IASM Notes (I) PDF

IASM Notes Semester I (Adapted from lecture notes) - Page 1 of 300 - Content L1 Organization and Homeostasis of Body Functions........................................ 4 L2 Genes are Made of DNA........................................................................

IASM Notes Semester I (Adapted from lecture notes) - Page 1 of 300 - Content L1 Organization and Homeostasis of Body Functions........................................ 4 L2 Genes are Made of DNA................................................................................ 7 L3 From DNA to Protein..................................................................................... 9 L4 From Amino Acids to Protein Structure...................................................... 11 L5 From Protein Structure to Protein Function................................................. 14 L6 Enzymes are Powerful and Specific Catalysts............................................. 19 L7 Nutrition....................................................................................................... 24 L8 Structure and Function of Cells................................................................... 28 L9 Lipids........................................................................................................... 37 L10, 12 Carbohydrate Metabolism and Its Regulation............................................. 48 L11 Generation of ATP........................................................................................ 57 L13 Amino Acids Metabolism............................................................................ 59 L14 Metabolic Integration................................................................................... 62 L15 Nucleotide Metabolism................................................................................ 67 L16 Nutrition: Vitamins and Minerals................................................................ 71 L17 Cell Membrane Transport............................................................................ 84 L18 Intracellular Communication: Signal Transduction..................................... 87 L19 Cell Proliferation – Cell Division Cycle...................................................... 94 L21 Thermoregulation......................................................................................... 97 L20, 22-3 Embryology: Embryogenesis..................................................................... 103 L24 Do Doctors Really Matter?........................................................................ 127 L25 What is Medicine? What is Public Health?............................................... 131 L26 How is healthcare organized in Hong Kong?............................................ 135 L28 Gastrointestinal Tract................................................................................. 141 L29 Epithelial and Glandular Tissue................................................................. 152 L30 Connective Tissues..................................................................................... 158 L32 Structural Organization of the Respiratory System................................... 163 L33 Mechanisms of Breathing.......................................................................... 171 L34 Blood Cells................................................................................................. 175 L35 Movement-generating Tissue: Muscle....................................................... 187 L36 Introduction to the Skin............................................................................. 196 L37 Introduction to Musculoskeletal System.................................................... 206 L38 Introduction to Endocrinology................................................................... 214 L39 Structural Organization of the Cardiovascular System.............................. 219 L40 Introduction to Kidney Function................................................................ 229 - Page 2 of 300 - L41 Neural Architecture.................................................................................... 236 L42 Functional Organization of the Cardiovascular System............................ 242 L43 Membrane Excitability............................................................................... 246 L44 Transmission of Nerve Signals.................................................................. 251 L45 Functional Organization of the Brain........................................................ 259 L46 Excitation and Contraction of Muscles...................................................... 267 L47 Structural Organization of the Nervous System........................................ 275 L48 Peripheral Nervous System (PNS)............................................................. 284 L49 Autonomic Nervous System...................................................................... 295 - Page 3 of 300 - L1 Organization and Homeostasis of Body Functions A. Hierarchical Organization of Body Body consists of 1014 cells organized into organs DNA, RNA, protein (biological molecules) Nucleus / cystosol / membrane (organelles) Cell (basic functional unit) Tissues Organs Organ systems Body Organ systems include nervous, endocrine, immune, CVS, respiratory, urogenital, musculoskeletal, digestive and reproductive working together Cells communicate via electrochemical signals: □ Endocrine via blood □ Paracrine for short-distanced □ Autocrine for itself □ Neural for electrical signal via neurons to excitable cells - Page 4 of 300 - B. Homeostasis Definition: maintenance of constant conditions in internal environment (i.e. extracellular fluid) Each cell benefit from homeostasis and in turn contributes towards it 1. Body Fluids and Electrolytes a. Classification and Composition Total body fluid: ~60% of body weight, ~42L in 70kg body Distribution: Intracellular Within cell 2/3 28L Extracellular Intravascular Blood plasma 1/4 x 1/3 3-3.5L interstitial In tissue 3/4 x 1/3 10.5-11L + Predominant cation in interstitial fluid: Na ~90% of K+ is intracellular No protein in interstitial fluid while plasma contains proteins (eg albumin) Total body stores of Na+ = K+ = 3000mmol - Page 5 of 300 - b. Osmolality and Osmolarity Osmolality (osmole, Osm/kg): amount of solute per unit weight of solvent Osmolarity (Osm/L): amount of solute per unit volume of solvent Plasma osmolarity ≈ 2 [Na+] + 2 [K+] + [urea] + [glc] *[Na+], [K+] x 2 to account for anions associated with the cations Osmolarity slightly > osmolality (because volume < weight due to solvent present) and their difference is called ‘osmolar gap’ (OG) 2. Maintenance of Homeostasis A combination of negative feedback and positive feedback a. Negative Feedback Direction of correction opposite to error → promote stability Eg. Thermoregulation correction Efficiency = > -1 error b. Positive Feedback Direction of correction same as deviation → reinforce change Eg 1. Ferguson reflex in labour: pressure on internal end of cervix → posterior pituitary gland secretes more oxytocin → uterine contraction → more pressure Eg 2. Blood clotting Eg 3. Pre-ovulatory LH surge: FSH ↑ → follicle develops → E↑ → FSH ↑ LH↑ → FSH increases LH receptors, LH increases E secretion → FSH↑ LH↑ E↑, follicle grows rapidly - Page 6 of 300 - L2 Genes are Made of DNA A. Discovery Avery’s experiment: 1) Two strains of Pneumococcus exist: S (Smooth) with sugar coat and R (Rough) without. S can kill but R cannot. 2) Heated S strain does not kill but can make R strain kill. Killing characteristics can be passed on to next generation → genetic material transferred. 3) After isolation procedures, he discovered that only DNA part of inactivated S can make R kill → DNA is genetic material B. DNA as Genetic Material In eukaryotic cells, bacteria and virus Some viruses stores genetic material in RNA (eg RSV) and use reverse transcription to produce DNA to manipulate cell machinery Composed of 3 parts: deoxyribose, phosphate, base 3’ and 5’ C in deoxyribose joined with phosphate (replication from 5’ end to 3’ end) In double helix shape (discovered by Watson and Crick) - Page 7 of 300 - C. DNA packing 1) DNA strand + 8 histone protein → 1 nucleosome (10nm fibre, euchromatin) 2) 6 nucleosome attached by 6 H1 histone protein → 30nm fibre (solenoid, heterochromatin) 3) Loops of 30nm fibre on scaffold protein 4) Condensation into chromosome - Page 8 of 300 - L3 From DNA to Protein A. Central Dogma of Molecular Biology B. Transcription DNA and RNA differs in 2’ carbon of ribose (w/ or w/o O between C and H) Transcription unit: (promoter) + (transcribed region) 1) Promoter on template strand recognized by transcription factors (protein) → guide RNA polymerase to attach to gene; 2) Free ribonucleotide binds to template strand and RNA polymerase catalyze formation of mRNA precursor (or pre-mRNA); 3) 5’ cap and 3’ poly(A) tail are added and introns are cleaved (to form circular DNA) by spliceosomes 4) Cap and tail joins together to form a ring structure (to ensure completeness of transcription) and exits nuclear envelope for translation *Fx of 5’ cap and 3’ poly(A) tail are to prevent degradation by enzymes - Page 9 of 300 - C. Translation tRNA brings amino acid to mRNA at ribosome Peptide linkage is formed between adjacent amino acids A polypeptide is thus formed according to genetic coding in DNA D. Control of Gene Expression Need: Different proteins have to be expressed in different cells at different stages for different purposes Controlled through: □ DNA: replication, rearrangement (eg memory WBCs) □ RNA: transcription, modification, degradation □ Protein: translation, modification, degradation E. Detection of Gene Expression DNA: Southern blot RNA: Northern blot, cDNA microarray (coupling DNA sequences in array with fluorescent material) Protein: Western blot - Page 10 of 300 - L4 From Amino Acids to Protein Structure A. Amino Acids Can be found in two forms: □ Powder (solid form): without charge □ Aqueous form: as zwitterion (doubly charged) Natural occurring amino acids are all L-amino acids List of 20 common amino acids: 1. Non-polar (9) Glycine Gly, G Alanine Ala, A Valine Val, V Leucine Leu, L Isoleucine Ile, I Proline Pro, P Phenylalanine Phe, F Methionine Met, M Tryptophan Trp, W - Page 11 of 300 - 2. Polar (6) Serine Ser, S Threonine Thr, T Tyrosine Tyr, Y Cysteine Cys, C Asparagine Asn, N Glutamine Gln, Q 3. Negatively charged (2) Aspartic Acid Asp, D Glutamic Acid Glu, E 4. Positively charged (3) Lysine Lys, K Arginine Arg, R Histidine His, H - Page 12 of 300 -  Things to note: □ Hydrophobic a.a. are typically used in hydrophobic protein core while hydrophilic a.a. tends to be found on surface of protein □ Proline: α-amino group secondary → exceptional conformation