gastrointestinal_week_1_20190518174122 Flashcards
(220 cards)
1
Q
what is the role of mouth and oropharynx
A
chops and lubricates food, starts carbohydrate digestion, propels food to oesophagi
2
Q
what is role of oesophagus
A
muscular tube, propels food to stomach
3
Q
what is role of stomach
A
stores/churns food, continues carbohydrate and initiates protein digestion, regulates delivery of chyme to duodenum
4
Q
what are the parts of small intestine
A
duodenum, jejunum, ileum
5
Q
what is role of small intestine
A
principle site of digestion and absorption of nutrients
6
Q
what is the parts of large intestine
A
caecum, appendix and colon
7
Q
what is role of large intestine
A
colon reabsorbs fluid and electrolytes, stores faecal matter before delivery to rectum
8
Q
what is role of rectum and anus
A
storage and regulated expulsion of faeces
9
Q
what is the accessory structures of the GI tract
A
salivary glandspancreasliver and gall bladder (hepatobillary system)
10
Q
what is motility
A
mechanical activity mostly involving smooth muscle
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
12
Q
what is secretion required for
A
digestion, protection and lubrication
13
Q
what is digestion
A
chemical breakdown by enzymatic hydrolysis of complex foodstuff to smaller, absorbable units
14
Q
what is absorption
A
transfer of absorbable products of digestion (with water, electrolytes and vitamins) from digestive tract to blood or lymph
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
16
Q
what is components of submucosa (digestive tract wall)
A
connective tissue larger blood and lymph vesselsglandsnerve network (submucos plexus)
17
Q
what is components of muscularis externa (digestive tract wall)
A
circular muscle layer nerve network (myenteric plexus)longitudinal muscle layer
18
Q
what is components of serosa (digestive tract wall)
A
connective tissue
19
Q
what happens during circular muscle contraction
A
lumen becomes narrower and longer
20
Q
what happens during longitudinal muscle contraction
A
intestine becomes shorter and fatter
21
Q
what happens during muscularis mucosae contraction
A
change in absorptive and secretory areas of mucosa (folding)mixing activity
22
Q
what drives the slow wave electrical activity of digestive tract
A
interstitial cells of Cajal (ICCs)
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
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
25
whether sloe wave amplitude reaches threshold depends on what
neuronal stimuli hormonal stimuli mechanical stimuli
26
how many waves per minute in stomach
3
27
how many waves per minute in small intestine
12 and 8 in duodenum and terminal ileum
28
how many waves per minute in large intestine
8 and 16 in proximal and distal (sigmoid) colon
29
what is the excitatory influences of parasympathetic system on digestive tract (synapse with ganglion cells in ENS)
increase gastric, pancreatic and SI secretionincrease blood flow and smooth muscle contraction
30
what is inhibitory influences of parasympathetic system
relaxation of some sphincters, receptive relaxation of stomach
31
what is excitatory influence of sympathetic system (synapse in pre vertebral ganglia)
increased sphincter tone
32
what is inhibitory influence of sympathetic system
decreased motility, secretion and blood flow
33
what is peristalsis (local reflex)
a wave of relaxation, followed by contraction that proceeds along gut in aboral directiontriggered by distension of gut wall
34
what is the short reflex of digestive tract
intestine-intestinal inhibitory reflex (causes inhibition of muscle activity in adjacent areas)
35
what is the long reflex of digestive tract
gastroileal reflex (increase in gastric activity causes increased propulsive activity in terminal ileum)
36
what is segmentation
rhythmic contractions of circular muscle layer that mix and divide luminal contents occurs in SI (in fed state) and LI (where its called haustration)
37
what is colonic mass movement
powerful sweeping contraction that forced faeces into rectum
38
what is migrating motor complex (MMC)
powerful sweeping contraction from stomach to terminal ileum
39
what is the role of upper oesophageal sphincter (UOS)
relaxes to allow swallowing, closes during inspiration
40
what is the role of lower oesophageal sphincter (LOS)
relaxes to permit entry of food to stomach and closes to prevent reflux of gastric contents to oesophagus
41
what is the role of pyloric sphincter
regulates gastric emptying and usually prevents duodenal gastric reflux
42
what is role of ileocaecal valve
