification Mesenchyme around notochord is derived predominantly from neural crest cells Preform in cartilage first Then later ossify
89
How is the viscerocranium formed?
Partly from branchial arches, partly from sensory capsules Derived from somites in head and neck region Preform in cartilage and ossify to form bones around sense organs

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