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gastrointestinal_week_1_20190518174122 Flashcards

1
Q

what is the role of mouth and oropharynx

A

chops and lubricates food, starts carbohydrate digestion, propels food to oesophagi

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2
Q

what is role of oesophagus

A

muscular tube, propels food to stomach

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3
Q

what is role of stomach

A

stores/churns food, continues carbohydrate and initiates protein digestion, regulates delivery of chyme to duodenum

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4
Q

what are the parts of small intestine

A

duodenum, jejunum, ileum

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5
Q

what is role of small intestine

A

principle site of digestion and absorption of nutrients

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6
Q

what is the parts of large intestine

A

caecum, appendix and colon

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7
Q

what is role of large intestine

A

colon reabsorbs fluid and electrolytes, stores faecal matter before delivery to rectum

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8
Q

what is role of rectum and anus

A

storage and regulated expulsion of faeces

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9
Q

what is the accessory structures of the GI tract

A

salivary glandspancreasliver and gall bladder (hepatobillary system)

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10
Q

what is motility

A

mechanical activity mostly involving smooth muscle

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11
Q

how does secretion take place

A

secretion into the lumen of digestive tract occurs from itself and accessory structures in response to presence of food, hormonal and neural signals

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12
Q

what is secretion required for

A

digestion, protection and lubrication

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13
Q

what is digestion

A

chemical breakdown by enzymatic hydrolysis of complex foodstuff to smaller, absorbable units

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14
Q

what is absorption

A

transfer of absorbable products of digestion (with water, electrolytes and vitamins) from digestive tract to blood or lymph

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15
Q

what is components of mucosa (digestive tract wall)

A

epithelial cellsexocrine cellsendocrine gland cells lammina propia (capillaries, enteric neurones, immune cells)muscularis mucosae

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16
Q

what is components of submucosa (digestive tract wall)

A

connective tissue larger blood and lymph vesselsglandsnerve network (submucos plexus)

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17
Q

what is components of muscularis externa (digestive tract wall)

A

circular muscle layer nerve network (myenteric plexus)longitudinal muscle layer

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18
Q

what is components of serosa (digestive tract wall)

A

connective tissue

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19
Q

what happens during circular muscle contraction

A

lumen becomes narrower and longer

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20
Q

what happens during longitudinal muscle contraction

A

intestine becomes shorter and fatter

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21
Q

what happens during muscularis mucosae contraction

A

change in absorptive and secretory areas of mucosa (folding)mixing activity

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22
Q

what drives the slow wave electrical activity of digestive tract

A

interstitial cells of Cajal (ICCs)

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23
Q

what is the only condition which allows contraction to occur

A

if slow wave amplitude is sufficient to trigger smooth muscle cell action potentials

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24
Q

where are ICCs located and what types of junctions do they form

A

between longitudinal and circular muscle layers and in submucosa gap junctions with SMC

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25
Q

whether sloe wave amplitude reaches threshold depends on what

A

neuronal stimuli hormonal stimuli mechanical stimuli

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26
Q

how many waves per minute in stomach

A

3

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27
Q

how many waves per minute in small intestine

A

12 and 8 in duodenum and terminal ileum

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28
Q

how many waves per minute in large intestine

A

8 and 16 in proximal and distal (sigmoid) colon

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29
Q

what is the excitatory influences of parasympathetic system on digestive tract (synapse with ganglion cells in ENS)

A

increase gastric, pancreatic and SI secretionincrease blood flow and smooth muscle contraction

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30
Q

what is inhibitory influences of parasympathetic system

A

relaxation of some sphincters, receptive relaxation of stomach

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31
Q

what is excitatory influence of sympathetic system (synapse in pre vertebral ganglia)

A

increased sphincter tone

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32
Q

what is inhibitory influence of sympathetic system

A

decreased motility, secretion and blood flow

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33
Q

what is peristalsis (local reflex)

A

a wave of relaxation, followed by contraction that proceeds along gut in aboral directiontriggered by distension of gut wall

