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HUBS192 > Gastro > Flashcards

Gastro Flashcards

1
Q

What is the name of the side of cells facing the lumen

A

Apical, mucosal or luminal

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2
Q

What is the name of the side of the cells facing the interstitium

A

Basolateral, serosal, interstitial

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3
Q

What is the transcellular pathway

A

Across apical and basal membranes, and cytosol

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4
Q

What is the paracellular pathway

A

Between cells, across tight junctions

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5
Q

What is exocrine secretion

A

Into the lumen

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6
Q

What is endocrine secretion

A

Into the bloodstream

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7
Q

What is the function of mucosal secretion in the GIT

A

Protection, lubrication, mechanical digestion

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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

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9
Q

What is the function of digestive enzyme secretions in the GIT

A

Chemical digestion of food, aids absorption

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10
Q

What are the three pairs of salivary glands

A

Submandibular, sublingual, parotid

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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

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12
Q

How is salivary secretion regulated

A

The autonomic nervous system (thought, smell, sight, presence of food) (PNS and SNS)

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13
Q

What does the parasympathetic nervous system result in the salivary secretion of

A

Copious quantities of fluid

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14
Q

What does the sympathetic nervous system result in the salivary secretion of

A

Small volumes of viscous fluid

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15
Q

What do goblet cells secrete in the stomach

A

Mucus (protection from abrasion) and bicarbonate (protection from stomach acid)

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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

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17
Q

What do chief cells secrete in the stomach

A

Pepsinogen (proteolytic enzyme which starts chemical digestion of proteins)

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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

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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+

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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)

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21
Q

How do Cl- ions get into parietal cells from the interstitium

A

Exchanged for HCO3-

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22
Q

How do Cl- ions get into the lumen to join with H+

A

Passively diffuse from cell

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23
Q

What are the three stages of gastric secretion

A

Cephalic, gastric, intestinal

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24
Q

What stimulates the cephalic phase

A

Smell, sight, taste of food

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25
Q

What is the detector for the cephalic phase

A

CNS

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26
Q

How is the signal sent from the CNS to the ENS in the cephalic phase

A

Vagus nerve (parasympathetic nervous system)

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27
Q

What are the effectors of the cephalic phase

A

ENS: myenteric (gastric motility and receptive relaxation) and submucosal plexus (secretion by G, parietal, chief and goblet cells)

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28
Q

What percentage of gastric secretion does the cephalic phase account for

A

20%

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29
Q

What is the stimulus of the gastric phase

A

Contents in the stomach

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30
Q

What are the detectors of the gastric phase

A

Mechanoreceptors (stretch), chemoreceptors (pH), G cells (peptides)

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31
Q

What coordinates the response of the gastric phase

A

ENS (myenteric: motility: 3 contractions/minute, submucosal: secretion) and G cells secretion of gastrin positively acting on parietal and chief cells

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32
Q

What percentage of gastric secretion does the gastric phase account for

A

70%

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33
Q

What stimulates the intestinal phase of gastric secretion

A

Arrival of acidic chyme, stretch, lipids, proteins, carbs

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34
Q

What are the detectors of the intestinal phase

A

Mechanoreceptors, chemoreceptors in the wall of the duodenum

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35
Q

What does a decrease in pH in the duodenum result in

A

Enteroendocrine cells secreting secretin

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36
Q

What coordinates the response of the intestinal phase

A

ENS and CNS (SNS) short and long reflex

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37
Q

What does the arrival of lipids, proteins and carbs in the duodenum result in

A

Secretion of CCK and GIP by enteroendocrine cells

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38
Q

What do G cells secrete and what does this stimulate

A

Gastrin, stimulates chief and parietal cells, and increased gastric motility (retropulsion)

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39
Q

What percentage of gastric secretion is the intestinal phase

A

10%

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40
Q

The arrival of what macronutrient especially stimulates the gastric phase

A

Protein

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41
Q

What is the function of the intestinal phase

A

Slow controlled release of food to small intestine

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42
Q

What does the decrease in pH result in EECs secreting (intestinal phase)

A

Secretin

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43
Q

What are the two types of exocrine pancreatic secretion

A

Pancreatic digestive enzymes and alkaline (HCO3-) fluid

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44
Q

What pancreatic cells secrete digestive enzymes

A

Acinar cells

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45
Q

What pancreatic cells secrete HCO3- fluid

A

Duct cells

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46
Q

What does the arrival of fatty acids and amino acids in the duodenum result in the secretion of from duodenal enteroendocrine cells

