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MPharm Year 2 MP220/221 > Normal Function of GI tract > Flashcards

Normal Function of GI tract Flashcards

1
Q

What happens when a drug is inside the body, and arrives at the site of action?

A

The drug binds to the receptors, usually on the outer membrane of the cells and this usually results in the activation of enzymes located within the cell

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2
Q

What are the 4 steps of drugs and how they act in the body?

A

Absorption, distribution, metabolism and excretion

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3
Q

Where are most receptors located and how do they work?

A

Receptors are typically found as integral membrane proteins at the plasma membrane - they recognise and bind to specific chemicals thereby invoking a biological response?

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4
Q

Receptor numbers can be…

A

Increased or decreased. This can happen in light of chronically high or low concentration of the agonist to optimise specificity.

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5
Q

What is affinity?

A

Affinity refers to the strength of binding to the receptor.

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6
Q

What is efficacy?

A

Efficacy refers to the intrinsic activity and how effectively a response is produced as a result of the binding.

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7
Q

What does an antagonist do?

A

It blocks the receptor from binding to the agonist - an antagonist has affinity to the receptors but does not exert efficacy.

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8
Q

Examples of signal transduction?

A
  1. Direct opening of ion channels
  2. Direct activation of an enzyme
  3. Indirect activation/ inactivation of enzyme or indirect opening/ closing of ion channel
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9
Q

How do ion channels get opened by agonists?

A

The agonist binds and causes a conformational change, leading to ion channel influx due to the channel opening.

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10
Q

Calcium is responsible for

A
  1. Muscle contraction
  2. Secretion
  3. Metabolism
  4. Neuronal excitability
  5. Cell proliferation
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11
Q

Calcium is a…

A

Secondary messenger (neither produced nor destroyed). It is moved between compartments and the effects are concentration dependant

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12
Q

Calcium acts via…

A

Activation of specific protein kinases, ion channels

Regulation of activity of many enzymes.

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13
Q

How does cell signalling affect the parietal cell?

A

Acetylcholine binds to the muscarinic acetylcholine receptor located on both the parietal cell and this results in the stimulation of acid secretion via the proton pump into the stomach.

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14
Q

Ranitidine acts at the…

A

Histamine receptors on parietal cells, to reduce gastric acid secretion.

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15
Q

Loperamide acts at the

A

Opioid receptors in the myenteric plexus - this results in reduced peristalsis and an increased tone of the anal sphincter

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16
Q

What is pharmaceutics?

A

The process of turning new chemical entity into a medication to be used safely and effectively. - It is also called the science of dosage form design

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17
Q

Medicines are

A

Drug delivery systems in normal terms - they are the same as drugs when there are no excipients in the drug formulation.

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18
Q

Why do medications sometimes need to be taken after meals?

A

Due to physiological differences between the stomach in both fasting and fed states.

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19
Q

What is the first pass effect?

A

This is where the drug has been ingested orally and due to the body perceiving the drug as a toxin, it is transported to the liver for elimination and around 50% of the drug is eliminated in the process.

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20
Q

Drug safety is dependant on…

A

its therapeutic index

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21
Q

At the molecular level, a drug target is a…

A

Biomacromolecule

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22
Q

What happens to COX when drugs like ibuprofen bind?

A

Drug binds to COX which prevents arachidonic acid from binding to COX and being converted to prostaglandins

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23
Q

What is the side effect of NSAID use

A

High prostaglandin levels increase mucosal thickness of the stomach wall, which protects it from acid degredation - non specific inhibition of COXwill result in the formation of an ulcer

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24
Q

Salbutamol is a

A

Beta-2 drug adrenoceptor-agonist which is able to mimic the affect of adrenaline and noradrenaline which is therefore able to dilate the airways

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25
Q

What structure of Cox enables the enzyme to perform its function?

A

The tertiary structure

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26
Q

Flurbiprofen binds in the COX active site, at a….

A

greater affinity than arachidonic acid.

