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PHGY 210 > Digestion > Flashcards

Digestion Flashcards

1
Q

gastrointestinal tract (GIT)

A
  • alimentary canal: continuous tube from mouth to anus
  • function: provide nutrient to body (convey good along GIT, so it can be broken down and be absorbed)
  • activity: ingestion –> secretion (chemical breakdown) –> motility (mixing, propulsion and physical breakdown) –> digestion –> absorption (transfer nutrient to blood circulation) –> defecation (waste removal)
  • digestive and absorptive capacity: carbohydrate –> 99%, fat –> 95%, protein –> 92%
  • length in living adult ~ 4.5m (10m in cadavers since no muscle contractions)
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2
Q

accessory digestive organs

A
  • salivary glands
  • pancreas
  • liver
  • gallbladder
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3
Q

GIT wall

A
  • folded inner wall to increase total surface area (600x larger than the outer wall)
  • 4 layers: inner wall, mucosa, submucosa, muscularis externa, serosa, outer wall
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4
Q

serosa

A

thin, tough layer of connective tissue that holds GIT in position

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5
Q

muscularis externa

A
  • longitudinal fibre: outer layer
  • circular fibre: inner layer
  • striated muscle: mouth –> upper 1/3 esophagus and external anal sphincter
  • smooth muscle:lower 2/3 esophagus –> external anal sphincter
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6
Q

submucosa

A
  • loss connective tissue
  • housing neuronal network, lymphatics, and blood vessels
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7
Q

mucosa

A
  • muscularis mucosae: smooth muscle
  • lamina propria: loose connective tissue
  • epithelial layer: secretory, exocrine/endocrine, absorptive cells
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8
Q

enteric nervous system (ENS)

A
  • neurons reside within wall of GIT
  • independent, integrative nervous system
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9
Q

plexus

A
  • collection of nerve bodies
  • submucosal plexus: between circular muscle and muscularis mucosae
  • myenteric plexus: between longitudinal muscle and circular muscle
  • submucosal and myenteric plexus are autonomically different, but behave has one functional unit
  • contains sensory neurons, motor/effector neurons, and interneurons
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10
Q

short enteric (intramural) reflexes

A
  • stimulus –> chemoreceptors/osmoreceptors/mechanoreceptors –> nerve plexus –> smooth muscle or gland cell –> response
  • pathway within GIT
  • acetylcholine (ACh): excitatory, inhibited by atropine
  • non-adrenergic, non-cholinergic (NANC): e.g. nitric oxide, inhibitory
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11
Q

autonomic nervous system (ANS) innervation of GIT (long extrinsic reflexes)

A
  • must via GIT enteric neurons
  • stimulus –> chemoreceptors/osmoreceptors/mechanoreceptors –> via afferent neurons –> central nervous system –> via efferent autonomic neurons (parasympathetic or sympathetic) –> nerve plexus –> smooth muscle or gland –> response
  • parasympathetic: pre-ganglionic, release nicotinic excitatory, vasodilation
  • sympathetic: post-ganglionic, release non-adrenaline inhibitory, vasoconstriction
  • parasympathetic and sympathetic neurons can synapse with excitatory or inhibitory enteric neurons
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12
Q

hormonal regulation of GIT

A
  • non-GIT hormones: influence growth and development of GIT
  • GIT hormones: influence activities outside of GIT, regulate activities inside GIT (e.g. ghrelin: stimulates appetite and leptin:decrease appetite)
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13
Q

diffuse endocrine system (DES)

A

-scattered among other cells in mucosa
- largest and most diver endocrine system body
- important hormones: gastrin, CCK, secretin, GIP, and VIP
- regulation: release into portal blood (hepatic portal vein) –> liver –> heart –> systemic circulation –> target cell, multiple targets (excitatory or inhibitory), interactions via neurotransmission (synergistically: activation or antagonistically: inhibition)

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14
Q

GIT propulsion (flow)

A
  • pressure gradient coordinates contractions
  • variations of resistance (normally little/no resistance)
  • segmentation: mixing
  • peristalsis: movement
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15
Q

phases of deglutition (swallowing)

