L5: Digestion and Absorption Flashcards Preview

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Flashcards in L5: Digestion and Absorption Deck (19)
1

Explain how digestion & absorption are separate but related processes

Define digestion

Process of breaking down complex nutrients into sample molecules

2

Explain how digestion & absorption are separate but related processes

Define absorption

transport of small molecules across intestinal wall

3

Explain how digestion & absorption are separate but related processes

How are digestion and absorption related?

Without digestion first occuring, most absorption of essential nutrients could not occur as the molecules they are contained in would be too complex to cross the intestinal wall

4

Explain the function of the small intestine & describe the specialised nutrient transport systems 

List the functions of the small intestine

  • Enzymatic digestion of CHD, proteins, fats
  • Absorption of digestion products, vitamins, bile salts, electrolytes, water
  • Secretion of electrolytes and water
  • Mixing & motility of digesta at appropriate rate

5

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe the function of chemical digestion in the SI

  • Reduces complex nutrients
  • For each major nutrient, accomplished by hydrolysis (splitting of a chemical bond by inserting H2O)
  • Usual hydrolysis sites:
    -CHD at glycosidic linkages
    -Proteins at peptide bonds b/w aa's
    -Fats at ester bonds

6

Explain the function of the small intestine & describe the specialised nutrient transport systems 

List the two types of digestive enzymes

  • 1. act w/in lumen of gut - luminal phase
  • 2. act at membrane surface of epithelium - membranous phase

7

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe the digestive enzymes in luminal phase of digestion

  • Originate from major gastrointestinal glands
  • Thoroughly mixed w/ digesta
  • Produces incomplete hydrolysis of nutrients to short-chain polymers

8

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe the digestive enzymes in membranous phase of digestion

  • Enzyme is chemically bound to epithelial surface
  • Break short-chain polymers into monomers that can be absorbed
  • Products of MP typically never re-enter lumen, absorbed by underlying epithelial cells

9

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe intestinal absorption (gradients and mechanisms briefly -why they exist)

  • Usually molecules move across cell membrane barriers in response to chemical and electrical gradients
  • Free movement determined by laws of diffusion
    => move from > [ ] to < [ ]
  • Charged particles attracted to areas of opposite charge
    => BUT charged ions/most org. nutrients cannot freely penetrate GIT
    => This is why there are specialised mechanisms

10

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe how transport mechanisms are classed

Proteins provide a highly specific, regulated pathway for ions and organic molecules

Transport mechanisms are classed as:

  • Active (primary)
  • Secondary active
  • Tertiary active
  • Passive

 

11

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe active transport
-give an example

  • Direct consumption of energy as ATP
  • Moves ions/molecules across membranes against an electrical or chemical gradient
  • Lrg & sml intestine have Na+, K+ -ATPase pump
    -uses e from hydrolysis of one molecule of ATP to drive 3 Na+ out of cell, in exchange for 2 K+ into cell against [ ] gradient

 

12

Explain the function of the small intestine & describe the specialised nutrient transport systems 

Describe passive transport

  • Ion channels
  • Completely passive, respond only to electrochemical gradients
  • Only regulatory control is open/close gates
  • Duodenum & upper jejunum channels are 'leaky'
    => freely permeable to H2O & sml inorganic ions
  • Food high [ ]  and blood low [ ] so transported across gradient

13

Draw this diagram, and describe it.

 

  • rumen motility acts as filter: can selectively retain actively fermenting larger particles of solid material
  • Ingesta is stratified & segregated by gravity & rumen motility
  • In dorsal sac -microbes adhere to forage particles & fermentation begins, producing gas which causes particles to rise to fibre mat
  • Changes in specific gravity cause particles to sink to slurry zone => further fermentation

14

Describe the relationship between dilution rates and microbes

  • high dilution rate = rapid removal of microbes
    -stimulates growth of microbes
    -selects for faster growing ones
    -improves microbial efficiency
  • High GR of microbes are nutritionally desirable
    -more microbial growth
    -less cellular maintenance
    -more VFA & microbial protein
  • Type of food affects dilution rate
    -too much easily digested food = acidosis
    -need fibre to produce saliva as buffer

15

Describe & understand the function of the equine hindgut & the role in fermentative digestion

  • Hindgut fermentation helped by prior gastric (enzymatic digestion), but this makes it less efficient than ruminant digestion
  • ...?

16

Describe the similarities b/w rumen (foregut) & colon/caecum (hindgut) fermentation

  • Need microbial population
  • substrate
  • control of pH and osmolality
  • anaerobic conditions
  • retention of fermenting material for long enough
  • continual removal of waste products & residue of spent fermentation substrate

17

Fermentative digestion of CHD to VFA

explain?

and importance of VFA

  • CHD attacked by hydrolytic microbial enzymes
  • Insoluble CHD => physical attachment of fungi & bacteria to particle surface
  • Enzymes release simple sugars from particles for microbes to use:
    -glucose
    -monosaccherides
    -short-chain polysacch.
  • Micro Ferm. produces SCFA (acetate, butyrate, proprionate) = VFA
  • Account for 50-70% digestible intake by ruminant

18

aerobic metabolism is?

gastric and enzymatic digestion

19

fermentative digestion of protein

explain

  • proteins are highly vulnerable to microbial attack = readily digested
  • Microbes can ferment and modify both feed & non-protein nitrogen (NPN)
    -urea
    -ammonia
    -nitrate
  • Microbes produce proteases
    -products of digestion absorbed into microbial cell bodies
  • Microbes use peptides for:
    -making microbial protein (MCP)
    -producing energy by further metabolism via VFA pathways