regulates flow from ileum to caecum - distension of ileum opens, distension of proximal colon closes
43
what regulates internal (smooth muscle) and external (skeletal muscle) anal sphincters
defection reflex
44
how to calculate BMI
weight (kg) / square of height (m)
45
what are the signals in satiation (feeling full)
CCK, PYY3-36, GLP-1, OXM and obestatin
46
what is chemical which signal for hunger
Ghrelin
47
what is the definition of satiety
period of time between termination of one meal and initiation of nxt
48
what is definition of adiposity
state of being obese
49
what two hormones are central appetite controllers
leptin (made and released from fat cells) and insulin (made and released from pancreatic cells)
50
what is the effect of diet induced obesity on leptin
leptin resistance
51
what happens to the insulin receptor which results in obesity
neuron specific deletion
52
what drug is licensed to treat obesity
Orlistat (Xenical or Alli)
53
how does this drug work
inhibits pancreatic lipase decreasing triglyceride absorption reduces efficiency of fat absorption
54
what is side effects of this drug
cramping and diarrhoea
55
what surgery is available for obesity
gastric bypass
56
what drug is in the pipeline for treating obesity
Contrave (mysimba) - combination of bupropion (dopamine reuptake inhibitor) and naltrexone (opioid antagonist)
57
what is the 5 parts of stomach
cardia (contains cardiac sphincter)fundus (below diaphragm)body (main part - where food breaks down)antrum (hold broken down food)pylorus (connects to SI)
58
what digests proteins in stomach
pepsin and HCl
59
how much gastric juice does stomach secrete
2 litres per day
60
how is food mixed
churning action of gastric smooth muscle against closed pyloric sphincter
61
when does the pylorus open intermittently
to allow movement of chyme into duodenum
62
what determines the escape of chyme through pyloric sphincter
strength of astral wave
63
what are the gastric factors which govern strength of astral wave
rate of emptying proportional to volume of chyme and the consistency of chyme
64
the duodenum also controls strength of astral wave since it must be ready to recieve chyme - how does it delay emptying
neuronal responses (enterogastric reflex decreases antral activity)hormonal response (release of enterogastrones eg secretin and CKK inhibits stomach contraction)
65
which stimuli within duodenum drives neuronal and hormone response
fat (high fat - delay)acid (time taken for neutralisation by bicarbonate from pancreas)hypertonicitydistension
66
what gastric secretions are released from oxyntic mucosa (fundus and corpus)
HCl, pepsinogen, intrinsic factor and gastroferrin, histamine and mucus
67
what is function of HCl
activates pepsinogen to pepsin (digestion of proteins), denatures proteins and kills most micro-organisms ingested with food
68
what is function of pepsinogen
inactive precursor of pepsin (once pepsin formed it activates pepsinogen)
69
what is function of intrinsic factor and gastroferrin
binds vitamin B12 and Fe2+ respectively, facilitating subsequent absorption
70
what is function of histamine
stimulates HCl secretion
71
what is function of mucus
protective
72
what gastric secretion are secreted by pyloric gland area (pylorus and antrum) and their function
gastric (stimulates HCl)somatostatin (inhibits HCl)mucus (protective)
73
what are three important secretoagogues that induce acid secretion from parietal cell
ACh, gastrin and histamine acting by direct and indirect mechanisms Acting on M2 and H2 receptors
74
which pathways do stimuli for secretion of H+ act by
PLC - IP3 (gastrin, ACh) andcAMP - PKA (histamine) signalling pathways
75
which pathways do stimuli for inhibition of secretion of H+ act by
cAMP - PKA (somatostatin, prostaglandins) signalling pathways
76
the rate of gastric secretion is controlled by what
stimulatory and inhibitory mechanisms that occur in three overlapping phases
77
what is the first phase
cephalic phase - before food reaches stomach preparing it to receive foodvagal stimulation which results in ACh release which directly activates parietal cells
78
what is second phase
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
79
what is the third phase
intestinal phase - after food left stomach
80
how can gastric acid secretion be inhibited in cephalic phase
vagal nerve activity decreases upon cessation of eating and following stomach emptying increased pain, nausea and negative emotions also decrease vagal nerve activity
81
how can gastric acid secretion be inhibited in gastric phase
