Chapter 28 The Digestive System

Functions Intake and digestion of food and water Absorption of nutrients Elimination of solid waste

Terminology 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 Absorption is the process of taking digested nutrients into the circulatory system

Structures Mouth (teeth) Pharynx Esophagus Stomach Small intestines Large intestines Accessory organs of digestion

Teeth Carnivores Herbivores Meat eaters - Use teeth for tearing and chewing food Dogs and cats - long incisors (fangs) Herbivores Plant eaters, Grind plant materials Horse, cow, sheep, goat

Teeth Omnivores Meat and plant eater Teeth adapt for variety of foods Humans

Teeth Deciduous Permanent Incisors small baby teeth; curved larger adult teeth; straight Incisors front teeth used to bite

Teeth Canines Pre-Molars Molars fangs used to tear food; longest teeth wider teeth used to crush and grind food Molars rear teeth

Teeth Crown Root Enamel Dentin Pulp Cavity portion above the gum line portion below the gum line Enamel covering of the crown Dentin second layer between crown and root Pulp Cavity where nerves, arteries, and veins enter the tooth

Tooth Anatomy

The Mouth Saliva 4 salivary glands that produce saliva used to break down foods and line the digestive tract Humans secret 1-2 L saliva / day Adult cow secrets 200L of saliva / day Tongue skeletal muscle obtains food and holds in mouth forms BOLUS Papillae- hair on tongue that acts as taste buds

Salivary Glands

Pharynx The pharynx is the cavity in the caudal oral cavity that joins the respiratory and gastrointestinal systems Also known as the throat Bolus enters pharynx Respiration is reflexively inhibited Larynx reflexively closes and pulls up and forward Base of tongue folds epiglottis over the laryngeal opening as it moves back Pharynx shortens and peristaltic action of pharyngeal muscles forces bolus into esophagus

The Stomach Food enters stomach Monogastric Divided into 3 sections: Single, simple stomach Divided into 3 sections: CARDIA (ENTRANCE) BODY PYLORUS (EXIT) FUNDUS- top of the stomach at the entrance Sphincter muscle control at entrance and exit Peristalsis- wave like contractions to pass food

The Small Intestines 3 major parts Duodenum Jejunum Ileum Primary site of enzymatic digestion and absorption of nutrients

The Large Intestines Cecum Colon Rectum Anus pouch that takes food from the ileum Colon varies among species Absorbs water Omnivores and herbivores: site of fermentation and microbial digestion Rectum caudal portion Anus caudal opening

Accessory Organs Liver Pancreas Produces bile (salty substance) that aids in the digestion of lipids; stored in gallbladder Pancreas Secretion of digestive enzymes; empties into the duodenum

Stomach Systems 3 types of animal digestive systems: Monogastric Ruminant Nonruminant

Monogastric Systems Has only one compartment to the stomach Process goes through the: Mouth Esophagus Stomach Small intestine: duodenum, jejunum, ileum Large intestine: cecum, colon, rectum

Monogastric System

Monogastric Systems Humans Dogs Cats Pigs

Monogastric Stomach

The Ruminant System The Ruminant Stomach Sheep, cows, llamas, and goats Occupies 3/4 of the abdominal cavity Four Components of Ruminant Stomach Rumen Reticulum Omasum Abomasum

The Ruminant System Rumen composes 80% of ruminant stomach in mature bovine animals Serves as a fermentation vat Reticulum composes about 5% of bovine stomach prevents indigestible objects from entering the stomach Most cranial Omasum composes 7-8% of bovine stomach absorbs mostly water Abomasum the “true” stomach composes 7-8% of stomach in mature animals and 70% in young animals

The Ruminant System Rumination: the process of regurgitation, re-mastication, re-salivation and re-swallowing of food Purpose: to smash and break up food which provides more surface area bacteria to break down Eructation: belching action as gas builds up in the rumen

The Ruminant System Multi-compartment stomach Ruminant animals are often called “cud chewers” No upper front teeth in ruminant mouth

The Nonruminant System System is noted in horses, rodents, and rabbits Simple stomach with enlarged cecum Plant fibers are broken down and digested in the cecum Uses bacteria to break down material by process of fermentation

Common Digestive Conditions Can be caused by many factors Typical reactions: vomiting or diarrhea Can lead to dehydration

Dehydration Loss of fluids in the body Skin turgor how it can be established area of skin at the base of neck and over the shoulders is elastic-like skin turgor will stay “tented” or appear not to go back in its normal position

Dehydration Mucous membranes (mm) hydration status can be determined by evaluating this gums or mm can be labeled tacky or dry Color and amount of moisture can help identify Can be seen in eye sockets if they are sunken into head

Dehydration Fluid replacement Intravenous (IV) or Subcutaneous (SQ) Fluids Lactated Ringer’s Solution (LRS) Sodium chloride Normal saline

Dehydration Percentages Moist mm; slight skin turgor; slightly sunken eyes 8-9% Dehydration Tacky mm; obvious sunken eyes; slow skin turgor with noted tenting 10-12% Dehydration Dry mm; very sunken eyes; very slow and very tented skin turgor