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SL12011 The Science of Medicine > Semester 1 Exam Deck > Flashcards

Semester 1 Exam Deck Flashcards

1
Q

What is the overall goal of medicine design?

A

To get the right drug to the right place at the right dose at the right rate

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2
Q

What is ADME? Why is it important?

A

ADME stands for:
- Absorption
- Distribution
- Metabolism
- Excretion

Its important because lists the ways in which a drug’s properties can influence the way it is processed by the body.

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3
Q

Why is thermodynamics relevant to biopharmaceutics?

A

Many processes associated with drug absorption are dictated by thermodynamics:

Formation of micelles (and vesicles)

Partition of membranes

Solubility

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4
Q

What is the difference between a drug and a medicine?

A

Drug = Active pharmaceutical ingredient (API)

Medicine = The combined package of drugs and their associated delivery system

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5
Q

What is the dosage form? Why is it significant?

A

The dosage form describes the physical form of the medication as it is produced and administered.

It is significant as it affects the onset action of the active ingredient.

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6
Q

What is a drug delivery system (DDS)?

A

A method or process by which a drug is delivered

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7
Q

List the steps of drug absorption via the GI tract

A

Dosage form dissolves in the GI tract, forming a solution

Absorbed into the superior and inferior mesenteric veins

Feed into the portal vein of the liver WHERE THE DRUG IS LIKELY METABOLISED

The remaining drug is then sent around the body

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8
Q

Describe the different absorption pathways in the GI tract

A

Paracellular - Absorbed in between epithelial cells

Transcellular - Absorbed through epithelial cells via various types of membrane absorption

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9
Q

What’s the difference between biopharmaceutics and pharmaceutics?

A

Biopharmaceutics - The study of the interaction between a medicine and associated biological systems

Pharmaceutics - The study of developing medicines

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10
Q

Define bioavailability. What does a high bioavailability mean?

A

A measure of the quantity of a drug which reaches its site of action and the rate at which it gets there

A high bioavailability means that a given drug is reaching its site of action quickly and efficiently

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11
Q

In what way are “fractions” relevant to the mindset of bioavailability?

A

The bioavailability of a drug is dictated by its absorption across multiple membranes.

At each of these membranes only a fraction of the drug is absorbed due to factors of metabolism and rate of absorption.

By thinking of the size of these fractions we can determine the bioavailability of a drug.

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12
Q

What is the generally accepted method of measuring drug bioavailability? Are there exceptions?

A

By determining drug concentration in the systemic circulation.

Yes, medications such as eyedrops won’t end up in the blood thus their bioavailability must be determined else how.

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13
Q

Pharmacokinetics Vs Pharmacodynamics?

A

Pharmacokinetics - What the body does to the drug

Pharmacodynamics - What the drug does to the body

(Think about how kinetics often refers to the metabolism of the drug)

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14
Q

What are the features of a plasma concentration Vs time graph for oral administration?

A

Initial lag in concentration of drug from administration (due to absorption)

Concentration then rapidly increases

Concentration slowly drops

Markers for minimum therapeutic concentration, minimum toxic concentration and peak concentration

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15
Q

What is an efflux pump?

A

A transmembrane transport protein that extrudes toxic substances from within cells

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16
Q

What is a patent’s lifetime?

A

20 years, can be extended by up to 5.

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17
Q

What is the difference between a patent lifespan and marketing lifespan? Why is this significant?

A

Patent lifespan defines the period during which a sole company has rights to produce a drug.

Marketing lifespan defines the time during the patent’s life where the drug can be sold on the market by said sole company.

This is important since in the small marketing life of a given drug, the parent company aims to recuperate the money spent on R&D, then some more in order to turn a profit.

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18
Q

Why is it important that drug companies have mixed portfolios?

A

Ensures that said companies can gain back money lost on failed or unpopular projects

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19
Q

What is a blockbuster drug?

A

A drug which reaches over $1 billion per annum

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20
Q

What is the blockbuster drug model? Why is this model relevant?

A

Aim to produce blockbuster drugs above all other drugs. In doing so you can pay for the R&D of other drugs. Rinse and repeat.

Relevant because this is the model that almost every major modern-day pharmaceutical company follows.

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21
Q

What was the Generic Era of drugs? Why is this significant?

A

The period from the 90’s to the 00’s where governments promoted the use of generics over name brands.

This is significant as it reduced the market share of large pharmaceutical companies and their control over the industry.

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22
Q

What is a generic drug? Why are they significant to hospital organisations (such as the NHS)?

A

A drug which is bioequivalent to a name brand (identical in dose and route of admission)

They flood the markets after a name brand’s patent expires

They are significant to hospital organisations since they can save money (up to roughly 80%) whilst maintaining efficacy

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23
Q

Why are epilepsy generic medicines sometimes less effective, if not harmful, for patients?

A

They can have slightly different rates of absorption which affects the action of the drug.

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24
Q

What are the three types of systems that we come across in thermodynamics?

A

Isolated system - Exchange of neither matter nor energy

Closed system - No exchange of matter but exchange of energy

Open system - Exchange of both matter and energy

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25
Q

Define work (thermodynamics)

A

The transfer of energy in an ordered fashion

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26
Q

Define enthalpy

A

The heat energy change within a system. Can be expressed as a relative or an absolute (change in heat energy values or absolute heat energy change).

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27
Q

Define entropy. How can we perceive it?

A

The amount of disorder within a system. Can be perceived as the probabilities of a form existing.

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28
Q

Where is thermodynamics relevant in pharmacology?

A

During the drug discovery process:
- Solubility
- Partitioning
- Melting point

These three factors relate to the ADME of a drug.

