Gastro Flashcards
(287 cards)
1
Q
What is the name of the side of cells facing the lumen
A
Apical, mucosal or luminal
2
Q
What is the name of the side of the cells facing the interstitium
A
Basolateral, serosal, interstitial
3
Q
What is the transcellular pathway
A
Across apical and basal membranes, and cytosol
4
Q
What is the paracellular pathway
A
Between cells, across tight junctions
5
Q
What is exocrine secretion
A
Into the lumen
6
Q
What is endocrine secretion
A
Into the bloodstream
7
Q
What is the function of mucosal secretion in the GIT
A
Protection, lubrication, mechanical digestion
8
Q
What is the function of electrolyte solution secretion in the GIT
A
Dilute food, provide optimal pH, essential for function of digestive enzymes
9
Q
What is the function of digestive enzyme secretions in the GIT
A
Chemical digestion of food, aids absorption
10
Q
What are the three pairs of salivary glands
A
Submandibular, sublingual, parotid
11
Q
What are salivary secretions composed of
A
Mucus for lubrication, NaHCO3 and NaCl for dilution of food, tasting, swallowing, talking, optimal pH for digestive enzymes, hygiene and irrigation of the mouth, and digestive enzymes: lingual lipase and salivary amylase
12
Q
How is salivary secretion regulated
A
The autonomic nervous system (thought, smell, sight, presence of food) (PNS and SNS)
13
Q
What does the parasympathetic nervous system result in the salivary secretion of
A
Copious quantities of fluid
14
Q
What does the sympathetic nervous system result in the salivary secretion of
A
Small volumes of viscous fluid
15
Q
What do goblet cells secrete in the stomach
A
Mucus (protection from abrasion) and bicarbonate (protection from stomach acid)
16
Q
What do parietal cells secrete in the stomach
A
HCl (activate pepsinogen to pepsin by denaturation, optimum pH, protection from microbes)
Intrinsic factor: absorption of vitamin B12 in the ileum
17
Q
What do chief cells secrete in the stomach
A
Pepsinogen (proteolytic enzyme which starts chemical digestion of proteins)
18
Q
Why are parietal cells above chief cells in gastric glands
A
Pepsinogen from chief cells needs to be activated to pepsin by HCl from parietal cells
19
Q
Where do parietal cells source H+ from
A
Carbonic anhydrase catalysing conversion CO2 and H2O to carbonic acid (H2CO3), then this dissociating into HCO3- and H+
20
Q
How do H+ ions get into the lumen from parietal cells
A
Pumped by H+/K+ ATPase (K+ pumped in, passively diffuses back out)
21
Q
How do Cl- ions get into parietal cells from the interstitium
A
Exchanged for HCO3-
22
Q
How do Cl- ions get into the lumen to join with H+
A
Passively diffuse from cell
23
Q
What are the three stages of gastric secretion
A
Cephalic, gastric, intestinal
24
Q
What stimulates the cephalic phase
A
Smell, sight, taste of food
25
What is the detector for the cephalic phase
CNS
26
How is the signal sent from the CNS to the ENS in the cephalic phase
Vagus nerve (parasympathetic nervous system)
27
What are the effectors of the cephalic phase
ENS: myenteric (gastric motility and receptive relaxation) and submucosal plexus (secretion by G, parietal, chief and goblet cells)
28
What percentage of gastric secretion does the cephalic phase account for
20%
29
What is the stimulus of the gastric phase
Contents in the stomach
30
What are the detectors of the gastric phase
Mechanoreceptors (stretch), chemoreceptors (pH), G cells (peptides)
31
What coordinates the response of the gastric phase
ENS (myenteric: motility: 3 contractions/minute, submucosal: secretion) and G cells secretion of gastrin positively acting on parietal and chief cells
32
What percentage of gastric secretion does the gastric phase account for
70%
33
What stimulates the intestinal phase of gastric secretion
Arrival of acidic chyme, stretch, lipids, proteins, carbs
34
What are the detectors of the intestinal phase
Mechanoreceptors, chemoreceptors in the wall of the duodenum
35
What does a decrease in pH in the duodenum result in
Enteroendocrine cells secreting secretin
36
What coordinates the response of the intestinal phase
ENS and CNS (SNS) short and long reflex
37
What does the arrival of lipids, proteins and carbs in the duodenum result in
Secretion of CCK and GIP by enteroendocrine cells
38
What do G cells secrete and what does this stimulate
