D2 digestion

Question 1

is digestive juice secreted continuously?

Answer 1

no – its coordinated w presence of food in part of the gut (vol and when)

Question 2

3 mechanisms that control the secretion of digestive juices

Answer 2

mechanical
hormonal
nervous

Question 3

describe the process of nervous control of secretion of digestive juices

Answer 3

sight/smell/taste food = medulla sends nerve impulses via VAGUS nerves = stimulate secretion of saliva and stomach wall cells

Question 4

parasympathetic vs sympathetic control of digestive juices (nervous)

Answer 4

parasym = speed up digestion when food is ingested

sym = slows down digestion when no foods available

Question 5

2 mechanical functions for control of digestive juice secretion

Answer 5

• stomach contraction
• peristalsis

Question 6

name the 4 hormones that make up hormornal control of secretion of digestive juices

Answer 6

1. secretin
2. cholecystokinin
3. gastrin
4. somatostatin

Question 7

how does secretin control secretion of digesive juices

Answer 7

• produced by special cells in SI in response to acid fluid
• release of alkali

Question 8

where are secretin, cholecystokinin, gastrin, and somatostatin secreted from

Answer 8

special cells in SI

SI

G cells in stomach, duodenum and pancreas

special cells in stomach, duodenum, pancreas

Question 8

how does cholecystokinin control secretion of digestive juices

Answer 8

• presence of food in SI
• release of bile
• secretion of pancreatic enzymes

Question 9

how does gastrin control the secretion of digestive juices

Answer 9

physical stimulation – presence of food
chemical stimulation – protein

release of gastric acids and enzymes

Question 10

how does somatostatin control the secretion of digestive juices

Answer 10

prevents release of acid

prevents release of gastrin, CCK, secretin (basicall cancels out the other 3 hormones)

Question 11

outline the mechanism of secretion control 6

Answer 11

1. sight/smell = secretion of gastric juices
2. food in stomach = wall stretched = further secretion
3. protein = gastrin secreted = further secretion
4. gastrin secretion slows at 3.5 pH, stops at 1.5 pH (protein in food acts as buffer to stomach acid)
5. partially digested chyme enters duodenum = proteins = secrete gastrin = more juice
6. chyme (low protein but w fatty acids and glu) = secretin + cholecytokinin = decr gastric juice secretion

Question 12

define exocrine gland

Answer 12

have DUCTS that carry their secretory product to surface of body / lumen of gut

Question 13

what do saliva glands secrete and what is the effect

Answer 13

saliva – mouth

amylase + mucus

starch –> maltose

Question 14

what do gastric glands secrete and whats the effect

Answer 14

gastric juice – stomach

pepsin + HCl

proteins –> polypeptides
acidic enviro –> kills bacteria

Question 15

what does the pancreas secrete and whats the effect (exocrine gland)

Answer 15

pancreatic juice – SI

amylase + proteases + peptidases + lipases + nucleases

starch –> maltose
proteins/polypeptides –> polypeptides + peptides + AAs
triglycerides –> fatty acids + glycerol
nucleotides –> pentose sugars + Pi + bases

Question 16

whats the pH of the stomach

Answer 16

2.0

Question 17

function of saliva

Answer 17

lubricating the mouth, throat, food bolus

amylase = digestion of starch

Question 18

outline the path of pancreatic juices 2`

Answer 18

transported by pancreatic duct

enters intestine in duodenum

Question 19

what cells secrete mucus

Answer 19

goblet cells

Question 20

what is the function of mucus

Answer 20

forms an effective barrier to HCl and proteases = prevents self digestion (autolysis)

Question 21

what is chyme

Answer 21

food mixed with gastric juice and churned by muscle action = semi-liquid

Question 22

what did william beaumont discover and establish

Answer 22

the role of gastric secretions

Question 23

how was gastric activity first observed and studied

Answer 23

through a opening from stomach interior to outside the body (bc gunshot)

gastric juice collected and tested w diff foods

Question 24

how is stomach acid produced

Answer 24

by combination of H+ ions and Cl- ions produced by epithelial cells (parietal cells) of stomach lining release of H+ ions thru protein carriers = intake of K+ ions from stomach lumen (needs ATP)

Question 25

what does stomach acid do to protease ensymes

Answer 25

activation pepsinogen (inactive) -- HCl removes 44 AA --> pepsin (Active) proteins --> peptides

Question 26

purpose of acid conditions in stomach?

