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
2
Q
What are the two types of digestive motility?
A
- propulsive motility to deliver
- non-propulsive motility to mix
3
Q
What is metering?
A
Delivering a portion of a semi-digested material to the next stage
4
Q
What are the phases of digestion
A
- Inter digestive - little activity
- Cephalic - mostly nerves
- Gastric - hormones and nerves
- Intestinal - mostly hormones
5
Q
What are the functions of the GIT?
A
- secretion
- mixing and metering
- absorption
- excretion
6
Q
What does saliva contain?
A
- mucous: lubricant
- amylase: carbohydrate breakdown
- lysozyme: antibiotic
7
Q
What activates the salivary glands when eating?
A
Parasympathetic nerves and chewing
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)
9
Q
What are the effector systems of the GIT?
A
Muscles, secretory epithelium, exocrine and endocrine cells
10
Q
What are the sensory systems of the GIT?
A
Stretch receptors and chemo receptors
11
Q
What does the stomach secrete?
A
HCl
Pepsinogen
Mucous with bicarbonate
Intrinsic factor
12
Q
HCl in the stomach
A
Breakdown protein, activates pepsinogen
13
Q
Pepsinogen in the stomach
A
Converted to pepsinogen (proteolytic enzyme)
14
Q
Mucous in the stomach
A
Protects the stomach
15
Q
Intrinsic factor in the stomach
A
Binds to vitamin B12 for absorption
16
Q
Retropulsion
A
Not the stomach contracting
17
Q
Areas of the stomach
A
- Fundus: extra storage area
- Body oxyntic mucosa: acid secreting
- Antrum: powerful muscular area
18
Q
What are the cells of the stomach?
A
Mucous cells
Parietal cells
Chief cells
ECL cells
19
Q
What do mucous cells secrete?
A
- mucous and bicarbonate rich secretion
- protects surface from abrasion and gastric acid
20
Q
What do parietal cells secrete?
A
- HCl
- intrinsic factor
21
Q
HCl in the stomach
A
- gastric germicidal barrier
- denatures protein, assisting absorption (unravels proteins)
- solubilises Fe3+, assists absorption
22
Q
What do the chief cells secrete?
A
- pepsinogen pro-enzyme
- converted to pepsinogen after exposure to acidic gastric contents
23
Q
What does HCl and pepsinogen produce?
A
Peptide fragments
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
25
Where are the H+/K+ pumps in interdigestive phase?
In vesicles, activates my parasympathetics to be incorporated into caniculi
Also activated by histamine and gastrin
26
Gastric acid release in the cephalic phase
- major inputs: smell, sights taste
| - parasympathetic stimulations to parietal and chief cells (preparatory acids and enzymes, increases efficiency)
27
What does ECL cell stand for?
Enterochromaffin-like cell
28
What do G-cells produce?
Gastrin
29
What do ECL cells produce?
Histamine
30
Where are g cells located?
Antrum
31
How do G cells detect food?
Have a sensory surface, detect gastric amino acids
32
What activates g cells?
Parasympathetics and amino acids
33
What activates ECL cells?
Parasympathetics and gastrin
34
Summary of gastric acid release in the cephalic phase
- 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
What is the main cause of H+ secretion in the cephalic phase?
Histamine
36
How is pepsinogen released the the cephalic phase?
The same as the parietal cell
37
How much of gastric secretions occur at the cephalic phase?
30%
38
What happens at the start of the gastric phase?
- stomach fills up
| - smooth muscle dilates to prevent pressure build up
39
What does filling of the stomach do?
- increased sensory feedback to brain (stretch receptors in gastric wall of antrum)
- increased sympathetic output to parietal, ECL and G cells
40
How much of gastric secretions occurs in the gastric phase?
60%
41
What cell is responsible for an overproduction of acid due to beer/wine?
G Cell
42
Why is the release of acid synergistic?
