GI ANATOMY Flashcards
What is the GIT/alimentary canal composed of?
mouth pharynx oesophagus stomach small intestine large intestine rectum anus
What are the secondary accessories of the GIT?
teeth tongue salivary glands liver pancreas gall bladder
What are the 4 parts of the large intestine?
cecum
colon
rectum
anus
What is the role of the rectum?
to store faeces
What is the role of large intestine?
Absorbs water and electrolytes from residual food contents from small intestine
What do the salivary glands produce?
Secrete saliva
What does saliva contain?
Amylase lipase mucin water ions
What are the 3 types of salivary glands?
Parotid- sides of cheek/face
sub mandibular- below jaw
sublingual- under tongue
What is the role of the oesophagus?
Transfers food from Pharynx to stomach
What is the structural composition of the oesophagus?
Upper sphincter- allows food to pass
lower sphincter- allows food into stomach and keeps it their and prevents heartburn and acid reflux
What causes gastric acid reflux into oesophagus?
Lower oesophageal sphincter relaxation
What is the role of the pancreas?
Secretes digestive enzymes amylase for starch digestion lipase for lipid digestion trypsin and chymotrypsin HCO3 secretion= neutralises duodenum gastric acid
What is the role of the liver?
Synthesises bile acids- taurocholic acids
bile acids needed for lipid emulsification for absorption of fat soluble vitamins
What is the mechanism of bile acid synthesis?
Acetyl co A produces bile acid
stored in gall bladder then into bile duct then into duodenum and absorbed from ileum to liver
AcoA recycled and reused
cholesterol= intermediate product and high levels= atherosclerosis
What is the role of the stomach?
protein digestion
some absorption
What are the contents of the stomach?
proteases- pepsinogen
gastric acid= hcl + mucous + water + enzymes + electrolytes
What cell types make up the stomach and what is their?
G cells= found in antrum and secrete gastrin
Mucous secreting cells in cardiac region
Chief cells found in fundus or stomach body and secretes pepsinogen and lipase
Parietal/oxyntic cells and secrete hcl by 3 processes
1. sight and smell of food= brain signals g cells to release gastrin and stomach stretching also releases gastrin this binds to parietal cell receptor synthesising H+/K+ atpase so H+ secreted into stomach
2. stomach nerves= Ach released and binds parietal cell receptor producing HCl
3. Ach binds enterochromaffin ECL cells and releases histamine which binds parietal cell receptor and produces HCl
Describe the positive feedback mechanism of chief cells?
pepsinogen secreted in inactive pepsin form/zymogen
pepsin secreted into stomach lumen
exposed to HCl
converted into active pepsin
when more pepsinogen secreted its converted into pepsin by the action of pepsin acting by a positive feedback mechanism
How is the stomach protected from HCl and proteases?
Alkaline mucous barrier from foveolar cells
Tight junctions between epithelial cells so HCl and protease movement restricted
High cell turnover
Cell migration every 2-3 days to replace damaged cells and maintain the barrier
What are the consequences of the mucous barrier being broken?
HCl and protease exposed to epithelial cells
food secretions and bacteria enter peritoneal cavity
cause damage to blood vessels and GIT bleeding= gastric/duodenal ulcers and peritonitis
What is the role of the small intestine?
Absorption
some digestion
What does the intestinal juice contain?
carb digesting enzymes maltase, lactase and sucrase
Describe the structure of the small intestine?
duodenum
jejunum
ileum
Explain the structural adaptations of the small intestine?
Plicae= folds= increase SA
Villi= finger like projections on the plicae= increase SA
Microvilli= microscopic projections on villi= increase SA
Epithelium one cell thick= short diffusion distance from lumen to circulatory system
Enterocytes= responsible for digestion as they have enzymes that convert non-absorbable macro molecules to absorbable small molecules
Describe carbohydrate digestion and absorption in the small intestine?
Digestion
Sucrase= sucrose to glucose + fructose
Lactase= lactose to glucose + galactose
Maltase= maltose to glucose + glucose
Absorption
Glucose and galactose= SGLT1 or Na/glucose transporter allows entry into enterocytes from lumen high conc down electrochemical gradient
Fructose= Na dependent GLUT 5 transporter in basolateral memb
Describe protein digestion and absorption in the small intestine?
Digestion
Proteins digested by protease into small peptides and AA’s
Absorption
small peptide= H+ dependent PEPT1 down electrochemical gradient form high conc lumen to low conc cell
Describe Lipid absorption in the small intestine?
triglyceride into free fatty acids
solubilised by bile acids into micelle
micelle absorbed by diffusion
What is another type of absorption that also occurs in the small intestine?
mineral absorption
What are the steps in the swallowing process?
- Food swallowed
- Food down oesophagus
- Oesophagus passes through diaphragm through the oesophageal hiatus then to stomach
What structures are involved in the swallowing process?
- Trigeminal nerve
- Facial- tongue, tonsils
- Glossopharyngeal nerve
- Hypoglossal nerve
- Vagus nerve
How is the swallowing process initiated?
Mouth and throat receptors relay information to medulla oblongata in brain stem
Brain processes information about food
Brain sends impulses to throat musculature
Process of swallowing triggered
Describe the gastric acid secretion mechanism?
G cells in antrum= gastrin into blood in response to food
Activates receptor on ECL cells
ECL releases histamine
Histamine binds parietal cell receptor
Induces h+/k+ atpase
Acid release into lumen suppresses gastrin release
What is peristalsis?
Wave of muscular contraction which propels contents along GIT
Describe the mechanism of peristalsis?
Circular muscles in intestine contract= moves food bolus along GIT
Material doesn’t move backwards
Longitudinal muscle contract: squeezes on the food pushing it forward
Then more circular muscle encountered
