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Gi System > GI physiology 2 > Flashcards

GI physiology 2 Flashcards

1
Q

Describe the function of the fundus?

A
  • The fundus is responsible for storage in the stomach
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2
Q

Describe the function of the body?

A
  • Storage
  • HCL
  • Mucous
  • Pepsinogen
  • Produciton of intrinsic factor
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3
Q

Describe the function of the antrum?

A
  • Mixing/Grinding

- Gastrin

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4
Q

What are chief cells responsible for?

A
  • Secretion of pepsinogens
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5
Q

What are parietal cells responsible for?

A
  • Secretion of HCL and Intrinsic factor
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6
Q

What is the cephalic phase of HCL secretion?

A

The cephalic phase of HCL secretion
- Sight smell of food triggers vagus nerve in turn increasing acentycholine and gastrin production

  • More gastrin production increases parietal cell secretion
  • Gastrin and ACh acts on ECL producing histamine
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7
Q

Name the chemicals that act on parietal cells and increase HCL production

A
  • Gastrin
  • Histamine
  • Prostoglandins
  • Acentylcholine
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8
Q

Describe the gastric phase of HCL production?

A
  • Distension of the stomach acts on vagal reflex’s producing ACh
  • Peptides in lumen acts on G cells, producing gastrin
  • Gastrin and ACh act on ECL producing histamine
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9
Q

Describe the mechanism’s stopping gastric secretion?

A

Cephalic
- Stopping eating - decreases vagal activity
Gastric
- Decrease of pH stops gastrin production
Intestinal phase
- Acid in duodenum
Secretin released in response lowers Gastric sectrion
CCK is released also lowers gastric secretion
-

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10
Q

What are enterogastrones and what do they do?

A

Enterogastrones hormones released from gland cells in duodenum, that prevent acid secretion and reduce gut motility
Examples, CCK, secretin

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11
Q

Why is pepsinogen a zymogen and how is it activated?

A
  • Zymogen is an inactive precursor
  • Pepsinogen is stored as a zymogen to stop cellular digestion
  • Pepsinogen is changed to pepsin in a pH enviroment lower than 3
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12
Q

Describe the role of gastric mucus?

A
  • Produced by surface epithelial cells and mucous neck cells

- Has a cytoprotective role and protects the mucosa from damage

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13
Q

What parts of the stomach are involved in peristaltic waves?

A

Body and Antrum

  • Body produces weak contraciton, thin muscle
  • Antrum produces strong contraction, thick muscle
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14
Q

What produces gastric peristaltic waves?

A
  • Peristaltic rhythm 3/mins - generated by pacemaker cells in longitudinal muscle
  • ## Slow waves, spontaneous depolarisation/depolarisation
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15
Q

What Increases motility?

A
  • Gastrin increases contraction

- Distension of stomach wall decreases contraction

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16
Q

What decreases motility?

A

Fat/acid/amino acid/hypertonicity causes inhibition of motility

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17
Q

Where is bicarbonate secreted from?

A

Brunners gland in submucosal cells

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18
Q

What does acid in the duodenum trigger?

A

Long vagal and short ENS reflex’s HCL secretion
Release of secretin from S cells
Secretin from pancreas and liver

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19
Q

What is the endocrine function of the pancreas?

A

Islets of langerhans: Produce insulin, glucagon and samostatin which controls secretion of insulin and glucagon

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20
Q

What is the exocrine function of pancreas?

A

Consists of ducts and acinar lobules
Secretion of bicarbonate by duct cells
Secretion of digestive enzymes by acinar cells

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21
Q

What are zymogens and where are they stored?

A
  • Zymogens are inactive granules, they are stored as inactive in order to prevent autodigestion
  • They are used in order to prevent autodigestion
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22
Q

What is trypsinogen and where is it converted?

A
  • Trypsinogen converts to trypsin when actived by enterokinase
  • Enterokinase is bound to the brush border of duodenal enterocytes
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23
Q

What is trypsin?

A

Trypsin converts all other zymogens to active forms

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24
Q

Name the pancreatic enzymes

A

Proteases - Cleaves peptide bonds
Nucleases - Cleaves DNA/RNA
Elastases - Collagen digestion
Phospholipases - Phospholipids to fatty acids
Lipases - Triglycerides to fatty acids and glycerol
Amylase - Starch and 1,4 glycosidic bonds

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25
Q

Why is bicarbonate secreted?

A

In response to secretin secretion

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26
Q

Why is secretin secreted?

A

In response to acid in duodenum

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27
Q

Why are zymgoens secreted?

A

In response to to CCK

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28
Q

Why is CCK secreted?

A

In response to fat/amino acid in the duodenum

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29
Q

What is the function hepatocytes of the liver?

A
  • Synthesis of bile
  • Lecithin synthesis
  • Cholesterol synthesis
  • Bile pigment production from from heamogloblin
  • ## Toxic metals detoxified in liver
30
Q

What are bile pigements?

A

Breakdown products from old damaged erythrocytes

31
Q

What is the predominant bile pigement?

A
  • Predominant bile pigment is bilirubin
32
Q

Bilirubin extracted by blood and secreted into bile will give what coloured bile?

A

Yellow bile

33
Q

Bilirubin that has been modified by bacterial enzymes will give what colour?

A

Brown pigment (feaces)

34
Q

Reabsorbed bilirubin excreted in urine will give what colour?

A

Yellow urine

35
Q

What are bile acids synthesised from?

A

Cholesterol

36
Q

Before secretion, what are bile acids conjugated with?

A

Tuarine or glycine to increase solubility

37
Q

What controls the release of bile into the duodenum?

A

Sphincter of oddi triggered by CCK

38
Q

What are the effects of secretin produced by acid in the duodenum?