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
82
how can gastric acid secretion be inhibited in intestinal phase
factors that reduce gastric motility also reduces gastric secretion (neuronal reflexes, enterogastrones)
83
which drug class influence acid secretion
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
84
how does prostaglandins (PGE2 and PGI2) work to protect mucosa from attack by HCl and pepsin
it reduces acid secretion, increases mucus and bicarbonate secretion and increases mucosal blood flow
85
infection of the gastric antrum with which bacterium causes peptic ulcer
helicobacter pylori - secretes agents causing inflammation that weakens mucosal barrier leaving submucosa and deeper layers subject to attack by HCl and pepsin
86
drug treatment of peptic ulcer aims to promote ulcer healing by what
reducing acid secretion, increasing mucosal resistance and eradicating H. pylori
87
which drugs can trigger gastric ulceration and cause bleeding
non steroid anti inflammatory (NSAIDs) eg aspirin as they reduce prostaglandin formation (COX 1 inhibition)
88
gastric damage due to long term NSAID treatment can be prevented by what drug - what is the adverse effects of this drug
PGE1 analogue (ie misoprostol)inhibits basal and food stimulated gastric acid formation maintains (or increases) secretion of mucus and bicarbonate
89
what conditions are drugs that reduce acid secretion used in treatment of
peptic ulcer gastro-oesophageal reflux disease acid hypersecretion (eg zollinger-ellison syndrome or cushing's ulcers)
90
how do proton pump inhibitors (PPIs) eg omeprazole work
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
when are PPIs used
peptic ulcer, GORD and Zollinger-Ellison
92
why is timing of dosing important
drug must be present in plasma at an effective concentration whilst proton pumps are active
93
how do H2 receptor antagonists eg cimetidine, ranitidine work
reduce acid secretion and increase healing of peptic ulcer by blocking action of histamine on parietal cells and reducing acid secretion
94
when are H2 receptor antagonists used
peptic ulcer and reflux oesophagitis
95
what two drugs are mucosal strengtheners
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
what is component of temporomandibular joint
two cavities divided by articular disc (superior cavity for translation, inferior cavity for rotation)
97
what four muscles control mastication (chewing)
temporalis majormassetermedial pterygoidlateral pterygoid (3 close and 1 open respectively)
98
all muscles of mastication are controlled by which nerve
mandibular division of trigeminal nerve CNV3
99
what is the course of CNV3
from pons, through foramen oval to muscles of mastication and sensory area
100
what is the course of the facial nerve
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
what supplies superior half of oral cavity (gingiva of oral cavity and palate)
general sensation CNV2
102
what supplies the inferior half of oral cavity (gingiva of oral cavity and floor of mouth)
general sensation CNV3
103
what sensory part of gag reflex is carried by nerve fibres within what
CNIX
104
the motor part of gag reflex is carried by nerve fibres within what
CNIX and CNX
105
what is the course of CNV2 (maxillary division of trigeminal nerve)
from pons, through foramen rotundum to sensory area (mid-face)
106
what is the course of CNIX (glossopharyngeal nerve)
from medulla, through jugular foramen to posterior wall of oropharynx (sensory), parotid gland (secretomotor) and post 1/2 tongue (sensation and taste)
107
what is the role of the parotid gland
parotid duct crosses face and secretes into mouth by upper 2nd molar
108
what is role of submandibular gland
submandibular duct enters floor of mouth and secretes via linguinal caruncle
109
what is role of sublingual gland
lays in floor of mouth, secretes via several ducts superiorly
110
what is the role of extrinsic muscles in tongue musculature
function to change position of tongue
111
what do the four pairs of skeletal intrinsic muscles in the tongue musculature do
located dorsally/posteriorly and modify shape of tongue during function
112
what is role of CNXII - hypoglossol nerves - in tongue
from medulla, through hypoglossal canal to extrinsic and intrinsic muscles of tongue (except palatoglossus)
113
what nerves innervate the pharynx
CNX and IX
114
what muscle and nerve work to close lips to prevent drooling
orbicularis oris and cranial nerve VII
115
what is the anatomical location of oesophagus