A

CCK and GIP

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47
Q

What does CCK stimulate from the pancreas

A

Digestive enzymes from pancreatic acinar cells

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48
Q

What are the digestive enzymes the pancreas secretes

A

Ribonuclease, deoxyribonuclease, lipase, colipase, pancreatic amylase, trypsinogen, chymotrypsinogen, procarboxypeptidase

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49
Q

How is trypsinogen converted to trypsin

A

Entereokinase(peptidase) bound to duodenal membrane

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50
Q

How are chymotrypsinogen and procarboxypeptidase converted to their active forms

A

By trypsin

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51
Q

What does secretin stimulate from the pancreas

A

Bicarbonate from duct cells (neutralise chyme, provide optimum pH for pancreatic enzymes)

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52
Q

What do hepatocytes secrete

A

Bile into bile canaliculi for chemical digestion of fat

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53
Q

What do bile duct cells secrete

A

Alkaline fluid which neutralises acid from chyme in the stomach

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54
Q

What excretory/waste products does bile contain

A

Bile pigments (bilirubin from breakdown of haem), excess cholesterol

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55
Q

What is the purpose of the gall bladder

A

Store and concentrate bile

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56
Q

What causes the initial release of bile from the gall bladder

A

CCK, via contraction of the gall bladder wall and relaxation of the hepatopancreatic sphincter

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57
Q

How much bile is reabsorbed in the ileum

A

95%

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58
Q

How is bile transported back to the liver

A

Enterohepatic circulation

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59
Q

How is the liver stimulated to produce more bile

A

Bile returning to liver via enterohepatic circulation, and mildly by secretin

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60
Q

What does the small intestine secrete

A

1.5L of fluid per day, mucus for lubrication and isosmotic fluid (NaCl and NaHCO3) to neutralise acid and dilute food to aid digestion

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61
Q

What does the large intestine secrete

A

Mucus for lubrication

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62
Q

Where is the submucosal plexus

A

Below the mucosa

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63
Q

Where is the myenteric plexus

A

Between layers of smooth muscle, controls smooth muscle

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64
Q

What effect does the parasympathetic nervous system have on the GIT

A

Increases overall activity by activating ENS

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65
Q

What effect does the sympathetic nervous system have on the GIT

A

Decreases overall activity by inhibiting ENS

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66
Q

What is the short reflex pathway

A

ENS only

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67
Q

What is the long reflex pathway

A

CNS, ENS back and forth

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68
Q

What is the function of the long and short reflex pathways

A

To integrate response of GIT to external stimuli, return the lumen of the GIT to its resting state

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69
Q

What is the short reflex stimulated by

A

Arrival of chyme (stretch, pH, osmolarity, protein/amino acids, lipids, carbohydrates) detected by chemo, osmo and mechanoreceptors

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70
Q

What is the long reflex pathway stimulated by

A

Change in contents of lumen, or sight/smell/taste of food, or emotional responses

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71
Q

What are tonic contractions

A

Sustained contractions for minutes to hours (think sphincters)

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72
Q

What are phasic contractions

A

Waves of contraction and relaxation, each wave lasting seconds. Controlled by pacemaker cells

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73
Q

How often does the stomach contract

A

3/min

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74
Q

How often does the duodenum contract

A

12/min

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75
Q

How often does the ileum contract

A

9/min

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76
Q

How does peristalsis work

A

Circular muscle behind bolus contracts, longitudinal muscle ahead contracts

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77
Q

What is relaxation of the stomach

A

Storage of food/chyme by increasing the volume without an increase in pressure

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78
Q

What is peristalsis

A

Movement of food along the GIT

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79
Q

What is segmentation

A

Mixing of chyme with secretions and exposure to absorptive surfaces

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80
Q

What are sphincters

A

Rings of muscle around the junction between parts of the GIT

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81
Q

What is the migrating motor complex (MMC)

A

Begins in stomach and travels to small intestine. Functions for house keeping, removing residual secretions, undigested material and promoting epithelial cell turnover

