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Physiology Of Body Systems > Digestive System > Flashcards

Digestive System Flashcards

1
Q

What are the requirements of the digestive system in order to function?

A
  • motility to mix and deliver food to appropriate sit at appropriate rate
  • digestion in the appropriate site
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2
Q

What are the two types of digestive motility?

A
  • propulsive motility to deliver

- non-propulsive motility to mix

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3
Q

What is metering?

A

Delivering a portion of a semi-digested material to the next stage

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4
Q

What are the phases of digestion

A
  1. Inter digestive - little activity
  2. Cephalic - mostly nerves
  3. Gastric - hormones and nerves
  4. Intestinal - mostly hormones
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5
Q

What are the functions of the GIT?

A
  • secretion
  • mixing and metering
  • absorption
  • excretion
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6
Q

What does saliva contain?

A
  • mucous: lubricant
  • amylase: carbohydrate breakdown
  • lysozyme: antibiotic
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7
Q

What activates the salivary glands when eating?

A

Parasympathetic nerves and chewing

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8
Q

Enteric nervous system

A
  • intrinsic control
  • myenteric plexus and submucosal plexus
  • has its own pacemaker
  • can be activated by parasympathetic or turned off by sympathetics (extrinsic Control)
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9
Q

What are the effector systems of the GIT?

A

Muscles, secretory epithelium, exocrine and endocrine cells

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10
Q

What are the sensory systems of the GIT?

A

Stretch receptors and chemo receptors

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11
Q

What does the stomach secrete?

A

HCl
Pepsinogen
Mucous with bicarbonate
Intrinsic factor

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12
Q

HCl in the stomach

A

Breakdown protein, activates pepsinogen

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13
Q

Pepsinogen in the stomach

A

Converted to pepsinogen (proteolytic enzyme)

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14
Q

Mucous in the stomach

A

Protects the stomach

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15
Q

Intrinsic factor in the stomach

A

Binds to vitamin B12 for absorption

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16
Q

Retropulsion

A

Not the stomach contracting

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17
Q

Areas of the stomach

A
  1. Fundus: extra storage area
  2. Body oxyntic mucosa: acid secreting
  3. Antrum: powerful muscular area
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18
Q

What are the cells of the stomach?

A

Mucous cells
Parietal cells
Chief cells
ECL cells

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19
Q

What do mucous cells secrete?

A
  • mucous and bicarbonate rich secretion

- protects surface from abrasion and gastric acid

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20
Q

What do parietal cells secrete?

A
  • HCl

- intrinsic factor

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21
Q

HCl in the stomach

A
  • gastric germicidal barrier
  • denatures protein, assisting absorption (unravels proteins)
  • solubilises Fe3+, assists absorption
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22
Q

What do the chief cells secrete?

A
  • pepsinogen pro-enzyme

- converted to pepsinogen after exposure to acidic gastric contents

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23
Q

What does HCl and pepsinogen produce?

A

Peptide fragments

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24
Q

Structure of a parietal cell

A
  • lots of canaliculi (finger like projections)
  • large surface area
  • lots of proton pumps (H+, K+ transport) pumping into a chamber
  • high levels of mitochondria, one H+ uses 1 ATP
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25
Q

Where are the H+/K+ pumps in interdigestive phase?

A

In vesicles, activates my parasympathetics to be incorporated into caniculi
Also activated by histamine and gastrin

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26
Q

Gastric acid release in the cephalic phase

A
  • major inputs: smell, sights taste

- parasympathetic stimulations to parietal and chief cells (preparatory acids and enzymes, increases efficiency)

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27
Q

What does ECL cell stand for?

A

Enterochromaffin-like cell

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28
Q

What do G-cells produce?

A

Gastrin

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29
Q

What do ECL cells produce?

A

Histamine

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30
Q

Where are g cells located?

A

Antrum

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31
Q

How do G cells detect food?

A

Have a sensory surface, detect gastric amino acids

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32
Q

What activates g cells?

A

Parasympathetics and amino acids

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33
Q

What activates ECL cells?

A

Parasympathetics and gastrin

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34
Q

Summary of gastric acid release in the cephalic phase

A
  • parasympathetic activation to parietal cell, G cell and ECL cell
  • parietal cell activated by parasympathetics to produce H+ ions
  • G cell activated by parasympathetics to produce gastrin
  • ECL activated by parasympathetics to produce histamine
  • gastrin activates ECL cell
  • parietal cell gets gastrin and histamine
35
Q

What is the main cause of H+ secretion in the cephalic phase?

A

Histamine

36
Q

How is pepsinogen released the the cephalic phase?

A

The same as the parietal cell

37
Q

How much of gastric secretions occur at the cephalic phase?

A

30%

38
Q

What happens at the start of the gastric phase?

A
  • stomach fills up

- smooth muscle dilates to prevent pressure build up

39
Q

What does filling of the stomach do?

A
  • increased sensory feedback to brain (stretch receptors in gastric wall of antrum)
  • increased sympathetic output to parietal, ECL and G cells
40
Q

How much of gastric secretions occurs in the gastric phase?

A

60%

41
Q

What cell is responsible for an overproduction of acid due to beer/wine?

A

G Cell

42
Q

Why is the release of acid synergistic?

A

Need all 3 (ACh, gastrin and histamine) for secretion, most potent is histamine

43
Q

What are the drugs used for reflux?

A
  • H2 receptor inhibitors

- proton pump inhibitors

44
Q

What does the antra somatostatin cell do?

