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What is the function of the Digestive System?
Provides the body with nutrients essential for growth and maintenance.
Organs of the GI tract make up the hollow tube, composed of smooth muscle, which extends from mouth to anus and are involved in Prehension, Mastication, Swallowing, Digestion, Absorbtion, Elimination
What activities is the GI tract involved in?
- Obtaining food materia from the outside world.
- Accomplished by lips and teeth
Chewing accomplished by the teeth
Pushing food into the esophagus so waves of Peristalsis may take the injesta further into the digestive tract
Smooth muscle contractions moving food along digestive tract.
- Chemical and Mechanical breakdown of food
- Occurs in mouth, stomach, and small intestine
- Moving digested material and water from the lumen of the digestive tract into the blood stream for use in the body
- Occurs mainly in the stomach and small and large intestines
- Removal of undigested ingesta
- Occurs through rectum and anus
- Organs of the GI system through which food does not pass
- These structures release their products into the digestive tract to aid in digestion and absorption of materials
What are the accessory organs
- Salivary Glands
- Three glands located inferior to the ear which work together to produce and release saliva. Saliva lubricates the food and begins the breakdown of starches using the enzyme amylase
- Accessory organ of the digestive system.
Parotid Salivary Gland
The largest of the three, it lays adjacent to the Masseter muscle, its duct actually lays on top of the muscle.
Submandibular Salivary Gland
A smaller gland which lays inferior and caudal to the parotid gland
Sublingual Salivary Gland
The smallest of the three found just rostral to the submandibular, often quite difficult to find.
- Lips in some species aid in the prehension of food
- These organisms can use their lips to grab food and pull it into the mouth
- Paralysis of the lips could be determined for these organisms as they may no longer be able to adequately feed themselves
Name a species that uses it's lips to obtain food.
Defined as the opening between the lips including the oral cavity and vestibule
What are the three superficial parts of the tooth?
- The portion of the tooth visible above the gum
- The crown is covered with enamel which is the hardest substance in the body
The portion of the tooth between the gum line and where the gum attaches to the tooth
- The portion of the tooth below the neck that extends into the bone
- The root is covered with cementum which attaches the tooth to the periodontal ligament holding the tooth in the socket.
What are the three deeper parts of the tooth?
- Pulp Cavity
- Root Canal
The layer of the tooth deep to the crown, neck, and root it makes up the bulk of the tooth and is similar in structure to bone.
Deep to the dentin, in this cavity is the Pulp which is the blood, nervous, and lymphatic supply to the tooth.
An extension of the pulp cavity deep in the root of the tooth, this canal allows for blood, lymph, and nervous supply to enter the pulp cavity.
How are teeth classified
- Time of Eruption
What are the four major categories of teeth?
Used for chewing
Used for chewing and grinding
What 2 types of teeth do mammals have during their life
- milk or baby teeth
- Only incisor, canines, and premolars are replaced by bigger adult teeth at certain times as the organisms mature
- Adult teeth
- All four types of teeth are seen in this set, the time of eruption of these teeth can be used to age young organisms
A highly mobile, muscular structure that aids in taste, mastication, swallowing, and grooming
What are the three types of papillae on the tongue of the cat?
- Spiny papillae used for grooming
- Found on front half of the tongue
- Have no taste buds
- Small rounded papillae found between the filiform papillae on the front half of the tongue and are also found more caudally
- Received their name for the mushroom like appearance
Difficult to locate on a preserved cat. They would be found on the lateral aspects at the base of the tongue.
Leaf shaped papillae found on the lateral aspects of the tongue and at the base
- Small structures on the dorsal surface of the tongue (on the papillae) and on the soft palate
- Provide information about the taste of food being eaten
- It is known that their are 5 taste bud sensations
What are 5 taste bud sensations?
- Sweet, Bitter, and Umami/Savory (which signal through a G-protein coupled receptor)
- Salty and Sour (which operate with ion channels)
Area between the teeth and cheek
- "Roof of the Mouth"
- Made up of the incisive, maxillae and palatine bones which are covered by Palatine Rugae or ridges
Soft, muscular area behind the hard palate which separates the nasopharynx and the oral cavity
- Long muscular tube which is found dorsal to the trachea and connects the oral cavity to the stomach.
- Proximal end near mouth
- Distal end attached to stomach
Why is the stomach a muscular tube while the trachea is a cartilaginous tube?
Pushing food down into the stomach
What is the function of the greater omentum?
- Protect abdominal cavity
- Vascular, shock absorber
What is the function of the spleen?
- Discard bad/dead RBC/WBC
A large dark reddish brown organ directly caudal to the diaphram, it is an accessory organ in the digestive system
What are the five lobe that the liver is divided into?
- Right Lateral lobe
- Right Medial lobe
- Left Medial lobe
- Left Lateral lobe
- Caudate Lobe
Right Lateral Lobe
- Divided into two sections by a deep cleft
- Cups over the top of the right kidney
Right Medial Lobe
Contains a cleft housing the gallbladder
Found Deep to the Lesser Omentum
Similar to the greater omentum but is much smaller and found in the smaller curvature of the stomach
Small green sac structure embedded in the right medial lobe of the liver, stores the bile created by the liver to emulysify fats
- An enlargement of the gastrointestinal system which connects the esophagus to the small intestine. It acts as a mixing and holding chamber for ingesta and is a site for partial digestion of protein
- There are four main components of the stomach
What are the four main components of the stomach?