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82
Q

When does MMC occur

A

4 hours after a meal

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83
Q

What is the first phase of MMC

A

45-60 minutes of inactivity

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84
Q

What is the second phase of MMC

A

30 minutes intermittent uncoordinated activity

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85
Q

What is the third phase of MMC

A

5-15 minutes intense coordinated peristaltic contractions

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86
Q

How often does MMC repeat

A

1.5-2 hours until food is consumed

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87
Q

What is the reflex part of swallowing

A

Strength and frequency/rhythm

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88
Q

What prevents food going into the nasopharynx

A

Soft palate and uvula rise

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89
Q

What prevents food going into the trachea

A

Folding of the epiglottis

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90
Q

What are the motility patterns of the stomach

A

Relaxation, retropulsion (peristalsis and contraction of pyloric sphincter), contraction and relaxation of pyloric sphincter

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91
Q

What are the parts of the stomach

A

Fundus, body, pylorus (pyloric antrum), pyloric sphincter

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92
Q

Where does relaxation occur in the stomach

A

Fundus and body

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93
Q

What are the two types of relaxation

A

Receptive (part of swallowing, stomach about to receive food and relaxes), accommodation (food has arrived and stomach needs to find space for it)

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94
Q

What is retropulsion

A

Peristalsis and contraction of pyloric sphincter. Physical breakdown of food particles into smaller particles. Food particles grind against pyloric sphincter

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95
Q

What is gastric emptying

A

Controlled movement of fully mechanically digested chyme from stomach into duodenum

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96
Q

What factors affect the rate of gastric emptying

A

Size of meal (larger meal = more stretch = faster emptying), composition of meal (fluids faster than solids)

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97
Q

What are the motility patterns in the small intestine

A

Segmentation, peristalsis, contraction and relaxation of ileocecal sphincter

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98
Q

What are the motility patterns of the large intestine

A

Segmentation, relaxation, peristalsis (mass movement 1-2 times per day)

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99
Q

Where does segmentation occur in the large intestine

A

All throughout

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100
Q

Where does relaxation occur in the large intestine

A

Descending and sigmoid colon

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101
Q

What are the accessory organs of the digestive system

A

Teeth, tongue, salivary glands, liver, gall bladder, pancreas

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102
Q

What are the major organs of the digestive system

A

Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine

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103
Q

What type of epithelium is in the mouth, oral cavity and oesophagus

A

Stratified squamous (protection from abrasion)

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104
Q

What type of epithelium is in the stomach, small and large intestine

A

Simple columnar (secretion and absorption)

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105
Q

What type of epithelium is in the anus

A

Stratified squamous (protection from abrasion)

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106
Q

In what type of epithelium are goblet cells found

A

Columnar

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107
Q

Describe the structure of goblet cells (unicellular glands)

A

Columnar, goblet shaped, apical mucous granules, basal nucleus

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108
Q

What is the purpose of goblet cells in the GI tract

A

Lubrication and protection

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109
Q

What are the two types of multicellular glands

A

Simple (single duct) and compound (2 or more ducts)

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110
Q

What are the four layers of the gut tube

A

Mucosa, submucosa, muscularis (externa/proper), adventitia

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111
Q

What does the mucosa consist of

A

Epithelium, basement membrane, lamina propria (FCT), muscularis mucosae, plus sometimes glands

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112
Q

Where are blood vessels and lymphatics located in the mucosa

A

Lamina propria (FCT)

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113
Q

What regulates secretion in the GIT

A

Submucosal plexus

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114
Q

What does the muscularis consist of in the GIT

A

Smooth muscle, inner circular and outer longitudinal

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115
Q

What regulates motility in the GIT

A

Myenteric plexus (located between the layers of muscle)

116
Q

What does the adventitia consist of

A

FCT, holds everything together like glad wrap

117
Q

What are the openings of the throat called

A

Fauces

118
Q

What is the order of pharynxes down the throat

A

Oropharynx, laryngopharynx, esophagus

119
Q

What are the three salivary glands and where are they each located

A

Parotid (back of cheek), sublingual (under tongue), submandibular (under mandible)

120
Q

What do parotid glands secrete

A

Serous fluid with amylase

121
Q

What do sublingual glands secrete

A

Mucus

122
Q

What do submandibular glands secrete

A

A mixture of serous fluid with amylase, and mucus (M for mixed)