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34
Q

what is the short reflex of digestive tract

A

intestine-intestinal inhibitory reflex (causes inhibition of muscle activity in adjacent areas)

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35
Q

what is the long reflex of digestive tract

A

gastroileal reflex (increase in gastric activity causes increased propulsive activity in terminal ileum)

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36
Q

what is segmentation

A

rhythmic contractions of circular muscle layer that mix and divide luminal contents occurs in SI (in fed state) and LI (where its called haustration)

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37
Q

what is colonic mass movement

A

powerful sweeping contraction that forced faeces into rectum

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38
Q

what is migrating motor complex (MMC)

A

powerful sweeping contraction from stomach to terminal ileum

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39
Q

what is the role of upper oesophageal sphincter (UOS)

A

relaxes to allow swallowing, closes during inspiration

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40
Q

what is the role of lower oesophageal sphincter (LOS)

A

relaxes to permit entry of food to stomach and closes to prevent reflux of gastric contents to oesophagus

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41
Q

what is the role of pyloric sphincter

A

regulates gastric emptying and usually prevents duodenal gastric reflux

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42
Q

what is role of ileocaecal valve

A

regulates flow from ileum to caecum - distension of ileum opens, distension of proximal colon closes

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43
Q

what regulates internal (smooth muscle) and external (skeletal muscle) anal sphincters

A

defection reflex

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44
Q

how to calculate BMI

A

weight (kg) / square of height (m)

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45
Q

what are the signals in satiation (feeling full)

A

CCK, PYY3-36, GLP-1, OXM and obestatin

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46
Q

what is chemical which signal for hunger

A

Ghrelin

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47
Q

what is the definition of satiety

A

period of time between termination of one meal and initiation of nxt

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48
Q

what is definition of adiposity

A

state of being obese

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49
Q

what two hormones are central appetite controllers

A

leptin (made and released from fat cells) and insulin (made and released from pancreatic cells)

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50
Q

what is the effect of diet induced obesity on leptin

A

leptin resistance

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51
Q

what happens to the insulin receptor which results in obesity

A

neuron specific deletion

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52
Q

what drug is licensed to treat obesity

A

Orlistat (Xenical or Alli)

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53
Q

how does this drug work

A

inhibits pancreatic lipase decreasing triglyceride absorption reduces efficiency of fat absorption

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54
Q

what is side effects of this drug

A

cramping and diarrhoea

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55
Q

what surgery is available for obesity

A

gastric bypass

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56
Q

what drug is in the pipeline for treating obesity

A

Contrave (mysimba) - combination of bupropion (dopamine reuptake inhibitor) and naltrexone (opioid antagonist)

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57
Q

what is the 5 parts of stomach

A

cardia (contains cardiac sphincter)fundus (below diaphragm)body (main part - where food breaks down)antrum (hold broken down food)pylorus (connects to SI)

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58
Q

what digests proteins in stomach

A

pepsin and HCl

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59
Q

how much gastric juice does stomach secrete

A

2 litres per day

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60
Q

how is food mixed

A

churning action of gastric smooth muscle against closed pyloric sphincter

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61
Q

when does the pylorus open intermittently

A

to allow movement of chyme into duodenum

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62
Q

what determines the escape of chyme through pyloric sphincter

A

strength of astral wave

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63
Q

what are the gastric factors which govern strength of astral wave

A

rate of emptying proportional to volume of chyme and the consistency of chyme

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64
Q

the duodenum also controls strength of astral wave since it must be ready to recieve chyme - how does it delay emptying

A

neuronal responses (enterogastric reflex decreases antral activity)hormonal response (release of enterogastrones eg secretin and CKK inhibits stomach contraction)

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65
Q

which stimuli within duodenum drives neuronal and hormone response

A

fat (high fat - delay)acid (time taken for neutralisation by bicarbonate from pancreas)hypertonicitydistension

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66
Q

what gastric secretions are released from oxyntic mucosa (fundus and corpus)

