Anatomy of the Distal GI Tract Flashcards Preview

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Flashcards in Anatomy of the Distal GI Tract Deck (35):
1

What are the components of the distal GI tract

  • Colon - Caecum, appendix, ascending, transvers and descending colon 
  • Rectum 
  • Anal canal 
  • Anus

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2

Whats the anatomy of Faecal continene 

Control of the excretion of faeces- complex 

  • Needs holding area (rectum) to store faeces until appropriate do defecate 
  • Normal visceral affarents nerve fibres to sense the fullness of the rectum 
  • Functioning muscle sphincters - around the distal end of the GI tract to respond to the fullness 
  • To contract preventing defecation and relax allowing defecation 

3

What can affect faecal continence 

  • Neurological pathology - dementia, stroke, MS, trauma 
  • Medications
  • Natural age-related degeneration of nerves innervation of muscle
  • Consistency of stool 

4

Describe the anatomy of the pelvic cavity

  • Lies within the bony pelvis
  • Continues with the abdominal cavity 
  • Lies between the pelvic inlet (superior aspect) and pelvic floor 
  • Contains pelvic organs and supporting tissues 
  • Rectum - located within the pelvic cavity 

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5

Which muscle formes the pelvic floor 

Levator ani 

Separates the pelvic cavity from the perineum 

6

Whats the significant of openings in the pelvic floor 

Permits the distal parts of alimentary, anal and reproductive tracts to pass from the pelvic cavity into the perineum 

7

At what level does the sigmoid colon become the rectum 

S3 - Recto-sigmoid junction 

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8

When does the rectum become the anal canal

Anterior to tip of coccyx -just after passing through levator ani muscle

9

What are locations of the rectum anal canal 

  • Anus is the distal end of the anal canal both- perineum 
  • Rectum - pelvis 

10

What is the rectal ampulla and whats its anatomy 

  • Lies immediately superior to the levator ani muscle 
  • Walls relax to accommodate faecal material 
  • contains functioning muscle and sphincters to hold faeces in the ampulla until appropriate to defecate 
  • Function: Stores faeces 

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11

Describe the anatomical relations of the rectum 

  • Rectouterine/rectovesical pouch lies anterior to the superior rectum 
  • Males - the prostate gland lies anterior to the inferior rectum 
  • females - the vagina and cervix lies anterior to the inferior/middle rectum 

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12

What is the superior rectum covered by 

Peritoneum 

13

Describe the anatomy to the Levator ani muscle 

  • Forms most of the pelvic diaphragm along with Fascial covering 
  • Made up of a number of smaller muscles -> Puboccygeus, puborectalis and illeococcygeus 
  • Forms most of the pelvis floor and most of the peritoneum roof
  • Skeletal muscle 

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14

What are the functions of the levator ani muscle 

  • support for pelvic organs - most of the time tonically contracted
  • Reflexively contracts further during increased intra-abdominal pressure - e.g coughing, Sneezing 
  • Relaxes during - urination and defecation 

15

What is the nerve innervation of the Levator ani

'nerve to levator ani'

  • Branch of the sacral plexus and pudendal S2,3,4 

16

Describe the anatomy of the Puborectalis muscle 

  • Part of levator ani
  • function: maintaining faecal continence 
  • Contraction decreases the Anorectal angle - acting like a sphincter
  • Skeletal muscle - controle
  • When the rectal ampulla is relax and filled with faeces this muscle will help to maintain continence 

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17

What is the anorectal angle 

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18

Describe the anatomy of the anal canal and anal sphincter 

  • Anal canal is below the anorectal junction 

   Two anal sphincters

  • 1 internal sphincter - Smooth muscle
  • 1 external sphincter - Skeletal muscle 

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19

Describe the anatomy of the internal anal sphincter 

  • Smooth muscle
  • Forms superior 2/3rd of anal canal 
  • Contraction -> sympathetic nerves
  • Contraction inhibited -> parasympathetic nerves
  • Contracted all the time will only relax reflexively in responce to destension of the rectal ampulla 