123
Q

What is a cluster of cells in a compound gland called

A

Acinus

124
Q

What do acinar cells in salivary glands secrete

A

Serous fluid and enzymes (amylase), and mucus

125
Q

Where are acinar cells located in compound glands

A

In the acini

126
Q

What do duct cells secrete in salivary glands

A

Bicarbonate for pH buffering

127
Q

Where are duct cells located in compound glands

A

At the top (duct)

128
Q

What structure ensures that food enters the oesophagus and not the trachea

A

Epiglottis

129
Q

Why is the esophagus mucosa and submucosa highly folded

A

Capacity to expand for passage of bolus

130
Q

How does the muscularis externa of the esophagus change as it moves down

A

First third skeletal, second third a mixture, third third smooth

131
Q

Which salivary glands can produce amylase

A

Parotid

132
Q

How is the oesophagus lubricated

A

Glands in submucosa with ducts to surface (no goblet cells as stratified squamous epithelium)

133
Q

What is the periotneum

A

Serous membrane that lines the abdomen

134
Q

What are the retroperitoneal organs

A

Pancreas, initial segment of small intestine, kidneys

135
Q

What does the parietal layer of the peritoneum line

A

Body wall

136
Q

What does the visceral layer of the peritoneum line

A

Organs

137
Q

What is a mesentery

A

Double layer of visceral peritoneum that connects organ to body wall

138
Q

What is an omenta

A

Double layer of visceral peritoneum that connects an organ to another organ

139
Q

What is the purpose of the peritoneum

A

Allow lubrication, enable movement without tangling organs

140
Q

What is the name of the structure through which the oesaphagus passes the diaphragm

A

Oesophageal hiatus

141
Q

What is the function of the lower oesophageal sphincter

A

Prevents reflux

142
Q

What are the regions of the stomach

A

Fundus, cardia, pylorus, body

143
Q

What is the extra layer of muscle in the stomach

A

Innermost layer of oblique muscle (plus inner circular and outer longitudinal)

144
Q

What does the lesser omentum attach

A

Lesser curvature of stomach to liver

145
Q

What does the greater omentum attach

A

Greater curvature of stomach to transverse colon

146
Q

What are the temporary folds that enable expansion of the stomach

A

Rugae (core of submucosa)

147
Q

What type of epithelium is in the stomach

A

Columnar

148
Q

What are gastric glands

A

In folding of columnar epithelium to increase area for secretion. Glands do not flatten

149
Q

What is a gastric pit

A

Top of gastric gland comprised of mucous epithelial cells

150
Q

What is a notable organelle in chief cells

A

Abundant rough endoplasmic reticulum to make proteins (pepsinogen), basal nucleus

151
Q

What are zymogen granules in chief cells

A

Apical secretory vesicles filled with inactive enzymes (pepsinogen)

152
Q

What is a notable organelle in parietal cells

A

Abundant mitochondria as they pump H+ ions against their gradient

153
Q

Describe the structure of parietal cells

A

Central nucleus, very folded (microvilli) membrane to increase SA for pumping H+ ions

154
Q

What are canaliculi

A

Channels between microvilli in parietal cells

155
Q

What hormones are secreted by the stomach

A

Gastrin and ghrelin

156
Q

How is the stomach controlled neurally

A

ENS (local reflexes), CNS modulating ENS function (long neural reflex)

