1
Q
Lumen
A
Cavity where food travels from mouth to anus and secretions from various organs drain
2
Q
Blender
A
Stomach, stays for at least 4 hours
3
Q
Reaction vessel
A
First part of small intestine, enzymes from pancreas neutralize acid, detergent is bile from liver
4
Q
Residue combuster
A
Where feces are formed
5
Q
Mouth
A
Mechanical shearing of ingested food, grinding to reduce size of food particles, saliva added
6
Q
Saliva
A
Moistens to taste, signifiant amount of enzymes, lubricates food bolus to allow swallowing, begins digestion of carbohydrates and lipids
7
Q
Esophagus
A
Transfers food to stomach by peristaltic waves, moves actively (without gravity), flexible tube with sphincter at each end
8
Q
Lower esophageal sphincter
A
Opens as soon as food is swallowed, and opens until food enters your stomach
Begins stomach
Tonically contracted
9
Q
Stomach
A
Begins with lower esophageal sphincter, 3 sections
1. Fundus
2. Body
3. Antrum
Exits antrum to small intestine through pyloric sphincter
Can also be divided into orad and caudad region
Stores food in upper stomach
Specialized cells secrete mucous, enzyme precursors, hydrochloric acid and hormones
Grinding occurs in lower stomach
10
Q
Chyme
A
Enters small intestine from stomach, pretty liquid: delivered to duodenum
11
Q
Small intestine
A
4-6 meters long 1. Duodenum 2. Jejunum 3. Ileum Absorption of nutrients occurs mostly in jejunum and ileum
12
Q
Duodenum
A
Very short
Secretions from pancreas and liver via pancreatic and common bile ducts
13
Q
Jejunum
A
40% of small gut
Larger diameter, thicker wall, more prominent circular folds, less fatty mesentery
14
Q
Mesentery
A
Connects small intestine to wall and important in blood circulation
15
Q
Ileum
A
60% of small gut
Empties into large intestine
Hard to say border between jejunum and ileum
Thinner than jejunum
16
Q
Large intestine (colon)
A
Re-absorbs water used in digestion process, starts at cecum and ends at anus
17
Q
Appendix
A
No function in humans
18
Q
Villi
A
Fingerlike extensions that face lumen of tract, increase surface area of small intestine
Microvilli project outwards to form brush border
19
Q
Crypt
A
Colon
Structurally and functionally different from villi
20
Q
Three major salivary glands
A
- Parotid gland (large, behind ear)
- Submandibular gland
- Sublingual gland
21
Q
Salivary glands
A
Units are called acini
Different types of cells producing enzymes and secretions
Produce large amount of saliva
Volume and amount of saliva under control of autonomic nervous system
22
Q
Pancreas
A
Exocrine and endocrine functions
23
Q
Exocrine functions of pancreas
A
Secretion of digestive enzymes and bicarbonate ions (HCO3) to the duodenum
Digestive enzymes break down nutrients
HCO3 neutralizes chyme
24
Q
Endocrine functions of pancreas
A
Insulin and glucagon secretion
25
Liver
Storing and releasing nutrients that have been absorbed by the digestive tract
Produces and releases bile (fat digestion)
26
Gallbladder
Bile storage, concentrates, and pH changes, gets pushed down common bile duct to duodenum
Bile assists in fat digestion
27
Mucosa layer
Epithelium and lamina propria
| Followed by submucosa
28
Submucosa
Contains many cells and glands that excrete into lumen
29
Muscular externa
Circular muscle contraction induces decrease in diameter of lumen
Longitudinal muscle contraction induces shortening of a segment of GI tract
30
Muscular muconsae
Innermost muscle layer that allows mucosa to fold and form ridges
31
Myenteric plexus
Outer nerve layer
Part of enteric nervous system
Between two muscle layers
Mainly controls motility of GI tract
32
Submucosal plexus
Inner nerve layer
Part of enteric nervous system
Located under mucosa
Control local secretion, absorption and submucosal muscle contraction
Receives sensory information from sensory neutrons in the GI tract
33
Epithelial cells in gut wall
Specialized in different parts of the GI tract for secretion or absorption, replaces al the time (every 5 days for total)
Includes secretory cells, endocrine cells and absorptive epithelial cells
Virtually all nutrients enter the body across the epithelium covering small intestinal villi
34
Central lacteal
