Explain the divisions of the fluid compartments of the body.
The body is 60% aqueous fluid - most of the fluid is intracellular (2/3rds) - the remainder is extracellular (1/3rd) The extracellular fluid is separated into interstitial fluid (80%, tissues that bathe the tissues) and plasma (20%, the fluid part of the blood). The exchange between these fluids occurs in the capillaries. The only difference between these two fluids is the presence of plasma proteins which are too large to pass through the capillaries into the interstitial fluid. The intracellular and extracellular fluid are separated by the cell membrane.
What are the concentrations of the major components of intracellular and extracellular fluid?
EXTRACELLULAR FLUID (mM) Na+ 140 K+ 5 Cl- 110 HCO3- 27 Ca2+ 2 Mg2+ 1 Anions- 8 pH 7.4 potential + (mV) IINTRACELLULAR FLUID (mM) Na+ 10 K+ 140 Cl- 5 HCO3- 10 Ca2+
The membrane is a barrier but diffusion of polar and non-polar substances can occur. What are the 2 types of diffusion?
PASSIVE DIFFUSION of fat soluble non-polar substances through the lipid bilayer FACILITATED DIFFUSION of hydrophilic substances through integral membrane protein pores or carriers
What is the difference between integral and membrane proteins?
Membrane proteins confer distinctive functions by acting as transport systems, enzymes, receptors etc. PERIPHERAL proteins are weakly bound and can be removed by mild treatment (changing the pH) INTEGRAL proteins are embedded in the bilayer and can only be removed by disrupting the bilayer.
What is the importance of the amphipathic properties of membrane lipids?
Membrane lipids are amphipathic: small molecules with hydrophobic and hydrophilic regions. Hydrophilic groups are charged (polar) and are readily soluble in aqueous environment. Hydrophobic groups are uncharged (non-polar) and are poorly soluble in an aqueous environment.
What are the key roles played by membrane transport processes?
1. Regulate cell volume and maintain intracellular pH and ionic composition within a narrow range 2. Concentrate essential nutrients from extracellular space and excrete metabolic waste products.
Use flux equation to explain diffusion into an enclosed compartment.
F = P (Co-Ci) note P = permeability constant. The rate of diffusion is measured as T90%, which is the time taken for concentration of the extracellular space to increase to 90% of the capillary concentration (in the case of movement from the capillary to extracellular space) Efflux is from inside to outside, influx is from outside to inside. Flux is the number of molecules crossing a unit area of membrane in a unit time i.e. moles/cm2/sec
What 3 things/processes occur in the first week of embryonic development?
fertilisation, cleavage, and transport to the nucleus
Describe the process of fertilisation. What does it result in? (HINT: there's 3 things)
Occurs in the ampulla of the uterine tube within 12 hours of ovulation (no more than 24 hours, however sperm can live for unto 48 hours in the female genital tract). Fertilisation results in: - completion of meiosis in the oocyte - restoration of the diploid number of chromosomes - determination of sex and initiation of cleavage of the zygote within the zona pellucida.
Describe the process of cleavage. When does it occur? What is it? What does it do? Where does it occur? What does it form?
Occurs within 36 hours of fertilisation, initially cells are totipotent up to the blastocyst stage. Cleavage is a series of mitotic divisions that gives an increase in the numbers of cells (blastomeres). As the cytoplasm is shared, cells become smaller with each division giving a high surface area to volume ratio that enhances the uptake of nutrients, O2 and removal of waste products. Cleavage occurs as the zygote passes along the fallopian tube to the uterus. 16 cells form the morula = a solid ball of cells arranged in inner and outer layers.
What is going on/happens 3-4 days AFTER fertilisation?
The morula consists of approximately 100 cells as it enters the uterus and the zona pelludica dissapears. The outer cells divide to become trophoectoderm Fluid begins to accumulate in the centre of the morula which now becomes know as the BLASTOCYST. Cavities develop between the cells and they fill with fluid. The outer wall of the blastocyst or trophoblast will form the embryonic part of the placenta and secretes early pregnancy factor (EPF) - an immunosuppressant protein to prevent mother recognising embryo as foreign and rejecting it. The inner cell mass consists of blastomeres and forms at one pole of the blastocyst; these cells will give rise to the embryo proper.
What occurs on days 5.5-6?