Drug receptor interactions:
-Toxicity predictions

Thermodynamic calculations can predict how strongly a drug can bond to a receptor, thus determining if it will enhance cellular activity too much (becoming toxic)

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29
Q

Why is drug dissolution important?

A

Drugs must first be dissolved before they can be absorbed by the body

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30
Q

Define liberation

A

The release of a drug from its administered form

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31
Q

What are the four distinct types of drug release in oral dosage forms?

A

Osmotic pump tablets: Suspension forms within tablet and is slowly released

Coated tablets: Coating dissolves to allow the tablet to dissolve and disintegrate

Coarse or fine granules: Drug can dissolve or further disintegrate (particularly if coarse)

Drug suspension: Already aqueous, sometimes contains granules to saturate suspension (0th order reaction)

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32
Q

What is the significance of disintegration in large drug particles?

A

Disintegration decomposes the large particles into smaller pieces. In doing so surface area is increased allowing for more dissolution to occur.

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33
Q

What are the two steps in crystal to liquid drug dissolution?

A
  1. Surface drug molecules are solvated, forming a stagnant DIFFUSION LAYER
  2. Drug molecules then diffuse across the diffusion layer into the BULK DISSOLUTION MEDIUM
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34
Q

What are the key parameters of the Noyes-Whitney Equation

A
  • dm/dt = dissolution rate
  • Effective surface area
  • Molecular weight
  • Solubility
  • Various GI tract variables
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35
Q

Why is transcellular the major and paracellular the minor absorption pathway for small molecules?

A

Rate of paracellular absorption is restricted by the tight intimate connections between cells (little room to diffuse). Transcellular absorption is favoured since there are a wide variety of channels and methods by which drugs can enter cells.

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36
Q

What type of drugs do travel via the paracellular pathway?

A

Small, light (<1,000) hydrophilic solutes

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37
Q

How can larger protein based drugs be absorbed?

A

Endocytosis; they are internalised by the plasma membrane. However, this pathway is very minor.

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38
Q

What is flux?

A

The net flow of particles in a given direction. The driving force of diffusion.

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39
Q

What is the significance of Fick’s First Law (what does its equation illustrate)?

A

The equation of Fick’s First Law illustrates that the further a system is from equilibrium, the faster it moves towards it.

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40
Q

What are the key parameters in the Stokes-Einstein Equation?

A
  • Local environmental conditions of the particle
  • Properties of the medium (viscosity etc.)
  • Properties of the diffusing particle
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41
Q

What are the steps to the passive diffusion of a drug across epithelia? What factors affect the rate of diffusion?

A
  1. Drug diffuses to the epithelium (aqueous)
  2. Diffuses across the epithelium (lipid)
  3. Through the epithelium (aqueous)

The thicker the membrane the slower the flux, the greater the conc. gradient the better the flux.

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42
Q

Define lipophilicity. How is it measured?

A

The capability of a drug to dissolve in lipids

Measured by the partition coefficient which quantifies the distribution of a drug between an aqueous and lipid (often octanol) phase

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43
Q

Why is lipophilicity important?

A

It determines how much of the drug will end up distributed between the aqueous phase and the lipid membrane, thus determining roughly how much of the drug will crossing the epithelium.

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44
Q

Why is acid base theory relevant to drug development and pharmacology overall?

A

Many drugs are weak organic acids/bases or salts.

Thus, the dissociation of the drugs affects their dissolution and bioavailability.

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45
Q

Define amphiprotic

A

A substance that can act as either an acid or a base

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46
Q

What is the most common amphiprotic solvent? Why is it relevant?

A

The most common amphiprotic solvent is water.

Importantly, water reacts with weak acids or bases to produce conjugate acid-base pairs as part of their Bronsted-Lowry chemistry

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47
Q

Why is pKa used when comparing acid/base strength?

A

It defines the strength of an acid/base independent of its concentration, on a sheer molecular level.

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48
Q

Define polyprotic

A

A substance capable of accepting or donating multiple protons.

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49
Q

What are the key differences between polyprotic and monoprotic substances?

A

Polyphonic can donate or accept multiple protons, thus multiple equilibria equations (each with their own pKa/pKb).

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50
Q

What information can be derived from the pKa of an acid/base?

A

Lower pKas suggest stronger, more polyprotic acids. Vice versa applies.

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51
Q

Why do strong acids/bases have a propensity to fully dissociate?

A
  • Their reactions are virtually irreversible
  • Their conjugate bases/acids are so weak that they have no effect on the corresponding acid’s/bases action
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52
Q

Why are weak acids considered weak?

A

They only partially dissociate in solution, release much fewer protons than a strong acid (at the same conc.)

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53
Q

What is an electrolyte?

A

A compound that ionises in aqueous solution. They can be weak or strong.

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54
Q

What are non-electrolytes?

A

Substances that do not yield ions when dissolved in water

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55
Q

What is the common ion in a buffer? What is its purpose?

A

The ion shared between the acid/base and the salt.

It soaks up additional protons/hydroxoniums as the “acting portion” of the buffer.

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56
Q

How can a buffer be formed?

A

Weak acid/base + conjugate salt
Strong base/acid + weak acid/base (to form a solution of weak acid/base + salt)

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56
Q

How can you derive the Henderson Hasselbach equation from the buffer equation?

A
  • Rearrange for [H+]
  • Take -Log10 of both sides
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57
Q

What is the relationship between electrolytes and acids/bases?

A

All acids/bases count as electrolytes as they ionise (to some degree in solution)

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58
Q

Why are acetate buffers so common?

A

They remain functional as pKw changes. Thus, they can be used at a variety of temperatures.

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59
Q

Why are acidic buffers preferred?

