D IGESTIVE S YSTEM

P ATH OF D IGESTION Food is grasped and collected into the oral cavity This is called prehension Mastication (chewing) breaks food into smaller pieces Deglutition moves chewed food into the pharynx and on into the esophagus The epiglottis closes off the entrance to the trachea Food moves down the esophagus by gravity and peristalsis Peristalsis is a series of wavelike contractions of smooth muscle -stalsis means contraction

P ERISTALSIS VERSUS S EGMENTATION Food moves through the small intestines by peristalsis and segmentation Peristalsis is a series of wavelike contractions that move ingesta caudally toward the anus Segmentation involves the side-to- side mixing of ingesta

S TRUCTURES AND F UNCTIONS The organs of the gastrointestinal tract (GI) form a tubelike passage through the body cavaties. – From the mouth to the anus by way of the pharynx, esophagus, stomach, and intestines The main functions of this system is – Prehension – Transport – Breakdown of food – Absorption of nutrients – Eliminate waste

S TRUCTURES AND F UNCTIONS Food moves through the digestive system aided by peristalsis, an involuntary, wavelike movement. The digestive tract in all mammals generally has the same parts – Mouth – Teeth – Tongue – Pharynx – Esophagus – Stomach – Small intestine – Large intestine

T HE M OUTH Lips form the entrance to the mouth. The lips of sheep, goats, and horses are soft and flexiable and aid in picking up food. Lips of cattle and swine are stiff and immobile and do little more than close the mouth.

T EETH The number of deciduous (baby teeth) and permanent teeth vary with the species and the natural diet of an animal. Teeth provide a variety of functions – Cutting and grinding of food – Defense mechanism Ruminants do not have upper incisors, just a pad.

S ALIVARY G LANDS Saliva is produced in 4 salivary glands Parotid Sublingual Mandibular Zygomatic Referred to as exocrine glands Saliva begins the breakdown of some foods (carbohydrates) in the mouth. Moistens food, lubricant for the bolus.

D IGESTION Digestion is the process of breaking down foods into nutrients that the body can use Metabolism is the processes involved in the body’s use of nutrients Meta- means change or beyond Anabolism is building up of body cells Catabolism is breakdown of body cells

A BSORPTION Absorption is the process of taking digested nutrients into the circulatory system also called assimilation Absorption occurs in the small intestine Villi are tiny hairlike projections that help increase the surface area of the small intestine allowing more nutrients to be absorbed Vill/i means tuft of hair The valleys that result from the projections of the small intestine are called crypts

D IGESTIVE S YSTEMS Man and pig have a simple stomach with an extensive intestinal system Ruminants have a complex stomach with a simpler intestinal system Horses and rabbits have a simple stomach with an extensive intestinal system and an enlarged cecum

3 M AJOR D IGESTIVE S YSTEMS All 3 systems will be addressed in detail in the lesson to follow: Ruminants—have four stomach compartments Monogastric—have one stomach Modified Monogastric—have one stomach but the ability to digest roughages

Ruminant Digestive System

D IGESTIVE S YSTEM Small Intestine : long coiled tube connecting stomach to large intestine rest of the digestion and absorption takes place here surface covered with villi (surface area) 3.5 times the length of animal – dog 18’ Large Intestine : Cecum, colon, rectum absorbs water (makes feces more solid) some vitamins and minerals absorbed here Cecal Fermenters (Horse): similar to rumen

D IGESTIVE S YSTEM Accessory organs: Pancreas secretes enzymes to break down fat Liver (largest internal organ) secretes bile, which digests fats also stores iron

D IGESTIVE S YSTEMS Man and pig have a ________stomach with an extensive intestinal system Ruminants have a ___________ stomach with a simpler intestinal system Horses and rabbits have a simple stomach with an extensive intestinal system and an enlarged__________

D IGESTIVE S YSTEM Mouth: “Prehension” tool (grasps food) ___________________secrete juices containing enzymes (digest food) Chewing food breaks down ____________: muscular tube that connects mouth to stomach Peristaltic Movement: sequential contraction of ring like___________ Reverse ___________= blowing chunks