A
  • oral
  • pharyngeal
  • esophageal
  • gastric: involuntary
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16
Q

oral phase of deglutition

A
  • voluntary initiation
  • transport of bolus from anterior mouth to pharynx
  • reflexes coordinated by deglutition centre in medulla oblongata
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17
Q

pharyngeal phase of deglutition

A
  • involuntary
  • passage to nose, mouth, and trachea are blocked by reflexive contraction of vocal chord and closure of the glottis –> short apnea
  • upper esophageal sphincter (RES) relaxes due to cessation of impulses from CNS that is mediated by vagus nerve (no release of ACh)
  • pharynx muscles contract (change in pressure gradient pushes bolus down the esophagus)
  • same actions every time
  • must occur in correct sequence for proper deglutition
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18
Q

esophageal phase of deglutition

A
  • involuntary
  • esophageal forces –> gravity and peristalsis: wave of contractions setting up a gradient of pressure favouring aboral movement
  • primary peristalsis
  • secondary peristalsis
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19
Q

primary peristalsis

A
  • generated every time an individual swallows
  • part of the deglutition reflex
  • sequential (proximal –> distal) activation om striated muscles: vagus somatic fibre
  • synchronous activation with increased latency in smooth muscles: vagus autonomic fibre
  • interruption high up –> no primary peristalsis
  • interruption transthoracically–> primary peristalsis continuous
  • continuation and propagation of peristalsis due to ENS in distal esophagus (smooth muscles)
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20
Q

secondary peristalsis

A
  • initiated by local distension
  • mediated by enteric reflex or vagal-vagal reflexes (long reflex)
  • several secondary peristalsis wave until bolus has been displaced
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21
Q

lower esophageal sphincter

A
  • half above and half below the diaphragm
  • no visible enlargement of circular muscle
  • anatomically insignificant, functionally significant
  • closure: myogenic contraction
  • relaxation: neurogenic due to release of NANC or vagal stimulation that activates inhibitory ENS neurons
  • intrinsic physiological sphincter, tonically contracted in the absence of swallowing
  • anti-reflux mechanisms assisted by presence of intra-abdominal segment
  • regulated by GIT hormones via gastrin (cause LES closure at high concentration) and progesterones (lowers resistance of LES –> increase likelihood of reflux)
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22
Q

hiatus hernia

A

displaced LES into the thorax –> increased intra-abdominal pressure with no increase in LES pressure –> reflux

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23
Q

stomach function

A
  • temporary storage: 1-2 L, upper portion (thin walled)
  • physical disruption and mixing of contents: bolus –> chyme (semi-liquid consistency)
  • regulated propulsion into duodenum, lower portion (thick-walled)
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24
Q

stomach

A
  • regions: fundus (top), body, antrum (end)
  • stomach wall (same 4 layers as GIT with modifications): gastric mucosa –> consists rugae (folds) and many different cell types, muscularis externa –> oblique muscles (extra layer of smooth muscle that allows the grinding movement of the stomach)
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25
Q

receptive relaxation

A
  • deglutition reflexes of the stomach
  • proximal stomach relaxes before meal arrives
  • further stomach relaxation when meal arrives due to local ENS inhibitory neurons
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26
Q

stomach movement

A
  • via peristalsis in the distal stomach only
  • amplitude of contraction influenced by magnitude of stimulus
  • frequency, direction and velocity influenced by electrical characteristics of smooth muscle
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27
Q

basic electrical rhythm (BER)

A
  • constantly present
  • do not initiate contraction
  • propagate from cell to cell
  • detectable in longitudinal and circular muscle
  • due to interstitial cells of Cajal (ICC): non-neuronal, not ENS pacemaking cell
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28
Q

electrical response activity (ERA)

A
  • intermittent
  • cause contractions
  • phase-locked to BER
  • stimulus: ACh/stretch
  • calcium dependent
  • amplitude of contraction must < #spikes/burst must be < magnitude of stimulus
  • maximal frequency of contraction limited by frequency of BER
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29
Q

pyloric sphincter

A
  • functionally insignificant
  • open at rest, closed by antral peristalsis
  • behave as filter
30
Q

gastric emptying of liquid

A
  • due to pressure difference between the proximal stomach and the duodenum (Pstomach > Pduodenum)
  • receptive relaxation to minimize pressure difference
  • vagotomy to proximal stomach –> large pressure difference
  • vagotomy to distal stomach –> little/no effect to liquid emptying
31
Q

gastric emptying of solids

A
  • distal stomach functions as antral pump
  • depends on frequence and stroke volume and amplitude of contraction (due to distension of the stomach: muscle stretch, local ENS reflex, vago-vagal reflex)
32
Q

gastric vs duodenal factors

A
  • gastric: increase motility
  • duodenal: decrease motility (e.g. distension, pH<3.5, osmotic pressure, fat»protein>carbohydrate)
33
Q

