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PSL301 > Gastrointestinal System > Flashcards

Gastrointestinal System Flashcards

1
Q

Digestive system

A
  • Tubular GI tract: Mouth, pharynx, esophagus, stomach, small and large intestine
  • Accessory organs: Teeth, tongue, salivary glands, liver, gall bladder, and pancreas
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2
Q

Mouth

A
  • Hard palate, tongue, trachea, esophagus, vocal fold, epiglottis, palatine tonsil, soft palate
  • Tongue tastes and guides food
  • Teeth grinds food
  • Mix food with saliva (from salivary glands)
  • Minimal digestion of carbohydrates and lipids
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3
Q

Pharynx

A
  • Swallowing reflex
  • Pushes tongue against soft pallet
  • Respiration is inhibited
  • Pushes food into esophagus
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4
Q

Esophagus

A
  • Tube that moves food to stomach by peristalsis
  • No digestion in the esophagus
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5
Q

Small intestine

A
  • Peristalsis
  • Digestion of all types of nutrients
  • Main site of nutrient absorption
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6
Q

Small intestine, liver, and pancreas work together

A
  • Digestion aided by secretions from liver (via gall bladder and pancreas)
  • Liver: provides bile salts and bilirubin
  • Pancreas: provides bicarbonate and various enzymes
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7
Q

Large intestine(colon)

A
  • Mass movement
  • Absorption of water and electrolytes
  • Storage of fecal matter for expulsion
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8
Q

Wall of GI tract has unique structure

A
  • Four layers:
    • Mucosa
    • Submucosa
    • Muscularis
    • Serosa
  • Contains networks of neurons: submucosal plexus and myenteric plexus
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9
Q

Specialized cells of mucosa

A
  • Transport cells: secrete acid, bicarbonate, absorb nutrients, water, and vitamins
  • Enteroendocrine cells: secrete hormones into blood
  • Exocrine cells: secrete enzymes, mucous, etc
    • Goblet cells: secrete mucous
    • Paneth cells: secrete antimicrobial compounds
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10
Q

Enteric nervous system contains 100 million neurons

A
  • Myenteric plexus (Auerbach’s plexus): regulates motility
  • Submucosal plexus (Meissner’s plexus): regulates secretion and absorption
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11
Q

Nervous regulation of digestive system

A
  • External stimulus -> sensory receptors -> cephalic brain -> symp and parasympathetic neurons -> neurons of myenteric and submucosal plexuses -> smooth muscles or secretory cells -> muscle contraction/relaxation or exocrine secretion, paracrines, or endocrine secretions
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12
Q

Parasympathetic control of digestive system

A
  • Key points:
    • Emanates from vagus nerve
    • Synapse on enteric system neurons
    • Postganglionic fibres release acetylcholine
      -Functions:
    • Increase gut muscle activity
    • Relax sphincters
    • Increase secretion to make food digest faster
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13
Q

Sympathetic control of digestive system

A
  • Key Points:
    • Postganglionic neurons innervate entire GI tract
    • Release noradrenaline
  • Functions:
    • Inhibit gut movements
    • Constrict sphincters
    • Reduce secretion
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14
Q

Contents of GI tract help regulate its own activity

A
  • Neural mechanisms regulating digestive activity: CNS -> myenteric plexus -> stretch receptors and chemoreceptors -> secretory cells
  • Hormonal mechanisms: Enteroendocrine cells -> release hormones -> circulate to secretory cells or trigger peristalsis and segmentation movements
  • Local mechanisms: Local factors (pH, chemical stimulation, physical stimulation) -> secretory cells or enteroendocrine cells
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15
Q

Splanchnic circulation

A
  • Blood supply in digestive system
  • O2 rich blood: Aorta -> hepatic artery -> liver or digestive tract arteries -> capillaries of digestive tract (stomach, intestines, pancreas, and spleen) -> hepatic portal vein -> liver
  • O2 poor blood: Capillaries of liver -> hepatic vein -> inferior vena cava
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16
Q

Arteries that supply the GI tract

A
  • Stomach: celiac artery
  • Small intestine: superior mesenteric artery
  • Large intestine: superior and inferior mesenteric arteries
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17
Q