rigidity □ Cysteine can be used in disulphide bridges (esp in oxidative conditions in ECF) □ Charged a.a. are critical in catalysis and other protein functions □ Aromatic a.a. have unique absorption wavelength at 280nm → can be used to measure protein conc. directly Amino acid sequence named from N-terminus to C-terminus (by convention) CO-NH act as rigid coplanar unit → equivalent to a single bond (virtual bond) Consecutive peptide links act as rigid coplanar units pivoting around α-C atoms F, V, T, W, I, M, L , K, H are the 9 essential amino acids B. Protein Structure Four levels of protein structure: □ Primary: by amino acid sequence □ Secondary: local conformation (eg α-helix and β-sheets) by H-bond □ Tertiary: 3D organization of domains (substructures that can fold independently) by disulphide bonds, H-bonds etc. □ Quaternary: complex of polypeptide chains Extracellular proteins are frequently stabilized by covalent cross-linkages including disulphide bonds between Cys (extracellular conditions are usually oxidative → removal of H from SH group in Cys) - Page 13 of 300 - L5 From Protein Structure to Protein Function A. Protein Functioning Protein can bind to other molecules Ligand: a molecule that bind reversibly via non-covalent forces □ Binding site: site where ligand binds □ Reversibility of binding enables interactions to be transient Prosthetic group: a molecule/group that is permanently bound to a protein by covalent forces B. Fibrous Proteins 1. Collagen Commonly found in connective tissues Collagen is a right-handed triple helix of three left-handed α-helices Structure stabilized by inter-chain H-bonds and a sheath of ordered water molecules of solvation Contains high level of hydroxyproline *Vit. C required in forming hydroxyproline from proline → important in maintaining c. t. 2. Hair Keratin - Page 14 of 300 - C. Hemoglobin and Myoglobin Hemoglobin (Hb): specialized protein in RBC that transports oxygen in blood □ Tetrameric (α2β2) with four heme groups Myoglobin: specialized protein in muscle that facilitates oxygen diffusion □ Monomeric with one heme group Heme: prosthetic group permanently bound to myoglobin and haemoglobin etc. □ Porphyrin ring surrounding Fe2+ □ Gives red colour of blood (most proteins have no colour) □ Fe2+ bound to protein with histidine on one side and oxygen on the other 1. Spectroscopic Detection of O2 binding to Hb Heme group is a strong chromophore (part of molecule that provides colour) that absorbs both in UV and visible range Fe2+ without O2 has an intense Soret band at 429 nm (blue) O2 binding alters electronic properties of heme, shifting position of Soret band to 414 nm (purplish blue) Binding of O2 can be monitored by UV-Vis spectrophotometry Deoxyhaemoglobin appears purplish while oxyhaemoglobin is red 2. Cooperativity of Hb to O2 binding Hb can exist in two states: tense (T) and relaxed (R) R has higher O2 affinity than T Deoxyhaemoglobin subunits are more stable in T state O2 binding triggers a T→R conformational change (by breaking of ion pairs between α1-β2 interface) As there is four subunits (i.e. 4 binding sites), binding of O2 at first subunit will facilitate binding at the other 3 - Page 15 of 300 -  Refer to graph on right: □ θ: degree of filling of haemoglobin by O2 □ As pO2 ↑, Hb transits from low-affinity to high-affinity state → sigmoid (cooperative) binding curve Also note Hill plot (graph showing cooperativity of protein) □ nH: Hill coefficient showing degree of cooperativity □ ↑Hill coefficient →↑cooperativity Phenomenon known as cooperativity: affinity of ligand varies with number of binding □ Positive cooperativity (nH > 1): first binding event increases affinity at remaining sites □ Negative cooperativity (nH < 1): first binding event reduces affinity at remaining sites Significance: □ In high pO2 (lungs, 13kPa), O2 binds stronger to Hb → can pick up O2 □ In low pO2 (tissues, 4kPa), O2 binds weaker to Hb → can release O2 effectively □ If no cooperativity (i.e. in myoglobin), O2 won’t be released at tissues 3. Cooperative Binding of CO CO has similar size and shape as O2 → can fit to the same binding site (O2 binds at an angle but not for CO) CO binds >20k times better than O2 because CO has a filled lone electron pair that can be donated to vacant d-orbitals on Fe2+ Protein pocket decreases affinity for CO but still ~250x better than O2 Toxicity originated from competitive effect and increase in cooperativity □ Shifts oxygen dissociation curve leftwards → stronger O2 affinity at tissue pO2 levels (O2 affinity of remaining 3 sites if COHb even higher than O2Hb)→ extra O2 retained at tissue → hypoxia (even when pO2 at normal) □ Even worse than being anemic CO poisoning accounts for > 1/2 yearly deaths from poisoning worldwide *15% COHb: headaches; 25%: nausea, dizziness; 50% COHb: coma, death - Page 16 of 300 - 4. Effect of pH on O2-Hb binding Affinity for O2 depends on pH: pH↑ → affinity ↑ i.e. O2 dissociation curve shifted leftwards at higher pH Protonation of amino acid residues stabilize Hb in T state Note blood in lungs has higher pH (because of lower CO2 content) → pH difference increase O2 transfer efficiency Phenomenon known as Bohr effect *Hb binds protons to several a.a., thus actually carrying 40% of total H+ from tissues 5. Haemoglobin and CO2 Export Some CO2 exported as dissolved bicarbonate in blood Some CO2 exported in form of a carbamate on amino terminal residues of hemoglobin Note that formation of a carbamate yields a proton which can bind to hemoglobin and promote O2 dissociation 6. Fetal Variant of Hemoglobin Adult Hb has α2β2 structure Fetal Hb (HbF) has α2γ2 structure (because one of subunits is transcribed/translated from a different gee) HbF binds to O2 more tightly than adult Hb → fetal blood in placenta can take O2 from maternal blood D. Importance of Protein Structure to Medicine 1. Sickle Cell Anaemia Gln at position 6 in β chain of Hb is mutated to Val → deoxygenated Hb stick to each other → sickle shaped RBCs Heterozygotes have evolutionary advantage in malaria endemic areas (as lower RBC half-life confers resistance to malaria parasites, which spend part of life cycle in RBCs) Homozygotes develop sickle cell anemia - Page 17 of 300 - 2. Drug Target in Avian Influenza Viral NS1 protein binds to CPSF30 protein Blocking such interaction provides target for antiviral drug development 3. G6PD Deficiency G6P dehydrogenase (G6PD) variants also confers resistance to malaria Also result in susceptibility to acute hemolytic anemia (AHA) 4. Prion Diseases Misfolding/aggregation of endogenous protein is cause of prion and Alzheimer’s disease When entering body, prions induces normal body protein to fold into faulty prion form → exponential growth in prion number Prion will then aggregate to form fibril structure → prion disease - Page 18 of 300 - L6 Enzymes are Powerful and Specific Catalysts A. Properties of Enzymes Enzymes: proteins that are able to accelerate (catalyse) a metabolic reaction Need for enzymes in body: □ Low concentration of metabolites in cells → low reaction rate □ More or less fixed pH in cells → protein will not denature □ Constant body temperature → protein will not denature □ High energy barrier of metabolic reaction → low reaction rate □ Need for metabolic regulation (change metabolic rate according to environment) Catalytic action of an enzyme is specific Enzymes are sensitive to pH and temperature (because thermal vibration may destroy protein structure of enzyme) Generic features of enzyme: Monomeric enzyme has only one polypeptide unit and binds only one substrate molecule Oligomeric enzyme has more than one polypeptide unit and binds several substrate molecules (more common than 1 polypeptide having multiple catalytic sites) - Page 19 of 300 - 1. Co-enzymes and co-factors Enzymes often require co-enzymes or co-factors to work Apoenzyme (inactive) + co-enzyme/co-factor → holoenzyme (active) Co-enzymes are organic in nature (eg. Vit. B, FAD, heme) Co-factors are inorganic in nature, usually metal ions (eg. Fe, Cu, Mo) Prosthetic group: a co-enzyme or co-factor that is very tightly bound (or covalently bound) to an enzyme 2. Reaction Model for Enzyme-catalyzed Reaction Enzyme + substrate → E/S complex → E/C complex → enzyme + products Rate = where km is the Michaelis constant (i.e. [S] at which V = ) Result is a hyperbolic curve a. Cooperative Reaction Model for Enzyme-catalyzed Reaction Enzyme + n(substrate) → enzyme/n(substrate) complex Each binding increase affinity for the next substrate Product formation curve is a sigmoidal curve B. Mechanism of Enzymatic Reaction Enzyme catalysis is due to a lowering of activation energy Proximity and orientation: Enzymes may help two molecules to get closer and into right orientation → lower energy barrier and increase reaction rate Such guidance in orientation of substrate can be done by electrostatic interaction (amino acid residues in enzymes may have different charges) Amino acid amphoteric→ can catalyze de-protonation or protonation of substrate May also be temporarily covalently bound with substrate Some metal ions may act as cofactors by charge shielding (situating in between two negatively charged surfaces to bring them together) Note that the lock-and-key hypothesis is not accurate in describing mechanism of actions of enzymes: - Page 20 of 300 - C. Regulation of Enzymatic Activity Enzymes allow a particular reaction to take place at a particular time and location with a carefully adjusted rate Transcription of enzyme mRNA often arise from physiological/pathological cues With enzymes controlling metabolic activity, it provides a way to regulate metabolism effectively - Page 21 of 300 - 1. Allosteric Regulators Oligomeric enzymes may have regulatory unit with regulatory sites binding to allosteric regulators (regulating molecules binding to sites other than the active site) Regulation of oligomeric enzymes by allosteric regulators: 2. Phosphorylation A phosphate group is added or removed from the enzyme to change its catalytic effect Protein kinase add a phosphate group to a protein Protein phosphatase remove a phosphate group from a protein Catalytic effect can either be increased or decreased by phosphorylation Characteristics: fast, reversible, involving protein kinases and protein phosphatases, alteration of kinetic parameters - Page 22 of 300 - 3. By Adjustment of Rate of Synthesis and Breakdown of Enzyme Protein Rate of synthesis and breakdown of enzyme controlled to alter the abundance of the enzyme Enzyme ‘life-cycle’: gene → mRNA → protein → active enzyme protein → degradation Every step of the ‘life-cycle’ can be regulated Characteristics: slow, irreversible, usually long term regulation, alteration of enzyme abundance 4. By Proteolysis Protease is used to cut a