BINDING TO UTERUS WALL - Binding at the uterus epithelium occurs (embryonic pole attaches) - Down regulation of anti-adhesion molecule MUCN1 - Allows binding via selectins (embryo) to glyco-components on epithelial cells (uterus) - Similar mechanism to white blood cell adhesion to blood vessel walls. - Integrins, laminin and fibronectin involved in initial penetration.
What are the main events which happen during days 6-7?
Implantation begins Trophoblast becomes the “invasive” syncytiotrophoblast and cytotrophoblast (cap the embryoblast which will become the embryo) Syncytiotrophoblast multinucleate syncitium invasion via metalloproteases Immunosuppression of host/graft and graft/host reactions
What occurs on (i) Day 8 and (ii) Day 9 or embryology?
(i) Trophoblast divides and part becomes “invasive” syncytiotrophoblast and cytotrophoblast Two layers form in the embryo – epiblast (inner) and hypoblast The amniotic cavity begins to form as a space within the epiblast. (ii) The flattened cells spread out from the hypoblast to line the inner surface of the cytotrophoblast forming the primitive yolk sac
What happens during days 11-12?
Spaces form in the extra embryonic mesoderm, fusion of these spaces forms the chorionic cavity The blastocyst burrows completely into the endometrium Syncytiotrophoblast (SCT) cells erode through the walls of large maternal capillaries which bleed into the spaces H primitive placental circulation (breakthrough bleeding may occur) The embryonic disk is now bilayered
Why is week 2 known as the week of 2s?
2 layers develop in the trophoblast: - syncytiotrophoblast - cytotrophoblast 2 layers in the inner cell mass: - epiblast (= ectoderm) - hypoblast ( = endoderm) 2 cavities form: - amniotic - chorionic
What site is the most common for ectopic implantation? Why can this occur?
Ampulla There may be a number of causes including mucosal adhesions due to pelvic inflammatory disease (can be caused by chlamydia) 95-97% of ectopic pregnancies are in the ampulla/isthmus of the fallopian tube
What does rupture of the fallopian tube during ectopic pregnancy result in? What are the symptoms of this often confused with?
Rupture of the tube causes blood loss that may be life threatening to mother and fatal for the embryo, the symptoms can be confused with appendicitis leading to misdiagnosis.
Apart from the ampulla of the fallopian tube, where is another place that an ectopic pregnancy can occur?
Very occasionally pregnancies develop on the mesentery and the baby may survive if surgical intervention occurs as mesentery has a good blood supply for early embryo development.
When is the embryo most vulnerable to environmental insult? What do the environmental causes include?
Embryonic period. Most organs and organ systems are formed during the 3rd week, critical period for normal development of organs systems. Drugs chemicals: nicotine/alcohol, chemotherapy/thalidomide/retinoic acid Infectious agents e.g. rubella Ionising radiation
Where are the (i) dorsal-ventral (ii) left-right axes determined in the embryo?
(i) in the oocyte (ii) determined cilia movement in the node
What is the function of (i) channel proteins (ii) carrier proteins?
(i) have watery spaces through the molecule allowing free movement of water and some molecules and ions that move along their concentration gradient. (ii) bind to molecules or ions and move them through the protein to cross the bilayer Channel proteins and carrier proteins are usually selective for a particular molecule
What is the role played by the permeability constant in determining transmembrane diffusion? What does P depend on?
The permeability constant (P) incorporates the factors inherent in both the molecule and the membrane that determines the probability of the molecule crossing the membrane P = ωRT k/a (NOTE: dont need to know this) P depends on: - the size of the molecule and viscosity of solution being diffused through (ω) - The thickness of the membrane (a) - And the molecule resistance (k) eg: lipids are ‘slippery’ and will move more easily than a charged particle which will offer some resistance
Explain the anomalous permeability characteristic permeability properties of water.
Water is one of the small molecules that have anomalous behaviour when comparing permeability across the lipid bilayer to k. Its permeability far exceeds the expected value from the trend of most of the other molecules. This shows that water must be moving by a different mechanism than simple diffusion through the lipid bilayer. ....AQUAPORINS
What is the structure and membrane organisation of the Aquaporin water channel?
