Session 1: Setting the Scene Flashcards
4 layers of the GI tube
Mucosa Submucosa Muscularis externae Serosa
3 parts of the mucosa
Epithelial layer Lamina propria Muscularis mucosae
Broad functions of the epithelial layer of the mucosa.
Selective permeability barrier (osmosis) Facilitation transport and digestion of food Promotion of absorption Production of hormones Production of mucus
Broad functions of the lamina propria +layout.
Immune system Lots of lymphoid nodules and macrophages for production of antibodies (IgA which is resistant to proteases) to protect against bacterial and viral invasion.
Broad functions of the muscularis mucosae.
Layers of smooth muscle orientated in different directions. Keeps epithelium in contact with gut contents Helps keep crypt contents dynamic
Layout and broad functions of the submucosa.
Dense connective tissue Blood vessels Glands Lymphoid tissue Contains the Meissner’s plexus for the enteric nervous system.
Layout and broad functions of the muscularis externae.
An inner circular muscle layer with the Auerbach’s plexus An outer longitudinal muscle layer. Motility.
Epithelia of the gut (type)
Stratified squamous in oesophagus and distal anus (where you can touch) Simple columnar in the rest
Predominant cell of the small intestine and colon.
The enterocyte.
Broad functions and layout of enterocytes.
One cell layer thick. Needed to transport nutrients through the apical membrane and the basolateral membrane where the blood vessels and lymphatics lie juxtaposed below the enterocyte. Has microvilli to increase surface area.
Functions of the goblet cells.
Secretion of mucus to protect the epithelia of the gut from friction (lubricant), protection from chemical damage (acidic environment) and protection from bacterial inflammation by forming a physical barrier.
Components of the serosa.
Blood and lymph vessels and adipose tissue and continuous with the mesenteric.
Where can goblet cells mainly be found in the gut (which parts)?
Duodenum to colon in increasing number.
What are foveolar cells?
Gastric surface mucous cells which line the gastric mucosa/gastric pits which secrete mucus/HCO3 that forms barrier to stomach acid in order to avoid chemical damage and irritation/inflammation.
What increases the surface area of the gut?
Permanent folds Villi Microvilli
Why are permanent folds, villi and microvilli important?
Because a larger surface area favours absorption.
Different types of permanent folds and where to find them.
Rugae in stomach Plica circulares in small intestine Haustra sacculations in large intestine
Where can you find villi?
In small intestines but not in colon
Where can you find crypts?
In small and large intestines Aka crypts of Lieberkuhn/intestinal glands.
What specialised cells do the crypts contain?
Stem cells Paneth cells Enteroendocrine cells
How quickly can stem cells replace epithelia in the gut?
Every 2-4 days
Location and function of the paneth cells.
Located at the base of crypts (Where you can find stem cells as well) Secrete antibacterial proteins to protect stem cells of the same crypts. Histologically the secretory vesicles are bright red (protein).
Location and function of the enteroendocrine cells.
Located deeper in crypts and gastric glands. Secrete hormones that control the function of the gut like gastrin (stomach acid), cholecystokinin (bile) and secretin (neutralising acid).
Examples of exocrine glands in the gut.
Salivary glands Pancreas Brunners glands (found in the duodenum which neutralise acid)
Layers of the abdominal wall
Skin Fascia and fat (superficial and deep) Anterolateral muscles which are: External oblique (hands in pocket fibre direction) Internal oblique (perpendicular fibre direction) Transverse abdominis (more or less horizontal direction) Rectus abdominis (vertical direction) Transversalis fascia Peritoneum
Aponeurosis of the abdominal wall.
Thin sheet like tendon which is associated with external oblique, internal oblique and transverse abdominis.
What is the rectus sheath?
The aponeurosis of the lateral muscles surrounding the rectus abdominis.
When can you find the arcuate line?
At the lower limit of the posterior layer of the rectus sheath. Roughly half way between the umbilicus and the pubic crest.
What is the peritoneal cavity lined with?
Mesothelium Flattened simple squamous epithelia with a basement membrane and dense irregular connective tissue.
Functions of the mesothelium lining.
Production of lubricating fluid Enveloping certain viscera (got both a visceral peritoneum (intraperitoneal) and a parietal peritoneum (lining the cavity wall) Also a retroperitoneal viscera which are not enveloped and lie posterior to peritoneal cavity.
How do the aponeuroses differ above and below the arcuate line?
Above the arcuate line the aponeurosis of the external oblique goes in front of the rectus abdominis. The aponeurosis of the internal oblique goes around the rectus abdominis. The aponeurosis of the transverse abdominis goes posterior to the rectus abdominis. However below the arcuate line all aponeuroses go anterior to rectus abdominis.
Purpose of the lubricating fluid of the peritoneal cavity.
To create a frictionless environment.
What is the mesentery?
A double fold of peritoneum of contiguous tissue that attaches certain viscera to the posterior abdominal wall. Fixes the viscera in place.
Viscera attached to the mesentery.
Jejunum Ileum Appendix Transverse colon Sigmoid colon Rectum
What does the mesentery contain?
Blood vessels Lymph vessels Nerves Fat
Purpose of the mesentery.
Fix viscera to posterior abdominal wall. Supply intraperitoneal viscera with blood, lymph, nerves etc…
Pain reception difference between the parietal peritoneum and the visceral peritoneum.
Parietal peritoneum has somatic nervous reception so it can feel pain much clearer than the visceral peritoneum. Localised and accurate pain will be expressed by parietal peritoneum, this is not possible with the visceral peritoneum (pain not originate where one might feel it).
