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Anatomy > Embryology > Flashcards

Embryology Flashcards

1
Q

GI Tract overview

A

Gut tube formed from endoderm lining yolk sac

Oropharyngeal membrane and cloacal membrane

During folding; somatic mesoderm –> parietal peritoneum, visceral mesoderm –> mesenteries

Nerves and neurons derived from neural crest

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2
Q

Foregut structures

A
  • Trachea and resp tract
  • lungs
  • oesophagus
  • stomach
  • liver
  • GB and bile ducts
  • pancreas
  • upper duodenum
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3
Q

Midgut structures

A
  • lower duodenum
  • jejunum
  • ileum
  • cecum
  • appendix
  • ascending colon
  • prox 2/3 transverse colon
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4
Q

Hindgut structures

A
  • distal 1/3 transverse colon
  • descending colon
  • sigmoid colon
  • rectum
  • upper anal canal
  • urogenital sinus
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5
Q

Arterial supply of foregut, midgut and hindgut

A

Foregut; coeliac artery
Midgut; SMA
Hindgut; IMA

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6
Q

Embryology of Stomach

A
  • appears first as fusiform dilation of foregut
  • undergoes 90º rotation; left side moves ventrally, right side dorsally
  • differential growth on left and right produces greater and lesser curves respectively
  • craniocaudal rotation tips pylorus superiorly
  • anterio-posterior rotation creates final adult position
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7
Q

Embryology of Lesser sac

A
  • stomach attached to both dorsal and ventral mesogastrium
  • it’s rotation & disproportional growth alters mesogastrium position
  • rotation along longitudinal axis, dorsal mesentery to the left = lesser sac
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8
Q

Embryology of Duodenum

A
  • caudal part of foregut and cranial midgut

- as stomach rotates, duodenum becomes C-shaped and also rotates

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9
Q

Embryology of Liver and biliary apparatus

A
  • outgrowth endoderm distal foregut
  • liver bud grows into septum transversum
  • connection between foregut and liver bud narrows –> bile duct
  • ventral outgrowth from bile duct forms GB and cystic duct
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10
Q

Embryology of Spleen

A
  • develops in dorsal mesogastrium
  • up to week 14 = haematopoetic function
  • weeks 15-17 colonised by T lymphocytes
  • week 23 B cell precursors arrive
  • spleen can begin lymphoid function
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11
Q

Embryology of Pancreas

A
  • forms from 2 buds which grow from endodermal lining of duodenum
  • dorsal and ventral buds fuse
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12
Q

Embryology of Midgut

A
  • primary intestinal loop
  • rotates 90º around SMA axis
  • as this occurs, herniates into extra-embryonic cavity
  • retraction of herniated loops
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13
Q

Embryology of Hindgut

A
  • terminal portion of hindgut joins with posterior cloaca
  • allantois enters into anterior part of cloaca
  • end week 7 cloacal membrane ruptures (hindgut opening)
  • ectoderm anal canal proliferates, closing caudal end
  • anal canal re-opens week 9
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14
Q

Where do neural crest cells arise from?

A

Cells at crest of neural fold which develops to form neural tube

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15
Q

Describe somites

A

Form from paraxial mesoderm

Go on to form structures like axial skeleton and muscles

Human embryos develop around 33, those around head region develop cranial bones

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16
Q

Embryology of Pharyngeal / branchial arches

A

Develop around future mouth and pharynx

  • support primitive pharynx
  • face and neck develop from them
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17
Q

What nerves develop from the pharyngeal arches?

A

1st arch; maxillary branch of trigeminal nerve
2nd arch; facial nerve
3rd arch; glossopharyngeal nerve
4th arch; sup laryngeal branch of vagus
NO FIFTH ARCH
6th arch; recurrent laryngeal branch of vagus

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18
Q

Describe where muscles of the facial nerve develop from

A

Muscles of the facial nerve develop from the 2nd branchial arch, the same as the facial nerve

Muscles supplied a nerve developed from a branchial arch will also have developed from this branchial arch

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19
Q

Facial development

A

From five processes

  • 1 frontonasal
  • 2 maxillary
  • 2 mandibular
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20
Q

How does the nostril develop?