A

HCl, pepsinogen, intrinsic factor and gastroferrin, histamine and mucus

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67
Q

what is function of HCl

A

activates pepsinogen to pepsin (digestion of proteins), denatures proteins and kills most micro-organisms ingested with food

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68
Q

what is function of pepsinogen

A

inactive precursor of pepsin (once pepsin formed it activates pepsinogen)

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69
Q

what is function of intrinsic factor and gastroferrin

A

binds vitamin B12 and Fe2+ respectively, facilitating subsequent absorption

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70
Q

what is function of histamine

A

stimulates HCl secretion

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71
Q

what is function of mucus

A

protective

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72
Q

what gastric secretion are secreted by pyloric gland area (pylorus and antrum) and their function

A

gastric (stimulates HCl)somatostatin (inhibits HCl)mucus (protective)

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73
Q

what are three important secretoagogues that induce acid secretion from parietal cell

A

ACh, gastrin and histamine acting by direct and indirect mechanisms Acting on M2 and H2 receptors

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74
Q

which pathways do stimuli for secretion of H+ act by

A

PLC - IP3 (gastrin, ACh) andcAMP - PKA (histamine) signalling pathways

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75
Q

which pathways do stimuli for inhibition of secretion of H+ act by

A

cAMP - PKA (somatostatin, prostaglandins) signalling pathways

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76
Q

the rate of gastric secretion is controlled by what

A

stimulatory and inhibitory mechanisms that occur in three overlapping phases

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77
Q

what is the first phase

A

cephalic phase - before food reaches stomach preparing it to receive foodvagal stimulation which results in ACh release which directly activates parietal cells

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78
Q

what is second phase

A

gastric phase - when food in stomachdistension of stomach activates reflex that cause acid secretionfood buffers, pH, D cell inhibition via ss of gastrin release is decreased

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79
Q

what is the third phase

A

intestinal phase - after food left stomach

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80
Q

how can gastric acid secretion be inhibited in cephalic phase

A

vagal nerve activity decreases upon cessation of eating and following stomach emptying increased pain, nausea and negative emotions also decrease vagal nerve activity

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81
Q

how can gastric acid secretion be inhibited in gastric phase

A

antral pH falls when food exits stomach - causes release of somatostatin from D cells to recommence, decreasing gastric secretionPGE2 continually secreted by gastric mucosa acts locally to reduce histamine and thus gastrin mediated HCl secretion

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82
Q

how can gastric acid secretion be inhibited in intestinal phase

A

factors that reduce gastric motility also reduces gastric secretion (neuronal reflexes, enterogastrones)

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83
Q

which drug class influence acid secretion

A

muscarinic receptor antagonists (pirenzepine) block ACh binding competitivelyproton pump inhibitors (omeprazole) block by covalent modification NSAIDs (aspirin) block cyclo-oxygenase irreversibly H2 histamine receptor antagonists (rantidine) block competitively

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84
Q

how does prostaglandins (PGE2 and PGI2) work to protect mucosa from attack by HCl and pepsin

A

it reduces acid secretion, increases mucus and bicarbonate secretion and increases mucosal blood flow

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85
Q

infection of the gastric antrum with which bacterium causes peptic ulcer

A

helicobacter pylori - secretes agents causing inflammation that weakens mucosal barrier leaving submucosa and deeper layers subject to attack by HCl and pepsin

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86
Q

drug treatment of peptic ulcer aims to promote ulcer healing by what

A

reducing acid secretion, increasing mucosal resistance and eradicating H. pylori

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87
Q

which drugs can trigger gastric ulceration and cause bleeding

A

non steroid anti inflammatory (NSAIDs) eg aspirin as they reduce prostaglandin formation (COX 1 inhibition)

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88
Q

gastric damage due to long term NSAID treatment can be prevented by what drug - what is the adverse effects of this drug

A

PGE1 analogue (ie misoprostol)inhibits basal and food stimulated gastric acid formation maintains (or increases) secretion of mucus and bicarbonate