Aquaporin is an integral membrane protein found in biological membranes allowing movement of water by offering an alternative route for the movement of water across the membrane without the molecule having to interact with the lipid. The basic aquaporin unit comprise 6 trans-membrane α-helices NPA : asparagine - proline - alanine (amino acid motif) Aquaporins form tetramers in the membrane – each monomer acts as a water channel.
How does ADH regulates of the transepithelial movement of water?
Anti diuretic hormone (ADH), also called vasopressin, is a 9 amino acid long polypeptide. It increases water reabsorption in the kidneys by up-regulating AQP-2 in the epithelial cells of the late distal tubules, collecting tubules and collecting ducts (requires urine output) Increased AQP-2 channels allows increased water up-take. Whilst AQP-3 channels remain constant.
What are the 2 types of active transport? Describe them.
1. PRIMARY ACTIVE TRANSPORT:
- molecules are pumped against an EC gradient at the expense of energy (ATP) = direct use of energy
2. SECONDARY ACTIVE TRANSPORT:
- Transport is driven by the energy stored in the
EC gradient of another molecule (usually Na+) that was already pumped into the cell using active transport = indirect use of energy
What are 3 examples of primary active transport? Describe them.
1. Sodium potassium pump transports sodium ions out and potassium ions into cells. Establishes a negative voltage inside the cell important for nerve function and signal transmission.
- When 2 x K+ are bound to the external K+ sites and 3 x Na+ to the internal sites ATPase is activated. One ATP is cleaved to ADP + 1 x high energy phosphate bond. Phosphorylation causes a chemical and conformational change to the carrier protein causing the 3 x Na+ to be extruded across the membrane and the 2 x K+ to be introduced into the cell.
- it is responsible for secondary active transport.
2. Ca2+ ATPase transporter: Present on the cell membrane and the sarcoplasmic reticulum in muscle fibers. Maintains a low cytosolic Ca2+ concentration
3. H+ ATPase transporter: Found in parietal cells of gastric glands (HCl secretion) and intercalated cells of renal tubules (controls blood pH). Concentrates H+ ions up to 1 million-fold
What are the 4 ways that molecules can move across cell membranes?
- Diffusion across the membrane (non-polar molecules)
- Diffusion through membrane pores
- Protein carrier facilitated diffusion
- Active transport (primary with specific ATPases and secondary with specific transporters)
Describe secondary active transport (co1 transport) with Na+ symporter.
[Na+] across the membrane is high outside / low inside the cell
Na+ high creates electrochemical energy due to pressure to diffuse through the membrane.
Na+ and a second molecule bind to the symporter and both are transported into the cell using Na+ electrochemical energy eg. glucose, amino acids and 2 x HCO3-
What is the function of (i) symporters (ii) antiporters?
(i) transport substance in the same direction as a 'driver' ion e.g. Na+. It involves the use of an EC gradient
(ii) transport substance in the opposite direction as a 'driver' ion like Na+
Describe secondary active transport with antiporters.
Antiporters use Na+ electrochemical energy to transport Calcium and Hydrogen ions out of the cell while Na+ enters.
Transport is in the opposite direction to the primary ion (eg. Na+)
Why is the sodium pump named the sodium pump?
Since the extrusion of Na+ takes place against a steep electrochemical gradient (concentration and electrical) the active transport system is called the sodium pump
Describe the structure of the sodium pump.
Consists of one alpha and one beta subunit, however they exist as dimers (2 sodium pumps, therefore 2 alpha & 2 beta subunits).
The alpha and beta subunits are both integral proteins, BUT alpha spans the entire width of the membrane and hence it must be the active subunit for the transport of sodium. The alpha protein also has ATP binding sites on the intracellular side which provides the energy for the movement of substance against a concentration gradient. On the extracellular side of the alpha subunits are cardiac glycoside binding sites which allows inhibition of the pump.
The beta subunit only reaches about half way through the membrane from the extracellular side and has extracellular glycoproteins on the surface.
What is necessary for the sodium pump to function? Approx how many pump sites to cells have in their membranes?
ATP available intracellularly
Cardiac glycosides must only be able to inhibit from the extracellular surface
Na ions bind internally (3 per alpha)
K ions bind externally (2 per alpha).
NOTE: Most cells have around 1 million sodium pump sites in their cell membrane
What is the clinical significance of the interaction between the binding of the cardiac glycosides and the extracellular potassium concentration?