inferior continuation of laryngopharynx begins at inferior edge of circropharyngeas muscle (C6)
116
where does the lower oesophageal sphincter lie
immediately superior to gastro-oesophageal junction presence of hiatus hernia reduce effectiveness of LOS - can lead to relfux
117
where does the stomach lie
mainly in left hypochrondium, epigastric and umbilical regions when patient supine
118
what is components of small intestine, from proximal to distal
duodenum, jejunum and ileum
119
what is components of large intestine, proximal to distal
colon (caecum, appendix, ascending colon, transverse colon, descending colon and sigmoid colon), rectum, anal canal and anus
120
where is pain from foregut structures felt and where do they enter spinal cord
epigastric region T6-T9
121
what are foregut structures
oesophagus to mid duodenum, liver and gall bladder, spleen, 1/2 of pancreas
122
where is pain from midgut structures felt and where do they enter spinal cord
umbilical regionT8-T12
123
what are midgut structures
mid duodenum to proximal 2/3rds of transverse colon 1/2 of pancreas
124
where is pain from hindgut structures felt and where do they enter spinal cord
felt in pubic region T10-L2
125
what are the structures of the hindgut
distal 1/3rd of transverse colon and proximal 1/2 of anal canal
126
how is referred pain caused
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
what direction is external oblique muscles
hands in pockets
128
what direction is internal oblique muscles in
hands on chest
129
what is guarding
abdomen becomes rigid muscles contract to guard abdominal organs when injury threatens
130
what is the peritoneal cavity
space between visceral and parietal layers - contains lubricating fluidperitonitis - blood pus or faeces in cavity - inflammation
131
what are intraperitoneal organs
almost completely covered in visceral peritoneum and minimally mobile
132
what are intraperitoneal organs with mesentery
covered in visceral peritoneum which wraps around organ to form double layer, making it very mobile
133
what are retroperitoneal organs
only has visceral peritoneum on its anterior surface
134
what is mesentery
usually connects organ to posterior body wall
135
what is omentum
double layer of perineum that passes from stomach to adjacent organs
136
what is the greater omentum
four layeredhangs like an apron attaches greater curvature of stomach to transverse colon
137
what is the lesser omentum
double layeredruns between lesser curvature of stomach and duodenum to liver has free edge
138
by which do the two omentum sacs communicate
omental foramen (foramen of winslow)
139
what is peritoneal ligaments
double layer of perineum that connects organs to one another or body wall
140
what are the four main peritoneal ligaments
hepatogastric ligament hepatoduodenal ligament gastrosplenic ligament splenorenal ligament
141
what pouch does peritoneum form in male by its inferior aspect draping over superior aspect of pelvic organs
rectovesical pouch
142
what 2 pouches does peritoneum form in female
vesico-uterine pouch and recto-uterine pouch
143
what is ascites
collection of fluid in peritoneal cavity commonly caused by liver disease - cirrhosis or portal hypertension
144
how is abdominocentesis perfomed
needle places lateral to rectus sheath - avoids inferior epigastric artery
145
what is the course of the abdominal sympathetic nerves
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
how is the adrenal gland sympathetic nerve different
leaves at T10-L1. Do not synapse, carried with periarterial plexus to adrenal gland and synapse directly onto cells
147
what is the course of abdominal vagus nerve (CNX)
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
what is course of pelvic splanchnic nerves (S2, 3 and 4)
presynpatic parasympathetic nerve fibressmooth muscle/glands of descending colon to anal canal
149
the somatic motor, sensory and sympathetic nerve fibres supplying structures of abdominal part of the body wall are conveyed within what
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
where is appendix usually located
right iliac fossa
151
describe the pain of appendicitis
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
what are 3 parts of small intestine
duodenum (30cm), jejunum (3.5m), ileum (2.5m)
153
what does the small intestine recieve
chyme from stomach (from pyloric sphincter), pancreatic juice from pancreas, bile from gall bladder (both via sphincter of oddi)
154
what is the other roles of small intestine
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
