digestion Flashcards
what are the functions of the gastrointestinal system (6 steps related to digestion and absorption)?
ingestion secretion motility digestion absorption defecation
what is ingestion?
taking food in
what are several products which are secreted and what is secretion?
water, acids, buffers and enzymes
substances discharged from a cell, gland or organ for a particular function in the organism or for excretion
what is motility? and give an example?
contraction and relaxation of smooth muscle
e.g gastric molitity used to form chyme and expel it from stomach
what are the 2 types of digestion and what is it?
mechanical & chemical
the breaking down of large insoluble food molecules into smaller water-soluble food molecules by either physical breakdown or through the use of enzymes
what is absorption and what % is done by the small intestine?
process of absorbing substances into cells or across tissues by diffusion/osmosis
95%
what is defecation?
the discharge of indigestible substances, cells or digested materials which weren’t absorbed
what is the first step in the digestion process and what does it serve to do?
mastication (chewing)
- grind up food for swallowing
- mix food with saliva
- stimulate taste buds
when is swallowing induced?
and what is another name for it?
deglutition
initiated when a food bolus is forced by the tongue to the rear of the mouth to the pharynx
what is saliva, what does it contain and what is it produced by?
serous (watery) solution containing electrolytes, mucous, proteins (lyzozyme) and enzymes (amylase and lipase)
produced by 3 branched glands which produce 95% of volume
- parotid (cheek)
- submandibular (under chin)
- sublingual (under tongue)
what occurs during salivary gland secretion?
acinar (mucous) cells produce primary secretion that is isotonic with plasma
duct cells actively reabsorb Na+ and Cl- ions, some secretion of K+ and HCO3- ions (protection from acid)
impermeable to water thus producing hypotonic saliva for lubricant
what does isotonic mean?
an isotonic solution is 2 solutions which have the same osmotic pressure across a semipermeable membrane
allows for free movement of water across the membrane without changing the concentration of the solutes on each side
what does impermeable mean?
impermeable membrane blocks movement of all substances
what is meant by a hypotonic solution?
any solution that has a lower osmotic pressure (more water) than another solution
what is the function of the stomach?
stores food and delivers to gut
produces 3 waves per minute of chyme from mucosa (consists of partly digested food and gastric juices and is sent to SI)
what does gastric juice contain?
these gastric juices contain:
ions and mucus for protection
pepsins for protein digestion
HCI to activate pepsin, breakdown of tissue and kill bacteria
intrinsic factor for parietal cells for vitamin B12 absorption
what are the 3 phases of gastric secretion?
- cephalic phase (30% response to meal)
- gastric phase (60% response to meal)
- intestinal phase
what occurs during the cephalic phase (1st phase of gastric secretion)?
prior to arrival of food in stomach, vision, smell, chewing and taste stimulate gastric secretion (inhibited by fear or depression)
gastrin also released (hormone which stimulates gastric secretion)
what occurs during the gastric phase (2nd phase of gastric secretion)?
gastric secretion activated by semi-digested proteins and food swallowed
lasts 3-4 hours
gastrin (stimulates secretion of gastric juice) released by stretch of stomach
all stimulate motility
what occurs during the intestinal phase (3rd phase of gastric secretion)?
how is gastrin inhibited?
- chyme enters duodenum so decrease in gastric secretion and motility
- removal of peptide fragments (no more stimulation for gastrin release)
- removal of food (leads to decrease in pH and if <2 inhibits gastrin release)
- distention (expansion) of duodenum leads to release of hormones (including cholecystokinin which inhibits gastrin release)
what are the 2 types of small intestine motility and when and what are they used for?
- peristaltic, longitudinal contractions (main propulsive force over short distances)
- segmentation -contraction and relaxation of whole segments of intestine (mixes chyme with pancreatic secretions & bile and increase exposure to mucosal surface)
what are main features of the gastrointestinal tract?
outer longitudinal smooth muscle
inner circular smooth muscle
lumen lined with mucosa
muscle primed by pacemaker cells (interstitial cells of cajal) which initiate a basal electrical rhythm
what is the role of the intrinsic/enteric nervous system?
myogenic muscles responsive to stretch
neurons that govern the function of the gastrointestinal tract
what is the gastrointestinal (GI) tract?
which organs are in it?
how long is food/bolus/chyme at each stage?
series of hollow organs:
1. mouth - 10 secs
- esophagus (15 secs)
- stomach (2-4 hours)
- SI (3-12 hours)
- LI (24-72 hours)
- anus
which other organs apart from those in the GI tract contribute to digestion?
liver (secretion of bile acids)
pancreas (secretion of digestive enzymes)
gallbladder (concentration of bile)
what occurs in the pancreas?
acinar cells secrete enzyme rich Cl- solution
duct cells secrete HCO3- solution
CCK stimulates enzyme secretion
secretin stimulates HCO3- production
HCO3- necessary for:
- digestive ezyme activity
- micelle formation
- protecting duodenal muscosa
what is an example of an endocrine and exocrine gland and what do these words mean?
the pancreas
endocrine - secretes products directly into blood
exocrine - secretes products into ducts that lead to target tissue
how many hours does chyme take to reach the terminal ileum?
12 hours
what is the function of the ileal-caecal sphincter?
prevents retrograde moevment of chyme and bacteria from the colon
what is the principle function of the large intestine?
reabsorption of water
storage of faeces
how is salt and water absorption maximised in the large intestine?
perstaltic and segmental movement is slow and non-propulsive
how often do mass movemetns occurs in the LI and what do they do?
