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The digestive system Flashcards

1
Q

why is chewing gum good for your teeth after a meal?

A
  • increase salivary secretion

- increase salivary amylase and material agents (lysozyme and IgA)

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2
Q

what is IgA?

A

he main immunoglobulin found in mucous secretions, including tears, saliva, sweat, colostrum and secretions from the genitourinary tract, gastrointestinal tract, prostate and respiratory epithelium.

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3
Q

why does your tummy grumble when you are hungry?

A
  • cephalic phase of digestion
  • gastric secretions and motility increased by
  • parasympathetic NS, gastrin, gherlin (the hunger hormone)
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4
Q

are there more cells or bacteria in your body?

A

bacteria

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5
Q

parts of the GI tract

A

oesophagus, stomach, small intestine (duodenum, jejunum, ilieum), large intestine (colon), rectum, anus

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6
Q

what is the role of the GI tract?

A

metabolise and digest/ferment carbohydrates and lipids

-synthesise vitamins (B and K)

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7
Q

How is vitamin B12 absorbed within the GI system?

A

vitamin B12 is ingested in protein form, it must first undergo a proteolytic cleavage in the stomach or duodenum where it will bind to an R-binder and enter into the duodenum for further cleavage.
-Vitamin B12 then enters the blood bound to another binding protein, transcobalamin, the complex is known as holotranscobalamin (Active B12). The majority of vitamin B12(70-80%) in blood is bound to haptocorrin and only a minor proportion (20-30%) is bound to transcobalamin.

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8
Q

How can a lack of B12 lead to anaemia?

A
  • Pernicious anaemia…specific type of anaemia that restults from the impaired absorption of vitamin B12 in the small intestine.
  • Vitamin B12 is structurally complex essential nutrient involved in many biological processes, including nervous system function and red blood cell formation.
  • Patients with this type of anaemia exhibit neurological symptoms such as muscle weakness, numbness and tingling sensation aswell as the typical symptoms of anaemia.
  • (RBCs don’d develop normally due to lack of B vitamins (B12 and folate), leads to decreased RBCs… causes include lack of intrinsic factor, diet low in in B vitamins, decreased absorption of B vitamins… treatment is life long supplements).
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9
Q

why is anaemia?

A

a condition that occurs when the number of red blood cells/ the amount of haemoglobin found in them drops below normal.

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10
Q

how is anaemia diagnosed?

A

testing blood (Hb conc)

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11
Q

what does a deficiency in B12 lead to?

A

MACROCYTIC ANEMIA

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12
Q

how does a lack in B12 lead to anaemia?

A
  • Atrophic gastric muscoa fails to secrete normal secretions
  • lack of intrinsic factor (IF) from gastric glands
  • no binding of B12 to IF
  • B12 isn’t protected from digestion by GIT enzymes and doesn’t bind to receptor sites in cells of terminal ileum
  • failure to absorb B12 from GIT (without IF)
  • pernicious anaemia
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13
Q

where do you find the parietal cells and what do they release?

A
  • In the gastric pits of the fundus

- release intrinsic factor and HCl

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14
Q

where would you find chief cells and what do they release?

A

Fundus and pepsinogen

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15
Q

where would you find D cells and what do they release?

A

found in the stomach and intestine and they release somatostatin

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16
Q

where would you find G cells and what do they release?

A
  • deep in the pyloric gland of the stomach (antrum) (occasionally in the duodenum)
  • release gastrin
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17
Q

What are the different glands found in the cell wall of the stomach?

A
  • pyloric
  • fundic
  • cardiac
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18
Q

Where is the funds in the stomach?

A

at the top

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19
Q

where is the body in the stomach?

A

the middle

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20
Q

where is the pyloric antrum in the stomach?

A

The bottom

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21
Q

Where would you find chief and parietal cells?

A

in the funds and the body

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22
Q

where would you find G and D cells?

A

In the pyloric antrum (and duodenum)

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23
Q

what do cardiac glands secrete and where would yo find them?

A

Mucus, near the neck

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24
Q

what do funcdic glands secrete?

A

HCl

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25
Q

what do pyloric glands secrete?

A

gastrin

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26
Q

What is gastric acid primarily released in response to?

A

proteins arriving in the stomach

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27
Q

how can the Parasympathetic NS increase gastric acid?

A

via gastrin

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28
Q

look at the diagram for stomach acid secretions

A

…

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29
Q

Stomach motility- which was does the peristaltic wave travel?

