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Semester 3 - Gastrointestinal > Session 1 - Introduction to the GI system > Flashcards

Session 1 - Introduction to the GI system Flashcards

1
Q

What is the overall function of the gastrointestinal system?

A
  • Secretion
  • Digestion
  • Motility
  • Absorption
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2
Q

What are the qualities of the products of digestion?

A
  • Sterile
  • Neutral
  • Isotonic
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3
Q

What solutions does the process of digestion create?

A
  • Small sugars
  • Amino acid and small peptides
  • Lipids in very small particles
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4
Q

Define absorption

A

• Specific active or passive uptake of nutrient molecules, water and electrolytes

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5
Q

Give three waste products of the GI tract

A
  • Residue from food
  • Gut debris
  • Materials secreted from liver
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6
Q

What needs to happen to food for digestion to occur?

A
  • Disrupted physically to release large molecules

* Broken down chemically to release small molecules

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7
Q

Why do ingested foods need to be stored?

A

• We can eat much faster than we can digest

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8
Q

Outline the overall process of digestion

A
  • Initial physical disruption
  • Ingestion & transport to storage
  • Initial chemical disruption & creation of suspension – forming chyme
  • Disinfection
  • Controlled release of chyme
  • Dilution and neutralisation of chyme
  • Completion of chemical breakdown
  • Absorption of nutrients and electrolytes
  • Final absorption of water and electrolytes,
  • Producing faeces for controlled excretion
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9
Q

List the two mechanisms involved in physical disruption of food

A

Mastication

Saliva

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10
Q

Outline the functions of saliva

A
  • Protects mouth
  • Lubricates food
  • Starts digestion
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11
Q

Give four ways in which saliva protects the mouth

A
  • Wet - maintains mucosae
  • Bacteriostatic
  • Alkaline - protects teeth
  • High calcium - protects teeth
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12
Q

What does saliva initially digest?

A

• Sugars

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13
Q

What is food called after it has been physically disrupted?

A

• Bolus

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14
Q

Where does storage, initial disruption and disinfection take place?

A

Stomach

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15
Q

How is chyme produced in the stomach?

A

• Action of acid, enzymes and agitation

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16
Q

Where does dilution and neutralisation of chyme take place?

A

• Duodenum and jejunum

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17
Q

Why does dilution take place?

A

• To ensure that the chyme is of the same osmotic potential as the small intestine

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18
Q

What do enzymes from pancreas and intestine do?

A
  • Cleave peptides to amino acids
  • Cleave polysaccharides to monosaccharaides
  • Breakdown and re-form lipids
  • Break down nucleic acids
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19
Q

How does absorption of nutrients and electrolytes take place?

A
  • Intestine has large SA due to brush border
  • Epithelial cells absorb small molecules - some actively, some passively
  • Often coupled to sodium absorption
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20
Q

What are absorbed nutrients taken into?

A

• Hepatic portal circulation

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21
Q

Where does final absorption of water and electrolytes occur?

A

• Large intestine

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22
Q

Where does faeces accumulate?

A

• Descending and sigmoid colon

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23
Q

How does defecation occur?

A
  • Faeces propelled into rectum

* Controlled relaxation of sphincters and expulsion of faeces occurs

24
Q

What is the function of the stomach?

A
  • Relaxes to accommodate food
  • Rhythmical contraction
  • Secretes acid and proteolytic enzymes to break down tissues
  • Disinfects bolus
25
Q

Outline the process of receptive relaxation

A
  • Stomach strongly contracted between meals
  • Relaxes as bolus enters
  • Prevents a rise in pressure of the stomach
26
Q

What takes place in the duodenum and jejunum?

A
  • Water drawn in from ECF
  • Bile added to chyme
  • Pancreas, liver and intestinal secretions (enzymes and bile acids)
  • Liver and pancreas secrete alkali and neutralise acid
27
Q

How is duodenum adapted to the highly concentrated chyme it receives from the stomach?

A
  • Wall permeable to water

* Draws water in to dilute contents

28
Q

Outline the four layers of alimentary canal

A
  • Mucous membrane
  • Submucosa
  • Muscularis externae
  • Serosa
29
Q

What makes up the mucous membrane?

A
  • Lining epithelium
  • Connective tissue
  • Thin layer of smooth muscle
30
Q

What makes up the submucosa?

A
  • Fibroelastic tissue with
  • Vessels
  • Nerves of the submucosal plexus
  • Leucocytes
  • Fat cells
31
Q

What makes up the muscularis externa?

A

An inner circular layer

Outer longitudinal layer

32
Q

What lies between the two layers of the muscularis externae?

A

• Myenteric plexus

33
Q

What is the serosa?

A

• A thin outer covering of connective tissue

34
Q

What is endoscopy?

A

• A long, thing tube which allows direct visual examination, biopsy sampling and therapeutic treatment of the gastro-intestinal tract

35
Q

What is nasendoscopy?

A

• Allows visualisation of the nose, mouth and pharynx

36
Q

What structure marks the beginning of the oesophagus?

A

• Cricopharyngeal sphincter

37
Q

Where does the diaphragm cuff the oesophagus, and why is this clinically relevant?

A
  • At the oesophagogastric mucosal junction

* This relationship may be disrupted by a hiatus hernia, which allows the stomach to herniate into the thorax

38
Q

Outline the venous drainage of the oesophagus

A

• Drains into the left portal system via the left gastric vein

39
Q

How is the oesophagus adapted to rapid transport?

A

• Streamlined structure which minimises friction

40
Q

What are the longitudinal ridges of the stomach called?

A

• Rugae, increase SA

41
Q

Where is gastric ulceration most common?

A

• Lesser curve at the angulus

42
Q

What is the normal maximal fluid contents of the gut?

A
  • 14L

* 1kg food, 1.5L saliva, 2.5L gastric secretions, 9l of water and alkali

43
Q

How are the contents of the gut removed?

A
  • Small intestine absorbs 12.5l
  • Large intestine absorbs 1.35
  • 150g faeces expelled
44
Q

What happens if the balance between secretion and absorption altered?

A
  • Considerable loss of water and electrolytes, mostly from body fluids
  • Rapid dehydration and electrolyte disturbance
45
Q

Name three control systems of the gut

A
  • Neural
  • Paracrine
  • Endocrine
46
Q

Why are three overlapping control systems needed in the gut?

A

• Motility and secretion need precise control

47
Q

What is the somatic motor used for in the gut?

A

• Ingestion (chewing) and excretion (defecation)

48
Q

What is the most significant neural control system of the gut?

A

• Autonomic (specifically parasympathetic) control

49
Q

What do post ganglionic neurones form in the gut?

A

• Plexuses

50
Q

What does the “gut nervous system” control?

A

• Coordinates secretion and motility

51
Q

What enteric nervous system of the gut made up of?

A

• Two nerve plexuses which may act independently of CNS and be modified by both branches of the ANS

52
Q

What is paracrine secretion?

A

• Chemical messengers diffuse locally

53
Q

Name a chemical messenger secreted via the paracrine method

A

Histamine

54
Q

Give three factors the endocrine system controls in the digestive system

A
  • Stomach acid
  • Alkali secretion from liver and pancreas
  • Enzyme secretion
55
Q

What type of structure do gut hormones share?

A

• All peptide derived

56
Q

What are the two groups of gut hormones?

A
  • Gastrin group

* Secretin group

Semester 3 - Gastrointestinal (28 decks)

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