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89
Q

what conditions are drugs that reduce acid secretion used in treatment of

A

peptic ulcer gastro-oesophageal reflux disease acid hypersecretion (eg zollinger-ellison syndrome or cushing’s ulcers)

90
Q

how do proton pump inhibitors (PPIs) eg omeprazole work

A

activated by pH of stomach. React with sulphydryl groups in H+/K+ATPase responsible for transporting H+ out of parietal cells. The enzyme is irreversibly blocked so acid secretion only resumes after synthesis of new enzyme

91
Q

when are PPIs used

A

peptic ulcer, GORD and Zollinger-Ellison

92
Q

why is timing of dosing important

A

drug must be present in plasma at an effective concentration whilst proton pumps are active

93
Q

how do H2 receptor antagonists eg cimetidine, ranitidine work

A

reduce acid secretion and increase healing of peptic ulcer by blocking action of histamine on parietal cells and reducing acid secretion

94
Q

when are H2 receptor antagonists used

A

peptic ulcer and reflux oesophagitis

95
Q

what two drugs are mucosal strengtheners

A

sucralfate - binds to ulcer base and forms complex gels with mucus - provides mucosal barrier to acid and pepsinbismuth chealate - mucosal strengthening, also toxic towards H.pylori so used in combo with antibiotics and H2 antagonists

96
Q

what is component of temporomandibular joint

A

two cavities divided by articular disc (superior cavity for translation, inferior cavity for rotation)

97
Q

what four muscles control mastication (chewing)

A

temporalis majormassetermedial pterygoidlateral pterygoid (3 close and 1 open respectively)

98
Q

all muscles of mastication are controlled by which nerve

A

mandibular division of trigeminal nerve CNV3

99
Q

what is the course of CNV3

A

from pons, through foramen oval to muscles of mastication and sensory area

100
Q

what is the course of the facial nerve

A

from pontomedullary junction, travels through tempura bone via internal acoustic meatus then stylomastoid foramen this supplies anterior 2/3rds of tongue, muscles of facial expression and glands in floor in mouth

101
Q

what supplies superior half of oral cavity (gingiva of oral cavity and palate)

A

general sensation CNV2

102
Q

what supplies the inferior half of oral cavity (gingiva of oral cavity and floor of mouth)

A

general sensation CNV3

103
Q

what sensory part of gag reflex is carried by nerve fibres within what

A

CNIX

104
Q

the motor part of gag reflex is carried by nerve fibres within what

A

CNIX and CNX

105
Q

what is the course of CNV2 (maxillary division of trigeminal nerve)

A

from pons, through foramen rotundum to sensory area (mid-face)

106
Q

what is the course of CNIX (glossopharyngeal nerve)

A

from medulla, through jugular foramen to posterior wall of oropharynx (sensory), parotid gland (secretomotor) and post 1/2 tongue (sensation and taste)

107
Q

what is the role of the parotid gland

A

parotid duct crosses face and secretes into mouth by upper 2nd molar

108
Q

what is role of submandibular gland

A

submandibular duct enters floor of mouth and secretes via linguinal caruncle

109
Q

what is role of sublingual gland

A

lays in floor of mouth, secretes via several ducts superiorly

110
Q

what is the role of extrinsic muscles in tongue musculature

A

function to change position of tongue

111
Q

what do the four pairs of skeletal intrinsic muscles in the tongue musculature do

A

located dorsally/posteriorly and modify shape of tongue during function

112
Q

what is role of CNXII - hypoglossol nerves - in tongue

A

from medulla, through hypoglossal canal to extrinsic and intrinsic muscles of tongue (except palatoglossus)

113
Q

what nerves innervate the pharynx

A

CNX and IX

114
Q

what muscle and nerve work to close lips to prevent drooling

A

orbicularis oris and cranial nerve VII

115
Q

what is the anatomical location of oesophagus

A

inferior continuation of laryngopharynx begins at inferior edge of circropharyngeas muscle (C6)

116
Q

where does the lower oesophageal sphincter lie

A

immediately superior to gastro-oesophageal junction presence of hiatus hernia reduce effectiveness of LOS - can lead to relfux