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27
Q

The oral mucosa is

A

a major barrier to drug delivery

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28
Q

The gingival and palatal tissue are…

A

located on the gums and roof of the mouth and are keratinised/ non polar

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29
Q

The buccal and sublingual tissue are…

A

Non-keratinised and polar

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30
Q

Buccal delivery can be via:

A
  1. Sublingual membrane - delivered under the tongue and very fast
  2. Buccal membrane - delivery from the cheek and lip cavity - slower and better suited to control release
  3. Topical delivery from a “tablet” retained within the mouth
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31
Q

Absorption from the Buccal cavity avoids

A

First-pass metabolism which can affect the drug pharmacokinetics

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32
Q

A buccal drug delivery system must be designed to…

A

stick to the buccal surface - this “glue” is usually a polymer that adheres to a biological surface or to the mucosal surface (mucoadhesion)

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33
Q

Mucoadhesive glue should typically…

A

Become tangled in the glycoprotein surface of the cells, and bonds with glycoproteins

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34
Q

Physical entanglement of mucoadhesives will occur when…

A

The adhesive is a high Molecular weight and allows for hydration swelling

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35
Q

What is a solution?

A

A mixture of 2 or more components that from a single phase that is homogenous down to the molecular level

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36
Q

What is dissolution?

A

the transfer of molecules or ions from a solid state into solution

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37
Q

What is solubility of a substance?

A

The amount that goes into a solution when equilibrium is established between the solute in solution and the excess undisssolved substance

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38
Q

Dissolution is the..

A

rate limiting step in drug absorption

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39
Q

What is the Noyes whitney equation?

A

DM/DT = DA x (Cs-C)/h

DM/DT refers to the rate of dissolution of the drug particles
D= diffusion coefficient
A= Effective surface area of the drug particles
h = thickness of the diffusion layer
Cs= the saturated solubility
C = Concentration of bulk solubility

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40
Q

Explain how the dissolution process occurs when a solid drug particle is amongst a solution?

A

The molecule detaches from the solid, and diffuses across the diffusion layer, and then leaves the diffusion layer for well stirred bulk.

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41
Q

Which factors affect dissolution rates

A

-Surface area of undissolved solid - this can be affected by the size of solid particles, the total area increases as particle size reduces and more porous particles have a bigger surface area.
-Saturated solubility of solid - solubility in dissolution medium as well as temperature can affect this
-Concentration of solute (drug) in solution - can be affected by volume of dissolution medium
-Dissolution coefficient - affected by type of dissolution medium as well as viscosity
-thickness of boundary layer - affected by degree of agitation e.g. mixing.

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42
Q

If you reduce particle size, what happens to the rate of dissolution?

A

This increases the rate of dissolution as the surface area of each particle is higher.

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43
Q

If you decrease porosity, what happens to the rate of dissolution?

A

This decreases the rate of dissolution as it reduces the surface area for each particle

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44
Q

If you increase solubility of the drug, what happens to the rate of dissolution?

A

This increases the rate of dissolution as the drug is able to dissolve much faster.

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45
Q

If you decrease the diffusion coefficient what happens to the rate of dissolution?

A

This decreases the rate of dissolution - refer to equation.

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46
Q

Physiological factors affecting drug dissolution include

A

Stomach contents - affected by food, pH, and buffer capacity
GI Motility - affetcting the emptying and transit of the stomach contents, Gastrointestinal secretions, and co-administered fluids.

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47
Q

How does fat affect gastric emptying?

A

It delays gastric emptying, due to the fat in the duodenum causing the fundus to relax, lowering intragastric pressure. It increases the feeling of fullness for a longer timeframe.

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48
Q

Food can….

A

Affect drug absorption

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49
Q

The villus appears curved in the GI tract and this is so….

A

There is a greater surface area in the GI tract which allows for a greater level of absorption

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50
Q

The enteric nervous system is composed of…

A

The myenteric plexus and submucosal plexus.

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51
Q

How are the CNS and ENS connected?

A

Via the vagus nerve, the tenth cranial nerve that runs from your brain stem down to your abdomen - lo

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52
Q

What neurotransmitter is produced both in the gut and the brain?

A

Serotonin - and this is why antidepressants which raise brain serotonin levels may be ineffective at curing depression whereas proper dietary change can help.

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53
Q

Afferent Neurons are…

A

Sensory receptor neurons which carry nerve impulses away from receptors or sense organs and towards the central nervous system.

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54
Q

Efferent Neurons are…

A

nerves which carry impulses away from the central nervous system to effectors such as muscles or glands.

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55
Q

The enteric nervous system is located….

A

within the wall of the GI tract from the oesophagus to the anus.

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56
Q

What does the myenteric plexus do?

A

Largely motor in function influencing motor activity

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57
Q

What does the Meissner’s plexus do?

A

It is largely secretory, receiving signals from epithelium and stretch receptors influencing secretory activity.

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58
Q

How are nerve plexuses linked tio the CNS activated by the afferent fibres?