157
Q

What enables controlled release of chyme into the small intestine

A

Pyloric sphincter

158
Q

Where is mucous for the small intestine provided from

A

Glands in the submucosa of the duodenum

159
Q

What does the pancreas provide to the small intestine

A

Enzymes and bicarbonate

160
Q

Where does the bile duct enter the duodenum

A

Duodenal papilla

161
Q

What is the exocrine function of the pancreas

A

Acinar cells secrete digestive enzymes, duct cells secrete bicarbonate

162
Q

What is the structure of pancreatic acinar cells

A

Apical zymogen granules, basal nucleus, abundant rough ER

163
Q

Where does the bile duct meet the pancreatic duct

A

The entrance to the hepatopancreatic ampulla

164
Q

What type of epithelia is in the small intestine

A

Simple columnar: goblet cells secrete mucus to neutralise chyme

165
Q

Where are mucous secreting glands located in the small intestine

A

Submucosa

166
Q

What is the order of the parts of the small intestine

A

Duodenum, jejunum, ileum

167
Q

How is the duodenum separated from the rest of the small intestine

A

Retroperitoneal

168
Q

What is the order of sizes of the parts of the small intestine

A

Duodenum (shortest), jejunum, ileum

169
Q

What is the purpose of the duodenum

A

Receive chyme, enzymes and bicarbonate from pancreas, bile from liver

170
Q

What is the purpose of the jejunum and ileum

A

Digestion and absorption

171
Q

What prevents tangling of the small intestine

A

Mesentery

172
Q

Describe mesentery

A

Made of peritoneum so slippery, contains blood vessels, nerves, lymphatics, fat

173
Q

Where do small intestine mesenteric veins drain to

A

Hepatic portal vein

174
Q

Where do lymph lacteals drain into

A

Cisterna chyli, thoracic duct, left subclavian vein

175
Q

What are the two mesenteric veins

A

Superior and inferior

176
Q

What is a mesentery (me)

A

Organ to body wall

177
Q

What is an omenta (O)

A

Organ to organ

178
Q

How is the huge surface area of the small intestine achieved

A

Length, folding of intestinal wall (plicae circulares), extensions of mucosa (villi), extensions of epithelial cells (microvilli)

179
Q

Describe plicae circulares

A

Permanent large folds of small intestine. Core of submucosa with overlying mucosa

180
Q

Describe villi

A

Found on surface of plicae circulares, part of mucosa, core of lamina propria, muscularis mucosae enables movement

181
Q

What is the purpose of movement of the villi

A

Small movements to enable more contact with nutrients of chyme

182
Q

What does each villi contain

A

Lymph lacteal (receives products of fat digestion), and a capillary network (receive products of protein and carbohydrate digestion)

183
Q

What are the absorptive cells of the small intestine with microvilli on their apical surface

A

Enterocytes

184
Q

What attaches enzymes to the brush border of enterocytes for contact digestion

A

Glycocalyx (also holds epithelial cells in place)

185
Q

What is the glycocalyx

A

Glycoproteins (branched filaments)

186
Q

Where are tight junctions between cells located

A

As high up as possible

187
Q

What are paneth cells of the small intestine

A

Secrete granules of antibacterial enzymes

188
Q

Where are paneth cells located in intestinal crypts

A

The bottom

189
Q

What are microvilli made of

A

Mucosa

190
Q

What is the first part of the large intestine called

A

Cecum

191
Q

What regulates the passage of material from the small to large intestine

A

Ileocecal valve

192
Q

What are the three parts of the large intestine

A

Cecum, colon, rectum

193
Q

What is the colon divided into

A

Ascending, transverse, descending, sigmoid

194
Q

What are the bobbles of the large intestine called

A

Haustra

195
Q

Which parts of the colon are retroperitoneal and which are intraperitoneal

A

Ascending and descending retroperitoneal, transverse and sigmoid intraperitoneal

196
Q

Where is the appendix located

A

At the cecum, where the teniae coli come together

197
Q

What is the purpose of the appendix

A

Reserve of large intestine bacteria

198
Q

What are the bands of longitudinal muscle on the large intestine called

A

Teniae coli

199
Q

What are the sacs of fat on the large intestine called

A

Omental appendices

200
Q

What are the modifications of the large intestine muscularis

A

Outer longitudinal is arranged into thick bands for stronger contraction

201
Q

Why does the large intestine not have vili

A

Large surface area no longer needed

202
Q

Why does the mucosa of the large intestine invaginate

A

To form intestinal glands

203
Q

What are the two cell types in the large intestine

A

Absorptive (water and salt) and goblet (mucus for protection and lubrication)

204
Q

What is the purpose of the rectum

A

Store faeces

205
Q

Which anal sphincter is voluntary

A

External

206
Q

What do the anal columns mark

A

Change of epithelium from simple columnar to stratified squamous

207
Q

How is the presence of faeces detected

A

Stretch receptors in rectum, relaxation of internal anal sphincter

208
Q

What is the long reflex pathway in defecation

A

Spinal reflex coordinated by sacral parasympathetic motor neurons. Mass movement of faeces toward rectum from descending and sigmoid colon

209
Q

What is the short reflex pathway in defecation

A

Series of peristaltic contractions in rectum that move faeces toward anus. Mediated by myenteric plexus in sigmoid colon and rectum