Area of the stomach which surrounds cranial opening of the stomach right below the esophageal sphincter
Rounded portion of the stomach which is cranial to the Cardia,blind sac which distends as the stomach fills
Main portion of the stomach which contains folds or rugae which allows the stomach to expand
Area of th stomach which connects to the small intestine, end at the pyloric sphincter
- The medial aspect of the stomach
- The lesser omentum attaches here
The lateral aspect of the stomach
What are the three parts of the small intestine?
- Extends from the pyloric sphincter to the tiny curve at the base of the mesentery, the descending duodenum is found on the right of the abdominal cavity
- The mesentery between the Duodenum and the stomach holds the small, granular pancreas
An accessory organ of the digestive system which releases digestive enzymes as well as insulin
The twisted, looped, longest section of the small intestine, there is no landmark separating this section of the small intestine from the next, much shorter ileum.
The last part of the small intestine which leads to the cecum and large intestine.
- Begins at the Ileoceal Sphincter and extends to the rectum, this organ functions in water reabsorption and storage of feces until it can be expelled
- This organ varies greatly between species, it is simple in carnivores and rather complex in nonruminant herbivores called hindgut fermenters.
- In its most simple for the large intestine can be divided into the cecum, ascending colon, transverse colon, descending colon, rectum, and anus
What are the divisions of the large intestine?
- Ascending Colon
- Transverse Colon
- Descending Colon
- Rectum and Anus
Small vestige in the cat which will be discussed further with the hindgut fermenters
Located on the right side of the cat, area of the large intestine which extends cranially then turns forming the Transverse Colon
Portion of the colon which extends from the right side of the body to the left, when the structure turns caudally the structure becomes the Descending Colon
Section of the large intestine which continues caudally to the rectum
Rectum and Anus
The terminal portion of the large intestine which allows for elimination of fecal matter in a process called defecation
What are the two systems utilized by herbivores to obtain nutrients from their food?
- Ruminant Stomach
- Hindgut Fermentation
Eats plant and meat
- Rumination or chewing cud is a process carried out by cattle, sheep, and goats
- This process involves swallowing and regurgitating food to chew it more before swallowing it again. Ruminants have four chambered stomach, the first three chambers are the components of the "forestomach" or fermenting stomach while the last chamber is the true stomach.
- The reticulum, rumen, and omasum are the chambers of the forestomach and the abomasum is the true stomach.
What are the chambers of the forestomach?
WHat is the true stomach called?
- The smallest, most cranial compartment of the ruminant stomach
- The walls of this chamber have a honeycomb appearance - these structures increase the surface area for absorption
- Also known as tripe
- Walls of this chamber are continuous with the rumen, they generally work together so their contractions are called reticulorumen contractions
- Magnets are inserted into this chamber to prevent hardware disease
This disease is caused by the ingestion of metal which lodges in the reticulum and punctures the diaphragm and heart if not contained
- Large fermentation vat which allows for generally unusable cellulose to be broken down for energy.
- This structure is divided by muscular folds called pillars into four parts
- Dorsal Sac, Dorsal Blind Sac, Ventral Sac, Ventral Blind Sac
- The muscular contraction of this vat allows for
- 1. mixing rumen contents
- 2. Partially digested food to be regurgitated, chewed, and reswallowed
- 3. This increases the surface area of the ingesta so that the microbes in the rumen can more efficiently break it down into its components
- 4. Expulsion of carbon dioxide and methane built up during fermentation. The bacteria and protozoa found in the rumen are able to break down the cellulose that animal systems are unable to utilize thus providing the ruminant with nutrients which would not be able to be obtained otherwise
What structure is divided by muscular folds called pillars into four parts?
- Dorsal Sac
- Dorsal Blind Sac
- Ventral Sac
- Ventral Blind Sac
- The opening for this compartment is off the reticulum
- Contractions of the rumen and reticulum send partially digested food ingesta into the omasum
- This compartment is comprised of muscular folds which function in
- 1. Breaking the food particles down further
- 2. Absorbing more nutrients and water from ingesta
- Removing the bicarbonate ions that would neutralize the pH of the abomasum
True or enzymatic stomach, much like the monogastric stomach studied in the previous section that connects the pylorus of the small intestine
- An alternative to the ruminant plan is the system used by the horse. Hindgut fermentation means that the fermentation or breakdown of cellulose into unusable carbohydrates occurs after the small intestine. In this plan the organism has a monogastric stomach and typical small intestine which allows for the digestion and absorption of easily digestible grains and the breakdown of the grasses consumed doesn't occur until the large intestine
- Organisms utilizing hindgut fermentation have an incredibly large cecum, this organ, which is usually a vestige, acts as the fermentation vat for these animals absorbing the nutrients released so they also have an extensive and elaborate large intestine commonly called the great colon
- Large comma shaped extending from the pelvis to the diaphragm
- Environment comparable to the rumen as it is filled with bacteria and protozoans which produce enzymes that will digest cellulose into absorbable material
- Filled by the ileum
- Food moves through the great colon which consists of several sections connected together by sharply bending pieces of colon called flexures
- It is these flexures that food and foreign bodies can become lodged and cause many difficulties for the animal
- Once food has traveled through the great colon it enters the small colon and the rectum and anus