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Nutritional physiology > Nutritional physiology > Flashcards

Nutritional physiology Flashcards

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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

A

exocrine chief cells

Autocatalytic reaction

21
Q

what is the gastric mucosal barrier

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

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

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

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
Q

what is bile composed of

A

bile salts + lecithin + cholesterol + bilirubin

26
Q

what is the purpose of the biliary system in the liver

A
  • Emulsify large fat molecules in GI tract – micelle formation

Detoxification

Hormone secretion

27
Q

what is the purpose of the biliary system in the gallbladder

A

Store and concentrate bile 10x – water and electrolytes absorbed

28
Q

explain the duct system flow of bile (bile pathway)

A
  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
Q

explain the control of bile secretion and release

A

 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
Q

what is enterohepatic circulation

A

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
Q

list some non-digestive functions of the liver

A

Detoxification

Vitamin D activation

Nutrient storage – glycogen & lipids, vitamins

Metabolic processing
o interconversion of nutrients (e.g. GNG)

32
Q

explain the cells involved in the liver structure

A

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
Q

what are the digestive functions of the liver

A

Immediate metabolic processing of products from sugar/protein digestion

Fat digestion bypasses hepatic portal system to circulation – delivered by lymph system

33
Q

what are the 4 major cells types in the small intestines mucosa

A

Absorptive (enterocytes, on microvilli. Contain digestive enzymes and absorption_

Goblet cells (produce mucous – protects)

Granular cells (defence)

Endocrine (regulatory hormones – secretin)

34
Q

explain segmentation in terms of motility in the small intestine

A

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
Q

what is the migrating motility complex

A

Peristaltic contractions removing any last debris to prep for next meal

Occurs in fasted state

3 phases

Regulated by motilin

36
Q

what are the 2 phases of small intestinal digestion

A

luminal phase

membrane phase

37
Q

explain the luminal phase of small intestine digestion

A

By enzymes from pancreas

Pancreatic amylase

Pancreatic proteolytic enzymes

Pancreatic lipase

Bile salts

38
Q

explain the membrane phase of small intestine digestion

A

By brush border enzymes (remain bound)
1. disaccharidases
2. aminopeptidases

39
Q

what are the modifications in the small intestine which suit it for absorption

A

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
Q

what is the ileocecal juncture

A

barrier between small and large intestine

ileocecal valve and sphincter prevent back movement

prevents SI contamination

41
Q

explain blood supply to the liver

A

Enters via hepatic artery (oxygenated from heart)

Enters via hepatic portal vein (venous from GI tract)

Exits via hepatic vein

42
Q

how to bile and blood flow through the liver

A

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
Q

list some of the unique characteristics of smooth muscle

A

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
Q

outline the process of how calcium activates smooth muscle contraction

A

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
Q

what is the difference between phasic and tonic muscle contraction

A

Phasic: rapid activity in bursts

Tonic: Resting contraction e.g. in sphincters

46
Q

compare multi unit vs. single unit muscle cells

A

Single unit: myogenic
 Self regulated
 Can be phasic or tonic

Multi unit:
 Phasic: (controls in bursts)
 neurogenic (under ANS control)

47
Q

what are the main receptors present in the GI tract

A

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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