117
Q

where does the stomach lie

A

mainly in left hypochrondium, epigastric and umbilical regions when patient supine

118
Q

what is components of small intestine, from proximal to distal

A

duodenum, jejunum and ileum

119
Q

what is components of large intestine, proximal to distal

A

colon (caecum, appendix, ascending colon, transverse colon, descending colon and sigmoid colon), rectum, anal canal and anus

120
Q

where is pain from foregut structures felt and where do they enter spinal cord

A

epigastric region T6-T9

121
Q

what are foregut structures

A

oesophagus to mid duodenum, liver and gall bladder, spleen, 1/2 of pancreas

122
Q

where is pain from midgut structures felt and where do they enter spinal cord

A

umbilical regionT8-T12

123
Q

what are midgut structures

A

mid duodenum to proximal 2/3rds of transverse colon 1/2 of pancreas

124
Q

where is pain from hindgut structures felt and where do they enter spinal cord

A

felt in pubic region T10-L2

125
Q

what are the structures of the hindgut

A

distal 1/3rd of transverse colon and proximal 1/2 of anal canal

126
Q

how is referred pain caused

A

pain from these organs tend to be perceived by patient in dermatomes of levels at which they enter spinal cord and there is little overlap

127
Q

what direction is external oblique muscles

A

hands in pockets

128
Q

what direction is internal oblique muscles in

A

hands on chest

129
Q

what is guarding

A

abdomen becomes rigid muscles contract to guard abdominal organs when injury threatens

130
Q

what is the peritoneal cavity

A

space between visceral and parietal layers - contains lubricating fluidperitonitis - blood pus or faeces in cavity - inflammation

131
Q

what are intraperitoneal organs

A

almost completely covered in visceral peritoneum and minimally mobile

132
Q

what are intraperitoneal organs with mesentery

A

covered in visceral peritoneum which wraps around organ to form double layer, making it very mobile

133
Q

what are retroperitoneal organs

A

only has visceral peritoneum on its anterior surface

134
Q

what is mesentery

A

usually connects organ to posterior body wall

135
Q

what is omentum

A

double layer of perineum that passes from stomach to adjacent organs

136
Q

what is the greater omentum

A

four layeredhangs like an apron attaches greater curvature of stomach to transverse colon

137
Q

what is the lesser omentum

A

double layeredruns between lesser curvature of stomach and duodenum to liver has free edge

138
Q

by which do the two omentum sacs communicate

A

omental foramen (foramen of winslow)

139
Q

what is peritoneal ligaments

A

double layer of perineum that connects organs to one another or body wall

140
Q

what are the four main peritoneal ligaments

A

hepatogastric ligament hepatoduodenal ligament gastrosplenic ligament splenorenal ligament

141
Q

what pouch does peritoneum form in male by its inferior aspect draping over superior aspect of pelvic organs

A

rectovesical pouch

142
Q

what 2 pouches does peritoneum form in female

A

vesico-uterine pouch and recto-uterine pouch

143
Q

what is ascites

A

collection of fluid in peritoneal cavity commonly caused by liver disease - cirrhosis or portal hypertension

144
Q

how is abdominocentesis perfomed

A

needle places lateral to rectus sheath - avoids inferior epigastric artery

145
Q

what is the course of the abdominal sympathetic nerves

A

leave spinal cord between T5-L2enter sympathetic chains but do not synapseleave chain within abdominopelvic splanchnic nervessynapse at pre vertebral ganglia which are located anterior to aorta at exit points of major branches of abdominal aorta

146
Q

how is the adrenal gland sympathetic nerve different

A

leaves at T10-L1. Do not synapse, carried with periarterial plexus to adrenal gland and synapse directly onto cells

147
Q

what is the course of abdominal vagus nerve (CNX)

A

presynaptic fibres enter abdominal cavity on surface of oesophagustravel into periarterial plexus around abdominal aortacarried to walls of organs where they synapse in gangliasupply parasympathetic nerve fibres to GI tract plus abdominal organs up to distal end of transverse colon

