0206 - Functions of the GI Tract Flashcards
What are the functions of the mouth?
Chewing (Mastication)
Voluntary movement, breaking food and mixing with saliva to form a bolus. Salivary amylase works to begin digestion.
What are the three phases of swallowing?
Oral phase (voluntary, tongue moves up, pushing bolus back) Pharyngeal phase (involuntary - food moves to oesophagus and UOS and LOS relax) Oesophageal phase (involuntary, food moves to stomach, LES closes last)
Outline the pharyngeal phase of swallowing
Reflex sequence. Food enters oropharynx, soft palate closes off the nasopharynx, the larynx moves upwards and is closed off by epiglottis, the UOS relaxes, and oesophageal peristalsis begins.
Outline the Oesophageal phase of swallowing.
Involuntary sequence controlled by swallowing centre. Two forms of peristalsis - primary peristalsis that starts below UOS and is caused by act of swallowing. If unsuccessful, secondary peristalsis is triggered by distension to keep the food moving.
What are the functions of the stomach?
Accommodation of food (largely in fundus)
Physical digestion (mixing, grinding, and peristalsis)
Secretion of gastric juice containing HCl and enzymes
Chemical digestion via Pepsin (protein-> peptides) and Gastric lipase (break down triglycerides)
Endocrine - Gastrin (stimulates acid secretion) Somatostatin (inhibits acid secretion).Stomach accommodation
What are the three forms of small intestine digestion?
3 areas - Pancreatic juices, bile, and membrane digestion
Briefly outline pancreatic juice digestion
In small intestine
Pancreatic amylases digest polysaccharide carbohydrates into oligosaccharides.
Trypsin and chymotrypsin hydrolize proteins into oligopeptides
Pancreatic lipases break down lipids (TAGs) into fatty acids and monoglycerides.
Briefly outline bile digestion
Bile salts assist in emulsification (into micelles) and absorption of lipids, cholesterol and phospholipids.
Briefly outline small intestine membrane digestion
Brush border enzymes contain oligosaccharidases to digest oligosaccharides into monosaccharides, and peptidases to digest oligopeptides into amino acids.
Briefly outline small intestine absorption
Monosaccharides and AAs are absorbed through specific membrane transporters, whereas FAs, cholesterol and lipids diffuse through the cell.
Outline the balance of fluid in the GI tract
2L of liquid ingested, plus 1L saliva, 2L gastric juice, 1L bile, 2L pancreatic juice and 1L intestinal juice secreted per day =9L/day ingested or secreted
SI absorbs 8L and LI absorbs 0.9L, leaving 8.9L absorbed and 0.1L excreted in faeces per day.
What are the small intestine endocrine hormones? What do they do?
Secretin stimulates pancreas secretion.
Cholecystokinin contracts the galbladder.
What is the small intestine’s immune function?
Lymphocytes are diffused in mucosa and aggregated in Peyer’s patches. They protect against bacteria, viruses and protozoa, and permit tolerance.
What are the functions of the large intestine?
Proximal colon - absorb fluids and electrolytes.
Distal colon - store colonic contents
Rectum - Defecation.
What is a major complication of a low fibre diet?
Diverticulosis - diverticula form in large intestine, essentially as outpouchings.
What are the two forms of motility in the colon?
Segmentation
Mass peristalsis - 1-3/day - push fecal matter long-distance. Haustra disappear with the contractions.
What are the three requirements for normal GIT motility?
- Smooth muscle in gut wall.
- ENS (control system)
- Communications - CNS, Sympathetic/parasymp, hormones.
What are the seven major functions of the liver?
Over 200 functions in seven major areas: Carbohydrate metabolism Lipid Metabolism Protein Metabolism Detoxification Bile secretion Defence Storage
Briefly outline the liver’s role in carbohydrate metabolism.
Maintain normal blood glucose level through glycogen synthesis, glycogenolysis, and gluconeogenesis.
Briefly outline the liver’s role in lipid metabolism
Synthesise cholesterol, fatty acids, and phospholipids. Synthesise VLDL to transport triglycerides and cholesterol.
Briefly outline the liver’s role in protein metabolism.
Synthesise over 30 proteins, incl albumin, lipoproteins, and coagulation factors
Uptake and metabolise amino acids
Synthesise glutathione for detoxification and protection against oxidative stress
Detoxify ammonia by forming urea.
Briefly outline the liver’s role in detoxifying bilirubin.
Macrophage releases unconjugated bilirubin from Hb into bloodstream where it conjugates with albumin (conjugated = water soluble). It is released from the albumin and enters hepatocytes, which conjugate it with glucuronic acid, and release it in bile where it enters the GIT and feces.
Briefly outline the liver’s role in bile production and secretion.
(Including role of bile)
Synthesise bile salts from cholesterol. Bile helps lipid digestion and absorbtion of lipid-soluble vitamins (A, D, E, K). The liver also excretes waste products through bile.
Briefly outline the liver’s role in defence of the body.
Kupffer’s cells (macrophages) in the liver filter the blood, removing bacteria, endotoxins, parasites, and aging red blood cells.
Briefly outline the liver’s role as a storage organ.
Liver stores lipid-soluble vitamins (A, D, E, K), copper, and iron.
What does the liver function test detect?
Detoxification, hepatic cell damage, bile duct cell damage, synthetic function (i.e. protein synthesis), and inflammation.
Summarise the functions of the GIT.
Ingestion - Eating/Drinking
Secretion - Produce and release fluids by epithelial cells and accessory organs
Digestion - Mechanical and chemical
Motility - Contractions mix food and juices, move along GIT
Absorption - Uptake small molecules from GIT to blood or lymph
Defecation - Pass faeces - mix of indigestible good, bacteria, and shed cells.
Liver functions.