Centre of villi, absorbs fat, lymphatic vessel, drains from intestine and rapidly flow into blood via thoracic duct
35
Splanchnic circulation
Blood supply to the intestine carries away absorbed water-soluble nutrients, flows to liver first via portal vein to be detoxified by hepatocytes
36
External anal sphincter
Under central control, skeletal muscle
| there are two anal sphincters, internal anal sphincter is smooth muscle
37
Upper esophageal sphincter
Under central control, skeletal muscle
38
GI sphincters
Mainly smooth muscle, mainly positive resting pressure and regulate forwards and reverse movement
39
Enteric nervous system
Intrinsic innervation, mediated by nerve plexus in gut wall
Full length of GI system
Can and does function completely autonomously
Normal digestive function requires communicate between the intrinsic and CNS
100 million neurons (equal to spinal cord)
40
Extrinsic innervation
Autonomic nervous system, both parasympathetic and sympathetic systems
41
Sympathetic regulation
Inhibitory
Mainly postganglionic, connects directly to myenteric plexus (NE and rarely epinephrine), connects to submucosal for secretary processes, connects directly to epithelium
Pregangiolinc fibres arise from spinal cord (T5-L2) and terminate in pre vertebral ganglia (Ach)
Constant innervation
42
Sensory neurons
Monitor distension and inform enteric nervous system and brain
43
Stimulation of myenteric plexus
Increases tonic contraction of gut wall
Increased intensity and rate of contractions
Increased velocity of excretory waves along the gut causing more rapid peristaltic waves
44
Autonomic nervous system
Integrates activity of the enteric nervous system with the rest of the body
Do not directly innervate GI structure, but interact with ENS
45
Parasympathetic regulation
Excitatory
Mainly preganglionic and cholinergic, nerve fibres terminate on ganglion cells in enteric nerve plexuses and act on nicotinic ACH receptors
No direct innervation of the effector cells in gut wall
Vagal nerve fibres to basically all areas of the gut
Significant enervation in rectal column and anus via pelvic nerves
46
Afferent sensory nerve fibers
Strong afferent presence
Cell bodies either in ENS or dorsal root of ganglia in the spinal cord
Stimulated by irritation of the gut mucosa, distention of the gut, presence of chemical substances in the gut - sent to CNS
Activation can cause excitation or inhibition
47
Gastrocolic reflex
Reflexes from gut to pre vertebral sympathetic ganglia and back to GI tract
If you start eating when colon is full: signals from stomach to evacuate colon
48
Enterogastic reflex
Reflexes from gut to pre vertebral sympathetic ganglia and back to GI tract
Tells stomach that small intestine is still full, signals from colon and small intestine to inhibit stomach motility and secretion
49
Colonoileal reflex
Reflexes from gut to pre vertebral sympathetic ganglia and back to GI tract
Signals from colon to inhibit stomach motility and secretion
50
Vagovagal reflex
Reflexes from gut to spinal cord or brain stem and back to GI tract
From stomach and duodenum to the brain stem and back to control gastric motor and secretory activity
51
Pain reflex
Reflexes from gut to spinal cord or brain stem and back to GI tract
Cause general inhibition of the gut
52
Defecation reflexes
Travel from colon and rectum to spinal cord and back to produce powerful colonic, rectal and abdominal contractions required for defecation
53
Gastrointestinal peptides
Regulate the functions of the GI tract
Contraction and relaxation of smooth muscle and the sphincters
Secretion for enzymes for digestion (peptides acting on pancreas)
Trophic (growth) effect on tissues
Can regulate secretion of other GI peptides
54
Somatostatin
Inhibits secretion of all GI hormones
55
Acetylcholine
Neurocrine
| Contraction of smooth muscle, relaxation of sphincters, increased salivary, gastric and pancreatic secretions
56
Norepinephrine
Neurocrine
Limited function under normal circumstances, relaxation of smooth muscle, contraction of sphincters, increased saliva secretion
57
Vasoactive intestinal peptide
Neurocrine
| Inhibits smooth muscle contraction, stimulates secretion and vasodilation
58
Serotonin (5-HT)