A decrease in the [K+]O results in an increased affinity between cardiac glycoside and the sodium pump. As [K+]O is decreased the sodium pump is inhibited as less substrate carrier complexes can be formed. This causes a build up of [Na+]I (inside the cell). This hence inhibits the action of the calcium/sodium contort transport carrier leading as sodium does not move into the cell via facilitated diffusion due to the increased intracellular concentration. Hence there is a build up of intracellular calcium which leads to increased heart contractions.
What is the function of diuretics? What are they used to treat? What side effects can occur?
They INCREASE urine output by the kidneys (i.e. promote diuresis)
High bp and excessive fluid retention
Loop diuretics such as Furosemide increase urinary excretion of potassium which may lead to hypokalaemia
Explain the link between cardiac glycoside toxicity and blood potassium concentrations. How can digoxin toxicity be treated?
Patients on digoxin (narrow therapeutic index) who start diuretics (furosemide) – may become hypokalaemic.
A reduction in competition between K+ and digoxin results in increased digoxin binding (though plasma concentration is unchanged) to the sodium pump.
Because of the very narrow therapeutic index, the patient develops digoxin toxicity.
This can be treated however by administering a digoxin binding antibody such as digibind. Digibind rapidly binds to the digoxin causing it to dissociate from the sodium pump reversing the toxicity associated with the increased sodium pump inhibition caused by the hypokalaemia.
What is the difference between primary and secondary active transport?
Primary active transport systems directly couple the hydrolysis of ATP to molecular movement (sodium, potassium pump).
Secondary active transport systems use the energy stored in the Na+ gradient (generated by the sodium pump) to drive molecular transport against the electrochemical gradient via co-transport or counter-transport.
Explain the mechanism of sodium dependent calcium transport.
Sodium, calcium exchange occurs by secondary active counter-transport.
Sodium pump provides the large concentration gradient, as sodium diffuses in and calcium is forced out against a concentration gradient and electrochemical gradient.
What are the mechanisms involved in the transepithelial transport of glucose? Describe intestinal uptake of glucose.
Na+ dependant transport of glucose occurs by secondary active co-transport. The high Na+ concentration gradient drives the uptake of glucose against a concentration gradient.
GLUT 1 = basal uptake in placenta and brain
GLUT 2 = transepithelial transport, beta cells
GLUT 3 = basal uptake in brain
GLUT 4 = skeletal muscle (insulin dependent)
GLUT 5 = intenstinal absorption of fructose
Intestinal uptake of glucose: 2 Na+ ions move into the cell per 1 glucose molecule through the sodium dependant glucose transporter (SGLT1 or SGLT2) from the apical compartment (lumen of the intestine) into the cell.
Glucose then passes into the blood vessel via facilitated glucose transporter GLUT2 (facilitated diffusion).
Define (i) sporadic (ii) endemic (iii) epidemic (iv) pandemic.
(i) occasional cases occuring irregularly
(ii) persistent backround levels of occurance (low to moderate level)
(iii) occurrence in excess of the expected level for a given time period
(iv) epidemic occurring in or spreading over more than one continent
What is the definition of an outbreak? (HINT: there's actually 2 definitions)
Two or more people who experience a similar illness or confirmed infection and are linked by a common factor OR when the observed number of cases unaccountably exceeds the expected number for a given place and time
What are the 3 parts of the epidemiological triad? Describe them.
Agent = the organism that causes the infection
Host = the potentially susceptible individual
Environment = the external factors that affect potential disease transmission
What is the chain of infection? (HINT: there's 6 steps)
- PORTAL OF ENTRY = The place the infectious agent enters the new host. E.g. mucous membrane, respiratory tract, broken skin (e.g. open wound, insect bite, cannula, central line), urinary tract, placenta etc
- SUSCEPTIBLE HOST = The person who is at risk of the infection (e.g. high risk groups: elderly, very young, chronic disease, immunosuppressed)
- INFECTIOUS AGENT = The disease causing organism. E.g. bacteria, virus etc
- RESERVOIR = The place where the infectious agent lives. E.g. in people (e.g. GI tract), animals, insects, environment (e.g. soil, water, furnishings, equipment) etc
- PORTAL OF EXIT = The means by which the infectious agent leaves. E.g. saliva, nose/throat discharges, faeces, vomit, blood etc
MODE OF TRANSMISSION = How the infectious agent moves to the susceptible host. E.g. skin contact, coughs/sneezes, droplet spread, ingestion of infected food/water, faecal-orally, by vector etc
MODE OF TRANSMISSION = How the infectious agent moves to the susceptible host. E.g. skin contact, coughs/sneezes, droplet spread, ingestion of infected food/water, faecal-orally, by vector etc
What is the equilibrium potential?
