Monogastric Digestion

Digestion Basics

• Digestion breaks down food into smaller nutrients.
• These nutrients are then used by the body.
• Digestion is similar across all species.
• There are four main digestive system types: monogastric, avian, ruminant, and pseudo-ruminant.

Monogastric Digestive System

• This system is found in humans and many mammals.
• Examples include humans, swine, dogs, and cats.
• Monogastric systems feature a simple stomach with a single compartment.

Monogastric Parts and Functions - Mouth

• Mastication, or chewing, occurs in the mouth.
• Salivary glands add saliva to the food.
• The tongue helps move food for the animal to taste and swallow.
• Prehension is how animals "grasp" their food.

Monogastric Parts and Functions - Other Organs

• The epiglottis closes the windpipe (trachea) during swallowing.
• The esophagus is a muscular tube delivering food from mouth to stomach, using peristalsis.
• The stomach stores and further breaks down food at a pH between 3 and 4 using hydrochloric acid (HCl).
• Pepsin, an enzyme, is produced for protein breakdown.
• The pyloric valve (a smooth muscle sphincter) guards or closes the stomach opening.

Monogastric Parts and Functions - Liver and Gall Bladder

• The liver controls nutrient storage/concentration like proteins, fats, carbs, vitamins, and minerals.
• It also produces proteins and clotting factors, as well as bile which is a digestive compound.
• The gall bladder stores and concentrates bile.
• Bile is then released into the small intestine.
• The gall bladder's structure and location vary between species.

Monogastric Parts and Functions - Pancreas

• The pancreas regulates the blood sugar level by producing insulin as part of the endocrine system.
• The pancreas also produces pancreatic juices as part of the exocrine system.
• These juices contain enzymes that break down carbs, fats, and proteins.

Monogastric Parts and Functions - Small Intestine

• Enzymatic digestion and absorption occurs in the small intestine.
• Digestion of proteins, carbs, and fats takes place here, along with nutrient absorption.
• The small intestine has three sections:
  • Most digestion occurs in the duodenum.
  • Some digestion and absorption occur in the jejunum.
  • Mostly absorption occurs in the ileum.
• Villi are finger-like projections that line the small intestine and contain blood vessels for nutrient transfer.

Monogastric Parts and Functions - Small Intestine Sections

• The duodenum is the first section of the small intestine.
• It connects the stomach to the small intestine.
• Bile and pancreatic juices are added here.
• The jejunum is the middle section and makes up about two-fifths of the small intestine.
• It absorbs digested carbohydrates, proteins, sugars, fatty acids, and amino acids.
• Nutrients enter the bloodstream and are then distributed throughout the body.
• Ileum translates to "twisted intestine" and is the final/longest section of the small intestine.
• It absorbs remaining nutrients, mainly vitamin B12 and bile acids.
• Bile slats are reabsorbed through active transport and returned by the blood to the liver.

Monogastric Parts and Functions - Enzymes

• Enzymes are proteins that break down nutrients within digestive systems.
• Enzymes biochemically break down specific nutrients.
• Different digestive systems have varying enzymes, with some using bacteria or microbes.

Monogastric Parts and Functions - Large Intestine

• Trypsin, chymotrypsin, and carboxypeptidases digest proteins with secretion from the pancreas.
• Pancreatic amylase digests carbohydrates.
• Lipases digest lipids.
• Disaccharidases digest carbohydrates and dipeptidases digest peptides; both are secreted from the small intestine.
• The ileocecal valve is a smooth muscle sphincter.
• It is where the ileum joins the large intestine.
• The large intestine, also called the colon, is shorter but larger in diameter than the small intestine.
• Bacterial activity continues breaking down indigestible food.
• Much water is absorbed, creating solid waste.

Avian Digestive System

• This digestive system is seen in chicken and other birds.

Avian Parts and Functions - Beak & Esophagus

• There are no teeth.
• Prehensile action refers to pecking food with their beak/bill.
• Saliva softens food and aids in swallowing.
• The tongue manipulates food, aiding in swallowing food whole.
• The esophagus connects the mouth to the stomach.
• It moves food using wave-like muscle contractions (peristalsis).
• Food is often deposited into the crop before going to the stomach.

Avian Parts and Functions - Crop & Stomach

• The crop, which is part of the esophagus, provides temporary food storage.
• It is located just outside the body cavity in the neck region.
• This evolutionary adaptation allows birds to eat large amounts of food at once.
• Swallowed feed and water are stored and then passed to the rest of the digestive tract.
• Very little digestion occurs in the crop.
• The avian stomach has two parts:
  • The proventriculus is the glandular section where food is partially digested.
  • Hydrochloric acid and digestive enzymes (like pepsin) are added.
  • The ventriculus/gizzard is part of the digestive tract of birds, reptiles, earthworms, and fish.
  • It has a muscular portion that grinds food, often with ingested stones or grit.