148
Q

what is course of pelvic splanchnic nerves (S2, 3 and 4)

A

presynpatic parasympathetic nerve fibressmooth muscle/glands of descending colon to anal canal

149
Q

the somatic motor, sensory and sympathetic nerve fibres supplying structures of abdominal part of the body wall are conveyed within what

A

thoracoabdominal nerves (7-11 intercostal nerves)subcostal nerve (T12 anterior rami)Illiohpogastric nerve (half of L1 anterior ramus)Illioguinal nerve (other half of L1 anterior ramus)

150
Q

where is appendix usually located

A

right iliac fossa

151
Q

describe the pain of appendicitis

A

visceral afferents enter spinal cord at T10as it worsens, appendix will start to irritate parietal peritoneum in right iliac fossa, which lies anterior to it

152
Q

what are 3 parts of small intestine

A

duodenum (30cm), jejunum (3.5m), ileum (2.5m)

153
Q

what does the small intestine recieve

A

chyme from stomach (from pyloric sphincter), pancreatic juice from pancreas, bile from gall bladder (both via sphincter of oddi)

154
Q

what is the other roles of small intestine

A

secretes intestinal juice (succus entericus) and moves remaining residues to the large intestine via the ileocaecal valve (opens in response to proximal pressure and in response to gastrin)

155
Q

the small intestine secretes (into blood) various peptide hormones from endocrine cells within mucosa. What are these hormones

A

Gastrin - from G cells of gastric antrumCholecystokinin (CKK) - from I cells of duodenum and jejunumSecretin - from S cells of duodenumMotilin - from M cells of duodenum and jejunum GIP - incretin from K cells of duodenum and jejunumGLP-1 - an incretin from L cells of gut Ghrelin - from Gr cells of gastric antrum, SI and elsewhere (pancreas)

156
Q

all of these secretions act on which receptors

A

G protein coupled receptors

157
Q

what is the control mechanism by which succus entericus (gastric juice) is secreted

A

distension/irritation, gastrin, CKK, secretin, parasympathetic nerve activity (all enhance)sympathetic nerve activity (decreases)

158
Q

what does this secretion (succus entericus) contain

A

mucus (protection/lubrication - from goblet cells) aqueous salt for enzymatic digestion (mostly from crypts of lieberkuhn)no digestive enzymes

159
Q

what does the secretion of succus entericus involve

A

Na+/K+ATPaseNa+/K+/2Cl- co transporterchloride channel (CFTR)

160
Q

how is segmentation (mixing) of chyme initiated

A

by SI pacemaker cells causing BER which is continuous. At threshold activates segmentation which in the duodenum is primarily due to distension by entering chyme

161
Q

what triggers segmentation in empty ileum

A

gastrin from stomach (gastroileal reflex)

162
Q

what is the difference in segmentation contractions between duodenum and ileum

A

duodenum - 12 per min ileum - 9 per min net movement if aboral

163
Q

what takes place after segmentation

A

peristalsis

164
Q

which two activities occur in interdigestive, or fasting, state

A

few localised contractionsmigrating motor complex (MMC) - occurs between meals, strong peristaltic contractions passing length of intestine (stomach - ileocaecal valve)

165
Q

what is beneficial about this MMC

A

clears small intestine of debris, mucus and sloughed epithelial cells between meals - housekeeper function

166
Q

what inhibits MMC

A

feeding and vagal activity

167
Q

what triggers MMC

A

motilin (it is suppressed by gastrin and CCK)

168
Q

what is endocrine secretions of pancreas (released directly into blood stream)

A

insulin and glucagon

169
Q

what is exocrine secretions of pancreas (secreted to duodenum collectively as pancreatic juice)

A

digestive enzymes (acinar cells), aqueous NaHCO3- solution (duct cells)

170
Q

what is the role of the HCO3- fluid released by pancreatic duct cells

A

neutralises acidic chyme entering duodenum - provides optimum pH for pancreatic enzyme function and protects mucosa from erosion by acid

