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BIOL370 Study Guide - Final Guide: Adipose Tissue, Emulsion, Peptide Yy

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Dinu Nesan
Study Guide

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Lecture 9: Introduction to Digestion
- Digestion is a highly complicated process
o Associated subordinate/symbiotic organisms
o Multiple interacting cell types & molecules
- Different nutrients undergo different digestive pathways
o Proteins vs. Carbohydrates vs. Lipids
- Digestive systems increase in size & specialization as they increase in complexity
o Structure-function relationships are present in almost all areas
Teeth, mouths, internal tissues
- Digestion:
o Assimilation: Process of nutrient acquisition, digestion, & absorption (GI tract - external)
o Egestion: Excretion of undigested food
- Energy content:
o Protein & carbohydrates = 4 kcal/gm; Fat = 9 kcal/gm
o Some food is indigestible (e.g. fibre), energy is lost in feces or urine
o Some energy is spend in digesting the food
Specific dynamic action (SDA): Increase in metabolic rate during digestion (thermal energy)
- Digestive enzymes: Converts macromolecules into absorptive forms
o Lipases: Break down triglyceride & phospholipids into FA
o Proteases: Break down proteins into polypeptides
o Amylase: Break down polysaccharides into oligosaccharides
o Nucleases: Break down DNA into nucleotides, then nucleosides, & N bases for absorption
- Symbiotic Organisms & Digestion (3)
o Enterosymbionts: Lives within the lumen of GI tract (e.g. cecum)
E.g. Birds eats wax in beehives, bacteria within the bird gut break down the wax into shorter
C units that can be absorbed by the bird
o Exosymbionts: Cultivated outside of the body
E.g. Leaf-cutter ants feed leaf fragments to fungi cultivated by the ant colony. Ants consume
both the fungi & the plant material that has been partially degraded by the fungi
o Endosymbionts: Grows in interstitial spaces or within host cells
E.g. Cyanelles are cyanobacteria living in association with sponges, uses photosynthesis to
produce Carbon skeletons that are taken up by the animal cells
- Transport across membranes:
o Facilitated diffusion (favorable)
o Active transport (ATP, non-favorable)
o Vesicles: Pinocytosis “drinking” vs. Phagocytosis “eating” vs. Exocytosis “expulsion”
- Carbohydrate Digestion
o Polysaccharides: Glycogen, starch, cellulose
o Disaccharides: Sucrose, lactose, maltose
Monosaccharides: Glucose, fructose, galactose
Break down occurs at the mouth & SI, absorbed by enterocytes of the gut
o Low glucose level:
Apical GLUT-5 takes in fructose & SGLT-1 “Na+/Glucose co-transporter” takes in glucose
Basolateral fructose exists via GLUT-5 & glucose exists via GLUT-2
o High glucose level:
GLUT-2 in vesicles are transported to apical surface to increase glucose uptake
- Protein Digestion
o Protein Dipeptides AA absorbed by epithelial cells via AA/Na+ cotransporter
o Some proteins can be transported across epithelial cells via endocytosis & exocytosis
- Lipid Digestion
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o Fats FAs & Monoglycerides, lipids diffuse across membrane into enterocytes
o GI tract secretes bile to emulsify lipids into small droplets “micelles
o Short chain FA & glycerol are transported into blood stream
o Triglyceride are transported to the lymph as chylomicrons
- Sensing Food “Different sense receptors”
o Gustatory “Blood” & Olfactory “Nose” detects chemical stimuli
o Other receptors detects energy emitted/reflected “Light – Eagle”, “Electricity – Knifefish, detect
muscle activity of potential prey
- Feeding mechanisms
o Filter feeding: depends on random encounters “Coral reefs”
o Food absorption from body wall “Endoparasites – Tape worm”
o Endocytosis Phagocytosis & pinocytosis “Protoozoans, sponges”
- Symbiosis w/ autotrophic microbes “Inorganic carbon”
o Photosynthetic:
E.g. Reef-building corals: Dinoglagellates are endosymbiotic, they provide food energy &
facilitate the formation of calcareous skeleton, gains protection
o Chemosynthetic:
E.g. Hydrothermal-vent communities rich in sulfur, provides food for sulfur-oxidizing bacteria
& worm species
- Symbiosis w/ heterotrophic microbes “organic carbon
o E.g. Fermenting microbes living in anaerobic environments (gut/lumen)
Rumen microbes can synthesize essential vitamins & amino acids
Microbes fermentative breaks down compounds that animals cannot digest
E.g. Cellulolytic bacteria contains cellulase enzyme that breaks down cellulose,
resulting in CO2 & methane production
Microbes permit waste nitrogen from the animal’s metabolism to be recycled
- Sponges: Ingest via phagocytosis
o Digestion occurs intracellularly in endocytic vacuoles
- Cnidaria: Ingest by bringing food into the gastrovascular cavity
o Digestion occurs extracellularly (enzymes) then intracellularly (endocytic vacuoles)
- Feeding structures: Specialized mouthparts for obtaining & processing food
o Siphons are attachment organs found in endoparasitic worms suckling (e.g. suckers & hooks)
o Tongues:
Radula Rasping tongue in snails to grind & cut chunks of food
proboscis tubelike tongue to obtain nectar
o Beaks & Jaws
E.g. bird beaks are composed of bones covered by overlapping epidermal scales, morphology
is diverse & reflect various feeding strategies, also used for vocalization, defense, & grooming
E.g. snakes have very mobile upper jaw & very strong neck muscles to crush the egg, egg shell
are vomited out
o Teeth (Mammal only, 4 types)
Incisors, canines, premolars & molars (shape of teeth reflects the type of diet)
First 2 for piercing & tearing, middle for tearing & grinding, last for grinding
- Digestive system & Evolution
o Increasing anatomical & functional specialization
o 1st 2 way gut: Food enters & leaves the gut through a single opening (e.g. flatworm)
Simple internal sac, may have diverticula “more branching” to increase SA
o 2nd 1 way gut “GI”: Specialized regions, passing through compartments regulated by sphincters
Mouth, pharynx & esophagus: Mechanical breakdown of food
Stomach: Acidic compartment
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