Summary HAP

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Summary - HAP

  • 1 HAP

  • Pepsin
    An endopeptidase
  • Digestive system, not digest itself:
    - Activity restricted to presence food
    - Regulation (local, distal, proximal)
    - Enzymes stored as inactive pro-enzymes (zymogens)
    - Non-digestible mucus coats walls
    - High replacement rate (turnover) of mucosal cells
  • Pepsin
    Starts digestion of dietary proteins
  • Pepsin
    Enhance acid (H+) release and pepsinogen release
  • Pepsin
    Leads to production of oligopeptides --> maintain gastrin secretion
  • Pepsin
    Is secreted in inactive form pepsinogen
  • Pepsin
    Specific for aromatic amino acids, leucine and methionine
  • Exopeptidase
    Cleaves at the end of amino acids
  • Fermentation
    May provide energy, NO amino acids
  • Exothermic
    Reactions in which relatively large complex molecules are broken down to smaller molecules (catabolic reactions)
  • Endothermic
    Reaction that involves synthesis of larger molecules from smaller ones (anabolic or biosynthetic reactions)
  • Exothermic
    - Output of energy greater than activation of reaction
    - Energy level of product is lower than of starting material
    - Take place with output of heat
  • Endothermic
    - Output of energy is less than activation of reaction
    - Energy level of product is higher than of starting material
    - Uptake of heat from surrounding, so that reaction can take place
  • Metabolism depends on
    - Balanced nutritional input and physiological output
    - Constantly has to switch, dependent on food intake and physical activities (metabolic pathways, energetic efficiencies and body composition/waste products)
  • Physiological output depends on
    Physiological status
    Health status
  • Nutritional input depends on
    Total daily intake
    Meal size/pattern
    Nutriënt composition
  • Endopeptidase
    Cleaves in between amino acids, NOT outside
  • Thermoneutral
    Output of energy is equal to activation energy of reactions, so the energy level of products is the same as the starting materials (energetically neutral)
  • Enzymes
    Proteins that catalyse metabolic reactions
  • Enzymes
    - Lowers the activation energy of chemical reaction
    - Increase rate at which the reaction attains equillibrium
  • Enzymes
    The reactive groups in AA side-chains and coenzymes at active site --> ease the making/breaking of specific chemical bonds in substrate --> by donating or withdrawing electrons
  • Random hydrolysis of peptide bonds (in vitro)
    10-12 hours in 12 mol/L HCl at 105 degrees
  • Specific bonds hydrolysed (in vivo)
    1-2 hours at 37 degrees
  • Anabolic reactions
    - Synthesis of body constituents
    - E.g. protein metabolism
  • Catabolic reactions
    - Release of energy from food or body constituents
    - Energy/ATP/Heat
  • Post prandial phase
    - Digestion - Absorption - Storage
    - Input higher than needs
    - Anabolic or Catabolic disposal (storage, interconversion, oxidation)
    - Storage of: amino acids, glucose and triacylglycerol in VLDL
  • Post prandial phase
    Storage of:
    - Amino acids in muscle cells as protein
    - Triacylglycerol in VLDL in adipose tissue as triacylglycerol (TG)
    - Glucose as glycogen in muscle cells, as triacylglycerol in adipose tissue and as glucose in brain cells
  • Post absorptive phase
    - 4-5 hours after meal, when all products of digestion have been absorped
    - Utilisation
    - Needs higher than input
    - Mobilisation (turnover, interconversion, oxidation)
  • Diet-induced thermogenesis (DIT)
    - Post prandial metabolism --> increase heat production
    - Depend on ingested nutrients and metabolic settings
    - Ingested ME is not corrected for energetic costs of PPM
    - Under specific conditions change in metabolic settings
  • Post absorptive phase
    - Metabolic fuels enter circulation from reserves --> glycogen, triacylglycerol and protein
  • Post absorptive phase
    Secretion of glucagon by alpha-cells increase:
    --> increased breakdown of liver glycogen to Glu-1-P
    --> release glucose into circulation
    --> muscle glycogen CANNOT be used directly as source of free glucose
    --> increased synthesis of glucose from AA in liver and kidney (--> gluconeogenesis)
  • Post absorptive phase