A

They are less prone to being affected by temperature changes in their ability to maintain pH (of a solution)

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59
Q

What does buffer capacity measure?

A

The magnitude of the resistance a buffer provides to pH changes

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60
Q

Why is drug stability important?

A
  • Unstable drugs can metabolise into toxic byproducts
  • Can lead to loss of active product via metabolism
  • Can affect solubility and bioavailability of drug
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61
Q

What are the common mechanisms of drug degradation?

A
  • Hydrolysis
  • Oxidation
  • Other pathways
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62
Q

What types of drugs are susceptible to hydrolysis? How is this susceptibility tested?

A

Drugs with groups such as esters, amides and lactam groups. To test the likelihood they undergo a UV test.

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63
Q

Oxidation degradation mechanism Lecture 11

A
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64
Q

Other pathways of drug degradation Lecture 11

A
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65
Q

What are the 4 routes of degradation?

A

Direct: A degrades to B (one constant)

Dynamic Equilibrium: A forms B and vice versa (2 associated constants)

Competitive: A degrades to B OR C (2 separate constants)

Sequential: A degrades to B, then B to C (2 separate constants)

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66
Q

What is the order of a reaction? Why is it important?

A

The sum of the powers in a rate equation?

It defines the kinetic rules the reaction abides by, very useful in modelling reactions.

(Can be 0th order or fractional)

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67
Q

Why is experimental data necessary to confirm the rate equation? How is this data gathered?

A

Though the rate equation can resemble the reaction, it doesn’t always.

The order of each reactant is determined individually in experiments, then combined with the other reactant data to determine the overall reaction order.

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68
Q

How do you determine the rate of a first order reaction?

A

Calculate the gradient of the LOGGED reaction line. Use a computer for maximal accuracy.

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69
Q

What information can we gather from the rate constant?

A

The theoretical reactivity of a substance or overall reaction

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70
Q

Why are zero order kinetics technically theoretical? By what mechanism do they actually occur?

A

Zero order kinetics depends on a constant supply of drug (to maintain initial value).

In reality, this occurs by having particles of solid drug within drug suspension to constantly replenish the suspension. This is maintained until the reservoir of solid drug runs out, at which point the reaction is modelled after first order kinetics.

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71
Q

What occurs when the solid particles of a 0th order suspension are fully solubilised?

A

The reaction is now modelled as first order

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72
Q

What reactions are often modelled by second order kinetics?

A

Bimolecular reactions

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73
Q

What is the ideal ration for second order kinetics?

A

t1/2 = 19*t95%

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74
Q

What methods can be used to determine reaction order?

A
  • Substitution method
  • Shelf-life method
  • Graphical method
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75
Q

What effect does pH have on rate equations? Where is this effect most prominent?

A

The presence of H+ and OH- can immensely effect the rate of many reactions particularly hydrolytic reactions.

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76
Q

What equations illustrates the relationship between temperature and the rate of a reaction?

A

Arrhenius equation

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77
Q

What is the pre-exponential factor?

A

A variable to describe the frequency of molecules that possess reactive conditions (collision energy, orientation etc.).

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78
Q

What is the purpose of stability testing?

A

To provide a more efficient alternative to observing the stability of a product over its entire shelf-life before it can reach the open market.

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79
Q

How do we accelerate the stability testing process?

A

We vary the temperature and humidity at which the medicine is stored.

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80
Q

What protocols are followed in stability testing?

A
  1. Temperature and humidity
  2. Storage time before sampling
  3. Number of batches sampled
  4. Number of replicates in a batch
  5. Suitable light challenge
  6. Details of the assay
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81
Q

What are the requirements of a good drug?

A
  • Efficacy
  • Chemical stability
  • Solubility
  • Oral bioavailability
  • Appropriate pharmacokinetics
  • Favourable safety profile
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82
Q

Why is lipophilicity the key physical parameter in drug development?

A

Enough lipophilic character is needed to partition the cell membrane, but not so much that it can’t partition back out, in order for the drug to have any effect in the body.

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83
Q

What factors affect LogP and lipophilicity? How can the Log P of a drug be modified?

A

Underpinned by chemical structure of the drug. Some groups are lipophilic, some are hydrophilic.

The lipophilicity of a drug (and thus its LogP) can be modified by the addition of hydrophilic or lipophilic groups to bring its LogP value into the appropriate range.

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84
Q

How does pH influence the lipophilicity of a drug?

A

pH can cause drugs to ionise, in doing so their lipophilicity is affected, potentially pushing it out of the ideal range (LogP≤5)

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85
Q

Describe the relationship between ionised drugs and HYDROphilicity

A

Ionised drugs have increased hydrophilicity, reduced membrane permeability

Unionised drugs have decreased hydrophilicity, increased membrane permeability

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86
Q

What’s the difference between LogP and LogD?

A

LogP only accounts for the partitioning of neutral unionised species

LogD ALSO accounts for charged species

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87
Q

What bonds must be broken for desolvation to occur?

Where/when does desolvation occur?

A

Hydrogen bonds between the drug and water must be broken for a drug to desolve.

This occurs when a drug enters the lipid plasma membrane.

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88
Q

State Lipinski’s Rule of Five

A

Poor oral absorption is likely if two or more of the following criteria are broken:

  • Molecular weight is ≤500
  • LogP is ≤5
  • # of H bond donors ≤5
  • # of H bond acceptors ≤10
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89
Q

State Lipinski’s Rule of Five

A

Poor oral absorption is likely if two or more of the following criteria are broken:

  • Molecular weight is ≤500
  • LogP is ≤5
  • # of H bond donors ≤5
  • # of H bond acceptors ≤10
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90
Q

State Lipinski’s Rule of Five

A

Poor oral absorption is likely if two or more of the following criteria are broken:

  • Molecular weight is ≤500
  • LogP is ≤5
  • # of H bond donors ≤5
  • # of H bond acceptors ≤10
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91
Q

What four variables are measured in Lipinski’s Rule of Five?

