Functional Anatomy � of � Digestive Tract � (Monogastric & Ruminant)

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Dr. Amar Chaudhary, ^{DVM, MS}

Assistant Professor

Department of Vet. Anatomy, Physiology and Biochemistry

Agriculture and Forestry University,

Rampur, Chitwan, Nepal

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Monogastric

Monogastric a single compartment stomach

Most monogastric are generally unable to digest much cellulose food material such as grasses

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Human

Swine

Horse

Cat & Dog

Rabbit

Functional Anatomy of Monogastric Digestive System

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Digestive function

Mouth

• Receive and mechanical breakdown of foodstuffs
• Saliva contains water, mucin, bicarbonate salts and enzyme amylase to begin starch digestion.
• Moistens the feed for chewing and swallowing
• Mucin lubricates the feed for swallowing
• Bicarbonate salts buffer the pH in the stomach
• Horse saliva does not contain enzymes while in Swine, saliva contains the enzyme salivary amylase and salivary maltase

Tongue

• It gathers feed in the mouth
• Mixes feed & directs the feed in the throat for swallowing

Esophagus

• Tube like passage leads from mouth to stomach
• Peristaltic waves send feed down the esophagus

�Monogastric animals stomach �

Consists of: cardia, fundus, body & pylorus

• Cardia 
• Is the top part of your stomach.
• It contains the cardiac sphincter, which prevents food from traveling back up your oesophagus.
• Fundus 
• Is a rounded section next to the cardia.
• It's below the diaphragm
•  Body (corpus) 
• Is the largest section of your stomach.
• In the body, stomach contracts and begins to mix food
•  Antrum 
• lies below the body.
• It holds food until your stomach is ready to send it to your small intestine.
•  Pylorus
• Is the bottom part of your stomach.
• It includes the pyloric sphincter.
• This ring of tissue controls when and how your stomach contents move to your small intestine

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Monogastric animals stomach

Cell types

• Mucous neck cells
• Mucus
• Bicarbonate
• Parietal cells
• Gastric acid
• Intrinsic factor
• Enterochromaffin cell
• Histamine
• Chief cell
• Pepsinogen
• Gastric lipase
• D cell
• Somatostatin
• G cell
• Gastric

�Organs of the Monogastric Digestive System�

Small Intestine

• Duodenum, Jejunum, Ileum
• Enzymatic digestion and absorption as site of final stages
• Function of small intestine:
• Digestion of protein, carbohydrate and fats
• Absorption of end product of digestion
• Duodenum: most digestion occurs
• Jejunum: some digestion and some absorption occurs
• Ileum : mostly absorption

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Organs of the Monogastric Digestive System�

Large Intestine

• Cecum, Colon, Rectum
• Site of water absorption from G.I. tract.
• Cecum:
• Essentially on functioning in many monogastric.
• Rabbit and horses have enlarged cecum that acts like a rumen and is involved with microbial digestion (fermentation)
• Summarized function:
• Bacterial activity
• Water absorption
• waste storage
• Feces formed.

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Large intestine

Swine

• Small intestine does the majority of absorption
• Cecum in swine has little or no function
• Cecum is the 1^st part of the Large intestine
• Colon is the middle and largest part of the large intestine

Horses

• Cecum is an important organ in horses
• Large intestine makes up approximately 60% of the total digestive tracts
• Divided into cecum, Large colon, small colon & rectum
• Horse can use large amounts of roughage because of the presence of bacteria in the cecum & colon
• These bacteria digest hemicelluloses and cellulose and ferment carbohydrates
• In the horse, the small colon is the site of the most of the water resorption

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� Accessory organs of the Monogastric Digestive System�

Liver

• Main organ for metabolism of carbohydrate, protein, fat, minerals and vitamins
• Storage function: Storage site for carbohydrate(glycogen), vitamins(mainly vitamin A, D, B12), Iron as ferritin
• Synthetic function: liver synthesizes
• Plasma protein except immunoglobulins
• Clotting factors II, VII, IX and X
• Vitamin K
• Urea
• Natural anticoagulants
• Secretory function: secretes mainly bile
• Excretory function: heavy metal, Cholesterol, bile pigment, calcium are excreted through bile
• Detoxification: detoxify the substance originating from the gut or elsewhere in the body
• Toxins(NH3)
• Drugs as penicillin, ampicillin
• Steroid and other hormone
• Haemopoietic function: In Human as intrauterine life produce RBC but at adult destruction site of RBC
• Immunity and Phagocytic : By Kupffer cell

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Accessory organs of the Monogastric Digestive System

Gall bladder & Bile

• Store and concentrate bile
• Function of Bile:
• Digestive function: digestion of fat with the help of bile salt
• Absorption of fat and fat soluble vitamin, Iron and calcium
• Choleratic : Increase secretion of bile from liver
• Laxative : increase peristaltic and help in defecation

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Organs of the Monogastric Digestive System�

Pancreas

• Mixed gland located in the abdominal cavity of the body.
• When food enters the stomach, these pancreatic juices are released into a system of ducts that culminate in the main pancreatic duct.
• Pancreatic duct joins the common bile duct to form the ampulla of Vater  enters the duodenum by the hepato-pancreatic duct.
• Pancreas produces an alkaline pancreatic juice that contains a variety of enzymes

Pancreatic enzymes are:

• Trypsin: It helps in the digestion of proteins.
• Chymotrypsin: It helps in the digestion of proteins.
• Procarboxypeptidase: It removes single amino acids from the carboxyl terminus of oligopeptides.
• Pancreatic amylase: It helps in the breakdown of carbohydrates and starch
• protease
• Pancreatic lipases
• Nuclease