part out of an enzyme May serves to activate/inactivate the enzyme Characteristics: fast, irreversible 5. By Activators or Inhibitors Addition of activators and inhibitors to enzymes to make them active and inactive respectively D. Importance of Enzymes in Medicine 1. Provide Valuable Information for Diagnosis Enzyme level at serum, plasma, urine, CSF can be tested Level of blood clotting enzymes → thrombotic tendency Intracellular enzymes are not supposed to be in blood, but upon tissue damage may leak into blood due to high cell:plasma ratio Measuring their level can give information about location of tissue damage and nature of disease Examples: transaminases for liver diseases, phosphatases for liver and bone diseases, amylases for pancreatic diseases 2. Enzymes as Therapeutic Targets Identify enzyme that is responsible for the regulation of a metabolic pathway Design chemical compounds which can inhibit the enzyme Examples: □ Synthesis of prostaglandins in platelet aggregation by prostaglandin synthase □ Production of angiotensin in high blood pressure by angiotensin converting enzyme □ Synthesis of cholesterol in high blood cholesterol by HMG-CoA reductase □ Synthesis of bacterial cell walls in bacterial infection by glocopeptidyl transpeptidase - Page 23 of 300 - L7 Nutrition A. Key Concepts of Nutrition Balance and variety can ensure nutritional adequacy For each nutrient, there is a safety range: eat foods in moderation There is no ‘one size fits all’ diet Malnutrition includes under-nutrition and over-nutrition Nutrition is a dynamic science 1. Factors that Influence Our Choice of Food Environmental: economics, lifestyles, cultural and religious beliefs and traditions Sensory: flavor, texture, appearance Cognitive: social and emotional factors, nutrition and health beliefs, advertising Health status: physical restrictions due to disease, declining taste sensitivity, age and gender Genetics: taste sensitivity, preference for sweet and salty food, etc 2. Diseases and Dietary Practices Chronic disease that can be influenced by our diet: □ Heart disease □ Stroke, hypertension, diabetes □ Obesity □ Some forms of cancer 3. Scientific Information in Nutrition Types of nutritional studies: □ Epidemiological studies → Experimental (intervention) epidemiological studies → Observational epidemiological studies □ Animal studies □ Cell culture studies □ Human studies Experimental results are published in peer-reviewed journals but may be simplified/sensationalize by the media Results from nutrition studies can be conflicting as they may arise from different designs of the scientific investigation and different sample base Nutrigenomics: study of how different foods can interact with particular genes to affect a person’s risk of developing nutrition-related diseases - Page 24 of 300 - B. Essential Nutrients Essential nutrients are nutrients that when missing can lead to a deficiency disease Examples of essential nutrients for humans: □ Water □ Vitamins □ Minerals □ Essential fatty acids □ Essential amino acids □ Glucose 1. Major Functions of Nutrients in Body Carbohydrates: energy Lipids: energy, cellular development etc. Proteins: production of structural and functional components, growth, maintenance Vitamins: regulation of body processes, maintenance of immune function etc. Minerals: fluid balance ad metabolism, components of various tissues, etc. Water: maintenance of fluid balance, regulation of body temperature etc. 2. Daily Reference Intakes (DRIs) a. Estimated Average Requirement (EAR) Estimated Average Requirement (EAR): the amount of the nutrient that should meet the needs of 50% of healthy people who are in a particular life stage/gender group Establishment of an EAR involves identification of a physiological marker that reflects proper functioning and can be measured to indicate whether the level of nutrient is adequate Conduct a nutritional study afterwards b. Recommended Daily Allowances (RDAs) Recommended Daily Allowances (RDAs) are the amounts of nutrients that meet the nutrient needs of 97.5% of all healthy individuals in a particular life stage/gender group Establishment of an RDA involves determination of EAR and addition of a safety margin - Page 25 of 300 - c. Other DRIs Adequate Intake (AI) is estimated amount of nutrient required when there is no RDA and the evidence is not firm Tolerable Upper Intake Level (UL) is the maximum amount of nutrient that can be consumed that is shown not to cause any adverse effects Estimate Energy Requirement (EER) is the estimated total energy required for a certain individual in a period of time C. Nutrition Assessment Methods Anthropometric measures: physical measures of body eg. Height, weight Biochemical tests: measure a metabolite in body fluids, a storage or transport compound, an enzyme etc. eg. Blood cholesterol level Clinical observations: physical examination Dietary intake: collection of dietary intake data eg. Diet history, food record and frequency D. Nutrition and Weight Control 1. Body Mass Index (BMI) Body mass index (BMI) = □ 25: obese 2. Body Fat Distribution Location of body fat an important predictor of health risks Upper body obesity: related to CV diseases and type 2 diabetes (waist circumference >102cm in men and >88cm in women) Lower body obesity: less health risk but may change to upper body fat distribution after menopause 3. Body Fat Content Body fat content can be estimated by ‘Siri formula’:."# □ Proportion of body fat = − 4.5 $% Desirable body fat for adults: □ Men: 8%-24% □ Women: 21%-35% - Page 26 of 300 - 4. Obesity Genes account for ~70% of weight differences between people Risks of being obese: □ Child with no obese parent: 10% □ Child with one obese parent: up to 40% □ Child with both obese parents: up to 80% Gene pool has not changed much in last 50 years yet proportion of obese people risen rapidly → obesity epidemic also caused by lifestyle changes Adult obesity in female is rooted to childhood obesity whereas there is no strong links in men (obesity tends to start at 30) 5. Eating Disorders Exact cause unknown, genetic/social/psychological factors contribute to development Risk factors: female, low self-esteem, being teased about weight etc Anorexia nervosa: severe psychological disturbance with self-imposed starvation (affects ~1 in 200 women) Bulimia nervosa: cyclic episodes of overeating (bingeing) followed by purging (getting rid of food by gagging etc) - Page 27 of 300 - L8 Structure and Function of Cells A. Diversity of Cells Most cells genetically identical (except lymphocyte → recombination of IgG gene) → diversity of cells given by differential gene expression Epigenetic changes: silencing or activating gene expression □ Methylation of DNA (promoter/cytosine(C) residue of promoter) silences gene transcription) □ Histone acetylation (activates) and deacetylation (inactivates) gene transcription B. Structures of Cell Cell membrane: surrounding wall of cell Cytosol: fluid part of cytoplasm (containing enzymes and metabolites) Golgi: organelle for packaging of protein Lysosome: organelle for breaking down things taken in from outside (with digestive enzymes) Cytoskeleton: internal scaffolding that controls the shape of cell and movement Centrioles: opposite poles for mitosis Peroxisome: organelle for metabolism of fatty acids Nucleolus: structure inside nucleus for rRNA transcription - Page 28 of 300 - 1. Cell Membrane Lipid bilayer (phospholipid molecules amphipathic → spontaneously form a bilayer in water with hydrophobic ends inside) High fluidity → allow lateral diffusion of membrane proteins and facilitate cell movement Lipid bilayer → virtually impermeable to charged ions but variable permeability to water, O2 and small hydrophobic molecules Break and tears are healed spontaneously → useful in modern molecular study during transfection of genes Membrane lipids: □ Phospholipids (50%) □ Cholesterol: stabilize mechanical property of membrane □ Glycolipid: on outer side of membrane Integral membrane protein: penetrates whole membrane Peripheral membrane protein: penetrates only a part of membrane Membrane protein functions: □ Attach cytoskeletal filaments to cell membrane □ Attach cells to extracellular matrix (ECM) □ Transport molecules in or out of cells □ Receptors for cell signaling □ Enzymatic activity, cell attachment and cell communication Membrane carbohydrates (glycocalyx; 2-20nm or more) in plasma membrane: precise composition varies with cell types □ Cell type specific antigen □ Major histocompatibility complex □ Blood group antigens □ Adhesion molecules *Amphipathic: possessing hydrophobic and hydrophilic parts **Glycocalyx: glycoprotein-polysaccharide complex covering that surrounds plasma membranes of cells esp epithelial cells - Page 29 of 300 - a. Transport in and out of Cells Diffusion Specialized membrane protein transport system or channels Endocytosis: □ Phagocytosis: ingestion of large particles □ Pinocytosis: ingestion of fluid and small molecules (from small vesicles 50nm) □ Some viruses also use endocytic pathways to infect cells Clathrin-associated receptor-mediated endocytosis: □ When certain ligands bind with receptors, clathrin (a type of special membrane-associated protein) binds to membrane and causes formation of a hexagonal lattice surrounding the vesicle □ Only occur at specialized patches on plasma membrane (coated pits) Endocytic vesicles: □ Clathrin-coated vesicles (100-150nm) □ Uncoated vesicles (100nm) □ Caveolae (50nm) → Common in endothelial cell → Formation due to caveolin (22kD integral membrane protein) → High binding affinity to cholesterol □ Phagosomes (large, 0.1-10μm) → From phagocytosis, common in phagocytes Exocytosis: □ Secretion (from trans face of Golgi apparatus), recycling of plasma membrane Endosomes (from endocytosis) □ Major sorting compartment along endocytic pathway □ Early endosome (pH 6.5), recycling endosomes (pH6.8), multivesicular bodies (pH 5.5) and late endosomes (pH 4.5) □ Multivesicular bodieslate endosomes fuse directly with lysosomes (low pH in late endosomes activates lysosomal acid hydrolases to degrade endosomal content) □ Endosomal pH affects fate of transported ligand and has profound effects on cell physiology *kD = kilodalton i.e. 1000 a.m.u. - Page 30 of 300 - 2. Endoplasmic Reticulum Complex intra-cytoplasmic membrane system Literal meaning of reticulum is ‘network’ Rough ER: Flattened sheets of membranes and tubules with ribosomes attached □ For protein synthesis (protein releases into ER cisternae) for export □ Well-developed in protein-secretory cells eg. Exocrine pancreas Smooth ER: Flattened sheets of membranes and tubules without ribosomes □ Different function in different cell types: → Lipid metabolism and detoxification (eg. Hepatocytes) → Steroid hormone