A

Either due to stretch or chemical stimulation

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59
Q

Which part of the nervous system stimulates gut motility and secretory activity?

A

Parasympathetic input stimulates gut motility and secretory activity

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60
Q

Which part of the nervous system inhibits muscle contraction in the GI?

A

Sympathetic nerves cause pre-synaptic inhibition of parasympathetic-induced contraction.

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61
Q

Segmentation is …

A

The mixing of food in the GI via circular muscle contraction

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62
Q

Peristalsis is…

A

concerned mainly with the propulsion of food along tract - this relies on longitudinal contraction and circular relaxation.

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63
Q

What is the ideal gut transit time?

A

The ideal gut transit time is anywhere between and 48 hours.

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64
Q

How can drugs affect gut transit time?

A

Some drugs have side effects due to their non-specific targeting and this may impact upon gut transit time.

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65
Q

Examples of drugs which can cause constipation are:

A

Antacids, anticholinergics, and antihypertensives

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66
Q

How do drugs affect gut transit times?

A

Opioid receptors are found on locations such as the myenteric plexus, which means medications such as loperamide can decrease peristalsis, and increased tone of the anal sphincter.

Tegaserod acts as a motility stimulant due to the activation of 5-HT4 receptors of the enteric nervous system

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67
Q

How much saliva on average is secreted per day?

A

1500ml

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68
Q

What does saliva contain?

A

Mucous to help lubricate food
Alpha amylase to initiate breakdown of carbohydrate
Lysozyme (antibacterial actions)

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69
Q

How is saliva formed?

A

The isotonic fluid is produced by acinar cells (which secretes electrolytes and water) - the fluid is then modified as it flows along the salivary duct - and the final composition depends upon flow rate and neuronal input.

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70
Q

Saliva secretion is primarily controlled by

A

The autonomic nervous system

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71
Q

The parasympathetic nervous system helps produce…

A

More watery saliva, rich in amylase and mucous. It also helps increase blood flow to the salivary glands

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72
Q

The sympathetic nervous system promotes….

A

Increased output of thicker mucous
Reduced blood flow to salivary glands
Overall effects a reduction in secretion of watery saliva

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73
Q

Swallowing has 2 stages - the…

A

Voluntary stage and pharyngeal stage

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74
Q

Absorption in the mouth is dependant on factors such as

A

Drug solubility in saliva
Passive diffusion - only small lipophillic molecules are well absorbed

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75
Q

Properties of the oral mucosa include

A
  1. Limited surface area (200cm squared)
  2. Passive diffusion of molecules
  3. There is a rich blood supply - resulting in a rapid onset of action with similar bioavailability to I-V formulation
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76
Q

Oral Ulcers

A

Usually clear up without treatment but can require anti-inflammatories and anti-microbial mouthwash to prevent infection

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77
Q

Oral Thrush can be caused by

A
  1. Over-use of antibiotics, poor immune system, underlying disease, smoking, dentures
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78
Q

Oral Thrush can be treated by

A

Using antifungal gel such as miconazole and/ or nystatin.

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79
Q

Medications which may cause tooth decay include:

A

Antacids - due to sugar and sweetener content
Pain medications - due to drying out mouth and hence erosion of the tooth enamel
Antihistamines - can block release of saliva, resulting in dry mouth.

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80
Q

What are the functions of the stomach?

A
  1. Temporary storage of food
  2. Mechanical digestion by stomach movements
  3. Chemical digestion of proteins
  4. Regulation of chyme into small intestine
  5. Secretion of intrinsic factor - essential for absorption of vitamnin B12
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81
Q

Food, when mixed with gastric juice forms…

A

CHYME!

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82
Q

Chyme passes through the pyloric sphinter to the….

A

Duodenum

83
Q

Which 3 types of cells together produce gastric juices?

A
  1. Zymogenic (chief/ peptic cells) - secrete pepsinogen
  2. Parietal (oxyntic) cells - secrete HCl and intrinsic factor
  3. Goblet (neck) cells - secrete mucous.
84
Q

What other cells are in the gastric glands apart from Zymogenic, parietal and goblet cells?

A

G cells - which secrete gastrin
Enterochromaffin (mast like) cells - secrete histamine
D cells - secrete somatostatin.

85
Q

Most parietal cells are found

A

In the lower body of the stomach, except from the area of the antrum

86
Q

Pepsin is only active

A

In the acidic environment - as it is then converted from pepsinogen by HCl

87
Q

Gastric lipase breaks down at pH

A

5-6

88
Q

Describe how stomach acid reaches the stomach lumen?