210
Q

What are the functions of the liver

A

Metabolic processes, detoxification of blood, bile production

211
Q

Where is the liver located

A

Superior right quadrant of abdominopelvic cavity

212
Q

What is the function of the gall bladder

A

Stores and concentrates bile

213
Q

How does the gall bladder connect to the liver

A

Cystic duct attached to bile duct

214
Q

What ducts come out of the liver

A

Left and right hepatic (become common hepatic)

215
Q

How much cardiac output does the liver receive

A

25%

216
Q

1/3 of blood supply to the liver comes from

A

Hepatic artery

217
Q

2/3 of blood supply to the liver comes from

A

Hepatic portal vein

218
Q

Where does the blood in the hepatic portal vein come from

A

Nutrient rich, deoxygenated blood from small intestine, to be processed by hepatocytes

219
Q

What structure do the hepatic portal vein, hepatic artery and bile duct travel in

A

Lesser omentum

220
Q

What are liver lobules

A

Hexagonal functional units made of rows of hepatocytes

221
Q

What do hepatocytes do

A

Produce bile

222
Q

What are between rows of cells in liver lobules

A

Liver sinusoids

223
Q

Where are bile canaliculi in liver lobules (small capillaries off bile duct)

A

Between cells

224
Q

What is a hepatic portal triad

A

Branch of hepatic artery, branch of hepatic portal vein, a bile duct

225
Q

How do bile and blood travel in liver lobules

A

Blood flows from corners of hexagon to central vein, bile travels from hepatocytes to bile duct (opposite directions)

226
Q

Where do central veins of liver lobules drain into

A

Hepatic vein, then into inferior vena cava

227
Q

Where does the bile duct join the pancreatic duct

A

Hepatopancreatic ampulla

228
Q

What are the two types of starch

A

Amylose (coil) and amylopectin (branched)

229
Q

How many essential amino acids cannot be made by the body

A

8

230
Q

Which lipids are essential to the body

A

Omega 3 and 6, and fat soluble vitamins A, D, E and K

231
Q

How long are short chain fatty acids

A

<6 carbons

232
Q

How long are medium chain fatty acids

A

6-12 carbons

233
Q

How long are long chain fatty acids

A

13-24 carbons

234
Q

How must the GIT absorb carbohydrates

A

As monosaccharides

235
Q

How must the GIT absorb proteins

A

As amino acids

236
Q

How must the GIT absorb lipids

A

As free fatty acids and monoglycerides

237
Q

Where are digestive enzymes located

A

Extracellularly

238
Q

Where are disaccharidases located

A

Bound to brush border in small intestine

239
Q

What are the three disaccharidases we know

A

Sucrase, lactase, maltase

240
Q

What is sucrose

A

Glucose + fructose

241
Q

What are the three pancreatic proteases

A

Trypsin, chymotrypsin and carboxypeptidase

242
Q

Do fats undergo contact digestion

A

No, only luminal digestion in the stomach and small intestine

243
Q

What enzymes digest TAGs in the stomach

A

Lingual and gastric lipase

244
Q

What enzyme digests TAGs in the small intestine

A

Pancreatic lipase

245
Q

What are the four stages of lipid digestion

A

Emulsification (mixing), stabilisation, digestion (hydrolysis), formation of micelles (bile salts)

246
Q

What is emulsification

A

Process by which large lipid droplets are broken down into smaller, stabilised droplets increasing the surface area for digestion

247
Q

What is the purpose of motility in lipid digestion

A

Retropulsion and segmentation breaks up large lipid droplets into smaller emulsification droplets to increase surface area for digestion

248
Q

How is stabilisation of emulsion droplets different between the stomach and small intestine

A

Stomach: simple emulsion (other molecules)
Small intestine: more complex emulsion (bile salts)

249
Q

What is the purpose of stabilisation of emulsion droplets

A

Form smaller droplets (increase surface area), prevent them from reforming into larger droplets, enables them to travel in an aqueous environment

250
Q

What is the most important property of bile salts

A

Amphipathic

251
Q

How are TAGs converted to 2 FFAs and 1 monoglyceride

A

By lipase and colipase

252
Q

What does colipase do

A

Anchors lipase to surface of droplet

253
Q

Where does hydrolysis of fats occur

A

In the small intestine at the surface of emulsion droplets

254
Q

What are micelles

A

A way to keep monoglycerides and long chain fatty acids in solution. Consist of 20-30 molecules (bile salts, fatty acids, monoglycerides)

