digestive system (wk 2) Flashcards
what does the prefix “Gastro-“ refer to?
the stomach (eg Gastrointestinal tract = stomach and intestines)
what does the prefix “Enter-“ refer to?
the intestines (eg Enteritis = inflammation of the intestines)
what does the prefix “Colo-“ or “Col-“ refer to?
the colon (large intestine, eg Colitis = inflammation of the colon)
what does the prefix “Hepato-“ refer to?
the liver (eg Hepatocyte = liver cell)
does the liver and kidneys change size at all during the day?
no
do the adrenal glands and pancreas change size during the day?
no
does the spleen and intestines change size during the day?
some size change
what type of cell… secretes acid which denatures protein and activates pepsinogen to the enzyme pepsin. also secretes intrinsic factor to bind vitamin B12 for absorption in the small intestine.
parietal cells
what type of cell… secretes gastrin, a hormone that helps regulate gastric function?
G cells
what type of cell… secretes mucus to protect the stomach lining from acid digestion?
mucous cells
what type of cell… secretes pepsinogen (precursor to pepsin, breaks down protein to peptides)
chief cells
true or false - the muscularis of the stomach is just the same as the muscularis in other parts of the gastrointestinal tract.
false - the muscularis of the stomach has a third, oblique layer of muscle that allows the contents of the stomach to be churned and mixed.
What is the main function of the pharynx?
to make sure air ends up in the trachea, and food/water in the oesophagus
which digestive processes occur in the oral cavity?
motility - (of food by tongue)
absorption (of some meds, anyway)
digestion (food broken up, amylase from saliva starts chemical digestion)
secretion - (saliva)
MADS
Why do you think pepsinogen is secreted from chief cells rather than the active form of the enzyme, pepsin?
if the active form was secreted in the gastric pit, it would start digesting the stomach walls… so converting it to the active form in the presence of acid in the stomach lumen sounds nicer
digested carbohydrates - what happens to them in the mouth?
mechanical breakdown, and salivary amylase starts to break down polysaccharides into disaccharides
digested carbohydrates - what happens to them in the stomach?
mechanical breakdown
digested carbohydrates - what happens to them in the small intestine?
pancreatic amylase breaks polysaccharides and oligosaccharides into disaccharides
digested carbohydrates - what happens to them in the Enterocytes (absorptive cells of the small intestine)?
brush-border enzymes break disaccharides into monosaccharides
digested carbohydrates - what is their final form and destination?
the monosaccharides created by enterocytes then enter blood vessels
digested proteins - what happens to them in the mouth?
mechanical breakdown
digested proteins - what happens to them in the stomach?
acid denatures proteins, and pepsin breaks proteins into polypeptides
digested proteins - what happens to them in the small intestine?
proteases break polypeptides into amino acids, dipeptides and tripeptides
digested proteins - what happens to them in the enterocytes?
peptidase further breaks some dipeptides and tripeptides into amino acids
digested proteins - what is their final form and destination?
amino acids and small peptides enter blood vessels
digested lipids - what happens to them in the mouth?
mechanical breakdown
digested lipids - what happens to them in the stomach?
mechanical breakdown
digested lipids - what happens to them in the small intestine?
bile salts emulsify lipids into smaller droplets.
pancreatic lipase breaks triglycerides into monoglycerides and fatty acids
bile salts form these into micelles
digested lipids - what happens to them in the enterocytes?
monoglyceride and fatty acids absorbed, cholesterol absorbed. inside cells triglycerides are reassembled and packed with cholesterol into chylomicrons. chylomicrons are then expelled by exocytosis
digested lipids - what is their final form and destination?
chylomicrons drain from extracellular fluid into lacteals - lymph drainage
short chain fatty acids diffuse into blood vessels
What is part of the cell membrane of an individual cell - microvilli, or villi?
microvilli are present on the membrane of intestinal epithelial cells (they’re also called the brush border)
which organ produces digestive enzymes - liver or pancreas?
pancreas
which nutrient can be absorbed when it is only partially digested - carbohydrates, or proteins?
proteins - can be absorbed as tripeptides, dipeptides and single amino acids, whereas carbohydrates have to be broken down into monosaccharides for absorption
which enzyme is found in the intestinal brush border, amylase or sucrase?
sucrase - it breaks down sucrose into glucose and fructose. (amylase is produced in the saliva and by the pancreas, breaks down starch into maltose)
What is the difference between a micelle and a lipid droplet?
lipid droplets contain undigested triglycerides, whereas micelles contain triglycerides in their digested form (monoglyceride and fatty acids)
Why are most fats absorbed into lacteals instead of blood capillaries?
fats are absorbed into lacteals because they are packaged into chylomicrons, which are too large to enter capillaries
what organ secretes bile?
the liver (either secreted straight into the small intestine, or stored in the gall bladder)
what does bile do?
