This pages gives outline details of the content of option D for SL students. There are essential questions and lists of student skills and applications. Helpful for revision. Student can check their understanding and prioritise areas for revision

D1 Human Nutrition

• Essential nutrients have to part of the diet because they cannot be synthesized by the body, These include:
  • Dietary minerals (chemical elements)
  • Vitamins are chemically diverse carbon compounds.
  • Some fatty acids
  • some amino acids - needed for protein production.
• Malnutrition may be caused by a deficiency, imbalance or excess of nutrients in the diet.
• The hypothalamus controls appetite.
• Hypertension and type II diabetes are more likely if a person is overweight.
• Starvation can cause body tissue to be broken down.

D2 Digestion

• The structure of cells of the epithelium of the villi, including microvilli
• Exocrine glands secrete to the surface of the body or the lumen of the gut.
• Nervous and hormonal mechanisms control the secretion of digestive juices.
• The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.
• Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food.
• The structure of cells of the epithelium of the villi, including microvilli and mitochondria, is adapted to the absorption of food.
• The rate of transit of materials through the large intestine is positively correlated with their fibre content.
• Materials not absorbed are egested.

D3 The Liver

• The functions of the liver
  • removes toxins from the blood
  • detoxifies toxins - e.g. alcohol.
  • recycles components of red blood cells. (erythrocytes)
  • Iron is carried to bone marrow for production of hemoglobin for new red blood cells.
  • Surplus cholesterol is converted to bile salts.
  • blood is intercepted from the gut.
  • regulates nutrient levels, eg: glucose
  • stores some nutrients; e.g. vit. A & D
• Hepatocytes produce plasma proteins (e.g. fibrinogen) using their endoplasmic reticulum and Golgi apparatus.
• Temporary slides of hepatocytes can be prepared from fresh liver.
• Kupffer cells use phagocytosis to begin recycling of red blood cells.
• Sinusoids carry blood through the liver, they are different in structure to capillaries.

D4 The Heart

• Structure of cardiac muscle cells includes branching and intercalated discs.
• This structure aids propagation of stimuli through the heart wall.
• Control of heart beat within the heart.
• Signals from the sino-atrial node that cause contraction of atria cannot pass directly from atria to ventricles.
• There is a delay between the arrival and passing on of a stimulus at the atrioventricular node.
• This delay allows time for atrial systole before the atrio-ventricular valves close in ventricular systole.
• Conducting fibres ensure coordinated contraction of the entire ventricle wall.
• Normal heart sounds are caused by the atrio-ventricular valves and semilunar valves closing & causing changes in blood flow.