Gastrointestinal System Flashcards
Outline the functions of the GI system?
to provide a port of entry for food into the body • to mechanically disrupt the food • to temporarily store the food • to chemically digest the food • to kill pathogens in the food • to move the food along the tract • to absorb nutrients from the resultant solution • to eliminate residual waste material
What is digestion?
Digestion is the conversion of what we eat into a solution from which we can absorb our nutrients
What is the role of saliva?
- Starts digestion (amylase and lipase)
- Bacteriostatic (contains Immunoglobulin A antibody (IgA))
- High calcium (protects teeth)
- Alkaline
- Assists swallowing
- Protects the mouth
What is the muscle distribution in the oesophagus?
Upper end oesophagus – voluntary control (some striated skeletal muscle)
Lower end oesophagus – involuntary control (solely smooth muscle)
What is the epithelium in the oesophagus?
Epithelium – stratified squamous non-keratinized (withstands abrasion)
What are the roles of the stomach?
-acts as a necessary food store (we can eat faster than digest)
• wall relaxes so pressure doesn’t rise (called receptive relaxation)
• contracts rhythmically to mix and disrupt (details in GI Unit)
• secretes acid and proteolytic enzymes to break down tissues and disinfect
• protects its epithelium by secreting mucus
• produces hypertonic chyme by combined action of acid, enzymes andagitation
• delivers incompletely digested chyme slowly, and in a controlled way, to the duodenum
What is the role of the mucous secreting cells in the gastric pits?
Surface mucous cells are abundant in the gastric pits but infrequent in the tubular gastric glands below. Their secreted mucus is resistant to pepsin (enzymatic) degradation. The mucus is released in response to distension, stomach contents, and acid secretion from the gastric glands. Alcohol or aspirin can damage the mucous cells but they are quickly replaced by mitosis in deeper cells in the neck of the gastric pit. The secreted mucus contains HCO ions which neutralise the effect of H+ ions and thereby protect the stomach lining.
What do parietal cells do?
Parietal cells secrete H+ ions into the lumen and HCO3- ions to nearby capillaries, which move it to surface mucous cells.
What do chief cells do?
Chief cells secrete pepsinogens which are converted into pepsins which partly hydrolyse proteins.
What do enteroendocrine cells do?
Enteroendocrine cells include G cells which secrete gastrin. The wider gastric mucosa responds to
this hormone by secreting acid.
What are Brunner’s glands?
Found in duodenum wall. They secrete bicarbonate–rich mucus, to neutralise acidic chyme.
How does hypertonic chyme become isotonic in the duodenum?
Water drawn in from ECF to render hypertonic chyme, isotonic:
• Liver releases bile (generally via the gall bladder).
bile contains: water, alkali, bile salts
• Pancreas & liver secrete alkali to neutralise acidic chyme (precisely controlled)
• Pancreas, liver and intestine secrete specific enzymes which act, with bile, to complete digestion of chime (enzymes come to lie in ‘unstirred layer’)
Summarise the result by the end of travel through the small intestine
Enzymes from pancreas and intestine have:
- Cleaved peptides to amino acids
- Cleaved polysaccharides to monosaccharides
- Broken down and re-formed lipids
- Broken down nucleic acids
right solution but it is in the wrong place (lumen)
How is absorption optimised?
- active process
- large surface area (it’s a slow process) as gut is folded/villi/micro-villi
- Adequate contact time (control of gut transit)
- Good blood supply/drainage (latter via hepatic portal vein; all nutrients travel via the liver)
Describe absorption at the duodenum, jejunum and ileum
- Duodenum absorbs iron
- Jejunum absorbs most of sugars, aa’s and fatty acids
- Ileum absorbs Vit B12, bile acids and remaining nutrients
By terminal Ileum:
- Nutrients absorbed
- Much water, still to be absorbed