The movement of an ion under the assumption that the membrane is only permeable to that ion.
The equilibrium potential of potassium is negative due to the high concentration of the positive potassium ion intracellularly (140mM) compared to extracellularly (5mM). This would cause a net outflow of positive ions from the cell and therefore the inside of the cell will become negative (-100mV).
The sodium equilibrium potential is a positive value. There is a high concentration gradient from extracellularly (140mM) to the intracellular concentration of sodium (10mM). Under the assumption that the membrane is only permeable to sodium, sodium ions (positive ions) diffuse into the cell and the cell becomes positively charged in comparison to outside the cell (60mV).
What is the origin of the resting membrane potential?
A very small number of K+ ions diffuse out of the cell down their concentration gradient. Because K+ ions are not accompanied by anions, charge separation occurs and the electrical potential of the cell interior becomes negative with respect to the extracellular solution. At rest the membrane is only slightly permeable to Na+ (50 times less so than K+, PNa+ : PK+, 1 : 50).
Define (i) depolarisation (ii) re-polarisation (iii) hyperpolarisation.
(i) The change in membrane potential from negative resting potential (-70mV) to positive peak (30mV).
(ii) From the positive peak (30mV) back to resting membrane potential (-70mV)
(iii) From the resting membrane potential (-70mv) to an even greater negative value (-90-100mV).
What is the difference in response of electrically excitable and inexcitable cells to depolarisation? (NOTE: Excitable cells are nerve and muscle cells, whereas all other cell types are inexcitable.)
When a depolarising current is applied to an inexcitable cell a proportional change in membrane potential will be recorded, as V=IR (R is membrane resistance which stays constant in an inexcitable cell).
This is the case in an excitable cell up to the threshold potential. After the threshold potential is reached (high enough voltage/current applied) the size of the current applied has no significance to the size of the depolarisation of the membrane. This is due to the resistance of the membrane changing. A change in permeability to ions cause this change in membrane resistance by the opening of voltage gated channel proteins.
What are the 5 main characteristic of an action potential?
- The initial depolarisation must reach a critical threshold
- Once the threshold is attained, the depolarising upstroke is regenerative
- The potential depolarises, overshoots zero and peaks at around +30mV
- The response is all-or-none
- The potential repolarises from the peak of the overshoot back to the resting level.
What is the relationship between the changes in membrane permeability and membrane voltage?
Permeability to sodium ions changes when an action potential is initiated. The change in sodium permeability is transient, this tells us the channels responsible for sodium permeability are only open for a limited period of time and they close after this. The permeability of sodium increases rapidly by x600 when an action potential is initiated.
There is a delayed increase in potassium permeability after the action potential, this causes hyper-polarisation to occur. The membranes permeability increases 10 fold during repolarisation.
What is the role of voltage-gated and time-dependant Na and K channels in the action potential?
At a resting potential (-70mV) the voltage-gated SODIUM channels are closed but capable of opening (activation gate shut).
- At the threshold potential of -50mV there is a rapid opening of the activation gate triggered which open the channel until the peak potential of +30mV is reached. The opening of the sodium voltage-gated channel proteins causes the 600 times increase in membrane sodium permeability hence allowing Na+ ions to diffuse into the intracellular fluid (ICF) and depolarise the membrane.
- At the threshold potential the slow closing inactivation gate is triggered. This closes at the peak membrane potential preventing any further movement of Na+ ions through the channel. The inactivation gate does not reopen again until the membrane is depolarised (-70mV) at which point the channel “resets” and the inactivation gate opens and the activation gate closes.
The sodium channels are controlled by a positive feedback mechanism, the Na+ channels open increasing Na+ permeability which increases flow of Na+ into the cell. This causes membrane depolarisation which causes Na+ channels to open, restarting the cycle. This feedback system is stopped by the set “timer” of the Na+ voltage-gated channel inactivation gate.
