No Slide Title

Lecture 6

The Gastrointestinal System

Asst. Prof. Dr. Wayne J. Fuller

The Digestive System

• The digestive system is

referred to as the

• digestive system (or tract)

• alimentary system

• GI system (or tract)

• The digestive system is

basically a long, muscular

tube that begins at the

mouth and ends at the anus

The Digestive System

• Functions of the digestive system

• intake and digestion of food and water

• absorption of nutrients

• elimination of solid wastes

• The combining form for nourishment is

aliment/o

Structures of the Digestive System

• Mouth or oral cavity

• Pharynx

• Esophagus

• Stomach

• Small intestines

• Large intestines

• Accessory organs of

digestion

Structures of the Mouth

• Mouth or oral

cavity

• Contains the lips,

cheeks, palates (hard

and soft), salivary

glands, tongue, teeth,

and periodontium

• Combining forms are

or/o and stomat/o

• Boundaries of the

mouth are the

maxilla and mandible

(jaw)

• Combining form for

jaw is gnath/o

• Prognathia means

having an elongated

mandible (overshot)

• Brachygnathia means

having a shortened

mandible (undershot)

Structures of the

Digestive System

• Mouth or oral

cavity

• Lips form the opening

to the oral cavity

• Combining forms are

cheil/o and labi/o

• Cheeks form the walls

of the oral cavity

• Combining form is

bucc/o

• The palate forms the

roof of the mouth

• Combining form is

palat/o

• Rug/o = wrinkle or fold

• Tongue is a movable

muscular organ

• Combining forms are

gloss/o and lingu/o

• Papillae are the

elevations on the

tongue

• Filiform = threadlike

• Fungiform =

mushroom-like

• Vallate = cup-shaped

Structures of the Mouth

• Teeth are arranged in

the maxillary and

mandibular arcade

• Combining forms are

dent/o, dent/I, and

odont/o

• Dentition refers to

the teeth as a whole

• The primary dentition

is temporary and

known as the

deciduous dentition

• decidu/o = shedding

• The secondary

dentition is

permanent

• Dental formula

represents the type and

number of each tooth

type found in that

species

• Adult dog is 2(I 3/3,

C 1/1, P 4/4, M 2/3)

Tooth Names

• Types of teeth

• incisor = front, cutting

tooth

• canine = long, pointed

bonelike tooth for

grasping and tearing

• premolar = cheek tooth

that grinds food

• molar = caudal cheek

tooth that grinds food

• Carnassial teeth

Dental Formula’s

• The number of each type of tooth varies from one species to

another and the conventional way of describing them is by a

"dental formula". The type of teeth are indicated by the first

letter, and the number of teeth on one side of the upper jaw is

indicated over the number of the same type of teeth on the

lower jaw. Because the formula is for one side of the mouth

the total number of teeth is the total in the formula x 2.

• The dental formula for different species are as follows

where I = incisors, C = canines, P = premolars and M = molars :

• Man (adult)

• I - 2/2 C - 1/1 P - 2/2 M - 3/3 = 16 x 2 = 32

Dog

a) Puppy (temporary teeth) Not present at

birth - but complete by 60 days.

I - 3/3 C - 1/1 P - 3/3 M - 0/0 = 14 x 2 =

b) Adult (permanent teeth) - emerge at

about 4 months of age

I - 3/3 C - 1/1 P - 4/4 M - 2/3 = 21 x 2 =

Cat

a) Kitten (temporary teeth). Not present at

birth but complete by 60 days.

I - 3/3 C - 1/1 P - 3/2 M - 0/0 = 13 x 2 =

b) Adult (permanent teeth) - emerge at

about 4 months of age

I - 3/3 C - 1/1 P - 3/2 M - 1/1 = 15 x 2 =

Horse

a) Temporary teeth

I - 3/3 C- 0/0 P - 3/3 M - 0/0 = 12 x 2 = 24

b) Adult (permanent teeth)

I - 3/3 C - 1/1 P - 3 or 4/3 M - 3/3 = 20

(or 21) x 2 = 40 (or 42)