Diverse motor and sensory function in GI tract, 90% serotonin in GI tract
59
Nitric oxide
Relaxes smooth muscle activity
60
Gastrin
Produces by G-cells in the antrum, released in blood circulation to act on parietal cells to release HCl in the stomach
Also has affect on mucosal growth
61
Cholecystokinin
CCK
Secreted by I-cells in the duodenum and jejunum, homologous to gastrin
Tries to inhibit gastric emptying
Stimulates gallbladder contraction and relaxation of sphincter of Oddi
62
Secretin
Secreted by S-cells in duodenum
Homologous with glucagon, stimuli for release is gastric juice entering into small intestine, leads to neutralization of acidity in the small intestine
63
Glucose-Dependent Insulinotropic Peptide
Secreted by K-cells in the duodenum and jejunum
Homologous to secretin and glucagon
Stimulates insulin release and gastric acid secretion (unlikely during normal physiological conditions)
64
Motilin
Biology not fully understood, in humans: 22 amino acid linear peptide
Released cyclically from gut in fasting state
Responsible for stimulating a specific pattern of GI motility: migrating motor complex
65
Ghrelin
Mainly released from stomach and pancreas, a little along complete gut
Stimulates vagal afferents that triggers the release of signals in the solitary nucleus and hypothalamus that promote food intake (including orexin and neuropeptide Y)
Release normally suppressed by leptin
66
Leptin
Released from adipose tissue
67
Somatostatin
Secreted by D-cells in gastric mucosa
Acidity of astral region stimulates somatostatin release
Also released by neutrons in the enteric nervous system
Inhibits release of gastrin and histamine, inhibits gastric acid secretion from parietal cells
68
Histamine
Secreted from enterochromaffin cells in the stomach, acts on H2 receptors on parietal cells
With gastrin and Ach, stimulates acid secretion by the gastric parietal cells
Secreted from mucosal mast cells and has a role as an immune mediator
69
Peristalsis
Food moves forward along tract
Ring of contraction on oral side of bolus that moves towards the anus, as ring moves, muscle in front of food bolus relaxes
Completely enteric
Usual stimulus if distention of the gut
Chemical irritation of the gut and strong parasympathetic stimulation can also induce peristalsis
70
Mixing movements
Allow digestive enzymes to come in contact with chyme and for chyme to come in contact with intestinal walls
Segments of contraction
Similar to peristalsis but no net movement
71
Single-unit types smooth muscle
Depolarization of area spreads via gap junctions to result in well coordinated contraction: ring of smooth muscle
72
Slow waves
Cyclic variations in GI smooth muscle resting potential
Typical in each part of the gut (3/min stomach, 12/min in duodenum)
Depolarizing phase caused by calcium influx and depolarization by potassium efflux
Maximal frequency that muscle contractions can happen
73
Threshold for contraction
Slow waves above this threshold cause contraction
74
Electrical threshold
Cause action potentials, contractions become bigger as action potentials increase
75
Slow wave amplitude
Increases with parasympathetic stimulation
| Decreases with sympathetic stimulation
76
Baseline tension
GI muscle does not relax completely, tonically contracted
77
Interstitial cells
Pacemaker activity and decide when contractions occur
Transfer signals from enteric motor nerves to muscle cells
Set smooth muscle membrane potential
Responsible for generating slow waves, peristalsis and segmentation
78
Mastication
Chewing
Both involuntary and voluntary reflexes are involved
Food in mouth activates mechanoreceptors which coordinate reflex activity
Breaks down and lubricates food, mixes it with salivary enzymes
Important in breaking down cellulose membrane of fruit and vegetables
79
Bolus
Moist, chopped up food
80
Oral phase (swallowing)
Voluntary
| Tip of tongue pushes food towards pharynx
81
Pharyngeal phase (swallowing)
Involuntary control
Series of protective reflexes initiated by the stimulation of afferent fibres in the pharynx and organized in the swallowing centre
Close off nasal, oral and laryngeal cavities
Respiration in inhibited
82
Swallowing centre
Medulla and lower pons
83
Esophageal phase (swallowing)