A

peristaltic wave travel towards the antrum (bottom) mixing the food

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30
Q

How long does gastric emptying take?

A

1-3hours depending on the nature of the food ingested

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31
Q

what opens to allow small amounts of chyme out of the stomach?

A

the pylorus

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32
Q

how is gastric motility regulated?

A

neurally and humorally

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33
Q

how is gastric motility regulated neurally?

A
  • mostly enteric reflexes, plus autonomic
  • stimulatory-parasympathetic
  • inhibitory- sympathetic
34
Q

where does the humoral response for the gastric motility stem from?

A

duodenum

35
Q

what is the stimulatory and inhibitory hormones in the humoral response for gastric motility?

A

Stimulatory- motilin

Inhibitory- secretin, CCK and somatostatin

36
Q

what does gastrin in the stomach do?

A

Gastrin is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid. The secretion of gastrin is stimulated by food arriving in the stomach.

37
Q

what does secretin in the stomach do?

A

Secretin is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the secretion of bile in the liver.

38
Q

what does Cholecystokinin (CCK) do with gastric motility?

A

Cholecystokinin (CCK) is in the duodenum and stimulates the release of digestive enzymes in the pancreas and the emptying of bile from the gall bladder.

39
Q

what does motion do in gastric motility?

A

Motilin is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.

40
Q

what does somatostatin do in the stomach motility?

A

exerts an inhibitory effect on the parietal cells, decreases stomach acid production and by preventing the release of other hormones, including gastrin, secretin and histamine which effectively slows down the digestive process.

41
Q

How are proteins absorbed within the small intestine?

A
  • brush bearer enzymes, plus intracellular peptidase complete the job of digesting small peptides to amino acids
  • amino acids transported across the GI epithelium by Active transport?
42
Q

what is secondary active transport?

A

form of active transport across a membrane which couple the movement of an ion down its electrochemical gradient to the uphill movement of another molecule or ion against a conc gradient

43
Q

how are simple fats absorbed in the small intestines?

A

monoglycides aan fatty acids pass across GI epithelium by simple diffusion

44
Q

what do the hormones secretin and CCK promote?

A

pancreatic secretions

45
Q

what are bile salts recycled via?

A

enterohepatic circulation

46
Q

what is secreted in the bile?

A
  • bile salts and lecithin to assist digestion and facilitate absorption of fats
  • bicarbonate
  • waste material
47
Q

what is in pancreatic secretions?

A

digestive enzymes, targeting proteins, CHOs and fats

-bicarbonate

48
Q

what are bile and pancreatic secretions stimulated by?

A
  • chyme in duodenum (distension, acid, fats and osmolarity)

- hormones: CCK, secretin

49
Q

what are HDLs? and what are they involved in?

A
  • high density lipoproteins (good cholesterol)

- involved in reverse cholesterol transport and collects cholesterol from peripheral tissues and deliver it to the liver

50
Q

what are LDLs? and what are they involved in?

A
  • low density lipoproteins (bad cholesterol)
  • involved in transporting cholesterol from the liver to the hepatic portal tissue, where it can become deposited in blood vessel walls, oxidised and attract inflammatory cells leading to arteriosclerosis.
51
Q

what do statins do?

A

Inhibit the synthesis of cholesterol within the liver, and up regulate the LDL receptors in the liver

52
Q

what is HMG CoA?

A

the intermediate between Acetyl coA and Mevalonic acid in the synthesis of cholesterol

53
Q

how is the HMG CoA regulated in the short term? and long therm?

A

Short term: hormonal regulation
Long term:
-High intracellular cholesterol
-Decreases the transcription of HMG-CoA gene
-Decreases the synthesis of cholesterol

54
Q

what are the 5 basic functions of the digestive system?

A
  • Digestion
  • Absorption
  • motility
  • secretion
  • excretion
55
Q

what are the 4 major roles of the salivary secretions?

A
  • moisten and lubricate food (bolus)- mucus
  • initiate digestion of polysaccharide and lipids
  • dissolve food
  • antibacterial actions (IgA + lysozyme)
56
Q

what is salivary secretions controlled by?

A

autonomic nervous system

57
Q

what type of muscle makes up the oesophagus?

A

-upper 1/3 striated
-middle 1/3 mixture
-lowest 1/3 smooth
…voluntary action initially then becomes reflex

58
Q

where does 90% of nutrient absorption occur?

