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ESS1606 Nutrition and metabolism > Digestion and absorption > Flashcards

Digestion and absorption Flashcards

1
Q

gastrointestinal system

A
  • One long tube
  • Ingestion
  • Secretion
  • Motility
  • Digestion
  • Absorption
  • Defecation
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2
Q

ingestion

A

taking food in

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3
Q

secretion

A

water, acids, buffers, enzymes

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4
Q

motility

A

contraction and relaxation of smooth muscle

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5
Q

digestion

A

mechanical and chemical

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6
Q

absorption

A

95% via small intestine

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7
Q

defecation

A

indigestible substances, cells, digested materials not absorbed

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8
Q

oral cavity

A

Mouth and pharynx - back of mouth

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9
Q

first step in digestion process

A

mastication (chewing)

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10
Q

what does mastication do?

A

o Grind up food for swallowing
o Mix food with saliva
o Stimulate taste buds

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11
Q

when is swallowing (deglutition) initiated?

A

when food bolus forced by tongue to rear of mouth to pharynx - stops food going into lungs

voluntary and involuntary - how hard and what side of mouth

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12
Q

saliva

A
  • Serous (watery) solution containing electrolytes, mucous, proteins (immunoglobulin A, lysozyme) and enzymes (amylase, lipase)
  • Produced by 3 pairs of branched glands that provide 95% of total salivary volume (1l/day)
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13
Q

glands that produce saliva

A 
o Parotid (cheek, 60%)
o Submandibular (under chin)
o Sublingual (under tongue)
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14
Q

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) - make cells more watery
  • Impermeable to water, producing hypotonic saliva for lubricant)
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15
Q

stomach

A

• Stores food/delivers to gut
o Ingestion mins, digestion hours
• Chyme (3 waves/min)
• Secretes 2-3 l/day of gastric juice from mucosa

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16
Q

regulation of gastric secretion

A
  • Cephalic phase
  • Gastric phase
  • Intestinal phase
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17
Q

cephalic phase

A
  • (30% of response to meal) - start secretion
    o Prior to arrival of food in stomach, vision, smell, chewing, taste stimulate gastric secretion (inhibited by fear or depression)
    o Gastrin also released (hormone stimulates gastric secretion)
    o Before anything goes to stomach - as chewing and when thinking and smell food
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18
Q

gastric phase

A
  • (60% of response to meal) - ramp up secretion
    o Stretch and products of protein digestion stimulate gastric secretions
    o Gastrin also released by stretch - stimulates secretion of more gastric fluid
    o All stimulate motility, larger meals increase rate of emptying
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19
Q

intestinal phase

A
  • slow down secretion
    o Chyme entering duodenum decrease gastric secretion and motility
    o Removal of peptide fragments (no longer stimulate gastrin release)
    o Removal of food leads to decrease in pH (pH < 2 inhibits gastrin release)
    o Distention of duodenum leads to release of hormones (inc cholecystokinin (cck)) which inhibits gastrin releas
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20
Q

small intestine

A
  • Absorption of nutrients
  • Passes food cyme down system
  • Mucosal lining and muscle layer round outside
  • Mucosal layer has more folds
  • Circular and longitudinal smooth muscle lining - propel food down intestine
  • Vascularised villi
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21
Q

why does mucosal layer of SI have more folds?

A

increase SA

finger like villi

rich blood supply

lymphatic supply

epithelial cells

microvilli

increases SA

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22
Q

vascularised villi

A

blood supply

capillaries

arterial supply to intestine and venous supply to collect nutrients across mucosal layer into supply delivered to liver

epithelial lining

microvilli

on lumen of gut

nutrients pass

into venous circulation

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23
Q

small intestine motility

A

• Peristaltic, longitudinal type contractions main propulsive force over short distances (10-15cm)
o Increases when chyme enters - 12x min - upper part - 2/3x min in distal part
o Wave of contractions
o Happens when under tone - increases when chyme enters SI
- Segmentation is alternate contraction and relaxation of whole segments intestine and serve to mix chyme with pancreatic secretions and bile and increase exposure to mucosal surface - adapted for absorption
o Circular smooth muscle

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24
Q

control of small intestine motility

A
  • GI tract has similar basic structure of outer longitudinal smooth muscle, inner circular smooth muscle and lumen lined with mucosa
  • Muscle primed by pacemaker cells (interstitial cells of Cajal) which initiate a basal electrical rhythm - smooth muscle under tone and contracting - wave down gastral intestine system
  • Intrinsic enteric NS
25
Q

pancreas

A
  • endocrine and exocrine organ
    • Releases hormones
    • Acinar cells secrete enzyme rich Cl- solution
    • Duct cells secrete aqueous HCO3- solution (1.5 l/day) - take sodium and water with it
    • CCK (released in response to fat and protein in duodenum) stimulates enzyme secretion
    • Secretin (released in response to acid in duodenum) stimulates HCO3- production
    o Protecting duodenal mucosa
    • Duct cells secrete bicarbonate - neutralises acid - imp for enzyme function - digest food
26
Q

what is HCO3- necessary for?