At resting potential the voltage-gated POTASSIUM channels are closed preventing movement of K+ ions through them.
- At the threshold potential the delayed opening of the activation gate is triggered which remains closed unit the peak membrane potential is reached. At the peak potential the activation gate opens, this allows K+ ions to diffuse out into the extracellular fluid (ECF) depolarising the membrane.
- The potassium channel stays open until hyper-polarisation (-80mV) is reached at which point it closes preventing further movement through the channel.
What is chemotherapy?
The use of chemicals (either natural or synthetic) to inhibit the growth/replication of “invading organisms” or cancerous cells within the body
Antibiotics and antibacterials can be used interchangably
What is selective toxicity?
These drugs are intended to be toxic to the invading organism or cancerous cell but be relatively harmless to the host or normal cells.
This approach depends upon the existence of biochemical differences between the target group of cells and the host.
This is what makes cancer hard to target by chemotherapeutic methods as they develop from the host’s cells, whereas bacteria are relatively easy to target in comparison due to the evolutionary differences of prokaryotes.
What are examples of different selective toxicity?
Penicillins: in the absence of allergy have very low toxicity and high doses can be used
Aminoglycosides have a narrow THERAPEUTIC INDEX thus the dose that causes toxicity is very close to the therapeutic dose
For anti-tuberculosis drugs such as isoniazid and pyrazinamide a number of pts will develop hepatotoxicity that is not dose related and may require treatment to be stopped
What is the function of peptidoglycans? (HINT: there's 5 points)
1) They make up the cell wall of bacteria and do not occur in eukaryotes.
2) Cell wall is made up from various numbers of strands of peptidoglycans
3) The strands are made up multiples of amino-sugars; N- ACETYLGLUCOSAMINE & N-ACETLYMURAMIC ACID dimers. The n-acetylmuramic acid has a short peptide side chain (hence peptidoglycan).
4) The peptide side chains are cross-linked to form a latticework.
5) Cross-linking gives the cell all its strength.
What are the 3 types of bacterial cell wall inhibitors? Describe why they are used to treat bacterial infections
ß-Lactam antibiotics - Penicillin family and drugs like it, share a common structure
- Stop the cross linking by targeting the enzyme responsible for forming cross linkages (peptidyl transferase). This prevents the cross-linking peptides from binding to the tetra-peptide side-chains.
Vancomycin - Come into play when there is resistance e.g. MRSA (meticillin resistance). However there can also be resistance to these e.g. VRSA (vancomycin resistant)
- Stops the elongation of the peptide backbone, stops the joining of one dimer to another (stops joining of one “brick” to another).
Bacitracin - stops the lipid mediated transfer of the “bricks” from one side of the cell membrane to the other
Why is penicillin an almost 'perfect' drug? What are the 4 main groups of penicillins? Describe them.
As we have no metabolism for penicillin and therefore it is excreted in the urine without interacting with our cells.
BUT ... 5% of the population are allergic to penicillin and bacteria can develop resistance to it.
1. Penicillin G & V - G is the original strain found and is still the most potent but it is not acid stable and therefore will be destroyed in the stomach. Penicillin V is acid stable and therefore is the most common
2. ß-Lactamase-resistant Penicillins (e.g. Methicillin, Oxacillin, Nafcillin, Cloxacillin, Dicloxacillin.) - If a bacteria has the ß-Lactamase enzyme present, which allows it to break down ß-Lactam rings, they are resistant to most penicillins. To counter this penicillins that aren’t destroyed by ß-lactamase were developed.
3. Broad-spectrum penicillins (e.g. Ampicillin and Amoxicillin.) - Not all bacteria were susceptible to penicillins as they had a waxy coating which prevented the penicillins getting to the enzymes. This is due to the differences in cell wall of Gram negative and Gram positive bacteria. To counter this more broad spectrum antibiotics were brought in.
4. Extended Spectrum Penicillins (e.g. carbenicillin, ticaracillin, azlocillin, piperacillin) - Pseudomonas aeruginosa infections are deadly hospital acquired bacteria and are not killed by antiseptic washing or the normal spectrum of penicillins. Here the extended spectrum penicillins are used
What are cephalosporins?