A
  • Decrease in gastric emptying
  • Decrease in gastric secretion
  • Increase HCO3 production in bile duct
  • Increase HCO3 production in Pancreas
  • Increase HCO3 production in lungs
39
Q

What are the effects of CCK production caused by fat/amino acids in the duodenum?

A
  • Decrease in gastric emptying
  • Increase in pancreatic enzyme section
  • Galbladder contraction, sphincter of oddi relaxation
40
Q

What are the functions of the duodenum and length of the duodenum?

A
  • Gastric acid neutralisation
  • Digestion
  • Iron absorption
  • Shortest of small intestine, 25cm
41
Q

What are the functions of the jejunum and length of the jejunum

A
  • Nutrient absorption 95%

- Middle length, 2/5 of total length

42
Q

What are the functions of the ilium and the length of the ileum?

A
  • Na/Cl absorption, Chyme dehydration

-

43
Q

Rank the highest absorbing surface area to the lowest

A
  • Microvilli - Highest absorbing
  • Villi
  • Circular folds
  • Intestine as a cylinder - Lowest absorbing
44
Q

What is villi responsible for absorbing?

A

Absorbs

  • NaCl
  • Monosacharides
  • Peptides
  • Vitamins
  • Fat
  • Minerals
  • Water
45
Q

What are crypt cells responsible for secreting?

A

Secrete water and Cl

46
Q

What chemical is involved in the active transport and absorption?

A

Sodium coupled active transport is used to absorb the carbohydrates, fats, vtiamins etc

47
Q

How much H20 is secreted into the intestinal lumen and what is this a consequence of?

A
  • 1500ml of H20 is secreted per day as a consequence of the secretion of Cl into the lumen
48
Q

Why is H2O secreted into the intestinal lumen?

A
  • Maintains luminal contents in liquid state
  • Promotes mixing in lumen with digestive enzymes
  • Acids nutrients presents to absorbing surface
  • Washes away potential injurious substances
49
Q

Describe segmentation and its function

A
  • Segmentation is most common during a meal
  • Contraction moves chyme up and down
  • Provides thorough mixing of stomach contents with digestive enzymes
  • Brings chyme into contact with absorbing surface
  • Segmentation produces slow migration of chyme towards the large intestine
50
Q

What generates segmentation contractions?

A
  • Initiated by depolarisation of the longitudinal muscle
    layer
  • Intestinal basic electrical rhythm (BER) produces oscillation in membrane potential
51
Q

What determines the strength of contraction?

A

Action potential frequency determines strength of contraction

52
Q

What determines the frequency of segmentation?

A

Frequency of segmention is determined by Basic electrical rhythm (BER)

53
Q

When is a bolus turned into Chyme?

A

After the acidity and digestive enzymes of the stomach act of the

54
Q

How does sympathetic/parasympathetic and the autonomic nervous system effect segmentation?

A
  • Sympathetic nervous system decreases contraciton
  • Parasympathetic increases contraction
  • Autonomic nervous system has no effect
55
Q

When does segmentation stop and peristalsis start?

A
  • Following the absorption of nutrients, segmentation stops and peristalsis starts
56
Q

What is MMC (migrating motility complex) and where does it start?

A
  • Its a pattern of peristaltic activity
  • It starts in the antrum of the stomach
  • MMC ends in the terminal ileum and another begins at it ends
57
Q

What causes the stop of MMC?

A
  • Arrival of food in the stomach
58
Q

What is the function of MMC?

A
  • Movement of undigested material down into the large intestine
  • Limit bacterial colonisation in small intestine
59
Q

What hormone is involved in the initation of MMC?

A

Motilin

60
Q

Describe the gastroileal reflex?

A
  • Opening of ileocaceal valve
  • Entry of chyme into large intestine
  • Distension of colon
  • Contraction of the ileoceacal valve
61
Q

Describe the muscle layer’s and epithelium of the colon?

A
  • The circular muscle layer in the colon is complete but the longitudinal is incomplete
  • Simple columnar epithelium in the large intestine
62
Q

Describe the anal canal

A
  • Between rectum and anus
  • Internal anal sphincter is smooth muscle
  • External anal sphincter is skeletal muscle
  • Stratified squamous epithelium
63
Q

Describe the role of the colon

A
  • Absorption of sodium from lumen into blood
  • Osmotic dehyrdation of water
  • ## Dehydration of chyme
64
Q

Describe the control of the anal sphincters

A

Internal anal sphincter - smooth muscle is under autonomic control
External anal sphincter - Skeletal muscle is under voluntary control

65
Q

Describe the defaecation reflex

A
  • Under parasympathetic control via the pelvic splachnic nerves
  • Contraction of rectum
  • Relaxation of internal anal sphincter and contraction of external anal sphincter
  • Increased peristaltic activity in colon
  • Pressure on external anal sphincter relaxes under voluntary control
66
Q

What causes diarrhea?

A
  • Pathogenic bacteria
  • Protozoans
  • Viruses
  • Toxins
  • Food
67
Q

What is the causes and consequences of constipation?

A
  • Causes of constipation is distension of the rectum

- No absorption of feacal material following long periods of retention

68
Q

Give examples of enterotoxigenic bacteria

A

Vibrio cholera, Escherichia coli

69
Q

What are the consequences of enterotoxigenic bacteria ?

A
  • Intestinal sodium chloride secretion causing massive H2O secretion
  • H2O secretion swamps absorptive capability of villus cells causing profuse watery diarrhoea
70
Q

What is the treatment of secretory enterotoxigenic bacteria diarrhea?

A
  • Sodium/glucose solution

- Oral rehydration therapy

71
Q

What triggers the defeacation reflex

A
  • Stretch receptors in the rectal wall activate parasympathetic nervous system

Gi System (16 decks)

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