A

Molecular weight
LogP (lipophilicity)
H bond donors
H bond acceptors

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5
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92
Q

Where is Lipinski’s Rule of five applicable?

A

Applicable for passive transcellular diffusion

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93
Q

What types compounds break the rule of 5 but are still absorbed?

A
  • Antibiotics
  • Natural compounds
  • Semi-synthetics
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94
Q

How can we optimise the effect of pH on lipophilicity?

A
  • Change the pKa functional groups on the molecule to change the resultant lipophilicity
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95
Q

What is a pro-drug? How can they be used to improve lipophilicity?

A

A pro-drug is a molecule that metabolises to form an active drug molecule. By designing a lipophilic pro-drug (by adding lipophilic groups) that degrades into an active drug once its absorbed, we can improve the lipophilicity of a drug where it is essential and thus improve its bioavailability.

96
Q

What organs make up the GI tract?

A
  • Mouth
  • Oesophagus
  • Stomach
  • Small and large intestine
  • Anus
97
Q

What accessory organs are associated with the GI tract? What role do they all share?

A
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas

They all secrete substances into the GI tract

98
Q

What is the mesentery tissue? What is its function?

A

The tissue that surrounds all GI tract organs.

It holds them in place and provides access to blood vessels and lymphatics.

99
Q

What key components make up the mouth? What are their functions?

A
  • Teeth (mechanical digestion)
  • Tongue (sense of taste)
  • Mucous membranes (secrete saliva to protect and lubricate)
  • Pharynx and epiglottis (to prevent food from reaching airway, swallow reflex)
100
Q

What are the two movement stages involved in swallowing?

A
  1. Initial voluntary movement, “choosing” to swallow
  2. Involuntary movement of the food bolus down the oesophagus
101
Q

What are the main layers of the stomach wall? What functions are they responsible for?

A
  • Mucosa (Layer of mucous that protects other layers from damage)
  • Submucosa (Layer of glands and blood vessels that secrete enzymes and mucous)
  • Muscularis (Layer of smooth muscle responsible for emptying stomach contents)
102
Q

What are the main functions of the stomach?

A
  • Secrete peptidases for protein digestion (and pathogen breakdown)
  • Defense against foreign pathogens via stomach acid
103
Q

What are the 3 “main” regions of the large intestine?

A

Ascending, parallel and descending colons

104
Q

What are the 3 main regions of the small intestine? What is the function of each section?

A
  • Duodenum (Receives stomach contents and uses contents from gallbladder and pancreas to digest)
  • Jejunum (Responsible for folate uptake)
  • Ileum (Longest section, absorbs most of the nutrient)
105
Q

From macro to micro list the structures responsible for the small intestine’s surface area

A

Small intestine > Intestinal folds > Villi > Epithelial cells > Microvilli

106
Q

What are the crypts of Lieberkuhn? What are the functions of the cells its comprised of?

A

A functional unit in the small intestine responsible for its immune response as well as protection and repair.

Comprised of:

  • Paneth cells (immune functions)
  • Stem cells (intestinal regeneration)
  • Goblet cells (secrete mucous)
107
Q

What’s the primary function of the large intestine?

A

To conserve water and ions which may have been lost from earlier sections of the GI tract epithelium

108
Q

What are the main functions of the salivary glands?

A
  • Lubrication (mucous)
  • Protection (lysozymes and thiocyanate)
  • Digestion (amylase and lipase)
109
Q

What is the role of thiocyanate in the mouth?

A

To prevent the build up of the toxic compounds hydrogen peroxide and hypochlorite

110
Q

What is the main function of the liver for the GI tract?

A

Produces and excretes bile into the gallbladder, important in emulsifying fats for absorption.

111
Q

What is the main function of the gallbladder?

A

Concentrating reservoir for bile from the liver. Releases the bile into the duodenum of the SI.

112
Q

What are the main functions of the pancreas?

A

Makes enzymes to digest the main food groups

Produces insulin and glucagon

113
Q

What are the 6 functions of the overall GI system?

A
  • Ingestion
  • Secretion
  • Movement
  • Digestion
  • Absorption
  • Excretion
114
Q

What two types of movement are a part of the GI system? Describe them.

A

Segmentation: Food squashed into sections so that enzymes can digest the food (before it moves on)

Peristalsis: Movement of a food bubble down the GI tract via sequential contraction of the smooth muscle tissue

115
Q

Where in the GI tract does ingestion and secretion occur?

A

Voluntary ingestion of food at the mouth in the form of eating and swallowing, involuntary secretion of saliva in response to sight and smell of food.

116
Q

What are the two main forms of digestion?

A

Mechanical digestion: Physical process of breaking down food into smaller particles

Chemical digestion: The use of enzymes or other chemicals (stomach acid) to break down food

117
Q

In what processes does mechanical digestion appear in the GI system?

A
  • Peristaltic contractions
  • Mastication (chewing)
118
Q

How is the swallowing reflex triggered?

A

Food bolus stimulates pressure receptors in the throat and pharynx.

Signals to swallowing centre of the brain to swallow.

119
Q

What are the 3 phases of swallowing?

A
  • Oral
  • Pharyngeal
  • Oesophageal
120
Q

How does motility appear in the stomach?

A

Mixing and churning motion to form chyme

Peristalsis to empty the stomach contents into the small intestine

121
Q

What is chyme?