A 
small intestine
(absorption occurs in the first 1/4- duodenum and jejunum)
59
Q

which enzymes break down proteins?

A

Trypsin, chymotrypsin, elastase and carboxypeptidate

60
Q

what breaks down fats?

A

lipases

61
Q

what breaks down polysaccharides?

A

amylase

62
Q

what breaks down nucleic acids?

A

Ribonuclease and deoxyribonuclease

63
Q

what do the liver and gall bladder secrete?

A

bile (bile salts, lecithin (phospholipid) bicarbonate ions, cholesterol, bile pigments, trace metals

64
Q

what happens in the large intestine?

A

reabsorption of water, absorption (10%) of nutrients (lack of villi, and doesn’t produce enzymes, provides lubrication for faecal material)

  • absorptoni of important vitamins produced by bacteria
  • storage and compaction of faecal matter (prior to defecation)
65
Q

what role does the enteric nervous system play in the digestive system?

A
  • can act independently of CNS
  • Myenteric plexus- controls mainly smooth muscle contraction/tone
  • Submucosal plexus- control mainly GI secretions and blood flow
66
Q

what role does the autonomic NS play in the control of the digestive system?

A

VAGUS NERVE (parasympathetic)- increases motility and secretions (rest and digest)

sympathetic- decrease motility and secretions (fight or flight)

67
Q

why are the 3 routes for gastrointestinal reflexes?

A

1) regulation of one area of enteric nervous system to another region
2) extrinsic nerves prevertebral sympathetic ganglia
3) vagus nerve via sensory neurones to brain and brain stem

68
Q

what are the 3 phases of gastric acid secretion and stomach emptying?

A
  • cephalic
  • gastric
  • intestinal
69
Q

what happens in the cephalic phase?

A
  • initated by smell/ taste

- mediated via enteric and parasympathetic NS

70
Q

what happens in the gastric phase?

A
  • initiated in the stomach
  • mediated via the enteric and Parasympathetic NS and the hormone gastrin
Initiated in stomach:
distension, protein
Gastrin mediated:
released by local and neural control
action both direct and indirect (via histamine)
71
Q

what happens in the intestinal phase?

A

-initiated in duodenum
-mainly inhibitory hormones
-promoted continued digestion within small intestine
-Stimulatory:
protein in duodenum gastrin release
Inhibitory:
lowers pH, fat in duodenum
secretin, GIP, CCK …gastrin inhibition
somatostatin: direct action and via gastrin

72
Q

Cephalic phase

A
  • parasympathetic and submucosal plexus stimulates:
  • mucus (mucous cells), pepsinogen (chief cells) and HCl production (parietal cells)

-gastrin (G cells), GI hormone stimulates gastric secretions

73
Q

gastric phase

A

-the arrival of food in the stomach leads to marked secretions and contractility
-histamine - stimulates parietal cells to release more HCl (response to parasympathetic NS and gastrin)
CNS- vagus nerve ( parasympathetic)

74
Q

what does Histamine do?

A

released from enterochromaffin-like (ECL) cells (paracrine mechanism) in response to ACh and gastrin

75
Q

what does somatostatin do?

A

Inhibits secretion of CCK, gastrin, secretin, GLIP – thus inhibiting a number of functions – also inhibits HCL secretion – released in response to HCL (neg feedback) – released from D-cells in pyloric gland and duodenum

76
Q

what happens in the intestinal phase?

A

Hormones that inhibit gastric acid secretions/ gastric emptying… CCK, secretin, somatostatin

77
Q

what does CCK do?

A

Cholecystokinin (CCK) – released by I cells in small intestine, stimulates pancreatic secretions & gall bladder contraction

78
Q

what does secretin do?

A

released by s cells in response to low pH, stimulates pancreatic and bile secretions

79
Q

what does somatostatin do?

A

inhibits everything, released by D cells

80
Q

Motilin

A

peptide hormone – m cells of duodenum and jejunum, stimulates gastric and intestinal motility – released in response to fat, pH and neuronal stimulation

81
Q

Factors inhibiting stomach emptying

A
  • Duodenal distension
  • Irritation of duodenum mucosa
  • Lipids, FA, Protein and CHO (moderately)
  • Acidity – pH <3.5-4
  • Increase in osmolarity – indicative of the entrance into the duodenum of large volumes of soluble partially-digested particles

ICS (11 decks)

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