The Gastrointestinal System

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the digestive system comprises organs concerned with processing food and water by:

• ingestion

• mechanical reduction

• chemical digestion

• absorption

• elimination of unabsorbed residues

another word for digestive tract

alimentary tract

the digestive system begins from the _____ and ends at the _____

mouth; anus

list the additional organs that interact and contribute to the digestive system through various tracts and ducts

• salivary glands

• pancreas

• liver and gall bladder

list the major components of the digestive tract in proper sequence

• oral cavity

• pharynx

• esophagus

• stomach

• small intestine

• large intestine

functions of the oral cavity

• prehension

• mastication

• insalivation

what does the size of the entrance into the oral cavity depend on?

an animal’s diet and feeding habits

what animal has smaller oral cavity openings?

herbivores — suffice for stationary food like grass and leaves

lips are also known as the …

labia

function of lips is highly dependent on what?

the species due to differences in diet and feeding habits

describe the size of the labia in different domestic animals

carnivores — reduced in size and less likely to get snagged in the dental arcade

horses, sheep, goats — highly tactile

cattle and swine — stiff and less mobile

what are the different tissue layers of the lips?

• skin

• oral mucosa

another name for cheeks

buccae

the inner lining of the cheek

buccal mucosa

the buccal mucosa may have a different appearance between …

species

describe the buccae of carnivores and ruminants

carnivores — smooth and delicate

ruminants — thick with large pointed papillae

how is the hard palate in ruminants unique?

it has a rostrally positioned dental pad

dental pad

a tough but cushion-like pad positioned where the upper incisors would be located (lacking in ruminants)

(true/false) there is a distinct demarcation between the hard and soft palate

false

the soft palate is lined with _____ ______ ventrally and _______ ______ dorsally

oral mucosa; respiratory mucosa

tongue

a highly muscular organ capable for both vigorous and precise movements

what movements do the tongue aid in?

• prehension

• lapping water

• grooming

• manipulating food

location of the tongue

• occupies the greater part of the oral cavity and extends into the pharynx

• attached to the floor of the oral cavity by a ventral fold of mucosa

what is the name of the fold of mucosa that attaches the tongue to the floor of the oral cavity?

frenulum

much of the surface of the tongue is covered with __________

papillae of various types

papillae

small nipple-like projections that assist with sense of taste

function of salivary glands

responsible for producing and releasing saliva into the oral cavity

list the main types of salivary glands

• parotid salivary gland

• mandibular sg

• sublingual sg

• zygomatic sg

function of saliva

serves to keep the mouth moist and facilitate mastication of food

once properly masticated, the food mixes with saliva to form a lubricated _______ and can be swallowed more easily

bolus

how is the temporomandibular joint formed?

formed by joining the condylar process of the mandible and the mandibular fossa of the temporal bone

function of the temporomandibular joint

promotes the articulation for opening and closing the mouth

mandibular symphysis

the joint that connects the left and right mandible

complete fusion in many species

little to no movement

muscles of mastication are muscles that serve to open or close the jaw. list these muscles

• temporalis m.

• masseter m.

• digastricus m.

pharynx

a passage that lies behind the mouth and continues into the esophagus

what parts is the pharynx divided into?

• oral

• nasal

• laryngeal

oropharynx

the region between the soft palate and back of the tongue; essentially the “bottom” of the throat

nasopharynx

the dorsal compartment of the pharynx or the “top” of the throat

laryngopharynx

the largest and most caudal region of the pharynx; dorsal to the larynx

esophagus

conveys the food from the oral cavity (more specifically the pharynx) to the stomach

the esophagus passes along the ______ side of the neck relative to the trachea

left

the structure that the esophagus passes through in the diaphragm 

esophageal hiatus

the outer layer of the esophagus in the cervical region is called __________, but is replaced by _________ in the thorax and abdomen

adventitia; serosa

in the pharyngeal region of the esophagus there is skeletal muscle, it begins to transition to smooth muscle in the _________

thoracic region

location of abdominal cavity

• portion of the trunk that lies caudal to the diaphragm

• begins at the diaphragm and extends pelvic region, and is the largest cavity of the body

what is the most cranial portion of the abdominal cavity called and where is it located?

called the Intrathoracic abdominal cavity

is surrounded and protected within the region of the caudal ribs and costochondral cartilages

list the structures that the abdominal cavity contains

• stomach

• small and large intestine

• liver

• pancreas

• spleen

• kidneys, ureters, urinary bladder

• uterus and ovaries

• adrenal glands

• blood vessels, nerves

• lymph nodes and vessels

peritoneum

thin layer of tissue that lines the abdominal cavity and its contents

parietal peritoneum

the layer of peritoneum that lines the abdominal wall

visceral peritoneum

the layer of peritoneum that lines the abdominal organs

the peritoneal layer

• provides a smooth surface within the abdominal cavity and its organs (lessening the chance for adhesions)