Blood circulation in the villi

A
  • Capillaries provide gas exchange, transport soluble nutrients, water, and electrolytes
  • Central lacteals absorb fat into the lymphatic system
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18
Q

Blood flow in liver

A
  • Hepatocytes clean blood of potentially harmful substances
  • Blood from hepatic portal vein and hepatic artery pools in sinusoids
  • Blood moves to central veins, drains into hepatic vein and returns to heart
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19
Q

Trafficking of substances moving to and from liver

A
  • Absorbed from GI tract (bilirubin, nutrients, drugs, etc.) -> hepatic portal vein -> Liver (glucose and fat metabolism, protein synthesis, hormone synthesis, urea production, detoxification, storage)
  • Metabolites and drugs from peripheral tissues (bilirubin, metabolites of hormones and drugs, nutrients) -> hepatic artery -> liver
  • Liver -> hepatic vein -> metabolites to peripheral tissues (glucose, albumin, clotting factors, angiotensinogen, urea, vitamin D)
  • Liver -> bile duct -> secreted into duodenum (bile salts, bilirubin, water, ions, phospholipids)
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20
Q

Functions of digestive system

A
  • Motility:
    • Moves food from mouth to anus
    • Mixes food for maximal exposure to enzymes and maximal absorption
    • Controlled by enteric nervous system (inhibits wall of GI tract)
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21
Q

GI smooth muscle operates as single unit

A
  • Cells connected by gap junctions
  • Action potentials travel in all directions
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22
Q

Electrical properties of GI smooth muscle

A
  • Slow waves do not cause contractions unless threshold is reached
  • Slow waves determine frequency of action potentials
  • Action potentials fire when slow wave potentials exceed threshold
  • Force and duration of muscle contraction are directly related to amplitude and frequency of action potentials
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23
Q

Interstitial cells of Cajal act as pacemakers in GI smooth muscle

A
  • Generate slow waves and action potentials
  • Located between nerve fibers and smooth muscle cells
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24
Q