A
89
Q

What prevents the stomach from digesting itself?

A
  1. The mucosal barrier - tight junctions between mucosal epithelial cells prevents leakage of gastric juice onto underlying tissue
  2. Mucous secreted by epithelial/ goblet cells has higher pH, providing localised neutralisation and physical barrier to acid
  3. Prostaglandins increase mucosal thickness and stimulate bicarbonate production
90
Q

What are the 3 phases of gastric secretion?

A
  1. The cephalic phase - stimulated by sight, smell, taste, thought of food or low glucose levels
  2. The gastric phase - stimulated by stomach distension due to presence of food.
  3. The intestinal phase - stimulated by digested proteins/ fat in the duodenum - presence of fat or low pH in duodenum inhibits gastric secretion.
91
Q

How does the cephalic phase occur?

A

The medulla oblongata cause parasympathetic neruones via the vagus nerves to increase HCl and pepsin in the stomach.

92
Q

How does the gastric phase occur?

A

Stomach distension triggers the parasympathetic reflex leading to further HCl, pepsin and gastrin secretion

93
Q

How does the intestinal phase work to decrease gastric secretion?

A

Chyme entering the duodenum containing fat or enough HCl to lower the pH to below 2 will trigger inhibition of gastric secretion via three main routes:
1. Neuronal impulse sent to medulla to decrease parasympathetic stimulation of gastric glands
2. Local reflexes in gut wall lead to decreased secretion
3. Release of 3 local hormones, secretin, gastric inhibitory peptide, and cholecystokynin travel via the blood to the gastric glands and inhibit secretion.

94
Q

What does solubility refer to?

A

The amount of a substance that goes into a solution when equilibrium is established between the solute in solution and the excess (undissolved) substance

95
Q

Describe the solution process

A

Consider 3 phases:

  1. Drug molecule is removed from its crystal
  2. A cavity from the molecule is created in the solvent
  3. Drug molecule inserts into this cavity
96
Q

What does drug saturation refer to?

A

When a solution contains a drug at the limit of its solubility at any given temperature and pressure.

97
Q

Factors which affect solubility of drugs (i.e. the amount of drug which can be dissolved, not the rate of dissolution)

A
  1. Temperature
  2. Molecular Structure of the drug
  3. Nature of the solvent
  4. Crystal characteristics
98
Q

How does the surface area of the drug affect solubility?

A

Surface area of the drug molecule affects solubility because placing the solute molecule in the solvent cavity requires a number of solute-solvent contacts

99
Q

What functional groups yield greater levels of solubility?

A

Polar groups such as OH which are capable of hydrogen bonding give higher solubility

Non polar groups such as methyl groups or Halogens like chlorine are hydrophobic hence not very soluble

100
Q

What is the rate limiting step of drug absorption?

A

Dissolution

101
Q

What is LogP?

A

Log P is the partition coefficient designed to show a measure of lipophilicity/ hydrophilicity of drugs in their unionised form

P =[Concentration in non-aqueous phase]/ [concentration in aqueous phase]

102
Q

What does the LogP number suggest?

A

When LogP is more than 0, the drug molecule is lipophilic overall, and overall hydrophillic if less than 0

103
Q

Describe crystal structures?

A

Crystals contain highly ordered arrays of molecules and atoms held together by non-covalent interactions - these structures vary in size, number and kind of faces depending on the drug molecule itself.

104
Q

What is polymorphism in relation to crystals?

A

This is where molecules arrange themselves in different ways in the crystal - this however can alter the physical properties of the drug, an example of which is the ritonavir problem - the new polymorph which was discovered has a much reduced solubility.

105
Q

How does digestion occur in the stomach from a mechanical perspective?

A

Muscularis enables food to be churned - particularly in antrum where the muscle wall is thicker

Food is mixed with gastric juice to form chyme

Chyme is then passed through the pyloric sphincter to the duodenum

106
Q

How does digestion occur in the stomach from a chemical perspective

A

Proteins - broken down by pepsin (hydrolysing of proteins to form amino acids and to further stimulate amino acids) - (pepsin is only active in acidic form and is converted from pepsinogen via HCl)

Gastric Lipase breaks down fat at higher pH (5-6) - this initiates fat digestion and digestion of breast milk in infants

107
Q

How does salivary amylase work?

A

It acts on carbohydrates if pH is around 6 and hence is far less active in the acidic environment of the stomach

108
Q

What determines the force of stomach contraction and amount of gastric emptying?

