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GASTROINTESTINAL > Week 1 > Flashcards

Week 1 Flashcards

1
Q

Define digestion

A

Digestion is the chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable units.

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2
Q

Define absorption

A

Absorption is the transfer of products of digestion from the digestive tract to the blood or the lymph

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3
Q

What are the four layers of the digestive tract wall

A

Mucosa (inner layer)
Submucosa,
Muscularis Externa,
Serosa (outer layer)

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4
Q

What effect does circular muscle and longitudinal muscle contraction have?

A

Contraction of circular muscle causes the lumen to become narrower and longer
Contraction of longitudinal muscle causes the intestine to become shorter and fatter.

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5
Q

How are smooth muscle cells in the GI tract arranged?

A

The cells are arranged in sheets and coupled by gap junctions

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6
Q

Explain the synchronous wave in smooth muscle

A
  • Spontaneous activity is triggered by pacememaker cells (modulated by nerves and hormones)
  • This activity causes slow waves which cause hundreds of cells contract at the same time
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7
Q

What is meant by slow waves?

A

Rythmic membrane depolarisation and depolarisation that spreads from cell to cell via gap junctions

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8
Q

What is the function of ICCs and where are they located?

A

These are the pacemaker cells which trigger electrical activity.
They are spread between the smooth muscle cells
(located between the longitudinal and circular muscle layers in the submucosa)

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9
Q

In a smooth muscle cell action potential, what is the upstroke and downstroke mediated by?

A

The upstroke is mediated by voltage-activated calcium channels
The downstroke is mediated by voltage activated potassium channels

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10
Q

What 3 stimuli affect whether slow wave amplitude reaches threshold?

A

Neuronal stimuli
Hormonal stimuli
Mechanical stimuli

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11
Q

In terms of basic electrical rhythm, what is the frequency of slow waves in the; stomach, small intestine and large intestine?

A 
Stomach - 3 per min 
Duodenum - 12 per min 
Ileum - 8 per min 
proximal colon - 8 per min
distal colon - 16 per min
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12
Q

In the ENS system, what is the purpose of the myenteric plexus and the submucosa plexus

A

Myenteric plexus - Regulates motility and sphincters

Submucous plexus - Modulates epithelia and blood vessels

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13
Q

Which is more important in terms of innervation of the G.I tract; parasympathetic or sympathetic?

A

PARASYMPATHETIC

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14
Q

What effects do parasympathetic have on the G.I tract?

A

Increase secretions
Increase blood flow
Increase smooth muscle contraction
Relax sphincters and the stomach

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15
Q

What effects do sympathetics have on the G.I tract?

A

Increase sphincter tone
Decrese motility
Decrease secretions
Decrease blood flow

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16
Q

Where do parasympathetic and sympathetic fibres synapse?

A

PARASYMPATHETIC - Ganglion cells

SYMPATHETIC - Prevertebral ganglia

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17
Q

What is peristalsis?

A

A wave of relaxation followed by contraction that proceeds along the gut in aboral direction

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18
Q

What do circular and longitudinal muscles do in peristalsis?

A

Circular muscles contract

Longitudinal muscles relax

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19
Q

What is segmentation?

A

The churning and mixing which is caused by contractions of the circular muscle layer

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20
Q

How many sphincters are there in the G.I tract?

A

6

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21
Q

Name the 6 sphincters in the G.I tract

A 
Upper oesophageal 
Lower oesophageal 
Pyloric 
Ileocaecal valve 
Internal anal 
External anal
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22
Q

Which two sphincters have skeletal muscle and are therefore usually under voluntary control?

A

Upper oesophageal sphincter

External anal sphincter

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23
Q

What are the 3 major phases in swallowing?

A

Oral
Pharyngeal
Oesophageal

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24
Q

What diseases can obesity contribute to?

A 
T2DM 
Hypertension 
Osteoarthritis 
NAFLD (fatty liver disease) 
Dementia 
Stroke 
E.T.C
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25
Q

What part of the brain is responsible for neural control of factors influencing energy intake and body weight?

A

HYPOTHALAMUS

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26
Q

What is CCK and when is it secreted?

A

Cholecystokinin

- Secreted in the duodenum and jejunum in proportion to meals

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27
Q

What is Ghrelin and when is it produced?

A

Grehlin is a hunger signal

Its level increase before eating and decrease after eating

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28
Q

What are the two hormones which inform the hypothalamus to alter energy balance?

A

LEPTIN and INSULIN

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29
Q

Outline the present drug therapy/management for obesity

A 
ORLISTAT
- Inhibits pancreatic lipase 
- Reduces fat absorption in the S.I
BARIATRIC SURGERY
- Gastric by-pass surgery 
- Restricts calorie intake
- Substantial weight loss 
- Can resolve T2DM
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30
Q

Define glycogenesis and glycogenolysis

A

GLYCOGENESIS - Synthesis of glycogen to from glucose

GLYCOGENOLYSIS -Breakdown of glycogen to form glucose

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31
Q

What is gluconeogenesis?