171
Q

what is special about pancreatic enzymes

A

can completely digest food in absence of all other enzymes eg trypsinogen directly converted to trypsin (proteases can go from inactive to active states)

172
Q

what controls 20% of total pancreatic secretion

A

cephalic - mediated by vagal stimulation of mainly the acinar cells

173
Q

what controls 5-10% of total pancreatic secretion

A

gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells

174
Q

what controls 70-80% of control of pancreatic secretion

A

intestinal phase - mechanism depends on wether its acid or fat and protein in duodenal lumen

175
Q

what happens when there is acid in duodenal lumen

A

increased secretin release from S cells (carried by blood) to pancreatic duct cells - increased secretion of aqueous NaHCO3 solution into duodenal lumen which neutralises acid

176
Q

what happens when there is fat and protein in duodenal lumen

A

increased CCK release from cells (carried by blood) to pancreatic acinar cells - increased secretion of digestive enzymes into duodenal lumen which digests fat and protein

177
Q

what is main constituent of carbohydrates (approx 400g per day)

A

starch (greater than 50% total carbohydrate ingested)cellulose (indigestible in humans)glycogen disaccharides (sucrose, lactose)

178
Q

what is main constituent of lipids (approx 25-160g per day)

A

triacylglycerols (approx 90% of total lipid ingested as fats and oils)phospholipidscholesterol and estersfree fatty acids lipid vitamins

179
Q

what is main constituent of protein

A

70-100g per day ingested, plus 35-200g from endogenous sources (eg digestive enzymes and dead cells from GI tract)

180
Q

what is definition of digestion

A

enzymatic conversion of complex dietary substances to a form that can be absorbed

181
Q

most digestive processes occur in the small intestne as what

A

luminal digestion (mediated by pancreatic enzymes secreted into duodenum)membrane digestion (mediated by enzymes situated at brush border of epithelial cells)

182
Q

what is absorption

A

process by which absorbable products of digestion are transferred across both apical and basolateral membranes of enterocytes (absorptive cells of intestinal epithelium)

183
Q

what is the overall process of digestion and absorption called

A

assimilation

184
Q

all dietary carbohydrates must be converted to which form to be absorbed

A

monosacchardies (glucose /fructose)

185
Q

what accomplishes the sequence of carbohydrate digestion

A

a-amylase (salivary and pancreatic)

186
Q

how is this achieved

A

starch converted to oligosaccharides (not absorbed) by intraluminal hydrolysis oligosaccharides converted to monosaccharides by membrane digestion (at brush border)

187
Q

give example of olgiosacchardies

A

lactose, sucrose (can come from diet)

188
Q

what is the role of a-amylase (endoenzyme)

A

breaks down linear internal a-1,4 linkages but not terminal a-1,4 linkages so no production of glucose products are thus linear glucose oligomers (maltotriose, maltose) and a-limit dextrins

189
Q

what is an olgiosaccharide

A

internal membrane proteins with a catalytic domain that faces the lumen of GI tract

190
Q

what do olgiosaccharides do

A

cleave terminal a-1,4 linkages of maltose, maltotriose and a-limit dextrins to yield glucose

191
Q

how is lactase special

A

only has one substrate - breaks down lactose to glucose and galactose

192
Q

what is specific role of maltase

A

degrade a-1,4 linkages in straight chain oligomers up to nine monomers in length

193
Q

what is specific role of sucrase

A

specifically responsible for hydrolysing sucrose to glucose and fructose

194
Q

what is specific role of isomaltase

A

unique in that it is the only enzyme that can split branching a-1,6 linkages of a-limit dextrins

195
Q

what is lactose intolerance

A

relative common digestive problem resulting from inability to adequately digest lactose - caused by lactase insufficiency

196
Q

what causes lactase persistence (LP) - continuance of digestion of lactose in milk in adults

