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Nutritional physiology > Nutritional physiology > Flashcards

Nutritional physiology Flashcards

Just try to keep up (48 cards)

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1
Q

what is the upper GI tract

A

 Mouth
 Oesophagus
 stomach

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2
Q

what is the middle GI tract

A

 duodenum
 jejunum
 ileum

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3
Q

what is the lower GI tract

A

caecum
colon
rectum

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4
Q

what are the accessory organs of the GI tract

A

 salivary glands
 gallbladder
 exocrine pancreas

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5
Q

what are the 4 layers of tissue lining the GI tract

A
  1. mucosa – inner, contacts foods, specialised for secretion/absorption
  2. submucosa – blood and nerve supply. Connective tissue. Has submucosal plexus
  3. muscularis – circular muscle layer and longitudinal muscle layer. Mixing and propulsion. Has myenteric plexus
  4. serosa – outer CT, simple squamous. Provides lubrication.
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6
Q

what are the 4 basic digestive processes

A
  1. motility – movement of intake of food
  2. secretion
  3. digestion – chemical breakdown
  4. absorption – mostly in SI
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7
Q

what are the 4 ways that digestive function is regulated

A
  1. autonomic smooth muscle
  2. intrinsic nerve plexus
  3. extrinsic nerves
  4. gastrointestinal hormones
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8
Q

explain how autonomic smooth muscle regulated digestive function

A

exhibits spontaneous rhythmic cycles of depolarisation/repolarisation

called SLOW WAVE POTENTIAL (smooth muscle only)

generated by Cajal cells – control frequency of contractions

fluctuations in membrane potential bringing membrane closer/further away from threshold

(different from action potentials all or nothing)

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9
Q

what is the enteric nervous system

A

network of submucosal and myenteric plexuses

3 major ENS neurobns:
1. Sensory
2. Moror
3. Interneurons

Major neurotransmitters:
1. Acetylcholine
2. Norepinephrine
3. Serotonin

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10
Q

how do GI hormones regulate digestive function

A

Regulate digestive function by acting on smooth muscle and glands, liver and pancreas

Secreted by endocerine GI cells

Excititary of inhibitory effect

 Gastrin – stomach/antrum
 Secretin: SI cells
 CCK: SI cells

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11
Q

what are the 2 main functions of the mouth

A

mastication

secretion

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12
Q

explain the function of mastication

A

4 muscle pairs in mandible

Reflex from medulla

Consciously initiated/stopped

Function: mechanical breakdown, mix with saliva (solvent for taste), taste

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13
Q

describe secretion in the mouth

A

3 pairs of Salivary glands

Starch digestion, swallowing, antibacterial & oral hygiene, neutralise acids

1-2L/day

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14
Q

what are the 2 main functions of the oesophagus

A

swallowing

secretion - protective mucus)

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15
Q

explain swallowing in the oesophagus

A

Voluntary

Unstoppable

Bolus stimulates pharyngeal pressure receptors – relayed to swallowing centre in medulla

Stimulates reflex activation of muscles

Involuntary stage has 2 stages:
1. Pharyngeal – elevation of soft pallet/pharynx, upper sphincter opens and closes after bolus. Epiglottis seals as this happens. Swallowing centre inhibits breathing centre.

  1. Oesophageal – peristaltic smooth muscle contractions. Primary wave by swallowing centre, subsequent waves by intrinsic n. plexus.
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16
Q

what is the function of sphincters in digestive process

A

Pharyngoesophageal sphincter

Skeletal muscles prevents air form entering GI tract during breathing
 Gastroesophageal sphincter
 Smooth muscle
 Prevents gastric reflux

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17
Q

list some functions of the stomach

A

Storage – hold bolus for chemical processes

Protein digestion

Food  chyme

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18
Q

explain the process of HCl secretion

A
  1. CO2 diffuses into parietal cell from blood
  2. CO2 combines with water in enzyme catalysed reaction carbonic anhydrase. Forms carbonic acid
  3. Dissociates into bicarbonate ion + H+
  4. Bicarbonate ion into bloodstream. Antiporter in plasma membrane swaps bicarbonate ion for chloride ion
  5. Hydrogen-potassium pumps moves H+ into gastric gland duct and K+ in parietal cell
  6. Chloride ions diffuse into gastric gland duct
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19
Q

what cells secrete HCl in the stomach?

A

parietal cells

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20
Q

what cells secrete pepsinogen in the stomach

Study These Flashcards
A

exocrine chief cells

Autocatalytic reaction

21
Q

what is the gastric mucosal barrier

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A

Mucus cells physically protect cell from acidity

Mucosal secretions alkaline to protect cells and neutralise acid

HCl (H+) is impermeable to mucosal cells

Tight junctions between cells

22
Q

explain the pancreas’ role in digestion

Study These Flashcards
A

Endocrine function:
Pancreatic islets – alpha/beta

Exocrine: function
* Pancreatic juice:
* Aqueous alkaline solution (duct cells)
* Digestive enzymes (acinar cells)
o Proteolytic enzymes
o Pancreatic amylase
o Pancreatic lipase

23
Q

explain the pathway for bicarbonate ion production in the pancreas

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A
  1. H2O and CO- combine through enzyme anhydrase  carbonic acid
  2. Carbonic acid dissociates to H+ + bicarbonate ions
  3. H+ swapped for Na+ by antiporter in blood
  4. Bicarbonate ions transported to intercalated ducts in exchange for Cl-
  5. Sodium ions and H2O follow bicarbonate ions into ducts
  6. Ions and water move through intercalated ducts to interlobular ducts
24
Q

how are pancreatic secretions controlled

Study These Flashcards
A

Vagus nerve (parasympathetic) stimulates pancreatic juice secretion

Secretin from duodenum stimulates increased release of secretin. Secretin is carried by blood back to pancreas, pancreatic duct cells are stimulated to release bicarbonate rich pancreatic juice