production (eg. Leydig cells of testis) → Calcium storage and release (eg. Muscle cells (as SR)) - Page 31 of 300 - 3. Golgi Stacked membranous cisternae (sing. cisterna) with vesicles Cis (forming) and trans (maturing) faces For modification and packaging of proteins (from RER) Formation of lysosome Recycling of cell membrane Movement of proteins through intracellular membrane system: 4. Nucleus Basophilic under H&E staining (blue) Bound by two concentric membranes: □ Outer membrane: continuous with membrane of ER □ Inner membrane: attached to filamentous proteins (lamins) of nuclear matrix inside nucleus Nuclear membrane perforated by many pores with special structures Chromatin: DNA + histones □ Euchromatin: light-staining (electron-lucent i.e. low electron affinity) → active gene transcription □ Heterochromatin: dense-staining area → highly condensed chromatin → non-coding DNA (eg. Centrosome and telomere) and inactive DNA (non-transcription form) - Page 32 of 300 - 5. Nucleolus Site of most ribosomal RNA synthesis (28S, 18S, 5.8S) and ribosomal assembly Prominent in interphase nucleus Size increase with metabolic rate of cells □ Tumour cells have prominent nucleolus rDNA located in C13, C14, C15, C21, C22 Nucleolus helps transcribe rDNA and package rRNA with ribosomal proteins imported from cytoplasm to form ribosomes Newly formed ribosomal subunits translocated to cytoplasm through nuclear pore Many other novel fucntions to be unraveled (assembly of telomerase protein, cell cycle regulation etc) Detailed structure: □ Clustering of tandemly repeated rDNA genes located on 5 pairs of chromosomes □ Pale fibrillar region (non-transcribed DNA) □ Dense fibrillar core (sites of rDNA gene transcription) □ Granular regions (sites of ribosome assembly) *S in 28S, 15S etc. refers to Svedberg unit, measuring rates of sedimentation - Page 33 of 300 - 6. Mitochondrion ‘Respiratory system’ of cells: □ Produce ATP, common energy currency in cells □ Vary in number among different cells, more numerous in active cells Globular or elongated in shape, double-membraned Genetic system: □ Circular DNA of maternal origin □ Encodes some proteins within mitochondria □ Most of the proteins in mitochondria are imported Suspected to have originated from a symbiotic bacterium → double membrane (outside is of the cell, inside is of the bacterium 7. Cytoskeleton Functions: 1) Mechanical support 2) Cell movement (actin) 3) Contraction (actin and myosin in muscles) 4) Transport of organelles, vesicles and macromolecules (microtubules) 5) Cell division (microtubules and actin) Three types: microfilaments (actin, ΔGo’ > 0) reaction → overall reaction becomes exergonic - Page 57 of 300 - 2. ATP Synthesis Compounds with high-energy phosphate bonds (ΔGo < -7.3kcal/mol) exhibit a high Pi transfer potential Substrate level phosphorylation: Coupling of hydrolysis of high-energy phosphate bonds with formation of ATP from ADP i.e. ROPO32- + ADP → ROH + ATP Example: □ 1,3-bisphosphoglycerate + ADP → 3-phosphoglycerate + ATP □ PEP + ADP → pyruvate + ATP Note that substrate level phosphorylation is independent of O2 availability Oxidative phosphorylation: ATP can also be synthesized by ATP synthase from transmembrane H+ gradient generated by electron transport chain *Note reason why glycolysis results in net production of ATP: - Page 58 of 300 - L13 Amino Acids Metabolism A. Amino Acids Metabolism Fed state: □ Proteins □ Enter CHO metabolic pathway to give ATP □ Gluconeogenesis then stored as glycogen □ TAG □ Other essential N-containing compounds (glutathione, creatine, monoamine neurotransmitter) Fasting state: □ Gluconeogenesis □ Ketogenesis to form ketone bodies for energy 1. Transformation of AAs into fuel molecules Note three types of AAs: □ Glucogenic AAs: can be used in gluconeogenesis □ Ketogenic AAs (Leu, Lys): cannot be used in glucogenesis, used to generate ketone bodies via Ketogenesis pathway instead □ Glucogenic and Ketogenic AAs (Ile, Phe, Trp, Try, Thr) Glucogenic AAs enter CHO metabolism pathway at TCA cycle or pyruvate, then used in gluconeogenesis □ TCA cycle intermediates rerouted at OAA due to high activity of PEP carboxykinase (due to glucagon) → OAA leaves mitochondrion to perform gluconeogenesis Ketogenic AAs enter CHO metabolism pathway at acetyl coA only, then used in Ketogenesis to form ketone bodies, ultimately degraded into CO2 in TCA cycle □ Acetyl coA rerouted to Ketogenesis pathway because high PEP carboxykinase activity rerouted most OAA to gluconeogenesis → no OAA available for TCA cycle → rerouted - Page 59 of 300 - 2. Production of Essential N-containing Compounds from AAs a. Glutathione (GSH) Essential antioxidant in cells: □ Oxidation: 2GSH → GSSG □ Regeneration: GSSG + 2NADPH → 2GSH + 2NADP Reducing power given by cysteine residue in GSH Production pathway on the right b. Creatine Converted to and from phosphocreatine to act as alternative energy storage form Production pathway: Blood and urine creatinine level used to gauge renal function (specifically glomerular filtration rate i.e. GFR) because there is no reabsorption or secretion in renal tubules - Page 60 of 300 - c. Adrenaline, Noradrenaline, Dopamine, Serotonin Important hormones and neurotransmitters for the body First three produced from tyrosine, serotonin produced from tryptophan: - Page 61 of 300 - L14 Metabolic Integration A. Metabolic Integration Metabolic integration: interconversion of fuel metabolites to suit physiological demands Metabolic output can be regulated by enzyme at regulatory step through: □ Synthesis and degradation □ Allosteric regulation □ Covalent modification □ Proteolysis Metabolic pathway output usually regulated at irreversible step (eg glycolysis and gluconeogenesis) Interconversion of fuel metabolites: - Page 62 of 300 - B. Exercise State Epinephrine rises during exercise → G protein pathway activated → adenylyl cyclase activated → cellular cAMP↑ → protein kinase A activated (i.e. cAMP-dependent PK) → relevant enzymes phosphorylated → changes in cellular metabolic reactions: □ Lipolysis ↑ FA synthesis ↓ □ Glycogenolysis↑ glycogenesis ↓ □ Glycolysis ↓ (↑ in cardiomyocytes) glyconeogenesis ↑ Metabolic integration during exercise: - Page 63 of 300 -  Regulation of glycogenolysis can also be performed in other ways: *Epinephrine also stimulates release of Ca2+ (from cytosol) through IP3 signaling for glycogenolysis (via protein kinase C pathway) Glucose-alanine (Cahill cycle) □ Transaminase removes amino group from AA to form α-keto acid for energy/gluconeogenesis □ Amino group transported to liver by alanine □ Amino group disposed of as urea and glucose regenerated by gluconeogenesis from pyruvate Facilitation of anaerobic respiration by Cori cycle □ Lactate generated by anaerobic respiration in muscles (releases ATP) □ Lactate transported to liver and reconverted into glucose via gluconeogenesis (requires ATP) □ Result: muscle ATP expenditure relocated to liver - Page 64 of 300 - 1. Fuel Consumption in Different Exercise Intensity Heavy burst of energy: □ ATP (muscle) □ Phosphocreatine (muscle) □ Glycogen (muscle) → glycogenolysis → glucose → glycolysis → ATP Moderately intense activity: □ ATP □ Phosphocreatine □ Muscle glycogen (aerobic respiration involving oxidative phosphorylation) Less intense but prolonged activity: □ Glycogen (liver) □ AAs (muscles) via glucose-alanine cycle □ FAs (adipose tissues) *Note expts show that human cannot rely 100% on FAs C. Fed State Insulin increases (while glucagon drops) → signal transduction pathway → changes in metabolism □ Glycolysis ↑ (by ↑F2,6P2 and activation of pyruvate kinase) □ Gluconeogenesis ↓ (by ↑F2,6P2 and inhibition of PEP carboxykinase) □ Glycogenolysis ↓ (by inhibition of glycogen phosphorylase) □ Glycogenesis ↑ (by stimulation of glycogen synthase) □ FA synthesis ↑ □ Lipolysis and FA breakdown ↓(by inhibition of adipose tissue lipase and of transport of FAs into mitochondria for β-oxidation) □ Muscle protein breakdown ↓ - Page 65 of 300 - D. Fasting State Main concern: fuel has to be provided without depletion of blood glucose (affect anerobic respiration + water potential) → FAs, AAs and ketone bodies used Glucagon increases (while insulin drops) → G-protein pathway activated → adenylyl cyclase activated → cAMP level ↑ → PKA activated → phosphorylation of a variety of metabolic enzymes → change in metabolism □ Glycolysis ↓ (by ↓F2,6P2 and inhibition of pyruvate kinase) □ Gluconeogenesis↑ (by ↓F2,6P2 and activation of PEP carboxykinase) □ Glycogenolysis ↑ (by stimulation of glycogen phosphorylase) □ Glycogenesis ↓ (by inhibition of glycogen synthase) □ FA synthesis ↓ □ Lipolysis and FA breakdown ↑ (by activation of TAG lipase and ↓ malonyl coA reducing inhibitory effect on lipolysis) □ Muscle protein breakdown ↑ Consequence: □ ↑ β-oxidation → acetyl coA accumulates □ PEP carboxykinase activated → OAA converted to PEP → OAA↓ □ Acetyl coA↑ + OAA↓ → TCA cycle cannot handle all acetyl coA → acetyl coA rerouted to Ketogenesis pathway → ketone bodies generated □ ↑acetyl coA → pyruvate carboxylase ↑ → pyruvate rerouted to gluconeogenesis pathway to form OAA - Page 66 of 300 - L15 Nucleotide Metabolism A. Structure of Nucleotides and Variants Nucleotide: phosphate + 5-C sugar + nitrogenous base □ Number of phosphates bound to nucleoside can vary from 1-3 to store different amounts of energy Nucleoside: 5-C sugar + nitrogenous base □ Adenosine, thymidine, uridine, guanosine, cytidine Two types of bases: □ Purine: two rings (A,G) □ Pyrimidine: one ring (C, T, U) Two types of sugars: □ Ribose: used in RNA □ Deoxyribose: used in DNA Nucleic acid: polymer of nucleotides Nucleotides can also have added complexities for different functions: □ Nicotinamide adenine dinucleotide (NAD+): Nicotinamide + 2Pi + adenosine □ Flavin adenine dinucleotide (FAD): riboflavin + 2Pi + adenosine □ Coenzyme A: β-mercaptoethylamine + pathothenic acid + 3’-P-ADP □ UDP-glucose: Glc + 2Pi + uridine (facilitate glycogen formation) - Page 67 of 300 - B. Functions of Nucleotides 1) Metabolic work: Nucleotides switch from high energy form to low energy form to release energy for metabolic work; 2) Hormone-like molecules: adenosine receptor found in many cells: cardiomyocytes, neutrophils, endothelial cells, macrophages etc; 3) Molecular timers: GTP-bound protein is switched off by conversion into GDP-bound protein → can act as enzyme regulator 4) Synthesis of nucleic acids: RNA from NTP via RNA polymerase (transferal of genetic info) DNA from dNTP via DNA polymerase (preservation of genetic info) - Page 68 of 300 - C. Metabolism of Nucleotides Supply of high-energy forms: NDP/dNDP receives a Pi from ATP (sometimes GTP) to form NTP/dNTP Supply of deoxyribonucleotides: NDP are converted to dNDP using ribonucleotide reductase and NADPH