Embryo - Lec 5 - Folding

Front 1

The head fold

Back 1

► The oropharyngeal membrane (future month), heart, pericardial cavity and septum transversum move ventrally

► The foregut forms

Front 2

The Tail fold

Back 2

► The allantois - a diverticulum of the yolk sac extending into the connecting
stalk, associated with urinary bladder development

► The connecting stalk with the allantois inside moves ventrally and forms the umbilical cord

► The primitive streak lies caudal to the cloacal membrane

► The hindgut forms

Front 3

Lateral folding

Back 3

► The abdominal walls close ventrally and form the peritoneal cavity

► The midgut forms

Front 4

Formation of the amniochorionic sac

Back 4

► Expansion of the amniotic cavity results in
obliteration of the chorionic cavity and formation of the amniochorionic sac

► Villi on most of the external surface of the chorionic sac degenerate

► The umbilical cord is covered by the amniotic membrane

Front 5

Fate of the pharyngeal arches

Back 5

► The 2nd arch overgrows the 3rd and 4th arches and forms the cervical sinus

► The 2nd, 3rd and 4th grooves and the cervical sinus disappear by the end of the 7th week

Front 6

What are the muscles derived from the first (mandibular) arch

Back 6

Muscles of mastication

Front 7

What are the skeletal structures derived from the first (mandibular) arch?

Back 7

Malleus (ear)

Incu (ear)

Upper Jaw

Lower Jaw

Front 8

What are the muscles derived from the second (hyoid) arch?

Back 8

Muscles of facial expression

Front 9

What are the skeletal structures derived from the second (hyoid) arch?

Back 9

stapes (of ear)

Front 10

Fate of 1st pouch

Back 10

pharynngotymapnic (auditory) tube

Front 11

Fate of 2nd pouch

Back 11

palatine tonsils (dervived from ectoderm)

Front 12

Fate of 3rd pouch

Back 12

Thymus and the inferior parathyroid gland

Front 13

Fate of 4th pouch

Back 13

superior parathryoid gland (calcium metabolism) and the ultimobranchial body

Front 14

Fate of the 1st groove

Back 14

external acoustic meatus (ear)

Front 15

Fate of the first membrane

Back 15

Tympanic membrane

Front 16

DiGeorge Syndrom - what is it and what are the signs?

Back 16

Caused by failure of the differentiation of the third and/or fourth pharyngeal
pouches into the thymus and parathyroid glands, possibly because of an abnormal
interaction between the pharyngeal endoderm and adjacent neural crest cell

Characterized by the absence of the thymus and parathyroid glands as well as
facial and cardiac anomalies

► Results in increased susceptibility to infections, hypocalcaemia and congenital
heart diseases

CATCH = Cardiac, Abnormal face, Thymic aplasia, Cleft palate, Hypocalcimia

Front 17

First Arc Syndrom

Back 17

► Caused by insufficient migration of neural crest cells into the first arch

► Results in anomalies of the face, eyes, ears, mandible and palate

Macrostomia
Hypoplasia of the mandible
Deformed auricle
Defect in cheek

Front 18

Development of the 4th week

Back 18

► The rostral and caudal neuropores are closing

► Early stages of eye and ear development are visible

► Four pharyngeal arches and upper and lower limb buds are present

Front 19

Development of the 6th and 7t h week

Back 19

► 6th week - eyes, eyelids, auricles and upper digital rays are visible

► 7th week - lower digital rays are visible

Front 20

Development of the 8th week

Back 20

► The embryo has a distinct human appearance, facial characteristics are clearly visible

► Eyes are heavily pigmented, fingers of hands
and feet are fully separated