Gastrin, stimulates chief and parietal cells, and increased gastric motility (retropulsion)
39
What percentage of gastric secretion is the intestinal phase
10%
40
The arrival of what macronutrient especially stimulates the gastric phase
Protein
41
What is the function of the intestinal phase
Slow controlled release of food to small intestine
42
What does the decrease in pH result in EECs secreting (intestinal phase)
Secretin
43
What are the two types of exocrine pancreatic secretion
Pancreatic digestive enzymes and alkaline (HCO3-) fluid
44
What pancreatic cells secrete digestive enzymes
Acinar cells
45
What pancreatic cells secrete HCO3- fluid
Duct cells
46
What does the arrival of fatty acids and amino acids in the duodenum result in the secretion of from duodenal enteroendocrine cells
CCK and GIP
47
What does CCK stimulate from the pancreas
Digestive enzymes from pancreatic acinar cells
48
What are the digestive enzymes the pancreas secretes
Ribonuclease, deoxyribonuclease, lipase, colipase, pancreatic amylase, trypsinogen, chymotrypsinogen, procarboxypeptidase
49
How is trypsinogen converted to trypsin
Entereokinase(peptidase) bound to duodenal membrane
50
How are chymotrypsinogen and procarboxypeptidase converted to their active forms
By trypsin
51
What does secretin stimulate from the pancreas
Bicarbonate from duct cells (neutralise chyme, provide optimum pH for pancreatic enzymes)
52
What do hepatocytes secrete
Bile into bile canaliculi for chemical digestion of fat
53
What do bile duct cells secrete
Alkaline fluid which neutralises acid from chyme in the stomach
54
What excretory/waste products does bile contain
Bile pigments (bilirubin from breakdown of haem), excess cholesterol
55
What is the purpose of the gall bladder
Store and concentrate bile
56
What causes the initial release of bile from the gall bladder
CCK, via contraction of the gall bladder wall and relaxation of the hepatopancreatic sphincter
57
How much bile is reabsorbed in the ileum
95%
58
How is bile transported back to the liver
Enterohepatic circulation
59
How is the liver stimulated to produce more bile
Bile returning to liver via enterohepatic circulation, and mildly by secretin
60
What does the small intestine secrete
1.5L of fluid per day, mucus for lubrication and isosmotic fluid (NaCl and NaHCO3) to neutralise acid and dilute food to aid digestion
61
What does the large intestine secrete
Mucus for lubrication
62
Where is the submucosal plexus
Below the mucosa
63
Where is the myenteric plexus
Between layers of smooth muscle, controls smooth muscle
64
What effect does the parasympathetic nervous system have on the GIT
Increases overall activity by activating ENS
65
What effect does the sympathetic nervous system have on the GIT
Decreases overall activity by inhibiting ENS
66
What is the short reflex pathway
ENS only
67
What is the long reflex pathway
CNS, ENS back and forth
68
What is the function of the long and short reflex pathways
To integrate response of GIT to external stimuli, return the lumen of the GIT to its resting state
69
What is the short reflex stimulated by
Arrival of chyme (stretch, pH, osmolarity, protein/amino acids, lipids, carbohydrates) detected by chemo, osmo and mechanoreceptors
70
What is the long reflex pathway stimulated by
Change in contents of lumen, or sight/smell/taste of food, or emotional responses
71
What are tonic contractions
Sustained contractions for minutes to hours (think sphincters)
72
What are phasic contractions
Waves of contraction and relaxation, each wave lasting seconds. Controlled by pacemaker cells
73
How often does the stomach contract
3/min
74
How often does the duodenum contract
12/min
75
How often does the ileum contract
9/min
76
How does peristalsis work
Circular muscle behind bolus contracts, longitudinal muscle ahead contracts
77
What is relaxation of the stomach
Storage of food/chyme by increasing the volume without an increase in pressure
78
What is peristalsis
Movement of food along the GIT
79
What is segmentation
Mixing of chyme with secretions and exposure to absorptive surfaces
80
What are sphincters
Rings of muscle around the junction between parts of the GIT
81
What is the migrating motor complex (MMC)
Begins in stomach and travels to small intestine. Functions for house keeping, removing residual secretions, undigested material and promoting epithelial cell turnover