They come from the fungus cephalosporium acremonium
Work by the same mechanism as pencillins
Classified in generations in the order in which they were developed
They can now be termed by means of administration; oral is cephalexin; parenteral are cefuroxime and cefotaxime
What are the 2 bacterial folate antagonists? Describe their function. What is sequential blocking?
SULPHONAMIDES & TRIMETHOPRIM
These are antibiotics which act through an inhibition of the folate pathway in bacteria (folate = folic acid). Folate is a vitamin involved in making haemoglobin in humans, we have to acquire it as a vitamin in the diet. However bacteria must make their own folate, so targeting how folate is made is specific to bacteria.
The folate system is important in cell metabolism and this makes bacteria susceptible to drugs which interfere with folate metabolism, thus we have our ‘selective toxicity’ target.
Sulphonamides mark the beginning of antimicrobial chemotherapy dating back to the 1930s and preceding the penicillins.
Folic acid is made by joint pteridine and PABA. The antibiotics are competitive antagonists as they have similar structures to the constituents of folic acid.
Sulphonamides inhibit the enzyme which converts PABA to folate. Trimethoprim inhibits the enzyme from folate to tetrahydrofolate.
Sequential blocking = the blocking of two enzymes in a sequence, this is much more effective than blocking one only.
What are aminoglycosides? Give examples. How do they inhibit protein synthesis?
Very powerful antibiotics which have to be injected
E.g. streptomycin, kanamycin, neomycin, gentamycin
1. They form ionic bonds at the cell surface
2. Penetrate the cell wall by a transport mechanism across the cell membrane.
3. They then diffuse into the cytoplasm and then bind to the bacteria ribosomes at the interface between the assembled 30s and 50s subunits OR directly to the individual subunits.
4. This inhibits protein synthesis by causing the misreading of mRNA, which causes the wrong tRNA, wrong amino acid, wrong protein.
What are tetracyclines? What is their function/MoA?
Have 4 benzene rings
They prevent attachment of the tRNA to the acceptor (A) site on the mRNA-ribosomal complex. This prevents the addition of amino acids to the peptide chain.
- Unlike the aminoglycosides, they are only weakly bound to the ribosomes.
- Differences in the activity of individual tetracyclines are related to their solubility in the lipid membrane of the bacteria.
What is the function of Chloramphenicol, Erythromycin and Clindamycin?
They prevent the addition of new amino acids to the growing peptide chain by binding to the ribosomes.
This prevents association of the peptidyl-transferase with the amino acid and no peptide bond is formed i.e. no transpeptidation.
It may also prevent translocation of the ribosome down the mRNA template (Erythromycin).
- They are also used when penicillins don’t work and anyone who is allergic to penicillin is given erythromycin
What synthetic antibiotics are Topoisomerase II inhibitors?
synthetic antibiotics recently introduced into clinical practice
Broad spectrum agents: ciprofloxacin, ofloxacin, norfloxacin. Narrower spectrum drugs: cinoxacin and nalidixic (first introduced and is not fluorinated).
They act by inhibiting bacterial DNA Topoisomerase II also known as DNA gyrase.
- This enzyme catalyses the introduction of negative supercoil in DNA permitting transcription and replication
What is gastrulation? When/what occurs?
Gastrulation is the process during which the three primary germ layers form. It involves cellular rearrangements and cell migrations and marks the beginning of the embryonic period.
The process of gastrulation occurs during days 14 /15
Epiblast cells stream into the embryo along the primitive streak/node. The migrating cells that first sink into the groove and replace the hypoblast cells form the endoderm.
The trilaminar disc is then established. Mesoderm is formed when epiblast cells spread between the the two layers. In front of the node a specialised mesoderm structure called the notochord forms (an importantsignalling structure) between the two layers
What is neurulation? When/what occurs?
Occurs at the beginning of week 3
The notochord induces the overlying ectoderm to thicken and form the neural plate
Neurulation is induced by the bar shaped tissue - notochord (deep to the neural epithelium)
- Epithelial cells become columnar. The plate will make a tube (neurulation). Day 19+ a midline groove becomes apparent
- on days 20-21 cells on neural plate edge thicken forming folds and a groove
- day 22 the edges roll over and the cells fuse to make a tunnel
- rostral neuropore closes day 25
- caudal neurpore closes day 27 and 3 brain vesicles develop into the brain
What are the 2 types of neural tube defects? What do they occur as a result of?