A

Largely neuronal and hormonal input to the antral smooth muscle

109
Q

The rate of gastric emptying is influenced by:

A

The physical and chemical nature of contents of stomach/ intestine
- Distension of stomach increases antral contraction
- Increased gastrin levels increase antral contraction

110
Q

What does stomach emptying involve?

A
  1. Constriction of lower oesophageal Sphincter
  2. Contraction of gastric muscularis
  3. relaxation of pyloric sphincter
111
Q

What things can inhibit gastric emptying?

A

Distension of duodenum
Presence of fat
Increased HCl

This is known as the enterogastric reflex and can have implications for oral drug absorption.

112
Q

Why does high fat meals delay gastric emptying?

A

Fat in the duodenum causes the fundus to relax, lowering the intragastric pressure, and it also increases the feeling of fullness

113
Q

What is a gastric ulcer?

A

This is where the mucosal layer of the stomach has been eroded, causing inflammation and damage to underlying tissue.

Acid may not be the initial damaging feature. It is however noted that acute or chronic ulceration of the GI tract in close proximity to acid producing cells.

114
Q

What was the main cause of Gastric and duodenal ulcers?

A

95% duodenal ulcers and 85% gastric ulcers are associated with H. Pylori infection. The remainder are believed to be linked to NSAID use.

115
Q

How is acid secretion controlled?

A
116
Q

How is gastric ulceration managed?

A
  1. Explanation and reassurance
  2. Dietary control
  3. Drug therapy - aimed at maintaining the balance between the damaging and protective factors of the intestinal mucosa. Control of acid production
  4. Eradication of H. Pylori
117
Q

Explain the function of the pancreas

A

The pancreas primarily has an exocrine effect (via 99% of the cells) - it acts as an accessory organ to digestion and secretes enzyme- rich fluid into the duodenum, to allow the breakdown of all categories of digestible food.

1% of cells do have an endocrine effect - they release hormones into the bloodstream which affect carbohydrate metabolism

118
Q

Which pancreatic cells exert an endocrine effect?

A

Islet Beta cells release insulin,
Islet alpha cells release glucagon, and Islet delta cells release somatostatin.

119
Q

What do Acinar cells do?

A

Secrete enzymes and fluid into the duct system

120
Q

What do duct cells do?

A

They fuse with the bile duct on entry to the duodenum and are responsible for expressing high levels of carbonic anhydrase and HCO3- secretion.

121
Q

What are pancreatic juices made of?

A

They have a aqueous component and a highly potent enzymatic component hence making the pancreas a dangerous organ to injure

122
Q

What is the aqueous component and what does it do?

A

Aqueous component is made up 200-800ml of fluid, is secreted each day, is rich in bicarbonate (pH of 8), and helps neutralise acidic chyme - its secretion is stimulated by secretin

123
Q

What does the enzymatic component do?

A

Produces proteolytic enzymes, pancreatic amylase, and lipolytic enzymes

124
Q

How is pancreatic secretions controlled?

A

Underlying nervous and hormonal control - nervous reflex involves medulla and vagal innervation, gastrin is released in response to stomach distension, secretin and cholecystokinin are secreted by the mucosa in response to presence of chyme in duodenum (intestinal phase)

125
Q

What is pancreatitis?

A

This is where the pancreatic enzymes are activated within the pancreas itself, causing the enzymes to attack the organ. This can be acute or chronic, but becomes chronic when pancreatic tissue is destroyed and scarring develops.

126
Q

What causes pancreatitis?

A

Gallstones, alcoholism, and various other causes which are unknown (idiopathic)

127
Q

What is the function of the liver?

A

Processing digested food from intestine
Making bile
Storing high levels of monosaccharides by converting them to glycogen
Storing iron, vitamins and other essential chemicals
Break down of fat, glycogen or protein to form glucose,
Metabolising drugs and break down poisons
Bactericidal activity (kupffer cells)

128
Q

How is the liver structured

A

Cells are arranged in radial pattern around central vein, Hepatocytes make up functional units called lobules, and lobules form lobes of liver.

129
Q

How do hepatic blood supplies work?

A

Receives double blood supply - oxygenated from the hepatic artery and deoxygenated from the portal vein

130
Q

What is bile?

A

Bile is a digestive secretion produced via liver metabolism

131
Q

What do bile salts do?

A

Bile salts emulsify fat into small droplets, and makes bile cholesterol soluble.

