ANSC 212: The Digestive System

Vocabulary flashcards defining core terms, organ structures, and physiological processes of monogastric, avian, and ruminant digestive systems from ANSC 212.

Feed

A material that, after ingestion by animals, is capable of being digested, absorbed, and utilized to meet their nutrient requirements.

Digestion

The process by which large complex molecules are broken down into simpler molecules capable of being used by the animal for metabolism.

What are the major complex molecules

protein

fats

carbohydrates

• fiber

• starch (rapidly digested)

Energy sources for livestock

corn

carbohydrates = cheapest option

fats = best for energy supply, but expensive and animals won’t eat a %100 fat diet

Protein sources for livestock

peas, canola, soybean, alfalfa

Functions of digestive system

ingestion of food

breakdown of food into nutrients

absorption of nutrients

elimination of waste products

What is contained in the Digestive system ?

mouth

pharynx

esophagus

stomach

small intestine

large intesine

rectum

accessory glands (salivary glands , liver , gallbladder , pancreas )

What animal does not have a gallbladder ?

horse

→ this means that they cannot store the bile produced by liver

Prehension

The manner in which animals harvest and convey feed to their mouth using structural adaptations such as lips ( horses ), teeth, tongue ( cattle ), or beak ( poultry ) .

Mastication

The mechanical reduction of feed particle size that increases surface area for enzymatic and microbial digestion

mixes feed with saliva for swallowing

Ruminants - eat feed quickly, then re-masticate at a later time

Chickens - rely on their gizzards to mechanically grind their feed

Herbivore

An animal classification for species that depend entirely on plants for nutrients

ex. sheep, cattle, horses, and deer.

Carnivore

An animal classification for species that depend almost entirely on meat for nutrients

ex. cats and wolves.

Omnivore

An animal classification for species that consume both meat and plants

ex. swine, chickens, humans, and dogs.

What are the three types of digestion ?

1. Mechanical - mastication and muscular contractions of alimentary canal

2. Chemical - enzymes secreted by animal in digestive juices and saliva

3. Microbial - activities of bacteria , protozoa , and fungi

Monogastric

An animal digestive system featuring a single true stomach compartment, limited gut capacity, primary reliance on enzymatic digestion, and limited fiber digestion ability

ex. dog , cat , pig , human , chicken , horse

Ruminant

An animal digestive system featuring four stomach compartments: the rumen, reticulum, omasum, and abomasum.

ex. cattle , sheep , goat , deer , elk , moose , giraffe

Pseudo-ruminant

An animal digestive classification for species that possess a three-chambered stomach system.

ex. camels , llama , alpaca

What animal does not enzymes in their saliva ?

cattle

• microbial breakdown food more than chemical digestion

Digestion in the mouth

teeth and lips grasp and chew feed to begin breaking it down to increase surface area

• mix it with saliva before swallowing (lubrication)

Digestion of carbohydrates begin taking place via salivary amylase for pigs and dogs

^ cattle don’t have salivary amylase enzymes

Traits of mono gastric digestion

single stomach (single compartment)

limited gut capacity → can’t digest all fibre

Digestion is aided by enzymes

Limited microbial activity → BUT present in large intestine

Why do mono gastric animals have a limited ability to digest fibre?

don’t have enough enzymes or bacteria to break it down

Functions of stomach

Feed travels down esophagus to stomach which serves as reservoir for short term storage and digestion

Enzymes start to break down food

• organic compounds (proteins )

• speeds up the chemical reaction without being used up in process

• stomach enzyme = PEPSIN

Low pH (around 2 or 3) in the stomach breaks down some feed particles

Hormone secreting area → GHRELIN = hunger hormone

Pepsin

A proteolytic stomach enzyme activated from pepsinogen by hydrochloric acid ($HCl$) that initiates the chemical breakdown of proteins.

Ghrelin

A hormone secreted in a specific area of the stomach that acts as the hunger hormone, with secretion levels increasing when the animal is hungry.

Small intestine

main site of Digestion and Absorption

• presence of bile

• digestive enzymes secreted largely from pancreas to help with breakdown

about 20 times the length of the animal

three sections of small intestine

Duodenum

Jejunum

Ileum

Duodenum

The first section of the small intestine that receives digestive juices and secretions from the pancreas, gallbladder (just stores the juices) , and liver.

Jejunum

The middle and longest section of the small intestine responsible for enzymatic digestion and nutrient absorption

Ileum

The final section of the small intestine closest to the large intestine, functioning primarily in nutrient absorption.

Mesentery

A supportive connective tissue fold in the abdominal cavity that holds the loops of the small intestine together.

Villi

Finger-like tissue projections in the small intestine that increase surface area of intestine

• secrete digestive enzymes,

• contain specialized cells that transport absorbed nutrients into the bloodstream

What enzymes are produced by the Villi ?

