E138 Digestion II

ruminants

group of animals that have achieved the highest degree of specialization in fermenting plant material

benefits of rumen

can use carbs in the plant cell wall as nutrients

ruminant stomachs

sufficient size and motility for microbes to brak down cellulose into fermentation products

compartments of the rumen

4 compartments

• forestomach: rumen (largest), reticulum, and omasum (smallest)

• reticulum

requirements of fementation

requires certin temp, pH, motility, and secretion for microbes

abomasum

similar function to the stomachs in nonruminants

• figests proteins and lysis of rumen microbes

• has large spiral folds

rumination

regurgitation, remastication, and reswallowing of ingesta

regurgitation

extra contraction of the reticulum is associated with a transient negative pressure created by closure of the glottis prior to an inspiratory cycle

rumination cycles

prolonged chewing phase following by a short redglutition phase

rumen environment for microbes

buffered by saliva, short-chain organics aids, and buffering capacity of the diet

ammonia decreases pH

epimural bacteria convert urea into ammonia

most important products for microbial fermentation

acetate, propionate, and butyrate

• propionate is the only VFA that can be used to synthsize glucose

vitamin byproduct of fermentation

synthesis of all B vitamins

• because of this, ruminants do not require a dietary source of VB

dynamics of digestive system

rat in a python stomach: over 6 days, the rat fully digests inside the pythons stomach

python small intestine expanded in size after eating, then shrinks back down

small intestine changes at the cellular level

python microvilli elongate to increase SA and absorption

enzyme activities and nutrient uptake increase rapidly after eating

• high levels of APN, maltase, L-proline, and D-glucose; upregulation

how is understanding of small intestine beneficial

useful for human starvation, surgeries, and digestion

large meal digestion

whole-body process

• multiple organs increase in mass

• VO2 may incrase up to 44-fold

amylase

digests starch

how digestive enzyme activity changes via evolution

variation in starch consumption across populations shapes the evolution of amylase gene copy number

• high starch: agricultural and tubers

• low starch: hunter-gatherer and pastoralist

amylase copy number and high starch diet

direct relationship

• higher amylase copy number with high starch diet: hadza (tanzania), european-americans, and japanese

• lower amylase copy number in lower starch diet

fluorescent validoation of AMY1 copies in diploids

in a japanese subject, there is a lot of variation in the number of copies

• varies within ethnicities

ruminants

have a rumen to digest starches

properties of the rumen

large fermentation chamber (one of the four chambers int he stomach)

• anaerobic

• breakdown plants and cellulose

• bacteria, fungi, protists (bacteria produce H+ and CH4)

what do animals get from the rumen

herbivores need bacteria and extra structures

they get:

• nitrogen processing

• AAs

• vitamins

• SCFAs

where are fermentation chambers located

different places based on species

• hindgut ferm in the colon of ponies

• koala has a large caecum to digest eucalyptus

double processing

herbivores have cecal pellets

• feces that are reingested for maximal digestion and nutrient uptake

culture-independent methods for microbiome mapping

16S amplicon sequencing

metagenomics

metagenomics

sequecning microbes’ genes

what influences the microbiome

host physiology

lifestyle

immune system

environment: skin vs. gut microbiome

• ruminants have an obligate relationship with microbes

ruminant microbiome

complex environment and more genes

• GIT region is more responsible for the variation thn the species type

how do fish solve the challenge of herbivory

rare in fish; herbivory is largely concentrated in coral reef systems

• gizzard-type stomach trituration (mechanical grinding)

• pharyngeal jaws (second set of teeth)

• gut length and hindgut fermentation (longer transit times, fiber-degrading microbes)