Food enters esophagus and upper sphincter closes, primary peristaltic contract moves and pushes food bolus down, lower esophageal sphincter relaxes and food bolus enters the stomach
Second peristaltic contraction clears esophagus of remaining food
84
Dysphagia
Difficulty in swallowing
Can result in abnormalities in any components of swallowing reflex or anatomical structures
Common, especially in elderly (stroke, ALS, Parkinsons)
Risk of malnutrition, aspiration, choking
85
Achalasia
Failure to relax
LES does not relax and open
Problem with myenteric ganglion nerves
86
GERD
Gastrointestinal reflux disease
Acid gastric contents reflux to the distal esophagus
Very common, severity varies
May result in inflammation, ulcers
87
Orad region
Stomach
| Main area of reception and storage
88
Caudad region
Main region of propulsion in stomach
89
Stomach muscles
Longitudinal, middle circular, inner oblique
| Body and fundus are thin walled, antrum is thicker with more muscle
90
Pyloric sphincter
End of antrum entering into duodenum, prevents bolus from entering duodenum, causes mixing of food
91
Gastric contractions
Allow stomach to grind, crush and mix ingested food
| Lower part of stomach contracts to propel liquid chyme into duodenum in spurts
92
Retropulsion
Lower and body and antrum contracts and propels food bolus to fundus
93
Gastric emptying
Takes about three hours, liquids empty more rapidly than solids (less than 1 mm diameter), isotonic liquids empty faster, nature of contents affect emptying
94
Migrating Myoelectric Complex
Empties non digestible material during inter digestive period
95
Gastoparesis
Disorder where gastric emptying is delayed without evidence of obstruction
Symptoms: early satiety, nausea, vomiting, bloating and upper abdominal discomfort
Causes: system disease affecting neuromuscular function, education, injury to vagus nerve
96
Pyloric stenosis
Congenital condition usually present infancy
Pyloric muscle thickens and pylorus fails to relax after a meal, leading to regurgitation and vomiting
Infants develop malnutrition and dehydration
Cured by surgical myotomey: longitudinal incision to muscle surrounding pyloric region
97
Segmented contractions
Small intestine muscle contraction
Squirt luminal contents bidirectionally
Contractions increase resistance to flow, and there are more contractions upstream causing overall aborad movement
98
Aborad
Away from the stomach
99
Peristaltic contractions
Entry of chyme into duodenum causes peristaltic wave: travels only a few centimetres before dying out
Intestinal contents are slowly mixed and chyme is steadily moved
100
Ileocecal valve
Prevents back flow from colon to ileum
Ileocecal sphincter is normally constricted, but strong peristaltic activity immediately after a meal relaxes the sphincter
101
Colon storage
Mainly in distal colon
102
Sigmoidscopy
Colonoscopy to sigmoid colon
103
Hautrations
Circular and longitudinal muscles of colon contract simultaneously to form haustra, move back and forth to move contents
104
Mass movements
1-3 times a day, move colonic contents over long distances
| Final mass movement propels faces to rectum where they are stored until defecation
105
Defecation
Involved both reflexes and voluntary actions
Upper portion of rectum relaxes to permit entry of faces
Rectal distention relaxes the internal anal sphincter
External sphincter is contracted until it is convenient to defecate (then voluntary)
Smooth muscle of rectum contracts and faces are forced out of body
106
Hirschsprung's Disease
Congenital megacolon, developmental abnormality where the ENS fails to develop
Segment of internal anal sphincter and upwards remains permanently contracted causing obstruction
Symptoms can be completely alleviated by surgical excision of diseased segment
107
Irritable Bowel Syndrome
Motility disorder caused by visceral hypersensitivity, very common (10-30% of people)
Causes cramping, abdominal pain, bloating, gas, diarrhea, constipation
Partially due to dysmotility (consistent motor abnormalities have not been seen)
Patients with diarrhea have shortened transit times though intestines and increase in propulsive contractions in the colon