Need all 3 (ACh, gastrin and histamine) for secretion, most potent is histamine
43
What are the drugs used for reflux?
- H2 receptor inhibitors
| - proton pump inhibitors
44
What does the antra somatostatin cell do?
Makes sure the stomach pH doesn’t get too high,
| Detects low pH and cell process turn of G cell
45
What activates the last 10% of stomach acid secretion?
Food entering the duodenum
46
Nervous reflexes between the duodenum and antrum
- 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
What do pancreatic acinar cells produce?
- proteases
- lipases
- amylases
- nucleic acid enzymes
48
What do intercalated duct cells produce?
Bicarbonate
49
What are the exocrine cells of the pancreas?
- acinar cells
| - intercalated duct cells
50
What are the controls of pancreatic secretions?
- vagus parasympathetic stimulations: enzymes and bicarbonate
- cholecystokinin (CCK): enzymes only
- secretin: bicarbonate only
51
What stimulates cholecystokinin?
- digested fat and proteins: long chain fatty acids
- CCK releasing factor
- H+
52
What inhibits CCK release?
- trypsin in lumem
| - somatostatin
53
CCK in the inter digestive phase
- no protein in the lumen
- CCK RF and trypsin are continuously released in the the duodenal lumen
- trypsin breakdown CCK RF
54
CCK in the intestinal phase
- trypsin breakdown protein
- CCK RF triggers CCK release by enterocytes
- triggers release of pancreatic enzymes
55
How does CCK act on the pancreas?
Binds to receptors on vagal afferent nerve
| Vagal efferent activates the pancreas
56
What are the other actions of CCK?
- stimulates gall bladder contraction
- relaxes sphincter of Oddi
- inhibits gastric secretions and emptying
57
Where is secretin secreted from?
Enterocytes
58
What stimulates secretin secretion?
Acid from stomach
59
How does secretin work?
- activates receptors on intercalated ducts cells (predominant)
- activates receptors on afferent vagal nerve
60
What are bile salts made from?
Cholesterol
61
Where is bile produced and stored?
Produced in the liver and stored in the gall bladder
62
What cell makes bile?
Hepatocyte
63
How does the recycling of bile work?
Bile is reabsorbed from the jejunum
Moves to one side of the hepatocyte
Then delivered to the other side by a duct system
64
What do bile salts do?
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
Where does most absorption occur?
Jejunum
66
What is absorbed in the ileum?
Bile salts, B12
67
What is the main function of the ileum?
Reserve absorptive area
68
What is the glycocalyx?
Network of proteins qnd collagen with enzymes attached that breaks food down when it comes in contact with it
69
How are fats absorbed?
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
What makes up sucrose?
Glucose-fructose
71
What makes up lactose?
Glucose-galactose
72
Where can’t alpha amylase cut?
- monosaccharide before or after a bend
- in between a bend
- the last glucose in a chain
73
What remains after digestion by alpha-amylase?
1. Sucrose
2. Lactose
3. Maltose
4. Maltotriose
5. Alpha-limit dextrins
74
How is lactose broken down?
- lactase breaks down into glucose and galactose
| - transported by SLGT1 transporters
75
How is sucrose broken down?
- by sucrose into glucose and fructose
| - fructose taken up by GLUT5, glucose taken up by SLGT1
76
What else can sucrose break down?
Moltose and moltotriose int glucose
77
How are alpha-limit dextrins broken down?
- by isomaltase into maltose and moltotriose
78
What transports all monosaccharides from the enterocytes to the interstitial space?
GLUT2 transporters
79
How are peptides and oligoproteins digested?
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
How are salts and and water absorbed?
- Na+ glucose co transporter
- increase osmotic pressure
- water moves through the cell and between cells
- creates a + charge, chloride moves through cells
81
What are the main functions of the colon?
- 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
What are the constituents of faeces?
- indigestible substances
- dead cells
- bacteria
- water
83
What is the function of the bacteria in the colon?
- 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