A

o Digestive enzyme activity
o Micelle formation
o Protecting duodenal mucosa

27
Q

large intestine

A
  • Storage of faeces - waste
  • Chyme takes 12h to reach terminal ileum
  • Ileal-caecal sphincter acts to prevent retrograde movement of chyme and bacteria from colon
  • Peristaltic and segmental movement mostly slow and non-propulsive serving to improve salt and water absorption
  • Mass movements occur infreq (2-3x day) and drive colonic contents towards rectum (high pressure moving 30cm/more)
28
Q

function of LI

A

reabsorption of water and storage faeces, some bacterial met of carb to produce short chain FAs

29
Q

overview

A

make sure to look through notes

30
Q

carbohydrate digestion

A

• Mono- and disaccharides
• Ingested as complex carbs
o Starch (plants) - sweeter when broken into saccharides
o Glycogen (meat)
• Digestion begins in mouth (salivary a-amylase), but ceases in acidic env of stomach
• Most carb digestion occurs in SI by action of pancreatic a-amylase - more alkaline env - pH 8

31
Q

carbohydrate absorption

A

diagram

32
Q

liver - hepatic portal supply

A

diagram

33
Q

transport from portal vein

A
  • Glucose, galactose and fructose directly transported to liver
  • Fructose and galactose converted to glucose derivatives and have same fate as glucose (liver glycogen/maintain blood glucose)
  • Glucose enters organs by fac transport, skeletal muscle and adipose tissue regulated by insulin (released from pancreas)
34
Q

blood glucose response to ingestion 50g glucose/starch

A
  • Polysaccharide has to be broken down first
  • Slower appearance with glucose
  • Glycaemic index - area under curve - ingesting carb
35
Q

protein digestion

A
  • Begins in stomach (pepsin - protease) - acid env - responsible for around 15%
  • Pepsin activity halted by alkaline pancreatic secretions
  • Majority protein (50% food, 25% gut secretions, 25% epithelial cells) digestion occurs in SI by action pancreatic enzymes - activated in duodenum
  • Enzymes activated outside pancreas (to prevent digestion of pancreatic proteins) by trypsin
36
Q

classes of protein digestive enzymes

A

o Endopeptidases - cleave interior peptide bonds

o Exopeptidases - cleave external peptide bonds

37
Q

protein digestion/absorption

A
  • Di- and tripeptides further broken down into AAs by intracellular peptidases of enterocyte (epithelial cell)
  • Absorption of AAs occurs by diffusion and sodium dependent transport
38
Q

blood AA response to ingestion 20g AAs/milk protein

A
  • No digestion with AAs
  • More steps in protein digestion
  • More sustained release
39
Q

liver functions

A

o Bile production
o Met - glucose and glycogen storage and production
o Detoxification of blood

40
Q

liver - digestion

A

• Gallbladder contracts following meal to eject into duodenum
o Stimulated by secretin and CCK
o 0.5-1.5/day
o 90% bile salts reabsorbed and recycled - continuously

41
Q

digestion of fat

A
  1. Lipids emulsified by bile
  2. Lipases break down triglycerides into FAs and monoglycerides
  3. FAs and monoglycerides packaged into micelles absorbed by microvilli
  4. FAs and monoglycerides converted back into triglycerides - aggregate with cholesterol, proteins and phospholipids to form chylomicrons
  5. Chylomicrons move into lymph cap, which transports them to rest of body
42
Q

blood lipid response to 70g triglyceride

A
  • Less rapid

- Longer digestion and absorption process

43
Q

fat soluble vitamin absorption in SI

A

o Some, but not all, require digestion absorbed from micelle mostly in SI
o Enter chylomicrons and lymph system
o Stored in tissues

44
Q

water soluble vitamin absorption in SI

A 
o Diffusion (high concs) - pass epithelial cells 
o AT (low concs) 
o Not stored
45
Q

water

A

• Approx. 8l absorbed each day, 6l secreted in GI tract
• 90% absorbed in SI, 10% LI (colon has greater absorption capacity if necessary)
• Water moves rapidly across intestine in response to osmotic grads ensuring luminal contents isosmotic with interstitial fluid
o Hypotonic solution increases water absorption

46
Q

the serosa is located where?

A

outer cover of the small intestine

47
Q

how much do the buccal glands contribute to saliva production?

A

5%

48
Q

what does alpha amylase break down?

A

amylose (1, 4) bonds

49
Q

what are the major hormones involved in digestion?

A

secretin

gastrin

cholecystokinin

50
Q

in what order do the stages of swallowing occur in?

A

Buccal phase

Pharyngeal stage

Oesophageal Phase

51
Q

which digestive phase of the stomach is pepsinogen released?

A

cephalic

52
Q

how long does it take food to reach the stomach?

A

a matter of s

53
Q

how long does a bolus usually stay in the stomach?

A

2-4h

54
Q

in the duodenum and jejunum, triacylglycerol digestion requires?

A

bile salts

lipases

bicarbonate

55
Q

how much saliva can we produce?

A

up to 6ml/min-1

56
Q

intrinsic enteric NS

A

o Myogenic mechanisms (inherent to smooth muscle) responsive to stretch - created within muscle - creates reflex where it contracts
o pH
o products of digestion such as FAs
o osmolality - more hypertonic chyme has greater effect on contraction

57
Q

bile

A

o Bile salts (digestion and absorption of fats) and HCl- - alkaline solution
o Continuously produced
o Between meals stored in gall bladder and concentrated
o Aids secretion bile pigments, cholesterol, steroids, heavy metals, drugs

58
Q

secretions in gastric juice

A

o Ions, mucus (protection)
o Pepsins, from chief cells (protein digestion), lipases
o Intrinsic factor from parietal cells (vit B12 absorption)
o HCl (activate pepsin, breakdown of tissue, kill bacteria

ESS1606 Nutrition and metabolism (19 decks)

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