255
Q

What is absorption

A

Movement of solutes and water from the GIT lumen across the epithelium, into the interstitial fluid and then into the blood or lymph

256
Q

What are the two pathways for absorption

A

Paracellular and transcellular

257
Q

Where is the main site of absorption

A

Small intestine (mouth, esophagus and stomach minimal, large intestine some)

258
Q

What enables the small intestine to absorb most effectively (compared to other structures)

A

Leaky epithelium

259
Q

What type of absorption does the large intestine do (9% of water and sodium)

A

Regulated/fine tuning absorption in tight epithelium

260
Q

What factors affect absorption

A

Reduction in nutrient size by chemical digestion, motility, transport across GIT epithelium, surface area available for absorption, removal from interstitial fluid

261
Q

Why must chyme travel at the correct rate through the GIT

A

To allow mechanical digestion, chemical digestion, absorption

262
Q

What is the paracellular pathway

A

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
Q

What is the transcellular pathway

A

Through epithelial cells, particles must cross two membranes. Lipid soluble particles can diffuse, water soluble require a channel or transporter membrane protein

264
Q

How is build up of particles in the interstitial fluid prevented after absorption

A

High blood flow to intestines, blood vessels and lacteals close to the basolateral side of epithelial cells

265
Q

How is glucose absorbed by the paracellular pathway

A

Glucose molecules diffuse down their concentration gradient across leaky tight junctions (passive)

266
Q

How is glucose absorbed by the transcellular pathway (active)

A

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
Q

How are amino acids absorbed by the paracellular pathway (di/tripeptides cannot be absorbed by this pathway)

A

Diffuse down their concentration gradient across leaky tight junctions

268
Q

How are amino acids absorbed by the transcellular pathway (active)

A

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
Q

How are di and tripeptides absorbed by the transcellular pathway (active)

A

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
Q

How are free fatty acids and monoglycerides absorbed

A

Simple diffusion from micelle into cell (micelle not absorbed but able to get very close to brush border)

271
Q

Where are bile salts absorbed

A

Ileum

272
Q

What happens to FFAs and MAGs intracellularly

A

Transported to ER, resynthesised to TAGs, packaged into chylomicrons

273
Q

How do TAGs leave the cell

A

Exocytosed in chylomicrons, enter lymph via lacteals of villi

274
Q

What is the driving force for water absorption (cannot occur actively)

A

Osmotic gradient generated by the absorption of nutrients and ions

275
Q

Where does the bulk re/absorption of water occur

A

Small intestine (most paracellular, some transcellular via aquaporins)

276
Q

Where does fine tuning re/absorption of water occur

A

Large intestine (tight epithelium, all absorption via transcellular pathway- aquaporins)

277
Q

How does passive absorption of sodium occur

A

Via the paracellular pathway, down concentration gradient

278
Q

How does active absorption of sodium occur

A

Secondary active transport coupled with glucose and amino acids (apical membrane), then Na+/K+ ATPase (basolateral membrane)

279
Q

Where does passive and active absorption of sodium occur

A

Small intestine: passive and active (trans and para)
Large intestine: active (trans)

280
Q

How does fat passively move into cells (apical membrane)

A

Diffusion: micelles come close to surface

281
Q

How does fat passively move out of cells (basolateral membrane)

A

Packaged into chylomicrons, diffuse out

282
Q

How are water soluble vitamins absorbed (apical membrane)

A

Secondary active transport via sodium cotransporter (e.g sodium-vit C cotransporter)

283
Q

How do water soluble vitamins leave the cell (basolateral membrane)

A

Transporter

284
Q

Where is vitamin B12 absorbed

A

Ileum

285
Q

What must happen in order for vitamin B12 to be absorbed

A

Bind to intrinsic factor (made by parietal cells in the stomach), then bind to receptor on epithelial cells in the ileum

286
Q

How does vitamin B12 bound to intrinsic factor and an epithelial cell receptor enter and exit the cell

A

Enters the cell by endocytosis, exits and travels in blood bound to transcobalamin

287
Q

What does CCK result in

A

Inhibits chief, G and parietal cells, stimulates digestive enzymes from pancreatic acinar cells, contraction of gall bladder and relaxation of hepatopancreatic sphincter

HUBS192 (6 decks)

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