Duodenum releases Cholecystokinin – stimulated juice release

25
what is bile composed of
bile salts + lecithin + cholesterol + bilirubin
26
what is the purpose of the biliary system in the liver
* Emulsify large fat molecules in GI tract – micelle formation Detoxification Hormone secretion
27
what is the purpose of the biliary system in the gallbladder
Store and concentrate bile 10x – water and electrolytes absorbed
28
explain the duct system flow of bile (bile pathway)
1. Hepatic ducts (carry bile from liver lobes) combine to common hepatic duct 2. Common hepatic duct + cystic duct combine = common bile duct 3. Common bile duct + pancreatic duct = hepatopancreatic ampulla 4. hepatopancreatic ampulla empties bile and pancreatic secretions into duodenum at major duodenal papilla 5. accessory pancreatic duct empties pancreatic secretions into duodenum at minor duodenal papilla
29
explain the control of bile secretion and release
 Vagal nerve (parasympathetic) contracts smooth muscle gallbladder to release bile  Secretin stimulates bile secretion (endocrine)  CCK stimulates gallbladder contraction  Bile salts stimulate bile secretion
30
what is enterohepatic circulation
Reabsorption of bile salts Bile salts reabsorbed at terminal ileum Through hepatic portal vein to liver 5% bile salts lost in faeces, 95% recycled.
31
list some non-digestive functions of the liver
Detoxification Vitamin D activation Nutrient storage – glycogen & lipids, vitamins Metabolic processing o interconversion of nutrients (e.g. GNG)
32
explain the cells involved in the liver structure
Hepatocytes – performs metabolic and secretory Arranged in hexagon structure Hepatic lobules – each has a triad (trio of vessels) Kupffer cells – phagocytes of RBCs and WBCs Sinusoidal endothelial cells – endocytosis and secretion
32
what are the digestive functions of the liver
Immediate metabolic processing of products from sugar/protein digestion Fat digestion bypasses hepatic portal system to circulation – delivered by lymph system
33
what are the 4 major cells types in the small intestines mucosa
Absorptive (enterocytes, on microvilli. Contain digestive enzymes and absorption_ Goblet cells (produce mucous – protects) Granular cells (defence) Endocrine (regulatory hormones – secretin)
34
explain segmentation in terms of motility in the small intestine
Segmented sections of smooth muscle contraction Greater frequency in beginning of SI Basoelectrical rhythm initiated by SI pacemaker cells (but can be modified by local factors, nerve factors, hormonal factors) e.g. o Local distention  duodenal segmentation o Gastrin  empty ilium segmentation  gastroileal reflux o Extrinsic nerves  modify strength: sympathetic/parasympathetic
35
what is the migrating motility complex
Peristaltic contractions removing any last debris to prep for next meal Occurs in fasted state 3 phases Regulated by motilin
36
what are the 2 phases of small intestinal digestion
luminal phase membrane phase
37
explain the luminal phase of small intestine digestion
By enzymes from pancreas Pancreatic amylase Pancreatic proteolytic enzymes Pancreatic lipase Bile salts
38
explain the membrane phase of small intestine digestion
By brush border enzymes (remain bound) 1. disaccharidases 2. aminopeptidases
39
what are the modifications in the small intestine which suit it for absorption
mucosal lining – villi/microvilli circular folds in lining membrane bound enzymes Rapid turnover of mucosal lining  New cells continuously produced  Migrate up, push older cells into lumen to be cleaned out  Cells adapt during migration: increase enzyme conc. and absorptive capacity transepithelial transport: transport of substance through epithelium:  substances must pass through epithelial cell to interstitial fluid to be absorbed
40
what is the ileocecal juncture
barrier between small and large intestine ileocecal valve and sphincter prevent back movement prevents SI contamination
41
explain blood supply to the liver
Enters via hepatic artery (oxygenated from heart) Enters via hepatic portal vein (venous from GI tract) Exits via hepatic vein
42
how to bile and blood flow through the liver
Hepatic ducts: carry bile from liver Hepatic veins: return processes molecules and waste to circulation via heart Hepatic artery: delivers oxygen and blood metabolites Hepatic portal vein: nutrients from intestines
43
list some of the unique characteristics of smooth muscle
Resting length is shorter than optimal Stress relaxation (sudden stretch can increase tension, then muscle rapidly adjusts) e.g. in gallbladder to accommodate large volumes. Slow contraction speed – crossbridges stay attached for longer. Uses less ATP Versatile energy supply – can use anaerobic or aerobic respiration
44
outline the process of how calcium activates smooth muscle contraction
Excitation --> APs --> rise calcium (calcium voltage gated channels) --> calcium calmodulin complex forms --> activates myosin light chains kinase --> phosphorylation of cross bridges in thick filament
45
what is the difference between phasic and tonic muscle contraction
Phasic: rapid activity in bursts Tonic: Resting contraction e.g. in sphincters
46
compare multi unit vs. single unit muscle cells
Single unit: myogenic  Self regulated  Can be phasic or tonic Multi unit:  Phasic: (controls in bursts)  neurogenic (under ANS control)
47
what are the main receptors present in the GI tract
Acetylcholine: PARASYMPATHETIC control. muscarinic receptors. E.g G protein receptor pathway Adrenaline/noradrenaline: SYMPATHETIC control. alpha (1 & 2) and beta receptors --> Alpha 1 receptors: excitatory response --> Alpha 2 receptors: inhibitory response

Nutritional physiology (3 decks)

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