82
When does MMC occur
4 hours after a meal
83
What is the first phase of MMC
45-60 minutes of inactivity
84
What is the second phase of MMC
30 minutes intermittent uncoordinated activity
85
What is the third phase of MMC
5-15 minutes intense coordinated peristaltic contractions
86
How often does MMC repeat
1.5-2 hours until food is consumed
87
What is the reflex part of swallowing
Strength and frequency/rhythm
88
What prevents food going into the nasopharynx
Soft palate and uvula rise
89
What prevents food going into the trachea
Folding of the epiglottis
90
What are the motility patterns of the stomach
Relaxation, retropulsion (peristalsis and contraction of pyloric sphincter), contraction and relaxation of pyloric sphincter
91
What are the parts of the stomach
Fundus, body, pylorus (pyloric antrum), pyloric sphincter
92
Where does relaxation occur in the stomach
Fundus and body
93
What are the two types of relaxation
Receptive (part of swallowing, stomach about to receive food and relaxes), accommodation (food has arrived and stomach needs to find space for it)
94
What is retropulsion
Peristalsis and contraction of pyloric sphincter. Physical breakdown of food particles into smaller particles. Food particles grind against pyloric sphincter
95
What is gastric emptying
Controlled movement of fully mechanically digested chyme from stomach into duodenum
96
What factors affect the rate of gastric emptying
Size of meal (larger meal = more stretch = faster emptying), composition of meal (fluids faster than solids)
97
What are the motility patterns in the small intestine
Segmentation, peristalsis, contraction and relaxation of ileocecal sphincter
98
What are the motility patterns of the large intestine
Segmentation, relaxation, peristalsis (mass movement 1-2 times per day)
99
Where does segmentation occur in the large intestine
All throughout
100
Where does relaxation occur in the large intestine
Descending and sigmoid colon
101
What are the accessory organs of the digestive system
Teeth, tongue, salivary glands, liver, gall bladder, pancreas
102
What are the major organs of the digestive system
Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine
103
What type of epithelium is in the mouth, oral cavity and oesophagus
Stratified squamous (protection from abrasion)
104
What type of epithelium is in the stomach, small and large intestine
Simple columnar (secretion and absorption)
105
What type of epithelium is in the anus
Stratified squamous (protection from abrasion)
106
In what type of epithelium are goblet cells found
Columnar
107
Describe the structure of goblet cells (unicellular glands)
Columnar, goblet shaped, apical mucous granules, basal nucleus
108
What is the purpose of goblet cells in the GI tract
Lubrication and protection
109
What are the two types of multicellular glands
Simple (single duct) and compound (2 or more ducts)
110
What are the four layers of the gut tube
Mucosa, submucosa, muscularis (externa/proper), adventitia
111
What does the mucosa consist of
Epithelium, basement membrane, lamina propria (FCT), muscularis mucosae, plus sometimes glands
112
Where are blood vessels and lymphatics located in the mucosa
Lamina propria (FCT)
113
What regulates secretion in the GIT
Submucosal plexus
114
What does the muscularis consist of in the GIT
Smooth muscle, inner circular and outer longitudinal
115
What regulates motility in the GIT
Myenteric plexus (located between the layers of muscle)
116
What does the adventitia consist of
FCT, holds everything together like glad wrap
117
What are the openings of the throat called
Fauces
118
What is the order of pharynxes down the throat
Oropharynx, laryngopharynx, esophagus
119
What are the three salivary glands and where are they each located
Parotid (back of cheek), sublingual (under tongue), submandibular (under mandible)
120
What do parotid glands secrete
Serous fluid with amylase
121
What do sublingual glands secrete
Mucus
122
What do submandibular glands secrete
A mixture of serous fluid with amylase, and mucus (M for mixed)
123
What is a cluster of cells in a compound gland called
Acinus
124
What do acinar cells in salivary glands secrete
Serous fluid and enzymes (amylase), and mucus
125