A

A semi-fluid pulpy contents that are formed by and expelled from the stomach

122
Q

Why is the stomach significant to oral drug administration?

A

In the stomach the drug starts to properly mix and dissolve

Low pH can affect the drug’s ionisation

Rate of gastric emptying can influence drug absorption

123
Q

How does the rate of gastric emptying influence drug absorption?

A

If the stomach empties too quickly then the drug won’t have enough time to dissolve

If the stomach empties too slowly then the drug is in contact with acidic contents for too long (affecting ionisation)

124
Q

How does motility appear in the small intestine? What allows this motility to occur?

A
  • Segmentation to mix contents
  • Peristalsis to move contents

This motility is possible due to the bands of smooth muscle tissue in the lining of the small intestine

125
Q

Describe the muscle contractions that occur in peristalsis

A

Contraction of ringed muscle behind bolus, contraction of longitudinal muscle alongside bolus.

126
Q

Describe the relation between the ENS and the motility and environment of the intestines?

A

Two sections: Submucosal and myenteric plexus.

Submucosal - Maintains chemical conditions optimal for absorption

Myenteric - Maintains optimal velocity and intensity of muscular contractions (and other muscle functions)

127
Q

How does the ENS control peristalsis? Can this process be influenced?

A

Sensory neurons detect the presence of food by the degree of stretch

Thus, causing motor neurons that innervate the smooth muscle tissue to contract or relax

Yes, it can be influenced by neurotransmitters

128
Q

What are the respective effects of the SNS and PNS on the ENS

A

Sympathetic inhibits ENS (have sympathy)

Parasympathetic stimulates

129
Q

What are the effects of ENS stimulation? What about when inhibited?

A

Increased peristalsis, blood flow, secretion and absorption. When inhibited, vice versa occurs.

130
Q

Describe the relationship between intestinal motility and drug absorption

A

The greater the transit time the greater the drug absorption (directly proportional)

131
Q

What is the migrating motility complex?

A

A recurring motility pattern that occurs between meals. It cleans the GI tract from the stomach to the large intestine.

132
Q

What is haustral shuttling? Why does it occur?

A

Segmentation that moves back and forth through the large intestine.

It allows us to reabsorb water more efficiently.

133
Q

What is mass movement?

A

A series of coordinated contractions that propel the contents of the large intestine towards the rectum.

134
Q

What are the two forms of motility in the large intestine?

A
  • Haustral shuttling (segmentation)
  • Mass movement (peristalsis)
135
Q

What process in the GI tract causes constipation and diarrhoea respectively? Why might this occur?

A

Constipation: Weak mass movement
Diarrhoea: Hyperactive mass movement

Some conditions such as Parkinson’s affect the muscle contractions.

136
Q

Outline the timeline for vomiting

A
  • Increased salivation
  • Relaxation of lower oesophageal sphincter (for food to come up)
  • Contraction of the diaphragm and abdominal muscles
  • Opening of the upper oesophageal sphincter (expulsion)
137
Q

What can cause vomiting to occur?

A
  • Toxins or potent drugs
  • Eating too much or too quickly
138
Q

What purpose does the kidney’s outer capsule serve?

A

Separates kidneys concentration gradients from the rest of the body

139
Q

Describe the structure of the kidney

A

Nephrons make up the cortex and medulla which drains urine out of the blood supply in.

Urine is sent to the central renal pelvis where it then goes through the ureter.

Surrounded in an outer capsule

140
Q

How many nephrons does a kidney contain? What purpose do they serve?

A

About 1 million nephrons. They are the functional unit of the kidney that filters waste out of the blood

141
Q

Describe the overall process of filtration in the nephron

A
  1. Blood enters through the glomerulus
  2. Water and nutrients are forced into the Bowman’s capsule via ultrafiltration
  3. Nutrients are reabsorbed in the proximal convoluted tubule
  4. Loop of Henle maximises the reabsorption of water by acting as a countercurrent multiplier
  5. More nutrients are reabsorbed in the distal convoluted tubule
  6. Collecting duct reabsorbs last bits of water. concentrating the urine
142
Q

Describe the overall structure of the nephron (follow the pathway)

A

Glomerulus is enclosed in the Bowman’s capsule. Capsule flows into the proximal convoluted tubule, then loop of Henle, distal and finally the collecting duct.

143
Q

What are the 3 main functions of the nephron?

A
  1. Glomerular filtration
  2. Tubular secretion
  3. Tubular reabsorption
144
Q

Describe the process of glomerular filtration. Explain why this occurs

A

Water and dissolved nutrients are forced out of the glomerulus (the blood stream) into Bowman’s capsule.

This occurs because the afferent arteriole is larger than the efferent arteriole. This increases pressure within the glomerulus forcing contents out of the blood.

145
Q

What is tubular secretion?

A

The process by which arterioles surrounding the tubules secrete waste into said tubules

146
Q

What is tubular reabsorption

A

The process by which arterioles reabsorb useful substances such as water and dissolved compounds from the tubules

147
Q

Describe how the structure of the glomerulus relates to its function

A

Blood vessel walls are one cell thick, increasing porosity.

Podocytes and basement cells surrounding the vessel prevent the filtration of larger particles (RBCs or plasma proteins, PREVENTS PROTEIN BOUND DRUGS FROM BEING FILTERED)

148
Q

What molecules do filter between the podocytes and what molecules don’t?

A

Do:
- Water
- Salts
- Glucose
- Amino acids
- Urea
- Uric acid
- Creatine
- Small drugs

Don’t:
- Cells
- Proteins
- Protein-bound drugs
- Anything >8nm

149
Q

What is the glomerular filtration rate?