Comparison between heart and GI pacemaker cells

A
  • Heart pacemaker cells:
    • Depolarize ~80 times/min
  • Interstitial cells of Cajal:
    • Depolarize ~3/min (stomach) to 12/min (duodenum)
    • Depolarize due to Ca2+ entry
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25
Modulation of GI smooth muscle cell membrane potential
- Stimulation by acetylchline and parasympathetics -> relaxes sphincters to allow food to go through -> depolarization - Stimulation by noradrenaline and sympathetics -> constricts sphincters to stop digestion -> hyper polarization
26
How does food move through GI tract
- Swallowing -> upper esophageal sphincter -> peristalsis -> lower esophageal sphincter -> grinding and peristalsis -> pyloric valve -> peristalsis and segmentation -> ileocecal valve -> segmentation and mass movement -> internal anal sphincter -> external anal sphincter -> defecation
27
Swallowing
- Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex -> upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of airways -> food moves down into esophagus, propelled by peristaltic waves and aided by gravity
28
Volunatary swallowing of food
- CN IX, X and swallowing center in medulla/lower pons and CN V, IX, X and XII - Tongue moves against hard pallet, respiration inhibited
29
Involuntary swallowing of food
- CN X and swallowing center in medulla/lower pons and CN V, VII, IX, and XII - Upward movement of soft palate, epiglottis closes, base of tongue pushes food
30
Esophagus uses peristalsis to move food
- Food stimulates the vagus nerve and swallowing centre which activates myenteric plexus - Peristalsis and relaxation of lower esophageal sphincter - Food moves into the stomach
31
How peristalsis moves food
- Contraction of circular muscles behind food mass -> contraction of longitudinal muscles ahead of food mass -> contraction of circular muscle layer forces food mass forward
32
Stomach relaxes to accommodate food
- Vagovagal reflex links the stretch of the stomach to the brain which then adjusts the stomach size
33
Stomach undergoes waves of peristalsis
- Waves mix stomach content and allow stomach to empty into duodenum
34
Segmentation mixes food in the small intestine
- Localized concentric contractions at intervals along intestine - Circular muscles contract, longitudinal muscles relax to allow digestion - Mixes food, no movement down
35
Ileocecal valve ensures one way flow from small to large intestine
- Controls emptying of small intestine - Prevents backflow - Opened by distension of ileum and by gastroileal reflex - Closed by distension of colon
36
Large intestine responsible for mass movement
- 1-3 defecations per day, usually after a meal - Waves of contractions move contents long distances - Slow movement (5-10cm/hr) - PNS increases motility - SNS decreases motility - Defecation requires voluntary relaxation of external anal sphincter and contraction of abdominal muscles
37
What happens during vomiting
- Stimulation of vomiting centre in medulla - Vagus: enhances salivation, relaxes esophagus and contracts pylorus - Spinal nerves: inspiration and contraction of abdominal muscles - Phrenic nerve: diaphragm descends - Stomach: undergoes reverse peristalsis
38
How much is secreted/absorbed by the GI tract per day
- Fluid into digestive system: Ingestion (2L food and drink), Secretion (1.5L saliva, 0.5L bile, 2L gastric secretions, 1.5L pancreatic secretions, 1.5L intestinal secretions) = 9L total input into lumen - Fluid removed from digestive system: Absorption (7.5L from small intestine, 1.4L from large intestine), Excretion (0.1L in feces) = 9L removed from lumen - Requires a large surface area for secretion/absorption
39
Structure of stomach massively increases its surface area
- Rugae: surface folding increases area - Gastric pits: Opening to gastric gland
40
Structure of the small intestine also increases surface area
- Plica (valvulae conniventes): Composed of submucosal layer - Villi - Crypts of lieberkuhn
41
Structure of large intestine also increases its surface area
- Haustra - Crypts of lieberkuhn
42
Microvilli are found throughout GI tract
- Found in mucosa layer
43
Saliva produced in salivary glands
- Constituents of saliva: water, electrolytes, buffers, mucous, IgA antibodies, lysozyme, enzymes (salivary amylase and lingual lipase) - Function of saliva: protection, lubrication, taste, digestion
44
Salivation is under neural control
- Parasympathetic: lots of watery (serous) saliva - Sympathetic: small amount of thick (mucous) saliva
45
Many substances secreted in the stomach
- Mucous cells - Parietal cells: HCl, intrinsic factor - Chief cells: Pepsinogen, gastric lipase - Enterochromaffin-like cells: histamine - D cells: somatostatin - G cells: gastrin
46
Mucous and bicarbonate protect the stomach lining
- Mucous layer is a physical barrier (w/o mucus layer, acid eat away at stomach) - HCO3 ensures pH7
47
Parietal cells in stomach secrete acid and intrinsic factor
- Function of stomach acid: breaks down plant cell walls, denatures proteins, activates pepsinogen - Functions of intrinsic factor: binds to vitamin B and ensures absorption in the ileum
48
Chief cells in stomach secrete pepsinogen and gastric lipase
- Breaks down proteins and fat
49
G cells in the stomach secrete gastrin
- Stimulates release of acid, histamine, pepsinogen, and mucous - Increases stomach motility and mass movement