S IMPLE S TOMACH Muscular contractions break down food Enzymes break down food: Gastric: ___________ Liver and ____________: fats

Ruminant Digestive System

Ruminant Facts (Bovine) Chews cud 40,000-60,000 jaw movements/day No upper incisors - dental pad Does not “bite” grass - wraps tongue Uses fermentation to digest plants Symbiotic relationship with bacteria Produces 13 gallons of gas/hour Produces 40 liters of saliva/day I thought Dumbo was an elephant

R UMINANT S TOMACH Stomach occupies 3/4 of abdominal cavity, mostly on the left side Rumen (paunch): 80% of stomach, lighter food collects here microbes digest cellulose lots of water Reticulum (hardware stomach): 5% of stomach, heavy foreign items are trapped here

R UMINANT S TOMACH Omasum (many plies): 8% of stomach, absorbs water Abomasum (true stomach): 8% of stomach, typical enzyme activity Rumination: regurgitation, rechewing of food

Rumen Largest compartment On left side of animal Contains micro-organisms Ferments cellulose Absorbs VFA’s Divided into chambers Continually contracting Contains papillae Produces CO 2 pH close to neutral (6 - 7)

Reticulum Smallest compartment Lies close to the heart Small sac - part of rumen body Catches dense, heavy feed for later rumination Contracts for regurgitation “Honeycomb” lining Catches hardware and stores it

Omasum Third compartment Globe-shaped Lining called “many plies” Reduces feed particle size Absorbs water and dries out ingesta Absorbs volatile fatty acids

Abomasum Final compartment Tubular in design “True” stomach (glandular) Secretes HCl and enzymes for chemical digestion Reduces pH to 2.5  Dissolves minerals  Kills rumen bacteria  Breaks down proteins Passes ingesta to small intestine

Ruminant Digestion

Intake Mastication (chewing) Swallowing Regurgitation Remastication Fermentation Eructation Absorption Digestion Rumination

Fermentation Anaerobic bacteria break down cellulose VFA’s released by bacteria passed to bloodstream through papillae CO 2 and CH 4 produced by bacteria Bacteria controlled by protozoa Ingesta passed to omasum by contractions

D IGESTIVE S YSTEM Converts feed into a form that can be used for maintenance, growth, and reproduction In a light horse, the tract is approximately 100 feet long and capacity of gallons. Includes: Mouth, esophagus, stomach, intestines, anus, liver, teeth, pancreas, and salivary glands

E QUINE D IGESTIVE S YSTEM Mouth Lips, pharynx, soft palate Lips pick up loose feed which is then passed into the mouth by the tongue Pharynx Short, funnel shaped tube between the mouth and the esophagus Food and water cannot return through the mouth after passing through Horse that chokes has food pass through nose

D IGESTIVE S YSTEM Esophagus is a long muscular tube from the pharynx to the stomach. Stomach is a U shaped muscular sac Peristalsis moves food through Gastric juices are expressed by the stomach walls.

H ORSE D IGESTIVE S YSTEM 1. Esophagus 5. Large intestine (80 quarts) 2. Stomach (8-16 quarts) 6. Pelvic flexure 3. Small intestine (48 quarts) 7. Colon 4. Cecum (28-32 quarts) 8. Rectum

L ARGE I NTESTINE, H ORSES The large intestine makes up approximately 60% of the total digestive tract. Divided into cecum, large colon, small colon and rectum. Cecum is an important organ in horses. Horses can use large amounts of roughage because of the presence of bacteria in the cecum and colon. These bacteria digest cellulose and ferment carbohydrates.

L ARGE I NTESTINE, H ORSES IMPORTANT- because the large intestine of the horse usually contains substantial quantities of ingested material, impaction occurs easily. This impaction is the start of what horse ailment? Signs and symptoms Kicking at abdomen, rolling, lying down and standing up repeatedly, restlessness.