the small intestine secretes (into blood) various peptide hormones from endocrine cells within mucosa. What are these hormones
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
all of these secretions act on which receptors
G protein coupled receptors
157
what is the control mechanism by which succus entericus (gastric juice) is secreted
distension/irritation, gastrin, CKK, secretin, parasympathetic nerve activity (all enhance)sympathetic nerve activity (decreases)
158
what does this secretion (succus entericus) contain
mucus (protection/lubrication - from goblet cells) aqueous salt for enzymatic digestion (mostly from crypts of lieberkuhn)no digestive enzymes
159
what does the secretion of succus entericus involve
Na+/K+ATPaseNa+/K+/2Cl- co transporterchloride channel (CFTR)
160
how is segmentation (mixing) of chyme initiated
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
what triggers segmentation in empty ileum
gastrin from stomach (gastroileal reflex)
162
what is the difference in segmentation contractions between duodenum and ileum
duodenum - 12 per min ileum - 9 per min net movement if aboral
163
what takes place after segmentation
peristalsis
164
which two activities occur in interdigestive, or fasting, state
few localised contractionsmigrating motor complex (MMC) - occurs between meals, strong peristaltic contractions passing length of intestine (stomach - ileocaecal valve)
165
what is beneficial about this MMC
clears small intestine of debris, mucus and sloughed epithelial cells between meals - housekeeper function
166
what inhibits MMC
feeding and vagal activity
167
what triggers MMC
motilin (it is suppressed by gastrin and CCK)
168
what is endocrine secretions of pancreas (released directly into blood stream)
insulin and glucagon
169
what is exocrine secretions of pancreas (secreted to duodenum collectively as pancreatic juice)
digestive enzymes (acinar cells), aqueous NaHCO3- solution (duct cells)
170
what is the role of the HCO3- fluid released by pancreatic duct cells
neutralises acidic chyme entering duodenum - provides optimum pH for pancreatic enzyme function and protects mucosa from erosion by acid
171
what is special about pancreatic enzymes
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
what controls 20% of total pancreatic secretion
cephalic - mediated by vagal stimulation of mainly the acinar cells
173
what controls 5-10% of total pancreatic secretion
gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells
174
what controls 70-80% of control of pancreatic secretion
intestinal phase - mechanism depends on wether its acid or fat and protein in duodenal lumen
175
what happens when there is acid in duodenal lumen
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
what happens when there is fat and protein in duodenal lumen
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
what is main constituent of carbohydrates (approx 400g per day)
starch (greater than 50% total carbohydrate ingested)cellulose (indigestible in humans)glycogen disaccharides (sucrose, lactose)
178
what is main constituent of lipids (approx 25-160g per day)
triacylglycerols (approx 90% of total lipid ingested as fats and oils)phospholipidscholesterol and estersfree fatty acids lipid vitamins
179
what is main constituent of protein
70-100g per day ingested, plus 35-200g from endogenous sources (eg digestive enzymes and dead cells from GI tract)
180
what is definition of digestion
enzymatic conversion of complex dietary substances to a form that can be absorbed
181
most digestive processes occur in the small intestne as what
luminal digestion (mediated by pancreatic enzymes secreted into duodenum)membrane digestion (mediated by enzymes situated at brush border of epithelial cells)
182
what is absorption
process by which absorbable products of digestion are transferred across both apical and basolateral membranes of enterocytes (absorptive cells of intestinal epithelium)
183
what is the overall process of digestion and absorption called
assimilation
184
all dietary carbohydrates must be converted to which form to be absorbed
monosacchardies (glucose /fructose)
185
what accomplishes the sequence of carbohydrate digestion
a-amylase (salivary and pancreatic)
186
how is this achieved
starch converted to oligosaccharides (not absorbed) by intraluminal hydrolysis oligosaccharides converted to monosaccharides by membrane digestion (at brush border)
187
give example of olgiosacchardies
lactose, sucrose (can come from diet)
188
what is the role of a-amylase (endoenzyme)