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Ruminant Animal

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Herbivorous animal’s having four compartments stomach, which are tasked with acquiring nutrients from plants based food by fermenting it prior to digestion

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Goats

Ruminants

Sheep

�� Ruminant Digestive System�

Ruminant digestive system

• Mouth and Tongue
• A ruminant uses its mouth and tongue to harvest forages during grazing or to consume harvested feedstuffs.
• Cattle harvest forages during grazing by wrapping their tongue around the plants and then pulling to tear the forage for consumption.
• They typically spend over
• one-third of their time grazing,
• one-third of their time ruminating (cud chewing), and
• slightly less than one-third of their time idling where they are neither grazing nor ruminating.
• Saliva of ruminants does not contain enzymes to help digest the starches
• It contains buffers which neutralizes the fatty acid produced in the rumen
• Forage and feed mixes with saliva containing sodium, potassium, phosphate, bicarbonate, and urea when consumed to form a bolus
• Rumen contents are maintained at approximately a pH of 6- 6.5, Promotes microbial growth in the rumen
• Mature cows produce about 50-150 lit. of saliva per day while sheep produces 6-10 lit.

Ruminant stomach

Stomach of the ruminant contains four compartments

• Rumen/ Paunch – 1^st part of the Ruminant stomach
• Reticulum/Honeycomb- 2^nd part of the Ruminant stomach
• There is not a clear partition between these two compartments
• No enzymes are secreted in these two parts
• Omasum/Many piles- 3^rd compartment of the Ruminant stomach
• It constituents 8% of the stomach
• The omasum contains strong muscles in the wall
• Abomasum/True Stomach- 4^th and last pat of Ruminant stomach
• It makes up 7% of the stomach
• Enzymes and Chemical are secreted in this part

Functional Anatomy of Ruminants the Digestive System�

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Parts of the Ruminant Stomach

Rumen

• largest stomach compartment and consists of several sacs and very thick muscular wall
• Occupy most of the left-side of the abdomen
• Looks like carpet due to papillae lining it allows for bacterial fermentation of fiber
• Fermentation vat
• Primary digestion site for ruminants
• Microbial digestion takes place here
• Breakdown cellulose, simple sugars, and Nitrogen containing compounds like protein
• Physical mixing and breakdown
• Not active in the early stages of life
• Rumen microbes ferment feed and produce volatile fatty acids, which is the cow’s main energy source

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• Rumen microbes also produce B vitamins, vitamin K and amino acids.
• Good blood supply to the rumen walls improves absorption of VFAs and other digestion products
• Tiny projections (papillae) line the rumen, which increases the rumen’s surface area and the amount it can absorb  
• In calves, the oesophageal grooves allows milk to bypass the rumen and directly enter the abomasum
• Rumen development occurs following a change in diet and microbial growth

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Parts of the Ruminant Stomach

Rumen (continued):

• Lined with millions of papillae (short projections on wall of rumen) needed for absorption.
• “Shag carpet” appearance

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Parts of the Ruminant Stomach

Rumen (continued):

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• Houses microorganisms.
• Protozoa – 100,000 per gram of rumen fluid.
• Bacteria/fungi – 100 million per gram of rumen fluid.

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• Functions of microorganisms.
• Digest roughages to make Volatile Fatty Acids (VFA’s), make microbial protein, and make vitamins K and B-complex.
• VFA’s absorbed in rumen.
• Contractions occur at a rate of 1-3 per minute
• Ruminants are well known for “cud chewing”.

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• Rumination involves:
• Bolus of previously eaten foodstuff carried back into the mouth by reverse peristalsis.
• Fluid in bolus is squeezed out with the tongue and reswallowed.
• Bolus is rechewed and reswallowed.
• Rumination may occupy about 1/3 of a ruminant’s day

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Parts of the Ruminant Stomach

Function:

• Continual flow of feed materials into and out of the rumen
• Saliva which is mixed with the feed helps control the pH of the rumen
• Papillae line the interior wall of the rumen, they increase surface area therefore increasing the absorption ability of the rumen wall

Eructation (belching):

• Fermentation of foodstuffs in the rumen generates enormous quantities of gas.
• 30-50 liters per hour in adult cattle.
• 5-7 liters per hour in adult sheep or goats.

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• Belching is how ruminants get rid of fermentation gases:
• Anything that causes a hindrance to belching can be life threatening.
• Bloating can result in death from asphyxiation.
• Small amounts are absorbed by the blood stream and then eliminated through the lungs

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Parts of the Ruminant Stomach

Reticulum:

• Contains microorganisms (like the rumen).

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• Provides additional area for fermentation.

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• As fermentation by microorganisms proceed and feedstuffs are digested,
• Lining has a honeycomb structure.
• Catches and holds hardware consumed by animal.
• Hardware can be removed with rumen magnate.
• Feed is moved back and forth between the rumen and reticulum by regular contractions originating in the reticulum

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Parts of the Ruminant Stomach

Omasum:

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• A heavy, hard organ with a lining that has many folds (leaves).
• Function not well understood.
• Believed to produce a grinding action on foodstuffs.
• May absorb residual VFA’s , water salt and bicarbonate.
• Little or no digestive action

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Omasum

Parts of the Ruminant Stomach

Abomasum:

• True, glandular stomach.
• Secretes acids and functions very similarly to monogastric stomach.
• There is little or no digestion of fat, cellulose or starch
• pH level of 3.5 -4.0
• Feed becomes highly fluid as it passes into the small intestine
• Unique feature is that it secretes lysozyme.
• Enzyme that efficiently breaks down bacterial cell walls.
• Needed to break down the large quantities of bacteria that pass from the rumen.

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