132
Q

What gives faeces and urine their colour?

A

Bile pigments (bilirubin) which is yellow/brown in colour. Absorbed from the blood.

133
Q

What does the gallbladder do?

A

It stores and concentrates bile by extracting water and ions - it can lead to increased insoluble cholesterol levels

Bile enters the gallbladder by the cystic duct when the small intestine is empty.

Bile is then ejected into the duodenum when protein/fat rich chyme enters the duodenum, as CCK causes the gallbladder to contract and the sphincter of oddi to relax which allows bile to enter the duodenum

134
Q

What is a gallstone?

A

Crystalline deposits that accumulate when there is too much cholesterol and not enough bile salts.

This can be dissolved but if severe, can cause gall bladder to be removed.

135
Q

Why do gallstones cause jaundice

A

This blocks the bile duct, meaning there is increased levels of bilirubin in the blood plasma, which then causes skin discolouration.

136
Q

Which factors affect the concentration of drugs in solution in GI fluids?

A

Complexation
Adsorption
Chemical stability
Micellar Solubilisation

137
Q

What is complexation?

A

This is where a component such as mucin which is present in the GI fluids forms complexes with some drugs and reduces the absorption and bioavailability

138
Q

What is Adsorption?

A

This is where the co-administration of drugs and medicines containing solid adsorbents may result in the adsorbents which interfere with the absorption of drugs from the GI tract.

139
Q

What is the issue with chemical stability?

A

This is where drugs that breakdown in the GI fluids will have reduced absorption and bioavailability

Instability can be caused by:

-Stomach pH (acidic hydrolysis)
-Enzyme degredation

140
Q

What is micellar solubilisation?

A

This increases the solubility of drugs in the GI tract.

141
Q

What are micelles?

A

Micelles initiates via surfactant molecules which have a hydrophobic tail and hydrophillic head

142
Q

What happens to micelles once added to water?

A

They will be found on the surface of water as the hydrophillic heads will create an interface

143
Q

What can act as surfactants in the GI

A

bile salts - such as either glycochenodeoxycholic acid or taurochenodeoxycholic acid

144
Q

What is log D

A

Log D is the distribution coefficient

It takes into account ALL forms of drug - e.g. ionised and unionised

Log D is pH dependant and is always less than Log P

145
Q

How to calculate Log D with known log P and known pH and Pka

A

Log D = Log P + Log (Funionised)

(Funionised) for acids = [1/ (1+10^pH-pka)]

(Funionised) for bases = [1/ (1+10^pka-pH)]

146
Q

How does the body react to different formulations when either in the fed or fast states?

A

when fed - Liquids and pellets/ distintegrated tablets empty with food - controlled release are retained for longer.

When fasting, there is little discrimination between formulation types.

147
Q

How does food affect pH?

A

Carbs do not affect pH significantly
Proteins elevate the pH
Liquid mixed meals do elevate the pH but levels return to basal numbers.

148
Q

What happens to pepsin above pH 5?

A

Gets denatured and the acid production is reduced.

149
Q

The intestines are composed of:

A

Small:
Duodenum
Jejunum
Ileum

Large:
Caecum
Colon
Rectum

150
Q

What is the structure of the intestinal wall?

A
151
Q

What is the structure of the small intestinal villi

A
152
Q

What do the small intestinal villi do

A

They have folds of mucosa and submucosa which increase the surface area for absorption

The microvilli increase the surface area further

Each villus has:
-arteriole
-capillary bed
-venule
-lymphatic

They contain vessels for transporting of nutrients

153
Q

How are the intestinal juices produced?

A

Secretion is regulated by reflex stimulated by the presence of chyme

CCK and secretin are also responsible for stimulating secretion

154
Q

How does digestion work in the small intestines mechanically?

A

Segmentation - allows mixing of chyme/ food

Peristalsis - concerned with propulsion of food along tract, via longitudinal contraction and circular contraction

155
Q

How does digestion occur from a chemical perspective in the intestine?

A

Digestive process started by salivary amylase and stomach pepsin

Process is completed in small intestine by combined actions of:

  • pancreatic juice
    -bile
  • intestinal juice
156
Q

How are carbs digested in small intestine?

A

starch Conversion to dissacharides by pancreatic amylase

Dissacharides (maltose, sucrose) converted to monosaccharide (glucose, fructose) by glycosidase

Monosaccharides then absorbed

157
Q

How are proteins digested in small intestine?

