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Physiology 1 : GI > Transport along the GI tract > Flashcards

Transport along the GI tract Flashcards

1
Q

How does gastric accommodation occur?

A

→ Decrease in cholinergic activity

→ VIP / NO promote accommodation

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2
Q

Where do tonic contractions start from?

A

→ The top of the antrum

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3
Q

What does the stomach do to store food and why?

A

→ The proximal stomach relaxes to store food at low pressure while it is acted on by acid and enzymes mechanically

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4
Q

Why is gastric emptying carefully regulated?

A

→ It ensures adequate acidification/neutralization
→ Action of enzymes, mechanical breakdown
→ avoid swamping the duodenum

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5
Q

What is a disorder of gastric emptying?

A

→ Gastric stasis

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6
Q

What is gastric emptying dependent on?

A

→ Propulsive force generated by the tonic contractions of the proximal stomach
→ The stomachs ability to differentiate types of meals ingested and their components

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7
Q

What decreases the force and rate of gastric emptying?

A

→ Fatty, hypertonic and acidic chyme in the duodenum

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8
Q

How do liquids pass?

A

→ in spurts

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9
Q

How do solids pass?

A

→ Broken down into 1-2mm sizes

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10
Q

How do large indigestible materials pass?

A

→ Cleared by migrating motor complex

→ or vomiting

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11
Q

How are liquids emptied?

A

→ Rapidly disperse

→ Empty without a lag time

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12
Q

What is the rate of liquid emptying dependent on?

A

→ The rate of emptying is influenced by nutrient content

→ Nutrient rich liquids are retained for longer

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13
Q

How many phases are there in solid emptying?

A

→ 2 phases ( lag time and linear phase)

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14
Q

What is the duration of the lag time related to in solid emptying?

A

→ Duration of the lag time is related to the size of the particle

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15
Q

How are solids emptied?

A

→ Trituration of larger particles to smaller ones
→ Pylorus regulated the passage of material
→ (60 mins for a typical solid-liquid meal)

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16
Q

What is the order of highest gastric motility to lowest?

A

→ carbohydrates > proteins > fatty foods > indigestible solids

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17
Q

What are the determinants of gastric motility?

A

→ Types of food eaten
→ Osmotic pressure of duodenal contents
→ Vagal innervation upon over distension
→Hormones

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18
Q

What hormones inhibit emptying?

A

→ Somatostatin
→ CCK
→ Secretin
→ GIP

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19
Q

What does injury to the intestinal wall and bacterial infections cause?

A

→ Decrease in motility

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20
Q

How does the osmotic pressure of duodenal contents affect gastric motility?

A

→ Hyperosmolar chyme decreases gastric emptying

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21
Q

What is BER?

A

→ Intrinsic basic electrical rhythm

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22
Q

What does BER allow?

A

→ smooth muscle cell to depolarize and contract rhythmically when exposed to hormonal signals

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23
Q

What do the stomach cells produce from resting potential?

A

→ Electrical depolarizations

→ Move ripples towards the antrum

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24
Q

What control is the fundus under?