• releases a small amount of fluid that lubricates the contents of the abdomen

peritonitis

the inflammation of the peritoneal cavity

describe greater omentum

thin delicate sheet of weblike translucent material

what is the weblike material seen when you open the abdomen from the ventral aspect?

greater omentum

greater omentum originates from the ______ ________ of the stomach and blankets the visceral organs from direct contact with the ventral abdominal wall

greater curvature 

function of greater omentum

a protective tool in the abdomen; primarily functioning to contain and isolate infections by wrapping around areas of inflammation or injury

the _________ is one of the first compartments where digestion takes place after ingestion

stomach

gastric emptying from the stomach can take up how much time?

as soon as 30 minutes and may take up to 10 hours to completely empty?

what is the convex aspect of the stomach serosal surface called? the concave aspect?

convex — greater curvature

concave — lesser curvature

what are the 3 regions of the stomach?

• cardiac part

• fundus

• pyloric part

what is the first portion of the stomach that is situated nearest to the esophagus?

cardiac part

what is just to the left and dorsal of the cardia of the stomach? (dome shaped region)

fundus

the body of the stomach is the large middle portion that extends from the fundus to the ________ ________, which then leads to a narrower Pyloric Canal which communicates with the Duodenum

pyloric part

where is a common location of gastric foreign body obstructions?

pyloric part of stomach

define gastrotomy

making a surgical incision in the stomach

what is the name of the procedure done to remove a gastric foreign body?

gastrotomy

where is the incision for a gastrotomy made?

in the least vascular portion of the stomach between the greater and lesser curvatures

the entire mucosal surface of the stomach is lined with characteristic gastric folds called…

rugae

gastric acid and mucous are secreted from the rugae of the stomach. what is their function?

to facilitate the initial phase of digestion before moving into the small intestine

within the stomach mucosa are the ________ _______, consisting of three types of cells responsible for the gastric secretions

gastric pits

what are the three cells responsible for gastric secretions?

• goblet cells

• chief cells

• parietal cells

goblet cells

• found in all parts of the stomach

• secrete mucus to lubricate the food and protect the stomach wall from damage by digestive enzymes

chief cells

• found within the fundus

• secrete pepsinogen, the precursor to the active enzyme pepsin

• pepsin breaks down proteins to peptides

parietal cells

• found within the fundus

• secrete hydrochloric acid (HCl); creates an acid pH which enables pepsin to work effectively

where does the intestine begin and end

begins at the pylorus and ends at the anus

where is the primary site of nutrient absorption?

small intestine

where are water and electrolytes absorbed?

large intestine

duodenum

relatively short in length and somewhat fixed in position near the mesentery region

the jejunum and ileum are less closely fixed in place and the coils of the intestines are carried by the ________

mesentery

(true/false) there is a sharp, identifiable boundary between the jejunum and ileum

false

what are the layers of the small intestine? (outer to inner)

• serosa

• muscularis

• submucosa

• mucosa

the mucosal lining of the small intestines are lined with _________, which greatly increase the absorption surface area

microvilli

what is the structure that separates the small intestine and large intestine?

cecum

there are anatomical differences of the large intestine between different ___________

species

what are the 3 regions of the large intestine?

cecum, colon, and rectum

what are the parts of the colon?

• ascending

• transverse

• descending

they are divided by flexures

what is the most dorsal structure of the pelvic viscera that lies above the reproductive organs, urinary bladder, and urethra?

rectum

in many species (including horses and pigs), the outer muscle layer of the large intestine is mainly concentrated in a number of bands called _______

Teniae

function of teniae

on shortening, the pucker the gut so that a linear series of sacculation’s (haustra) are produced

are teniae present in dogs and cats?

no

the anal canal is a short passage that is constricted at the __________ __________

rectoanal junction

many glands are present in the anal region (both in the anal tissue and skin issues). the dog and cat possess two sacs called…

anal sacs

location of anal sacs

about the size of a hazelnut and located ventrolateral to the anus between the internal and external anal sphincters

the anal sac secretes an odorous fluid that drains through a single duct to the opening at the _____________ __________

mucocutaneous junction

how do anal sacs empty?

they are compressed during defecation

where are anal sacs commonly found?

in carnivores and more; most notorious in skunk

anal sacculitis

inflammation of the anal sac

what main vessels provide blood to the intestines?

cranial and caudal mesenteric arteries

what is the most cranial part of the abdomen, immediately behind the diaphragm?

liver

function of liver

• produces bile

• metabolism of protein, carbohydrates and fat