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Medicine Notes Gastrointestinal (GI) System Notes

Development Of The Gi System (Embryology) Notes

Updated Development Of The Gi System (Embryology) Notes

Gastrointestinal (GI) System Notes

Gastrointestinal (GI) System

Approximately 57 pages

These notes helped me achieve a mark of 73% in my GI exam, which is the equivalent of a 1st. The notes are based on a series of lectures on the subject. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the GI tract (e.g. physiology or anatomy), would benefit greatly from these notes. There are lecture in the series on th...

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The following is a more accessible plain text extract of the PDF sample above, taken from our Gastrointestinal (GI) System Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Lecture 6

Development of GI system (embryology)

  • Gastrulation

    • Week 3- Epiblast cells migrate through primitive streak to form Trilaminar disc

      • Displace hypoblasts= ENDODERM (CNS/PNS and epithelium of skin)

      • Lie in middle= MESODERM (Body connective tissues, GI connective tissue)

      • Remain in epiblast= ECTODERM (GI tract organs & epithelium of GI)

  • Development of the GI system

    • Primitive gut tube

      • Stomadeum to proptadeum

      • Buds coming off= organs

    • Divisions of gut tube

      • Pharyngeal gut (part of foregut)

      • Foregut (COELIAC AXIS)

      • Midgut (SMA)

      • Hindgut (IMA)

    • Differentiation of gut

      • Dependent on interaction between endoderm “SHH genes” and mesoderm “HOX genes”

      • All different genes go to different places

    • Autonomic innervation

      • Sympathetic

        • Coeliac ganglion- Foregut structures

        • SMA- Midgut structures

        • IMA- Hindgut structures

      • Parasympathetic

        • Vagus nerve- Foregut & midgut structures

        • Pelvic splanchnic nerve- Hindgut structures

    • Mesenteries

      • Dorsal

        • Structures support gut tube to body wall

        • Derived from intraembryonic coelom (mesoderm)

        • Includes

          • Megogastrium (greater omentum); mesoduodenum; mesentery proper; mesocolon

      • Ventral

        • Only related to foregut

        • Derived from septum transversum

          • Falciform ligament- extending liver to ventral wall

            • Embryo: Unbilical vein

            • After birth: round ligament

          • Lesser omentum- extending stomach to liver

            • Portal triad: bile duct, hepatic artery, portal vein

            • Forms entrance to lesser sac: EPICLOIC FORAMEN OF WINSLOW

    • From which germ layer are the following parts of developing gut tube derived?

      • GI organs & GI mucosa= ENDODERM

      • Peritoneum, GI smooth muscle & dorsal mesentery= MESODERM

  • Pharyngeal foregut (oropharyngeal membrane to respiratory diverticulum)

    • Mouth

      • Oropharyngeal membrane ruptures at ~4 weeks

      • Oral cavity formed alongside nasal cavity in face development

      • Pharyngeal arches

        • Externally

          • 5 arches (1, 2, 3, 4, 6) with 4 clefts

          • Form muscle and skeleton of face

        • Internally

          • 4 pouches

            • 1= Auditory tube & middle ear cavity

            • 2= Palatine tonsil

            • 3= Inferior parathyroid gland

            • 4= Thymus

            • 5= Parafollicular cells of thyroid

          • Pocketing of foregut

          • Failure 2-4 to close correctly= fistula (internally/externally)

    • Tongue

      • Develops from pharyngeal arches

      • Innervation

        • Sensory

          • Anterior 2/3= 1st arch, trigeminal (mandibular)

          • Posterior 1/3= 3rd arch, glossopharyngeal

        • Motor

          • Occipital somites, hypoglossal

    • Thyroid

      • Develops at foramen caecum in floor of tongue

      • Descends via thyroglossal duct, lie below larynx anterior to trachea (week 7)

    • CLINICAL CORRELATIONS

      • Branchial fistula- failure of clefts 2-4 to close

      • Thyroglossal cyst

        • Remnant of thyroglossal duct, contains thyroid tissue in midline

  • Foregut (oesophagus to liver/bile duct outgrowth)

    • Oesophagus

      • Exactly same point trachea comes off

      • 4 week embryo lung buds off ventral wall of foregut

      • Oesophagus

        • Rapidly lengthens as descends through thorax

      • CLINICAL CORRELATION- Oesophageal atresia

        • Failure of correct closure of tracheoesophageal septum

        • Fistula formed between lower part of trachea & distal oesophagus

    • Stomach

      • Week 4, starts to dilate

      • Dorsal wall grows faster than ventral (greater/lesser curvature)

      • Originally found along midline

      • Rotates longitudinally and anterioposteriorly

      • Both dorsal and ventral mesentery

      • As stomach rotates, mesenteries alter position

    • Duodenum

      • ...

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