2-3 times a day
drive colonic contents towards the rectum
what is the function of bile?
bile acids help digestion and absorption of fats in SI
also route of excretion of bilirubin (waste product of red blood cells)
describe carb digestion?
ingested as complex carbs (starch and glycogen)
begins in mouth (amylase in saliva)
stops in acidic enviro of stomach
most digestion in SI by pancreatic-alpha-amylase
describe the absorption of carbs?
starch/glycogen (poly)
to lactose/maltose/sucrose (di) which are exposed to microvilli which has enzymes to break them down (sucrase etc.)
now mono
transporter (containing sodium) transports mono into cells (facilitated diffusion as high concentration of sodium out of cell and lower concentration within the cell)
in cell at higher concentration than in blood
describe liver blood supply?
hepatic artery supplies 30% of blood to liver
70% of blood from portal vein (deoxygenated but contains glucose)
where are glucose, fructose and galactose transported to?
directly to liver
what happens to fructose and galactose?
fructose and galactose converted to glucose derivatives
what happens to glucose?
glucose enters many organs by facilitated transport, skeletal muscle and adipose tissue regulated by insulin
what is the blood glucose response to ingestion of glucose or starch?
glucose - increases rapidly (30 mins) then drops
starch - longer to be absorbed and longer to be removed from blood
describe protein digestion?
begins in stomach (pepsin)
halted by alkaline
pancreatic secretions
majority occurs in SI by action of pancreatic enzymes (endo and exopeptidases) which must be activated outside of pancreas by trypsin
why must enzymes be activated outside of pancreas for protein digestion?
so that digestion of pancreatic proteins doesn’t occur
what is the difference between endo and exopeptidases?
endo - cleave interior peptide bonds
exo - cleave external peptide bonds
describe protein absorption?
di and tri peptides are further broken down to amino acids by intracellular peptidases of epithelial cell either inside or outside of it
absorption of amino acids occurs by diffusion and sodium dependent transport
what is the blood amino acid response to ingestion of amino acids or milk protein?
rapid rise in amino acids in blood until about 30 mins as no digestion needed then tails off
milk protein - have to be digested into amino acids before absorption so takes longer to peak and longer, slower release
what are the main functions of the liver?
- bile production
- metabolism
- detoxification of blood
what is the main function of the liver in digestion?
bile production
describe the properties of bile in digestion?
made up of bile salts and HCO3-
produced by liver and stored by gallbladder
aids excretion of bile pigments
90% of bile salts reabsorbed
describe the role of the gallbladder in digestion?
contracts following a meal to eject bile into duodenum
stimulated by secretin and CCK
function of a Kupffer cell?
break down and allow for detoxification of blood
describe the digestion of fat?
lipids emulsified by bile
lipases break down trigylcerides into fatty acids and monoglycerides
fatty acids and monoglycerides packaged into micelles absorbed by microvilli
fatty acids and monoglycerides converted back into triglycerides which aggregate with e.g cholesterol to form chylomicrons
move into lymph capillary which transports them to rest of body
what is the blood lipid response to ingestion of triglyceride?
steady increase which peaks at 6 hours (long digestion and absorption process)
what are the 2 types of vitamins absorbed into small intestine?
fat and water soluble vitamins
how are fat soluble vitamins absorbed?
absorbed same way as fat
how are water soluble vitamins absorbed?
pass through system quickly and not stored
through epithelial cells by diffusion if high concentration
active transport if low concentrations
how is water absorbed?
moves rapily across intestine in response to osmotic gradients ensuring lumial contents are isosmotic with interstitial fluid
hypotonic solution increases water absorption
what are the 3 main dissaccharides?
what are the monosaccharides that make them up?
what are the enzymes that hydrolyse them?
surcose - made up of glucose and fructose - hydrolysed by sucrase
maltose - made up of glucose and glucose - hydroolysed by maltase
lactose - made up of glucose and galactose - hydrolysed by lactase
what are the 2 forms of starch in the human diet?
what is their prevalence?
how do they differ?
amylose - 15-20% of diet - coiled for storage
amylopectin - 80-85% of diet - branched and 2 types of bonds: 1,4 and 1,6)
what are the names and functions of the 3 main hormones involved in digestion?
and where do they operate?
1) secretin - stimulates HCO production to neutralise acids in small intestine
2) gastrin - stimulates glands to secrete hydrocholric acid and pepsinogen in stomach
3) CCK - stimulated when fat is presented and stimulates gall bladder to release bile in small intestine
how does exercise intensity effect gastric emptying?
when is this important?
above 80% VO2 max, reduction of delivery fluids and nurteints to small intestine from stomach may occur
only important if doing interval exercise as can’t maintain such high intesnity exercise for long periods
why might a gall bladder be removed?
what happens when it is removed?
presence of gallstones causing inflammation
when removed - reduced ability to breakdown and absorb fat so less dietary lipid as lost in faeces
how does Alli work?
and what is it?
weight loss pill
fat converted into waste and not absorbed
how does alpha amylase work?
what do alpha amylase inhibitors do?
secreted in saliva or pancrase to breakdown amylose
inhibitors - impede digestion of dietary starch by inhibiting breakdown of amylose so not available for absorption
