BIO PAPER 3

• Essential amino acids cannot be synthesised by the body + need to be ingested as part of diet
• Non-essential amino acids: can be synthesised by the body or have a replacement nutrient which serves the same purpose
• Protein deficiency causes PKU (phenylketonuria)
• PLK: genetic condition resulting in impaired metabolism of the amino acid phenylalanine / autosomal recessive disease caused by mutation to the gene encoding for the enzyme / instead converted into phenylpyruvate which results in toxic build up of urine / if left untreated can cause brain damage and mental retardation
• 2 cis-polyunsaturated essential fatty acids can be OMEGA 3 and OMEGA 6
• Lipoproteins transport cholesterol through LDL and HDL: LDL carries cholesterol from the liver to the cells HDL carries cholesterol from the cells back to the liver
• LDL raises cholesterol levels whereas HDL decreases cholesterol levels
• Atherosclerosis: high cholesterol levels in the bloodstream --> leads to hardening and narrowing of the arteries / high LDL levels lead to particles forming deposits in artery walls / accumulation of fat develops plaques / risk of coronary disease
• Vitamin C deficiency can cause scurvy and general weakening of the immune system
• Vitamin D deficiency can cause osteomalacia (softening of bones) or rickets (deformed bones)
• Vitamin D used in the absorption of calcium in the body = contributes to bone mineralisation / naturally synthesised by the body when chemical precursor is exposed to sunlight / can be stored in the liver when levels are low
• Obesity consequences include being more likely to suffer from hypertension / places more strain on the heart to pump blood / may lead to atherosclerosis narrowing vessels / more likely to suffer from type II diabetes
• Starvation consequences include breakdown of body tissue and muscle loss which can lead to eventual organ damage
• Anorexia consequences include the body breaking down the heart muscle, reduced blood flow, and possible arrythmia
• recommended dietary intake is 2000 calories
• Exocrine glands produce and secrete substances via a duct onto an epithelial surface --> e.g salivary (amylase), gastric (HCL + proteases), pancreatic (lipase, protease, amylase) + intestinal glands
• Exocrine gland structure: composed of cluster of secretory cells (forming an acinus) / surrounded by basement membrane + held together by tight junctions / possess highly developed ER and golgi network for material secretion and mitochondria
• Nervous mechanism of digestion: sight and smell triggers immediate response where gastric juice is secreted by the stomach before ingestion / when food enters the stomach, it causes distension (build up of gas+fluid in abdomen) detected by stretch receptors in the stomach lining / signals are sent to the brain, which triggers the release of digestive hormones to achieve sustained gastric stimulation
• Hormonal mechanism of digestion starts with GASTRIN secreted into the bloodstream from the stomach and stimulates the release of stomach acids / if stomach pH drops too low, gastrin secretion is inhibited by gut hormones (secretin + somatostasin) / when chyme passes into small intestine, duodenum releases digestive hormones / secretin and CCK stimulate pancreas and liver to release digestive juices / pancreatic juices contain bicarbonate ions which neutralise stomach acids, while liver produces bile to emulsify ions
• Proton pumps maintain low pH environment in the stomach and parietal cells of the gastric pits / secrete protons via active transport which combine with Cl- ions to form HCl / proton pump inhibitors are drugs which irreversibly bind to proton pumps + prevent H+ secretion / raises pH in stomach to prevent gastric discomfort caused by high acidity (acid reflux) / increased susceptibillity to gastric infections due to reduction of gastric secretion
• Specialised features facilitate the absorption of digestive products: tight junctions (create impermeable barrier + ensure a one way concentration gradient) / microvilli (increases SA) / large number of mitochondria (generate large amounts of ATP for aerobic respiration, active transport) / pinocytic vesicles (absorption via endocytosis)
• Stomach ulcer is due to inflammed + damaged areas in the stomach wall due to exposure to gastric acids / damages epithelial cells of the stomach / helicobactera pylori can penetrate the mucus lining = results in degradation of protective mucus lining, exposing the stomach wall to gastric acids and causing ulcer / prolonged exposure may lead to stomach cancer but can be treated via antibiotics
• Vibrio cholarea is a bacterial pathogen that infects the intestines + causes acute diarrhea and dehydration = releases a toxin that binds to ganglioside receptors on the surface / internalised by endocytosis and triggers the production of cyclic AMP within the cell / activates specific ion channels within the cell membrane causing efflux of ions --> build up draws out H20 from cells and tissue via osmosis causing diarrhea
• FUNCTIONS OF THE LIVER