Where are acinar cells located in compound glands
In the acini
126
What do duct cells secrete in salivary glands
Bicarbonate for pH buffering
127
Where are duct cells located in compound glands
At the top (duct)
128
What structure ensures that food enters the oesophagus and not the trachea
Epiglottis
129
Why is the esophagus mucosa and submucosa highly folded
Capacity to expand for passage of bolus
130
How does the muscularis externa of the esophagus change as it moves down
First third skeletal, second third a mixture, third third smooth
131
Which salivary glands can produce amylase
Parotid
132
How is the oesophagus lubricated
Glands in submucosa with ducts to surface (no goblet cells as stratified squamous epithelium)
133
What is the periotneum
Serous membrane that lines the abdomen
134
What are the retroperitoneal organs
Pancreas, initial segment of small intestine, kidneys
135
What does the parietal layer of the peritoneum line
Body wall
136
What does the visceral layer of the peritoneum line
Organs
137
What is a mesentery
Double layer of visceral peritoneum that connects organ to body wall
138
What is an omenta
Double layer of visceral peritoneum that connects an organ to another organ
139
What is the purpose of the peritoneum
Allow lubrication, enable movement without tangling organs
140
What is the name of the structure through which the oesaphagus passes the diaphragm
Oesophageal hiatus
141
What is the function of the lower oesophageal sphincter
Prevents reflux
142
What are the regions of the stomach
Fundus, cardia, pylorus, body
143
What is the extra layer of muscle in the stomach
Innermost layer of oblique muscle (plus inner circular and outer longitudinal)
144
What does the lesser omentum attach
Lesser curvature of stomach to liver
145
What does the greater omentum attach
Greater curvature of stomach to transverse colon
146
What are the temporary folds that enable expansion of the stomach
Rugae (core of submucosa)
147
What type of epithelium is in the stomach
Columnar
148
What are gastric glands
In folding of columnar epithelium to increase area for secretion. Glands do not flatten
149
What is a gastric pit
Top of gastric gland comprised of mucous epithelial cells
150
What is a notable organelle in chief cells
Abundant rough endoplasmic reticulum to make proteins (pepsinogen), basal nucleus
151
What are zymogen granules in chief cells
Apical secretory vesicles filled with inactive enzymes (pepsinogen)
152
What is a notable organelle in parietal cells
Abundant mitochondria as they pump H+ ions against their gradient
153
Describe the structure of parietal cells
Central nucleus, very folded (microvilli) membrane to increase SA for pumping H+ ions
154
What are canaliculi
Channels between microvilli in parietal cells
155
What hormones are secreted by the stomach
Gastrin and ghrelin
156
How is the stomach controlled neurally
ENS (local reflexes), CNS modulating ENS function (long neural reflex)
157
What enables controlled release of chyme into the small intestine
Pyloric sphincter
158
Where is mucous for the small intestine provided from
Glands in the submucosa of the duodenum
159
What does the pancreas provide to the small intestine
Enzymes and bicarbonate
160
Where does the bile duct enter the duodenum
Duodenal papilla
161
What is the exocrine function of the pancreas
Acinar cells secrete digestive enzymes, duct cells secrete bicarbonate
162
What is the structure of pancreatic acinar cells
Apical zymogen granules, basal nucleus, abundant rough ER
163
Where does the bile duct meet the pancreatic duct
The entrance to the hepatopancreatic ampulla
164
What type of epithelia is in the small intestine
Simple columnar: goblet cells secrete mucus to neutralise chyme
165
Where are mucous secreting glands located in the small intestine
Submucosa
166
What is the order of the parts of the small intestine
Duodenum, jejunum, ileum
167
How is the duodenum separated from the rest of the small intestine
Retroperitoneal
168
What is the order of sizes of the parts of the small intestine
Duodenum (shortest), jejunum, ileum
169
What is the purpose of the duodenum
Receive chyme, enzymes and bicarbonate from pancreas, bile from liver
170
What is the purpose of the jejunum and ileum
Digestion and absorption
171
What prevents tangling of the small intestine
