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Nutrition & metabolism > digestion > Flashcards

digestion Flashcards

1
Q

what are the functions of the gastrointestinal system (6 steps related to digestion and absorption)?

A 
ingestion
secretion
motility
digestion
absorption
defecation
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2
Q

what is ingestion?

A

taking food in

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3
Q

what are several products which are secreted and what is secretion?

A

water, acids, buffers and enzymes

substances discharged from a cell, gland or organ for a particular function in the organism or for excretion

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4
Q

what is motility? and give an example?

A

contraction and relaxation of smooth muscle

e.g gastric molitity used to form chyme and expel it from stomach

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5
Q

what are the 2 types of digestion and what is it?

A

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

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6
Q

what is absorption and what % is done by the small intestine?

A

process of absorbing substances into cells or across tissues by diffusion/osmosis

95%

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7
Q

what is defecation?

A

the discharge of indigestible substances, cells or digested materials which weren’t absorbed

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8
Q

what is the first step in the digestion process and what does it serve to do?

A

mastication (chewing)

  1. grind up food for swallowing
  2. mix food with saliva
  3. stimulate taste buds
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9
Q

when is swallowing induced?

and what is another name for it?

A

deglutition

initiated when a food bolus is forced by the tongue to the rear of the mouth to the pharynx

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10
Q

what is saliva, what does it contain and what is it produced by?

A

serous (watery) solution containing electrolytes, mucous, proteins (lyzozyme) and enzymes (amylase and lipase)

produced by 3 branched glands which produce 95% of volume

  1. parotid (cheek)
  2. submandibular (under chin)
  3. sublingual (under tongue)
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11
Q

what occurs during salivary gland secretion?

A

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

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12
Q

what does isotonic mean?

A

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

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13
Q

what does impermeable mean?

A

impermeable membrane blocks movement of all substances

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14
Q

what is meant by a hypotonic solution?

A

any solution that has a lower osmotic pressure (more water) than another solution

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15
Q

what is the function of the stomach?

A

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)

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16
Q

what does gastric juice contain?

A

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

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17
Q

what are the 3 phases of gastric secretion?

A
  1. cephalic phase (30% response to meal)
  2. gastric phase (60% response to meal)
  3. intestinal phase
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18
Q

what occurs during the cephalic phase (1st phase of gastric secretion)?

A

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)

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19
Q

what occurs during the gastric phase (2nd phase of gastric secretion)?

A

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

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20
Q

what occurs during the intestinal phase (3rd phase of gastric secretion)?

how is gastrin inhibited?

A
  1. chyme enters duodenum so decrease in gastric secretion and motility
  2. removal of peptide fragments (no more stimulation for gastrin release)
  3. removal of food (leads to decrease in pH and if <2 inhibits gastrin release)
  4. distention (expansion) of duodenum leads to release of hormones (including cholecystokinin which inhibits gastrin release)
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21
Q

what are the 2 types of small intestine motility and when and what are they used for?

A
  1. peristaltic, longitudinal contractions (main propulsive force over short distances)
  2. segmentation -contraction and relaxation of whole segments of intestine (mixes chyme with pancreatic secretions & bile and increase exposure to mucosal surface)
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22
Q

what are main features of the gastrointestinal tract?

A

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

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23
Q

what is the role of the intrinsic/enteric nervous system?

A

myogenic muscles responsive to stretch

neurons that govern the function of the gastrointestinal tract

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24
Q

what is the gastrointestinal (GI) tract?

which organs are in it?

how long is food/bolus/chyme at each stage?

A

series of hollow organs:
1. mouth - 10 secs

  1. esophagus (15 secs)
  2. stomach (2-4 hours)
  3. SI (3-12 hours)
  4. LI (24-72 hours)
  5. anus
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25
Q

which other organs apart from those in the GI tract contribute to digestion?

A

liver (secretion of bile acids)
pancreas (secretion of digestive enzymes)
gallbladder (concentration of bile)

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26
Q

what occurs in the pancreas?

A

acinar cells secrete enzyme rich Cl- solution
duct cells secrete HCO3- solution
CCK stimulates enzyme secretion
secretin stimulates HCO3- production

HCO3- necessary for:

  1. digestive ezyme activity
  2. micelle formation
  3. protecting duodenal muscosa
27
Q

what is an example of an endocrine and exocrine gland and what do these words mean?