A

The volume of fluid filtered from the glomeruli to bowman’s space per unit time

150
Q

How is the glomerular filtration rate (GFR) modified by the body?

A

By adjusting the blood pressure either side of the glomerulus

151
Q

Why do the kidneys modify the GFR?

A

To maintain a water and salt balance (there are other ways)

152
Q

Describe the relationship between GFR and water/salt excretion

A

Increased GFR increases water/salt excretion. Proportional relationship.

153
Q

What is the interstitial space?

A

The space in between tubules. It is involved in the concentration gradients for reabsorption from the tubules.

154
Q

How is Na+ reabsorbed into the proximal tubule cells?

A

Na+ is co transported with other molecules and also counter-transported against H+ to bring Na+ into the tubule cells.

155
Q

How is Na+ transferred from proximal tubule cells to the body (interstitial space)?

A

Na+ is pumped into the interstitial space by antiporter Na+/K+ pumps. K+ is recycled to the interstitial space by ion channels.

156
Q

In which section of the loop of Henle does Na+ reabsorption occur?

A

The ascending portion of the loop of Henle.

157
Q

How is Na+ reabsorbed into Loop of Henle’s tubule cells from the tubule?

A

Na+ is cotransported with K+ and Cl- by NKKCs. K+ is recycled back into the tubule by an ion channel.

158
Q

What is a NKCC?

A

A Na-K-Cl Co transporter

159
Q

How do ions reabsorbed into the loop of Henle tubule cells transfer into the interstitial space?

A

Na+ is antiported by a Na+/K+ pump. K+ is recycled by K+ ion channels. 2Cl- ions move via ion channels.

160
Q

How is Na+ reabsorbed in the collecting duct? Describe the movement of K+ too.

A

Na+ is drawn into the tubule cells, diffusing down its conc. gradient via Na+ channels. Na+ then antiported into the interstitial space by Na+/K+ pump (which maintains the Na+ conc. gradient for the channel). K+ moves in the opposite direction

161
Q

Describe the effect of aldosterone on salt reabsorption.

A

Aldosterone promotes salt reabsorption.

Does so by increasing expression of ion channels and Na+/K+ pump in the membrane.

162
Q

How long does it take for aldosterone to increase the amount of salt reabsorption in the collecting duct? Why does it take this amount of time?

A

Takes hours to occur.

This is due to the amount of time required for gene expression to substantially effect the number of channel proteins synthesised.

163
Q

Where is water reabsorbed in the nephron?

A

In the descending portion of the loop of Henle

164
Q

How is water reabsorbed in the loop of Henle?

A
  1. Descending loop is permeant to water, ascending loop isn’t.
  2. Ascending loop reabsorbs salts, makes low water concentration interstitial fluid
  3. Water diffuses down conc. gradient into the interstitial fluid

(The longer the loop the greater the countercurrent multiplier for water reabsorption)

165
Q

Describe how blood flow around the loop of Henle ensures that concentration gradients are maintained.

A

Blood flow around the loop is counter to the flow through the loop.

Filtered blood (low in salt) encounters ascending loop where it absorbs salt.

Salt-rich blood then encounters descending loop where it absorbs water.

The balance of water and salt maintains concentration gradients.

166
Q

Describe how water is reabsorbed in the collecting ducts.

A

Water diffuses through aquaporins from the tubules into the tubule cells into the interstitial space (two membranes with aquaporins).

167
Q

How long does it take for vasopressin to increase water reabsorption? Explain why.

A

Vasopressin modifies the rate of water reabsorption within minutes.

This is because when vasopressin binds to its receptor, aquaporin-rich vesicles fuse with the cell membrane to rapidly increase the number of channels for reabsorption.

Unlike with the protein channels from aldosterone’s response, the aquaporins are already made and just need to be inserted.

168
Q

What is the other common name for vasopressin?

A

Anti-diuretic hormone (ADH)

169
Q

What is proteinuria? Why does this happen?

A

High levels of protein in urine. Happens when kidney is damaged and its function is diminished.

170
Q

What is the body’s buffer system?

A

Carbonic acid/carbonate buffer system?

171
Q

What enzyme is responsible for the carbonic acid/carbonate buffer system?

A

Carbonic anhydrase

172
Q

How does the kidney regulate pH?

A

By regulating the carbonate as part of the body’s buffer system.

173
Q

Why do the kidney’s reabsorb carbonate ions from their tubules?

A

Since carbonate is essential to the body’s buffer system, loss of carbonate would impact the buffer. Instead of replacing the carbonate, the kidneys reabsorb it.

174
Q

Describe how carbonate is reabsorbed in the nephron.

A

Protons are transported from tubule cells into the tubule, reacting with carbonate ions to form carbonic acid.

Carbonic acid forms water and carbon dioxide which diffuses into the tubule cell.

In the tubule cells it reforms carbonic acid thus producing carbonate ions which are transported into the interstitial space.

175
Q

How are excess protons from carbonate reabsorption secreted?

A

Diffuse into the tubule where they bind with phosphates in order to maintain the conc. gradient out of the tubule cells.

176
Q

How does glutamine metabolism generate carbonate ions?

A

Filtered glutamine is reabsorbed into tubule cells.

Glutamine is metabolised into ammonium and carbonate ions.

Ammonium is secreted into the tubules and secreted whilst carbonate ions are transported into the body.

177
Q

Define alkalosis

A

When the body becomes more alkaline, loses protons, pH increases.

178
Q

Define acidosis

A

When the body becomes more acidic, gains protons, pH decreases.

179
Q

Why must body pH be so tightly balanced? What pH range does a healthy body maintain?

A

Since many processes are dependent on pH it must be controlled.

