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STH2203 LU2:DIGESTIVE PHYSIOLOGY (2.3 FOOD ABSORPTION (Large Intestine…
STH2203 LU2:DIGESTIVE PHYSIOLOGY
2.1 FOOD INTAKE
Way of Animals to Obtain Food
Hunt, Identify, Chase and Capture
Lions
Tigers
Cats
Sit and Wait Strategy
Reptiles (Crocodiles)
Amphibians (Frog)
Fish
Graze/Browse on Plants
Herbivores
Strain for Food from Water
Whales
require handling and skills
monkey, lion, tiger
Measuring Food Intake
Voluntary Food Intake (ad libitum intake)
VFI = Weight of the amount of the original food - the weight of the amount of leftover
Control mechanism
Short term control
:pencil2: pressure receptor
Long term control
:fountain_pen: Fat deposition - hormone leptin (polypeptide)
Metabolites detection
:pen: hungry and satiety :pen: integrate signal :pen: initiate feeding
2.2 FOOD DIGESTION
Intracellular Digestion
Secreted enyzme into lumen
Via passive diffusion, Active transport, Phagocytosis
Complete digestive tracts
Annelids, Arthropods, Vertebrates
Extracellular Digestion
Lysosomes break down by enzyme hydrolytic
Protozoans (unicellular eukaryotic), Some porifera, Cnidaria (multicellular)
Simple but incomplete
Digestive Tracts of Animals
Invertebrates
Annelids (Earthworm)
Anthropods (Ants)
Fish
Shark (elasmobranch)
Ray-finned fish (teleost)
Amphibians (Frog)
Aves
proventriculus and gizzard
Herbivores
Ruminants (Cows)
Digestive tract of a cow
Digestive System
Saliva neutralizes consumed food.
Also known as fore-gut fermenter
Rumen
Soluble and insoluble materials fermented by bacteria before enzymatic digestion further down.(into obamasum).
Chyme - fluid form, 10^9 bacteria and 10^6 protozoa per mL.
do not need additional nutritional supplements - bacteria release the needed supplements by the host.
Obamasum: true stomach, digestive enzymes present
Advantages
extract energy (abundant)
able to use non-protein nitrogen (not really beneficial when compared with other the former) - good protein sometime got wasted
bacteria synthesized essential nutrition for absorption
Mono-gastric Herbivores (Horses)
Digestive tract of a horse
Also known as hind-gut fermenters
Spend a lot of time eating
Food moved faster in small intestine - moved slower in large intestine
Soluble materials digested in small intestines - insoluble materials digested in large intestines
Mammals (Human)
Elaborated functions
Mouth
Special Characteristics
cardiac orfice: opening for bolus from mouth to oesophagus
enzyme amylase: digest carbohydates
Process involving:
Peristalsis
Wave of contraction and relaxation - going down (alternatively)
Move food unidirectional (from mouth to stomach)
Animals not doing peritalsis
Flatworm
One way in and one way out
Segmentation
All about contractions
Rhythmic
'Re-shuffle' bolus content
enable mixing of chyme with digestive juice
Circular Muscle
Move materials back and forth - helps in mixing
Stomach
Secretion
Protein molecule --> Stimulate G-cells
G-cells --> stimulate parietal cells
Parietal cells --> secrete HCl (pH 2)
Chief cells --> secretes pepsinogen --> pepsin (help from HCl or any active pepsin)
Digestion
Pepsin + HCl --> digest protein --> polypeptides
HCl
Acidic environment n stomach
Kill bacteria
Absorption
Limited by mucous layer (thick)
Special Characteristics
Pyloric sphincter
'door' from stomach to small intestine
preventing backflow of food from small intestine to stomach
Intestines
Motility
Chyme being 'pushed' into small intestines from stomach - via peristaltic contractions
segmentation mix the chyme
Secretion
receives bile (from gall bladder and liver)
bicarbonate and enzymes (from pancreas)
Digestion
Amylase: starch --> maltose
Maltase: Maltose --> glucose
trypsin and chymotrypsin: long polypeptides --> short fragments
Dipeptidase: dipeptides --> amino acids
Bile salts: emulsify lipids
Lipase: triglycerides --> FFA, glycerol and monoglycerides
Structure
glands: secrete digestive juices
Contraction of muscle: mixing food with digestive enzyme
in-floding and villus: increasing area of absorption
Enzymes Characteristics
Hydrolases
breaking chemical bonds via water addition
Group specific
a certain enzyme only digest a certain molecule, specifically
pH sensitive
enzymes work accordingly to pH
sensitive to pH
Temperature dependant
increasing temperature = increasing enzymatic reaction
will work at optimum rate within reaching denaturing temperature of the enzyme
different enzyme has different denature temperature
2.3 FOOD ABSORPTION
Absorption of Amino Acid and Glucose
Go through lumen of intestines
Move across epithelial cells (mucosa) via active transport - using carrier and linked to Na transport
Into body fluid - such as blood
Digestion and Absorption of Lipid
Absorption through epithelial cells
Emulsification of Lipid
Lipase (from intestine) digesting lipid
Chylomicrons formed and occurence of cellular modifications
Chylomicrons intrude into lymphatic vessels via lacteal
Minerals Absorption
Apical membrane by facilitated diffusion
Adsorption of Calcium via endocytosis
Large Intestine (Colon)
Generate gases (fart) or extra gases
insoluble dietary (fiber) undigested materials
Eliminate feces (undigested materials)
