T1 L11: Gastrointestinal system

• What are the Functions of the Digestive System with their organs?

  1. Ingestion and mastication: mouth
  2. Secretion of digestive fluid: stomach & duodenum (+ ducts into duodenum)
  3. Peristalsis – mixing and propulsion: stomach & small intestine
  4. Nutrient absorption: small intestine
  5. Water reabsorption: large intestine
  6. Defecation: rectum + anal canal
• What is the pharynx?

  region that surrounds the posterior aspect of nasal cavity and posterior aspect of oral cavity

  runs behind larynx (airways)

  
• What is the level where pharynx transitions into oesophagus at the pharyngoesophageal junction?

  cricoid cartilage

  
• What are the constrictions of the oesophagus?


  cervical part: pharyngoesophageal junction

  thoracic part: as it passes over arch of aorta and main bronchus

  abdominal part: as it passes through the diaphragm

  
• What is the Lower oesophageal sphincter and its function?

  physiological sphincter formed by:

  • musculature of the crura of the diaphragm (extrinsic)
  • muscles of the oesophagus (intrinsic).

  Protects oesophagus from reflux of gastric contents. Located at oesophageal hiatus of the diaphragm

  
• What is Hiatus hernia?

  Relatively common condition involving herniation of the stomach through the oesophageal hiatus of the diaphragm.

  May not cause any symptoms, or it may be associated with symptoms of gastro-oesophageal reflux

  
• What are the three layers of muscle of walls of the stomach?

  Outer - longitudinal

  Middle - circular

  Inner - oblique

  
• What are the external areas of the stomach?

  1. Cardia
  2. Fundus
  3. Body
  4. Pyloric antrum
  5. Pyloric canal

  
• What are the 2 external landmarks on the stomach?

  1. Cardinal notch: between cardia and fundus
  2. Angular incisure: between lesser curvature and pyloric antrum

  
• What are the interior parts of the stomach and their function?


  1. Gastric folds (rugae): Allow stomach to expand
  2. Pyloric sphincter: At irregular intervals, gastric peristalsis pushes chyme through pyloric canaland orifice into small intestine
  3. Gastric canal: Enables liquids travelling through stomach to fast track to the pylorus

  
• What are the connections of the stomach to its surroundings?

  1. Hepatogastric ligament: from lesser curvature to liver
  2. Gastrosplenic ligament: from greater curvature to spleen
  3. Greater omentum: from greater curvature
  4. Lesser omentum: Hepatogastric + hepatoduodenal ligaments

  
• What are the parts of the small intestine?

  Begins at pyloric orifice of stomach

  First part: duodenum

  Second part: jejunum

  Third part: ileum

  Ends at ileocecal junction

  
• What are the microscopic structures of the small intestine and their function?

  All of the small intestine contains:

  1. plicae circularis
  2. villi
  3. microvilli (except for proximal 2.5cm ofduodenum).

  These features increase surface area for food absorption. Ileum: 3.5 m

  
• What are the 4 parts of the duodenum?

  1. Superior
  2. Descending
  3. Horizontal / inferior
  4. Ascending

  
• What is the anatomical border between duodenum and jejunum called?

  duodenal-jejunal flexure

  
• What are the characteristics of jejunum ?

  • wider lumen
  • thicker walls
  • dense plicae circularis
  • longer vasa recta (long branching arteries)
  • fewer arcades (layers / horizontal branches of arteries)

  
• What are the characteristics of the ileum?

  • narrow lumen
  • thinner walls
  • plicae circularis are sparse
  • more arcades
  • shorter vesa recta
  • Peyer's patches

  
• What are Aggregated Lymph Nodules / Peyer's Patches?


  Small clusters of lymphatic tissue found in the wall of the small intestine

  Immune system's first line of defence against microbial and dietary antigens

  Highly concentrated in the distal ileum, where they form a distinct lymphoid ring

  
• What is the mesentery?


  membrane that covers all of jejunum and ileum (intraperitoneal) and connects to posterior abdominal wall

  
• What peritoneum is the duodenum associated with and how?

  Mostly retroperitoneal

  Descending, horizontal and ascending parts of duodenum are retroperitoneal

  Hepatoduodenal ligament: From superior part of duodenum to liver (Intraperitoneal)

  
• What are the parts of the colon?

  1. Ascending
  2. transverse
  3. descending
  4. sigmoid.

  
• What are the functions of the large intestine?

  • Water and salt absorption
  • Temporary storage of faeces
  • Little or no digestive function
  • Secretion of mucus
  • Extensive action of microorganisms
• What is the appendix?

  • Blind intestinal diverticulum
  • Contains masses of lymphoid tissue
  • Position can vary

  
• What are the features of the large intestine?

  1. ileocoecal junction
  2. Haustra: lines created by the bulging
  3. Hepatic flexure: folding from ascending to transverse colon
  4. splenic flexure: folding from transverse to descending colon
  5. Taenia coli: bands of longitudinal muscle
  6. Omental appendices: aggregations of fat covered by peritoneum. Function poorly understood

  
• What peritoneal relationship do the ascending and descending colon (and caecum) have?

  secondarily retroperitoneal

  
• What peritoneal relationship does the transverse colon have?

  intraperitoneal

  is suspended by transverse mesocolon

  
• What peritoneal relationship does the sigmoid colon have?


  intraperitoneal

  suspended by sigmoid mesocolon

  
• What peritoneal relationship does the appendix have?

  intraperitoneal

  suspended by mesoappendix

  
• What are the structures of the rectum?

  rectosigmoidal junction: where sigmoid colon becomes rectum

  • No taeniae coli or omental appendices
  • Transverse rectal folds: help suspend a little bit of the weight of faeces before defecation

  
• At what point does rectum become the anal canal?

  at anorectal flexure

  tip of coccyx past Pelvic diaphragm

  
• What is Ampulla of rectum?

  dilated terminal part – supported by pelvic diaphragm (storage of faeces)

  
• What peritoneal relationship does the rectum have?


  each third has a different relationship:

  • Upper third: Intraperitonel
  • Middle third: Retroperitoneal
  • Lower third: Subperitoneal

  
• What are the sphincters of the anal canal?

  1. internal anal sphincter
  2. external anal sphincter

  
• What are the structures of the anal canal?

  1. anal columns: longitudinal ridges of mucosa
  2. anorectal junction: indicated by superior part of anal columns
  3. Anal valves - no function, however clinical significance as can get infected
  4. (+ internal and external anal sphincters)

  
• What is the Pectinate line?


  line where embryonic origin changes in anal canal

  Superior to line: embryonic hindgut

  Inferior to line: embryonic proctodeum

  Results in difference in blood supply, innervation and lymphatic drainage

  
• What is the Anocutaneous white line?

  Transition from non-keratinised squamous epithelium to keratinised squamous epithelium in the anal canal

  
• What is the Ampulla?

  site for faeces storage

  
• What is the Anorectal flexure?

  A sharp bend in the rectum

  80 degree flexure

  important for continence - straightens during defecation

  
• How is Faecal continence controlled (involuntary)?

  Involuntarily via Internal anal sphincter:

  • Thickening of circular muscle layer
  • Tonic contraction (sympathetic)
  • Contraction inhibited (parasympathetic) in response to distension of rectal ampulla

  
• How is Faecal continence controlled (voluntary)?

  Voluntarily via External anal sphincter:

  • Attached to perineal body and coccyx and blends with puborectalis (muscle of pelvic floor)
  • somatic innervation (inferior rectal. nerve and nerve to levator ani)