A

Polypeptides arrive from stomach catabolised by pancreatic trypsin and chymotrypsin

Digestion completed by peptidases released from glandular epithelium

Peptidases cleave peptides.

158
Q

How is fat digested in the Small intestine?

A

Bile plays an essential role

Fat globules in the duodenum coated with bile salts to create emulsion and disperse fat globules into smaller entities

Emulsification allows breakdown of triglycerides by increasing the surface area for water soluble pancreatic lipases to act upon and produce monoglycerides and free fatty acids

159
Q

By what mechanisms does absorption occur via the intestinal mucosa

A

Active transport

and diffusion

160
Q

How are monosaccharides absorbed?

A

Glucose absorbed via Epithelial cell by co-transport with Na+ via sodium-glucose transporters then leave epithelial cell and enter blood via facilitated diffusion via the GLUT transporters

Fructose just absorbed in and then leaves to go to blood via GLUT’s

161
Q

How are peptides absorbed?

A

Uptake into epithelial believed to be H+ linked. Then broken down to amino acids inside epithelial cell

Amino acids are uptaken into epithelial cells by Na+ dependant co-transport (active)

They leave the epithelial cell via facilitated diffusion

162
Q

How are fats absorbed in small intestine?

A

Monoglycerides and free fatty acids associate with bile salts to form micelles/ emulsions

These diffuse passively into epithelial cells

Bile salt remains in the lumen of the gut until terminal ileum then re-cycled via enterohepatic circulation

Lipids accumulate in vesicles of smooth ER of epithelial cells to form chylomicrons.

These leave the cell by fusing with the plasma membrane

Chylomicrons leave intestine in the lymph since they are too large to enter circulation immediately. They are eventually delivered into venous circulation.

163
Q

What does the lymphatic system do?

A

Absorbs nutrients (primarily fat), electrolytes, fluid and protein from interstitial spaces.

Removal of haemorrhaged red blood cells from tissue and invading bacteria.

It also allows uptake of chylomicrons due to the size preventing them from entering systemic circulation

164
Q

Advantages of lymphatic flow

A

Bypasses the liver and nutrients/drugs are delivered into systemic circulation close to the heart

It is high capacity - can process 100g of triglycerides per day

165
Q

How does the lymphatic system affect drugs?

A

The lymphatic system gets involved if the solubility of drugs in triglycerides is 50mg/ml or greater

166
Q

What happens to digestive juices in the GI tract?

A

Although 7-8 litres are secreted, almost all is re-absorbed.

Most electrolytes are actively absorbed along the intestine

167
Q

How are vitamins absorbed?

A

Fat soluble ones such as A, D, E and K must be absorbed in micelles

Water soluble vitamins (B and C) are absorbed by diffusion

Vitamin B12 requires intrinsic factor- produced by the stomach

168
Q

What is segmentation?

A

It is rhythmic contraction and relaxation of the intestine

Mixes chyme in both directions

Allows full contact of contents with intestinal juices for digestion and the intestinal wall for absorption

169
Q

Where is skeletal muscle found in the GI tract?

A

Upper third part of oesophagus and lower part of large intestine - contraction is under voluntary control

170
Q

Which ion is responsible for generating force and contraction?

A

Calcium - removal of calcium from the cytosol is required for relaxation

171
Q

How are smooth muscle cells connected?

A

Gap junctions

172
Q

How is segmentation initiated?

A

Via the electrical activity of interstitial cells of cajal (pacemaker cells) in circular smooth muscle

173
Q

How is Smooth muscle contraction regulated?

A

Via neurotransmitters released by autonomic nerve endings - no specialised motor end plate but swollen regions of axon (known as varicosites) contain NT’s

It can also be regulated by hormonal or mechanical input via receptor activation

174
Q

How does E-C coupling occur in smooth muscle?

A

No troponin involved - instead, contractile proteins regulated by Ca2+/ CaM activation of myosin light chain kinase resulting in phosphorylation of myosin.

175
Q

Which neurotransmitters are excitatory and inhibitory for the smooth muscle of the GI tract?

A

Acetylcholine and serotonin - excitatory

VIP and Noradrenaline - inhibitory

176
Q

Which disorders can cause a fast Small intestine motility and transit time?

A

Diarrhoea, thyrotoxicosis, Irritable bowel syndrome, chronic pancreatitis

177
Q

Which disorders slow the small intestine motility and transit time

A

Constipation, myxoedema, pseudo-obstruction, ileal resection, partial gastrectomy, jejunal bypass, and diabetes.

