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True or false
- A. In the human, starch digestion begins in the stomach.
- F, starts in mouth with salivary amylase.
- B. Amino acids enter the lacteal by diffusion.
- F, enter blood stream, fat enters the lacteal.
- C. In humans the major digestive and absorptive processes take place in the small intestine.
- T, this has the greatest surface area for absorption
- D. The swallowing reflex facilitates closure of the glottis by raising the larynx.
- T, closure of the glottis is aided by muscles of the neck, which raise the larynx.
- E. Trypsinogen is converted to its active form trypsin by HCl.
- F, activated by enterokinase (now called enteropeptidase), an enzyme in the cells that line the duodenal mucosa; pepsinogen is activated by HCl.
- F. Pancreatic juice is an aqueous acidic solution.
- F, it is an alkaline solution, rich in bicarbonate that is secreted mainly by the ducts.
- G. Vitamin B and C are fat soluble.
- F, these are water soluble vitamins. A, D, E and K are fat soluble vitamins
- H. Calcium is absorbed only by simple diffusion.
- F, up to 50% is an active process involving a binding protein and a calcium stimulated ATPase pump. The remaining 50% is simple diffusion.
Enzymes of digestion
|Food group||Enzyme||Source||Site of action||Breakdown product|
|Sugar||Salivary amylase||Salivary glands||Mouth/Stomach||Disaccharides (i.e., maltose)|
|Pancreatic amylase||Pancreas||Small intestine||Disaccharides|
|Disaccharidases (i.e., maltase, sucrase, lactase)||Small intestine||Small intestine||Monosaccharides (e.g., glucose)|
|Protein||Pepsin||Stomach||Stomach||small peptide fragments|
|Trypsin||Pancreas||Duodenum||small peptide fragments|
|Chymotrypsin||Pancreas||Duodenum||small peptide fragments|
|Carboxy- peptidase||Pancreas||Duodenum||single amino acids|
|Enteropeptidase||Intestinal brush border (mucosa)||Small intestine||small peptide fragments|
|Fat||Lipase / co-lipase||Pancreas||Small intestine||free fatty acids, monoglycerides|
|Phospholipase A2, cholesterol esterase||Pancreas||Small intestine||cholesterol, lyso‐ lecithin (+fatty acid)|
- Ingest 2000 mL/day
- Saliva:1500 mL/day
- Gastric secretions: 2000 mL/day
- Bile: 500 mL/day
- Pancreatic secretions: 1500 mL/day
- Intestinal secretions: 1500 mL/day
- Small intestine absorbs 8500 mL/day
- Colon absorbs 400 mL/day
- 100 mL/day water excreted
True or false
- A. The Na+/Ca2+ exchanger is responsible for establishing the Na+ gradient by which many nutrients are transported across the enterocytes.
- F, a sodium gradient is important but it is established by a Na+/K+-ATPase.
- B. Water soluble vitamins are absorbed with the help of micelles.
- F, if they are water soluble they can not enter the hydrophobic/fatty micelle. Instead they are absorbed with the aid of transport proteins.
- C. The enzyme pepsin is required for activation of chymotrypsinogen
- F, pepsin is a stomach enzyme which is inactivated by normal pH, thus it can not activate chymotrpsinogen which is located in the neutral duodenum - enterokinase is responsible.
- D. Reduced absorption of vitamin B12 in the stomach can result in anaemia
- F, vitamin B12 malabsorption does cause anaemia, but this takes place in the terminal ileum.
- E. Lactose build up in the colon causes symptoms of lactose intolerance.
- T, lactose acts as an osmotic laxative and as a nutrient for bacteria with produce gas. Together this causes irritation, bloating and diarrhoea.
- F. The accommodation of the stomach is initiated by the enteric nervous system.
- F, the ENS contracts the stomach, but the vagus controls relaxation as the stomach fills.
- G. The enteric nervous system contains sympathetic and parasympathetic neurons.
- F, the ENS contains enteric neurons, with some terminals from symp and parasymp. The cell bodies for these are in peripheral ganglia.
- H. The secondary peristaltic wave during swallowing requires the enteric nerves.
- T, the ENS is responsible for peristalsis after the the initial peristaltic wave is started by the swallowing centre in the brain stem.
Control of the GIT
|Three motility reflexes||Function|
|3. Migrating Motility Complex (MMC)||Housekeeping|
|Two nerve layers||Function|
|1. Myenteric plexus (Auerbach's)||Motor and integrative functions|
|2. Submucosal plexus (Meissner's)||Secretion, vasodilation|
|Three types of enteric neuron||Function - Transmitter|
|1. Intrinsic sensory neurons||Detect stretch/nutrients - ACh / SP|
|2. Interneurons||Integrate reflexes - ACh / 5-HT, SOM, NO|
|3. Motor neurons||Relax smooth muscle - ATP, NO, VIP Contract smooth muscle - ACh, SP|
VIP = vasoactive intestinal peptide
- Pyloric sphincter
- A. increases intestinal surface area.
- B. absorbs fat.
- C. splits molecules by the addition of water.
- D. emulsifies fat.
- E. contains bacteria.
- F. secretions empty into the mouth.
- G. secretes watery alkaline fluid.
- H. sucrase and maltase.
- I. activates trypsin.
- J. guards exit of the stomach to small intestine. K. splits polypeptides into amino acids.
Hormones of digestion
|Hormone and class||Source||Stimulus||Action|
|Gastrin (polypeptide)||endocrine (G) cells of the stomach||entry of food into the stomach||stimulates secretion of HCl from the parietal cell of the stomach|
|Histamine (amine)||endocrine (ECL) cells of stomach||gastrin or ACh||stimulates secretion of HCl from the parietal cell of the stomach|
|Somatostatin (polypeptide)||endocrine (D) cells of stomach||low luminal pH or Ach||inhibits release of gastrin, histamine and acid|
|Chole-cystokinin (CCK) (polypeptide)||endocrine cells of the duodenum||arrival of food into the duodenum||contracts gall bladder and releases bile, stimulates pancreas secretion of enzymes|
|Secretin (polypeptide)||endocrine cells of the duodenum||acid in the duodenum||stimulates pancreas secretion of bicarbonate, stimulates liver duct cell secretion of bicarbonate|
There were two additional slides included here:
- What's the difference between somatostatin from the pancreas and the stomach