A

→ Vagal excitatory control

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25
What is an ICC?
→ Cajal cells | → Pacemaker cells in the wall of the stomach, small intestine and large intestine
26
What produces the BER?
→ Regular migrating ripples from the ICC
27
What are the depolarizations due to?
→ Entry of K+ and Ca2+
28
What mediates a decrease in fundic motor activity?
``` → Cholecystokinin → Secretin → VIP → Somatostatin →Duodenal distension → Gastrin releasing peptide ```
29
What increases fundic contractions?
→ Motilin
30
What initiates and maintains peristalsis in the small intestine?
→ Hormonal and nervous factors
31
What decreases activity in the small intestines?
→ Secretin
32
What does antral over distension cause?
→ Inhibitory signals | → Vago- vagal reflex
33
What does distension of the fundus cause?
→ Excitatory effects in the antrum | → Antrum contracts
34
What happens during duodenal over distension and chemical stimulation?
→ Vago-vagal reflex and hormones
35
What does the pyloric sphincter contract in response to?
→ Antral or duodenal rhythms
36
What do fatty acids in the duodenum cause?
→ Contraction of the pylorus
37
What promotes the relaxation of the pyloric sphincter when the duodenum has no food in it?
→ NO and VIP
38
What causes the pylorus to relax?
→ Descending inhibitory reflex
39
What are the types of movements in the intestine?
→ Segmentation (mixing contractions) → Peristalsis → Migrating Motor Complex → Mass movements
40
What are the phases of motor activity in the small intestine?
→ Phase 1 : quiescent/ quiet period → Phase 2 : Irregular propulsive contractions → Phase 3 : Burst of uninterrupted phasic contractions
41
Where does segmentation originate?
→ In the pacemaker cells (ICC)
42
What is segmentation and why is it needed ?
→ Divisions and subdivisions of chyme | → Brings chyme into contact with intestinal walls
43
What does segmentation cause?
→ Slow migration of chyme towards the ileum
44
How long are the contractions in the jejunum/duodenum?
→ 10-12 contractions per min
45
How long are the contractions in the ileum?
→ 8-9 contractions per min
46
What is peristalsis?
→ The propagating contraction of successive sections of circular smooth muscle preceded by relaxation/dilatation
47
What is the difference between segmentation and peristalsis?
→ Peristaltic contractions spread the food out allowing digestive enzymes to mix with it → Push food towards the anus (global movement) → Segmenting contractions primarily churn the food but also propel it towards the anus
48
When does the migrating motor complex occur and where does it start?
→ Between meals when the stomach/intestine are empty → Starts in the lower portion of the stomach
49
What is phase 3?
→ Burst of high frequency large amplitude contractions that migrate along the length of the intestine and die out
50
What are the functions of the MMC?
→ Intestinal housekeeper → Indigestible residues are moved out by large contractions and wide opening of the pyloric sphincter during phase III → Removes dead epithelial cells by abrasion → Prevents bacterial overgrowth → prevents colonic bacteria entering small intestine
51
What inhibits motility in the intestine?
→ Increased sympathetic activity
52
What stimulates motility in the intestine?
→ Increased parasympathetic activity
53
What decreases motility?
→ Pain and fear
54
What is the large intestine for?
→ Storage while water is absorbed from the contents | → Intensive mixing and slow movement of waste and indigestible material aborally
55
What are the fermenting chambers for in the large intestine?
→ Hydrolysis of fibre and indigestible nutrients
56
What mixes the contents in the large intestine?
→ Segmental or haustral contractions
57
What are the features of motility in the large intestine?
→ Intensive mixing → Fermentation → Slow propagating aboral flow
58
What is mass movement?
→ Powerful contraction of mid-transverse colon that sweeps colon contents into rectum
59
What is diarrhoea?
→ Frequent discharge of liquid feces | → 3x a day
60
What is constipation?
→ Difficulty/ constraint in opening bowels
61
What are adaptations of the small intestine to absorb food?
→ Epithelial folds → Villi + microvilli → Increase SA
62
What is absorbed when it enters the upper small intestine?
→ Dietary nutrients → Water → Electrolytes
63
What is in the crypt cells?
→ Stem cells
64
What are the two modes of transport across enterocytes?
→ Transcellular | → Paracellular
65
How can carbohydrates be absorbed?
→ In the form of monosaccharides
66
What are complex carbohydrates reduced to and how?
→ Disaccharides and by amylases
67
What converts disaccharides to monosaccharides?
→ Brush border enzymes
68
What is the equation for the breakdown of sucrose?
Sucrose + sucrase → Glucose + fructose
69
What is the equation for the breakdown of lactose?
lactose + lactase →Glucose + galactose
70
What is the equation for the breakdown of glucose oligomers?
Glucose oligomers + glucoamylase → glucose
71
How are glucose and galactose absorbed?
→ rapidly | → by a secondary active transport process
72
Describe the way glucose and galactose are transported?
→ On the basolateral side Na+ is transported into the blood → Gradient is created for Na+ to come into the lumen → Driving force of Na+ allows glucose to come with it
73
What is the glucose/galactose co-transporter called?
→ SGLT 1
74
What are the transporters for glucose and fructose called?
→ F - GLUT-5 | → G - GLUT-2
75
How are polypeptides produced from proteins?
→ Action of pepsin
76
How are di and tri peptides formed from polypeptides?
→ Action of pancreatic proteases
77
How are amino acids completely digested?
→ Di-peptidases in the brush border
78
How is pepsin secreted and how is it activated?
→ Secreted as a zymogen (pepsinogen) | → HCl converts it into pepsin
79
How are amino acids transported?
→ Na+ coupled carrier system → Separate carriers for different types of AA → Some di+tri peptides are transported using an inwardly directed H+ gradient
80
What forms the majority of dietary lipids?
→ Triglycerides
81
What do triglycerides include?
→ phospholipids → Cholesterol →Fat soluble vitamins (A,D,E,K)
82
What are dietary triglycerides broken down into?
→ Simpler units to facilitate absorption
83
Where are most TGs digested?
→ In the small intestine
84
What digests a small fraction of TGs?
→ Salivary lipase
85
What must TGs be dissolved in before they can be digested?
→ Aqueous phase
86
What is the digestion and absorption of lipids facilitated by?
→ Emulsification | → Micelle formation
87
How much fat does gastric lipase break down and what is the remainder digested by?
→ 10-30% of fats | → Pancreatic lipase
88
What does lipase action require?
→ Emulsification of TGs by bile salts
89
Where does pancreatic lipase bind?
→ To the surface of the small emulsion particles
90
What does the duodenum detect?
→ Lipids which must be emulsified
91
How do bile salts work?
→ They make the lipid molecules much smaller | →enzymes from the pancreas can break down the lipid and get to the core
92
How are lipids transported?
``` → Micelles fuse with the gut mucosa → Resynthesis of TGs occurs on the SER → Lipoprotein is added → Chylomicrons are formed → This is transported and ends up in the blood →Goes through lymphatic system ```
93
Where do digestive components of lipids end up?
→ Do not end up directly in the blood they go via the lymphatic system
94
Where do bile salts go?
→ Recycled by enterohepatic circulation
95
What disorders can lead to fat malabsorption?
→ Crohns disease → Liver disease → Gallstones → Pancreatitis
96
What is one of the causes of steatorrhea?
→ Having gall stones

Physiology 1 : GI (15 decks)

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