A

the pancreas

endocrine - secretes products directly into blood

exocrine - secretes products into ducts that lead to target tissue

28
Q

how many hours does chyme take to reach the terminal ileum?

A

12 hours

29
Q

what is the function of the ileal-caecal sphincter?

A

prevents retrograde moevment of chyme and bacteria from the colon

30
Q

what is the principle function of the large intestine?

A

reabsorption of water

storage of faeces

31
Q

how is salt and water absorption maximised in the large intestine?

A

perstaltic and segmental movement is slow and non-propulsive

32
Q

how often do mass movemetns occurs in the LI and what do they do?

A

2-3 times a day

drive colonic contents towards the rectum

33
Q

what is the function of bile?

A

bile acids help digestion and absorption of fats in SI

also route of excretion of bilirubin (waste product of red blood cells)

34
Q

describe carb digestion?

A

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

35
Q

describe the absorption of carbs?

A

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

36
Q

describe liver blood supply?

A

hepatic artery supplies 30% of blood to liver

70% of blood from portal vein (deoxygenated but contains glucose)

37
Q

where are glucose, fructose and galactose transported to?

A

directly to liver

38
Q

what happens to fructose and galactose?

A

fructose and galactose converted to glucose derivatives

39
Q

what happens to glucose?

A

glucose enters many organs by facilitated transport, skeletal muscle and adipose tissue regulated by insulin

40
Q

what is the blood glucose response to ingestion of glucose or starch?

A

glucose - increases rapidly (30 mins) then drops

starch - longer to be absorbed and longer to be removed from blood

41
Q

describe protein digestion?

A

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

42
Q

why must enzymes be activated outside of pancreas for protein digestion?

A

so that digestion of pancreatic proteins doesn’t occur

43
Q

what is the difference between endo and exopeptidases?

A

endo - cleave interior peptide bonds

exo - cleave external peptide bonds

44
Q

describe protein absorption?

A

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

45
Q

what is the blood amino acid response to ingestion of amino acids or milk protein?

A

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

46
Q

what are the main functions of the liver?

A
  1. bile production
  2. metabolism
  3. detoxification of blood
47
Q

what is the main function of the liver in digestion?

A

bile production

48
Q

describe the properties of bile in digestion?

A

made up of bile salts and HCO3-
produced by liver and stored by gallbladder
aids excretion of bile pigments

90% of bile salts reabsorbed

49
Q

describe the role of the gallbladder in digestion?

A

contracts following a meal to eject bile into duodenum

stimulated by secretin and CCK

50
Q

function of a Kupffer cell?

A

break down and allow for detoxification of blood

51
Q

describe the digestion of fat?

A

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

52
Q

what is the blood lipid response to ingestion of triglyceride?

A

steady increase which peaks at 6 hours (long digestion and absorption process)

53
Q

what are the 2 types of vitamins absorbed into small intestine?

A

fat and water soluble vitamins

54
Q

how are fat soluble vitamins absorbed?

A

absorbed same way as fat

55
Q

how are water soluble vitamins absorbed?

A

pass through system quickly and not stored

through epithelial cells by diffusion if high concentration
active transport if low concentrations

56
Q

how is water absorbed?

A

moves rapily across intestine in response to osmotic gradients ensuring lumial contents are isosmotic with interstitial fluid

hypotonic solution increases water absorption

57
Q

what are the 3 main dissaccharides?

what are the monosaccharides that make them up?

what are the enzymes that hydrolyse them?

A

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

58
Q

what are the 2 forms of starch in the human diet?

what is their prevalence?

how do they differ?

A

amylose - 15-20% of diet - coiled for storage

amylopectin - 80-85% of diet - branched and 2 types of bonds: 1,4 and 1,6)

59
Q

what are the names and functions of the 3 main hormones involved in digestion?

and where do they operate?

A

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

60
Q

how does exercise intensity effect gastric emptying?

when is this important?

A

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

61
Q

why might a gall bladder be removed?

what happens when it is removed?

A

presence of gallstones causing inflammation

when removed - reduced ability to breakdown and absorb fat so less dietary lipid as lost in faeces

62
Q

how does Alli work?

and what is it?

A

weight loss pill

fat converted into waste and not absorbed

63
Q

how does alpha amylase work?

what do alpha amylase inhibitors do?

A

secreted in saliva or pancrase to breakdown amylose

inhibitors - impede digestion of dietary starch by inhibiting breakdown of amylose so not available for absorption

Nutrition & metabolism (20 decks)

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