7.35-7.45 = pH of the blood

180
Q

How do the kidneys respond to acidosis?

A
  • Excess protons in the tubule cells
  • More protons diffuse into tubule
  • More carbonate ions taken up as a result
  • More protons bind to phosphate for elimination
  • More glutamine is metabolise to release carbonate ions

Thus increasing the amount of carbonate in the body, mitigating the acidosis.

181
Q

How do the kidneys respond to alkalosis?

A
  • Less protons in the tubule cells
  • Less protons diffuse into tubule
  • Less carbonate ions taken up as a result
  • Less glutamine is metabolised to release carbonate ions

Thus decreasing the amount of carbonate in the body, mitigating the alkalosis.

182
Q

How does urine pH effect drug excretion?

A

Most drugs are either weakly acidic or basic.

In alkaline urine, acidic drugs are ionised. Vice versa applies.

Ionised drugs are less likely to be reabsorbed thus increasing excretion.

183
Q

How can modifying urine pH increase aspirin excretion?

A
  • Aspirin metabolises into salicylic acid
  • IV infusion of sodium bicarbonate releases carbonate ions into the blood
  • Carbonate ions make their way to the urine where they ionise the salicylic acid
  • Ionised salicylic acid no longer reabsorbed
184
Q

What is the biological process of elimination? How can something be eliminated by the body?

A

The removal of a substance or termination of its biological action.

It can be metabolised or excreted.

185
Q

Define the two types of metabolism

A

Anabolism: Build up
Catabolism: Breakdown

186
Q

What types of molecules does the liver metabolise? How does it eliminate them?

A

The liver metabolises lipophilic molecules, forming polar products which can then be excreted in the urine.

187
Q

Describe phase 1 reactions in the liver

A
  • Catabolic reaction
  • Introduces a functional group as a point of conjugation for phase II
  • Product often reactive
  • Carried out by hepatic microsomal enzymes on smooth ER of hepatocytes
188
Q

Why do phase 1 reactions mainly apply to lipid soluble molecules?

A

Since the reaction is carried out by enzymes on the smooth ER, the molecules must be able to enter cells. Thus, likely requiring some degree of lipid solubility.

189
Q

What is the cytochrome P450 monooxygenase system?

A
  • A family of haem enzymes located on the smooth ER of hepatocytes
  • Possess species and inter-individual variation
190
Q

Why is the genetic variation in the cytochrome P450 monooxygenase system significant?

A

The variations found in the enzymes implicates drug testing and drug response from patient to patient

191
Q

Describe the P450 cycle

A

DH = Drug

  • P450 combines with the drug
  • Fe3+ iron in the P450 is reduced to Fe2+
  • This combines with the released e-, O2 and a proton to form FeOOH-DH
  • Combines with another proton to form water and (FeO)3+ DH
  • FeO3+ extracts a hydrogen ion (isn’t oxygen being extracted?), releasing DOH and regenerating P450
192
Q

Describe phase II reactions in the liver

A
  • Anabolic, involve conjugation
  • Product is often inactive
  • Hydrophilic conjugates are secreted into bile where conjugation is move and molecule is reabsorbed (enterohepatic recirc.)
193
Q

What is conjugation? What is a conjugation point?

A

Conjugation refers to the attachment of a substituent group

A conjugation point is a location on a molecule where a substituent group can be attached

194
Q

Where else can phase I and II reactions occur?

A

In the kidneys and the lungs

195
Q

How do stereoisomers differ in their metabolism? Why is this significant?

A

Stereoisomers are metabolised differently. This has potential for a large range of drug interactions and effects of polymorphisms.

196
Q

What is first pass metabolism?

A

The process by which a drug given orally must first pass through the liver where it is metabolised by hepatic microsomal enzymes before it enters systemic circulation.

197
Q

Why are drugs given by IV exempt from first pass metabolism?

A

Since they directly enter systemic circulation they have an effect before they are metabolised in the liver unlike drugs delivered orally.

198
Q

How would first pass metabolism be impacted in patients with decreased GI/liver function?

A

In the case of decreased GI function: Less of the drug would make its way into the blood stream and would therefore be less bioavailable once metabolised.

In the case of decreased liver function: Less of the drug would be metabolised and more would enter systemic circulation. Thus making the drug more bioavailable.

199
Q

What are prodrugs?

A

Drugs which only become active once metabolised by microsomal enzymes

200
Q

What common agent(s) can induce CYP450 function?

A
  • Brussel sprouts
  • Smoking
  • St Johns Wort
201
Q

What common agent(s) can inhibit CYP450 function?

A
  • Grapefruit juice
202
Q

What are enzyme inducer/inhibitor drugs? Why are they significant?

A

Drugs which increase/decrease the activity of CYP enzymes.

In doing so they can affect the metabolism of other compounds/drugs

203
Q

What is the main aim of phase I and II reactions?

A

To decrease lipid solubility and enhance renal elimination

204
Q

Define bioavailability

A

A quantitative measure of the amount of drug that reaches its site of action and of the rate at which it gets there

205
Q

What does LADME stand for?

A
  • Liberation
  • Absorption
  • Distribution
  • Metabolism
  • Excretion
206
Q

Why does drug release/liberation oppose its membrane transport?

A

Drug release is dependent on its capability to dissolve (hydrophilicity) whereas membrane transport is dependent on its lipophilicity.

207
Q

State the Noyes-Whitney equation

A

dC/dt = ((DS)/h)(Cs-Cb)

Where

Cs = Solubility of drug
S = Surface area of the particle

208
Q

How can the solubility (Cs) of a weakly acidic/basic drug be predicted?