A

polymorphisms in MCM6 gene that regulates expression of lactase (LCT) gene

197
Q

lactose intolerance can result from what

A

primary lactase deficiency (primary hypolactasia - due to lack of LP allele)secondary lactase deficiency (caused by damage to proximal SI)congenital lactase deficiency (rare autosomal recessive - no ability to digest lactose from birth)

198
Q

what do the ileum colonic microflora produce if lactose is delivered to the colon

A

short-chain fatty acids (which can be absorbed), hydrogen (can be detected in breath of lactase deficient individuals) CO2 and methane

199
Q

what is the by-product of these productions

A

bloating, abdominal pain and flatulence

200
Q

what does undigested lactose cause

A

acidification of colon and an increased osmotic load - loose stools and diarrhoea

201
Q

where does the absorption of the final product of carbohydrate digestion (glucose, galactose and fructose) take place

A

duodenum and jejunum - it is a two step process involving entry and exit from the enterocytes via the apical and basolateral membranes respectively

202
Q

what absorbs these final products

A

glucose and galactose are absorbed by secondary active transport mediated by SGLT1fructose by facilitated diffusion mediated by GLUT5

203
Q

exit for all monosaccharides is mediated by what

A

facilitated diffusion by GLUT2

204
Q

which form must SGLT1 be in to absorb glucose

A

a hexose in the D-conformation an one that can form a pyranose ring

205
Q

what is the mode of operation of SGLT1

A

2Na+ binds Affinity for glucose increases, glucose binds Na+ and glucose translocate from extracellular to intracellular2Na+ dissociate, affinity for glucose fallsGlucose dissociates Cycle repeated

206
Q

proteins must be digested to oligopeptides and amino acids for efficient absorption within how long

A

6 months

207
Q

how many different pathways exist and what is the basic pathway

A

4 protein - peptides - amino acids - amino acid in enterocyte - amino acid in bloodthird pathway (contains intracellular hydrolysis) is different: protein - peptides - peptide in enterocyte - amino acid in enterocyte - amino acid in blood

208
Q

what different enzymes and transporters are used

A

luminal enzymes, (can be bush border enzymes - 2), apical membrane transporters, (can be intracellular hydrolysis - 3), basolateral membrane transporters

209
Q

what is special about the fourth variant

A

when peptide transported out of enterocyte without intervening intracellular hydrolysis by proteases

210
Q

how does digestion of proteins take place in stomach

A

HCl denatures proteins and pepsin cleaves proteins into peptides (is endopeptidase with preference for bonds between aromatic and larger neutral amino acids)

211
Q

how does digestion of protein take place in duodenum

A

five pancreatic proteases are secreted as proenzymes from exocrine pancreas and converted to active form in duodenum - they act as endopeptidases or exopepitases

212
Q

what are examples of endopeptidases that produce oligopeptides (2-6 amino acids)

A

trypsin, chymotrypsin, elastase

213
Q

what are examples of exopeptidase that produces single amino acids

A

procaroxypeptidase A and procarboxypeptidase B

214
Q

what completes protein digestion

A

additional proteases which are present at the brush border and within the cytoplasm of enterocyte

215
Q

step 1 in summary of protein digestion and absorption

A

protein digested in lumen to amino acids or olgiopeptides by pepsin and pancreatic proteases

216
Q

step 2 in summary of protein digestion and absorption

A

peptidases at the brush border further hydrolyse oligopeptides to amino acids

217
Q

what is step 3 in summary of protein digestion and absorption

A

amino acids transported . across the apical membrane via variety of amino acid transporters, 5 of which are Na+ dependent (system B0AT1) and 2 are Na+ independent (system b0+AT)

218
Q

what is step 4 in summary of protein digestion and absorption

A

olgiopepties transported across apical membrane by H+/oligopeptide co-transporter - PepT1

219
Q

what is step 5 in summary of protein digestion

A

olgiopeptides within cytoplasm are hydrolysed to amino acids by peptidases within enterocyte

220
Q

what is step 6 in summary of protein digestion

A

amino acids exit enterocyte across the basolateral membrane by several Na+ independent transporters

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