Cattle

a) Temporary teeth

I - 0/4 C - 0/0 P - 3/3 M - 0/0 = 10 x 2 =

b) Permanent teeth

I - 0/4 C - 0/0 P - 3/3 M - 3/3 = 16 x 2 =

In cattle the permanent teeth are not fully

erupted until 3.5-4 years of age

Sheep

a) Temporary teeth

I - 0/4 C - 0/0 P - 3/3 M - 0/0 = 10 x 2 =

b) Permanent teeth

I - 0/4 C - 0/0 P - 3/3 M - 3/3 = 16 x 2 =

In sheep the permanent teeth are not

completely erupted until 3.5 - 4 years of

age

Tooth Anatomy

• The anatomy of a tooth

consists of

• enamel = outer surface

located in the crown

• cementum = outer surface

located in the root

• dentin = connective tissue

surrounding the pulp

• pulp = inner part of tooth

that contains nerves,

vessels, and loose

connective tissue

Other Mouth Structures

• Gingiva is the mucous

membrane that

surrounds the teeth

• The combining form for

gingiva is gingiv/o

• Salivary glands are

groups of cells that

secrete saliva

• Named for their location

• Combining forms are

sialaden/o and sial/o

The Throat

• The pharynx is the cavity in the

caudal oral cavity that joins the

respiratory and gastrointestinal

systems

• Also known as the throat

• Combining form is pharyng/o

The Gullet

• The esophagus is a

collapsible, muscular tube

that leads from the oral

cavity to the stomach

• Also known as the

gullet

• Combining form is

esophag/o

• Enters the stomach

through an opening

that is surrounded by a

sphincter

• Sphincter is a ring-like

muscle that constricts an

opening

The Abdomen

• The remaining digestive organs are

found in the abdomen

• Also known as the peritoneal or

abdominal cavity

• Located between the diaphragm

and pelvis

• Combining forms are abdomin/o

and celi/o

• Combining form for abdomen or

flank

is lapar/o

Abdominal Structures

• The peritoneum is the membrane lining that

covers the abdominal and pelvic cavity and some

of the organs in this area

• The layer that lines the abdominal and pelvic cavities is

called the parietal peritoneum

• The layer that covers the abdominal organs is called

the visceral peritoneum

• The omentum is a fold of the peritoneum that

connects the stomach to the other visceral organs

The Stomach

• The stomach is a saclike organ that

aides in digestion of food

• Combining form is gastr/o

• Animals can be classified as

monogastric or ruminant

• Monogastric animals have one

true, glandular stomach (one that

produces secretions)

• Ruminants have one true,

glandular stomach plus three

forestomachs

Stomach Parts

• Parts of the stomach

• cardia (entrance near

esophagus)

• fundus (cranial, rounded

part)

• body (main part)

• antrum (caudal part)

• pylorus (narrow passage

between

the stomach and

duodenum)

• pyloric sphincter (muscle

ring that controls flow of

material from the stomach

to the small intestine)

• rugae (folds in the mucosa)

Ruminant Stomach Parts

• Ruminants regurgitate

and remasticate their

food

• Ruminant stomach parts:

• rumen: largest part that

serves as a fermentation

vat

• reticulum: most cranial

portion

• omasum: third part that

squeezes fluid out of the

food bolus

• abdomasum: fourth part

that is the true glandular

stomach

Small Intestines

• Small intestine extends from the pylorus to the

large intestine

• It is held in place by the mesentery

• Enter/o means small intestine

• Three segments of the small intestine are

• duodenum: proximal part

• duoden/i or duoden/o

• jejunum: middle part

• jenun/o

• ileum: distal part

• ile/o

Large Intestine

• Large intestine extends from

the ileum to the anus

• Four segments of the large

intestine are

• cecum: pouch that takes food

from the ileum

• cec/o

• colon: varies among species

• col/o

• rectum: caudal portion

• rect/o

• anus: caudal opening

Accessory Organs

• Liver: located caudal to

the diaphragm

• hepat/o

• Gallbladder

• chol/e = bile

• cyst/o = sac

• doch/o = receptacle

• Pancreas

• pancreat/o

• Salivary glands

• previously covered

Digestion

• 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

Absorption

• 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

Path of Digestion

• 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

Peristalsis versus

Segmentation

• 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