A

It can be predicted given the:

  • pH of the solution
  • pKa
  • Solubility of free (unionised) drug
209
Q

What is the main pathway of drug absorption? How does this influence drug design?

A

The main pathway of drug absorption is passive diffusion

Thus, most drug design aims to optimise lipophilicity, in order to partition into and then out of the lipid bilayer

210
Q

What is the flux equation?

A

J = CvA

Where

J = Flux
C = Concentration
v = Velocity
A = Area

211
Q

What is Fick’s first law equation? NEEDS TO BE EDITED, INCOMPLETE

A

J = ((ADK)/∆x)*(C1-C2)

Where

J = Flux
A = Surface area
D = Diffusion coefficient (diffusivity)
∆x = Membrane thickness
K = Partition coefficient
C1-C2 = Difference between drug’s concentrations on either side of the membrane

212
Q

What does the partition coefficient (K) quantify? Can you define this as an equation?

A

The distribution of a drug between membrane and aqueous phases which it separates

K = Coil/Cw

213
Q

What oil is often used as a standard for calculating the partition coefficient of a drug?

A

Octanol

214
Q

What is the difference between K and P?

A

No difference. They both represent the partition coefficient (be careful though K doesn’t always).

215
Q

How does drug ionisation and pH partition affect the absorption of weakly acidic/basic drugs?

A

Ionised versions of drugs (A- and BH+) are more hydrophilic, reducing membrane transport of a given species.

216
Q

What is the pH partition hypothesis? Why isn’t it always applicable?

A

A drug will accumulate on the side of the membrane where pH favours ionisation.

Doesn’t take into account a variety of factors associated with absorption.

217
Q

State Lipinski’s Rule of Five

A
  1. Molecular weight ≤ 500
  2. log P ≤ 5
  3. No more than 5 hydrogen bond donors
  4. No more than 10 hydrogen bond accceptors

(All units in the rules are multiples of five)

218
Q

How has gastric transit influenced medicine design?

A

Gastric acid degrades certain drugs. To allow oral administration, gastro-resistant dosage forms have been developed.

Pepsin completely degrades polypeptide drugs so they must be administered by other means.

219
Q

Where are oral drugs principally absorbed?

A

The small intestine

220
Q

How do meals influence gastric emptying rate?

A

The larger the meal the quicker the initial rate of gastric emptying

221
Q

What order can be used to model gastric emptying?

A

Zero order

222
Q

How do fatty acids influence emptying rate?

A

Reduce emptying rate proportional to conc. and chain length

223
Q

How do triglycerides influence emptying rate?

A

Reduce emptying rate. Unsaturated more than saturated.

224
Q

How do carbs and AAs influence emptying rate?

A

Reduce rate in a conc.-dependent manner (relative to osmotic pressure)

225
Q

Describe the gastric transit of a gastro-resistant dosage form. How does this impact its absorption?

A

Won’t break down in gastric acid, so can’t pass through pylorus due to size. Must wait for house-keeper wave to pass through.

Therefore, lag-time between when drug is taken and SI absorption.

226
Q

Describe the gastric transit of a suspension/powdered dosage form. How does this impact its absorption?

A

Drug is rapidly decomposed into gastric fluid, dissolving into the solution. Drug rapidly passes via the pylorus.

Therefore, little lag-time between when drug is taken and SI absorption.

227
Q

What is an excipient?

A

Any component besides the API in a medicine. Often used to improve administration of the API.

228
Q

How can we improve the membrane permeability of a drug?

A
  • Modifying a drug with lipophilic groups to allow it to partition easier
  • Developing a prodrug that can partition easier and then metabolise to form the active drug
229
Q

What is enterohepatic recycling?

A

The process by which drugs can be eliminated by biliary secretion only to be absorbed again in the SI.

230
Q

What are the 3 main factors that the amount of drug absorbed depends on?

A
  • The amount released from the dosage form
  • The amount metabolised (stomach, intestines and liver)
  • The amount that permeates through the GI membrane
231
Q

How can a drug be transported across the GI membrane?

A

Via:

  • Paracellular transport
  • Diffusion
  • Facilitated diffusion
  • Drug transporters
232
Q

What is an efflux pump? What is its purpose?

A

A membrane protein that pumps a given molecule outside of a cell. This allows for the efflux pump to eliminate/reduce the presence of potentially toxic molecules inside the cell.

233
Q

How can efflux pumps explain the resistance of tumour cells to anticancer drugs?

A

Drug is pumped out of the tumour cells faster than it is transported in, preventing it from reaching a therapeutic level.

234
Q

What is the function of P-Glycoprotein (PGP)? What effect does this have on drugs?

A

PGP is a typical efflux pump that is found in many different tissues.

PGP is responsible for the poor bioavailability and low CNS conc. of numerous drugs.

235
Q

Why are P-Glycoprotein (PGP) inhibitors so important when administering chemotherapeutic drugs?

A

They prevent PGP from pumping chemotherapeutic drugs out of epithelial cells after they’re absorbed. In doing so they improve the oral bioavailability of the drug in question.

236
Q

Why is food a significant consideration for drug absorption?

A

Presence of food can improve or worsen the absorption of the drug and thus impact its bioavailability. For this reason some drugs must be taken with food or during fasting conditions.

237
Q

What drugs can most easily permeate the oral mucosa? How do they permeate?

A

Small lipophilic drugs, they do so via passive diffusion.

238
Q

What are the benefits of the buccal pathway for drug absorption?

A

There is a good supply to the oral mucosa making absorption efficient. It also bypasses hepatic first-pass metabolism.

239
Q

Why can’t insulin be orally administered?

A

Insulin would be completely degraded

SL12011 The Science of Medicine (7 decks)

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