A

GLUCONEOGENESIS - Generation of glucose from non-carbohydrate precursors

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32
Q

What is the primary source of glucose overnight?

A

Gluconeogenesis

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33
Q

What are the 4 enzymes involved in glycogenesis?

A

Hexokinase
Phosphoglucomutase
UDP-glucose pyrophosphorylase
Glycogen synthase

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34
Q

What are the 3 enzymes involved in glycogenolysis?

A

Glycogen phosphorylase
Phosphoglucomutase
Glucose-6-phosphatase

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35
Q

What does Insulin do?

A

It stimulates glycogenesis by stimulating glycogen synthase

It inhibits glycogenolysis by inhibiting glycogen phosphorylase

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36
Q

What does glucagon do?

A

It stimulates glycogenolysis by stimulating glycogen phosphorylase
It inhibits glycogenesis by inhibiting glycogen synthase

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37
Q

What are 3 of the main precursors for gluconeogenesis?

A

Lactate
Amino Acids
Glycerol

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38
Q

What is meant by a saturated or an unsaturated fatty acid?

A

Saturated have no double bonds
Unsaturated have a double bond

N.B polyunsaturated have multiple double bonds

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39
Q

What is lipolysis

A

The breakdown of stored fat to produce free fatty acids and glycerol
Catalysed by lipases

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40
Q

What can high levels of ketone bodies cause?

A

Severe acidosis which impairs tissue function, particularly in the CNS

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41
Q

What is lipogenesis

A

Synthesis of lipids

Reductive process in which electrons are required

42
Q

Where is the main site for amino acid degradation?

A

THE LIVER

43
Q

What potentially toxic substance can amino acid breakdown release?

A

Ammonia and ammonium ions

44
Q

What are the 3 steps in the synthesis of urea?

A

TRANSAMINATION
DEAMINATION
UREA CYCLE

45
Q

What are the important points about the disease; phenylketonuria?

A

Degradation of phenylalanine is blocked, causing it to accumulate in all body fluids.
Can cause severe mental problems.
Can be controlled by an adequate diet.

46
Q

What are the three major salivary glands?

A

PAROTID
SUBMANDIBULAR
SUBLINGUAL

47
Q

Which part is the functional unit of a salivary gland and what does this part consist of?

A

The salivon

  • a secretory acinus
  • an intercalated duct
  • a striated duct
48
Q

The composition of saliva varies according to flow rate. What happens to bicarbonate and potassium concentrations with altering rate?

A

Bicarbonate concentration increases as rate increases

Potassium concentration decreases as rate increases

49
Q

Explain the unconditional and conditional reflexes involved in the control of salivary secretion

A

UNCONDITIONAL - simple - due to presence of food in the mouth
CONDITIONAL - acquired - due to thinking/smelling food

50
Q

What is the effect of parasympathetic and sympathetic stimulation on saliva production?

A 
PARASYMPATHETIC causes ;  
Increased blood flow to the glands 
Increased fluid flow 
Increased contraction of myoepithelial cells
SYMPATHETIC causes; 
decreased blood flow to the glands

both cause Increased secretion of a-amylase

51
Q

What are the 5 gastric secretions of the oxyntic mucosa?

A 
HCL 
Pepsinogen 
Intrinsic factor 
Histamine 
Mucus
52
Q

What are the 3 gastric secretions of the pyloric gland area?

A

Gastrin
Somatostatin
Mucus

53
Q

What is the function of gastrin?

A

Stimulates HCL secretion

54
Q

What is the function of somatostatin?

A

Inhibit HCL secretion

55
Q

What is the role of intrinsic factor?

A

It binds vitamin B12, allowing absorption in the terminal ileum

56
Q

What are the three phases of gastric secretion?

A

Cephalic
Gastric
Intestinal

57
Q

Name 4 classes of drugs that influence acid secretion

A

NSAIDs e.g aspirin
Histamine receptor antagonists
Proton-pump inhibitors
Muscarinic receptor antagonists

58
Q

What effect do prostaglandins have on the mucosa?

A

Reduce acid secretion
Increase mucus and bicarbonate secretion
Increase mucosal blood flow

59
Q

Are ingested lipids soluble or insoluble?

A

Insoluble

60
Q

How much of the daily energy requirement is provided by lipids?

A

55%

61
Q

What substance emulsifies lipids? What is the purpose of this process?

A

Bile salts

- emulsifying large lipid droplets to small droplets increases their surface area for enzymatic hydrolysis

62
Q

Which enzyme hydrolyses TAGs to monoglycerides and free fatty acids? (this is the main lipid digestive enzyme)

A

Pancreatic lipase

63
Q

Which substance present in pancreatic juice neutralises stomach acid to provide a suitable pH for enzyme action?

A

HCO3-

64
Q

Which hormone is released when there is fat present in the duodenum and what does secretion of this hormone cause?

A

CCK

- causes bile salts o be secreted in bile from the gall bladder

65
Q

Where are bile salts synthesised and stored?