Answer 26

favour hydrolysis reactions, helps to control pathogens ingested with food

Question 27

what happens in stomach pH falls to low

Answer 27

- stomach wall endangered - secretin and somatostatin = inhibit gastrin secretion = decr acid - inhibitory drugs presecribed (eg PPI)

Question 28

when do stomach ulcers form

Answer 28

when stomach lining is disrupted

Question 29

symptoms of gastric ulcers

Answer 29

tummy owie + hearburn + nausea + shit blood sometimes

Question 30

causes of gastric ulcers

Answer 30

excess secretion of gastric acid + presence of Helicobacter pylori

Question 31

what prevents H.pylori from being reached by immune response

Answer 31

the mucus layer

Question 32

what does H. pylori attach to

Answer 32

cells of stomach mucosa (underneath mucus lining)

Question 33

why cant H+ ions reach H.pylori

Answer 33

its neutralised by HCO ions and ammonium ions (from bacterias secretion of urease = action on urea)

Question 34

what is gastritis

Answer 34

inflammation at site of h.pylori infection

Question 35

what could be a further outcome of h.pylori infection

Answer 35

goblet cells fail = decr secretion of mucus = stomach lining exposed to HCl and protease

Question 36

3 ways h.pylori ulcers are treated

Answer 36

- amoxicillin - clarithromycin - proton pump inhibitor

Question 37

how does amoxicillin treat in gastric ulcers

Answer 37

is an antibiotic directly inhibits synthesis of bacterial cell walls

Question 38

how does clarithromycin treat stomach ulcers

Answer 38

is also an antibiotic prevents growth of bacteria -- inhibits translation = no protein synthesis

Question 39

how do proton pump inhibitors treat stomach ulcers (short)

Answer 39

inhibits acidification

Question 40

impact of proton pump inhibitors

Answer 40

blocks proton pump (the hydrogen-potassium one) in parietal cells of gastric gland = decr H+ secretion into lumn = decr hcl prod may encourage growth of gut microflora

Question 41

wall of SI contains _______ muscle tissue

Answer 41

involuntary

Question 42

what does the innermost surface of the SI consist of

Answer 42

epithelium layer (mucosa) - contains many goblet cells

Question 43

what does mucus from goblet cells do

Answer 43

adheres to cells lining the gut protects gut from mechanical damage, resists self-digestion

Question 44

what cells does the epithelium of the villi contain many of!

Answer 44

goblet cells

Question 45

name the 4 components of cross section of small intestine wall (Starting from innermost)

Answer 45

1. mucosa: enterocytes 2. submucosa 3. circular muscle layer + longditudinal muscle layer 4. serosa

Question 46

what are enterocytes

Answer 46

cells that have microvilli -- digest and absorb substances

Question 47

name the 5 adaptations of the villi

Answer 47

1. microvilli 2. large number of mitochondria 3. pinocytotic vesicles 4. basal channels betw epithelial cells 5. tight junctions

Question 48

how does microvilli improve food absorption

Answer 48

foldings on cell surface (Facing lumen) = incr surface area

Question 49

how do pinocytotic vesicles impvoe food absorption

Answer 49

in villus -- fluid taken up/released in tiny vesicles across plasma membrane (basically cell drinking)

Question 50

what do tight junctions do in the villus

Answer 50

bind the individual epithelial cells tgt = only way into tissues is thru epithelium basal channels below tight junctions

Question 51

why is insoluble fibre important

Answer 51

incr faecal mass = stinulates peristaltic movements (non digestible carbs -- cellulose, lignin)

Question 52

materials not absorbed are _______ as __________

Answer 52

egested faeces

Question 53

main constituents of insoluble fibre

Answer 53

cellulose and lignin

Question 54

what are the benefits of a high fibre diet

Answer 54

- improved bowel movement (Stimulates movement of chyme thru gut) - slows absorption of glucose = decr risk of diabetes - decr disease of large intestine

Question 55

why cant humans digest celluose

Answer 55

we dont have cellulase :(

Question 56

what bacteria is cholera caused by

Answer 56

Vibrio cholerae

Question 57

how is cholera aquired

Answer 57

drinking water contaminated with shit from infected ppl - large no. req. -- more than 108-109

Question 58

what toxin does cholera release

Answer 58

enterotoxin

Question 59

what is the effect of enterotoxin (simple)

Answer 59

loss of irons = loss of water

Question 60

symptoms of cholera

Answer 60

massive loss of body fluid = dehydration vomiting, diarrhea weakness, incr thirst, seizures, drop in blood pressure, decr urine, kidney failure

Question 61

how does cholera enterotoxin work in DETAIL 4

Answer 61

1. enterotoxin consists of two-protein complex 2. B part -- binds to binding site (glycolipid on plasma membranes of epithelial cells) 3. A part -- activates enzyme systems of plasma membrane = secretion of Cl ions into gut lumen = sodium ion uptake inhibited 4. hypersecretion of CL ions = water loss

Question 62

treatment of cholera

Answer 62

immediate administration of dilute solution of electrolytes (oral rehydration salts) = rebalance fluid and ions lost

Question 63

challenges in treating cholera

Answer 63

ppl weakened by food shortage drinking water may need to be carreid some distance (inaccessible) boiling water to make it safe requires scarce fuel

Question 64

__________ water makes it safe from cholera

Answer 64

boiling