  • regulates metabolic processes in the body
  • process nutrients absorbed from the gut
  • stores and controls release of key nutrients (e.g glycogen, cholesterol)
  • detoxifies harmful substances (medications + alcohol)
  • produces plasma proteins
  • breaks down red blood cells + produces bile salts
• sinusoids are small blood vessels responsible for material exchange / increased permeability allowing larger molecules to enter and leave the bloodstream / incomplete and discontinuous surrounding basement membrane / lined by the endothelial layer containing large intercellular gaps and fewer tight junctions
• Carbohydrate metabolism happens when excess glucose in the bloodstream is stored as glycogen and coordinated by pancreatic hormones (insulin + glucagon)
• Protein metabolism happens when amino acid breakdown releases a toxic amine group / converted into urea by liver and excreted within urine by kidneys / can also synthesise non-essential amino acids from surplus stocl
• Liver detoxification acts on drugs that have entered the bloodstream and converted into less harmful and more soluble forms by either:

  1. toxins are converted into less harmful compounds via oxidation, reduction and hydrolysis reaction
  2. converted chemical attached to another susbtance via conjugation reaction -> makes less harmful compound + water soluble
• Erythrocyte recylcing is the process of the red blood cells returning to the bone marrow: liver is responsible for the breakdown of red blood cycles + recycling its components (bile)

  • Kupffer cells are specialised phagocytes within the liver that engulf red blood cells and break them down
  • haemoglobins made up of globins + heme groups
  • globin is digested by peptidases to produce proteins
  • heme groups made up of iron and bilirubin (bile pigment)
• Jaundice is caused by excess of bilirubin within body that leaks to surrounding tissue / causes yellowish skin discoloration and whites of eyes + itchiness and darkened urine
• specialised features of the heart muscle:

  • myogenic cardiac muscles : no need of central nervous system
  • branched cells : faster signal propagation
  • connected at intercalated discs: easier transmission between cells
  • many mitochondria for aerobic respiration
• Atrial contraction caused by specialised cluster of cardiomyocytes (SAN) in the wall of the right atrium that acts as a primary pacemaker

  Atria and ventricles are seperated by a fibrous cardiac skeleton composed of connective tissue that cannot conduct electrical signals

  signals from SAN must be relayed to second node (AV) that propagates electrical signals more slowly, creating a delay in the passing of the signal
• Ventricular contractions consist of the sepearation of contraction to optimise blood flow --> allows blood to fill ventricles before the AV valve closes

  Excitation of AV node sends signals down via bundle of His

  Stimulates Purkinje fibres in ventricular wall - causes cardiac muscles to contract
• Heart sounds are produced when 2 valves close in response to pressure changes (valves are present to prevent backflow - one way circulation and are AV + SL)

  1. AV closes at start of ventricular systole
  2. SL closes at start of ventricular diastole
• Electroradiograph composed of:

  1. P wave - atrial systole
  2. QRS complex - ventricular systole
  3. T wave: ventricular diastole
  4. 2 intervals for blood flow (PR interval + ST segment)
• Thrombosis is the formation of a blood clot in a blood vessel

  Occurs in arteries when vessels are damaged due to cholesterol deposition (atherosclerosis) - reduces vessel diameter

  high blood pressure damages the arterial wall, forming lesions (atherosclerosic plaques)

  If a plaque ruptures, blood clotting is triggered - forms a thrombus that restricts blood flow
• Artificial pacemaker delivers electrical impulses to the heart to regulate heart rate / used to treat arrythmia and abnormally slow heart rate
• defribillator depolarises the heart tissue to terminate unsynchronised contractions of the heart muscle fibres / helps optimise blood flow and re-establish normal heart rate by SAN node
• Stomach secretes PEPSIN and RENIN
• Pancreas secretes TRYPSIN, CHYMOTRYPSIN, ELASTASE