50
Variety of pancreatic secretions enter small intestine
- Acinar cells secrete pancreatic amylase, pancreatic lipase, nucleases, proteases (trypsinogen, chymotrypsinogen, procarboxypeptidase, proelastase, etc.) - Duct cells secrete sodium bicarbonate and water
51
Secretion of bicarbonate and water from intestine
- HCO3 secreted out, Cl- secrete in - Cl- secrete out via CFTR channel
52
Cystic fibrosis patients ingest pancreatic enzymes
- CFTR channels stop working - Thick mucous builds up in pancreatic ducts, enzymes cannot travel to small intestine
53
What is secreted from the liver
- Bile contains: bile salts, cholesterol, bilirubin, bicarbonate - All secreted by the liver into the gall bladder then to the small intestine
54
Intestine releases many hormones
- Secretin - Cholecystokinin - Motilin (released during fasting -> migrating myoelectric complex) - Glucagon-like peptide 1 (GLP-1) - Gastric inhibitory peptide (GIP) -> stimulate insulin
55
Secretin promotes digestion
- Stimulate release of bicarbonate - Decrease gastric acid/emptying -> give time for digestion - Acid in small intestine -> release secretin
56
Cholecystokinin promotes digestion
- Contraction of gall bladder - Stimulate release of pancreatic enzymes - Decrease gastric acid/emptying - Fatty acids and amino acids in small intestine -> release CCK
57
GLP-1 stimulate digestion and satiety
- Stimulate insulin, decrease glucagon, increase B cell growth -> feeling of being full (satiety) - Decrease gastric acid emptying - Fatty acids and carbohydrate in small intestine -> release GLP1
58
Food ingestion and nutrient absorption
- Input: Carbohydrates, Fats, Proteins, Water, Electrolytes, Vitamins - Absorbed: Monosaccharides, Fatty acids, Monoglycerides, Cholesterol, Amino acids, water, vitamins, electrolytes
59
Carbohydrate digestion in mouth, stomach, and small intestine
- Mouth: 5% of starch broken down to maltose by salivary amylase - Stomach: 35% of starch is broken down to maltose by amylase - Small intestine: remaining starch is broken down by salivary amylase
60
Brush border enzymes convert and absorb monosaccharides
- Maltase-glucoamylase - Dextrinase (double sugars) - Sucrase - GLUT-5 - Sodium glucose linked transporter - Lactase
61
Mechanism of monosaccharide absorption
- Glucose enters cell with Na+ on SGLT symporter and exits on GLUT2 - Fructose enters on GLUT5 and exits on GLUT2
62
Protein digestion begins in the stomach
- Pepsinogen is released from chief cells - Pepsin cleaves protein at specific amino acids (aromatics: phenylalanine, tryptophan, tyrosine)
63
Proteins digested by endopeptidase and exopeptidase enzymes
- Endopeptidase digests internal peptide bonds -> 2 smaller peptides - Exopeptidase digests terminal peptide bonds to release amino acids (aminopeptidase and carboxypeptidase) -> cleave amino end and carboxyl end -> cleave again by more exopeptidase
64
Proteins digested by pancreatic enzymes in the intestine
- Trypsin and trypsinogen are endopeptidases - Carboxypeptidase removes single amino acids from carboxyl end of protein - Autodigestion is prevented by zymogen packaging, trypsin inhibitor synthesis, and trypsin autolysis
65
Protein absorption in small intestine
- Proteins -> Peptides -> Di and tripeptides cotransport with H+ (PepT1) , amino acids cotransport with Na+ , small peptides carried intact across cell by transcytosis
66
Fat digestion starts in mouth and stomach
- Triglycerides cleaved to monoglycerides and free fatty acids by linguinal lipase and gastric lipase - Minimal digestion - Agitation in stomach forms smaller droplets
67
Bile salts emulsify fat in small intestine
- Bile salts and lecithin from the liver emulsify fat - Increase contact area of fat with intestinal cells for more efficient digestion
68
Bile salts help form micelles
- Free fatty acids and cholesterol packaged in polar micelles to be transported
69
Fat absorption in small intestine
- Micelles contact brush border - Monoglycerides and fatty acids diffuse into the cell - Re-esterify to triglycerides in the smooth ER - Cholesterol enters through an energy-dependent transporter (NPC1L1) - In golgi, triglycerides and proteins form chylomicrons - Chylomicrons are packaged into vesicles and secreted by exocytosis - Chylomicrons are absorbed by lymphatic system
70
Chylomicron
- In capillaries, triglycerides in the chylomicron are converted to free fatty acids and glycerol by lipoprotein lipase - Products used for energy or stored as triglycerides - Chylomicron remnants taken up by liver
71
How are vitamins and water absorbed
- Fat soluble vitamins (A, D, E, K): absorbed with fat - Water soluble vitamins (C and most B): absorbed through a transporter - Vitamin B12: absorbed by intrinsic factor and transported into ilium - Water moves by osmosis into intestinal epithelial cell, out of cel on basolateral side - Co transport: Na+/glucose transporter
72
How is calcium and iron absorbed
- Calcium absorbed in by Ca2+ channel, calbindin(calcium binding protein) -> Ca2+ pumped out by Ca2+ ATPase - Fe2+ and H+ secreted in by DMT1 -> Fe2+ secreted out by ferroportin (leels decreased by hepcidin)
73
NaCl absorption in small intestine and colon
- Na+ enters cell by multiple pathways - Na+-K+ ATPase pumps Na+ into ECF

PSL301 (6 decks)

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