Sucrase - converts sucrose to glucose and fructose

Maltase - converts maltose to two molecules of glucose

Lactase - hydrolyses lactose to one molecule of glucose and one of galactose

Aminopeptidases - act on the peptide bond adjacent to the free amino group of simple peptides

Dipeptidases - complete the breakdown of dipeptides to amino acids

Parts of large intestine

Cecum

Colon

Rectum

• microbial fermentation occurs in the large intestine

Cecum

A large pouch located at the junction of the small and large intestines

• serves as a site for hindgut microbial fermentation in animals like horses, pigs, and chickens.

Colon

A segment of the large intestine primarily responsible for water reabsorption, microbial activity, and digesta passage.

Rectum

The final segment of the large intestine responsible for waste storage and the excretion of waste products.

Unique features of Avian digestive tract

Beak / mouth

Crop

Proventriculus

Gizzard

Cloaca

Vent

Cloaca

A common chamber in the avian digestive system shared by both the gastrointestinal and urinary tracts.

• both feces and urine are expelled from this single opening

Vent

The common external opening and exit for both the gastrointestinal and urinary tracts in poultry

• very similar to rectum

Crop

An expanded pouch of the esophagus in birds used for feed storage, moistening, and softening prior to chemical digestion.

Proventriculus

The glandular stomach of birds that secretes hydrochloric acid ($HCl$) and pepsin to chemically break down feed

Gizzard (Ventriculus)

The muscular stomach of birds responsible for the mechanical breakdown and grinding of feed.

Accessory glands for digestion

salivary glands , liver , pancreas

Liver

An accessory digestive gland divided into right and left lobes

functions in detoxification, vitamin and carbohydrate storage, and bile formation (bile salts play big role in digestion of fats via saponification )

Pancreas

An organ positioned in the duodenal loop functioning as both an endocrine and exocrine gland

Functions: produces insulin, glucagon, and enzymes like amylase (starch) , lipase (fat) , proteases (protein), and nucleases (DNA / RNA )

What animals are ruminants?

sheep, cows and goats

Saliva

Fluid secreted by salivary glands producing up to $180\text{--}250\text{ L/d}$ in dairy cattle,

Functions:

• lubrication

• enzymatic activity → baby calves have enzymes when young to drink and breakdown milk

• sources of nutrients for ruminal microorganisms

• influences nutrient removal rate

• Buffer capacity → VERY IMPORTANT to off set basic pH of rumen

• antifoaming agent

• source of antibodies

Ruminant stomach compartments

Rumen ( located on left side of animal body ) full of bacteria, fungi / microbiome

Reticulum

Omasum

Abomasum ( most like monogastric stomach )

then goes into the small intestine

Rumination

The process in resting ruminants of regurgitating ingesta from the reticulum back to the mouth for re-mastication and re-swallowing.

Eructation

The oral release of fermentation gases, primarily carbon dioxide ($CO_2$) and methane ($CH_4$), produced in the rumen.

• release of gas mainly happen in mouth via burps

*can’t remove this from animal, but can manipulate and change diet to try to limit it

Rumen

The largest compartment of the ruminant stomach

functioning as an anaerobic fermentation vat lined with papillae to absorb short-chain fatty acids and increase absorptive surfaces

• there are three levels of feed in the rumen with layer of gas on top

How does the rumen work symbiotically with mircobial

microbes digest or ferment feed to make short chain fatty acids (SCFA) like acetate , propionate , butyrate

• rumen walls absorbs SCFA as energy source for animal

• 
  

When bacteria die , they are digested as protein source for animal

Short-Chain Fatty Acids (SCFAs)

Fermentation end-products—principally acetate, propionate, and butyrate—produced by ruminal microbes that provide ruminant's energy

Functions of rumen

major feed/ digesta storage site → allows for large meals and regurgitation

digestion through anaerobic fermentation * no O2 because of microbiome

contains billions of microorganisms

• bacteria, protozoa , fungi, archaea

• give ability to digest fibre for energy producing 75% of energy supply

• make vitamin K and B

Type of micro-organisms chains with the type of feed consumed (grain vs forage)

Produce gases such as CO2 and CH4

Normal rumen pH

5.5 to 6.9

High grain diet = more acidic

high forage diet = more basic

How long does it take to change / adapt ruminal microbial populations?

14-21 days , around 3 weeks

Ruminal Acidosis

A pathological metabolic condition in ruminants caused by excessive production of short-chain fatty acids that lowers ruminal pH below normal levels ($5.5\text{--}6.9$).

Reticulum

A pouch-like ruminant stomach compartment located near the heart with a distinct honeycomb inner lining that connects to the rumen and assists in regurgitation.

it is hard to determine the start and end of rumen to reticulum because they look very similar and are very interconnected

Esophageal Groove

Muscular folds in young ruminants that close to bypass the rumen, reticulum, and omasum, directing ingested milk directly into the abomasum.

Omasum

A globe-shaped ruminant stomach compartment containing laminae (leaf-like folds) that squeezes and absorbs excess fluids and short-chain fatty acids from digesta.

Abomasum

The fourth stomach compartment of ruminants, known as the true stomach, where glandular (only compartment with glands) secretions of acid and enzymes

• conduct digestion similar to a monogastric stomach