Mesentery
172
Describe mesentery
Made of peritoneum so slippery, contains blood vessels, nerves, lymphatics, fat
173
Where do small intestine mesenteric veins drain to
Hepatic portal vein
174
Where do lymph lacteals drain into
Cisterna chyli, thoracic duct, left subclavian vein
175
What are the two mesenteric veins
Superior and inferior
176
What is a mesentery (me)
Organ to body wall
177
What is an omenta (O)
Organ to organ
178
How is the huge surface area of the small intestine achieved
Length, folding of intestinal wall (plicae circulares), extensions of mucosa (villi), extensions of epithelial cells (microvilli)
179
Describe plicae circulares
Permanent large folds of small intestine. Core of submucosa with overlying mucosa
180
Describe villi
Found on surface of plicae circulares, part of mucosa, core of lamina propria, muscularis mucosae enables movement
181
What is the purpose of movement of the villi
Small movements to enable more contact with nutrients of chyme
182
What does each villi contain
Lymph lacteal (receives products of fat digestion), and a capillary network (receive products of protein and carbohydrate digestion)
183
What are the absorptive cells of the small intestine with microvilli on their apical surface
Enterocytes
184
What attaches enzymes to the brush border of enterocytes for contact digestion
Glycocalyx (also holds epithelial cells in place)
185
What is the glycocalyx
Glycoproteins (branched filaments)
186
Where are tight junctions between cells located
As high up as possible
187
What are paneth cells of the small intestine
Secrete granules of antibacterial enzymes
188
Where are paneth cells located in intestinal crypts
The bottom
189
What are microvilli made of
Mucosa
190
What is the first part of the large intestine called
Cecum
191
What regulates the passage of material from the small to large intestine
Ileocecal valve
192
What are the three parts of the large intestine
Cecum, colon, rectum
193
What is the colon divided into
Ascending, transverse, descending, sigmoid
194
What are the bobbles of the large intestine called
Haustra
195
Which parts of the colon are retroperitoneal and which are intraperitoneal
Ascending and descending retroperitoneal, transverse and sigmoid intraperitoneal
196
Where is the appendix located
At the cecum, where the teniae coli come together
197
What is the purpose of the appendix
Reserve of large intestine bacteria
198
What are the bands of longitudinal muscle on the large intestine called
Teniae coli
199
What are the sacs of fat on the large intestine called
Omental appendices
200
What are the modifications of the large intestine muscularis
Outer longitudinal is arranged into thick bands for stronger contraction
201
Why does the large intestine not have vili
Large surface area no longer needed
202
Why does the mucosa of the large intestine invaginate
To form intestinal glands
203
What are the two cell types in the large intestine
Absorptive (water and salt) and goblet (mucus for protection and lubrication)
204
What is the purpose of the rectum
Store faeces
205
Which anal sphincter is voluntary
External
206
What do the anal columns mark
Change of epithelium from simple columnar to stratified squamous
207
How is the presence of faeces detected
Stretch receptors in rectum, relaxation of internal anal sphincter
208
What is the long reflex pathway in defecation
Spinal reflex coordinated by sacral parasympathetic motor neurons. Mass movement of faeces toward rectum from descending and sigmoid colon
209
What is the short reflex pathway in defecation
Series of peristaltic contractions in rectum that move faeces toward anus. Mediated by myenteric plexus in sigmoid colon and rectum
210
What are the functions of the liver
Metabolic processes, detoxification of blood, bile production
211
Where is the liver located
Superior right quadrant of abdominopelvic cavity
212
What is the function of the gall bladder
Stores and concentrates bile
213
How does the gall bladder connect to the liver
Cystic duct attached to bile duct
214
What ducts come out of the liver
Left and right hepatic (become common hepatic)
215
How much cardiac output does the liver receive
25%
216
1/3 of blood supply to the liver comes from
Hepatic artery
217
2/3 of blood supply to the liver comes from
Hepatic portal vein