Patients with constipation-predominant disorders have slowed transit of intestinal contents
108
Vomiting
Always centrally controlled, many triggers
Usually good to vomit
1. Hypersalivation
2. Fundus becomes flaccid
3. Sold palate rises, glottis closes, larynx moves forward, esophagus dilates, LES relaxes and moves upward
4. Diaphragm contracts, abdominal muscle contracts, gastric contents forced upwards
109
Vomit control centre
Vomiting centre and nuclease tracts solitaires
110
Parotid glands
Big, by ear
| Serous glands
111
Submandibular glands
Close to jaw bone
Mixed mucous and serous glands
Serous acinar cells secrete salivary amylase
Mucous cells secrete mucins
Intercalated duct drains into salivary duct which has striated and excretory ducts
112
Sublingual glands
Under bottom teeth
| Mixed mucous and serous glands
113
Buccal glands
Smaller glands present in oral cavity, only secrete mucous
114
Serous acinar cells
Secrete salivary amylase
115
Two state model of saliva secretion
Primary secretion
| Secondary secretion
116
Primary secretion
Nearly isotonic, levels of Na, K, Cl and HCO3 are similar to plasma
117
Secondary secretion
Ductal cells reabsorb Na and Cl ions from the saliva and secrete K and HCO3 into the saliva
Water does not follow ions but remains so saliva becomes more watery
118
Saliva composition
Function of flow rate, the faster the flow rate the less time there is for ductal cells to act: saliva is closer to isotonic
~1L/day, pH 6-7
119
Parasympathetic regulation of saliva secretion
Autonomic nervous system
Messages from tongue and other parts of oral cavity, stimulated by taste and pressure
Otic ganglion stimulation increases Ach and stimulates parotid gland
Submandibular ganglion stimulation increases Ach and stimulates submandibular gland
120
Sympathetic regulation of saliva
Changes composition of saliva but no affect on volume
121
Xerostomia
Dry mouth
Several different conditions cause decreases saliva secretion
Sjorgrens syndrome, side effects of many drugs, secondary to head and neck radiation
Decreased pH in mouth leads to tooth decays and esophageal erosions
Difficulty swallowing
122
Gastric secretions
Mixture of secretions of the surface epithelial cells, mucous neck cells and gastric glands
1.5-2L/day
Largest volume is contributed by parietal cells
pH 1-3.5
123
Mucous cells
All parts of gastric mucosa
| Secrete mucus that coats and lubricates the gastric surface and protects epithelium
124
Parietal cells
Body of stomach
| Secrete HCl and intrinsic factor
125
Chief (peptic) cells
```
Body of stomach
Secrete pepsinogen (pepsin precursor)
```
126
G-cells
Antrum of stomach
| Secrete gastrin hormone
127
Gastric oxyntic gland
Located on body of stomach
| Contains: epithelial cells, mucous neck cells, parietal cells, and chief cells
128
Gastric acid secretion
1. H/K pumps H into lumen
2. Cl ions flow via Cl ion channels into lumen
3. HCO3 is absorbed into the blood stream in exchange for Cl
129
Pepsinogen
Inactive precursor of pepsin
Secreted by chief cells
Vagovagal reflex and gastrin release stimulates acid and pepsinogen release
130
Intrinsic factor
Secreted by gastric parietal cells
Essential for absorption of vitamin B12 in the ileum
Secretion is only gastric function that is essential for human life
131
Vitamin B12
Cobalamin
Involved in synthesis of all cells, affects DNA synthesis
Couples with R protein in small intestine, and breaks down from component R in alkaline conditions and binds to intrinsic factor
Absorbed when complex interacts with receptors in final parts of small intestine
132
Pernicious anemia
Red blood cells fail to mature because of problem in intrinsic factor production and B12 absorption
133
Regulating HCl secretion
Vagus nerves stimulate G-cells to release gastrin and parietal cells to release HCl
Distension on the antrum stimulates G cells to release gastrin
134
Ulcer disease
Breaks in the stomach or in the duodenal mucosa
Corrosive action of pepsin and HCl on supper gastrointestinal tract mucosa
Caused be excess secretion of acid and pepsin by mucosa or diminished protective abilities of gastric mucosal barrier: Helicobacter pylori, non steroidal anti-inflammatories, alcohol, smoking, gastrinoma
135
Gastric ulcers
