GI Tract Flashcards
What are the major functions of the digestive tract ?
- motility - propel ingested from mouth downwards
- secretion of juices - aid in digestion & absorption
- digestion - food broken down into absorbable molecules
- absorption - nutrients, electrolytes, water absorbed or transported from lumen of GIT to blood
What does the GI tract consist of ?
- oral cavity/mouth
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
- rectum
- anus
Define bolus
- portion of food swallowed at one time
Describe saliva
- water, salts, enzymes, mucus secreted by salivary glands to;
- moisten food & aid swallowing
- begins carbohydrate digestion
Describe what occurs in the oesophagus during digestion ?
- epiglottis closes airway
- bolus moved along by peristalsis
- cardiac sphincter - keeps food from backing up into oesophagus
Describe the anatomy of the oesophagus
- 25cm long
- 2 muscular rings - 1 at top and 1 at bottom = upper & lower oesophageal sphincter
Describe the upper oesophageal sphincter
- open reflexively upon swallowing
- remains open for 0.5-1 s
- this allows bolus to enter oesophagus
Describe the lower oesophageal sphincter
- relaxes reflexively 2 seconds after being stimulated by swallowing
- controls how quickly food travel from the throat to the stomach after being swallowed
- prevents the regurgitation of food, gastric juice & air
Describe what happens in the stomach ?
- gastric glands secrete gastric juice kills most bacteria, protein digestion begins & mucous secreted to protect lining
- chyme = semi-liquid mass of partially digested food
- pyloric sphincter - regulates passage of chyme into small intestine
Describe Chyme
- semi-fluid mass of partly digested food that is expelled by stomach via pyloric valve into duodenum
- results from chemical & mechanical breakdown of bolus
- slowly passes through pyloric sphincter into duodenum where nutrient extraction begins
Define the pyloric sphincter
- muscular valve that opens to allow food to pass from the stomach to the top of the small intestine (duodenum)
Define mucus
- physical barrier between lumen & epithelium
Define bicarbonate
- buffers gastric acid to prevent damage to epithelium
Define intrinsic factor
- complexes with vitamin B 12 to permit absorption
- glycoprotein produced by parietal cells of the stomach
What are the 2 types of pancreatic secretions ?
- Endocrine functions = secretes insulin & glucagon
- Exocrine functions = secretion of pancreatic juice, 2 components - aqueous & enzymatic component
Describe the aqueous component
- HCO3
- Important for neutralising stomach acid, so pancreatic enzymes can function
Describe the enzymatic components of exocrine pancreatic secretions
- Essential for digestion & absorption of carbohydrates, fats, proteins
- trypsin, chemotrypsin, lipase & amylase
What are the 3 sections of the small intestine ?
- duodenum
- Jejunum
- Ileum
Describe the duodenum
opening from common bile duct secretes fluid from;
- liver & gallbladder - bile emulsifies fats
- pancreas - amylase breaks down carbohydrates, sodium bicarbonate neutralises acidic chyme & lipase
Describe the small intestine
- 3 sections = duodenum, jejunum, ileum
- majority of nutrient absorption occurs
- receives bile & pancreatic juice
- folded many times to fit in the abdomen
What are the main functions of the large intestine ?
- absorbing water & electrolytes
- producing & absorbing vitamins
- forming & propelling faeces towards the rectum for elimination
What are the secretions of the large intestine ?
- alkaline secretion - neutralises acids produced by intestinal bacteria
- mucous for protection, lubrication of faecal matter
Describe the absorption of carbohydrates
- enterocytes absorb glucose & galactose through an Na-dependant secondary active transport, while fructose is absorbed by facilitated transport
Briefly describe the absorption of proteins
- whole proteins = endocytosis
- amino acids & di & tripe-tides by Na-dependent 2ry active transport
What can cause a peptic ulcer?
Heliobacter pylori infection = major cause
How do you test for H.pylori infection?
Urea Breath Test = depends on urease activity of organism to detect activate infection
- 13 C labelled urea given by mouth, CO2 detected in breath
Describe Zollinger-Ellison syndrome
- rare endocrine disorder with 3 interrelated pathologies
1. gastrinoma = gastrin secreting tumour
2. increased gastric acid secretion
3. peptic ulcers
What are some examples of upper GI tract issues ?
- dysphagia = difficulty swallowing
- gastritis = inflammation of stomach lining
- peptic ulcers = erosions of lining of stomach or duodenum
Define pancreatitis
- commonly caused by gallstones & alcoholism
- plasma amylase activity measured - for diagnosing acute pancreatitis
Define Plasma amylase
- arises from pancreas & salivary glands
- activity 10x normal diagnostic of acute pancreatitis
- activity returns to normal within 3-5 days
What are some symptoms of acute pancreatitis ?
- severe belly pain that may spread to back/chest
- nausea/vomiting
- rapid heart rate
- fever
- fluid build up in belly
- lowered BP
Describe the Xylose Absorption test
- test for carbohydrate absorption
- D-Xylose given, rapidly absorbed from small intestine, excreted in urine, little metabolised in liver
- assess intestines ability to absorb monosaccharide
- bacterial overgrowth & renal disease can give false positives
Describe Disaccharidase Deficiency
-most common = intolerance to one of the disaccharides (lactose, maltose,sucrose)
- defect may be congenital or acquired
- activity measured in intestinal mucosa biopsy specimens
Describe Hartnup Disease
- impaired transport of neutral amino acids & deficiency of some essential amino acids
What are some specialist tests that can be carried out on the GI tract ?
- endoscopy
- abdominal ultrasound
- barium X-ray
- MRI