218
Where does the blood in the hepatic portal vein come from
Nutrient rich, deoxygenated blood from small intestine, to be processed by hepatocytes
219
What structure do the hepatic portal vein, hepatic artery and bile duct travel in
Lesser omentum
220
What are liver lobules
Hexagonal functional units made of rows of hepatocytes
221
What do hepatocytes do
Produce bile
222
What are between rows of cells in liver lobules
Liver sinusoids
223
Where are bile canaliculi in liver lobules (small capillaries off bile duct)
Between cells
224
What is a hepatic portal triad
Branch of hepatic artery, branch of hepatic portal vein, a bile duct
225
How do bile and blood travel in liver lobules
Blood flows from corners of hexagon to central vein, bile travels from hepatocytes to bile duct (opposite directions)
226
Where do central veins of liver lobules drain into
Hepatic vein, then into inferior vena cava
227
Where does the bile duct join the pancreatic duct
Hepatopancreatic ampulla
228
What are the two types of starch
Amylose (coil) and amylopectin (branched)
229
How many essential amino acids cannot be made by the body
8
230
Which lipids are essential to the body
Omega 3 and 6, and fat soluble vitamins A, D, E and K
231
How long are short chain fatty acids
<6 carbons
232
How long are medium chain fatty acids
6-12 carbons
233
How long are long chain fatty acids
13-24 carbons
234
How must the GIT absorb carbohydrates
As monosaccharides
235
How must the GIT absorb proteins
As amino acids
236
How must the GIT absorb lipids
As free fatty acids and monoglycerides
237
Where are digestive enzymes located
Extracellularly
238
Where are disaccharidases located
Bound to brush border in small intestine
239
What are the three disaccharidases we know
Sucrase, lactase, maltase
240
What is sucrose
Glucose + fructose
241
What are the three pancreatic proteases
Trypsin, chymotrypsin and carboxypeptidase
242
Do fats undergo contact digestion
No, only luminal digestion in the stomach and small intestine
243
What enzymes digest TAGs in the stomach
Lingual and gastric lipase
244
What enzyme digests TAGs in the small intestine
Pancreatic lipase
245
What are the four stages of lipid digestion
Emulsification (mixing), stabilisation, digestion (hydrolysis), formation of micelles (bile salts)
246
What is emulsification
Process by which large lipid droplets are broken down into smaller, stabilised droplets increasing the surface area for digestion
247
What is the purpose of motility in lipid digestion
Retropulsion and segmentation breaks up large lipid droplets into smaller emulsification droplets to increase surface area for digestion
248
How is stabilisation of emulsion droplets different between the stomach and small intestine
Stomach: simple emulsion (other molecules)
Small intestine: more complex emulsion (bile salts)
249
What is the purpose of stabilisation of emulsion droplets
Form smaller droplets (increase surface area), prevent them from reforming into larger droplets, enables them to travel in an aqueous environment
250
What is the most important property of bile salts
Amphipathic
251
How are TAGs converted to 2 FFAs and 1 monoglyceride
By lipase and colipase
252
What does colipase do
Anchors lipase to surface of droplet
253
Where does hydrolysis of fats occur
In the small intestine at the surface of emulsion droplets
254
What are micelles
A way to keep monoglycerides and long chain fatty acids in solution. Consist of 20-30 molecules (bile salts, fatty acids, monoglycerides)
255
What is absorption
Movement of solutes and water from the GIT lumen across the epithelium, into the interstitial fluid and then into the blood or lymph
256
What are the two pathways for absorption
Paracellular and transcellular
257
Where is the main site of absorption
Small intestine (mouth, esophagus and stomach minimal, large intestine some)
258
What enables the small intestine to absorb most effectively (compared to other structures)
Leaky epithelium
259
What type of absorption does the large intestine do (9% of water and sodium)
Regulated/fine tuning absorption in tight epithelium
260
What factors affect absorption
Reduction in nutrient size by chemical digestion, motility, transport across GIT epithelium, surface area available for absorption, removal from interstitial fluid
261