    Reduction secretion of insulin:
    - decreased uptake of glucose into muscle and adipose tissue (glucose transporter is internalised (automatisch gedragen naar) in absence of insulin
    - decreased protein synthesis --> AA arising from protein catabolism available for gluconeogenesis
    - Non-esterified fatty acids released from triaglycerol in adipose tissue --> due to  HSL (insulin can inhibit HSL)
  • Post absorptive phase
    - Main substrates for gluconeogenesis are AA and glycerol from hydrolysis of triacylglycerol
    - FA can NEVER be substrates for gluconeogenesis
    - Liver has greater capacity for oxidation of FA required for its energy needs (muscle and adipose tissue not)
  • Post absorptive phase
    Liver synthesises ketone bodies (acetoacetate and beta-hydroxybutyrate) --> to other tissues for use as metabolic fuel --> provide brain about 20% of energy needs during starvation
  • Post absorptive phase
    - Plasma glucose decrease --> but maintained during fasting/starvation due to gluconeogenesis
    - Plasma non-esterified fatty acids increase till starvation
    - Ketone bodies increase continually trough starvation
  • Homeostasis
    Tendency to resist change/factors that disturb vital functions
    - glucose concentrations in blood
    - pH in blood (acid-base balance)
    - Oxygen supply
    - Body temperature
  • Positive energy balance
    Overweight and obesity
  • Nutritional paradox
    - Food and body are no natural allies
    - Material composition of foodstuff is related to their natural function (only milk), not to our nutritional requirements
    - Some materials can be used as nutrients, some are even toxic
  • Nutritional paradox
    Diabetes --> body needs glucose, but cannot be absorbed in diabetes patients
  • Metabolism can be influenced by:
    - Environmental conditions
    - Nutritional input
    - Physiological output
  • GI tract
    Hollow muscular tube running from mouth to anus
  • Sphincters
    Circular muscles that can contract and relax, thereby isolating or connecting 2 compartments of the GI tract, respectively
  • Enzymes mouth
    - Salivary amylase
    - Lingual lipase
  • Enzymes stomach
    - Gastric acid
    - Pepsin
    - Gastric lipase
  • Enzymes small intestine
    - Pancreatic amylase
    - Lipase
    - Phospholipase
    - Trypsin
    - Chymotrypsin
    - Elastin dipeptidases disaccharidases
  • Rectum
    - Bacterial fermentation
    - Absorption of water
  • Duodenum
    - Secretion of CCK, secretin, GIP, HCO3
    - Absorption of Fe 
  • Small intestine
    - Intraluminal and surface digestion (large in duodenum, small in ileum)
    - Absorption of ions, nutrients, H2O (large in duodenum, small in ileum)
    - Motility: segmentation (digestive phase) and peristalsis (interdigestive phase)
  • Jejunum
    Absorption of: monosaccharides, amino acids, fatty acids, glycerol, fats and water
  • Ileum
    - Secretion of PYY and HCO3
    - Absorption of Bile acids and vitamin B12
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Potential product by amylase digestion
Which aspect mainly determines the timespan of arrival of food at ileo-caecal after meal
Rate of gastric emptying
No digestion by brush-border enzymes for
Fat and oils, dont need them for final digestion
- Pylorus
Small intestine
- Ileo-ceacal
Large intestine
- Anal-sphincter
Volume water used for digestion and absorption
- Endogenous secretions --> 7000 ml
- Total presented to intestine --> 8500 ml
- Absorbed in small and large intestine --> 8300 ml
- Stool --> 200
Colon defecation response
- Voluntary defecation reflex --> Intra abdominal pressure increase (closure of glottis, descent of diaphragm, contraction of adominal wall muscles)
- Involuntary defecation reflex --> propulsive motility of descending colon and rectum, relaxation of internal anal sphincter and relaxation of external anal sphincter
Microbiota in colon produce
small chain fatty acids and gas
Colon - response to meal
Initiated by signals from stomach and intestine
Colon - 3 contraction patterns
- mixing movements --> locally
- haustral migration --> into larger areas
- mass movement --> transport left parts to end
Colon - conversion of storage motor patterns to propulsive motor patterns and defecation
- stimulus --> rectal distention
- transmission --> neural (intrinsic and extrinsic nerves)