20

Describe the External anal sphincter 

  •  Skeletal muscle 
  • Inferior 2/3 of the anal canal - superior part of sphincter is continous with puborectalis muscle 
  • Contraction- sitmulated by pudendal nerve
  • Voluntarliy contracted (along with puborectalis) in responce to rectal ampulla distension and internal sphincter relaxation 

21

What are the two important spinal cord levels 

T12-L2 and S2-S4

22

What types of fibres are carried within the S2-S4 nerves

  1. Visceral afferents back to S2-S4 - Run with parasympathetics 
  • Function: sense Stretch, ischaemia ​​

    2.  Parasympathetic fibres from S2-S4 - Via pelvic spkanchic nerves, Synapse in walls of rectum 

  • Function: inhibit internal anal sphincter and sitmulate peristalsis 

    3.  Somatic motor form pundendal nerve and nerve to levator ani 

  • Function: Contraction of external anal sphincter and puborectalis 

 

           

          

 

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23

What type of nerve fibres are carried within the T12-L2

  1. Sympathetic fibres- Travel to inferior mesenteric ganglia - synapse then travel via periarterial plexus around branches of IMA
  • Function: contraction of internal anal sphincter and inhibit peristalsis 

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24

Whats the nerve supply to the external sphincter 

pundendal nerve 

25

Describe the pundendal nerve

  • Branch of the sacral plexus 
  • S2, S3, S4, Rami
  • Supplies external anal sphincter 
  • Exits pelvis via -> Greater sciatic foramen 
  • Enters perineum via -> Lesser sciatic foramen 
  • branches to supply structures of perineum 

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26

What happens when there is pundenal nerve or sphincter damage 

During labour

  • Branches of pundendal nerve could be stretched
  • Fibres within puborectalis or external anal sphincter muscle could be torn 
  • Result -> weakness of muacle and faecal incontinence 

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27

What is the pectinate line in the anal canal

  • Marks the junction between the part of the embryo which formed the GI tract (endoderm) and the part which formed the skin (ectoderm) 
  • Aterial supply, venous drainage, neve suppy and lympathetics all differ above and below the pectinate line 
  • Superior to line -> visceral 
  • Interior to line -> Parietal

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28

What are the differences above the pectinate line and below it 

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29

Describe the lymphatics of the pelvis 

  • internal illiac nodes - inferior pelvic structures 
  • External iliac nodes - lower limbs and more superior structures
  • Common iliac nodes - drains from internal and external iliac nodes
  • Common illiac then drains into lumbar nodes

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30

What is the blood supply to the rectum and anal canal

  • The inferior mesenteric artery - supplies hindgut (all the way to petinate line) 
  • The remainder of the GI Tract = Internal iliac artery 
  • There is some degree of anastomoses between these vessels 

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31

What is the venous drainage from the anal canal and the rectum

  • Inferior mesenteric vein - Hingut - above pectinate line into the portal venous system
  • The internal illac vein - drains below the pectinate line - into the systemic venous system 

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32

Whats the difference between rectal varices and haemorrhoids 

  1. Varices -
  •  form due to Dillation of collateral veins between portal and systemic venous system
  • Portal hypertension

    2. Haemorrhoids 

  • Prolapses of rectal venous plexus- not due to Porta hypertension
  • Raised pressure - chronic constipation, straning and pregnancy

33

What is the Ischioanal Fossae 

  • Right and left fossae that lie each side of the anal canal
  • Filled with fat and loose connective tissue
  • The two fossae communicate with each other posteriorly 
  • Infection in fossa - Ischioanal abcess 

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34

What is the PR exam use for 

To asses anal tone, the effectiveness/ Strenght of the external sphincter

  • Female: palpate cervix anteriorly 
  • Males: palplate the prostate anteriorly

35

What are the different types of endoscopies for the distal GI tract

  • Proctoscopy - rectum 
  • Sigmoidoscopy - sigmoid colon
  • Colonoscopy - colon