L5: Digestion and Absorption Flashcards
Explain how digestion & absorption are separate but related processes
Define digestion
Process of breaking down complex nutrients into sample molecules
Explain how digestion & absorption are separate but related processes
Define absorption
transport of small molecules across intestinal wall
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
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
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
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
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
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
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
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
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
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
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
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
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
- …?
