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Conditions + definitions > Embryology > Flashcards

Embryology Flashcards

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
Q

What is the effect of development dysplasia of the hip?

A

Increased risk of dislocation

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26
Q

With which system does the reproductive system share embryological links?

A

Urinary system

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27
Q

What are the three types of kidneys that develop?

A

Pronephros (cervical region)
Mesonepros (thoracolumbar region)
Metanepros (pelvic region)

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28
Q

What happens to each type of kidney?

A

Pronephros degenerated
Mesonephros goes on to form reproductive system
Metanepros forms kidneys

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29
Q

When does the gonadal ridge form?

A

weeks 5-6

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30
Q

How does the genital ridge form?

A

The mseonephris forms a long ovoid structure, associated with thoracib/lumbar vertebrae
Medial part of this ridge thickens forming the genital ridge

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31
Q

How is the indifferent gonad formed?

A

When germ cells from the yolk sac migrate towards the genital ridge
Migrate via dorsal mesentery
Embed into Primartive sex cords

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32
Q

Why are they called indifferent gonads?

A

Because at this point it is impossible to tell which gonad they will become

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33
Q

What cells becomes the paramesonephric duct?

A

Epithelium invaginates to form a tube, which becomes the paramesonephric duct

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34
Q

Where does the paramesonephric ducts open into and develop?

A

Paramesonephricdevelops laterally to developing gonads
Cranial end opens into peritoneal cavity
Caudal end crosses centrally to mesonephric ducts into dorsal wall of urogenital sinus

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35
Q

What do the primordial reproductive structures form in males?

A

Gonad forms testis
Mesonephric duct into epipidymis, vas defernes + seminal vesicle
Paramesonephric duct degenerates
Urogenital sinus forms ballder, prostate and urethra

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36
Q

What do the primordial reproductive structures form in females?

A

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
Q

What part of the X chromosome causes the changes in development?

A

SRY encoding form TDF (testis determining factor)

Expressed by cells within sex cords

38
Q

What do the sertoli cells develop from?

A

Primordial supporting cells in promitive sex cords

39
Q

What do the leydig cells develp from?

A

Mesenchymal cells between the primitive sex cords

40
Q

How do the tesits develop?

A

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
Q

How do the seminiferous tubules develop?

A

TDF stimulates sex cords to eleongate forming seminiferous tubules
Extend into medulla

42
Q

What forms the seminal vesicles?

A

Outgrowth from caudal end of mesoneprhic duct

43
Q

What forms the prostate?

A

Outgrowths from the urethra (urogenital sinus)

44
Q

How does the ovary develop?

A

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
Q

What brings rise to the female reproductive tract?

A

Paramesonephric ducts

The abscence of tesosterone causes mesonperos/duct to degenerate

46
Q

How does the female genital tract develop?

A

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
Q

How do the gonads descend?

A

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
Q

How do the ovaries descend?

A

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
Q

What is cryptorchidism?

A 
Absence of testes in scrotum:
Undescended testes
Ectopic
Retraticle testes
Absent testes
50
Q

What are the complications of the undescended testis?

A

Infertility if left
Malignant transformation
Testicular torsion

51
Q

What tissue forms the genital system (and urinary) in the developing embryo?

A

Intermediate plate mesoderm

52
Q

What does the gubernaculum form in females?

A

Round ligament

Ovarian ligament

53
Q

What are the common birth defects in relation to th reproductive system?

A

Cryotirchidism
Remants of mesonephric duct (gartners cysts)
Anomalies of female reproductive tract

54
Q

What are some common anomalies of the female reproductive tract?

A

Complete duplication of uterus
Septate uterus (has septum)
Bicornate uterus
Arcutate uterus

55
Q

What is mesenchyme?

A

> 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
Q

What is special about the areas that become the future mouth and anus?

A

There is no mesoderm present

57
Q

How is the neural tube formed?

A

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
Q

How do neural crest cells develop?

A

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
Q

How do somites develop?

A

They are derived from paraxial mesoderm
Form structures like axial skeleton and muscles
33 develop

60
Q

What do the somites do?

A

In future head region:
>Help cranial skeleton development
>Bulbous somites at top form brain + two eyes
>Folds embryo

61
Q

What are the pharyngeal arches?

A

(AKA branchial arches because gills in a fish)
>Series of arches that develop around future mouth and pharynx
>Support primative pharynx

62
Q

How many pharyngeal arches are there? (total + at end?)

A

6 in total formed

5th Arch degenerates

63
Q

What makes up a branchial arch?

A 
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
Q

What nerve arises from the 1st branchial arch?

A

CN V3

>Mandibular branch of the trigeminal nerve

65
Q

What nerve arises from the 2nd branchial arch?

A

CN VII

>Facial nerve

66
Q

What nerve arises from the 3rd branchial arch?

A

CN IX

>Glossopharyngeal

67
Q

What nerve arises from the 4th branchial arch?

A

CN X
>Specifically superior laryngeal branch
>Vagus

68
Q

What nerve arises from the 6th branchial arch?

A

CN X
>Specifically recurrent laryngeal branch
>Vagus

69
Q

How can you tell what arch forms what muscle?

A

All muscles innervated by nerves from branchial arches have migrated upwards
>During migration take nerve with them
>Same origin as nerve

70
Q

What arch forms the facial muscles?

A

2nd brachial arch

>Supplied by facial

71
Q

What arch forms the anterior belly of the diagastric muscle?

A

1st branchial arch

>Supplied by mandibular nerve of trigeminal

72
Q

What arch forms the posterior belly of the diagastric muscle?

A

2nd brachial arch

>Supplied by facial

73
Q

What cartilage arises from the 1st pharyngeal arch?

A

Mandible

Hammer/anvil of ear (Malleuls, incus)

74
Q

What cartilage, bone and ligament arise from the 2nd pharyngeal arch?

A

Upper part of hyoid bone
Styloid process
Stylohyoid ligament

75
Q

What bone arises from the 3rd pharyngeal arch?

A

Lower part of hyoid bone

76
Q

What cartilage arises from the 4th pharyngeal arch?

A

Upper thyroid cartilage

77
Q

What cartilage arises from the 6th pharyngeal arch?

A

Lower thyroid cartilage

Cricoid cartilage

78
Q

What glands arise from the branchial arches?

A

Thyroid gland
Parathyroid gland
Part of the pituitary gland

79
Q

What processes does the face develop from?

A

1 frontonasal process
2 Maxillary processes
2 mandibular processes

Important for understanding how clefts form

80
Q

What does the frontonasal process develop from?

A

Mesenchyme superior to future mouth

81
Q

What do the maxillary processes develop from?

A

Mesoderm of 1st branchial arch

82
Q

What do the mandibularprocesses develop from?

A

Mesoderm of 1st branchial arch

83
Q

What are the steps in the face’s development?

A

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
Q

How does the palate develop?

A

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
Q

What are the three sections of the skull?

A

Cranial vault
Base of skull
Viscerocranium

86
Q

How is the cranial vault formed?

A

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
Q

What condition occurs if cranial bones ossify at the wrong time?

A

craniossynostosis

88
Q

How is the base of the skull formed?

A

Formed by endochondral ossification
Mesenchyme around notochord is derived predominantly from neural crest cells
Preform in cartilage first
Then later ossify

89
Q

How is the viscerocranium formed?

A

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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