option d: human physiology

• Discuss the significance of the oxygen dissociation curves for adult haemoglobin and foetal haemoglobin.

  1. oxyhemoglobin forms when pO2 is high
  2. respiring tissues have low pO2
  3. «small» decrease in pO2 over steep part of curve results in dissociation of oxyhemoglobin
  4. foetal haemoglobin is structurally different from maternal haemoglobin
  5. foetal dissociation curve to left of adult dissociation curve
  6. foetal haemoglobin has greater affinity for oxygen than maternal blood
  7. foetus obtains its oxygen from mother’s blood «at placenta at any given pO2
• Thyroxin: A hormone produced by the thyroid gland that regulates basal metabolic rate.
• How is heartbeat initiated:

  a. sinoatrial node/SAN initiates contraction of atria;

  b. SAN sends messages to the atrioventricular/AV node;

  c. AV node initiates ventricular contraction;

  d. through conducting fibres;
• How does liver regulate nutrient levels:

  1. storage of glucose as glycogen OR breakdown of glycogen to glucose

  2. deamination/breakdown of «excess» amino acids

  3. storage/recycling of iron/copper

  4. produces/eliminates cholesterol «as necessary»

  5. storage of vitamin A/vitamin D/vitamin B12/vitamin K
• Causes of hypertension:

  a. deposition of fat in arteries thus losing elasticity/forming fibrous tissues

  b. deposition of fat/formation of plaque in arteries thus narrowing of lumen/causing a blockage

  c. high salt levels in diets thus retaining more fluids

  d. smoking because nicotine is a vasoconstrictor molecule

  e. prolonged high levels of stress thus causing vasoconstriction / exposure to stress hormones

  f. genetic predisposition makes it more likely that other factors will lead to hypertension
• Outline the role of the sinoatrial node in the contraction of the heart:

  a. initiates action potentials / electrical impulses (at start of cardiac cycle)

  b. acts as pacemaker/ continuous beating without external stimuli

  c. signal spreads over atria / causes contraction of atria (systole)

  d. impulses transmitted to AV (atrioventricular) node / cannot pass directly to ventricles
• Explain the importance of dietary fibre:

  a. ensure correct transit rate / movement of food through the intestines

  b. avoid constipation / difficulty in empty bowels / difficulty in egestion

  c. correct levels of water reabsorbed

  d. avoid overlong exposure to fat soluble chemicals

  e. decreased risk of colon cancer/hemorrhoids/appendicitis

  f. decreases the rate of absorption of glucose

  g. decreases hunger so less obesity/diabetes
• Importance of iodine:

  a. iodine is absorbed/used/needed by the thyroid

  b. «needed» to synthesise thyroxin

  c. lack of iodine causes swelling of thyroid gland/goiter/hypothyroidism
• Outline the role of nerves in the secretion of gastric juice:

  a. sight/smell of food stimulates brain 

  b. food entering stomach stimulates chemoreceptors/stretch receptors to send impulses/signals to brain 

  c. impulse/signal from brain causes cells in stomach lining/parietal cells to secrete acid/HCl/gastric juice 

  d. brain sends impulses/signals «via vagus nerve» to endocrine cells in wall of stomach to release gastrin 

  e. gastrin stimulates «more» production of acid/HCl/gastric juice