vomitting

A
  • passive emptying contents of the upper GIT due to increase in intra-abdominal pressure
  • stimulus activates vomiting centre –> cause autonomic discharge, nausea (psychic experience), retching and emesis (vomit due to relaxation of upper GIT and spasm or pyloric antrum and duodenum or contraction of abdominal muscles and diaphragm)
  • circulating emetic agents stimulates chemoreceptor trigger zone (CTZ, outside blood-brain barrier) –> activates vomiting centre
34
Q

small intestine

A
  • 3 regions: duodenum, jejunum, ileum
  • most digestion and all absorption of nutrients
  • upper small intestine function: neutralization, osmotic equilibrium, digestion and absorption
35
Q

intestinal contractions

A
  • governed by electrical characteristics of smooth muscle
  • similar mechanism as stomach contractions
  • frequency of BER decreases from duodenum to ileum (12/min –> 8/min) due to greater excitability and thickness of the proximal small intestine
36
Q

segmentation in small intestine

A
  • most common type of intestinal contraction activity after a meal
  • modulated by myogenic response to distension, ENS organization, ANS and hormone regulations
  • functions: mixing and slow propulsion (due to greater contraction in the proximal small intestine)
37
Q

peristalsis in small intestine

A
  • infrequent and irregular
  • weak and shallow
  • only allow a very short travel distance
  • mediated by series of local relaxations involving interactions of longitudinal and circular muscles
  • modulated by ANS and hormones
38
Q

law of intestin

A
  • contraction of longitudinal muscle and relaxation of circular muscle ahead bolus
  • contraction of circular muscle and relaxation of longitudinal muscle behind bolus
39
Q

colon contractile activity

A
  • similar to small intestine contractile activity, but slower, more sluggish and irregular
  • functions: mixing, propulsion and storage
  • segmentation and peristalsis governed by irregular BER
40
Q

colon/large intestine emptying after meal intake

A
  • gastroileal reflex: increase ileam activity
  • gastrocolic reflex: increase colon activity
  • ileocolif reflex: increase ileam and distal colon activity
41
Q

migrating motor complex (MCC)

A
  • propel luminal contents all the way from the distal stomach to the distal ileum
  • phase I: 60 minutes, no spike potentials –> no contractions
  • phase II: 20 minutes, irregular spike potentials –> contractions
  • phase II: 10 minutes, regular spike potential –> contractions, maximized frequency due to short duration
  • initiation due to ENS
  • propagation via ENS with modulation via ANS and gut peptides
  • interruption by intake of new meal
  • function: gastric emptying of large, non-digestible particles
42
Q

enzymes for digestion

A
  • amylases: carbohydrate
  • proteases: protein
  • lipase: fat
43
Q

secretion regulation

A
  • nervous via ANS
  • hormonal via gut peptides
44
Q

secretion in mouth

A
  • by salivary glands: parotid (serous fluid), submandibular (mixed fluid) and sublingual (mucin-rich fluid)
  • secretion of mucin for protection and lubrication
  • secretion allow chemical digestion due to presence of salivary amylase and lingual lipase
  • gland regulation via parasympathetic (increases secretion) and sympathetic (decreases secretion)
45
Q

saliva

A
  • 0.5-1.5 L/day
  • hypotonic
  • pH: 6.5-7.0
  • contains mucin, lipase, lysozyme and amylase
46
Q

phases of secretion

A
  • cephalic: psychic (before ingestion) and gustatory (taste)
  • gastric
  • intestinal
47
Q

mixed gastric juice

A
  • 1.5-2.9 L/day
  • isotonic
  • pH: 1-2
  • contains HCl, pepsinogen (precursor to pepsine, enzyme that digests proteins)
  • modified by non-parietal alkaline gastric secretions
48
Q

cardia and pyloric tubular glands

A

secrets alkaline, mucin rich-fluid

49
Q

fundus and body tubular glands

A

secrets acid, enzyme and intrisic factor

50
Q

parietal cell secretion

A
  • secretes HCl (function: precipitate soluble proteins, denature proteins –> ready for digestion, activation of pepsin and provide optimal pH for pepsin activity)
  • production of HCl also cause excess of OH- within the cell –> production of H2CO3 via carbonic anhydrase –> diffuse into circulation –> increase alkalinity of venous blood
  • secrets intrinsic factors that allow vitamin B12 absorption in the ilium, dificiency –> pernicious anemia
51
Q

chief cell secretion

A
  • secretes pepsinogen
52
Q

mucus neck cell secretion

A

secretes mucin (as well as by all surface epithelial cells, cardia and pyloric tubular glands) to protect GIT mucosa from acid damages by forming gastric mucosal barrier (GBM) in the stomach (not rest of teh GIT) that cause H+ impermeability

