digestion

• explain reason for dual supply of blood in liver:

  1. the dual supply is the hepatic artery and the hepatic portal vein
  2. blood in «hepatic» artery provides oxygen to the liver «tissues»
  3. the «hepatic portal» vein carries blood from the gastrointestinal tract/intestines
  4. the «hepatic portal» vein carries blood rich in nutrients OR sugar/glucose/glycogen is stored and released in response to hormones
  5. this allows the nutrients to be stored/processed
  6. prevents osmotic imbalance due to absorbed nutrients in the blood
• Cause and consequence for malnutrition in humans:

  Cause:

  1. deficiency in essential nutrient
  2. excess of a nutrient
  3. due to social/socioeconomic/political factors OR unbalanced diet due to malfunctioning of hypothalamus

  Consequence:

  1. starvation - break down of body tissues
  2. obesity - diabeties/CHD
  3. anorexia - organ failure
  4. vitamin deficiency - scurvy from lack of Vit. C
• State structural characteristic of intestinal villus cells that adapts them to the absorption of nutrients:

  1. large surface area due to presence of microvilli
  2. tight junction
  3. protein channels/membrane pumps
  4. large number of mitochondria
• Cause of stomach ulcers:

  1. H. pylori
  2. use of non-steroidial anti-flammatory drugs/NSAID/asprin/ibuprofen
• Consequences of protein deficiency:

  1. protein/muscle lost for energy
  2. lack of blood plasma proteins
  3. leading to tissue fluid retention/edema/swollen abdomen/kwashiorkor
  4. lethargic/little interest in surroundings
  5. thin muscles/flaky appearance of skin/sparse hair with lack of pigmentation
  6. physical/mental development retarded
  7. lack of menstrual cycle
• Cause and symptom of type II diabetes:

  Cause:

  1. body becomes resistant to insulin
  2. pancreas does not produce enough insulin

  Symptom:

  1. hyperglycaemia
  2. thirst
  3. frequent urination
• Explain how gastric juice is secreted

  1. through nervous and hormonal control
  2. sight and smell of food stimulates brain to send nerve impulse
  3. cause parietal cells to secrete acid/gastric juice
  4. food entering the stomach stimulates the chemoreceptors/stretch receptors, and send impulses to the brain
  5. vagus nerve sends nervous impulse to endocrine cells in stomach wall, which releases gastrin into blood
  6. gastrin induces release of gastric juice
  7. secretin/somatostatin decrease gastrin secretion
• How intestinal epithelium is adapted for maximum absorption:

  1. microvilli/brush border to increase surface area
  2. numerous mitochondria for energy for active transport
  3. have transport proteins for specific nutrients
  4. single layer of cells/short distance allowing for diffusion
• How does Vibrio cholerae cause dehydration:

  a. V. cholerae releases toxin

  b. chloride channels activated

  c. chloride ions are pumped out of cells

  d. leading to fluid loss from intestine/diarrhea

  e. associated vomiting contributes to dehydration
• Bolus is food that has been mixed with saliva. Chyme is food that has been mixed with gastric juice.
• Outline control of digestive juice secretion so that digestive juices are only secreted into the gut when there is food present.

  1. combination of nervous AND hormonal control
  2. food in stomach stimulates chemoreceptors/stretch receptors / stretches the wall
  3. causes production of gastrin
  4. arrival of chyme to the small intestine triggers the release of hormones/secretin
  5. volume and composition of gastric juices are controlled
• Causes and treatment of PKU (Phenylketonuria)

  Causes:

  1. phenylketonuria is an inherited / genetic condition / caused by a mutation
  2. enzyme phenylalanine hydroxylase/PAH not present/deficient
  3. phenylalanine is an essential amino acid
  4. inability to convert phenylalanine into tyrosine / phenylalanine builds up in the body

  Treatment:

  1. requires diet rich in tyrosine
  2. low in phenylalanine
  3. monitor blood phenylalanine levels
  4. monitor growth rates/intellectual development
• Vitamin D deficiency:

  1. poor bone mineralisation
  2. rickets/osteoporosis/osteomalacia
  3. poor absorption of dietary calcium
  4. «lack of vitamin D results in» calcium «ions» not absorbed from gut in sufficient quantities
  5. calcium salts not deposited or reabsorbed OR affects bone mineralization
  6. bones become softened/weakened
  7. can cause rickets «in children»/osteomalacia «in adults»
• Osteomalacia: a condition in which the bones become soft and brittle due to a lack of vitamin D
• In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys.
• How drugs that stimulate leptin receptors treat obesity:

  1. appetite control (centre) is located in the hypothalamus
  2. leptin is a hormone made by adipose cellsOR promotes feeling of satiety/fullness
  3. to inhibit appetite/feeling of hunger
  4. the drug mimics the action of leptin
  5. (reduced hunger) leads to less food intake/weight loss
• Comparing gastric and pancreatic juice:

  Gastric:

  1. produced by glands in stomach wall
  2. low pH
  3. contains HCl
  4. no enzymes for starch digestion
  5. contains mucus

  Pancreatic:

  1. produced by pancreas
  2. high pH
  3. contains HCO3-
  4. lipase/amylase
  5. no mucus
• Why are acidic conditions favoured in the stomach

  1. provides optimum pH for enzyme activity in stomach
  2. denatures protein and starts breakdown of organic substances
  3. converts pepsinogen to pepsin
  4. destroys pathogens in ingested food