A

Ectodermal thickening (nasal placode) invaginates to form nostril

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21
Q

Describe palate formation

A

Medial nasal process grows downwards and forms philtrum

Maxillary process develops palatine shelves which grow inwards and meet in the midline

*Abnormalities cause cleft palate

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22
Q

Describe cranial vault bone formation (skull cap)

A

Membranous ossification of calvaria
- mesenchyme derived from mesoderm directly above developing brain ossify directly

Not fully formed at birth; sutures are soft & 6 membrane covered fontanelles (anterior closes at 1.5yrs, posterior 2-3months)

23
Q

Describe base of skull formation (irregular bones)

A

Mesenchyme around notochord mostly derived from neural crest cells

Preform in cartilage and later ossify (endochondral ossification)

24
Q

Describe viscerocranium formation (facial bones)

A
  • partly from branchial arches
  • partly from sensory capsules

sensory capsules are derived from mesoderm of somites in head and neck region

they preform in cartilage and then ossify to form bones around sense organs

25
Q

When does the neuro system start to form?

A

Beginning of third week

26
Q

When do each of the neuropores close?

A

Anterior ~day 25

Posterior ~day 27

27
Q

Describe neural tube closure

A

Up to 5 closure sites in humans

Both cranial and caudal directions

28
Q

Describe the failed features of neural formation in anencephale, encephalocoele and spina bifida

A

Anencephalocoele; failure anterior neuropore to close thus skull fails to form

Encephalocoele; failure rostral neural tube to close causing herniation brain tissure through skull

Spina bifida; failure vertebral arches to fuse

29
Q

What are the primary brain vesicles?

A

Prosencephalon
Mesencephalon
Rhombencephalon

30
Q

What are the secondary brain vesicles? (in order)

A 
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
31
Q

What forms from the telencephalon?

A

Cerebral hemispheres
Hippocampus
Basal ganglia

32
Q

What forms from the diencephalon?

A

Thalamus, hypothalamus, pineal gland and pituitary gland

33
Q

What forms from the mesencephalon?

A

MIDBRAIN

Superior and inferior colliculi

34
Q

What forms from the metencephalon?

A

Cerebellum and pons

35
Q

What forms from the myelencephalon?

A

Medulla

36
Q

Describe the cephalic flexure formation

A

End of third week

Between midbrain and hindbrain

37
Q

Describe the cervical flexure formation

A

End of fourth week

Between hindbrain and SC

38
Q

Describe the pontine flexure formation

A

End of fifth week

In hindbrain

39
Q

What does the renal system develop from?

A

Intermediate plate mesoderm

40
Q

What is the allantois?

A

outpouching of ectoderm at hindgut that extends into body stalk

41
Q

What does the body stalk form?

A

umbilical cord

42
Q

What is the remnant of the allantois?

A

medial umbilical ligament

43
Q

What does the cloaca divide to form?

A

rectum and urogenital sinus

44
Q

What does the mesonephric duct drain into?

A

Urogenital sinus; becomes urinary bladder and caudal end of urethra

45
Q

Describe kidney development

A

Week 4 IMD neck region –> pronephros with pronephric duct (drains into cloaca) and rudimentary tubules

Late week 4 mesonephros (functioning kidney for 4weeks) develops from IMD trunk region

Pronephric duct becomes mesonephric duct

metanephros is definitive kidney and starts functioning around week 9
- ureteric bud develops from mesonephric duct

46
Q

What does the mesonephric duct become?

A

Vas deferens

47
Q

Describe the ureteric bud and its developments

A

Develops from mesonephric duct

Repeated branching at distal end

Stalk becomes ureter, expanded cranial end becomes renal pelvis

First 4 generations of branches become major calyces
Next 4 become minor calyces
Remaining form collecting tubules

48
Q

Describe the nephron

A

Develops from metanephric mesoderm, ureteric bud and metanephric mesoderm reciprocally induce one another

Renal corpuscle + PCT + loop of Henle + DCT

49
Q

Describe kidney ascent

A 
Initially either side bladder
Differential growth lower body
Adult position t12-l3 abdomen
Hilum rotates ventral to medial 90 degrees
Ascent stops when reach adrenal glands
50
Q

Renal developmental anomalies

A

Duplicated ureter

Horseshoe kidney

51
Q

What does surface ectoderm in eye embryology form?

A

Eyelids
Conjunctiva
Corneal epithelium

52
Q

Describe development of the eye; lens and optic cup

A

Small grooves develop either side neural folds = optic grooves
Their connection to the forebrain becomes optic stalk which becomes optic nerve
Surface ectoderm thickens forming lens placode which invaginates to form lens pit and vesicle. Lens vesicle loses connection with surface ectoderm.
At the same time the optic vesicle invaginates to becomes the optic cup

53
Q

Describe the optic cup

A

2 layers;

  • inner layer is neural layer of retina, ciliary body and inner layer of iris
  • outer layer is pigment layer of retina and iris
54
Q

Describe formation of the choroid fissure

A

As optic cup is forming, blood vessels that pass through form fissure in inferior wall called choroid fissure

Anatomy (10 decks)

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