Avian Parts and Functions - Small and Large Intestine

• The small intestine is composed of the duodenum, jejunum, and ileum, with the duodenal loop surrounding the pancreas.
• Its length depends on diet, longer in carnivorous birds and shorter in herbivorous birds.
• The remainder of digestion occurs here, as well as nutrient absorption.
• Bile helps absorb fat-soluble vitamins (A, D, E, and K).
• Ceca are two pouches where the small and large intestines meet.
• Remaining water is absorbed here.
• Fermentation of remaining coarse materials occurs here.
• The large intestine, also called the colon, absorbs water, dries out indigestible items, and eliminates waste.
• It contains bacteria, to help birds metabolize remaining nutrients.
• It connects to the cloaca.

Avian Parts and Functions - Intestinal Microflora & Cloaca

• Both the small and large intestines contain beneficial organisms (microflora).
• Microflora translates to 'micro' meaning "small" and 'flora' meaning "plants”.
• Microflora aids in digestion
• Avian species are born with sterile digestive tracts, and microflora needs to be consumed.
• Sources for aquiring microflora can include mother's fecal material, and probiotics in feed.
• The cloaca/vent is where digestive wastes mix with urinary system wastes.
• Chickens void fecal material with uric acid crystals on the surface.
• Chickens do not urinate here, and eggs come out of this chute.

Ruminant Digestive System

• Ruminants are animals that get nutrients from plant-based food by fermenting it in a specialized stomach.
• This fermentation occurs before digestion, primarily through microbial actions.

Ruminant Parts and Functions - Mouth and Esophagus

• In the mouth, food is moistened to aid in chewing.
• The lips, tongue, teeth, and saliva start the digestion process.
• Ruminants have front teeth on the lower jaw only, which cut grass against the dental pad.
• Upper and lower molars are used for grinding food.
• The esophagus transports food back and forth from the mouth and stomach.
• Food can make multiple trips.
• Ruminants regurgitate, re-masticate, and re-swallow their food ("chewing their cud") for up to 8 hours daily.

Ruminant Parts and Functions - Stomach

• The stomach has four parts within one stomach.
• Each compartment has a specific function.
• The first and third compartments are considered forestomachs, aiding digestion through microbial fermentation.
• Microbes help break down fibrous material.

Ruminant Parts and Functions - Stomach Components

• The rumen, a.k.a. “the paunch”, is the largest compartment.
• It can hold up to 40 gallons in a cow and makes up 80% of the stomach.
• The top third is gas, the middle third is solid feedstuffs, and the bottom third is digested feedstuffs.
• The rumen contains a large population of microorganisms.
• It helps digest feed, provide energy, and produce the majority of amino acids.
• Papillae are finger-like structures that texture the inner lining of the rumen, which provides more surface area.
• The reticulum is also known as the honeycomb or "hardware" stomach.
• It is relatively small in a cow (2 gallons, or 5% of the stomach).
• Contractions cause movement for the rumen, which mixes feed.
• It pumps food back up the esophagus for rumination and acts as a sieve.

Ruminant Parts and Functions - Omasum and Abomasum

• The omasum, a.k.a. “the butcher’s Bible”, is a round, muscular section that grinds and squeezes feed.
• It holds 4 gallons in a cow and makes up 8% of the stomach.
• The many folds on the interior walls' structure look like a book.
• Water is absorbed here.
• The abomasum is the "true stomach".
• Its functions are similar to that of a monogastric stomach
• Bile is added to help break down proteins and lipids.
• The abomasum is the only compartment that produces enzymes and mucus.

Ruminant Parts and Functions - Small and Large Intestine, Anus

• Most nutrients are absorbed into the bloodstream here.
• The small intestine is about 20 times the length of the animal; for example, a 6-foot cow would have 120 feet of small intestine.
• It consists of the duodenum, jejunum, and ileum.
• The large intestine prepares unused food material for removal.
• The cecum has a minor role in further breakdown of roughages.
• The colon absorbs water and forms undigested wastes into feces.
• The rectum stores feces until it is passed out of the body.
• The anus is the opening through which solid waste exits.

Pseudo-ruminants

• These animals eat large amounts of roughage, but do not have stomachs with several compartments.
• The digestive system preforms similar functions to ruminants; the cecum ferments forages.
• These can digest large amounts of roughage because of a greatly enlarged cecum and large intestine (many areas for microbial digestion of fiber).
• Pseudo-ruminants also often eat forages.