178
Q

What therapies affect GI tract dysmotility?

A
179
Q

How does the large intestine mechanically digest chyme?

A

Chyme enters through the ileocaecal valve

Haustral churning occurs

Peristalsis occurs slowly - due to mass movement

180
Q

How does the large intestine digest chyme chemically?

A

Chemically there is limited action - there is only bacterial enzymes, which ferment the remaining carbs to produce flatus and they also break down remaining amino acids

181
Q

Describe the motility patterns in the large intestines

A

Segmental contractions occur more often - propulsive movements are only seen 3-4 times a day

Slow peristaltic contractions facilitate and retard movement through colon

Mass movements - giant migrating contraction. Intense and prolonged peristaltic contractions which cab clear sections of the colon of all contents.

182
Q

How does defecation occur?

A

The reflex is initiated by distention of the rectum (parasympathetic input to open internal anal sphincter).

Therefore the pressure in the rectum increases - causing longitudinal muscles to shorten

Voluntary contractions of diaphragm and abdomen

External anal sphincter opens.

183
Q

What are the disadvantages of using Sodium bicarbonate for neutralising stomach acid?

A

Used in the body as a buffer to maintain plasma pH is an advantage - but if used excessively can risk alkalosis

184
Q

Why can we not use drugs which block muscarinic acetylcholinergic receptors?

A

They are likely to produce unwanted side effects - and the receptors are found throughout the parasympathetic nervous system and involved in cardiac respiratory control

185
Q

Why do antihistamines not reduce acid secretion by parietal cells?

A

Antihistamines act on H1 receptors, but parietal cells predominantly have H2 receptors.

186
Q

Which virus is responsible for cold sores?

A

Herpes simplex

187
Q

What stages are there for cold sore infections?

A
  1. Tingle stage - slight tingle or itch around mouth or nose
  2. Blister stage - this is where the small raised blotch swells and forms a blister
  3. Weeping stage - blisters collapse and join together to form a large weeping sore
  4. Scab stage - scab forms and later falls off.
188
Q

How does impetigo get treated?

A

Antibiotics and creams such as fusidic acid.

189
Q

What is the referral criteria for dry mouth?

A
  1. Severely dry
  2. Medications being used which may be causing it
  3. If cause is unclear
  4. Difficulty swallowing
190
Q

What is the referral criteria for gingivitis?

A

Bleeding, foul taste, severe symptoms

191
Q

What can the cause of mouth ulcers be?

A

Stress, food, trauma, genetics, and nutritional deficiencies.

192
Q

Referral criteria for ulcers?

A

Apart from minor aphthous ulcers, refer all the time.

Refer for minor Aphthous when symptoms last more than 14 days, when child is under 10, or adult over 40

Note: Aphthous ulcers are almost always round.

193
Q

Referral criteria for Oral thrush?

A

symptoms more than 3 weeks, no apparent risk factors, or when diabetic, when severe, treatment did not work, immunocompromised.

194
Q

What are fillers used for in tablet prep and examples of fillers?

A

Fillers are used to add necessary bulk.

Lactose, glucose, and mannitol - water soluble

Cellulose - water insoluble

195
Q

What are binders and examples?

A

Binders promote adhesion of the particles

Solution binders include starch, sucrose, gelatin as well as PVP, cellulose derivatives.

Dry binders include microcrystalline cellulose.

196
Q

What are glidants and examples?

A

Glidants improve the flowability and they reduce friction between particles.

Colloidal Silica and Talc are an example of these.

197
Q

What do lubricants do and example:

A

Lubricants are responsible for reducing friction between particles and the die wall

Magnesium Stearate is an example.

198
Q

How does colon targeting work?

A

This is where the drug core needs to be coated with the extended-release membrane - exposure to bacterial enzymes generates holes in the coating, which results in the drug core being released

Ethylcellulose is an example of a component which is stable in the stomach, and is only digested by colonic bacteria.

199
Q

Example of gastro-resistant coatings?

A

Acrylic polymers, phthalate polymers

200
Q

Advantages of film coating vs sugar coating:

A
  1. Less volume increase
  2. Better stability of the tablet
  3. Better mechanical strength
  4. One step process.
201
Q

Describe the structure of the rectum:

A
202
Q

What are the advantages and disadvantages of rectal drug delivery?

A
203
Q

Examples of rectal formulations:

A

Enema (solution, foams, gels, creams, ointments, and suppositories

204
Q
A

MPharm Year 2 MP220/221 (1 decks)

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