Supply of dTMP: from dUMP using tetrahydrofolate *Anti-cancer drugs target regeneration of tetrahydrofolate → dTMP cannot be produced → DNA cannot be synthesized → cell division inhibited - Page 69 of 300 - De novo synthesis: nucleotide synthesized by body from other substrates □ 5-C sugar from glucose □ Nitrogenous base synthesized from AAs and other nutrients □ Metabolically costly (need ATP and other nutrients) Purine nucleotide metabolism: purine nucleotides degraded to uric acid and secreted → continuous loss of nucleotides □ Salvaging pathway in place to recycle nucleotides → Brain relies heavily on salvaging pathway to maintain homeostasis (since de novo synthesis activity is low in brain) □ When faulty → depletion of purine bases → impaired brain development → Lesch Nyhan syndrome □ Also note when uric acid excretion is inefficient → uric acid accumulates in circulation → uric acid crystals form at joints → gout - Page 70 of 300 - L16 Nutrition: Vitamins and Minerals A. Vitamins Vitamins: naturally occurring organic molecules which are required in small amountsfor the normal health and functioning of the human body and must be provided in the diet Types: □ Fat soluble: A, D, E, K □ Water soluble: B1, B2, B3 (niacin), B5 (pathothenic acid), B6, B9 (folic acid), B12, C Deficiency: □ Possible causes: → Inadequate intake → Malabsorption due to disease states → Increased tissue needs (eg pregnancy, fever, diabetes) → Inborn errors of metabolism (causing altered enzyme affinity for coenzyme) □ Usually lead to characteristic symptoms (hypovitaminosis / hypervitaminosis) - Page 71 of 300 - 1. Vitamin A Definition A group of chemicals including retinol, retinal, retinoic acid and few carotenoids that aids in retina detection of light Structure Function Retinal is an essential light-sensitive molecular component of rhodopsin pigment (visual purple) [photopsin in cones] in the photoreceptors on the retina. Light changes retinal from trans form to cis form, leading to its release and a subsequent nerve signal to the brain: Retinoic acid also serves as a hormone-like growth factor for epithelial and other cells. - Page 72 of 300 - Deficiency / excess *Xerophthalmia: failure to produce tears by eyes 2. Vitamin D Definition A group of chemicals that promotes intestinal absorption of several minerals especially calcium and phosphate. Structure - Page 73 of 300 - Function Mediates (stimulates) Ca2+ and PO43- absorption from intestine and deposition in bones (together with parathyroid hormone PTH) Deficiency Deficiency: rickets syndrome in children, osteomalacia in adult / excess *Rickets syndrome: poor bone mineralization before closure of epiphyseal plate *Osteomalacia: bone softening due to inadequate Ca2+ and PO43-. - Page 74 of 300 - 3. Vitamin E Definition A group of chemicals (including tocopherols) that protects biological membranes from oxidative damage Structure α-tocopherol Function Normally, O2 is reduced as in O2 + 4e- + 4H+ → 2H2O. When there is not enough e-, O2 is not fully reduced → reactive oxygen species (ROS) formed (eg.O2-,.O) Vitamin E helps provide e- for reduction of ROS: ROO. + TocOH → ROOH + TocO. ROO. + TocO. → ROOH + non-free radical product *Note that ROO. is lipid peroxide, ROOH is its non-reactive form and TocO. is relatively stable radical *Selenium (Se) is a cofactor for glutathione peroxidase Deficiency Deficiency: skin diseases especially over-sensitivity to light / excess Deficiency is uncommon (rice is rich in vit E), secondary deficiency may be due to malabsorption or liver diseases - Page 75 of 300 - 4. Vitamin K Definition A group of chemicals (including phylloquinone) that is needed for blood clotting Structure phylloquinone Function Vitamin K is required for the synthesis of blood coagulation factors II (prothrombin), VII, IX and X by the liver Also involved in carboxylation of glutamyl residues (Gla is required in some clotting factors in clotting cascade) Deficiency Deficiency: hemorrhagic disease in newborn / excess - Page 76 of 300 - 5. Vitamin B a. Vitamin B1 (thiamin) Thiamin pyrophosphate (TPP): coenzyme of pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, also activates transketolase (in PP pathway) b. Vitamin B2 (Riboflavin (FMN)) Flavin adenine dinucleotide (FAD): Riboflavin + 2Pi + adenine Used as redox cofactor in cell metabolism (especially in electron transport chain) - Page 77 of 300 - c. Vitamin B3 (niacin, nicotinic acid) Derived to form nictotinamide (+NH2) and then NAD+ or NADP+ as redox cofactors in cell metabolism - Page 78 of 300 - d. Vitamin B6 (pyridoxal phosphate and derivative) Pyridoxal 5’-phosphate: cofactor for many enzymes in metabolism (incl. transaminase, biosynthesis of 5 important neurotransmitters and glycogen phosphorylase) Structure: Action: - Page 79 of 300 - e. Vitamin B9 (folic acid) Structure: Acts as a coenzyme for transfer of 1-C units in synthesis of purines, thymidine, serine and methionine Action: f. Vitamin B12 (cobalamin) Functions: □ Intermediate in generation of methylated compounds (eg methionine, thymine) □ Reducing ribonucleotides to deoxyderivatives Deficiency: pernicious anemia □ Reduction in erythrocyte formation □ Disorders in GI tract and nervous system - Page 80 of 300 - 6. Vitamin C (ascorbic acid) Function: □ Hydroxylation of proline in collagen synthesis → connective tissues □ Degradation of tyrosine □ Synthesis of epinephrine from tyrosine □ Bile acid formation □ Absorption of iron □ Water-soluble free radical scavenger (due to reducing property) Deficiency: scurvy □ Inability to form stable collagen → connective tissue weakness □ Bleeding of mucous membrane, spongy gums, brown spots on skin *Various types of antioxidants in body: - Page 81 of 300 - B. Minerals Requiring >100mg/day: □ For tissue structures: Ca, P □ For cellular/ECF: Na, K, Mg Requiring a few mg/day: □ Enzyme activators, prosthetic group of proteins: Fe, Cu, Zn, F, Mn Requiring a few μg/day: □ Regulatory or catalytic processes: I, Se, Mo 1. Calcium Functions: □ Structural: important component of bone □ Important regulator of intracellular processes: → Muscle contraction → Ca-dependent intracellular signaling processes, eg protein kinase C → Blood clotting Deficiency: □ Osteomalacia due to inadequate Ca2+ and vitamin D (more susceptible in pregnant woman) □ Osteoporosis: complete loss of bone tissue in small areas within the bones → porous and brittle bones - Page 82 of 300 - 2. Iron Functions: a wide range of functions connected with oxidative reaction □ Oxygen uptake in haemoglobin and myoglobin □ Electron transport in cytochromes and ferridoxins □ Activation of oxygen: oxidases and oxygenases □ Activation of nitrogen: nitrogenases Proteins for iron transport and storage: □ Ferritin → Stores iron as mobile, diffusible fractions → May hold up to 4500 molecules of ferric ions → Greatly elevated in iron overload □ Transferrin → Essential for efficient distribution of iron → Plasma concentration rises in iron deficiency 3. Sodium Functions: □ As an electrolyte □ Maintain osmotic balance of body fluid □ Maintain electrophysiological state of cells □ Conduction of nerve impulse Deficiency: muscle cramps, nausea, vomiting, dizziness, shock and coma Excess: risk of hypertension - Page 83 of 300 - L17 Cell Membrane Transport A. Plasma Membrane Cell membrane separates intracellular fluids from extracellular fluids Note that many substances occur at very different concentrations across cell membranes → selective permeability and transport of substances helps maintain the gradient for survival Selective permeability regulates type and rate of molecule traffic into and out of the cell Note that H2O can pass through phospholipid bilayer because it is small enough to squeeze through between phospholipid molecules B. Transmembrane Transport 1. Physical Transport Does not require a living cell nor outside energy Example: passive diffusion, osmosis a. Passive Diffusion Diffusion: random movement of molecules from a higher to a lower concentration until equilibrium is reached A passive process for molecules to travel across a membrane No energy and special proteins Non-polar and lipid-soluble substances diffuse directly through the lipid bilayer Small lipid-insoluble substances diffuse through channel proteins b. Osmosis Osmosis: diffusion of water across a semi-permeable membrane Osmolarity: total concentration of solute particles in a solution (in osmole/L) Osmolality: total concentration of solute particles in a solution (in osmole/kg) Tonicity: osmotic property of a solution (isotonic, hypotonic, hypertonic) - Page 84 of 300 - 2. Biological Transport Requires a living cell and can either be active (against conc. gradient) or passive Example: facilitated diffusion, active transport, endocytosis and exocytosis a. Facilitated Diffusion Diffusion of large, polar molecules (eg simple sugars) across the cell membrane using protein carriers b. Active Transport Use of ATP to move solutes across a membrane with protein carriers Primary active transport: transport substances by conformational change of protein carrier with energy from hydrolysis of ATP (eg Na+/K+ pump) Secondary active transport: transport substances by conformational change of protein carrier with energy from electrochemical gradient (energy from bring an ion ‘downhill’) (eg Na+/Glc symport transporter) Direction of transport: □ Symport system: two substance ares moved across a membrane in the same direction □ Antiport system: two substances are moved across a membrane in opposite directions Example: Na+/K+ pump: - Page 85 of 300 - c. Vesicular Transport Vesicular transport: Transport of large particles and marcomolecules across plasma membranes using vehicles Exocytosis: vesicular transport of large particles OUT of the cell □ Examples: neurotransmitter release, hormone and mucus secretion Endocytosis: vesicular transport of large particles INTO the cell □ Examples: macrophages and WBCs (phagocytosis), absorption of nutrients (bulk-phase endocytosis) Receptor-mediated transport: uses clathrin-coated pits as major mechanism for specific uptake of macromolecules □ Examples: iron, insulin, enzyme, LDL absorption Endocytosis often followed by fusing of phagosome with lysosome for digestion - Page 86 of 300 - L18 Intracellular Communication: Signal Transduction A. Overview on Signal Transduction Three steps of signal transduction: □ Ligand-induced receptor conformation change → Receptor dimerization □ Information-relaying by second messengers → cAMP → DAG/PI3 → Ca2+ □ Regulatory changes in metabolism → Protein phosphorylation → Protein ubiquitination → GTP binding - Page 87 of 300 - 1. Ligand-induced receptor conformation change Ligand binding drives receptor to the active conformation (eg by dimerization) Example: ligand-induced