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104-theme 1- the alimentary system > macronutrients > Flashcards

macronutrients Flashcards

1
Q

what are the functions of carbohydrates? 4

A
  • energy substrate
  • builds macromolecules
  • glycogenesis
  • spares protein and fat
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2
Q

where can linoleic acids be found? 3

A
  • vegetable oils
  • sunflower oils
  • meat, poultry and eggs in the form of arachidonic acid
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3
Q

where can linolenic acids be found? 2

A
  • green leafy vegetables

- in oily fish as eicosapentaenoic acid and docosahexaenoic acid

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4
Q

what are the functions of dietary fat? 3

A
  • TAG is the primary energy substrate stored in adipose tissues to sustain animals during fasting
  • Influx of TAG into adipose tissue largely mediated by the action of adipose tissue lipoprotein lipase (LPL)
  • This is upregulated in the presence of insulin, fatty acids during fasting
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5
Q

what are essential amino acids?

names? 9

A
  • not synthesised in the body, there is a dietary requirement
  • histidine
  • isoleucine
  • leucine
  • methionine
  • phenylalanine
  • threonine
  • tryptophan
  • valine
  • lysine
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6
Q

describe mechanical digestion in the mouth? 2

A
  • chewing and swallowing

- chemical digestion of carbohydrates and fats

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7
Q

describe the mechanical digestion in the stomach? 3

A
  • peristaltic mixing and propulsion
  • chemical digestion of carbohydrates and fats
  • absorption of lipid-soluble substances such as alcohol and aspirin
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8
Q

describe the mechanical digestion in the small intestine? 3

A
  • mine and propulsion, primarily by segmentation
  • chemical digestion of carbohydrates, fats and polypeptides, nucleic acids
  • absorption of peptides, amino acids, glucose, fructose, fats. water, minerals and vitamins
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9
Q

describe the mechanical digestion of the large intestine? 3

A
  • segmental mixing and propulsion
  • no chemical digestion (except by bacteria)
  • absorption of ions, water, minerals, vitamins and organic molecules
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10
Q

describe 2 adaptations to the GI tract to facilitate different functions?

A
  • Stomach= acidic environment= mucous and bicarbonate ions
  • Small intestine= peristalsis becomes segmentation to squeeze food against the intestinal wall and maximise digestion and absorption
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11
Q

describe the sequence of sphincters in the GI tract? 4

A
  • Cardiac
  • Pyloric
  • Ileocecal valve
  • Internal and external sphincters
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12
Q

describe carbohydrate digestion in the buccal cavity?

A

salivary amylase, limited activity. initiates the breakdown of starches by catalysing the hydrolysis of polysaccharides into disaccharides

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13
Q

describe dat digestion in the buccal cavity?

A

lingual lipase secreted by the serous glands

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14
Q

describe fat digestion in the stomach? 3

A
  • Stomach- gastric lipase secreted by gastric cells in the fundic mucosa.
  • An acid enzyme that does not require bile acid from the liver or colipase from the pancreas for optimal functioning
  • Theses enzymes are important in neonates (50% of lipid hydrolysis) and adults (30%)
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15
Q

describe protein digestion in the stomach? 2

A
  • Chief cells produce pepsinogen converted to pepsin int eh presence of HCl
  • Acid environment denatures proteins and reduces the bacterial load
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16
Q

describe bile acids from the liver for fat digestion? 2

A
  • Cholic and chenodeoxycholic acid
  • Molecules are amphipathic- act as a detergent and have both hydrophobic and hydrophilic properties. This means they can solubilize lipids to form mixed micelles
17
Q

describe the pancreas and fat digestion? 4

A
  • Small intestine= pancreatic lipase secreted from the pancreas alongside the cofactor pro-colipase
  • Pro-colipase is activated in the intestinal lumen by trypsin to form colipase
  • Colipase stabilises pancreatic lipase increasing its efficiency
  • Pancreatic lipase hydrolyses TG to form monoglycerol, fatty acids and glycerol
18
Q

describe the primary pancreatic proteases? 4

A
  • The two primary pancreatic proteases are trypsin and chymotrypsin
  • These are synthesised and packaged within secretory vesicles as inactive pro-enzymes: trypsinogen and chymotrypsinogen
  • The pro enzymes are activated by an enteropeptidase -enterokinase secreted by the mucosal membrane of the duodenum
  • The secretory vesicles also contain a trypsin inhibitor to serve as a safeguard against trypsinogen converting to trypsin within the pancreas or pancreatic ducts
19
Q

describe absorption of nutrients in the small intestine? 2

A
  • Blood supply= 9 litres of fluid enter the GI tract with 8 litres absorbed through the small intestine
  • Large surface area to maximise secretion and absorption
20
Q

describe small intestine disaccharide digestion?

A
  • Disaccharides further digestion occurs by action of brush border enzymes- gluco-amylase, alpha-dextrinase, sucrase and maltase to form monosaccharides glucose, fructose and galactose
21
Q

describe carbohydrate absorption in the small intestine? 3

A
  • Absorption of CHO is limited to monosaccharides- glucose, galactose and fructose
  • Small intestine
  • Capacity to absorb fructose is limited
22
Q

describe fat absorption? 3

A
  • Small intestine
  • Water soluble mixed micelles pass through the unstirred water overlying the microvillus
  • Monoclyglycerol and fatty acids cross the apical membrane of the microvillus through passive diffusion and lipid protein transporter mechanisms
23
Q

describe protein absorption? 6

A
  • Small intestine
  • Pepsin (stomach)
  • Trypsin (pancreatic proteases)
  • Peptidases (brush border enzymes)
  • Human peptide transporter 1 (PEPT1)
  • Sodium hydrogen exchanger 3 (NHE3)
24
Q

describe non-starch polysaccharides and other carbohydrates? 7

A
  • NSP (fibre) resistant starch and most oligosaccharide are not digested and absorbed in the small intestine
  • Soluble fibres (pectin/gum) are fermented by bacteria in the colon
  • Insoluble fibres make up the cellulose roughage in the diet
  • Microbial fermentation leads to the production of:
  • gas (CO2, H2, CH4),
  • short chain fatty acids (acetate (enters the peripheral circulation), propionate (taken up by liver) and butyrate (used by the colonic cells)
  • this also enhances microbial growth

104-theme 1- the alimentary system (17 decks)

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