53
Q

contributing factors to ulcers

A
  • normal HCL output, but weak barrier: aspirin, NSAIDS, bacteria
  • normal barrier, but excess HCl output: gastrin-producing tumors
54
Q

gastrin

A
  • secretion stimulated by long enteric reflexes, vagally-mediated reflexes, and secretagogues (amino acids or partially digested proteins that act on gastrin-releasing cells)
  • release is self-regulating
  • stimulates HCl secretion or production or more parietal cells (HCl secreting cell)
55
Q

histamine

A
  • binding to parietal cells sensitizes parietal cell’s affinity to bind to ACh or gastrin
56
Q

pancreatic juice

A
  • 0.5-1.5 L/day
  • isotonic
  • pH: 7.2-8.2
  • 3 g% protein: amylases, proteases and lipases
  • released into the small intestine via sphincter of Oddi
  • secretion regulated by cells that release large volume of HCO3- rich juice or cells that releases small volume of enzyme rich juice
57
Q

trypsin

A
  • precursor: trypsinogen
  • must be activated at level of the small intestine and not pancreas (could cause pancreatic tissue damages), process can be inhibited by trypsin inhibitor (secreted by the pancreas) that inactivates trypsin
58
Q

liver

A
  • largest gland in body
  • function: storage, synthesis, detoxification and metabolism
  • secretes bile continuously from hepatic duct (released into small intestine at the same location as pancreatic juice)
  • entrance of bile into duodenum is intermitted, mostly stored and concentrated in the gallbladder
59
Q

liver bile

A
  • 0.4-1.0 L/day
  • isotonic
  • pH: 7.8-8.2
  • 3 %g: bile acid/salts, bile pigments (hemoglobin breakdown products), cholesterol, phospholipids, no digestive enzymes
60
Q

gallbladder function

A
  • concentrate solids: hepatic bile, gallbladder bile –> increases viscosity
  • reduces pH
61
Q

bile salts

A
  • synthesized in liver from cholestrol
  • facilitate digestion, transportation and absorption of fat
  • facilitate transportation and absorption of fat-soluble vitamins (A,D,E and K)
  • reduce surface tension and stabilizes emulsion (large lipid globules are broken down into several small lipid globules)
  • pool: 3.5 g
  • daily synthesis: 0.5 g
  • daily release into intestine: 15-20 g (reabsorbed via enterohepatic circulation, EHC (liver –> GIT –> liver), to maintain bile salt pool of 0.5 g)
62
Q

intraportal functions of bile salt

A
  • positive feedback that regulates hepatic bile flow (bile secretion decrease if ileum is removed)
  • negative feedback that regulates synthesis of new bile salts (bile salt synthesis increases if ileum is removed)
63
Q

intrahepatic function of bile salts

A

keep cholesterol in solution, if precipitated –> gallstones

64
Q

intracolonic functions of bile salts

A
  • inhibit sodium transport and water absorption
  • excess bile salt in colon –> diarrhea
65
Q

intra-intestinal function of bile salts

A
  • act as detergent and help form stable emulsions
  • assist in transport of fat and fat-soluble vitamins
66
Q

regulation of bile flow

A
  • choleretics: cause liver to secrete more bile
  • cholagogues: increase gall bladder emptying –> increase release of concentrated bile saltes
67
Q

law of reciprocal activity

A
  • if gall bladder contracts –> sphincter of Oddi relaxes
  • if gall bladder relaxes –> sphincter of Oddi contracts
68
Q

crypt cells

A

secret succus entericus: alkaline fluid, pH:7.5-9, isotonic, 3L/day, lacks digestive enzymes

69
Q

villi cells

A
  • do not secret fluid
  • completes digestion
  • absorb nutrients and fluids
  • enterocyte: synthesizes digestive enzymes that remains in the brush boarder
69
Q

colonic secretion

A
  • small volume
  • alkaline
  • lots of mucin for lubrication
  • no digestive enzymes
  • no absorption of nutrient
  • bacterial activity
70
Q

absorption

A

via:
- simple diffusion
- facilitated diffusion
- active transport
- pinocytosis
- osmosis
require adequate:
- digestion, site of absorption, transit time for absorption, co-factors and transporters
~ 7L in small intestine and 2L in colon per day

71
Q

GIT transit time

A
  • pharynx: < 1s
  • esophagus: seconds
  • stomach: minutes to hours
  • small intestine: hours
  • colon: hours to days

PHGY 210 (5 decks)

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