A

Makes sure the stomach pH doesn’t get too high,

Detects low pH and cell process turn of G cell

45
Q

What activates the last 10% of stomach acid secretion?

A

Food entering the duodenum

46
Q

Nervous reflexes between the duodenum and antrum

A
  • receptors in duodenal walls and plexuses in duodenal and antrum walls
  • triggered by distension or irritant material
  • slows gastric emptying and inhibits gastric secretion
  • extrinsic control is also involved
47
Q

What do pancreatic acinar cells produce?

A
  • proteases
  • lipases
  • amylases
  • nucleic acid enzymes
48
Q

What do intercalated duct cells produce?

A

Bicarbonate

49
Q

What are the exocrine cells of the pancreas?

A
  • acinar cells

- intercalated duct cells

50
Q

What are the controls of pancreatic secretions?

A
  • vagus parasympathetic stimulations: enzymes and bicarbonate
  • cholecystokinin (CCK): enzymes only
  • secretin: bicarbonate only
51
Q

What stimulates cholecystokinin?

A
  • digested fat and proteins: long chain fatty acids
  • CCK releasing factor
  • H+
52
Q

What inhibits CCK release?

A
  • trypsin in lumem

- somatostatin

53
Q

CCK in the inter digestive phase

A
  • no protein in the lumen
  • CCK RF and trypsin are continuously released in the the duodenal lumen
  • trypsin breakdown CCK RF
54
Q

CCK in the intestinal phase

A
  • trypsin breakdown protein
  • CCK RF triggers CCK release by enterocytes
  • triggers release of pancreatic enzymes
55
Q

How does CCK act on the pancreas?

A

Binds to receptors on vagal afferent nerve

Vagal efferent activates the pancreas

56
Q

What are the other actions of CCK?

A
  • stimulates gall bladder contraction
  • relaxes sphincter of Oddi
  • inhibits gastric secretions and emptying
57
Q

Where is secretin secreted from?

A

Enterocytes

58
Q

What stimulates secretin secretion?

A

Acid from stomach

59
Q

How does secretin work?

A
  • activates receptors on intercalated ducts cells (predominant)
  • activates receptors on afferent vagal nerve
60
Q

What are bile salts made from?

A

Cholesterol

61
Q

Where is bile produced and stored?

A

Produced in the liver and stored in the gall bladder

62
Q

What cell makes bile?

A

Hepatocyte

63
Q

How does the recycling of bile work?

A

Bile is reabsorbed from the jejunum
Moves to one side of the hepatocyte
Then delivered to the other side by a duct system

64
Q

What do bile salts do?

A

When fat globules are broken down by the churning of the intestine, the bile salts surround the smaller globules to prevent hem from rejoining with each other

65
Q

Where does most absorption occur?

A

Jejunum

66
Q

What is absorbed in the ileum?

A

Bile salts, B12

67
Q

What is the main function of the ileum?

A

Reserve absorptive area

68
Q

What is the glycocalyx?

A

Network of proteins qnd collagen with enzymes attached that breaks food down when it comes in contact with it

69
Q

How are fats absorbed?

A
  1. Monoglycerides diffuse into the enterocytes
  2. Triglycerides resynthesised
  3. Coated with a protein (chylomicron)
  4. Exocytosed
  5. Enter lymphatic system
  6. Re-enter the bloodstream near the heart
70
Q

What makes up sucrose?

A

Glucose-fructose

71
Q

What makes up lactose?

A

Glucose-galactose

72
Q

Where can’t alpha amylase cut?

A
  • monosaccharide before or after a bend
  • in between a bend
  • the last glucose in a chain
73
Q

What remains after digestion by alpha-amylase?

A
  1. Sucrose
  2. Lactose
  3. Maltose
  4. Maltotriose
  5. Alpha-limit dextrins
74
Q

How is lactose broken down?

A
  • lactase breaks down into glucose and galactose

- transported by SLGT1 transporters

75
Q

How is sucrose broken down?

A
  • by sucrose into glucose and fructose

- fructose taken up by GLUT5, glucose taken up by SLGT1

76
Q

What else can sucrose break down?

A

Moltose and moltotriose int glucose

77
Q

How are alpha-limit dextrins broken down?

A
  • by isomaltase into maltose and moltotriose
78
Q

What transports all monosaccharides from the enterocytes to the interstitial space?

A

GLUT2 transporters

79
Q

How are peptides and oligoproteins digested?

A

By surface peptidases
AA1, AA2 and AA3 can all be transported into the cell
All are broken down into amino acids once inside the enterocytes by dipeptidases or tripeptidases

80
Q

How are salts and and water absorbed?

A
  • Na+ glucose co transporter
  • increase osmotic pressure
  • water moves through the cell and between cells
  • creates a + charge, chloride moves through cells
81
Q

What are the main functions of the colon?

A
  • desiccation: colon extracts more water and salt from lumen contents
  • storage of fractal matter before defacation
  • contains a large and diverse population of bacteria
82
Q

What are the constituents of faeces?

A
  • indigestible substances
  • dead cells
  • bacteria
  • water
83
Q

What is the function of the bacteria in the colon?

A
  • digest dietary fibre eg. Lignin svia intestinal bacteria, glucose produced can be absorbed
  • digest dead enterocytes
  • synthesis vitamin K
  • raise colonic acidity levels, increases absorption of calcium, magnesium and zinc

Physiology Of Body Systems (7 decks)

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