dimerization of EGFR (EGF: epidermal growth factor) □ Dimerization allows Tyr kinase to phosphorylate Tyr (Y) residues on each other □ Phosphorylated Tyr domains can bind SH2 domains of downstream proteins → cellular growth □ Clinical application: trastuzumab (monoclonal antibody) blocks EGFR dimerization → ↓cellular growth signals → target for cancer treatment - Page 88 of 300 - 2. Second Messengers Concentration of second messengers can increase (or decrease occasionally) in response to ligand binding to receptor → diffuse to regulate activities of proteins at a distance Examples: cAMP, cGMP, DAG, IP3 and Ca2+ Formation of cAMP (by adenylyl cyclase from ATP): Formation of DAG and IP3 (by phospholipase C (PLC) from PIP2, a minor component of phospholipid bilayer): - Page 89 of 300 - 3. Metabolic Regulation Mechanisms a. Protein Phosphorylation (and Dephosphorylation) A phosphate group (Pi) is added to a hydroxyl-containing AA residue (i.e. Ser, Tyr, Thr) to modify its activity Catalyzed by protein kinase and protein phosphatase Source of Pi usually from ATP to compensate for large ΔG of phosphorylation Can take place in less than a second or over a span of hours A single activated kinase can phosphorylate many target proteins → highly amplified effect Kinase inhibitors can be used to understand and treat human diseases Example: Bcr-Abl tyrosine kinase □ Normally well-regulated □ Mutant form is always activated → unregulated cell division → cancer □ Bcr-Abl inhibitor Imatinib blocks ATP binding to Bcr-Abl kinase → anti-cancer effect Example: EGFR tyrosine kinase receptor □ Normally important in cell cycle, cell proliferation/maturation, apoptosis, angiogenesis and metastasis regulation □ Constitutively activated in many cancers due to mutations (EGFR level regulated by ubiquitination) □ Tyrosine kinase inhibitors that blocks ATP binding sites can be used to treat cancer patients with mutated EGFR gene □ EGFR signaling can also be inhibited by monoclonal antibodies b. Ubiquitination Ubiquitin (a protein) is used to ‘mark’ protein for proteolysis A few ubiquitin subunits form a chain and attach on proteins (polyubiquitination) c. GTP binding GTP-bound proteins switch between an active state when GTP is bound and an inactive state when GDP is bound Activation is achieved by GTP binding while inactivation is achieved by hydrolysis of the bound GTP unit Example: Ras GTP-bound protein □ Ras signaling regulated by GTP binding □ Mutant Ras in cancer constitutively binds GTP but not GDP - Page 90 of 300 - B. G-Protein Coupled Receptor Pathways G-protein coupled receptor (GPCR): important class of receptors that binds G-proteins G-protein: GTP-binding proteins responsible for acting as molecular switches □ Has Gα, Gβ and Gγ subunits □ Gα subunit: the GTP-binding part □ Gβ and Gγ subunits usually associated together 1. Main Mechanism 1) Primary ligand binds to GPCR → Gα releases GDP and acquires a new GTP; 2) GTP-Gα and G-βγ subunits detach from GPCR; 3) GTP-Gα and G-βγ subunits bind to transmembrane intracellular effectors to produce downstream effect; 4) Gα soon hydrolyzes GTP into GDP → inactivation → re-association with Gβγ; 5) G protein recombines with GPCR → activated if ligand is still present. - Page 91 of 300 - 2. Main Classes of GPCRs and Their Effects Three main classes of GPCR: Gs (stimulatory), Gi (inhibitory) and Gq a. Action of Gs Proteins Mechanism: 1) Activation of Gs-associated receptors causes Gsα subunit to activate adenylyl cyclase; 2) Adenylyl cyclase converts cytosolic ATP into cAMP (and pyrophosphate); 3) cAMP binds to and activates protein kinase A (cAMP-dependent protein kinase, PKA); 4) PKA phosphorylates a variety of downstream target proteins to produce cellular effects; 5) cAMP is then converted by phosphodiesterase into 5’-AMP to prevent constitutive activation. Example: β-adrenergic receptor Downstream targets of PKA: □ L-type Ca2+ channels in cardiac muscles → stimulatory □ Myosin light chain kinase (MLCK) in smooth muscles → inhibitory □ Phosphorylase kinase which goes on to phosphorylate glycogen phosphorylase → stimulatory *Note that although both smooth muscle and striated muscle contraction are controlled by intracellular calcium levels, smooth muscles lack the troponin complex found in striated muscles and thus rely on MLCK (activated by calcium-calmodulin complex) for calcium-dependent contraction. b. Action of Gi Proteins Giα subunit binds to and inhibits adenylyl cyclase action → ↓cAMP Examples: α2-adrenergic, M2 and M4 muscarinic - Page 92 of 300 - c. Action of Gq Proteins Mechanism: 1) Gqα subunit activates phospholipase Cβ (PLCβ); 2) PLCβ cleaves PIP2 on plasma membrane into IP3 (released) and DAG (membrane-bound); 3) IP3 binds IP3 receptor at ER → Ca2+ release from ER stores; 4) DAG activates downstream protein kinase C (PKC) which phosphorylates downstream protein for cellular effects. Example: α1 adrenergic (vascular smooth muscles), M1, M3 and M5 muscarinic Intracellular calcium level is normally tightly controlled by SERCA (at SR) and Na+/Ca2+ exchange (NCX) □ RyR binds calcium and causes Ca-induced Ca release from SR Increase in cytosolic Ca2+ leads to Ca2+ binding with calmodulin to form calcium-calmodulin complex → binds downstream protein kinases and phosphatases to produce effects Examples of Ca-CaM targets: □ MLCK in smooth muscles → main mechanism for sm contraction control □ NO synthase in endothelium → NO production → diffuse to vascular sm → activates guanylyl cyclase → ↑cGMP → protein kinase G activated → smooth muscle relaxation - Page 93 of 300 - L19 Cell Proliferation – Cell Division Cycle A. Cell Proliferation ~1014 cells in the body developed from one cell (zygote) Note various irreversible changes in cells during development: □ Differentiation: Cells become more differentiated i.e. specialized during development → Cell potency: Ability of differentiation into other cells → During development, totipotent → pluripotent → limited potential □ Proliferative: cells become less proliferative In adult, □ Cell lost or died = cells reproduced → natural turnover with no net ↑ in cell number □ Cells replaced by differentiated progeny (offspring) of proliferative stem cells → Intestinal cells, WBCs: ~3-5 days, continuous regeneration → Skin cells: 2-4 weeks, continuous regeneration → RBCs: ~4 months, continuous regeneration → Brain cells: slow loss with little regeneration Cancer results from genetic alterations that lead to abnormal regulation of cell divisions: □ Benign tumour: excessive proliferation in defiance of normal constraints, remain clustered □ Malignant tumour: invasive and colonize other sites B. Cell Cycle Cyclic process with defined events (phases) happening in a fixed sequence: G1 → S → G2 → M → G1 →… □ G1, G2 (gap): preparative stages, cell growth □ S (synthesis): DNA replication □ M (mitosis): nuclear division and cytokinesis Interphase: G1 + S + G2 - Page 94 of 300 - 1. Checkpoint System for Cell Cycle Specific points along cell cycle can be stopped upon sensing of unfavourable signals Examples of unfavourable signals: □ Intrinsic: cell size, DNA damage, extent of DNA replication, proper alignment of chromosomes on mitotic spindle □ Extrinsic: environmental signals (soluble factors or factors presented on cell surface) 2. Cyclin Control of Cell Cycle Cyclins: group of proteins that control the cell cycle through cyclin-dependent protein kinases (Cdks) Cyclin-dependent protein kinases (Cdks): Catalytic subunits that require association with cyclins (regulatory subunits) to become active serine/threonine kinase □ Cyclin binding confers substrate specificity to the kinases Different cyclin-cdk complexes are cyclically activated in a cell cycle phase-specific manner (cyclin levels fluctuate periodically) → phosphorylate different target proteins → regulates cell cycle □ G1 cyclin-cdks (cyclin D-Cdk 4/6) phosphorylate pRb leading to transcription of cyclin E and other genes needed for DNA replication → enter S phase □ S cyclin-Cdk (Cyclin E-Cdk2) further phosphorylates pRb to drive S phase entry (positive feedback) □ M phase cyclin-Cdk (Cyclin B-Cdk1) phosphorylates nuclear lamins and other proteins → breakdown of nuclear envelop → M phase entry - Page 95 of 300 - Regulation of Cdk activities: □ Periodic synthesis (regulated transcription) and degradation (regulated proteolysis of cyclins □ Phosphorylation/dephosp horylation by other kinases and phosphatases □ Cdk inhibitors (CKIs): CIP/KIP and INK4 proteins that mediate DNA-damage checkpoint control Mutations of cell cycle regulators may lead to cancer - Page 96 of 300 - L21 Thermoregulation A. Normal Body Temperature Body temperature is maintained at a stable level because temperature affects speed of metabolic reaction Balance between heat production and heat loss determines core body temperature Various parts of body set at different temperatures: □ Core body temperature (37o ± 0.5oC) → Regulated by thermoregulatory mechanisms → Displays diurnal rhythm: lowest in predawn hours and rises in the afternoon → Rectal temperature is best representative of core temperature □ Surface temperature → Fluctuates widely in healthy adults depending on environmental temperatures → Temperature of extremities cooler than rest of the body 1. Heat Gain Heat gain = heat production + heat transferred from environment Heat production from: □ Basal rate of metabolism □ Muscle activity including exercise or shivering □ Extra metabolism by effect of thyroxine on cells □ Extra metabolism by effect of epinephrine, norepinephrine and sympathetic stimulation on cells □ Extra metabolism caused by increased temperature of body (due to heat gain from environment) Most heat produced generated in the deep organs → transferred to skin 2. Heat Loss Heat is loss from the skin by radiation, conduction, convection and evaporation of sweat (and insensible water loss) - Page 97 of 300 - B. Body Temperature Regulation Temperature regulated by negative feedback mechanisms: □ Control centre: temperature-regulating center in posterior hypothalamus □ Receptors: peripheral thermoreceptors (cold/warm receptors on skin), central thermoreceptors (preoptic area in anterior hypothalamus 1. Temperature Sensors a. Thermoreceptors in Hypothalamus Anterior hypothalamic-preoptic area contains large numbers of heat-sensitive neurons and about a third as many cold-sensitive neurons □ Heat-sensitive neurons ↑ firing rate when temp ↑ □ Cold-sensitive neurons ↑ firing rate when temp ↓ □ More sensitive to temperature↑ → initiates heat-losing mechanism Posterior hypothalamus contains cold-sensitive neurons □ Temperature ↓ → initiates heat-conserving mechanisms - Page 98 of 300 - b. Superficial and Deep Thermoreceptors Skin contains both cold and warmth receptors □ Cold receptors ~10x warmth