A

Synthesised in the liver and stored in the gall bladder

66
Q

What kind of pH is required for the process of emulsification?

A

Neutral/ Slightly alkaline

67
Q

What 2 adverse effects can occur if there is failure to secrete bile salts?

A
  • Lipid malabsorption (steatorrhoea - fat in faeces)

- Vitamin deficiency due to failure to absorb lipid vitamins

68
Q

What are micelles and where are they formed?

A

Small lipid particles - formed in the duodenum

69
Q

What factor determines the fate of a fatty acid on entering a cell?

A

Its length

70
Q

Which protein is involved in cholesterol absorption and transport?

A

NPC1L1

71
Q

Which drug prevents the action of NPC1L1 for cholesterol absorption and can therefore be used for hypercholesterolaemia?

A

Ezetimibe

72
Q

Which mode of transport is used in calcium absorption for low vs high concentrations of calcium in chyme?

A

Low concentrations - Active transport

High concentrations - Passive transport

73
Q

What two substances regulate calcium absorption?

A

1,25-dihydroxyvitamin D3 (calcitriol)

Parathyroid hormone

74
Q

Is Ferrous(Fe2+) or Ferric (Fe3+) the absorbable form of iron?

A

Ferrous (Fe2+)

75
Q

What is the main storage form of iron within the cell?

A

Ferratin

76
Q

What hormone is released from the liver when iron levels in the body are too high?

A

Hepcidin

77
Q

What must all carbohydrates first be broken down into for digestion?

A

monosaccharides

78
Q

What are the two main enzymes involved in the digestion of carbohydrates?

A

a-amylase

ogliosaccharidases

79
Q

List some causes of lactose intolerance

A
  • Lack of the ‘lactate persistence allele’
  • Damage to the S.I e.g coeliacs disease/crohn’s disease
  • Congenital
80
Q

Signs and symptoms of lactose intolerance

A 
Bloating 
Abdominal pain 
Flatulence
Loose stools 
Diarrhoea
81
Q

Which sodium-glucose transporter works in the small intestine?

A

SGLT1

82
Q

Fructose, unlike galactose and glucose, is not a substrate for SGLT1, what is its alternative transport mechanism?

A

Fructose is transported by GLUT5

83
Q

Which GLUT is responsible for EXIT of all monosaccharides from a cell? Across which membrane does this occur?

A

GLUT2

- basolateral membrane

84
Q

Which two substances must proteins be digested to for efficient absorption?

A

Oligopeptides

Amino acids

85
Q

Which two substances are important for digestion in the stomach?

A

HCL (denatures proteins)

Pepsin (cleaves proteins in to peptides)

86
Q

Which group of enzymes are important for digestion in the duodenum?

A

Pancreatic proteases

87
Q

What is the difference between endopeptidases and exopeptidases?

A

ENDOpeptidase - cleave peptide bonds in the centre of the chains
EXOpeptodase - split off amino acids from the ends of the chains

88
Q

Amino acids exit enterocytes across the basolateral membrane by which transporters?

A

Na+ independent transporters

89
Q

HCL is a gastric gland secretion, from which area of the gastric glands is it secreted and what is its function?

A

Secreted from parietal cells in the oxyntic mucosa.

  • It activates pepsinogen to pepsin
  • Denatures proteins and kills microorganisms
90
Q

Enterochromaffin like cells are cells in the oxyntic mucosa of the gastric glands. What do these cells secrete?

A

Histamines

stimulates HCL secretion

91
Q

Chief cells are cells within the oxyntic mucosa area of the gastric glands. What do these cells secrete?

A

Pepsinogen

92
Q

Which two secretions come from the parietal cells in the oxyntic mucosa of the gastric glands?

A

HCL and Intrinsic factor

93
Q

Which two cell types make up the pyloric gland area?

A

D cells and G cells

94
Q

What is secreted from D cells in the pyloric gland area of the gastric glands and what is the function of this secretion?

A

Somatostatin

- Inhibits HCL secretion

95
Q

What is secreted from G cells in the pyloric gland area of the gastric glands and what is the function of this secretion?

A

Gastrin

- Stimulates HCL secretion

96
Q

a-amylase is an endoenzyme, meaning it can break down internal linkages but not terminal linkages. What are the products of carbohydrate digestion by a-amylase?

A

Linear glucose oligomers and a-limit dextrins

97
Q

Ogliosacchardies cleave terminal linkages in carbohydrates to farm what product?

A

GLUCOSE

98
Q

Pepsin is a protease enzyme (cleaves proteins into peptides). Is it an endopeptidase or an exopeptidase?

A

ENDOPEPTIDASE

99
Q

Give an example of an endopeptidase enzyme and an example of an exopeptidase enzyme

A

ENDOpeptidase - trypsin

EXOpeptidase- procaroxypeptidase

100
Q

How are oligopeptides transported across the apical membrane?

A

H+ oligopeptide co-transporter PepT1

GASTROINTESTINAL (13 decks)

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