Complex Digestion

Introduction Functions of the digestive system

Receive ingested food Store ingesta temporarily Reduce it physically Reduce it chemically Absorb the products of digestion Hold and then eliminate undigested wastes

Digestive system: Digestive tract- mouth to anus Accessory tissues:

salivary glands pancreas liver

Stomach (ventriculus, gaster) Dilated section in which digestion is started Variation in size and complexity among species Functions:

Retention Digestion due to HCl and enzymes

Small intestine Principle organ of digestion and absorption in most species Relatively simple anatomyLarge intestine Cecum, colon, rectum Variation in size and complexity among species Function:

Absorption of water and electrolytes Storage of feces Fermentation of unabsorbed, and undigested ingesta that escapes

the sm. intestine

Digestive tract Extremely diverse Adapted to varied diets

Carnivorous Omnivorous Herbivorous

Carnivorous diet Easily digested concentrated food Simple stomach Short & simple intestinal tractOmnivorous diet Mixture of food types

Simple stomach and small intestine Expanded large intestineHerbivorous diet Low nutritive value- therefore increased volume neededHerbivorous diet (con’t) Less digestible

Cellulose Complex carbohydrates

Appetizing?2 possible anatomical solutions: Foregut adaptation Hindgut adaptationForegut adaptation

Large, divided stomach Intermittent feeders Ruminants

cattle camel

Non-ruminants kangaroo

Hindgut adaptation Expanded, compartmentalized large intestine Grazers Horse, pig, rabbitHorse Foregut adapters-

ruminant digestion 2 suborders:

Ruminantia- deer, giraffe, ox stomach- 4 compartments

reticulum, rumen, omasum, abomasum Tylopodia- camel, llama, alpaca

stomach- 3 compartments reticulum, rumen, abomasum

cardiac glands in wall of rumen and reticulum omasum- vestigial or absent

Ruminant foregut adapters Forestomach (proventriculus): cellulose and carbohydrate breakdown

Volume (cattle): Rumen- 80% (75% in goat) Reticulum- 5% (8% in goat) Omasum- 8% (4% in goat)

“True” stomach (ventriculus):

Volume (cattle): Abomasum- 7% (13% in goat)

Ruminoreticular compartment Rumen and reticulum are often considered together as a unit Entrance of esophagus (at cardia) is located dorsal to the

ruminoreticular fold Lining mucosa varied

Dependant on age, location, diet, etc. Microbial fermentation occurs here Absorption- volatile fatty acidsReticular groove Reflex to divert ingesta beyond the ruminoreticular compartment Unweaned animal- strongest Adult- still functions, stimulated by ADH Initiated when receptors in the mouth and pharynx are stimulated Dorsal vagus nerve

Reticular grooveRuminoreticular stratificationOmasum Round in cattle, bean shaped in small ruminants Ingesta is squeezed between many mucosal folds Absorption of fluidsAbomasum Similar to simple stomach Glandular mucosa, simple columnar epithelium Neonatal calf- 50% of the total volume of the ruminant stomach Motility of the ruminant stomach Reticulum motility

biphasic or triphasic 1-2 contractions/min.

Rumen motility uniphasic or biphasic 1-2 contractions/min.

Omasum motility Slow

Abomasum motility Sluggish contractions

Motility Change in motility is dependant on type of ingestaRuminant digestion Ruminoreticulum

Large divided chamber allows: Soaking Mixing

Fermentation by bacteria and protozoaRumination

time spent ruminating is dependant on coarseness of diet Regurgitation

↓ intraesophageal pressure due to forced inspiration with a closed glottis Reverse peristalsis in esophagus

Remastication Reinsalivation

A cow will produce 100-200 L/day of saliva RedeglutitionEructation 0.5-1 liter of gas/min. produced in the ruminoreticulum of a dairy cow Primary stimulus for eructation is gas in the dorsal sac of the rumen Occurs once in 2 cycles of ruminoreticular contractionsInnervation Predominantly parasympathetic

Dorsal and ventral vagal trunks Dorsal vagotomy- complete paralysis of rumen

Vascularization Branches of the celiac artery

Pig stomachHindgut adapters- Simple stomach Fermentation occurs in an enlarged, compartmentalized cecum and

ascending colon

Motility Vascularization What branches of the aorta?Colic = abdominal pain