Digestive Tract Anatomy & Function

digestive system

to obtain and use nutrients

Ingestion, digestion, absorption, elimination

Ingestion

w/ teeth, tongue, lips

Digestion

process of breaking down food/feed by mechanical and chemical (enzymes) into smaller molecules to be absorbed and nutrients used for body function

Absorption

process of moving products of digestion (ie. glucose, amino acids, fatty acids) form digestive tract into bloodstream. most in SMALL INTESTINE; also rumen

Elimination

removal of undigested

Teeth

none in poultry

upper in monogastric but not in ruminants

mastication = chewing

Prehension in mouths

varies, seize and grasp to bring food into mouth

variations in lip & number/type/size of teeth 

ie. canine teeth - tearing; molars - grinding

Salivary glands

lubricate for deglutition (aka swallowing)

sodium bicarbonate (very basic pH)

may have enzymes secreted (ie. lipase - breakdown lipids)

monogastric and ruminant esophagus

transport food from mouth to stomach

peristalsis - wavelike contraction of smooth muscles

Monogastric stomach

“gastric” - of the stomach - ie. gastric juices

temporary food storage

begin/continue breakdown of nutrients absorption

hydrochloric acid (HCL) secretion - low pH; very acidic

enzyme secretion - pepsin: protein; lipase: lipids

leaves as chyme

chyme

mixture of feed, saliva, and gastric secretions

Monogastric and ruminant small intestine

3 segments: duodenum, jejunum, ileum

major site of nutrient digestion and absorption

pancreas empties into duodenum

Monogastric large intestine

3 segments: cecum, colon, rectum

key role is water absorption

aka. “hindgut”

“hindgut”

much larger in horse than other monogastric

key in horses; some digestion/absorption in other monogastric 

horse is hindgut fermenter

microbes present to digest fiber

Horse as “hindgut fermenter”

~38% volume foregut - mouth through small intestine

~62% volume hindgut - large intestine

Colic

abdominal pain originating from gastrointestinal tract

“gut ache”

Common causes of colic

gas buildup (abrupt diet change)

impaction of feed/other obstructions

abnormal contractions

inflammation of GI tract (ENTERITIS)

“twisted gut” - intestines twisted

Colic prevention

avoid dehydration

ample forage/limited grains

smaller meals at regular intervals

gradual vs abrupt ration changes

“Rumination” in ruminants

process of regurgitation of undigested feed and chewing it a second time and swallowing again

aka. “chewing their cud”

further breakdown of feedstuffs

regurgitation, remastication, resalivation, redeglutition

Ruminant digestive tract

reticulum, rumen, omasum, abomasum

Reticulum

aka. honeycomb; “hardware stomach”

assist in regurgitation

fermentation of feed

trap indigestible foreign materials

no glands

less absorptive then rumen

Rumen

aka. paunch

w/ reticulum 85%+ of volume in mature ruminant

left side of anima

“fermentation vat”

microbial fermentation

bacteria, protozoa, fungi

normal pH 5.8 to 6.8

Omasum

aka. many piles; like pages of book

Abomasum

“true stomach”

fermentation

an enzymatically controlled anaerobic breakdown of an energy-rich compound

papillae

increase surface area for absorption

volatile fatty acids (VFAs)

key product of carbohydrate fermentation absorbed here

are waste product for rumen microbes

key source of energy

includes: acetate (C2), propionate (C3), butyrate (C4)

acidosis

challenge in feedlot cattle/lambs/goats

pH becomes too low (>5.5)

abrupt diet changes; too much grain (highly fermentable) in short period of time

beneficial rumen microbes killed

Ruminant digestive issues

acidosis and bloat

bloat

trapped excess gas in rumen - distended left side of animal

inability to eructate

types: frothy (bubbles) - lush pastures; dry (free gas) - feedlot

adequate hay in diet to lessen incidence

Abomasum

functions exactly like monogastric stomach

glands - secrete HCl, enzymes

animal begin to digest microbes here too

horse gets limited use of microbes as protein sources

cow digestive tract image

chicken digestive tract image