ansc314 - comparative nutrition & digestion

comparative digestion

digestive tract is adaption to animal’s food environment

digestion

process by which foodstuffs are broken down into GI tract → absorbable units

• during digestion, food nutrients (external) since GIT is hollow outside body

absorption

process of transport/transfer of digestion products through gut mucosal wall

nutrient transport

mvmt of carriage of nutrients into gut cell/blood

digestion types

1. mechanical

2. chemical

3. enzymatic

mechanical digestion

physical digestion

• Mastication (chewing) 

• Peristalsis (muscular contraction) of GI tract

• Grinding action of gizzard (birds) 

• Mvmts of rumen & reticulum (ruminants)

chemical digestion

Gastric HCl (hydrochloric acid, pH 2) 

enzymes

• Animal’s digestive enzymes secreted into digestive tract 

• Microbial digestive enzymes (rumen, cecum, colon/large intestines)

carnivore

(dog, cat, mink, some fish, etc)

• Simple digestive structures 

  • No/small cecum

• Feed usually low in fiber (cellulose, hemicellulose) 

• Meat diet

• fish have large variety of GI tracts

panda exception

• carnivore gut w/ tough esophagus & stomach

  • slightly enlarged colon

• adapted vegetarian diet for unknown reasons

  • only digests 10-20% of nutrients in bamboo so it eats A LOT

    • 30-60 lbs food/day

omnivore

 (human, pig, squirrel, raccoon, rat, black bear, ect)

• Eat mostly plants (grains), some meat 

• Larger cecum/colon

  • Pigs have enlarged cecum

• Some microbial fermentation 

  • Microbes make protein as by-product (w/ volatile fatty acids)

herbivore

(horse, rabbit, ruminants, small herbivores)

• Enlarged digestive structures (cecum) for microbial digestion (fermentation) of plant fibers 

• Pre-gastric fermenters (ruminants)

• hind-gut fermenters

pre-gastric fermenters

organisms that break down nutrients before the GI tract (intestines)

• Ruminants (cattle, sheep, goats, deer, antelope, giraffes) 

• Camelids (camel, llama, alpaca: 3 chambers ruminant) 

• Hippopotamus (not ruminant) 

• Kangaroo

• Hamster (2 chamber) 

• Hoatzin (stink bird) 

• Hoatzin has large crop, folded in 2 chambers w/ large, multichambered lower esophagus

ruminants

• Chewing cud to increase digestive efficiency 

• 4 stomach chambers → rumen, reticulum, omasum, abomasum 

  • Pseudo ruminants (camel, llama) have 3 chambers & chew cud

• Microbes in rumen digest & ferment feed before presentation to stomach

ruminant stomach

• Allows fiber fermentation & detoxification of toxins 

• Undeveloped GI tract gets nutrients form milk

rumen walls

Stomach increases absorption by increasing surface area

llama GI tract

hind-gut fermenters

Horses, zebras, elephants, rabbits, guinea pig, some birds

• Enlarged cecum (hind-gut) & large intestine 

rumen digestion

• volatile → gaseous

  • acetate, butyrate, propionate

large intestine

• carbs & protein degrade → VFA, microbial protein & NH₄

  • VFA → carbs & fats in body

  • NH₄ & recycled or excreted

• microbial protein & microbial vitamins excreted in feces

• post-gastric have disadvantage b/c microbial fermentation is happening AFTER small intestine

  • where most nutrient absorption is happening

hindgut vs ruminants

avian

poultry, song birds, ostrich, emu

• crop → storage, no digestion

• proventriculus → gastric or glandular stomach

• gizzard - functions as “teeth” for birds

• ceca (2 cecum) → fermentation of fiber & other less digestible material

enzyme production

1. mouth → site of nutrient/enzymatic digestion

• amylase

• no proteins or fats digested in mouth

stomach

• stomach divided into cardia, fundus, pylorus

• gastric juice mixture of water, mucus, HCl, pepsinogen, inorganic salts

• parietal (oxyntic) cells produce HCl

  • need acid to digest protein → amino acids

  • stomach where protein digestion STARTS

gastric pit

indentations in the stomach which denote entrances to the tubular shaped gastric glands

• deeper in pylorus

• human stomach has millions on surface of epithelium lining

  • surface mucous cells line puts themselves but give way to a series of other types that line glands themselves

• eat something → carbohydrate digestion in mouth → stomach → acid (HCl) denatures proteins → activates pepsinogen by cleaving it → pepsin → breaks down protein

• bile produced by liver, but stored by gall bladder

  • bile breaks down lipids

• high acidic food (2 pH) moves into duodenum → pH changes w/ help of bicarbonate (more basic) from pancreas → pH 6-8 → start digestive processes

• everything has to get dumped into mix w/ food to break down & absorb nutrients

  • sodium & potassium salts of bile acids (glycocholic & taurocholic) acids in digestion by activating pancreatic lipase & emulsifying fats

  • pancreatic ducts delivers pancreatic juice (insulin, digestive enzymes, water & electrolytes) into diodenum

small intestine

• kerkrig valves - circular folds of mucous membrane

• sphincter of Oddi - muscular valve that controls flow of digestive juices (bile & pancreatic juice) → duodenum

small intestine villi

• Paneth cells line crypts of lieberkuh - secrete intestinal juice as gradually migrate along side of crypt and the villus

• villi important to increase surface area

  • healthy gut important for survival

• gut accounts for ~6% of body weight → accounts for 20-25% O₂ consumption

  • very metabolically active

small intestine villi

• nutrient absorption includes entry & exit out of enterocyte

nutrient transport mechanisms

• energy from ATP from nutrients

  • ATP is used for active transport of nutrients in/out of cells

• simple diffusion, facilitated diffusion, active transport

simple diffusion

passage of molecule or ion in membrane w/o help of another intermediate like protein

• osmosis

facilitated diffusion

process in which type of transport is passive that is enabled by proteins

• movements of glucose, Na & K ions

active transport

uses ATP to provide energy to proteins providing transport

• unlike simple diffusion, molecules can be moved against gradient

  • Na-K pump

small intestine

large intestine

• absorption of fluids & electrolytes in large intestine

• not have villi but have small projections to increase surface area

• glands in large intestine mainly mucous glands

• extensive microbial activity occurs in large intestine

  • favor digestion of cellulose & higher polysaccharides → produce VFAs

• certain species w/ extensive microbial activity, large intestine plays larger role in digestion

overview

• liver’s major role → detoxification & produces bile & UREA from protein synthesis glucose

  • ~95% glucose produced in liver

• hepatic vein or hepatic portal vein transfers nutrients from gut to liver