ANSC 301

alimentary canal

a tube beginning with the mouth and ending at the anus in which digestion and absorption of nutrients occurs

what is the lumen

inside of the alimentary canal and is exterior to the body

GI tract

the region of the alimentary canal that runs from the stomach to the colon

parts of the alimentary canal structure

mucosa
submucosa
muscularis
serosa

mucosa

inter part of the canal

submucosa

structural and immune cells

muscularis

muscle for motility

serosa

interface with body

prehension

mechanisms vary with behavior and diet

mastication

physical reduction of feed
important in nonruminant herbivores

salivation

3 main glands that secrete fluid with different composition
size differs between species

parotid gland

serous
water

sublingual gland

mucous
mucin (snot)

submaxillary aka submandibular

mixed
mucus

functions of saliva

moisten (ions

deglutition

reflex initiated by presence of food in pharynx
propulsion of food to stomach by esophageal peristalsis

major functions of gastric digestion

mixing and mechanical breakdown
hydrolytic digestion of acid enzymes
reservoir for controlled release of digesta to sm in.

stomach

nonglandular v secretory

functions of the stomach

storage
mixing
partial digestion

does the stomach have absorptive capacity

alcohol and certain drugs

4 sections of the stomach

C

cardiac region

secretory or glandular portion
mucus for lubrication
top portion

esophageal

non glandular portion

fundus

secretory
gastric pits

what two cells are in the fundic region of the stomach

chief cells and parietal cells

chief cells

proteolytic enzymes
pepsinogen

parietal cells

secrete HCl
decreased by pepcid

how is pepsinogen activated

by low pH from HCl

what happens if there is not enough HCl production in the stomach

the activation of pepsinogen will be limited and digestion will be impaired

pyloric

mucus
endocrine g cells

what do endocrine g cells do

secrete gastrin
gastrin stimulates HCl from parietal cells in the fundus

cephalic phase

vagal reflex
increased gastric motility

gastric phase

depends on food in stomach
reinforced by gastrin
increases HCl and pepsinogen

intestinal phase

from duodenal distension

what does gastric motility do

aids in mixing

how is emptying of the stomach stimulated

distension of antral wall and presence of liquid chyme

bile

made in the liver from cholesterol but stored in the gall bladder

pancreas exocrine functions

digest fat

sm intestine

long in all species
majority of digestion
absorption
secretions

types of cells in the sm intestine

absorptive
mucus secreting
endocrine
stem cells

how fast is the turn over of cells in sm intestine

3-6 days

duodenum

secretions from enterocytes (lactase

jejunum

most of absorption

ileum

less absorption but can if need be

GALT

intestinal immune system

peyers patches

immunological tissue which samples contents of GI tract and protects host

heat stressed ileum

enterocytes break down from heat stress allowing for disease to enter
pigs do not heal from this

large intestine

size and shape varies

appendix in humans

a blind pouch of the cecum

functions of lg intestine

high capacity for water absorption
little enzyme or hormone secretion

cecum

bacterial fermentation and absorption of VFAs but not proteins and vitamins

nutritional ecology

adaptation of animals to their environments by development of dietary habits and physiological mechanisms that allow them to exploit available food sources in their habitats

obligate eaters

must consume a certain thing
cats are considered obligate carnivores

facultative eater

preference of food but dont have to eat just that

frugivore

preferring fruit
fruit bat

folivore

koala
preferring leaves

insectivore

only eat insects

selectors

sheep bcz of their lips

non selectors

cows bcz they use their tongues

grazers

cattle or buffalo

prehensile adaptations

forelimb

masticatory adaptations

large canines and incisors
specialized molars
relative toothlessness of edentates

deglutition varies little with diet

but quantity and composition of saliva varies considerably

gastric capacity and structure

capacity greatest in pregastric fermenters

stomach capacity in carnivores

digest meal quickly and needs to be small so they can move quickly to hunt prey

distribution and composition of epithelial lining

varies between species and dietary adaptations

glandular stomach

mucus
parietal cells
chief cells
endocrine

nonglandular stomach

fermentation

sm intestine length

generally shorter in carnivores than in herbivores

significance of fermentative digestion

directly related to fiber intake
location differs but function doesnt

swine digestion

most similar to humans
very long sm in.
moderate colonic fermentation

why do we feed higher fiber diets to sows

so they slow down the intake and rate of passage to give fermentation in the hind gut a chance

avian anatomy

crop- mechanical breakdown
proventriculus- true stomach
gizzard-grinded food
SI
ceca-fiber
cloaca-uric acid

dog

omnivore like pig
short SI
limited fermentation

cat

obligate carnivore
short SI
limited fermentation

sheep

ruminant
large pre gastric fermentation
moderate hindgut fermentation

what animals have the largest stomach and GI tract as % BW

Ruminants

humans vs sheep

similar body weight
-sheep have 20x more stomach and 5x more GI

forage feeders

give up size and speed for ability to use low quality and abundantly available feed

key differences rumen microbes provide

microbial protein synthesis
beta 1

what is the difference between starch and cellulose

starch is a long chain of glucose linked by 1

4 chambers of the stomach

reticulum
rumen
omasum
abomasum

how much fermentative capacity is in a ruminant vs human vs dogs

83%
17%
14%

what is the main reason for rumination

allows for more leisurely physical breakdown of feeds after initial ingestion

reticulum

honeycomb
mixing and regurgitation
no enzymes secreted

rumen

main compartment
main site of vfas and absorption
papillae

vfas

2c acetate
3c propionate
4c butyrate

reticulo-rumen

mix feed and aid rumination and passage

omasum

gate to lower tract
no coarse fiber to enter
WATER absorption

abomasum

glandular
HCl

left displaced abdomen

abomasum comes down under rumen

right displaced abdomen

abomasum comes up on the right and twists
more deadly because torsion cuts the blood flow and tissue dies in 24hrs

rumen

main compartment (30-40 gallons in holstein cows)
main site of vfa and absorption
papillae

rumen microbes

archaea
protozoa
fungi
5000+ different species

host provides

warm

what is the rumen ph range

5.5-8.5 bcz of acid
more starch- lower ph
more saliva- higher ph

microbes provide

digestion of cellulose and hemi
synthesis of high quality protein
synthesize vitamins

what vitamins are synthesized

b vitamins
c
k

bad side of host

microbes get free sugars and most starch
ruminants absorb very little glucose
most energy absorbed in vfas

hypoglycemic

ruminants always have too little glucose
cows about 60