Due to the failure of the neural tube to close
Failure of rostral nueropore = anencephaly (lack of development in brain)
Failure of caudal neuropore = some forms of spina bifida (vertebral column doesn't form)
What are neural crest cells? What cell types do they produce?
Specialised cells that migrate away from the neural tube epithelium. They produce a variety of cell types:
Cranial nerve ganglia, Dorsal root ganglia, Autonomic ganglia, Adrenal medulla, Schwann cells
Smooth muscle of cardiac outflow
Odontoblasts, Craniofacial skeleton
Thyroid parafollicular (C) cells, Melanocytes
What 2 symptoms can arise as a result of defective neural crest development? Describe them both.
Waardenburg’s Syndrome (autosomal dominant 1/50,000)
- Some types have Pax-3 gene deletion
- Pigment abnormalities (even albinism)
- Heterochromia of eyes
- Telecanthus (widely separated eye “corners”)
Treachers Collins Syndrome (autosomal dominant 1/50,000)
- Defective protein called Treacle (TCOF1 gene)
- Failure of formation/apoptosis of neural crest cells
- Abnormal eye shape
- Conductive hearing loss,
- Underdeveloped zygoma
- Malformed ears
What are derivatives of the ectoderm?
CNS, PNS, neural crest cells, sensory epithelium of the ear, nose and eye
Epidermis (skin, hair, nails, sweat glands)
Cornea and lens of the eye
Epithelium of the oral and nasal and paranasal air sinuses and anal canal
Some facial bones (intra-membranous ossification), cartilages of the pharyngeal arches and tooth enamel
Pineal and pituitary glands
What are the 3 aggregates of mesoderm that develop on either side of the notochord? Describe them (including mainly what they form).
1. Paraxial Mesoderm (forms the somites - close to the midline)
- Sclerotome hard tissue migrates medially to form the vertebrae that surround the notochord and neural tube
- Dermatome forms the dermis (NB the epidermis is derived from the ectoderm)
- Myotomes forms the skeletal muscle of the trunk and limbs via the limb buds
2. Intermediate Mesoderm
- Forms the gonads and kidneys
3. Lateral Mesoderm (forms paired plates)
- Somatic mesoderm forms the dermis ventrally, the heart and blood vessels and most connective tissues of the body.
- Splanchnic mesoderm forms smooth muscle connective tissues and serosal linings of the abdominal and thoracic cavities (peritoneum, pleura and pericardium)
What are the derivatives of the mesoderm?
All muscle types (smooth, striated and cardiac)
Cartilage, bone and connective tissues
Blood, bone marrow and lymphoid tissues
Endothelial lining of blood vessels
Sclera and vascular tunic of the eye
Synovial membranes of joints
What is endoderm? How is it formed?
The yolk sac becomes the gut tube
Amnion enwraps the embryo almost completely cuttng off gut from yolk sac
What are the derivatives of the endoderm?
Lens and retina
Oral Cavity Epithelium
Sensory organs of ear
Glands: Salivary gland, Sweat Gland and Mammary Gland Adenohypophysis (ant. pituitary)
What is the scientific method? (HINT: there's 7 points)
2. Explanation (Hypothesis) which can be tested
4. Experimentation and data interpretation
5. Confirmation (or not) of the hypothesis
6. Peer review
7. Publication (conference/academic journal)
Explain the importance of evidence based medicine in the provision of care
Comment on the effect of bias on scientific research
Differentiate between primary and secondary research studies
Explain the purpose of peer review
Explain what is meant by an evidence pyramid
How do you access the accuracy of information?
`Through an EVIDENCE PYRAMID:
Systematic reviews and meta-analyses
Randomised controlled double blind studies
Case control studies
Cross sectional studies
Case study, series or report
Read it in a textbook
Somebody told me
What are types of (i) primary studies (ii) secondary studies in research?
(i) Direct experimentation:
- in vitro models = molecular biology, cell and tissue culture, isolated tissue and organs
- in vivo testing = animal models and volunteers (artificial control over biological variables)
Clinical trials: drug treatments and follow up
(ii) Research overviews
Review – expert summary of a number of research studies
Systematic review – objective analysis of all qualifying primary research studies
Meta- analysis – integrated analysis of the numerical data from all qualifying studies