receptors → peripheral temp detection mainly concerns detecting coldness instead of warm temperatures □ Rate of firing ∝ to both rate of change of temperature and steady-state temperature □ Receptors unevenly distributed: particularly high density of cold-receptors on face (esp tip of nose) and hands Deep thermoreceptors present in certain part of body □ Mainly in spinal cord, abdominal viscera, great veins □ Function differently from skin receptors (exposed to core temperature) □ Mainly detect cold rather than warmth Likely that both types are concerned with preventing hypothermia 2. Temperature-regulating Center Signals that activate the hypothalamic thermoregulatory center come: □ Temperature-sensitive cells in the anterior hypothalamus □ Peripheral temperature receptors, especially cold receptors Reflex effector mechanisms activated by warmth controlled primarily from anterior hypothalamus Reflex effector mechanisms activated by coldness controlled from posterior hypothalamus Temperature signals from preoptic area and peripheral thermoreceptors are integrated and compared to the set-point value in posterior hypothalamus, any difference → trigger heat-conserving/heat-losing mechanisms 3. Temperature-regulating Effector Mechanisms a. Response to Heat ↑Heat loss: □ Vasodilation of cutaneous arterioles (by inhibition of sympathetic centers in posterior hypothalamus that causes vasoconstriction) □ Sweating: increase heat loss by evaporation ↓ Heat production: □ Anorexia (loss of appetite) □ Apathy and inertia (inactivity) Behavourial response: changes in clothing, choice of surroundings, decrease voluntary activity - Page 99 of 300 - b. Response to Coldness ↓ Heat loss: □ Cutaneous vasoconstriction (by stimulation of sympathetic centers □ Piloerection (contraction of arrector pili muscles → piloerection → improves insulation) ↑ Heat production: □ Hypothalamic stimulation of shivering: → Primary motor centre located in dorsomedial portion of the posterior hypothalamus near the wall of the third ventricle → Normally inhibited by heat center (in anterior hypothalamic-preoptic area), excited by cold signals from skin and spinal cord → When body temp < critical temperature level → shivering center activated → Signals transmitted through bilateral tracts down brain stem → lateral columns of spinal cord → anterior motor neurons → ↑ tone of skeletal muscles throughout body → When tone > a certain critical level, shivering begins → Body heat production can ↑ as high as 4-5x normal during max shivering □ Sympathetic ‘chemical’ excitation of heat production: → Chemical thermogenesis stimulated by increased sympathetic stimulation and circulating catecholamines (epinephrine, dopamine etc) → In infants, brown fat mediated chemical thermogenesis □ ↑ thyroxine secretion → Long-term response (may take several weeks for thyroid gland to hypertrophy before reaching new level of thyroxine secretion) → Exposure to cold → ↑TRH in hypothalamus → ↑TSH in pituitary → ↑thyroxine secretion by thyroid gland → ↑ cellular metabolic rate throughout the body *Muscle tone: residual tension of muscle **Thermoregulatory response mainly dominated by sympathetic nerve, no role by parasympathetic nervous system - Page 100 of 300 - C. Fever Fever (pyrexia): an increased body temperature caused by elevation in thermal set-point Mechanism of pyrexia: Note that since set point is raised in pyrexia, fever will result in chills and rigors (physical sign of shivering) Pulsatile release of pyrogenic cytokines may also lead to sudden reduction of set-point → feels hot, vasodilation, sweating Crisis: removal of pyrogen →↓thermal set-point → body effects responses to lose heat → vasodilation and sweating - Page 101 of 300 - D. Hyperthermia Hyperthermia: increase in body temperature above thermal set-point Note difference in heat exhaustion and heat stroke: □ Heat exhaustion: dehydration causing problems in negative feedback system (skin is moist) □ Heat stroke: temperature limit reached → depression in thermoregulatory center → positive feedback (skin is dry) → Strenuous physical exertion in high ambient temperature and humidity → profuse sweating and salt and water depletion → Dehydration + ↓BP → ↓blood flow to kidneys, splanchnic (organs) and brain → CNS symptoms: ↑ brain temp and ↓ cerebral blood flow → fatigue, confusion, unconsciousness *Acclimatization to heat: body may get used to high temperature when lived in hot regions for a long time Physiological changes: - ↑max rate of sweating - ↑ plasma volume - ↓ NaCl concentration in sweat and urine (due to ↑aldosterone secretion) **Hypothermia: core temp 1%) □ X-linked disorders - Page 122 of 300 - 3. Twinning Incidence: ~1 in 85 pregnancies 10-20% die at birth 12% premature infants are twins Two types: □ Monovular (identical) → Dichorial, diamniotic → Monochroial, diamniotic → Monochorial, monoamniotic □ Biovular (fraternal) - Page 123 of 300 - Abnormality: conjoined twins - Page 124 of 300 - 4. Chromosomal Anomalies Nondisjunction: failure of homologous pair to separate in anaphase, meiosis I Monosomy: only one chromosome of a homologous pair is found □ Cause: non-disjunction in one of the gametes □ E.g. XO or Turner’s syndrome Trisomy: an extra chromosome (for a certain homologous pair) is found □ Cause: dispermic fertilization, non-disjunction in one of the gametes □ E.g. trisomy 21 or Down’s syndrome □ E.g. trisomy 17-18 or Edward’s syndrome □ E.g. trisomy 13-15 or Patau’s syndrome *Chromosomal anomalies more common in later (smaller) chromosomes (∵ ↓ loss in genetic material → ↓ disruption on genetic expression → ↑ survival chance) a. Edward’s Syndrome - Page 125 of 300 - b. Down’s Syndrome Note that incidence of Down syndrome in newborn infants rises with maternal age - Page 126 of 300 - L24 Do Doctors Really Matter? A. Public Health Role of doctors □ Improving health for individuals (Hippocratic oath) □ Improving health for humanity (declaration of Geneva) Public health: □ Prevention of disease and improvement in health in populations rather than individuals (older definition) □ Also concerned with the broader determinants of health (eg. Social structure) rather than individual risks B. Preventive Approach in Medicine 1. Levels of Prevention Level Phase of Disease Aim Target Actions Primordial Underlying Establish and Total Public policies and economic, social maintain population or inter-sector action and conditions that selected (eg sanitation, environmental minimize groups clean air) determinants hazards to health (eg poverty) Primary Specific causes Reduce incidence Total Public health and risk factors of disease population, programmes and (eg smoking) selected health promotion groups or (eg. Smoking high-risk cessation, individuals vaccination Secondary Early stage Reduce Individuals Early diagnosis prevalence of with early and treatment disease disease (eg. Cancer screening) Tertiary Late stage Reduce disease Individuals Rehabilitation complications with (eg. Stroke rehab) and disability established disease - Page 127 of 300 - 2. Preventive Approaches Cause of cases vs. cause of incidence: □ A population-oriented knowledge □ Characteristics of population (not individuals) have to be studied to find determinants of prevalence and incidence a. Individual (High-risk) Approach Intervention appropriate to individual (tailor-made) Subject motivation Physician motivation Cost-effective use of resources Benefit : risk ratio favourable Difficulties and costs of screening Palliative and temporary – not radical Limited potential for individuals and populations Large number at small risk may give rise to more cases of diseases than the small number who are at high risk Behaviourally inappropriate b. Population Strategy Radical – attempts to remove underlying causes that make the disease common Large potential for population Attempts to shift the whole distribution of exposure in a favourable direction Behaviourally appropriate – changes norm ‘Prevention paradox’: a preventive measure which brings much benefit to the population offers little benefit to each participating individual Poor motivation of subject Poor motivation of physician Benefit : risk ratio worrisome - Page 128 of 300 - C. Medicine as a Social Science Epidemics are ‘indications of large disturbances of collective life’ → elimination of social inequality to prevent epidemic McKeown thesis: population growth primarily due to ↓ mortality from disease due to ↑ social conditions (living standard) □ Criticized medicine as placing too much emphasis on ‘cure’ rather than ‘care’ Preston’s theory: life expectancy rose between 1930 and 1960 regardless of income level □ Factors exogenous to income accounted for most of the gain in life expectancy → major effect of mortality Illich’s theory of iatrogenesis: medicine does more harm than good to general population health □ Clinical iatrogenesis: injury done to patients by ineffective, toxic and unsafe treatment □ Social iatrogenesis: ‘medicalisation of life’ → unrealistic health demands → more treatments → individuals lose autonomous coping skills and become more reliant on institutional care □ Cultural iatrogenesis: destruction of traditional ways of dealing with and making sense of death, pain and sickness → people less tolerant to diseases □ Health more dependent on individual action than on new treatments □ Iatrogenesis theory rebutted by Bunker: 17% of gain in life expectancy since 1900 attributed to medical and public health intervention; loss of life expectancy due to iatrogenesis only 6-12 months - Page 129 of 300 - Reality is something in between: both improvements in social conditions and healthcare contributed to increase in life expectancy: □ Social conditions are ‘fundamental causes’ of disease and death □ People with more resources (higher income) have better health □ Note average BP↓, self-rated health↑, subjective happiness↑and family harmony↑ as income ↑ Overall life expectancy increase attributed to: □ Economic wellbeing/standard of living □ Public health □ Personal healthcare □ Individual health-related behaviour ‘Ladder of political activism’ for doctors: □ 1st rung: political passivism; info on health risk and opportunities for health improvement is exchanged within the health sector only □ 2nd rung: public health professionals actively disseminate relevant information among politicians □ 3rd rung: public health professionals try to directly influence the political process □ 4th rung: public health professionals become politicians themselves - Page 130 of 300 - L25 What is Medicine? What is Public Health? Four key health challenges: □ Unfinished epidemic of infectious diseases □ Emerging epidemic of chronic conditions □ Unethical epidemic of inequalities □ Unnecessary epidemic of environmental insults