Bile salts in bile emulsify fats in the small intestine so they are accessible to digestive enzymes.
what are the two secretions from the pancreas?
pancreatic juice - contains bicarbonate to neutralise the acid chyme in the small intestine, and provides enzymes for the digestion of starch, polypeptides, and triglycerides
pancreatic hormones - help regulate blood glucose concentrations
is pancreatic juice or bile secreted by acinar glands?
pancreatic juice
Describe the path of fats from absorption to the liver
- lipids are packaged into chylomicrons in the epithelial cells of the small intestine
- they then enter the lymphatic system through lacteals, and are transported into the large veins via the thoracic duct.
- they then travel through the systematic circulation and enter the liver through the hepatic artery.
what is bile produced by, secreted into, and then emptied into?
- produced by hepatocytes, then secreted into bile canaliculi, which empty into bile ducts.
bile can be stored in the gall bladder, or directly secreted into the small intestine via…
the common bile duct
how are hepatocytes supplied with oxygen?
sinusoids - they carry arterial blood from the hepatic artery as a source of oxygen for hepatocytes. they also receive venous blood from the hepatic portal vein (lower in oxygen)
water soluble vitamins - what other substance is needed for absorption?
No specific substance needed, move by diffusion into blood. Exception is B12.
B12 - what other substance is needed for absorption?
water soluble, but needs to be bound to intrinsic factor, mostly absorbed in the ileum
fat soluble vitamins - what other substance is needed for absorption?
need fat for absorption into lymphatics
minerals - what other substance is needed for absorption?
none needed, it’s directly absorbed in small intestine
water - what other substance is needed for absorption?
none - moves by osmosis (affected by solute concentration though)
ruminants - the colonic epithelium does not produce enzymes, and accessory organs do not secrete into the colon. Does any chemical digestion occur in the colon? If so, how?
enzymatic (chemical) digestion does occur in the colon, but the enzymes are all from the microbes
When comparing hindgut fermentation with forestomach fermentation, which statement is TRUE?
1 - The microbial populations are considerably different, but the products of digestion are the same.
2 - The microbial populations are the same, but the products of digestion are considerably different.
3 - Both the microbial populations and the digestion products are similar.
3 - Both the microbial populations and the digestion products are similar.
true or false - Structural carbohydrates of plants are not digested by hindgut fermentation.
false - hindgut fermentation (and foregut fermentation) allows breakdown of structural carbohydrates (including cellulose) by microbial enzymes
What are the main products of microbial fermentation of carbohydrates in the large intestine? Can the animal use these?
volatile fatty acids (VFAs) are the product of microbial fermentation, and can be absorbed as an energy source. in the horse, VFAs can be the major energy source when they are on a high fibre diet
true or false - the large intestine of cats and dogs has no circular folds, villi, or microvilli. some microbial digestion occurs in the hindgut, but it is of little importance to the animal.
true - it’s also relatively short
why are there lots of goblet cells in the mucosa of the large intestine - to produce mucus to lubricate the mucosa surface, or to produce mucous to protect against acid?
the former - mucus helps lubricate the mucosal surface, so faeces can easily pass along.
which structure is primarily affected by the cephalic phase of digestion - intestine, or stomach?
the stomach - thinking of, smelling, or seeing food results in signals to the stomach to prepare for food. this is the cephalic phase of digestion
which hormone increases the activity of the gastric muscularis - gastrin, or secretin?
gastrin - encourages more contractions of the muscularis of the stomach
Which hormone stimulates pancreatic enzyme secretion - Cholecystokinin (CCK) or Secretin?
Cholecystokinin (CCK) - stimulates pancreatic enzyme secretion to help digest peptides and sugars in the small intestine
Which hormone is released in response to decreased intestinal pH - gastrin or secretin?
secretin - this is released in response to acidic chyme entering the small intestine. it stimulates secretion of bicarbonate from the pancreas to buffer the acids
the sight, smell or thought of food gets the stomach prepared for the arrival of food… how?
with muscular contractions and secretion of acid and pepsinogen (this is the cephalic phase)
what cells secrete HCL, chief cells or parietal cells?
parietal cells
gastrin is released (from G cells) in response to….
stomach distension and the presence of peptides/amino acids
What are the main sources of energy in ruminants?
Volatile fatty acids - these are the byproduct of microbial fermentation of carbohydrates
What are proteins in ruminant diets broken down into extracellularly by peptidase - Pepsinogen, Propionate, or smaller peptides?
smaller peptides - peptidases released by rumen proteolyctic bacteria break down proteins to form small peptide chains
true or false - enzymes are not involved in fermentative digestion
false - microbial enzymes are part of fermentative digestion
What is the benefit of recycling large amounts of urea in ruminant animals?
urea is a waste product of amino acid metabolism, but microorganisms can convert urea into ammonium, which can be converted into amino acids then used to make microbial protein. when this ends up in the small intestine it can be broken down and absorbed