Why must chyme travel at the correct rate through the GIT
To allow mechanical digestion, chemical digestion, absorption
262
What is the paracellular pathway
Between epithelial cells, particles do not cross cell membranes, only barrier is tight junctions. If leaky and particle is small enough, will move through
263
What is the transcellular pathway
Through epithelial cells, particles must cross two membranes. Lipid soluble particles can diffuse, water soluble require a channel or transporter membrane protein
264
How is build up of particles in the interstitial fluid prevented after absorption
High blood flow to intestines, blood vessels and lacteals close to the basolateral side of epithelial cells
265
How is glucose absorbed by the paracellular pathway
Glucose molecules diffuse down their concentration gradient across leaky tight junctions (passive)
266
How is glucose absorbed by the transcellular pathway (active)
Sodium electrochemical gradient generated by Na+/K+ ATPase, transported across apical membrane by secondary active transport via sodium-glucose cotransporter. Transported across basolateral membrane by glucose carrier/transporter
267
How are amino acids absorbed by the paracellular pathway (di/tripeptides cannot be absorbed by this pathway)
Diffuse down their concentration gradient across leaky tight junctions
268
How are amino acids absorbed by the transcellular pathway (active)
Sodium electrochemical gradient generated by Na+/K+ ATPase, transported across apical membrane by secondary active transport via sodium-amino acid cotransporter. Transported across basolateral membrane by amino acid carrier/transporter
269
How are di and tripeptides absorbed by the transcellular pathway (active)
Negative membrane potential generated by Na+/K+ ATPase creates electrical gradient for H+. Secondary active transport via H+/peptide cotransporter, in cytoplasm peptidases digest into amino acids, facilitated diffusion out of basolateral membrane via amino acid carrier/transporter
270
How are free fatty acids and monoglycerides absorbed
Simple diffusion from micelle into cell (micelle not absorbed but able to get very close to brush border)
271
Where are bile salts absorbed
Ileum
272
What happens to FFAs and MAGs intracellularly
Transported to ER, resynthesised to TAGs, packaged into chylomicrons
273
How do TAGs leave the cell
Exocytosed in chylomicrons, enter lymph via lacteals of villi
274
What is the driving force for water absorption (cannot occur actively)
Osmotic gradient generated by the absorption of nutrients and ions
275
Where does the bulk re/absorption of water occur
Small intestine (most paracellular, some transcellular via aquaporins)
276
Where does fine tuning re/absorption of water occur
Large intestine (tight epithelium, all absorption via transcellular pathway- aquaporins)
277
How does passive absorption of sodium occur
Via the paracellular pathway, down concentration gradient
278
How does active absorption of sodium occur
Secondary active transport coupled with glucose and amino acids (apical membrane), then Na+/K+ ATPase (basolateral membrane)
279
Where does passive and active absorption of sodium occur
Small intestine: passive and active (trans and para)
Large intestine: active (trans)
280
How does fat passively move into cells (apical membrane)
Diffusion: micelles come close to surface
281
How does fat passively move out of cells (basolateral membrane)
Packaged into chylomicrons, diffuse out
282
How are water soluble vitamins absorbed (apical membrane)
Secondary active transport via sodium cotransporter (e.g sodium-vit C cotransporter)
283
How do water soluble vitamins leave the cell (basolateral membrane)
Transporter
284
Where is vitamin B12 absorbed
Ileum
285
What must happen in order for vitamin B12 to be absorbed
Bind to intrinsic factor (made by parietal cells in the stomach), then bind to receptor on epithelial cells in the ileum
286
How does vitamin B12 bound to intrinsic factor and an epithelial cell receptor enter and exit the cell
Enters the cell by endocytosis, exits and travels in blood bound to transcobalamin
287
What does CCK result in
Inhibits chief, G and parietal cells, stimulates digestive enzymes from pancreatic acinar cells, contraction of gall bladder and relaxation of hepatopancreatic sphincter