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
what is an olgiosaccharide
internal membrane proteins with a catalytic domain that faces the lumen of GI tract
190
what do olgiosaccharides do
cleave terminal a-1,4 linkages of maltose, maltotriose and a-limit dextrins to yield glucose
191
how is lactase special
only has one substrate - breaks down lactose to glucose and galactose
192
what is specific role of maltase
degrade a-1,4 linkages in straight chain oligomers up to nine monomers in length
193
what is specific role of sucrase
specifically responsible for hydrolysing sucrose to glucose and fructose
194
what is specific role of isomaltase
unique in that it is the only enzyme that can split branching a-1,6 linkages of a-limit dextrins
195
what is lactose intolerance
relative common digestive problem resulting from inability to adequately digest lactose - caused by lactase insufficiency
196
what causes lactase persistence (LP) - continuance of digestion of lactose in milk in adults
polymorphisms in MCM6 gene that regulates expression of lactase (LCT) gene
197
lactose intolerance can result from what
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
what do the ileum colonic microflora produce if lactose is delivered to the colon
short-chain fatty acids (which can be absorbed), hydrogen (can be detected in breath of lactase deficient individuals) CO2 and methane
199
what is the by-product of these productions
bloating, abdominal pain and flatulence
200
what does undigested lactose cause
acidification of colon and an increased osmotic load - loose stools and diarrhoea
201
where does the absorption of the final product of carbohydrate digestion (glucose, galactose and fructose) take place
duodenum and jejunum - it is a two step process involving entry and exit from the enterocytes via the apical and basolateral membranes respectively
202
what absorbs these final products
glucose and galactose are absorbed by secondary active transport mediated by SGLT1fructose by facilitated diffusion mediated by GLUT5
203
exit for all monosaccharides is mediated by what
facilitated diffusion by GLUT2
204
which form must SGLT1 be in to absorb glucose
a hexose in the D-conformation an one that can form a pyranose ring
205
what is the mode of operation of SGLT1
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
proteins must be digested to oligopeptides and amino acids for efficient absorption within how long
6 months
207
how many different pathways exist and what is the basic pathway
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
what different enzymes and transporters are used
luminal enzymes, (can be bush border enzymes - 2), apical membrane transporters, (can be intracellular hydrolysis - 3), basolateral membrane transporters
209
what is special about the fourth variant
when peptide transported out of enterocyte without intervening intracellular hydrolysis by proteases
210
how does digestion of proteins take place in stomach
HCl denatures proteins and pepsin cleaves proteins into peptides (is endopeptidase with preference for bonds between aromatic and larger neutral amino acids)
211
how does digestion of protein take place in duodenum
five pancreatic proteases are secreted as proenzymes from exocrine pancreas and converted to active form in duodenum - they act as endopeptidases or exopepitases
212
what are examples of endopeptidases that produce oligopeptides (2-6 amino acids)
trypsin, chymotrypsin, elastase
213
what are examples of exopeptidase that produces single amino acids
procaroxypeptidase A and procarboxypeptidase B
214
what completes protein digestion
additional proteases which are present at the brush border and within the cytoplasm of enterocyte
215
step 1 in summary of protein digestion and absorption
protein digested in lumen to amino acids or olgiopeptides by pepsin and pancreatic proteases
216
step 2 in summary of protein digestion and absorption
peptidases at the brush border further hydrolyse oligopeptides to amino acids
217
what is step 3 in summary of protein digestion and absorption
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
what is step 4 in summary of protein digestion and absorption
olgiopepties transported across apical membrane by H+/oligopeptide co-transporter - PepT1
219
what is step 5 in summary of protein digestion
olgiopeptides within cytoplasm are hydrolysed to amino acids by peptidases within enterocyte
220
what is step 6 in summary of protein digestion
amino acids exit enterocyte across the basolateral membrane by several Na+ independent transporters
