This pages gives outline details of the content of option D for HL students. There are Revision 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 sinoatrial 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.

D5 Hormones - HL

• Endocrine glands secrete hormones directly into the bloodstream.
• Steroid hormones
  • bind to receptor proteins in the cytoplasm of the target cell to
  • form a receptor–hormone complex.
  • which promotes the transcription of specific genes.
• Peptide hormones
  • bind to receptors in the plasma membrane of the target cell.
  • this binding activates a cascade of reactions
  • mediated by a second messenger inside the cell.
• The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland.
• Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis.

D6 Respiratory gases - HL

• Oxygen dissociation curves show the oxygen affinity of hemoglobin.
• The increased release of oxygen by hemoglobin in respiring tissues is explained by the Bohr shift.
• Fetal hemoglobin is different from adult hemoglobin. This allows the transfer of oxygen in the placenta from mother's hemoglobin to fetal hemoglobin.

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• Carbon dioxide is carried in the blood in three ways:
  • in solution
  • bound to hemoglobin
  • transformed in red blood cells into hydrogencarbonate ions which diffuse into the blood plasma.
• changes in blood pH caused by changes in CO₂ concentration are detected by chemoreceptors.
• The respiratory control centre in the medulla oblongata controls the the rate of ventilation in response to the amount of CO₂ in the blood.  (during exercise!)