What type of surface is the GI tract?
External = epithelial lined
What other connections are made to the gut?
Salivary glands, liver, gallbladder, pancreas (exocrine)
Why do we need water in the gut lumen?
For chemical reactions to occur
What is the purpose of sphincters?
Divide sections to have functional areas (upper oesophageal sphincter, lower oesophageal, pyloric sphincter, ilieo-secal sphincter, anal sphincter)
What is the enteric nervous system?
Or the intrinsic nervous system = main divisions of the nervous system and consists of a mesh-like system of neurones that governs the function of the GI tract
What is the longest part of the gut?
SI = Jejunum, ileum – where most of the absorption takes place
What is the overall purpose of the gut?
Get food to – monosaccharides, small peptides, AA, FA, glycerol
Absorb water, vits, minerals
Expel waste produces that were not absorbed/not needed
What areas of the GI allow for mechanical disruption of food?
Mouth/teeth
Stomach = contractions liquify food to chyme
What enables the stomach to expand?
Rugae – temporary folds
What is the function of the colon?
Temp storage facility
Briefly outline the chemical digestion of the GI tract
Saliva = amylase, lipase
Stomach = acid, pepsin
Duodenum/jejunum = bile, exocrine pancreas
What is the function of the brush border of the SI?
Increase surface area
Briefly outline how the GI tract prevents entry of pathogens?
Saliva, HCL, liver (kupffer cells), peyers patches (lymphoid follicles, mucosa)
Outline the types of movement in the GI tract
Peristalsis = successive waves of involuntary contraction of longitudinal muscles
Segmentation = contractions of circular muscles
Haustral shunting = One haustrum distends as it fills with chyme, which stimulates muscles to contract, pushing the contents to the next haustrum
Mass movement = forcible peristaltic movements of short duration, 3-4 times a day
What features aid absorption in the gut?
Length
Folds
Villi/microvilli
What are the broad functions of the mouth?
Physical breakdown
Digestive enzymes released
Infection control
What is the broad function of the stomach?
Storage
Produce chyme
Infection control
Secrete intrinsic factor (vit B12)
What is the function of the UOS vs the LOS?
UOS = prevents air from entering the GI tract (weaker)
LOS = helps prevent reflux into oesophagus
What is the broad function of the duodenum?
Neutralisation/osmotic stabilisation of chyme
Pancreatic secretions
Bile is added
What are the broad functions of the jejunum/ileum?
final digestion
Nutrient absorption
Water/electrolyte absorption
Bile recirculation
B12 absorption
What drives water absorption in the large bowel?
Presence of aquaporins
What are the broad functions of the large bowel?
Final water/electrolyte absorption
Where is the largest amount of water absorbed in the GI tract?
SI
What is the peritoneal cavity?
Potential space between the parietal peritoneum and visceral peritoneum
What is the parietal peritoneum?
Surround the abdominal wall
What is the visceral peritoneum?
Surround the internal organs
What is the greater omentum?
Large apron-like fold of visceral peritoneum that hands down from the stomach, passes in front of the SI and doubles back to ascend to the transverse colon before reaching the posterior abdominal wall
What is the difference between the abdominal cavity and the peritoneal cavity?
P = cavity within the abdominal cavity - space between the parietal and visceral peritoneum, see-through
A = space bounded by the abdominal walls, diaphragm and pelvis
What is in the peritoneal cavity?
Nothing, apart from a small amount of fluid it secrets for lubrication
However it is a potential space
What are retro-peritoneal viscera?
Lie behind the peritoneal viscera with only there anterior surface in contact with the peritoneal but not enveloped
E.g. Kidneys
What is intra-peritoneal?
Inside the peritoneum
What is the mesentery?
Fold of peritoneum which attaches the stomach, SI, pancreas, spleen to the posterior abdominal wall, that allows a conduit of venous drainage, blood supply
What are the muscles of the abdominal wall?
External oblique abdominal muscle.
Internal oblique abdominal muscle.
Rectus abdominis.
Transverse abdominal muscle.
Pyramidalis muscle.
What does the transverse colon divide?
Divides the peritoneum into the supracolic and infracolic regions
What forms the rectus sheath?
Aponeuroses of the transverse abdominal and the external and internal oblique muscles
What are the paracolic gutters?
Space between the colon and the abdo wall
What is the pouch of douglus (recto-uterine)?
Extension of the peritoneal cavity between the rectum and back wall of the uterus
Only females
Deepest point in the peritoneal cavity
What is the vesico-uterine pouch?
Shallower pouch formed by peritoneum over the uterus and bladder
In females
What is the recto-vesicle pouch?
In men
Lies between the urinary bladder and the rectum
What are the quadrants of the abdo?
Lines = zifisternum to pubis (midline) + one side to another through the naval
Quadrants = RU, RL, LU, LL
What are the 9 regions of the abdo?
Lines = Midclavicular line each side, subcostal line (under costal cartilage), transtubecular line through iliac tubercles
Right/left hypocondrial (below anterior ribs) (top corners)
Right/left lumbar area (ouside middle)
Right/left inguinal regions (iliac fossa) (bottom corners)
Midline zones = Epigastric, umbilical, suprapubic
What are the layers of the anterolateal abdo wall?
Skin
Superficial fasica
Investing facia
Abdo muscles = external oblique, internal oblique, transverse abdominis, rectus abdominis
Endoabdominal fascia
Extraperitoneal (fascia) fat
Peritoneum – parietal + visceral
How does the innervation of the peritoneum affect pain?
Parietal = somatic afferent fibres = well-localised pain
Visceral = visceral afferent fibres = poorly localised (referred pain)
What regions are the stomach divided into?
Cardiac region
Fundus
body
Pyloric region (antrum and canal)