Systematic solution to challenges: 1) Identify the problem; 2) Break down the problem into manageable, soluble components; 3) For each component, deploy optimal combination of resources (human, financial, capital etc) in a targeted fashion (optimal = more efficient/value-added) A. Unfinished Epidemic of Infectious Diseases Examples: animal-origin influenza, antibiotic resistance, vaccine-preventable infections, aetiologic (causal) potential associated with non-communicable diseases Methods adopted: □ Control on poultry supply chain □ Childhood immunization programme (CIP) - Page 131 of 300 - B. Emerging Epidemic of Chronic Conditions Lifestyle determinants: smoking, alcohol, total and form of energy intake, physical activity, dietary salt intake, fruits and vegetables Note that non-communicable diseases (NCDs) account for >85% of all deaths (esp neoplasm, CVD etc.) Major health risks: □ Overweight/obesity: 51.8% □ Hypertension: 31.6% □ Tobacco: 11.5% □ Type II diabetes: 9.8% Obesity dependent on diet and exercise □ Intake (food availability and portion size, high (trans) fat diets and high energy density foods) □ Expenditure (exercise already displaced as preferred mode of leisure activity and lack of conducive built environment (reliance on transportation) Rule of Halves in Hypertension in HK: □ 50% high BP (31.6%) □ 50% diagnosed (46.2%) □ 50% with medication (69.7%) □ 50% under control (42.4%) - Page 132 of 300 - C. Unnecessary Epidemic of Environmental Insults Problems: □ Air pollution, incl indoor (secondhand/thirdhand smoke) □ Environmental contamination of food chain Tobacco control: □ Health education □ Fiscal: 50% rise in tobacco duty in 2009/10 budget □ Legislative: Smoking (Public Health) Ordinance □ Challenges: → Legal and judicial interpretation of new law (advertisement, definition of ‘indoor area’ → Illicit import and sales → Tobacco lobby (eg product differentiation of age and gender-specific markets, pressure through media and other PR strategies) → Improvement in provision of smoking cessation across all sectors Air pollution problem: □ 1990, EPD restricted S content of fuel to 0.5% by weight □ Both SO2 concentration in air, prevalence of bronchial hyperresponsiveness in primary school children and increase in deaths from heart and lung diseases reduced after the restriction D. Unethical Epidemic of Inequalities Social determinants of health Pathways to ill health: psychosocial, neomaterial, cultural, behavioural, lifecourse Commoditization of healthcare → inverse care law: availability of good healthcare varies inversely with the need of population group (better income → less need but better healthcare available) - Page 133 of 300 - E. Public Health Public health is: □ Population based Emphasises collective responsibility for health, its protection and disease prevention □ Recognises the key role of the state, linked to a concern for the underlying socio-economic and wider □ determinants of health, as well as disease □ Emphasises partnerships with all those who contribute to the health of the population Difference between medicine and public health: Specialty of community medicine in HK to do public health work - Page 134 of 300 - L26 How is healthcare organized in Hong Kong? A. Health System Well-functioning health system responds (in a balanced way) to a population’s needs and expectations by: □ Improving health status □ Defending population against health threats □ Protecting population against financial consequences of ill health □ Providing equitable access to healthcare □ Making it possible for people to participate in decisions affecting their health and their health system 1. Components of a health system 1) Individuals and bodies that deliver healthcare: - Public vs private - Western vs traditional - Licensed vs unlicensed - Persons vs institutions 2) Money flows that finance healthcare: - General revenue - Social insurance - Private insurance - Out-of-pocket payments - Medical saving accounts 3) Activities providing specialized inputs into the healthcare process: - Medical and nursing schools - Drug manufacturers - Medical device manufacturers etc. 4) Financial intermediaries, planners and regulators who control, fund and influence provider of healthcare: - Government: ministries of health and finance - Insurance companies - Regulatory bodies, etc. 5) Activities of organizations that deliver preventive services: - Immunisation - Family planning - Infectious disease control - Health promotion activities, etc. - Page 135 of 300 - 2. Health System Reform Forces driving reform: □ Healthcare is central to improvement in health status and general development of populations □ Rising cost of healthcare □ Rising expectations of the public □ Limits on government’s capacity to pay □ Growing skepticism about conventional approaches ‘Control knobs’ for health system reform: areas of a health system that significantly determine how the system affects the population and can be adjusted by government action □ Financing: mechanisms for raising money that pays for healthcare □ Payment: methods for transferring money to healthcare providers, creating incentives for providers □ Organizations: mechanisms to affect the mix of providers, their roles and functions and how they operate internally □ Regulation: use of coercion by the state to alter the behavior of providers, insurance companies and patients □ Behaviour: efforts to influence how providers and patients behave - Page 136 of 300 - B. Health System in Hong Kong Total expenditure on health (TEH): □ 5.1% of gross domestic product (GDP) □ 49% public sources and 51% private sources Comparison with other economies: □ Comparable quality and health outcomes at relatively low total and public health expenditure (HE) as % GDP Health financing sources: □ Household out-of-pocket payments accounted for 68% of private HE □ Employer-provided group medical benefits and individually purchased private health insurance each accounted for 14% of private HE Healthcare providers: □ Spending at providers of ambulatory care and hospitals accounted for 73% of TEH □ Public HE was mostly incurred at hospitals (69%) Healthcare functions: □ Public HE mostly incurred in inpatient curative care (32%) and ambulatory care (i.e. outpatient care) (26%) □ Private HE concentrated in ambulatory care (42%), inpatient curative care (22%) and medical goods outside patient care setting (19%) Note: healthcare professionals (doctors, nurses, pharmacists etc.) per population still significantly lower than world average - Page 137 of 300 - 1. Organization Food and Health Bureau oversees the entire system Most public health functions carried out by Department of Health Food and Environmental Hygiene Department for food safety and inspection (Centre for Food Safety) and environmental hygiene Agriculture, Fisheries and Conservation Department for prevention and control of animal and plant disease as well as regulation of animal husbandry (agriculture) and fishing practices a. Department of Health (DH) Disease surveillance, prevention and control (Centre for Health Protection) Health promotion Statutory and regulatory functions (Chinese medicine, drugs, port health, tobacco control, medical devices, private healthcare institutions) Preventive clinical services (elderly health, maternal and child health, student health, HIV/AIDS, tuberculosis) Other clinical services (forensic pathology, clinical genetics, child assessment, primnary health and dental care for civil servants and dependants) - Page 138 of 300 - b. Hospital Authority (HA) Public statutory body directly accountable to the Food and Health Bureau Manages public hospital system: □ 42 public hospitals and institutions □ 48 specialist out-patient clinics □ 73 general out-patient clinics □ Organized into 7 geographical clusters 2. Ecology 3. ‘Health Financing Paradox’ - Page 139 of 300 - 4. Future Reform a. The Harvard Report (1999) Assessment of HK health system by Harvard University, commissioned by HK government Criticisms: □ Compartmentalized, hospital-based delivery system □ Incoherent financing □ Questionable financial sustainability □ Supplier-dominated decision-making Proposal: □ Financing: → Compulsory social insurance scheme to pool risk across entire population (health security plan) → Long-term health savings account (MEDISAGE) □ Organization: → Reorganization of HA into competing integrated health systems □ Payments: → Payments made on per episode or packaged basis to reduce oversupply; to be negotiated between Health Security Fund and providers - Page 140 of 300 - L28 Gastrointestinal Tract A. Histological Layers - Page 141 of 300 - 1. Mucosa Functions: absorption, secretion, protection Epithelial lining: □ Oesophagus: stratified squamous non-keratinizing epithelium □ Stomach: protective simple columnar epithelium (predominantly mucus-secreting) □ Intestines: simple columnar epithelium (absorptive cells and mucus-secreting cells) Lamina propria: □ Accommodates the mucosal gland (epithelial invagination) □ Loose connective tissues □ Lymphatic and fenestrated blood capillaries □ Supports and nourishes the epithelium □ Unencapsulated lymphoid nodules and plasma cells (for protection) Muscularis mucosae: □ Thin layers of smooth muscle (inner circular and outer longitudinal) □ For local movement and folding of the mucosa (controlled by Meissner’s plexus and some paracrine hormones) □ Modulates the heught of villi in small intestines 2. Submucosa Loose c.t. with larger blood vessels and lymph vessels Meissner’s plexus: submucosal plexus of ANS ganglion cells and nerve fibres Contains mucus-secreting glands in duodenum and esophagus only 3. Muscularis Externa Two layers of smooth muscles: inner (circular) and outer (longitudinal) Regulate luminal diameter of the intestine Moves luminal contents along the tract by peristalsis Peristaltic waves coordinated by Auerbach’s (myenteric plexus) (between circular and longitudinal muscle layers and by paracrine hormones 4. External Layer Serosa: visceral (of organ) peritoneum (mesothelium (simple squamous) + c.t.), i.e. serous membrane Adventitia: loose connective tissues in esophagus and retroperitoneal (retro- = behind) segment of intestines - Page 142 of 300 - B. Oesophagus Muscular walls to convey chewed food from pharynx to the stomach Stratified squamous non-keratinized epithelium to withstand abrasion Esophageal cardiac glands (simple tubular, mucous) in lamina propria at upper submucosa to eases passage of ingested food Substantial muscularis mucosae Muscularis externa: □ Striated in the upper third, smooth in lower third, mixed in middle third □ Physiologic sphincters at two sites: pharyngoesophageal and gastroesophageal Adventitia (not serosa) as outermost layer - Page 143 of 300 - C. Stomach Function: for br