Breaks in the stomach mucosa
136
Duodenal ulcers
Breaks in the duodenal mucosa
137
Helicobacter pylori
Bacteria that colonizes in the gut
| Main cause for ulcers
138
Gastrinoma
Zollinger-Ellison Syndrome
| Rare tumour that releases gastrin hormone leading to excess HCl secretion
139
Ductal cells
In pancreas
Secrete bicarbonate
Stimulated by secretin, CCK and Ach
140
Aqueous component of pancreatic secretion
High bicarbonate concentration that neutralizes chyme in duodenum
pH ~8, isotonic with plasm
About 1L/day
141
Enzyme components of pancreatic secretion
Proteases - proteins
Amylases - carbohydrates
Lipases - lipids
142
Anicar cells in pancreas
Secrete enzyme components
| Stimulated by CCK and Ach
143
Pancreatic secretion and flow rate
Na remains constant
Bicarbonate increases with flow rate
Cl decreases with flow rate
144
Pancreatic insufficiency
Rare
Secretion can drop down to 10% of normal without an effect on nutrient absorption: pancreatic enzymes are secreted in excess
145
Pancreatitis
Inflammation of the pancreas
Auto digestion of pancreatic tissue due to enzyme retention
Can be caused by gallstones in ducts, malignancy, alcohol abuse
Medical emergency
146
Cystic fibrosis
Pancreatic ducts are inefficient to secrete bicarbonate and water
Enzymes cannot be flushed properly from pancreas and limited quantities reach the intestinal lumen
Enzymes that reach lumen are inactive because of failure to neutralize gastric acid
Enzymes provided as supplements
147
Bile
```
Secreted by liver continuously, 1L/day
pH 7.8-8.6
Isotonic
Flow into duodenum is intermittent
Diverted to gallbladder for concentration, acidification and increase in viscosity during inter digestive periods
```
148
Bile acids
Synthesized from cholesterol in liver
| In small intestine, bile salts that are more soluble
149
Phospholipids (bile)
Lecithins: major
150
Bile pigments
Bilrubin: major
151
Sphincter of Oddi
Allows entry to duodenum from gallbladder
Closed while gallbladder is filled with bile
Relaxes shortly after eating (CCK induced gallbladder contraction)
152
Primary bile acids
Chalice acid
Chenodeoxycholic acid
>90% of bile salts are reabsorbed from ileum not portal blood and resecreted by liver
153
Secondary bile ducts
Deoxycholic acid
Lithocholic acid
Small amount of bile salts dehydroxylated by colonic bacteria, reabsorbed, returned to liver to be resecreted
154
Gallstones
Collection of solid material, mainly cholesterol, in gallbladder
Often asymptomatic
Abdominal pain (upper middle, right), nausea, jaundice, fever
155
Hyper secretion of cholesterol
Caused by obesity, oral use of contraceptives, estrogen, old age, sudden weight loss and genetic factors
156
Diminished bile acid pool
Enterohepatic circulation is interrupted
157
Cholecystectomy
Gallbladder removal
Gallbladder is not essential for normal digestive function: removal has no effect on life expectancy or metabolic status
Balance of specific bile acids may change, but no change on cholesterol
Inability to form concentrated bile and to secrete in coordinated fashion: patients have a harder time tolerating large fatty meals
Can have diarrhea
158
Crohn's disease
Inflammation that affects the full thickness of the bowel wall
Early onset, usually teens to early twenties
Abdominal cramps, diarrhea, weight loss, fever, anemia, ulcers, fistulae, abscess
Abnormal immune response to intestinal bacteria, mutations in NOD2 gene
No cure, but symptoms can be alleviated using medication, surgery, dietary adjustments ileal resection
159
Ileal resection
40% resection is tolerated well
More causes bile salts to not be recirculated but secreted in diarrhea: causes depletion of bile salt, and fat absorption is impaired, also affects absorption of some vitamins, iron and calcium
160
Transcellular route (epithelial cells)
Through epithelial cells from lumen to blood circulation
| Large molecules only go via transcellular route
161
Paracellular route
Between tight junctions
162
Apical membrane
Lumen
163
Basolateral membrane
Blood
164
Sucrose
Cane sugar
Disaccharide
Glucose + fructose
165
Lactose
Milk sugar
Disaccharide
Glucose + galactose
166
Starches
Large polysaccharides present in almost all non-animal foods
167
Glycogen
Small amounts
| Animal polysaccharides
168
Cellulose
Large amount
| Cannot digested and contributes to dietary fiber
169
Amylase
Salivary and pancreatic alpha-amylases partially break down glucose polymers (alpha 1,4 bonds of amylose and amylopectin)
Not necessary for healthy humans, important in infants and pancreatic insufficiency
Inactivated by acidic pH in stomach
170
Isomaltase
Only enzyme that an break down alpha 1,6 bonds of alpha-limit dextrins
171
Sucrase-isomaltase
Brush border enzyme that binds sucrose
172
Lactase
Brush border enzyme
Especially important in infants
If it is lacking, milk sugar does not break down and causes diarrhea
173
GLUT5
Fructose transporter
Fructose is not natural product from corn
Excess amount can overwhelm transporter
Apical membrane
174
SGLT1
Na-glucose transporter
Active transport
Apical membrane
175
GLUT2
Transports glucose, galactose, fructose over basolateral membrane
Facilitated diffusion
176
Essential amino acids
Many need to be obtained from dietary sources
177
Pepsins
Inactive in the duodenum (pH >5)
Max, pepsin digests 15% of dietary proteins to small peptides and amino acids
Not necessary for protein digestion
178
Enteropeptidase
Absolutely necessary to activate trypsinogen to trypsin and activate other pancreatic enzymes
179
PEPT1
Absorbs peptides with a proton
| Apical membrane
180
Cytosolic proteases
Digests peptides absorbed into cells
Amino acids are secreted over basolateral side using transport proteins
Most are Na dependent
181
Vitamin A
Retinoid acid
Regulates gene transcription
Fat soluble
182
Vitamin D
Important in Ca absorption
Supplements: Cholecalciferol, ergocalciferol
Fat soluble
183
Vitamin E
Tocopherol
Important antioxidant
Fat soluble
184
Vitamin K
Important in blood clotting
| Fat soluble
185
Gastric lipase
```
pH optimum of 4-5.5
Resistant to pepsin
Hydrolyzes fatty acid linked to first position of triglyceride
Does not fully break down triglyceride
Inhibited by bile acids
```
186
Pancreatic lipase
Acts on 1 and 3 positions of glycerol molecule to liberate esterified fatty acids
Neutral pH optimum
Inhibited by bile acids
187
Lipase
Can absorb on the surface of fat droplet
Displaced by bile acids
Colipse binds both bile acids and lipase
188
Phospholipase A2
Breaks down dietary phospholipids
189
Cholesterol esterase
Degrades cholesterol esters derived form dietary sources and esters of vitamins A, D and E
Breaks down position 2 in triglycerides
190
Emulsifiation
Large fat aggregate is exposed to bile, and non polar portions of bile salts and lecithin intercalate into the lipid
Polar parts demain at the surface
Bile sat/lecithin coat makes fat droplets easily fragmentable causing increased surface area
191
Micelles
Formed from lipids breakdown products and bile acids
Transport lipids to brush border
Not necessary for triglycerides or glycerol
Necessary for cholesterol, plant sterols and fat soluble vitamins
192
Apolipoproteins
Synthesized in rough ER and glycosylated, then coated in lipid cores to form chylomicrons
193
Chylomicrons
Secreted from basolateral side of enterocyte via exocytosis and enter central lacteal
194
Vitamins
Act as cofactors for many metabolic reactions
| Must be acquired from diet
195
Vitamin B9
Folate
| Absorbed by at least three different transport mechanisms
196
Water-soluble vitamins
B1, B2, B6, C, biotin, nicotinic acid, pantothenic acid
| Absorbed by sodium dependent cotransport
197
Sodium-coupled nutrient transport in intestines
Glucose transport is coupled to Na transport
198
Na absorption in colon
ENaC
No glucose absorption
K absorbed with lumen concentration is high, or secreted if lumen concentration is low
199
NHE3 and DRA
Na/H exchanger and Cl/HCO3 exchanger transport NaCl into epithelial cells
200
KCC1
Transports Cl out of epithelial cells
201
CFTR
Cl exists epithelial cells via cystic fibrosis transmembrane regulators
Phosphorylated by PKA, which is activated by cAMP (Gs protein, VIP and PGE2)
HCO3 also exits, either coupled with Cl or by itself
202
Cholera toxin
Activates Gs protein, which leads to cAMP increase, activating CFTR, Cl efflux and watery diarrhea
Physiology 2044
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